Sample Preparation,  Sample Mounting,
& Sources of Samples

Philosophy for Sample Preparation – used by The XPS Library for this Database

Our fundamental philosophy is to collect spectra that are readily reproduced in laboratories that use monochromatic Al_K-α X-ray sources, and to work under real-world practical analysis conditions with minimal sample preparation. We have avoided special sample preparations or special cleaning procedures because they are not generally available.

In general, samples should be handled with freshly cleaned tools and analyzed in its' "as-received" condition. Vital information about the chemical or sample is provided by analyzing the as-received surface so it is vital to analyze the surface as-received.

After analyzing the sample in its' "as-received" condition, then we decide how best to prepare the sample to analyze the bulk of the sample which represents the true chemistry of the sample.  Clean, silicone oil free gloves should be used to handle all sample handling tools and the sample stage. Your service engineer should wear the same type of gloves when repairing your instrument.  If the analysis results reveal the presence of unexpected elements, then those elements are probably the result of natural minor components of the natural crystal, or accidental contamination by the chemical supplier, storage conditions, or sample preparation. This is valuable information that guides future sample preparation.

Types and Shapes of Samples and Materials used by The XPS Library for this Database

There are two basic types of chemicals that have been analyzed for this database. They are Inorganic and Organic chemicals. The database that uses a Periodic Table as its' interface, has spectra from Inorganic materials.  The database that uses a List of Polymers Table as its' interface has spectra from organic polymers and organic chemicals.

There are ten (10) basic shapes of samples (materials) that have been analyzed for this database.  The most common shapes are fine grained powders and thin sheets.

Shapes of Samples

1. fine grained powders (easy to press into a pellet)
2. thin sheets of pure metals
3. small lab-grown single crystals – ranging from 5 x 10 mm, 0.5 mm thick to 10 x 10 mm, 2 mm thick
4. large lab-grown single crystalline wafers of semiconductor materials (25 – 100 mm diameter, 1-2 mm thick)
5. natural crystals (poly-crystals) with various shapes and sizes
6. viscous oils and greases
7. films and sheets made from polymers
8. powders, pellets and beads made from polymers
9. thin coatings on wafers
10. coarse grains that require grinding with a mortar and pestle

Sample Preparation Method That Produces Clean Surface of Pure Bulk Chemistry

Sample Preparation Guide – listed in The PHI Handbook on XPS

This set of sample preparation guides provides an excellent brief set of instructions on preparing various types and shapes of sample and materials.

Click Here.

Preparation of "Native Oxide" Samples – used by The XPS Library for this Database

The samples known as "Native Oxides" are, in general, native oxides that formed in the lab air over many months time. These "Native Oxides" provide valuable information about the surface chemistry and the auto-oxidation of various metals.  These native oxides were analyzed as received without any treatment of any kind. All of these samples had been stored in a set of open-top drawers which were not air-tight and so the samples were exposed to the normal atmosphere of a laboratory for many months or years.

Most native oxides are 1-6 nm thick, and nearly all native oxides are less than 9 nm thick, but a there are a few of the native oxides were more than 10 nm thick due to the reactive nature of the metal (eg Mg, V, Pb).  These "thick" native oxides were too thick because we wanted to have an XPS signal from the underlying pure metal at the same time as have a signal from the native oxide.  The pure metal serves as a reference BE and may allow use to measure useful chemical shifts between the metal and the native oxide, which is often the most thermodynamically stable oxide of that metal.

To have useful spectra the "thick" (>10 nm) native oxides were scraped clean with a razor or a clean knife edge and then exposed to the normal atmosphere of the laboratory for a time period between 5 minutes and several days.  This scraping was done because the naturally formed native oxide or carbonate film was thick enough to hide the pure metal signal when the samples were analyzed by XPS. This method produces "freshly" formed native oxides which have probably not reached a thermodynamically stable state.

In the production of some spectra no attempt to produce a pure, clean surface, but some effort was made to produce surfaces with a minimum amount of natural surface contamination if needed. When ion etching was used to clean a material that contained more than one element, then ion etching was done with conditions that should minimize preferential sputtering.

