Crist Handbook of XPS Spectra – Experimental Parameters Used

Handbooks of Monochromatic XPS Spectra

by Vincent Crist, Ph.D.
XPS International LLC
www.xpsdata.com

Vincent Crist and XPS International, LLC

Published by
XPS International, LLC

Internet Web Site: http://www.xpsdata.com

Introduction…………………………………………………………………………………………………………………………………… 11

Organization and Details of Spectral Sets………………………………………………………………………………………… 11

A. Organization of Spectra………………………………………………………………………………………………………. 11

Contents of Each Set of Spectra……………………………………………………………………………………………. 11
Philosophy of Data Collection Methods………………………………………………………………………………… 12
Peak-Fitting (Curve-Fitting) High Energy Resolution Spectra…………………………………………………. 13
Charge Compensation of Non-conductive Materials……………………………………………………………….. 13
Abbreviations Used…………………………………………………………………………………………………………….. 14

Instrument and Analysis Conditions used to Collect Spectral Data………………………………………………………………………………………….. ……………………………………………15

Instrument Details………………………………………………………………………………………………………………. 15
Experimental Details…………………………………………………………………………………………………………… 16
Data Processing Details………………………………………… …………………………………………………………………………………17
Sample Details…………………………………………………………………………………………………………………… 17

Sources of Commercially Pure Binary Oxides……………………………………………………………. 17

Powdered Samples – Pressed into 3 mm Diameter Pellets…………………………………………….. 18

Benefits of Pressing Powders into Pellets…………………………………………………………………… 18

Problems Caused by Pressing Samples into Pellets……………………………………………………… 19

Solution to Pressure Induced Contamination of Pellets………………………………………………… 19

Energy Resolution Details……………………………………………………………………………………………………………. 20
Energy Scale Reference Energies and Calibration Details………………………………………………………………… 21

Reference Energies of Adventitious Hydrocarbon Contaminants………………………………………….. 22

Instrument Stability and Long Term Energy Scale Calibration……………………………………………… 22

Electron Counting and Instrument Response Function Details………………………………………………………….. 23

Instrument Response Function………………………………………………………………………………………….. 23

Signal / Background Ratios for Ion Etched Silver (Ag) using a 250 x 1000m X-ray Beam………………………………………………………………………………………………………………………………………….. 23

Lens Voltage Settings Available via Software under Instrument Calibration Routines…………….. 23

Effects of Poorly Focusing the Distance between the Sample and the Electron Collection Lens…………… 24
Quantization Details and Choice of “Sensitivity Exponent” ……………………………………………………………… 24
Tests of the Reliability of Scofield Based Relative Sensitivity Factors………………………………………………. 25
Traceability Details……………………………………………………………………………………………………………………… 25

Traceability of Reference Binding Energies (Calibration)…………………………………………………….. 25

Transfer of Traceability from Pure Metals to Non-Conductive Binary Oxides………………………… 26

Traceability of Instrument Response (Throughput) Function………………………………………………… 26

Traceability of Relative Sensitivity Factors (RSFs) used for Quantization……………………………… 27

Traceability of Sample Purity……………………………………………………………………………………………. 27

Reference Papers Describing the Capabilities of S-Probe XPS Systems……………………………………………. 27

INTRODUCTION

This handbook contains wide scan survey spectra and high energy resolution narrows scan spectra from commercially pure samples of binary oxides, a few natural minerals, several hydroxides and carbonates. The spectra were collected under conditions that maximized the accuracy and reliability of the binding energies. The reference energies used to calibrate the energy scale were those reference energies recommended by the National Physical Laboratory in the UK, and now ISO TC/201. Section “F” provides the details of energy scale calibration. For those compounds that were non-conductive or semi-conductive in behavior, the reference energy for the hydrocarbon carbon (1s) signal from those samples was defined as 285.0 eV. The binding energies of all truly conductive samples were reported exactly as measured and without correction.

ORGANIZATION AND DETAILS OF SPECTRAL SETS

Organization

The spectra are organized alphabetically by using the chemical formula (e.g. AgO to ZrO₂). Data and spectra from the binary oxide known as “aluminum (III) oxide” has chemical formula “Al₂O₃” in the upper right and left corners of the pages that belong to that set of spectra. This means that spectra and data for “Antimony Oxide” will be found by looking for the chemical formula: “Sb₂O₃”. Just underneath of this chemical formula the mineral name is reported if the sample was a natural mineral.

