NAP-XPS Systems

Methanol is a promising chemical for the safe and efficient storage of hydrogen, where methanol conversion reactions can
generate a hydrogen‐containing gas mixture. Understanding the chemical state of the catalyst over which these reactions
occur and the interplay with the adsorbed species present is key to the design of improved catalysts and process conditions.
Here we study polycrystalline Cu foils using ambient pressure X‐ray spectroscopies to reveal the Cu oxidation state and
identify the adsorbed species during partial oxidation (CH₃OH + O₂), steam reforming (CH₃OH + H₂O), and autothermal
reforming (CH₃OH + O₂ + H₂O) of methanol at 200 °C surface temperature and in the mbar pressure range. We find that the
Cu surface remains highly metallic throughout partial oxidation and steam reforming reactions, even for oxygen‐rich
conditions. However, for autothermal reforming the Cu surface shows significant oxidation towards Cu₂O. We rationalise
this behaviour on the basis of the shift in equilibrium of the CH₃OH^* + O^* ⇌ CH₃O^* + OH^* caused by the addition of H₂O.

B. Eren, C. G. Sole, J. S. Lacasa, D. Grinter, F. Venturini, G. Held,
C. S. Esconjauregui, and R. S. Weatherup
Physical Chemistry Chemical Physics, 2020, 00, 1‐8

The success of many emerging molecular electronics concepts hinges on an atomistic understanding of
the underlying electronic dynamics. We employ picosecond time-resolved x-ray photoemission spectroscopy
(tr-XPS) to elucidate the roles of singlet and triplet excitons for photoinduced charge generation at a copperphthalocyanine–
C₆₀ heterojunction. Contrary to common belief, fast intersystem crossing to triplet excitons
after photoexcitation is not a loss channel but contributes to a significantly larger extent to the time-integrated
interfacial charge generation than the initially excited singlet excitons. The tr-XPS data provide direct access to
the diffusivity of the triplet excitons D_CuPc = (1.8 ± 1.2) × 10⁻⁵ cm²/s (where CuPc is copper-phthalocyanine)
and their diffusion length L_diff = (8 ± 3) nm.

F. Roth, S.Neppl, A. Shavorskiy, T. Arion, J.Mahl, H. O. Seo,
H. Bluhm, Z.Hussain, O. Gessner, and W. Eberhardt.
PHYSICAL REVIEW B 99, 020303(R) (2019)

X-ray photoelectron spectroscopy (XPS) is one of the most powerful techniques to quantitatively ana-lyze the chemical composition and electronic structure of surfaces and interfaces in a non-destructivefashion. Extending this technique into the time domain has the exciting potential to shed new lighton electronic and chemical dynamics at surfaces by revealing transient charge configurations withelement- and site-specificity. Here, we describe prospects and challenges that are associated with theimplementation of picosecond and femtosecond time-resolved X-ray photoelectron spectroscopy atthird-generation synchrotrons and X-ray free-electron lasers, respectively. In particular, we discuss aseries of laser-pump/X-ray-probe photoemission experiments performed on semiconductor surfaces,molecule-semiconductor interfaces, and films of semiconductor nanoparticles that demonstrate the highsensitivity of time-resolved XPS to light-induced charge carrier generation, diffusion and recombinationwithin the space charge layers of these materials. Employing the showcase example of photo-inducedelectronic dynamics in a dye-sensitized semiconductor system, we highlight the unique possibility toprobe heterogeneous charge transfer dynamics from both sides of an interface, i.e., from the perspectiveof the molecular electron donor and the semiconductor acceptor, simultaneously. Such capabilities willbe crucial to improve our microscopic understanding of interfacial charge redistribution and associatedchemical dynamics, which are at the heart of emerging energy conversion, solar fuel generation, andenergy storage technologies.

S. Neppl, O. Gessner
Journal of Electron Spectroscopy and Related Phenomena 200 (2015) 64–77

Progress in the development of plasmon-enabled light-harvesting technologies requires a
better understanding of their fundamental operating principles and current limitations. Here, we employ
picosecond time-resolved X-ray photoemission spectroscopy to investigate photoinduced electron transfer in
a plasmonic model system composed of 20 nm sized gold nanoparticles (NP_s) attached to a nanoporous film
of TiO₂. The measurement provides direct, quantitative access to transient local charge distributions from
the perspectives of the electron donor (AuNP) and the electron acceptor (TiO₂). On average, approximately
two electrons are injected per NP, corresponding to an electron injection yield per absorbed photon of 0.1%.
Back electron transfer from the perspective of the electron donor is dominated by a fast recombination
channel proceeding on a time scale of 60 ± 10 ps and a minor contribution that is completed after ∼1 ns.
The findings provide a detailed picture of photoinduced charge carrier generation in this NP−semiconductor
junction, with important implications for understanding achievable overall photon-to-charge conversion
efficiencies.

M. Borgwardt, J. Mahl, F.Roth, L. Wenthaus, F. Brauße, M.Blum,
K. Schwarzburg, G. Liu, F.M. Toma, and O.Gessner
The Journal of Physical Chemistry Letters. 2020, 11, 5476−5481

Understanding interfacial charge-transfer processes on the atomic level is
crucial to support the rational design of energy-challenge relevant systems such as solar cells,
batteries, and photocatalysts. A femtosecond time-resolved core-level photoelectron spectroscopy
study is performed that probes the electronic structure of the interface between
ruthenium-based N3 dye molecules and ZnO nanocrystals within the first picosecond after
photoexcitation and from the unique perspective of the Ru reporter atom at the center of the
dye. A transient chemical shift of the Ru 3d inner-shell photolines by (2.3 ± 0.2) eV to higher
binding energies is observed 500 fs after photoexcitation of the dye. The experimental results
are interpreted with the aid of ab initio calculations using constrained density functional
theory. Strong indications for the formation of an interfacial charge-transfer state are presented,
providing direct insight into a transient electronic configuration that may limit the
efficiency of photoinduced free charge-carrier generation.

K.R. Siefermann, C. D. Pemmaraju, S. Neppl, A. Shavorskiy,
A. A. Cordones, J. Vura-Weis, D. S. Slaughter, F. P. Sturm, F. Weise,
H. Bluhm, M. L. Strader, H. Cho, MF Lin, C. Bacellar,
C. Khurmi, J. Guo, G. Coslovich, J. S. Robinson, R. A. Kaindl,
R. W.
The Journal of Physical Chemistry Letters. 2014, 5, 2753−2759

Interfacially confined microenvironments have recently gained attention in catalysis, as they can be used to modulate reaction chemistry. The emergence of a 2D nanospace at the interface between a 2D material and its support can promote varying kinetic and energetic schemes based on molecular level confinement effects imposed in this reduced volume. We report on the use of a 2D oxide cover, bilayer silica, on catalytically active Pd(111) undergoing the CO oxidation reaction. We “uncover” mechanistic insights about the structure‐activity relationship with and without a 2D silica overlayer using in situ IR and X‐ray spectroscopy and mass spectrometry methods. We find that the CO oxidation reaction on Pd(111) benefits from confinement effects imposed on surface adsorbates under 2D silica. This interaction results in a lower and more dispersed coverage of CO adsorbates with restricted CO adsorption geometries, which promote oxygen adsorption and lay the foundation for the formation of a reactive surface oxide that produces higher CO 2 formation rates than Pd alone.

C. Eads, J. A. Boscoboinik, A. R Head, A. Hunt, I. Waluyo, D. J. Stacchiola, and S. A Tenney
Wiley, 18.01.2021

Near-ambient-pressure x-ray photoelectron spectroscopy (NAP-XPS) and x-ray-induced Auger electron spectroscopy were used to characterize gas-phase carbon monoxide, CO(g). In this submission, the authors show the survey, valence band, O 1s, C 1s, O KLL Auger, and C KLL Auger spectra acquired using high-resolution synchrotron NAP-XPS with a photon energy of 647.08 eV.

C. R. O’Connor, J A. Boscoboinik, M. Karatok, and M. A. van Spronsen
Surface Science Spectra 27, 014002 (2020)

Near ambient pressure-x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., at greater than 2500 Pa. With NAP-XPS, XPS can probe moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this paper, we show the NAP-XPS survey; O 1s, Ca 2p, C 1s, K 2p, Al 2s, Al 2p, Si 2p, and Si 2s narrow scans; and the extended valence band spectrum of clinoptilolite, a natural zeolite that would be difficult to analyze by conventional XPS. A small N 1s signal from N₂(g) is also observed in the survey spectrum. Signals in the narrow scans are fit to Gaussian–Lorentzian sum and Gaussian–Lorentzian product functions.

T. G. Avval, V. Carver, S. C. Chapman, S. Bahr, P. Dietrich, M. Meyer, A.Thißen, and M. R. Linford
Surface Science Spectra 27, 014007 (2020)

Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less-traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., at ca. 2500 Pa, or even higher in some cases. With NAP-XPS, XPS can probe moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission, the authors show NAP-XPS survey spectra, and C 1s and O 1s narrow scans of two samples of paper (a white office paper and the nonsticky side of a yellow post-it note). The white office paper was analyzed at three specific positions: an unprinted portion, a light blue letter, and a dark blue letter in the “SPECS” logo. Survey spectra show the presence of carbon, oxygen, nitrogen, and calcium in all the samples. The yellow paper shows a small amount of silicon. Fits to the C 1s and O 1s regions are shown. The O 1s narrow scans are fit with four peaks using a literature approach previously employed for paper and with three peaks in a more ad hoc fashion. The latter approach yields better fits.

