NAP-XPS and NAP-UPS

NAP-PES combines the strengths of XPS, a quantitative determination of the surface chemical composition at a low detection limits, with the ability to measure liquids, gases and their interfaces to solids, simulating environmental conditions, avoiding degradation and allow for operando-studies.

X-ray photoelectron spectroscopy (XPS) and Ultraviolet photoelectron Spectroscopy (UPS) is used to analyze the surface chemistry of a material. XPS spectra are obtained by illuminating the sample surface with monochromatic X-rays and eventually measuring the photo emitted electrons. With XPS the elemental composition and the chemical state of the detected elements can be determined quantitatively in the surface region with an information depth of up to 10 nm.

EnviroESCAs special system design and many NAP-XPS system designs allow for investigations of a large variety of different samples, including insulating samples, gases, liquids and their interfaces that are not accessible with standard XPS systems. The sample to be investigated is the central part of every X-ray Photoelectron Spectroscopy (XPS) system. In a NAP-XPS system or the EnviroESCA the sample needs to be positioned underneath the analyzer nozzle which is the entrance to the analysis section of the machine. Samples can be flat surfaces or really rough three dimensional structures. They can be very tiny with a diameter of just a few hundreds of microns or as large as 10 mm in NAP-XPS and 120 mm in EnviroESCA.

Besides the sample itself and the analyzer an X-ray source is the third part needed to perform an XPS analysis of a surface to gain insights into its chemical composition on the molecular level. The X-rays used in the EnviroESCA are called soft X-ray because of their energy. Their energy is so low, compared to medical X-ray sources that the stainless steel or µ-metal chamber walls of the machine will absorb them completely so that no X-rays will leave the system. The beam of X-rays is focused into a spot on the sample to be analyzed of about 300 µm in diameter defining the analysis region.

X-ray Photoelectron Spectroscopy based on the physical principle of Photoionization. Whenever a photon of high enough energy interacts with an atom in the uppermost surface layers (roughly 10 nm) an electron of a specific energy is being released. The energy is characteristic for the element and the nearest neighbors of the atom in the surface layer. Therefore it is not only possible with XPS to determine the surface concentration of an element down to 0.1 atomic percent but also its binding conditions to other atoms and molecules.

In conventional XPS systems where the analysis region needs to be kept under vacuum an effect occurs that is named surface charging. Imagine a sample that is nonconductive and the impinging X-ray photons continuously removing electrons from the analysis region than the sample will slowly be charged up positively. The escaping electrons will be influenced in their path and energy by the positive charges at the surface. To prevent the surface from charging up conventional XPS systems are equipped with electron and ion guns that can be tuned in a way that additional charges will be brought to the surface region compensating the lost charges due to the photoionization process. A really difficult and time consuming task.

NAP-XPS systems or EnviroESCA are not conventional XPS systems but Ambient Pressure XPS (AP-XPS) systems. Which means it does not require the sample to be kept under vacuum. A low pressure of less than 50 mbar is sufficient. This extremely high working pressure when compared to conventional systems opens up the field of biology, biochemistry, astrobiology, medicine and others.  Non vacuum conditions to operate in means that the sample can be outgassing or even be a liquid with a vapor pressure in this range. Mainly it means that there are neutral gas atoms surrounding the sample. Whereby it does not matter if they evaporate from the surface or if one uses the built-in gas delivery system of the to bring gas molecules to the analysis region.

The impinging X-ray photons will also interact with the neutral gas atoms and ionize those generating free positive charged ions and electrons. These free charges act as a charge cloud above the surface layer of the sample. Allowing every escaping electron from the surface to be exchanged against an electron of the charge cloud. We call this intrinsic charge neutralization effect Environmental Charge Compensation. It allows the user to easily acquire high resolution XPS spectra from nearly any surface independent if it is liquid, solid, conductive or nonconductive with ease.