A special experiment was performed on pure metals that were freshly ion etched to remove all of the native oxide on the pure metal. All of the freshly exposed pure metal surfaces were in a reactive state.  The reactivity of these fresh surfaces were measure by using the depth profile software routine with the ion gun turned OFF and the argon gas turned OFF so that the Argon ion beam was not active.  Immediately after turning off the argon ion beam, the depth profile routine was started.  Spectra were collected overnight for the metal signal, the O (1s) signal, and the C (1s) signal.  The delay time between data collection cycles was roughly 20 minutes during which the surface reacted with the gases that are residual in a cryo-pumped vacuum. In some cases, carbides and oxides progressively formed during the overnight run, and is other cases the surface collected only carbon without forming oxides or carbides.

Preparation of "Powdered" Samples – produced by The XPS Library for this Database

Fine-grained powdered samples were either pressed:

• into a 3 mm diameter pellet using a mechanical KBr pellet hand-press (from Aldrich) or
• pressed onto the surface of the sample stage by using a freshly cleaned spatula. Mild pressure was applied while sliding the spatula to the edge of the stage trying to make a smooth surface

Until analyzed, all powdered samples were kept stored in their original glass or plastic containers, which were packaged inside of plastic-lined aluminum bags. Just prior to XPS analysis, each bottle was opened in the normal air of the room where the XPS system was kept, and a small 50-100 mg portion of the sample was removed via a clean nichrome spatula and placed in the compression chamber of a hand-operated, stainless steel "KBr" pellet press. All finely powdered samples were compressed without any chemical treatments, which, if done, may have introduced unusual contamination or produced some change in the samples. The resulting pellets varied in thickness from 0.3 – 0.8 mm.

To avoid iron and /or chromium contamination transferred from the anvil, a thin sheet of paper was placed over the powder while it was in the compression chamber. Any powders, which were clumped together, were very gently ground into a loose powder just prior to compression. To avoid unnecessary heat-induced oxidation, those samples which were hard and granular were very gently ground into a fine powder in a agate marble mortar and pestle. As soon as each sample was removed from the compression chamber, it was mounted onto a small blob of silver (Ag°) paint sitting on a small aluminum block or a 5 mm wide round brass boat which was 1.3 mm in height.

Silver paint was used to trap black, conductive oxides inside of a small brass boat so that true conductors could produce true electron binding energies for those oxides that were indeed conductive. In general, each oxide was exposed to room air for <15 min.

Benefits of Pressing Powders into Pellets – produced by The XPS Library for this Database

A comparison of the electron count rates produced by using two different powder mounting methods revealed that a hard, smooth hand-pressed pellet produces 2-4 times higher electron count rates than a powdered sample dropped and loosely pressed onto double-sided tape or Indium foil.

By pressing the finely powdered oxides into hard smooth pellets, it was also found the surface charging behavior of these glossy or semi-glossy samples was very easy to control.  In general, we used the mesh-screen electron flood-gun combination with the flood gun set to 4-6 eV acceleration energy and approximately 0.5 mA filament current.

Problems Caused by Pressing Samples into Pellets – produced by The XPS Library for this Database

By pressing the finely powdered oxides into pellets, the surface of the resulting samples were usually smooth enough to appear glossy or semi-glossy, but some samples had iron or chromium contamination which indicated that the sample had undergone a pressure induced transfer of iron or chromium oxides from the stainless steel anvil. Very strong hand pressure caused some oxides to react with the stainless steel anvil, but "medium" hand pressure usually did not produce undesired iron and chromium contamination. All analyses that showed any unexpected contamination were repeated. Other forms of accidental contamination (chlorine or previously analyzed oxides) were caused by insufficient cleaning of the stainless steel anvil, which had been cleaned with a metal polishing solution (Pikal) and rinsed with distilled water and isopropanol. All analyses that showed any unexpected contamination were repeated.

Solution to Pressure Induced Contamination of Pellets

Experiments on ways to avoid the pressure-induced iron or chromium contamination, produced pellets with semi-smooth non-glossy surfaces which required more effort to produce good charge control.