D. Shah, S. Bahr, P. Dietrich, M. Meyer, A. Thißen and M. R. Linford
Surface Science Spectra 26, 024009 (2019)

Beamline 8A (BL 8A) is an undulator-based soft X-ray beamline at Pohang
Accelerator Laboratory. This beamline is aimed at high-resolution ambientpressure
X-ray photoelectron spectroscopy (AP-XPS), soft X-ray absorption
spectroscopy (soft-XAS) and scanning photoemission microscopy (SPEM)
experiments. BL 8A has two branches, 8A1 SPEM and 8A2 AP-XPS, that share
a plane undulator, the first mirror (M1) and the monochromator. The photon
beam is switched between the two branches by changing the refocusing mirrors
after the monochromator. The acceptance angle of M1 is kept glancing at 1.2^o,
and Pt is coated onto the mirrors to achieve high reflectance, which ensures a
wide photon energy range (100–2000 eV) with high resolution at a photon flux
of ~10¹³ photons s^-1. In this article, the main properties and performance of the
beamline are reported, together with selected experiments performed on the
new beamline and experimental system.

G. Kim, Y. Yu, H. Lim, B.Jeong, J. Lee, J. Baik, B. S. Muna and K.-J. Kim
J. Synchrotron Rad. (2020). 27, 507–514

Bulk ZrO₂ has shown high activity and selectivity for propane dehydrogenation (PDH). Its catalytic performance
can be enhanced by substitution of the Zr ions with suitable dopant ions. In this study, a series of Cu-doped ZrO₂
metal oxides (CuZrO-x) have been prepared using the co-precipitation method and the effects of the amount of
dopant on their properties have been investigated. The appropriate amount of Cu dopant promotes the creation
of oxygen vacancies and coordinatively unsaturated Zr_cus⁴⁺ sites, active sites for PDH; however, excess Cu forms
bulk CuO in the CuZrO-x catalysts resulting in decreased activity. The catalytic activity for PDH is closely
correlated to the amount of weak Lewis acid sites in CuZrO-x. Moreover, a comparison of the CuZrO-x properties
with those of Cu-impregnated ZrO₂ has shown that the amount of acid sites and therefore, the catalytic performance,
depends on the doping method.

N. Jeon, H. Choe, B.Jeong, and Y. Yun
Applied Catalysis A, General 586 (2019) 117211

Bulk ZrO₂ is a highly active and selective catalyst for dehydrogenation of propane (PDH), in which coordinatively
unsaturated Zr cations (Zr_cus⁴⁺) serve as active sites. Substitution of dopant ions into Zr lattice can improve its catalytic activity by generating more Zr_cus⁴⁺ sites. In this work, a series of vanadium-doped ZrO₂ metal oxides (VZrO-x) have been prepared and the influences of vanadium content on their properties have been systematically investigated. Various characterization techniques showed that an appropriate amount of vanadium dopant helps more Zr_cus⁴⁺ sites to be created by a structural transformation and H₂ pretreatment. However, excess vanadium dopant led to a negative effect on the catalytic activity owing to the formation of
bulk-like V₂O₅ crystallites. The catalytic activity of VZrO-x is well correlated with the amount of Lewis acid sites
because Zr_cus⁴⁺ cations correspond to Lewis acid sites. The VZrO-8 catalyst exhibited two times higher activity
than pure ZrO₂. Moreover, for repeated cycles the activity was totally recovered by oxidative regeneration
followed by reductive pretreatment. Finally, the performance test results showed that H₂ co-feeding can further
enhance the activity by suppressing coke deposition during PDH.

N. Jeon, H. Choe, B.Jeong, and Y. Yun
Catalysis Today

In this study, the oxidation of a two-dimensional (2D) MoS₂ was performed as an alternative route
for the synthesis of a 2D-layered MoO₃ structure with high work function (WF) and hole mobility.
The proposed method can also be used to tune the electronic properties (WF and bandgap) of MoO₃/
MoS₂ composite-based semiconductors. By ambient pressure x-ray photoelectron spectroscopy
(AP-XPS), in situ monitoring of the WF and chemical state of the surface was carried out during
the oxidation of MoS₂ to MoO₃ layers. By heating the MoS₂ sample in an O2 + Ar gas environment,
the chemical transformation of the MoS₂ to a MoO₃/MoS₂ composite layer and eventually to MoO₃
was observed. The chemically transformed MoO₃ film had a properly layered structure, according
to cross-sectional transmission electron microscopy and high-resolution grazing-incidence x-ray
diffraction analyses. During the oxidation, the WF change according to the change in surface
chemical state was simultaneously measured using Ar gas as a surface potential probe. This study
demonstrates the capability of AP-XPS for the monitoring and optimization of the conditions for
chemical transformation (oxidation) to achieve desired physical properties (e.g. WF).

D. Lee, J. H. Jang, W.Song, J. Moon, Y. Kim, J. Lee,
B. Jeong, and S. Park
2D Mater. 7 (2020) 025014

The development of high performance gas sensors that operate at room temperature
has attracted considerable attention. Unfortunately, the conventional
mechanism of chemiresistive sensors is restricted at room temperature by
insufficient reaction energy with target molecules. Herein, novel strategy for
room temperature gas sensors is reported using an ionic-activated sensing
mechanism. The investigation reveals that a hydroxide layer is developed by
the applied voltages on the SnO₂ surface in the presence of humidity, leading
to increased electrical conductivity. Surprisingly, the experimental results
indicate ideal sensing behavior at room temperature for NO₂ detection with
sub-parts-per-trillion (132.3 ppt) detection and fast recovery (25.7 s) to 5 ppm
NO₂ under humid conditions. The ionic-activated sensing mechanism is
proposed as a cascade process involving the formation of ionic conduction,
reaction with a target gas, and demonstrates the novelty of the approach. It
is believed that the results presented will open new pathways as a promising
method for room temperature gas sensors.

Y. G. Song, Y.-S. Shim, J. M. Suh, M.-S. Noh, G. S. Kim,
K. S. Choi, B. Jeong, S. Kim, H. W. Jang, B.-K. Ju,
and C.-Y. Kang
Small 2019, 15, 1902065

Design and synthesis of multi-dimensional metal organic frameworks has attracted much attention not only due to their intriguing structures and unique properties, but also for their potential applications especially in catalysis. Recently, much effort has been devoted to develop new photocatalyst based on MOFs, motivated largely by a demand for solving pollution problems in view of their potential applications in the green degradation of organic pollutants. MOFs, known as coordination polymers are crystalline materials constructed from metal ions or clusters bridged by organic ligands to form one-, two-, or three-dimensional infinite networks. There are several methods have been applied for synthesis of MOFs particularly solvothermal, hydrothermal, microwave-assisted, electrochemical, mechanochemical and sonochemical synthesis. In this work, new Cadmium and Copper based Metal Organic Framework (MOF) was synthesized under hydrothermal and solvothermal conditions. Its structure was resolved by single crystal X-ray diffraction and further characterized by Powder X-ray diffraction (PXRD), Field Emission Scanning Electron Microscopy (FESEM), Infrared Spectra (IR), Thermogravimetric (TGA), UV-Vis, Photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS) analysis. The Cd-MOF and Cu-MOF were photocatalytically active for degradation of 2-chlorophenol (2-CP) under solar light irradiation where 69% and 100% of phenol removal was observed respectively. To improve photocatalytic activity of Cd-MOF, different metal ions such as Ag+, Fe3+ and Zn2+ were introduced into the framework through ion-exchange reaction. The UV-Vis results revealed that Fe-Cd-MOF showed an enhanced photoresponse in the visible region, whereas the photoresponse of Ag-Cd-MOF and Zn-Cd-MOF in the ultraviolet light region. Photocatalytic performances of synthesized materials were investigated fordegradation of 2-CP. Among them, Cd-MOF intercalated with Fe3+ exhibited excellent photocatalytic activity compared with Cd-MOF, degrading 92% of 2-CP in 5 hours. It can be attributed to the intercalation of Fe3+, which reduced energy gap of pure MOF, thus increases photocatalytic efficiency.

N. A. Surib
Thesis (M.Eng.Sc) - Faculty of Engineering, University of Malaya, 2018

Electrocatalysis is at the heart of our future transition to a renewable energy system. Most energy storage and conversion technologies for renewables rely on electrocatalytic processes and, with increasing availability of cheap electrical energy from renewables, chemical production will witness electrification in the near future1,2,3. However, our fundamental understanding of electrocatalysis lags behind the field of classical heterogeneous catalysis that has been the dominating chemical technology for a long time. Here, we describe a new strategy to advance fundamental studies on electrocatalytic materials. We propose to ‘electrify’ complex oxide-based model catalysts made by surface science methods to explore electrocatalytic reactions in liquid electrolytes. We demonstrate the feasibility of this concept by transferring an atomically defined platinum/cobalt oxide model catalyst into the electrochemical environment while preserving its atomic surface structure. Using this approach, we explore particle size effects and identify hitherto unknown metal–support interactions that stabilize oxidized platinum at the nanoparticle interface. The metal–support interactions open a new synergistic reaction pathway that involves both metallic and oxidized platinum. Our results illustrate the potential of the concept, which makes available a systematic approach to build atomically defined model electrodes for fundamental electrocatalytic studies.