Contents of Each Set of Spectra

The compounds in this volume include: AgO, Ag₂O, Al₂O₃, Al(OH)₃, AlOOH (Diaspore), As₂O₃, Au₂O₃, B₂O₃, BaCO₃, BeO, Bi₂O₃, (BiO)₂CO₃, CaO, CaCO₃ (Calcite), CdO, Cd(OH)₂, CdCO₃, CeO₂, CoO, Co₂O₃, Co₃O₄, Co(OH)₂, CrO₃, Cr₂O₃, Cs₂O, CuO, Cu₂O (Cuprite), Cu(OH)₂, CuCO₃(Azurite), Dy₂O₃, Er₂O₃, Eu₂O₃, FeO, a-Fe₂O₃(Hematite), g-Fe₂O₃, Fe₃O₄, FeOOH (Goethite), Ga₂O₃, Gd₂O₃, GeO₂, HfO₂, HgO, Ho₂O₃, In₂O₃, IrO₂, K₂O, La₂O₃, Li₂O, Li₂CO₃, Lu₂O₃, MgO, Mg(OH)₂, MgCO₃, MnO, MnO₂, Mn₂O₃, MnCO₃(Rhodochrosite), MoO₂, MoO₃, Na₂O, NbO, NbO₂, Nb₂O₅, NiO, Ni(OH)₂, PbO, PbO₂, Pb₂O₃, PbCO₃(Cerrusite), PdO, Pr₆O₁₁, PtO₂, Re₂O₇, Rh₂O₃, RuO₂, Sb₂O₃, Sb₂O₅, Sc₂O₃, SiO, SiO₂ (Quartz), Si(OH)₄(Opal), Sm₂O₃, SnO, SnO₂ (Cassiterite), SrCO₃, SrO, Ta₂O₅, Tb₄O₇, TeO₂, ThO₂, TiO, TiO₂, Ti₂O₃, Tl₂O₃, Tm₂O₃, VO₂, V₂O₃, V₂O₅, WO₃, Y₂O₃, Y₂(CO₃)₃, Yb₂O₃, ZnO, and ZrO₂.

The first page of each data set includes a title line that reports the chemical name, the oxidation state of the element, and its’ formula weight (FW). Just below the title line the “Surface Composition Table” lists the peak assignments from each wide scan survey spectrum, corrected and measured binding energies of all major and minor peaks, relative sensitivity factors, relative peak areas and the atom % abundance of each major signal. Each data set includes a wide scan survey spectrum, a valence band spectrum, a 1,000-1,400 eV range spectrum and high energy resolution spectra of the primary metal signal, secondary metal signals, the carbon (1s) signal, the oxygen (1s) signal and several Auger signals. The spectra and their annotations are presented exactly as produced and exported by the Spectral Data Processor v4.1 software from XPS International LLC.

Descriptions above each subsequent spectrum include the original key information about the sample, the source of the sample if known, and peak labels. Detailed information about the operating capabilities of the SSI XPS system and analysis conditions used to collect these data are presented in the next section of this book.

The remaining pages of each set include the high energy resolution narrow scan spectra which were obtained by measuring the main XPS signals found in the wide scan survey spectrum. These spectra contain detailed peak-fit results in a table at the top left corner of the spectrum and the actual peak-fit results. The binding energies of the non-conductive samples were corrected to the binding energy of the hydrocarbon carbon (1s) signal at 285.0 eV which is a common practice. This method of energy referencing non-conductive materials is widely used and accepted because there is currently no standard method for charge referencing spectra from insulating materials. Each peak-fit table includes the binding energies of each peak, their FWHM, peak height, percentage of Gaussian peak-shape used, percentage of asymmetry used, normalized peak area and relative peak area. The relative peak area percentages are based on the total peak area intensity of that signal only. Relative peak area percentages are not atom % values.