The non-glossy surfaces of loose powders gave electron count rates that were about 10-50% lower than the hand pressed glossy or semi-glossy surfaces. As a result, we learned that smooth surfaces, which appear glossy or semi-glossy, greatly simplify efforts to control surface charging under the charge-control mesh-screen and also enhance the electron count rate by 10-50% more than a pellet that has a non-glossy, semi-rough appearance.

Extensive experiments on different methods to avoid contamination of the pellets revealed that contamination is minimized or avoided by using freshly cleaned aluminum foil as a "buffer" between the oxide powders and the metals in the steel anvil components. The aluminum foil, which is sold as a kitchen wrap material, is cleaned with 100% isopropanol (isopropyl alcohol) just prior to use. The foil is cut to a size that is readily useful with the pellet press device after it is cleaned. Alternately, we have also used a type of "glycine" paper which is commonly used to as a paper to hold powders when weighing a powdered sample. This "weighing" paper is common in many chemical laboratories and can be substituted for the aluminum foil whenever the pressing results with the aluminum foil produce undesired binding results. The glycine paper method sometimes introduces very small amounts of contaminants which produce a N (1s) and C (1s) signals. The amount of these contaminants is much smaller than the amount of contaminants that occur by simply pressing the powder without any sort of paper or aluminum foil buffers.

XPS Sample Preparation by PHI

in PHI Handbook on XPS
by Ulvac-Phi (Physical Electronics, PHI)

Preparing and Mounting Samples

For the majority of XPS applications, sample preparation and mounting are not critical. Typically, the sample is mechanically attached to the specimen mount, and analysis is begun with the sample in the as-received condition. Vital information is often hiding in the as-received surface so it can be vital to analyze the surface as-received.  Additional sample preparation is discouraged because any preparation might modify the surface composition. For those samples where special preparation or mounting cannot be avoided, the following techniques are recommended.

1. Removing Volatile Material
Ordinarily, materials known to retain solvents or gases are dried in a separate small vacuum chamber before analysis. In exceptional cases, when the volatile layer is of interest, the sample may be cooled for analysis. The cooling must be to a sufficiently low temperature to guarantee that the volatile element is not warmed to evaporation by any heat load that the analysis conditions may impart. Removal of unwanted volatile materials is usually accomplished by long-term pumping in a separate vacuum system or by washing with a suitable solvent. If you rinse a surface with a volatile solvent, then use freshly distilled solvent to avoid contaminating the surface with high boiling point impurities hiding in the solvent. Choice of the solvent can be critical. Hexane or other light hydrocarbon solvents are probably least likely to alter the surface, providing the solvent properties are satisfactory. Samples may also be washed efficiently in a Soxhlet extractor using a suitable solvent.

2. Removing Nonvolatile Organic Contaminants
When the nature of an organic contaminant is not of interest or when a contaminant obscures underlying material that is of interest, the contaminant may be removed with appropriate organic solvents. As with volatile materials, the choice of solvent can be critical.

3. Ion Sputtering – Ion Etching
Ion sputter-etching or other erosion techniques, such as the use of an oxygen plasma on organic materials, may be used to remove surface contaminants. This technique is particularly useful when removing adventitious hydrocarbons from the sample or when the native oxides, formed by exposure to the atmosphere, are not of interest. Argon ion etching is commonly used to obtain information on composition as a function of the exposure time to ion etching. Calibration of the sputter rates can be used to convert sputter time to information on depth into the specimen. Because sputtering may cause changes in the surface chemistry, identification of the changes in chemical stales with depth may not reflect the true composition.

4. Abrasion
Abrasion of a surface can be done without significant contamination by using a laboratory wipe or a cork. To remove more material, use fine sandpaper, a file or a single edged razor blade. This may cause local heating, and reaction with laboratory air may occur (e.g., oxidation in air or formation of nitrides in nitrogen). To prevent oxidation of more active materials, perform abrasion in an inert atmosphere such as a glove bag or glove box or while immersing the sample in an appropriate volatile organic solvent. The abraded material should then be transferred to the load-lock with immediate pump-down, or if possible load the sample into a high vacuum transfer box in a sealed vessel to preserve the clean surface.