NAP-XPS also works at synchrotron beamlines with variable photon energies. A special beam entrance stage either with differential pumping or a Si3N4-window has to be used in this case.

With special small spot UV-sources with additional differential pumping and a Al-window ín front also UV light (classically He I and He II radiation) can be used to excite electrons under NAP conditions, so that also changes in the valence band structure in pressure of up to 1 mbar can be studies.

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APPLICATION NOTES

XPS of Ag and N2 at 25 mbar
This application note shows near ambient pressure (NAP) measurements performed with the NAP XPS System for the University of Norte Dame, Prof. Franklin Tao.
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Investigation of Polymers and Plastics with EnviroESCA
This application note describes how EnviroESCA can be used to analyze the surface of polymers and bulk insulating material. EnviroESCAs ability to perform X-Ray Photoelectron Spectroscopy (XPS) at non vacuum conditions shows its main advantage when being applied to insulating material. Specimens that tend to charge up under vacuum conditions and need to be extensive charge compensated with expensive low energy electron and low energy ion sources can be measured with ease and without the problem of overcompensation.
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Real World Device Inspection Application with EnviroESCA
This application note introduces EnviroESCA as a tool for real world device inspection for microelectronics. A printed circuit board was taken directly from the sales packaging and was investigated with XPS. The measurements concentrate on the crucial parts like contact surfaces and soldering joints. EnviroESCA and near ambient pressure XPS (NAP-XPS) in quality control applications aims to optimize manufacturing processes and device quality in general.
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Investigation of Hydrogel Contact Lenses with EnviroESCA
In this application note we analyze the surface of water filled hydrogels with EnviroESCA, Here, contact lenses serve as an example for medical and biomaterials. The advantage of such investigations under non ultrahigh vacuum conditions is demonstrated and results from wet and dry samples are compared.
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XPS surface analysis of Zeolites with EnviroESCA
In this note we demonstrate how the surface of Clinoptilolite, a natural zeolite, can be analysed with EnviroESCA. It describes how the Environmental Charge Compensation can be used to compensate for charging of the sample surface to be able to measure X-ray Photoelectron Spectra with ease.
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XPS surface analysis of a leaf with EnviroESCA
This application note presents the application of EnviroESCA to the field of biology and surface spectroscopy of biological samples. X-ray Photoelectron Spectroscopy (XPS) measurements on different sites of a leaf will be discussed. It will be shown that XPS is able to detect residues of calcium chloride, being used as a fertilizer, on the leafs surface.
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EnviroESCA and NAP-XPS in the field of Cosmetic Science
This application note presents the application of EnviroESCA to the field of Cosmetic Sciences and Forensic Sciences. Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS) measurements on human hair treated with different personal hair care products.
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EnviroESCA applications in Scientific Archaeology
In the present application note EnviroESCA is used for chemical Analysis in the field of Archaeometry. Besides the ability of Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS) to analyze the surface composition of metallic and nonmetallic specimens, EnviroESCA allows for a nondestructive analysis of artifacts without special pretreatment procedures.
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XPS surface analysis of a coffee bean with EnviroESCA
The Analysis of food and natural products under environmental conditions is of great importance due to their daily use and direct interaction with humans during consumption. In this study we investigated a roated coffee bean. Charge compensation of this insulating natural product is accomplished by Environmental Charge Compensation enabling X-ray photoelectron spectroscopy on such biological material with ease.
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XPS surface analysis of an ionic liquid with EnviroESCA
This application note presents how EnviroESCA can be used to analyze the surface of ionic liquids in contact with gases under application relevant conditions in the near ambient pressure region.
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XPS surface analysis of sesame seeds with EnviroESCA
Results of the surface analysis of untreated food samples, e.g., sesame seeds, measured with EnviroESCA are presented. High resolution and high quality spectra are recorded using Environmental Charge Compensation even for samples in bulk quantities.