Philosophy of Data Collection

The spectra in this book were collected under analysis conditions that are practical, readily reproduced, and typically used in laboratories that use monochromatic X-ray sources and are working under real world practical analysis conditions. We have produced this volume of reference spectra because many XPS laboratories need practical reference spectra and do not have the time or money to produce XPS spectra from common reference materials. The signal to noise (S/N) ratios in the wide scan survey spectra is large enough to reveal the presence of minor components that are often not detected. The high energy resolution spectra were obtained under analysis conditions that would give a FWHM = 0.75 eV from the Ag (3d_5/2) signal of freshly ion etched silver (Ag).

A few high energy resolution spectra, labeled with the superscript “UR” were obtained under the “ultimate energy resolution” conditions available on the SSI S-Probe XPS system. This “ultimate” level of energy resolution produced a FWHM = 0.44 eV from the (3d_5/2) signal of freshly ion etched silver (Ag). In the production of these spectra we did not attempt to clean the surfaces of any sample because that would make charge referencing of the non-conductive samples a difficult task. For practical reasons we used the hydrocarbon carbon (1s) spectra from the naturally formed layer of adventitious hydrocarbons for charge referencing because that signal is the “de facto” standard for charge referencing non-conductive materials. This method of correcting for charge-up increases the uncertainty in the accuracy of the related binding energies.

The spectral data contained within this 5 volume series of handbooks are designed to assist engineers, scientists, analysts, theoreticians, and teachers who use XPS on an everyday basis under practical working conditions. We hope that these spectra will help XPS users to analyze industrial problems, gather high grade reference data, perform basic research, test theories and teach others. These spectra are designed to be practical tools for everyday use and were obtained under practical working conditions. We have not attempted to produce research grade spectra, but we have, in fact, produced research grade spectra because of our self-consistent methods. In the production of these spectra no attempt was made to produce a pure, clean surface, but an effort was made to produce surfaces with a minimum amount of natural surface contamination.

Peak-Fitting (Curve-Fitting) of High Energy Resolution Spectra

Peak-fitting was performed by using Spectral Data Processor (SDP v4.1) from XPS International LLC (www.xpsdata.com). This software allows the user to control the full width at half maxima (FWHM) value of any peak, the binding energy (BE) of any peak, peak areas, peak heights, the ratio of pairs of peak areas, the ratio of pairs of FWHM, the energy difference between two peak maxima, the shape of a peak as a sum-function of Gaussian and Lorentzian peak shapes, and the percentage of asymmetry in any peak.

By empirically peak-fitting the spectra from large sets of closely related materials in a trial and error method and analyzing the trends, it was possible to recognize several fundamental peak-shape and peak-fitting parameters for pure elements, binary oxides, polymers, and semiconductors. We have used those empirical findings to guide our efforts to peak-fit the many spectra which had complicated peak shapes. In some cases we used the theoretical peak area ratio of a spin-orbit coupled pair to assist the peak-fitting of a spectrum, and also the energy interval between spin-orbit coupled signals derived from pure element spectra.

The reduced “chi-squared” value, which indicates the goodness of a peak-fit, was used to determine if a peak-fit was reasonable or not. Based on practical experience a “chi-squared” value between 1 and 2 implies a relatively good peak-fit. A “chi-squared” value between 2 and 4 implies that the fit has not yet been optimized. A “chi-squared” value larger than four (4) implies that one or more signals are missing from the peak-fit.

A Shirley-type (sigmoid) baseline was used for most peak-fits. Peak-fits for the main XPS signals were optimized by using a Gaussian:Lorentzian ratio between 80:20 and 90:10. After peak-fitting many binary oxides, we observed that the FWHM of the C(1s), O(1s) and the main metal signal of the binary oxide were usually in range 1.0-1.4 eV. We used this observation as an indicator of charge compensation quality. If one of the peaks fell with this range (1.0-1.4 eV), then all other spectra were expected to represent spectra without charge induced broadening. If all three of the main spectra were found to have FWHM > 1.5 eV, then we understood that charge compensation was not adequate. In response, we repeated some measurements until at least one of the main signals had FWHM < 1.5 eV, by moving the mesh-screen closer to the surface of the sample or by increasing the flood gun voltage by 1-3 eV.