F. Faisal, C.Stumm, M. Bertram, F. Waidhas, Y. Lykhach, S.Cherevko, F. Xiang, M. Ammon,
M. Vorokhta, B. Šmíd, T. Skála, N. Tsud, A. Neitzel, K. Beranová, K. C. Prince, S. Geiger,
O. Kasian, T. Wähler, R. Schuster, M. A. Schneider, V. Matolín, K. J. J.
Nature Materials volume 17, pages 592–598 (2018)

Here we present a study on agarose thin-film samples that represent a model
system for the exopolysaccharide matrix of biofilms. Povidone-iodide (PVP-I) was
selected as an antibacterial agent to evaluate our XPS-based methodology to trace
specific marker elements, here iodine, commonly found in organic matrices of
antibiotics.
The in-depth distribution of iodine was determined by XPS analyses with variable
excitation energies and in combination with argon gas cluster ion beam (GCIB) sputter
cycles. On mixed agarose/PVP-I nanometer thin films, both methods were found to solve
the analytical task and deliver independently comparable results. In the mixed
agarose/PVP-I thin-film we found the outermost surface layer depleted in iodine,
whereas the iodine is homogeneously distributed in the depth region between this
outermost surface layer and the interface between the thin-film and the substrate.
Depletion of iodine from the uppermost surface in the thin-film samples is assumed to
be caused by UHV exposure resulting in a loss of molecular iodine (I₂) as reported earlier
for other iodine-doped polymers.

P. M. Dietrich, M. Kjærvik, E. A. Willneff, and W. E. S. Unger
Biointerphases (Vol. 17, Issue 3)

Ever since the invention of photoelectron spectroscopy, researchers have attempted to analyze materials under conditions
closely resembling their application environment. Near-Ambient Pressure X-ray Photoelectron Spectroscopy is a logical
development in this quest, since it allows for analyzing non-vacuum compatible samples in general, and phase boundaries,
such as solid|liquid or solid|gas interfaces, in particular. With the development of spectrometer systems compatible with
analysis pressures of up to 100 mbar, many novel experimental geometries have been realized since the early 2000s. Since
then, experimental capability and variety have further progressed through the proliferation of off-synchrotron laboratory
systems, and advanced sample environments to simulate material usage conditions. This progress has, e.g., enabled the
performance of operando spectroscopy during catalytic or electrochemical experiments. The present work gives, from an
instrumental point of view, a short overview over basic system design considerations and recent developments in the field.

M. Weidner and V. Streibel
表面と真空 Vol. 65, No. 3, pp. 133–138, 2022

Seeds are vulnerable to physical and biological stresses during the germination process. Seed priming strategies can alleviate such stresses. Seed priming is a technique of treating and drying seeds prior to germination in order to accelerate the metabolic process of germination. Multiple benefits are offered by seed priming techniques, such as reducing fertilizer use, accelerating seed germination, and inducing systemic resistance in plants, which are both cost-effective and eco-friendly. For seed priming, cold plasma (CP)-mediated priming could be an innovative alternative to synthetic chemical treatments. CP priming is an eco-friendly, safe and economical, yet relatively less explored technique towards the development of seed priming. In this review, we discussed in detail the application of CP technology for seed priming to enhance germination, the quality of seeds, and the production of crops in a sustainable manner. Additionally, the combination treatment of CP with nanoparticle (NP) priming is also discussed. The large numbers of parameters need to be monitored and optimized during CP treatment to achieve the desired priming results. Here, we discussed a new perspective of machine learning for modeling plasma treatment parameters in agriculture for the development of synergistic protocols for different types of seed priming.

A. Shelar, A. V. Singh, P. Dietrich, R. S. Maharjan, A. Thissen, P. N. Didwal, M. Shinde, P. Laux, A. Luch, V. Mathe, T. Jahnke, M. Chaskar and, R. Patil
Issue 17, 2022, Issue in Progress, RSC Advances

Polyethylene production through catalytic ethylene polymerization is one of the most common processes
in the chemical industry. The popular Cossee-Arlman mechanism hypothesizes that the ethylene be
directly inserted into the metal–carbon bond during chain growth, which has been awaiting microscopic
and spatiotemporal experimental confirmation. Here, we report an in situ visualization of ethylene
polymerization by scanning tunneling microscopy on a carburized iron single-crystal surface. We
observed that ethylene polymerization proceeds on a specific triangular iron site at the boundary
between two carbide domains. Without an activator, an intermediate, attributed to surface-anchored
ethylidene (CHCH3), serves as the chain initiator (self-initiation), which subsequently grows by
ethylene insertion. Our finding provides direct experimental evidence of the ethylene polymerization
pathway at the molecular level.

W. Guo, J. Yin, Z. Xu, W. Li, Z. Peng, C. J. Weststrate, X. Yu,
Y. He, Z. Cao, X. Wen, Y. Yang, K. Wu, Y. Li,
J. W. Niemantsverdriet, und X. Zhou
Science 375, 1188–1191 (2022)

Pseudomonas fluorescens (Gram-negative) bacteria purchased from Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures were analyzed using high-resolution x-ray photoelectron spectroscopy at near ambient pressure conditions (NAP-XPS), 1500 Pa water vapor atmosphere. Fresh layers of P. fluorescence bacteria were grown on Luria Broth agar plates. Bacteria were taken from the agar plate with a sterile spatula and gently spread on a Si-wafer piece for NAP-XPS analysis. The NAP-XPS spectra of the bacterial envelope of P. fluorescence were obtained using monochromatic Al Kα radiation and include a survey scan and high-resolution spectra of C 1s, N 1s, P 2p, and O 1s as well. The presentation of the C 1s high-resolution spectrum includes the results of peak fitting analysis.

M.Kjærvik, K. Schwibbert, P. M. Dietrich, and W. E. S. Unger
Surface Science Spectra 29, 014008 (2022)

Using the nascent band theory of solids, Cabrera and Mott designed in the late 1940s a model for the low-temperature oxidation of metals that still stands today as a landmark. The core assumption is that an electric field set up in the growing oxide at thermodynamic equilibrium drives the transport of the ionic species responsible for the oxidation process. The existence of an electrostatic potential has long been sought experimentally by in situ measurement of the work function changes in the presence of gaseous O₂. Here, we demonstrate that the work function measurement is insufficient to test the model. Instead, the oxide band structure characteristics (surface dipole energy barrier and band bending) should be followed. We exemplify this for the paradigmatic case of the Al(111) surface oxidation at room temperature using near-ambient pressure X-ray photoemission spectroscopy (operated up to a pressure of 1 mbar). Using an in situ spectroscopic tool, we monitor the oxide growth in real time and obtain detailed energetic information on the metal/oxide/gas system. This allows us to validate the central hypothesis of the Cabrera–Mott model (i.e., the existence of the Cabrera–Mott potential). The original assumption that oxygen anions are adsorbed at the oxide/gas interface is also discussed. The concept of “realistic conditions” also means that the issue of water coadsorption (inherent to near-ambient O₂ conditions) is addressed. The specific consequences of the Cabrera–Mott regime of oxidation are also discussed with respect to the functioning of aluminum-based superconducting qubits. The in situ, real-time spectroscopic methodology used here is effective and can be generalized far beyond the specific case of aluminum oxidation.
 

L. Pérez Ramírez, F. Bournel, J.-J. Gallet, L. Dudy and F. Rochet
J. Phys. Chem. C 2022, acs.jpcc.1c09388.

We present a newly developed end-station at BESSY II dedicated to in situ Spectroscopic Analysis with Tender X-rays (SpAnTeX). The core of the end-station is a new SPECS PHOIBOS 150 HV NAP electron spectrometer. First, we show that the system has successfully achieved high electron transmission and detection efficiency under gas pressures up to 30 mbar and photon energies ranging between 200 eV and 10 keV. Second, using two features of this spectrometer (a new lateral resolution lens and a 3D delay line detector), we show that the endstation enables collection of the photoelectron spatial distribution under realistic working conditions (p ≥ 20 mbar) with a resolution better than 30 μm and the possibility to perform time resolved studies using a continuous tender X-ray source. We conclude by reporting an example of the possible experiments that can be performed using this new endstation using the Dip-and-Pull technique.

Although mainly focused on the characterization of solid/liquid interfaces using AP-HAXPES, the end-station can be used at soft X-ray beamlines for more traditional AP-XPS experiments. The Dip-and-Pull module also demonstrates good electrochemical performance. The wide pressure and photon energy range covered by this end-station also enables investigations of solid/solid, solid/gas, liquid/vapor and liquid/liquid interfaces at pressures up to 30 mbar with tender X-rays.