5. Fracturing and Scraping inside High Vacuum
With proper equipment many materials can be fractured or scraped within the test chamber under UHV conditions. While this minimizes contamination by reaction with atmospheric gases, attention must be given to unexpected results which might occur. Fracturing might occur along the grain boundaries which may not be representative of the bulk material. Scraping can cover hard material with soft material whcn the sample is multiphase.

6. Grinding Grains into Powder
If spectra that are more characteristic of the bulk composition are desired, then samples may be ground to a powder in a mortar or if possible fractured in air (e.g. single crystal of NaCl). Protection of the fresh surfaces from the atmosphere is required so use a gently flow or Argon or Nitrogen gas to minimize reaction with air. When grinding samples, localized high temperatures can be produced, so grinding should be done slowly to minimize heat-induced chemical changes at the newly created surfaces. The mortar and pestle should be well cleaned before reuse.

7. Mounting Powders for Analysis
There are a number of methods which can be used to mount powders for analysis. Perhaps the most widely used method is dusting the powder onto a polymer-based adhesive tape with a camel-hair brush. The powder can be dusted across the surface carefully and lightly, with no wiping strokes.

Some researchers shun double-sided adhesive tape for UHV work, but many have successfully used certain types of tape in the 9e(-10) Torr range.

Alternative methods for mounting powders include pressing (he powder into indium or other soft foils, supporting the powder on a metallic mesh, pressing the powder into pellets or simply depositing the powder by gravity.

With the foil method, the powder is pressed between two pieces of pure foil. The pieces arc then separated, and one of them is mounted for analysis. Success with this technique has been varied. Sometimes regions of bare foil remain exposed and, if the sample is an insulator, regions of the powder might charge differently.

Differential charging can also be a problem when a metallic mesh is used to support the powder. If a press is used to form the powder into a pellet of workable dimensions, a press with hard and extremely clean working surfaces should be used. Protecting the surface of the pellet by inserting either fresh Aluminum foil, weighing paper or wax paper.

Gravity can effectively hold some materials in place, particularly if a shallow well or depression is cut in the surface of a 1-2 mm thick of Aluminum metal.

Allowing a liquid suspension of the powder to dry on the specimen holder is also an effective way of mounting a powdered sample on a sample mount.

8.  Sample Heights and Instrument Geometries must be Considered

The incident angle of the X-ray beam can be as low as 30 degrees relative to the plane of the sample so be sure that other samples on the sample mount will not block the X-ray beam or the flood gun beam or the Ar+ ion beam if needed.  If you can use a rotating sample stage, then it can help avoid blockage of one of the beams.

Sample Mounting Details

Sample Mounting – used by The XPS Library for this Database

In general, the "as-received" sample is mechanically trapped or attached onto the sample mount, sample stage, or inside a short sample cup. Additional sample preparation is discouraged because any preparation might modify the surface composition. For those samples where special preparation or mounting cannot be avoided, the following techniques are recommended. The methods used to mechanically trap solid samples involved the use of a spring-clip, double sided non-conductive tape, Indium foil, metal screws with large washers, or silver (Ag) paint (allowed to dry in lab air).

Because we wanted spectra with strong signals and high energy resolution, many samples were oriented to a 90 degree electron take-off-angle which is normal to plane of the sample mount.  To keep samples attached to the tilted sample holder which gave the strongest signal, we used double-sided adhesive tape, clips, screws and large washers, and silver (Ag) paint. In this orientation, we found that the electron flood gun in the S-Probe XPS instrument was still effective.

Sample Heights and Instrument Geometries – used by The XPS Library for this Database

Because it is possible to mount several samples at the same time we always checked the sample heights and geometries of adjacent samples to be sure that none of the samples block the X-ray beam or the flood gun beam or the Ar+ ion beam for each of the other samples.  By using a rotating sample stage, we were able to avoid blockage of any of the input beams.