Charge Compensation of Non-Conductive Compounds

Charge compensation of non-conductive materials was handled by using the patented SSI mesh-screen together with a low voltage flood gun of electrons which used an acceleration voltage adjusted to 2-4 eV, unless otherwise noted. The mesh-screen device uses an 85% 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 was positioned so 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 null. This mesh-screen method has been found to useful on a wide variety of XPS systems that use monochromatic X-rays and a source of electrons that are from a flood source or a poorly focused source of low voltage electrons.

The mesh-screen is understood to function as an electron cut-off lens with some tendency to allow incoming flood gun electrons to focus on the area being irradiated with monochromatic X-ray beam because the X-ray beam does not have a uniform flux density of 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.

The mesh-screen was used above every sample except for a few that were analyzed before the mesh-screen method was invented. Because the electrical nature of many of the samples was unknown until we attempted to collect data, nearly all samples were covered by the mesh-screen device. When the mesh-screen covers a conductive sample there is a very slight drop in counts because the mesh-screen captured or deflected some of the photo-emitted electrons. If ion etching is done with the mesh in place, then a slight amount of nickel appears on the ion etched sample.

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:

TOA = take-off-angle for the electrons (the angle between the surface plane and the main axis of the electron collection lens)

FG = flood gun

mesh = mesh-screen used for charge control

1mm = 1 mm height used for the mesh-screen

semi-con = semi-conductive behavior

Tech = technical grade purity

pellet = sample pressed into pellet form by pellet press used to make infrared KBr pellets,

Instrument and Analysis Conditions Used to collect XPS Spectra

Instrument Details

Manufacturer: Surface Science Instruments (SSI)

Model: S-Probe (upgraded from M-Probe model 2703)

Operation Software: 1.36.05 (Compiled in MS-DOS “C” v6.0)

Analyzer Type: Fixed Analyzer Transmission (FAT), which is the same as:

Fixed Pass Energy = Constant Analyzer Energy (CAE)

180° Hemi-spherical (truncated)

Input Lens Field of View: 30° for sample normal to lens axis (1″ diameter port)

(always larger than X-ray beam; retarding potential scanned)

X-ray Type: Al° K_a monochromatic (one 2″ diameter, thin, natural SiO₂

wafer glued onto a Zerodur substrate and heated to 65° C)

X-ray Source: 10 kV, 1.5-22.0 mA (depending on spot size used)

X-ray Energy Defined as: 1486.7 eV (8.3393 Å), Bragg angle = 78.5°

Excitation Source Window: 0.6 µ aluminum in S-Probe (10µ Mylar in X-Probe)

Angle of X-ray Incidence: a = 71° (relative to sample normal)

Electron Emission Angle: b = 0° (relative to sample normal)

Angle between X-ray Axis and Electron Analyzer Axis: f = 71° (fixed, non-variable)

Pass Energies of Analyzer: 150 V for Resolution 4 setting

100 V for Resolution 3 setting

50 V for Resolution 2 setting

25 V for Resolution 1 setting

Type & Size of Input Slit: Fixed (2 mm X 35 mm) with magnetic compression

Type & Size of Output Slit: None (dispersion limited by hemisphere voltages)

Electron Collection Lens

Field of View: ~ 1 mm² for b = 0° at 1,000 eV KE

Electron Collection Lens Efficiency: 7% over 2p steradians

Sample Surface to Tip of Electron

Collection Lens Distance: ~33 mm

Crystal to Sample Surface Distance: ~190 mm

Crystal to X-ray Anode Distance: ~190 mm

True Background Noise: <10 electrons/second at -50 eV (shot noise limited)

Detector Type: SSI Position Sensitive Detector, resistive anode encoder,

40 mm X 40 mm, electronically defined as 128 active channels with max ct rate of 1,000,000 cps

Dead Time: zero (unless ion etching pure element while collecting data)

Base Pressure: 4 x 10^-10 torr

Normal Operating Pressure: 1.6 x 10^-9 torr

X-ray FWHM Diffracted by natural SiO₂: ~0.25 eV

Power Settings: 200 Watts in a 250 x1100µ X-ray beam

100 Watts in a 150 x 800µ X-ray beam

45 Watts in an 80 x 350µ X-ray beam

15 Watts in a 40 x 250µ X-ray Beam

X-ray Induced Current: 1.1 x 10^-9 amps for a 600µ spot in X-Probe

Approximate True X-ray Power: ~6 x 10^-6 W in a 600µ spot

Approximate True X-ray Irradiance: ~8 W/m²

Approximate True X-ray Photon Flux: ~7 x 10⁹ photons/sec

Experimental Details

Electron Take-Off-Angle: 90° relative to sample surface (unless otherwise reported)