M. Favaro, P. C. J. Clark, M. J. Sear, M. Johansson, S. Maehl, R. van de Krol, and D.E. Starr
Surface Science
Volume 713, November 2021, 121903

In this article, we present the results of an investigation into chemical processes which take place at the surface of SnO₂-based chemiresistor in various atmospheres (1 mbar of argon, 1 mbar of oxygen, 0.1 mbar of ethanol, 1 mbar of oxygen + 0.1 mbar of ethanol mixture) at common working temperatures (450 and 573 K). The key method for nanoscale analysis was the Near Ambient Pressure X-ray Photoelectron Spectroscopy. In parallel the resistance and DC-responses of SnO₂ layer were in-situ monitored providing information about macroscale processes during gas sensing. The change in the sensor resistance after exposure to the ethanol-containing atmospheres together with the disappearance of the band bending effect and observation of different carbonaceous groups including ethoxy groups and acetaldehyde molecules on the sensor surface in the XPS spectra supported the theory of chemical interaction of ethanol with the chemisorbed oxygen. The NAP-XPS spectra also showed that the nanostructured tin oxide is partially reduced even after being exposed to pure oxygen at 573 K. Exposing this surface to the mixture of O₂/EtOH did not significantly increase the surface reduction probably due to slow kinetics of the ethanol reduction process and fast kinetics of the oxygen re-oxidation process. However, it was demonstrated that the surface of sensor is slowly getting contaminated by carbon.

M. Vorokhta, I. Khalakhan, M. Vondráček, D. Tomeček, M. Vorokhta, E. Marešová, J. Nováková, J. Vlček, P. Fitl, M. Novotný, P. Hozák, J. Lančok, M. Vrňata, I. Matolínová, and V. Matolín
Surface Science, Volume 677, November 2018, Pages 284-290

This article presents an investigation of the sensing properties of chemiresistors based on Cu₂O/CuO core–shell nanowires containing p–p′ heterojunctions. The nanowires were synthesized by a conventional hydrothermal method and used for the detection of ethanol and nitrogen dioxide, reducing and oxidizing agents, respectively. To unravel the chemical processes connected with gas detection, an in situ approach was applied. This approach was based on near-ambient pressure X-ray photoelectron spectroscopy combined with simultaneous monitoring of sensor responses. The in situ measurements were performed during exposure to the analytes at a total pressure of 0.05–1.05 mbar and 450 K and were correlated with chemiresistor response measurements carried out at a standard pressure and under an ambient atmosphere. The study revealed that heterojunction treatment with ethanol vapors, accompanied by partial reduction of the nanowires, is the key step to obtaining chemiresistors with good sensing performance. While the untreated heterojunctions exhibited poor n-type sensing responses, the treated ones showed significantly improved p-type responses. The treated sensors were characterized by a stable baseline, high reversibility, detection limits estimated as 50 ppm for ethanol and 100 ppb for nitrogen dioxide, and with response times in tens of seconds. In all cases, we propose a band scheme of Cu₂O/CuO heterojunctions and a gas-sensing mechanism.
 

P. Hozák, M. Vorokhta, I. Khalakhan, K. Jarkovská, K. Jarkovská
J. Cibulková, P. Fitl, J. Vlček, J. Fara, D. Tomeček, M. Novotný, M. Vorokhta, J. Lančok, I. Matolínová, and M. Vrňata
J. Phys. Chem. C 2019, 123, 49, 29739–29749

Modulating electronic structure of graphene overlayers is highly demanding for its potential applications in
microelectronics, sensors, and catalysis, which however remains a grand challenge. Here, we report electrochemistry-
involved treatments to tune the electronic structure of graphene overlayers. Both galvanic corrosion
and potential-aided intercalation of H₂O were employed to change the graphene/Cu interfaces to graphene/
Cu₂O/Cu and graphene/H₂O/Cu interfaces, respectively. Electronic properties and structural changes of the
graphene/Cu interfaces were investigated by X-ray photoelectron spectroscopy, in-situ Raman, and atomic force
microscopy. The formed Cu₂O interlayer blocks the charge transfer between graphene overlayer and Cu substrate,
which turns n-type doping of the as-grown graphene to free-standing state. In contrast, the intercalated
H₂O interlayer induces much stronger n-type doping in graphene through the electrostatic field effect generated
by confined H₂O. This work offers efficient but mild methods to modulate the doping state of graphene layers.

S. Zhao,b, Rentao Mu, Y. Ninga, Q. Fua and X. Bao
Applied Surface Science 522 (2020) 146359

Bacteria generally interact with the environment via processes involving their cell-envelope. Thus, techniques that may shed light on their surface chemistry are attractive tools for providing an understanding of bacterial interactions. One of these tools is Al Kα-excited photoelectron spectroscopy (XPS) with its estimated information depth of <10 nm. XPS-analyses of bacteria have been performed for several decades on freeze-dried specimens in order to be compatible with the vacuum in the analysis chamber of the spectrometer. A limitation of these studies has been that the freeze-drying method may collapse cell structure as well as introduce surface contaminants. However, recent developments in XPS allow for analysis of biological samples at near ambient pressure (NAP-XPS) or as frozen hydrated specimens (cryo-XPS) in vacuum. In this work, we have analyzed bacterial samples from a reference strain of the Gram-negative bacterium Pseudomonas fluorescens using both techniques. We compare the results obtained and, in general, observe good agreement between the two techniques. Furthermore, we discuss advantages and disadvantages with the two analysis approaches and the output data they provide. XPS reference data from the bacterial strain are provided, and we propose that planktonic cells of this strain (DSM 50090) are used as a reference material for surface chemical analysis of bacterial systems.

M. Kjærvik, M. Ramstedt, K. Schwibbert, P. M. Dietrich and W. E. S. Unger
Front. Chem., 30 April 2021

Ionizing radiation damage to DNA plays a fundamental role in cancer therapy. X-ray photoelectron-spectroscopy (XPS) allows simultaneous irradiation and damage monitoring. Although water radiolysis is essential for radiation damage, all previous XPS studies were performed in vacuum. Here we present near-ambient-pressure XPS experiments to directly measure DNA damage under water atmosphere. They permit in-situ monitoring of the effects of radicals on fully hydrated double-stranded DNA. The results allow us to distinguish direct damage, by photons and secondary low-energy electrons (LEE), from damage by hydroxyl radicals or hydration induced modifications of damage pathways. The exposure of dry DNA to x-rays leads to strand-breaks at the sugar-phosphate backbone, while deoxyribose and nucleobases are less affected. In contrast, a strong increase of DNA damage is observed in water, where OH-radicals are produced. In consequence, base damage and base release become predominant, even though the number of strand-breaks increases further.

M. Benjamin Hahn, P. M. Dietrich und J. Radnik
Communications Chemistry volume 4, Article number: 50 (2021)

Bismuth vanadate (BiVO₄) is an established n-type oxide semiconductor for photoelectrochemical oxygen evolution. Direct charge carrier recombination at the solid/liquid interface is a major cause of efficiency loss in BiVO₄-based devices. Intrinsic and extrinsic surface states (SSs) can act as electron and hole traps that enhance the recombination rate and lower the faradaic efficiency. In this study, we investigate the BiVO4/aqueous KPi interface using two types of samples. The samples were prepared at two different deposition and annealing temperatures (450 °C and 500 °C) leading to different morphologies and stoichiometries for the two samples. Both samples exhibit SSs in the dark that are passivated under illumination. In situ ambient pressure hard x-ray photoelectron spectroscopy experiments performed under front illumination conditions reveal the formation of a bismuth phosphate (BiPO₄) surface layer for the sample annealed at 450 °C, whereas the sample annealed at 500 °C exhibits band flattening without the formation of BiPO₄. These results imply that the light-induced formation of BiPO₄ may not be responsible for SS passivation. Our study also suggests that slight differences in the synthesis parameters lead to significant changes in the surface stoichiometry and morphology, with drastic effects on the physical-chemical properties of the BiVO₄/electrolyte interface. These differences may have important consequences for device characteristics such as long-term stability.

M. Favaro, I.Y. Ahmet, P. C. J. Clark, F. F. Abdi, M. J. Sear, R. van de Krol, and D. E. Starr
Marco Favaro et al 2021 J. Phys. D: Appl. Phys. 54 164001

n situ x-ray spectroscopies offer a powerful way to understand the electronic structure of the electrode–electrolyte interface under operating conditions. However, most x-ray techniques require vacuum, making it necessary to design spectro-electrochemical cells with a delicate interface to the wet electrochemical environment. The design of the cell often dictates what measurements can be done and which electrochemical processes can be studied. Hence, it is important to pick the right spectro-electrochemical cell for the process of interest. To facilitate this choice, and to highlight the challenges in cell design, we critically review four recent, successful cell designs. Using several case studies, we investigate the opportunities and limitations that arise in practical experiments.