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XPS surface analysis of printed paper samples with EnviroESCA
Results of the surface analysis of four paper samples obtained in EnviroESCA are presented. Neutralization of this insulating biopolymer is accomplished by Environmental Charge Compensation enabling X-ray Pho-toelectron Spectroscopy (XPS) on such important natural material with ease.
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XPS surface analysis of Italian hard cheese with EnviroESCA
This application note presents how EnviroESCA can be used to analyze the surface of food samples, e.g., Italian hard cheese. Due to the advanced vacuum system of EnviroESCA the surface analysis of Food samples even in the presence of fat and oils or volatiles is performed without problems.
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Investigation of a Superabsorbent Polymer (SAP) with EnviroESCA
In this study we show how EnviroESCA can be used to analyze the surface of superabsorbent polymers under different environmental conditions. EnviroESCA’s ability to perform X-ray Photoelectron Spectroscopy (XPS) under ambient conditions shows its main advantage when being applied to insulating material that change their surface (chemistry) when they come in contact with different liquids and gases - in this case water. Specimens that tend to charge up under vacuum conditions can be measured with ease.
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XPS surface chemical analysis of aqueous solutions with EnviroESCA
In this study we present the capabilites of EnviroESCA to analyze the surface of various aqueous solutions under near ambient pressure conditions. Such investigations of aqueous solutions are of paramount importance due to the vast number of essential water based processes in nature and industry.
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XPS surface analysis of a human urolith with EnviroESCA
A single human urinary stone (urolith) was characterized using EnviroESCA. The result of surface chemical analysis of the as received samples is presented. Charge neutralization on this insulating material is accomplished by Environmental Charge Compensation.
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XPS surface analysis of human tooth samples with EnviroESCA
Human teeth from an adult and a baby were studied using EnviroESCA. The results of surface chemical analysis of the as-received human tissues samples are presented. Neutralization of the insulating bio-material is accomplished by Environmental Charge Compensation enabling X-ray Photoelectron Spectroscopy (XPS) on tissues as tooth or bone.
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XPS surface analysis of cuttlefish bone samples with EnviroESCA
Biological mineral samples from a cuttlefish (sepia) were studied using EnviroESCA. The results of surface chemical analysis of the native and ion implantation treated samples are presented. Neutralization of the insulating biomaterial is accomplished by Environmental Charge Compensation enabling X-ray Photoelectron Spectroscopy (XPS) on tissue samples.
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XPS surface analysis of V2O5 upon heating with EnviroESCA
This application note presents how EnviroESCA can be used to analyze samples during heating under near ambient pressure conditions using various gas atmospheres. Such investigations of surfaces at elevated temperatures and pressures are of paramount importance for catalysis in nature and industry.
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XPS surface chemical analysis of bacterial samples with EnviroESCA
This application note presents how EnviroESCA can be used to analyze bacterial samples under near ambient pressure conditions in various states of hydration using different levels of humidity. Such investigations of bacterial cell wall surfaces in their hydrated state are essential for studying biological interfaces at work.
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Near-ambient pressure XPS of hydrated Escherichia coli samples with EnviroESCA
This application note presents how EnviroESCA can be used to analyze E. coli biofilms on silicon under near ambient pressure conditions in various states of hydration. Such investigations of the outer bacterial cell surface in their hydrated state are essential for studying biological interfaces at work.
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Gas Cluster Ion Beam (GCIB) sputtering with EnviroESCA
This application note presents how the optional GCIB source at the EnviroESCA can be used to clean samples prior to XPS analysis to get reproducible analytical data and reliable quantification results. Moreover, Argon cluster Arn⁺ (n=500-5000) sputtering and depth profiling of (bio)organic samples is possible which cannot be done when using monoatomic Arn+ sputtering.
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Corrosion study of a paper clip in vinegar with EnviroESCA
In this note we present (N)AP XPS results from the first comparative ex-situ and operando corrosion study on the reaction of commercial paper clips in concentrated vinegar solution containing 25% acetic acid.
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