Pass Energies Used: Wide scans were done at PE = 150 eV

Narrow scans were normally done at PE = 50 eV

Valence band scans were done at PE=150 eV

X-ray Beam Size Used: Wide scans: 250 x 1500 µ ellipse (at 90° TOA)

(S-Probe system) 250 x 1100 µ ellipse (at 35° TOA)

Narrow Scans: 250 x 1500 µ ellipse (at 90° TOA)

150 x 1000 µ ellipse (at 90° TOA)

SSI Mesh-Screen: An 85% transmission (20 µ diameter wire with 200 µ

spacing) nickel metal mesh screen was adhered to

a small 25 mm x 25 mm x 1.5 mm (W x L x H)

aluminum plate with a 20 mm x 20 mm aperture.

The mesh-screen was placed over all insulating samples

So that the distance between the sample surface

and the mesh-screen was <1.0 mm but >0.5 mm.

Dwell Time (counting time): 200 milliseconds/channel

Data Transfer Time: 4 milliseconds

Max. Number of Channels: 5,000 (channels = data points)

Scan Time for One Wide Scan: ~ 3.5 minutes (using 1024 data points)

Scan Time for One Narrow Scan: ~100 seconds (using 256 data points)

Energy Range: -100 to +1400 eV (BE range)

Typical Step Size: 0.1 eV/step (i.e. 0.1 eV/data point)

Data Processing Details

Baseline Subtraction: None, unless S/BG gave a small display. When the

baseline was removed, the intensity of the lowest

point was subtracted from all points.

Data Smoothing: None (the 128 channel PSD system producing a smoothing effect)

Energy Shifting: All non-conductive samples were charge referenced so that the hydrocarbon
carbon (1s) signal appeared at 285.0 eV

Sample Details

The “Description” given on the first page of each data set reports: the empirical chemical formula for the oxide, the hydroxide or carbonate, the reported bulk purity, source, a production lot number, the electron take-off-angle (TOA), the height of mesh-screen above the surface, the electrical behavior of the sample under analysis conditions, sample color, sample preparation, sample size, known melting point in degrees Centigrade, density in grams/cubic-centimeters, and a note on solubility.

Sources of Commercially Pure Binary Oxide, Carbonate and Hydroxide Samples

Most of the commercially pure binary oxides were purchased from the Aldrich Chemical Co. Most of the packages from the Aldrich Chemical Co. included an “Analytical Information” sheet which reported an ICP or AA analysis summary, a production lot number, the Aldrich product number, sample purity (e.g. 99+%), sample appearance (color and physical form), date of chemical analysis, formula weight and a label on the bottle that reported the melting point, toxicity, a Chemical Abstracts registry number and density. The samples from Aldrich were generally quite pure. Other oxide samples were obtained from either Cerac Inc. (USA) or Rare Metallics Co., Ltd. (Japan). These samples tended to have mixed oxides. 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 as a fused plate) were obtained from in-house sources and do not have any purity reports.

Powdered Samples – Pressed into 3 mm Diameter Pellets

Until analyzed, all finely powdered samples were kept un-opened, in their original glass or plastic containers, which were packaged inside of plastic-lined aluminum bags and stored in an electrically controlled dehumidifier. Just prior to 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 powdered sample was removed via a clean Nichrome spatula and placed in the compression chamber of a hand-operated, stainless steel pellet press (Qwik Handi-Press) that is normally used to produce pellets for infrared analyses. All finely powdered samples were compressed without any treatments. The resulting pellets varied in thickness from 0.3 – 0.8 mm. The “Qwik Handi-Press” was manufactured by the Barnes Analytical Division of Spectra-Tech Inc. (652 Glenbrook Road, Stamford, Connecticut, 06906, FAX#: 203-357-0609). Part # 0016-111 to 0016-121 contains 1, 3, and 7 mm die sets. Our hand-press was purchased through the Aldrich Chemical Co.