J.-J. Velasco-Vélez, L. J. Falling, D. Bernsmeier, M. J Sear, P. C. J. Clark, T.-S. Chan, E. Stotz, M. Hävecker, R. Kraehnert, and A. Knop-Gericke
Juan-Jesús Velasco-Vélez et al 2021 J. Phys. D: Appl. Phys. 54 124003

In this topical review we catagorise all ambient pressure x-ray photoelectron spectroscopy
publications that have appeared between the 1970s and the end of 2018 according to their
scientific field. We find that catalysis, surface science and materials science are predominant,
while, for example, electrocatalysis and thin film growth are emerging. All catalysis
publications that we could identify are cited, and selected case stories with increasing
complexity in terms of surface structure or chemical reaction are discussed. For thin film
growth we discuss recent examples from chemical vapour deposition and atomic layer
deposition. Finally, we also discuss current frontiers of ambient pressure x-ray photoelectron
spectroscopy research, indicating some directions of future development of the field.
Keywords: ambient pressure x-ray photoelectron spectroscopy, synchrotron radiation,
catalysis, atomic layer deposition, chemical vapour deposition, operando

J. Schnadt, J. Knudsen, and N. Johansson
J. Phys.: Condens. Matter 32 (2020) 413003 (29pp)

Liquid jet X-ray photoelectron spectroscopy is used under near ambient pressure conditions to characterize Fe²⁺ aqueous solutions. Counter ions, such as Cl⁻ and Br⁻ ions, added to the solution lead to changes in the first solvation sphere of the Fe-aqua complex in solution. Binding energy shifts of 0.4 eV to lower binding energy are observed in the Cl 2p spectra, 2 eV to higher binding energy in the Fe 2p spectra and no shifts are observed in the Br 3d spectra. Depletion of the Cl⁻ species is observed at the interface,
caused by coordination with Fe². Depletion of Cl⁻ at the liquid/vapor interface may have significant impacts on oxidative chemistry at the interface of atmospheric aerosols that contain both chloride and iron. The Cl⁻ complexation with the Fe²⁺ ions will also affect the Fenton chemistry that is dependent on this metal ion.

J. P. Bruce and J. C. Hemminger
J. Phys. Chem. B 2019, 123, 8285−8290

Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., at ca. 2500 Pa, or even higher in some cases. With NAP-XPS, XPS can probe moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission, we show NAP-XPS survey and narrow scans from nitrogen gas (N2), a material that could not be analyzed at moderate pressures by conventional approaches. Nitrogen gas is an important reference material for NAP-XPS because residual N2 from the air and/or venting produces an N 1s signal in many NAP-XPS spectra. Nitrogen gas may also be deliberately employed as the gaseous background for NAP-XPS experiments. The survey spectrum of N2 gas contains N 1s, N 2s, N KLL (Auger), and valence band signals. This submission is part of a series of articles on NAP-XPS that has been submitted to Surface Science Spectra.

D. Shah, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 014023 (2019)

Interfacially confined microenvironments have recently gained attention in catalysis, as they can be used to modulate reaction chemistry. The emergence of a 2D nanospace at the interface between a 2D material and its support can promote varying kinetic and energetic schemes based on molecular level confinement effects imposed in this reduced volume. We report on the use of a 2D oxide cover, bilayer silica, on catalytically active Pd(111) undergoing the CO oxidation reaction. We “uncover” mechanistic insights about the structure‐activity relationship with and without a 2D silica overlayer using in situ IR and X‐ray spectroscopy and mass spectrometry methods. We find that the CO oxidation reaction on Pd(111) benefits from confinement effects imposed on surface adsorbates under 2D silica. This interaction results in a lower and more dispersed coverage of CO adsorbates with restricted CO adsorption geometries, which promote oxygen adsorption and lay the foundation for the formation of a reactive surface oxide that produces higher CO 2 formation rates than Pd alone.

Calley Eads, J Anibal Boscoboinik, Ashley R Head, Adrian Hunt, Iradwikanari Waluyo, Dario J Stacchiola, Samuel A Tenney
Angewandte Chemie is a journal of the German Chemical Society (GDCh).

Hydrogen energy is considered to be a promising alternative for the sustainable and environmentally friendly solution of the global energy problem. One of the major obstacles of hydrogen energy applications is to maintain safe and efficient storage of hydrogen which can also be achieved chemically using suitable carrier materials. Formic acid (HCOOH, FA) can be utilized as a hydrogen carrier due to its low molecular weight (46 g/mol) and high hydrogen density (%4.4 weight). FA is a stable, non-flammable, and non-toxic biomass side-product rendering it a perfect candidate for an alternative hydrogen vector. Design of novel heterogeneous catalysts which can substitute the existing homogeneous catalytic systems may allow overcoming catalyst isolation and recovery costs and associated logistical problems hindering their applications in on-board operations.

FA can be catalytically decomposed via dehydrogenation and dehydration reactions. Selective dehydrogenation of FA is crucial because, the production of CO from dehydration mechanism can suppress the activity of the catalyst by blocking/poisoning the precious metal sites. Consequently, development of CO-resistant, selective, catalytically active, and reusable heterogeneous catalysts has a great significance. In the current work, a new material that can produce H₂(g) from FA under ambient conditions in the absence of additives with high CO-poisoning tolerance will be introduced, which is comprised of Pd-based trimetallic active centers functionalized with Ag and Cr in addition to amine-functionalized MnO_x promoters dispersed on a SiO₂ support surface.

E. Perşembe
Perşembe, E. (2017). (Unpublished Thesis)
Bilkent University, Ankara, Turkey.

Near ambient pressure - x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., at 2500 Pa or higher. With NAP-XPS, one can analyze moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission we show C 1s, O 1s, and survey NAP-XPS spectra from poly(_L-lactic acid). The C 1s and O 1s envelopes were fit with three and two Gaussian-Lorentzian sum functions, respectively. Water vapor (800 Pa) was used as the residual gas for charge compensation, which was confirmed by the sharp peak at 535.0 eV in the O 1s narrow scan. The uniqueness plot corresponding to the C 1s fit shows that the fit parameters had statistical significance. C 1s and O 1s spectra of PLLA damaged by exposure to x-rays for ca. 1 hour are also included.

D. I. Patel, S. Noack, C. D. Vacogne, H. Schlaad, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 024004 (2019)

Near ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., at ca. 2500 Pa, or higher in some cases. With NAP-XPS, XPS can be used to analyze moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission, we show survey, O 1s, O KLL, and valence band NAP-XPS spectra from liquid water, a material that could not be analyzed at moderate pressures by conventional approaches. The O 1s signal was fit to two components attributed to liquid and vapor phase water. The carbon in the survey spectrum is attributed to contaminants in the water and/or adventitious carbon.

D. Shah, D. I. Patel, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 024003 (2019)

Near ambient pressure-x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., at ca. 2500 Pa, or higher in some cases. With NAP-XPS, XPS can probe moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission, we show an NAP-XPS survey spectrum, and also O 1s and C 1s narrow scans, of a commercial soft drink, Coca-Cola. Clearly this is a material that could not be analyzed at moderate pressures by conventional XPS. The C 1s narrow scan is fit to five synthetic components. The O 1s narrow scan shows strong contributions from both liquid and gas phase water. A small N 1s signal in the survey spectrum is attributed to background nitrogen. The shape of the uniqueness plot corresponding to the C 1s fit suggests that the fit parameters are statistically significant.

D. Shah, C. V. Cushman, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 024005 (2019)

Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., at 2500 Pa or higher. With NAP-XPS, XPS can analyze moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. Because of the relatively high working pressure of NAP-XPS, the components of ambient air may be present in the analytical chamber during data acquisition. In this submission, we show survey, O 1s, N 1s, valence band, oxygen Auger (KLL), and nitrogen Auger (KLL) NAP-XPS spectra from ambient air, a material that could not be analyzed at moderate pressures by conventional XPS.

D. I. Patel, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 024002 (2019)

Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., greater than 2500 Pa. With NAP-XPS, XPS can analyze moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission, we show C 1s, O 1s, and survey NAP-XPS spectra from ethylene glycol, an organic solvent that could not be analyzed at near-ambient pressures by conventional approaches. An N 1s signal is present in the survey spectrum of the material.

D. I. Patel, J. O'Tani, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 024007 (2019)

Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., up to 2500 Pa, or higher in some cases. NAP-XPS can probe moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission, we present NAP-XPS C 1s and O 1s narrow scans and a survey spectrum of a coffee bean, a material that would be difficult or even impossible to analyze by conventional XPS. Coffee beans are ground to produce coffee powder, which is the source of one of the world’s most common beverages, coffee. The survey spectrum shows small amounts of sulfur and calcium.

D. Shah, S. Bahr, P. Dietrich, M. Meyer, A. Thißen and M. R. Linford
Surface Science Spectra 26, 024006 (2019)

Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., at greater than 2500 Pa. In this study, poly(γ-benzyl L-glutamate) (PBLG) with a molar mass of 11.3 kg/mol was analyzed by NAP-XPS; here, we show the survey, C 1s, N 1s, and O 1s narrow scans of PBLG. The C 1s peak envelope was fitted in three different ways, to five, six, or seven synthetic peaks. In each fit, there was also a shake-up signal. The O 1s narrow scan was well fit with three peaks: C—O and C=O in a 1:2 ratio from the polymer, and a higher energy signal from water vapor. Hartree–Fock orbital energies of a model monomer served as a guide to an additional fit of the C 1s envelope.