Benefit of Tilting Sample to Produce an Elongated X-ray Analysis Area

A comparison of the electron count rates produced by using different electron take-off-angles revealed that a grazing X-ray beam produces 2-4 times higher electron count rates than the normal flat angle of the sample stage. This is due to an elongation of the X-ray beam shape which produces more photoelectrons that can be collected by the larger electron collection lens (30 deg) of the SSI S-Probe.  Most XPS instruments had much smaller electron collection lens angles (7-15 deg) which improved angle-resolved XPS.

A comparison of the electron count rates produced by using two different powder mounting methods also revealed that a hard, smooth hand-pressed pellet produces 2-4 times higher electron count rates than a powdered sample dropped and loosely pressed onto double-sided tape or Indium foil.

A test using a clean pure silver coated silicon wafer or polymer film was very useful to learn the limits and to optimize the electron count rates obtained from the silver surface at various tilt angles.

Using "Charge-Control Mesh-Screen" to produce spectra for The XPS Library and for this Database

On the X-Probe and S-Probe XPS instruments, charge compensation of insulating materials was handled by using the patented SSI mesh-screen together with a low voltage flood gun of electrons which used an acceleration voltage that was adjusted to 3-4 eV for optimum results. The mesh-screen device uses a 90% transmission electro-formed mesh made of nickel metal that is supported above the surface of the sample by mounting the mesh on a conductive metal frame that is grounded to the sample mount. To achieve good charge compensation the mesh-screen is positioned so that the distance between the mesh and the surface of the sample is between 0.5 – 1.0 mm. When the distance between the mesh-screen and the surface of the sample is greater than 1.2 mm, the usefulness of the mesh screen flood gun system was normally null.

The mesh-screen is understood to function as an electron cut-off lens with some tendency to allow incoming flood gun electrons to focus onto the area being irradiated with monochromatic X-ray beam. This occurs because the X-ray beam does not have a uniform flux density over the area of the beam. In effect, the mesh-screen produces a nearly uniform electric potential at the surface of the sample and allows incoming flood-gun electrons to pass through whenever they are needed (on demand).

The mesh-screen was used on every insulating material except for a few materials that were analyzed before the flood gun mesh-screen method was developed.

On the XPS instrument that uses a magnetic lens to focus the photo-electrons, the mesh screen was found to bend upwards due to the magnetic field.  Even so, charge control was still found to be better than without the mesh screen. To get the best charge control on this instrument, we had to turn off the voltage of input lens #1 which then allowed proper changing of the voltage of the flood gun.

On the Thermo K-alpha XPS instrument, the dual beam of low voltage argon ions and low voltage electrons were deflected by the mesh screen causing poor charge control results.  One the Ar+ ion beam was turned off, the charge-control mesh-screen was then very effective to control sample charging on the Thermo K-alpha XPS.

Maintaining a Clean Sample Surface:

Gloves: Use only polyethylene gloves. Other gloves may contain silicones that can contaminate the surface. Clean: Use only clean utensils (tweezers, etc) when handling samples. Make sure theses have been cleaned to remove hydrocarbon and silicone contaminants and dedicate their use to ESCA samples only. Keep your samples in a "clean" environment. A laminar flow hood or a clean laboratory environment is strongly suggested.

Common Contaminants: Common surface contaminants include:

			Hydrocarbon: Pump oil, greasy finger prints, dirty desiccators, dirty solvents.
			Silicones: Non-approved gloves, glass-fitting-grease, dirty desiccators, hair, hand lotion.
			Salts: Sodium, chlorine, potassium, can be introduced through improper rinsing or exposure to water that has not been properly purified.

Useful Analysis Requires Good Planning:

Controls: Always include control samples with the sample of interest. A control could include a sample of just the underlying substrate and/or a sample of the underlying substrate exposed to solvent used for the surface modification without the actual modifying agent.  Duplicates: It is best, if possible, to send duplicate samples, even if only one is to be analyzed. Sometimes samples are damaged in transport or, on a very rare occasion, can be damaged while loading for analysis.

Include With Samples:

			Samples Summary: Include a sheet with a list of the specific samples that are included and what is on them.
			Structure: Proper ESCA analysis requires the structure of the surface bound species and knowledge of the underlying substrate. Without this information accurate analysis of the ESCA data is difficult.