To avoid iron and/or chromium contamination from the anvil, a small piece of freshly cleaned aluminum foil was placed over the sample in the compression chamber. This aluminum foil is standard kitchen grade foil which was gently rubbed with a cotton swap lightly soaked with iso-propanol (IPA) and allowed to dry in air. Those powders, that were clumped together, were very gently ground into a powder just prior to compression. To avoid unnecessary heat-induced oxidation, those samples which were hard and granular were very gently and slowly hand ground into a fine powder using an agate marble mortar and pestle. As soon as each sample was removed from the compression chamber, it was mounted on top of a fresh drop of silver (Ag°) paint placed in the center of a 5 mm diameter brass boat that was 1.3 mm in height. Silver paint was used so that conductive oxides could behave as true conductors thereby providing true electron binding energies for those oxides that were indeed conductive. This arrangement kept the mesh-screen at a suitable distance from the sample surface. In general, each oxide was exposed to room air for <15 min.

Benefits of Pressing Powders into Pellets

A comparison of the electron counts obtained from powdered samples pressed onto double-sided adhesive tape and positioned at a 35° electron take-off-angle with the electron counts obtained from hand-pressed glossy or semi-glossy pellets positioned at a 90° electron take-off-angle (TOA) revealed that the pellet form at a 90° electron TOA produces 3-5 times higher electron counts than a powdered sample pressed onto double-sided tape at a 35° electron TOA. By pressing the finely powdered oxides into pellets, it was also found the surface charging behavior of these glossy or semi-glossy samples was very easy to control with the mesh-screen flood-gun device.

Problems Caused by Pressing Powdered Samples into Pellets

By pressing finely powdered oxides into pellets, the surface of the resulting pellets were usually smooth enough to appear glossy or semi-glossy. A few samples were found to be contaminated with iron or chromium which indicated that the oxide had undergone a pressure induced reaction with the stainless steel anvil. Very strong hand pressure was indeed found to cause some oxides to react with the stainless steel anvil, but medium hand pressure did not produce the undesired iron and chromium contamination. Other forms of accidental contamination (chlorine or previously analyzed oxides) were caused by insufficient cleaning of the stainless steel anvil, which was normally cleaned with a chlorine-containing 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

Extensive experiments on different methods to avoid contamination while producing 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 fits inside the pellet press device.

We have also used “glycine” weighing paper which is commonly used as a paper to hold powders when weighing them. This weighing paper is common in chemical laboratories and can be substituted for the aluminum foil whenever the pressing results with the aluminum foil produce undesired binding of the foil to the sample. The glycine paper method sometimes introduces very small amounts of contaminants which produce very weak N (1s) and C (1s) signals.

Energy Resolution Details

Table 1: Experimentally Observed Relation between Energy Resolution and Analysis Conditions

Signal and Material used to Define Effective
Energy Resolution (treatment)

Energy Resolution
FWHM (eV)

Pass Energy

X-ray Spot Size

Si (2p_3/2) (fractured edge of crystal)

0.38 eV

10 eV

40 x 250m

Si (2p_3/2) (fractured edge of crystal)

0.43 eV

25 eV

80 x 350m

Au (4f_7/2) (foil – ion etched clean)

0.64 eV

10 eV

250 x 1000m

Au (4f_7/2) (foil – ion etched clean)

0.79 eV

25 eV

250 x 1000m

Au (4f_7/2) (foil – ion etched clean)

0.86 eV

50 eV

250 x 1000m

Au (4f_7/2) (foil – ion etched clean)

1.40 eV

150 eV

250 x 1000m

Ag (3d_5/2) (foil – ion etched clean)

0.42 eV

10 eV

40 x 250m

Ag (3d_5/2) (foil – ion etched clean)

0.64 eV

25 eV

40 x 250m

Ag (3d_5/2) (foil – ion etched clean)

0.75 eV

50 eV

40 x 250m

Ag (3d_5/2) (foil – ion etched clean)

1.00 eV

100 eV

40 x 250m

Ag (3d_5/2) (foil – ion etched clean)

1.30 eV

150 eV

40 x 250m