V. Jain, J. J. Wheeler, D. H. Ess, S. Noack, C. D. Vacogne, H. Schlaad, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, and M. R. Linford
Surface Science Spectra 26, 024010 (2019)

Near-ambient pressure-x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., at ca. 2500 Pa. With NAP-XPS, XPS can probe moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. Here, we show the NAP-XPS analysis of untreated/blank human hair, and human hair that has been colored (red) and treated with a commercial conditioner, or bleached and treated with a different conditioner. Survey spectra are shown of each material along with figures comparing their Si 2p, S 2p, and C 1s spectra. The survey spectrum of untreated hair shows S 2p, S 2s, C 1s, Ca 2p, N 1s, and O 1s peaks and corresponding O, N, and C Auger signals. The survey spectra of the colored and bleached hair show significant Si 2s and Si 2p signals and reduced or eliminated S 2p and S 2s peaks, presumably due to the deposition of dimethicone (polydimethylsiloxane) from the corresponding commercial hair treatment products. Narrow scans similarly indicate the deposition of a silicon-containing material on the two types of treated hair, with a concomitant decrease in the intensity of the sulfur signals from the hair. Upon treatment, the C 1s envelope also changes—the chemically shifted peak attributable to amide-type carbon disappears.

V. Jain, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, and M. R. Linford
Surface Science Spectra 27, 014001, 2020

This study aimed to obtain possible materials for future antimicrobial food packaging applications based on biodegradable bacterial cellulose (BC). BC is a fermentation product obtained by Gluconacetobacter xylinum using food or agricultural wastes as substrate. In this work we investigated the synergistic effect of zinc oxide nanoparticles (ZnO NPs) and propolis extracts deposited on BC. ZnO NPs were generated in the presence of ultrasounds directly on the surface of BC films. The BC-ZnO composites were further impregnated with ethanolic propolis extracts (EEP) with different concentrations.The composition of raw propolis and EEP were previously determined by gas-chromatography mass-spectrometry (GC-MS), while the antioxidant activity was evaluated by TEAC (Trolox equivalent antioxidant capacity). The analysis methods performed on BC-ZnO composites such as scanning electron microscopy (SEM), thermo-gravimetrically analysis (TGA), and energy-dispersive X-ray spectroscopy (EDX) proved that ZnO NPs were formed and embedded in the whole structure of BC films. The BC-ZnO-propolis films were characterized by SEM and X-ray photon spectroscopy (XPS) in order to investigate the surface modifications. The antimicrobial synergistic effect of the BC-ZnO-propolis films were evaluated against Escherichia coli, Bacillus subtilis, and Candida albicans. The experimental results revealed that BC-ZnO had no influence on Gram-negative and eukaryotic cells.

A. Mocanu, G. Isopencu, C. Busuioc, O. M. Popa, P. Dietrich and L. Socaciu-Siebert
Scientific Reports volume 9, Article number: 17687

Hydrothermal carbonisation (HTC) has been demonstrated to be a sustainable thermochemical process,
capable of producing functionalised carbon materials for a wide range of applications. In order to better
apply such materials, the local chemistry and reaction pathways governing hydrothermal carbon growth
must be understood. We report the use of scanning transmission X-ray microscopy (STXM) to observe
chemical changes in the functionality of carbon between the interface and bulk regions of HTC. Spatiallyresolved,
element-specific X-ray photo-absorption spectra show the presence of differing local carbon
chemistry between bulk “core” and interface “shell” regions of a glucose-derived hydrothermal carbon
spherule. STXM provides direct evidence to suggest that mechanistic pathways differ between the core
and shell of the hydrothermal carbon. In the shell region, at the water-carbon interface, more aldehyde
and/or carboxylic species are suspected to provide a reactive interface for bridging reactions to occur
with local furan-based monomers. In contrast, condensation reactions appear to dominate in the core,
removing aryl-linking units between polyfuranic domains. The application of STXM to HTC presents
opportunities for a more comprehensive understanding of the spatial distribution of carbon species
within hydrothermal carbon, especially at the solvent-carbon interface.

L.J.R. Higgins, A. P. Brown, J. P. Harrington, A. B. Ross, B. Kaulich and B. Mishra
Carbon 161 (2020) 423-431

In this paper, we present for the first time the obtaining and characterization of new antibacterial and biocompatible nano-ZnO–bacterial cellulose (BC) material with controlled interfaces for studying in vitro microorganisms (Escherichia Coli (ATCC 8737), B. subtilis Spizizenii Nakamura (ATCC 6633), Candida albicans (ATCC10231)) and mammalian cells (human dermal fibroblast cells) response. The use of BC based material with controlled characteristics in terms of quantity and distribution of ZnO onto BC membrane (with 2D and 3D fibers arrangement) is directly correlated with the surface chemical and topographical properties, the method of preparation, and also with the type of cells implied for the specific application within the bioengineering fields. In our study, the uniform distribution and the control on the quantity of ZnO nanoparticles onto 3D BC were obtained using matrix assisted pulsed laser evaporation (MAPLE) method. The influence on particle distribution onto 3D bio cellulose were investigated based on two types of solvents (water and chloroform) involved in target preparation within MAPLE deposition. The attachment of the nanoparticles to the bacterial cellulose surface and fibrils was demonstrated by SEM and FT-IR studies. The BC-ZnO showed both resistance to bacteria-sticking and non-cytotoxic effect on the human dermal fibroblasts cells at a mass distribution onto surface of 1.68 µg ZnO NPS/mm². These results represent a good premise in terms of tailoring BC substrates with ZnO particles that could determine or enhance both the biocompatibility and antibacterial properties of BC-composite materials.

V. Dinca, A. Mocanu, G. Isopencu, C. Busuioc, S. Brajnicov, A. Vlad, M. Icriverzi, A. Roseanu,
M. Dinescu, M. Stroescu, A. Stoica-Guzun, M. Suchea
Arabian Journal of Chemistry
Volume 13, Issue 1, January 2020, Pages 3521-3533

Furfuryl alcohol, a vital intermediate for the production of foundry resins, fragrances, pharmaceuticals and
pesticide, is produced by hydrogenation of furfural in gas phase or liquid phase. The furfuryl alcohol production
in gas phase over silica supported copper catalyst is favored thanks to the environmental and technical advantages.
The effect of preparation methods of silica supported copper catalysts on the structure and performance
was investigated by means of ICP, N₂ physisorption, ex-situ/in-situ XRD, in-situ XPS, FT-IR, H₂-TPR, TEM,
N₂O titration, TG as well as furfural hydrogenation. The results indicated that the different catalyst synthesis
strategies led to the diverse copper species in the calcined samples and disparate Cu⁰ surface area as well as
different molar ratio of Cu⁺/(Cu⁺+Cu⁰) in the fresh samples. The performance of impregnation derived
sample was poorer than that of commercial CuCr-Strem catalyst. The catalysts prepared by deposition precipitation
and ion exchange exhibited similar performance to the CuCr-Strem. The ammonia evaporation derived
catalyst (Cu/SiO₂-EA) showed superior performance in the activity, selectivity and stability among all the studied
catalysts. The excellent performance was related to the highest surface area of Cu⁰, smallest copper particle
size, large surface area and pore volume as well as appropriate higher Cu⁺/(Cu⁺+Cu⁰) ratio. Furthermore, all
the copper catalysts went through deactivation, which was caused by carbon deposition, during the reaction.
Owing to the largest amount of Cu⁰ sites and large SBET, the Cu/SiO₂-EA exhibited the slowest deactivation rate.

H. Dua, X. Ma, P. Yana, M. Jianga, Z.Zhaoa and C. Zhang
Fuel Processing Technology
Volume 193, October 2019, Pages 221-231

The production of furfuryl alcohol from furfural hydrogenation in gas
phase is of great significance for the valorization of biomass. The existing catalyst for
this transformation suffers from high cost and complex preparation process. Thus, a
highly efficient copper catalyst was developed by a simple impregnation method
using ethanolamine modified granular silica as carrier.
The catalytic performance was related to the amount of ethanolamine used in modification.
Highly dispersed copper with uniform particle size distribution was obtained from appropriate amount of
ethanolamine modified granular silica. The ethanolamine modified granular silica
(mass ratio between ethanolamine and silica was 3 in the initial modification mixture)
supported copper catalyst exhibited the best performance in terms of catalyst lifetime
thanks to its maximum amount of Cu⁰ sites and largest amount of Cu⁺ sites. A slow
deactivation of the catalyst after extended time on stream evaluation is attributed to
carbon deposition and slow copper sintering.

H. Du, X. Ma, M. Jiang, P. Yan and Z. C. Zhang
Applied Catalysis A, General
APCATA 117598

Although graphite-like carbon (GLC) films have been used to protect the engineering components due to their
high mechanical properties and low friction coefficients, the poor interfacial bonding strength and high internal
stress can lead their rapid failure. In this study, the bias-gradient (30–120 V) as well as the usual constant bias
protocols (30, 60 and 120 V) has been adopted to deposit the GLC films on 316 L stainless steel and silicon using
unbalanced magnetron sputtering technology. Based upon the microstructure and composition analysis by SEM,
AFM, XRD, Raman and XPS, the sp³ content and compactness of the films are increased with the increase of the
deposition bias. Compared to the film at the constant bias of 120 V, the bias-graded film has a comparable
hardness but superior adhesive strength. Detailed fretting wear testing under ambient air and dry N₂ atmospheres
against 25mm diameter Si₃N₄ ball has been carried out. The friction curves disclosed a three-stage
evolution feature: the surface working area, the interlayer transition area and the coating failure area. The biasgraded
film displayed the lowest friction coefficient and the longest fatigue life. Further the fretting mechanisms
at different stages have been elaborated in terms of the chemical composition, microstructure and mechanical
properties.