Figure 1: ESCA sample holder (side and top views) showing the mounting of 1cm x 1cm conductive samples. The sample holder is ~5cm in diameter and can hold samples slightly larger than the holder size.

Sample Shipping

Packaging: We suggest shipping samples in tissue culture polystyrene (TCPS) dishes sealed with parafilm. To prevent the samples from rattling around during transport, we use a small amount of double sided tape to secure the back of the samples to the bottom of the TCPS dish. It is very important to only stick a small corner of the sample to the tape. If the center of the samples is stuck to the tape or there is tape under the entire sample it is nearly impossible to remove the samples without damaging them. Please try sticking down a "test" sample and be sure it can easily be removed before packaging other samples. We have shipped many samples without incident and have discovered that only taping a small part of the corner is required to secure the sample.

Know Your Contact: Be sure that you are shipping your samples to the correct address and contact person. Our shipping address is NOT the same as the usual mailing address. The shipping address will be given out once samples have been approved for analysis. Also, inform your contact that the samples are being shipped to ensure that they will look out for your samples, and inform you if they do not arrive.

---

Sample Physical Requirements

Sample Size: Our ESCA systems can accommodate a wide variety of sizes and shapes in samples. We have also been known to "cut" samples down to size if necessary. Please inform your NESAC/BIO contact of the shape and size of the sample and we will suggest options.

Outgassing: One of the main limitations for ESCA samples is their outgassing properties. ESCA is a technique which MUST be preformed in a vacuum chamber with pressures of ~5×10-9 Torr. .Samples such as polymerized tetraglyme, "wet" silicones, or any "spongy" type sample which soaks up water will have some trouble pumping down to the appropriate pressure. However, there are methods we can use to analyze these samples, such as reducing the size of the sample. If your sample may present a problem, please notify your contact person and arrangements will be made for special analysis.

Figure 2: Only a small piece of tape at the sample corner should be sufficient to fix your samples in place for shipping.

Good sample preparation methods are vital in surface science as the signals emanating from surface contamination can overwhelm the signals from the sample.  Gloves and clean tweezers must be used and any glassware must be thoroughly cleaned before use. Tweezers should be cleaned regularly by sonication in isopropyl alcohol (IPA).

Samples can be stored or transported in clean poly(styrene) petri dishes and well plates, or clean glass vials. Avoid ALL other plastic containers, including plastic sample bags. A good alternative to plastic or glass containers is new, clean aluminium foil.  An argon etch is available to XPS users for in situ sample cleaning. This method is recommended for the removal of thin oxide layers however it will reduce your available analysis time so it should be avoided where possible.

Typical samples for XPS are 0.5 – 1 cm² in size and up to 4 mm thick. Thicker samples may also be accommodated – please contact us for details.

Magnetic samples:
The Axis Ultra and Thermo XL systems use magnetic immersion lenses to focus the photoelectrons emitted from the surface towards the detector. Magnetic samples can still be analyzed, but the experimental set up for these samples is slightly different. If you have magnetic samples that you would like to submit for XPS analysis, then please contact us prior to booking the instrument to discuss the available options.

Powders:
There are a few universally accepted methods of preparing powdered samples for XPS. Of these the favored method is to press the powder into clean, high purity indium foil. Alternatively, the powder may be dissolved in a suitable solvent and then drop cast onto the surface of a clean silicon wafer. Finally, powders that can not be prepared by either of the above methods can be either sprinkled onto the surface of sticky carbon tape or pressed into a tablet for analysis. Please discuss these latter two options with the experimental officer prior to booking the instrument.

Sources of Samples

Sources of Elements and Chemical Compounds used by The XPS Library for this Database

The pure element samples were obtained from various sources without any specific information about sample purity so pure element samples must be assumed to be pure at the 99%+ level. The "halide" salts used to produce spectra from gaseous or highly reactive elements were also obtained from various sources. These halide samples were obtained as crystalline "windows" which are normally used in Infrared spectroscopy and have purities at the 99% level. The Boron Nitride (BN) sample was a white ceramic electrical standoff which was fractured in air. The copper foil material, which was always used to determine reference energies, were obtained as 99% pure foil which was designed as a multiple purpose foil for use around the home. The gold ingot material, which was also used to determine reference energies was obtained as a 99.999% pure sample from Aldrich Chem. Co.