X. Shi, T. W. Liskiewicz, B. D. Beake, Z. Sun and J.Chen
Applied Surface Science 494 (2019) 929–940

A solar light-active copper-metal organic framework (Cu-MOF) was constructed through a multiple-linker
strategy employing 1,2,4,5-benzenetetracarboxylic acid (H4btec) and 4,40^´ -bis(1-imidazolyl)biphenyl (bimb)
as ligands. A reaction mixture consisting of ligands and Cu-metal salts was heated to a critical point in a
hydrothermal reactor. The constructed MOF was studied for materials chemistry through successive
analytical techniques. The MOF exhibited a planar structure as seen from the topography obtained from
electron microscopy and substantiated further by crystallographic analyses. Spectroscopic analyses clearly
revealed its remarkable ability to harvest visible light. Photoluminesce demonstrated the effect of organic
conjugation over the transition of d–d electrons. Our study clarified the crucial part played by ligand to
metal charge transfer in charge-carrier generation. The adopted bi-linker approach enhanced the
photoactivity and prolonged the lifetime of the charge carriers. This was evident in a solar photocatalysis
experiment through complete removal of 2-chlorophenol in a short period of time. The robust structural
stability provided by the linkers was established through thermogravimetric analysis, whereas photostability
was established through successive photocatalytic experiments employing the recovered MOF.

N.A. Surib, A. Kuila, P. Saravanan, L. C. Simc and K. H. Leong
NewJ.Chem., 2018, 42, 11124

Near-ambient pressure–x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., at ca. 2500 Pa, or even higher in some cases. With NAP-XPS, XPS can probe particles, moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission, we show survey, narrow (Zr 3p, Zr 3d, and O 1s), and Auger (O KLL) NAP-XPS scans of ZrO₂ particles. Charge compensation for this insulating sample took place via the residual gas in the chamber. Zirconia is an important ceramic material. Accordingly, the XPS spectra of zirconia should be useful references.

D. Shah, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 024001 (2019);

Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., greater than 2500 Pa. With NAP-XPS, a wide variety of unconventional materials can be analyzed, including moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. Charge compensation with NAP-XPS takes place simply through the residual/background gas in the chamber, which is ionized by the incident x-rays. High quality spectra—high resolution and good signal-to-noise ratios—are regularly obtained. This article is an introduction to a series of papers in Surface Science Spectra on the NAP-XPS characterization of a series of materials. The purpose of these articles is to introduce and demonstrate the versatility and usefulness of the technique.

D. I. Patel, T. Roychowdhury, V. Jain, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 016801 (2019)

Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., at greater than 2500 Pa. With NAP-XPS, XPS can probe moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission, we show survey, C 1s, O 1s, and N 1s narrow scans from an aqueous solution of a common protein, bovine serum albumin. The C 1s peak envelope is well fit to four symmetric peaks of equal width that correspond to carbon bonded to carbon and hydrogen (C-1), carbon singly bonded to oxygen (C-2), carbonyl and/or amide carbon (C-3), and carboxyl carbon (C-4). Two possible peak fits are considered for the N 1s and O 1s peak envelopes. The N 1s signal is fit to four peaks that correspond to amine (—NH₂), amide (O˭C‒NH₂), ammonium (—NH₃⁺), and N₂(g) nitrogen, and alternatively to three peaks that correspond to amine, amide, and N₂(g) nitrogen. The O 1s peak envelope is similarly fit to three and four components.

V. Jain, M. Kjærvik, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 014027 (2019)

Near-ambient pressure–x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., at greater than 2500 Pa. With NAP-XPS, XPS can probe moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. Polytetrafluoroethylene (PTFE) is an important polymer with many applications in science and industry. It is an insulator that charges under x-ray illumination at high vacuum. In this submission, we show NAP-XPS spectra of PTFE. Survey spectra are shown at different background gas (air) pressures. These spectra contain F 2s, C 1s, O 1s, N 1s, F 1s, and F Auger signals. Also presented are F 1s narrow scans over a range of background pressures and illumination times. Peaks decrease in width, shift toward literature values, and improve in shape with increasing background gas pressure.

V. Jain, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 014028 (2019)

In this submission, we show survey, O 1s, and C 1s near ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) spectra from a hard Italian cheese, a material that could not be analyzed by conventional approaches without special sample preparation. The C 1s spectrum is fit under the assumption that the surface of the cheese is primarily fat (triglyceride), which is expected to be the lowest free energy component of the material. The O 1s envelope corresponding to the cheese was well fit to two components of equal area.

T. Roychowdhury, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 014015 (2019)

In this article, we focus on the features of a modern XPS software package: the Specslab Prodigy system, which is used in most SPECS instruments. Software packages are an integral part of almost any analytical instrument these days, and purchasing decisions are often based as much on the software of an instrument as its hardware.

Here, we discuss some of the software innovations that are part of the EnviroESCA. These capabilities make this instrument and other SPECS instruments relatively easy to use and improve their data collection and workup capabilities. Two areas of focus
here will be the software’s ability to save and allow examination of every individual narrow scan, and its ability to interlace during data acquisition, i.e., alternate between taking different narrow scans and survey scans to avoid taking a block of any one type of scan.

S. Chatterjee, A. Thißen, P. Dietrich, C. Fleischer, C. V. Cushman, J, Banerjee, N. J. Smith, M. R. Linford,
Vacuum Technology & Coating, December 2017

Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., greater than 2500 Pa. With NAP-XPS, XPS can probe moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission, we show the survey, O 1s, valence band, and O KLL Auger NAP-XPS spectra of oxygen gas, O2, a material that would be difficult to analyze by conventional XPS. A small N 1s signal from N₂(g) is also observed in the survey spectrum. The O 1s narrow scan is fit to Gaussian-Lorentzian sum functions. The Lorentzian character of this synthetic line shape was varied to obtain the best fit. Since it is likely that O₂(g) will be present in other NAP-XPS analyses, these data should serve as a useful reference for other researchers.

T. G. Avval, S. Chatterjee, G. T. Hodges, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 014021 (2019)

Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., greater than 2500 Pa. With NAP-XPS, XPS can probe moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission, we show survey, O 1s, C 1s, S 2p, and S 2s NAP-XPS spectra from dimethyl sulfoxide (DMSO), a widely used organic solvent that is miscible with water. The sample was analyzed directly in its native, liquid state at room temperature. In general, both liquid and gas phase peaks are observed in the narrow scans. Due to the importance of DMSO in both chemistry and biology, it is likely that it will appear in future NAP-XPS analyses. Accordingly, these data may serve as a reference for future work.

T. G. Avval, C. V. Cushman, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 014020 (2019)

Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., at greater than 2500 Pa. With NAP-XPS, XPS can probe moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission, we show the survey, O 1s, C 1s, valence band, O KLL Auger, and C KLL Auger NAP-XPS spectra of gaseous carbon dioxide, CO₂, a material that would be difficult to analyze by conventional XPS. A small N 1s signal from N₂(g) is also observed in the survey spectrum. The C 1s and O 1s signals in the narrow scans are fit to Gaussian–Lorentzian sum and asymmetric Lorentzian (LA) functions. Better fits are obtained with the LA synthetic line shape. Since it is likely that CO₂(g) will be present in other NAP-XPS analyses, these data should serve as a useful reference for other researchers.

T. G. Avval, S. Chatterjee, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 014022 (2019);

Near-ambient pressure–x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., greater than 2500 Pa. With NAP-XPS, XPS can analyze moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission, we show survey, 2s, 2p, 3s, 3p, and the Auger LMM NAP-XPS spectra from argon gas, a material that could not be analyzed at moderate pressures by conventional methods. A small N 1s signal from residual nitrogen gas in the chamber is also present in the survey spectrum.

D. I. Patel, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 014024 (2019)

Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., greater than 2500 Pa. With NAP-XPS, XPS can be used to probe moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission, we show survey and O 1s NAP-XPS spectra from water vapor, a material that could not be analyzed at moderate pressures by conventional approaches and that is expected to be present in many analyses.

D. I. Patel, D. Shah, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 014026 (2019)

Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., at greater than 2500 Pa. With NAP-XPS, XPS can analyze moderately volatile liquids, biological samples, porous materials, minerals, and/or polymeric materials that outgas significantly. In this submission, we show NAP-XPS survey and Ca 2p, O 1s, and C 1s narrow scans from calcite, which was analyzed here without external charge compensation. Quantitation of the peaks in the narrow scan gives a ratio that is very close to the theoretical 1:1:3 ratio expected for Ca:C:O in the material. The small N 1s signal in the survey spectrum is attributed to residual nitrogen gas in the analysis chamber.

T. Roychowdhury, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 014025 (2019)

Bacteria are inherently in a hydrated state and therefore not compatible to ultra‐high vacuum techniques such as XPS without prior sample preparation involving freeze drying or fast freezing. This has changed with the development of near‐ambient pressure (NAP)‐XPS, which makes it possible to characterise the bacterial surface with minimal sample preparation. This paper presents NAP‐XPS measurements of Escherichia coli under various NAP conditions: at 11 mbar in a humid environment, at 2 mbar after drying in the chamber, pre‐dried at 4 mbar, and at 1 mbar after overnight pumping at 10⁻⁴ mbar. The high‐resolution spectra of carbon, nitrogen, and oxygen are presented and found to be in general agreement with XPS measurements from freeze‐dried and fast‐frozen bacteria. However, it was found that the amount of carbon components associated with polysaccharides increases relative to aliphatic carbon during drying and increases further after overnight pumping. This implies that drying has an impact on the bacterial surface.

M. Kjærvik, K. Schwibbert, P. Dietrich, A. Thissen, W. E. S. Unger
Surf Interface Anal. 2018;1–5.

Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., greater than 2500 Pa. With NAP-XPS, XPS can be used to analyze moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission, the authors present the NAP-XPS survey, C 1s, O 1s, Ca 2p, and P 2p narrow scans from a human adult molar tooth, a biological material that would be challenging to analyze by conventional approaches. No pretreatment or cleaning of this dental specimen was performed prior to analysis. Three different regions (top, middle, and root) of the tooth were analyzed. The survey spectra, which differed considerably from each other, show the presence of carbon, oxygen, nitrogen, calcium, and phosphorous. Tin and sulfur are also present in small amounts on the top part of the tooth. C 1s narrow spectra are well fitted with four synthetic peaks.

D. Shah, T. Roychowdhury, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 014016 (2019)

Nitrogen fixation in a simulated natural environment (i.e., near ambient pressure, room temperature, pure water and incident light) would provide a desirable approach to future nitrogen conversion. As N≡N triple bond has a thermodynamically high cleavage energy, nitrogen reduction under such mild conditions typically undergoes associative alternating or distal pathways rather than follows a dissociative mechanism. Here we report that surface plasmon can supply sufficient energy to activate N₂ through a dissociative mechanism in the presence of water and incident light, as evidenced by in-situ synchrotron radiation-based infrared spectroscopy and near ambient pressure X-ray photoelectron spectroscopy. Theoretical simulation indicates that the electric field enhanced by surface plasmon, together with plasmonic hot electrons and interfacial hybridization, may play a critical role in N≡N dissociation. Specifically, AuRu core-antenna nanostructures with broaden light adsorption cross section and active sites achieve an ammonia production rate of 101.4 μmol·g^-1·h^-1 without any sacrificial agent at room temperature and 2-atm pressure. This work highlights the significance of
surface plasmon to activation of inert molecules, serving as a promising platform for developing novel catalytic systems.

C. Hu, X. Chen, J. Jin, Y. Han, S. Chen, H. Ju, J. Cai, Y. Qiu, C. Gao, C. Wang, Z. Qi, R. Long, L. Song, Z. Liu, Y. Xiong
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 30 Apr 2019

Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., greater than ca. 2500 Pa. With NAP-XPS, XPS can probe moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission, we show NAP-XPS of sesame seeds, a food sample that could not be analyzed at moderate pressures by conventional approaches. Survey spectra from three separate seeds are shown. In addition to the expected C 1s and O 1s signals, seeds show calcium. The C 1s narrow scans from the three seeds are well fit by four components. The largest of these is attributed to carbon singly bonded to oxygen (C—O), which suggests carboydrates or cellulose in the material. A small N 1s peak is observed in all the survey spectra.

T. Roychowdhury , S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 014018 (2019)

Near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., greater than 2500 Pa. With NAP-XPS, XPS can be used to probe moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission, we show O 1s, C 1s, and Ca 2p narrow scans and a survey NAP-XPS spectrum from a human urolith, i.e., a kidney stone, which is a biomaterial that could not be analyzed at moderate pressures by conventional approaches.

T. Roychowdhury, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 014017 (2019)

Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., at greater than 2500 Pa. With NAP-XPS, XPS can probe moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission, we show NAP-XPS survey, Ca (3p, 2p, 2s), O 1s, C 1s, and N 1s narrow, and valence band spectra from a clamshell, a material of biological origin that would be challenging to analyze by conventional XPS approaches. Like most shells of biological origin, clamshells are primarily composed of calcium carbonate.

T. Roychowdhury, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 014019 (2019)

X-ray photoelectron spectroscopy (XPS) has become a routine analysis method to determine the chemical composition and bonding states of elements of sample surfaces in many industrial applications, like materials development, failure analysis, quality control and device certification. To obtain significant results the analyses of such samples require a fast analysis with reliable quantification and stable data for repeated experiments. In standard XPS experiments under ultrahigh vacuum (UHV) conditions the significance of the results can be affected by changing surface compositions under the analysis conditions, different degrees of degassing and thus changing degrees of differential charging in insulating samples. In this publication the positive influence of XPS analysis under elevated pressures, often named Near-Ambient Pressure XPS or “Environmental XPS” is shown for different samples. Furthermore the process of charge compensation in gas pressures of 1–2 mbar is introduced, followed by a discussion of the perspectives of this “Environmental Charge Compensation”. The paper discusses the efficiency and stability of Environmental Charge Compensations for typical insulating test samples, as well as for different bulk insulators. The additional capability of XPS in elevated pressures is demonstrated on a superabsorbent polymer typically used in diapers, showing the difference of the analysis results for its wet and dry state. The paper ends with the example of a commercial printed circuit board demonstrating the power of the method for routine analysis of complete devices.

P. Dietrich, S. Bahr, T. Yamamoto, M. Meyer, A. Thissen
Journal of Electron Spectroscopy and Related Phenomena;
Volume 231, February 2019, Pages 118-126

Porous silicon (PSi) offers extremely attractive optical, electronic and biofunctional properties for the development of biosensors. In the present work, we have studied the step by step sandwich biofunctionalization cascade of a PSi platform by near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and, in parallel, we have developed a three electrode PSi device sensitive to changes in surface conductance. Prior to the NAP-XPS characterization, the organosilanization with glycidyloxy-propyl-trimethoxy-silane, the bioconjugation, and the gold nanoparticle (AuNP) sensitization layer were monitored by spectroscopic ellipsometry. The NAP-XPS analysis revealed outstanding results: a) the NAP-XPS chamber allows detecting the pristine PSi with negligible adventitious carbon contamination, b) the single oxygen bonded carbon component of the Glycidyl group dominates the C1s core level after organosilanization, c) the good progress of the biofunctionalization/recognition is confirmed by the increase of the silica to silicon component ratio in the Si2p core level and, d) the N1s core level describes identical features from the presence of aminoacid sequences in the capture/detection steps. A FET sensing of a prostate specific antigen (PSA) marker was performed through conjugation with AuNPs. For a given concentration of PSA (and AuNPs) the conductance increased with the increase of the gate voltage. For a given gate voltage, the conductance was observed to increase for increasing concentration of PSA. This allowed proposing a calibration line for the biosensor, which is valid from a clinically relevant range of 0.1 ng/mL.

C. Rodriguez, P. Dietrich, V. Torres-Costa, V. Cebrián, C. Gómez-Abad, A. Díaz, O. Ahumada, M. M. Silván
Applied Surface Science, Available online 6 June 2019

Two systems of suspended nanoparticles have been studied with near-ambient pressure x-ray photoelectron spectroscopy: silver nanoparticles in water and strontium fluoride—calcium fluoride core-shell nanoparticles in ethylene glycol. The corresponding dry samples were measured under ultra high vacuum for comparison. The results obtained under near-ambient pressure were overall comparable to those obtained under ultra high vacuum, although measuring silver nanoparticles in water requires a high pass energy and a long acquisition time. A shift towards higher binding energies was found for the silver nanoparticles in aqueous suspension compared to the corresponding dry sample, which can be assigned to a change of surface potential at the water-nanoparticle interface. The shell-thickness of the core-shell nanoparticles was estimated based on simulated spectra from the National Institute of Standards and Technology database for simulation of electron spectra for surface analysis. With the instrumental set-up presented in this paper, nanoparticle suspensions in a suitable container can be directly inserted into the analysis chamber and measured without prior sample preparation.

M. Kjærvik, A. Hermanns, P. Dietrich, A. Thissen, S. Bahr, B. Ritter, E. Kemnitz, W. E S Unger
Marit Kjærvik et al 2017 J. Phys.: Condens. Matter 29 474002

Liquid phase adsorption is a common technique in waste water purification. However, this process has some downsides. The removal of environmentally harmful contaminants from organic liquids by adsorption produces secondary waste which has to be treated afterwards. The treatment can be e.g. high temperatures or a landfill. Photocatalysts such as CN6 can remove the dye under light irradiation but most times they have to be separated afterwards. Immobilisation of these photocatalysts can be one way to address this problem. The resulting photocatalyst layers were analysed in operando by near-ambient pressure XPS. This enabled us to detect the active species, i.e. oxygen radicals, at the surface, responsible for the dye degradation.

J. Rieß, M. Lublow, S. Anders, M. Tasbihi, A. Acharjya, K. Kailasam, A. Thomas, M. Schwarze, R. Schomäcker
Photochem. Photobiol. Sci., 2019, Advance Article

D. Shah, S. Bahr, P. Dietrich, M. Meyer, A. Thißen, M. R. Linford
Surface Science Spectra 26, 014023 (2019)