Source of Polymers used by The XPS Library for this Database

A special kit (#205) of the 100 polymer materials was obtained from Scientific Polymer Products, Inc. which is located at 6265 Dean Parkway, Ontario, New York, USA 13519 (Tel 716-265-0413).  Thin films of Kynar, and related fluorinated polymers were obtained from private suppliers.

Source of Alloys used by The XPS Library for this Database

A special kit of 54 metallic alloys was obtained from the Metal Samples Co., which is located at Route #1, Box 152, Munford, Alabama, USA, 36268 (Tel 205-358-4202). This kit includes a materials analysis report on each alloy in weight percent. The National Research Institute for Metals (NRIM) in Tsukuba, Japan has provided a series of various binary alloys made of AuCu and CoNi alloys.

Sources of Semi-Conductor Materials used by The XPS Library for this Database

Over the course of many years, many people in the Japanese semi-conductor business have given samples of various semi-conductor materials in crystalline wafer form. Various samples were donated by the Oki Electric Company, Mitsubishi Materials, Canon, and various universities. The source of each material is included with the individual sample descriptions whenever that information was provided.

Sources of Commercially Pure Binary Oxide Samples used by The XPS Library for this Database

Most of the commercially pure binary oxides were purchased from the Aldrich Chem. Co.. The packages from the Aldrich Chemical Co. included an "Analytical Information" sheet which described an ICP or AA analysis summary, a production lot number, the Aldrich product number, sample purity number (e.g. 99+%), sample appearance (color and physical form), date of chemical analysis, formula weight and a label on the bottle that reports the melting point, toxicity, Chemical Abstracts registry number and density. The samples from Aldrich were generally quite pure at the surface. Other oxide samples were obtained from either Cerac Inc. (USA) or Rare Metallics Co., Ltd. (Japan). The packages from Cerac Inc. included a "Certificate of Analysis" with an ICP or AA analysis summary, a production lot number, a product number, purity (e.g. 99+%), and mesh size. The packages from Rare Metallics Co. did not include analytical data reports, but instead had stock numbers and a purity statement. Two samples (i.e. SiO2 natural crystal and Al2O3 fused plate) were obtained from in-house sources and do not have any purity reports.  Recent purchases of binary and ternary oxides, sulfides and sulfates was from the ChemCraft Co located in Russia.

Sources of Commercially Pure Rare Earth Materials used by The XPS Library for this Database

The rare earths were purchased from Aldrich Chemical Co, Rare Metallics Company (in Japan) and ChemCraft Co. (in Russia).

Source of Pellet Press Equipment used by The XPS Library for this Database

"Qwik Handi-Press" from Barnes Analytical Division, Spectra-Tech, Inc.652 Glenbrook Road, Stamford, Connecticut, 06906 (FAX 203-357-0609) Kit: Part # 0016-111 to 0016-121 contains 1,3, and 7 mm die sets. Originally purchased through Aldrich Chem. Co. in 1989.

Sample Sizes and Sample Mounts for XPS

Sample Sizes and Shapes

Abbreviations Used

Due to the limited space provided to describe each sample in each electronic data-file, it was necessary to use various abbreviations. The abbreviations are:

scr = screen used for charge compensation
scrn = screen used for charge compensation
TOA = take-off-angle for the electrons
Aldr = Aldrich Chemical Co.
RMC = Rare Metallics Co.
SPP = Scientific Polymer Products Co. MS Co. = Metal Samples Company
FG = flood gun,
mesh = mesh-screen used for charge control,
1 mm=1 mm height used for the mesh-screen,
semi-con = semi-conductive behavior
conduc, = conductive behavior
Tech = technical grade purity,
pellet = sample pressed into pellet form by pellet press used to make Infrared KBr pellets,
plt = pellet
pel = pellet