Measurements & Characterization • National Center for Photovoltaics

Surface Analysis

Surface analytical techniques help to determine the chemical, 

elemental, and molecular composition, and electronic structure of 

material surfaces and interfaces. The properties of the surface and 

outer few micrometers of a material often control the electrical, 

chemical, or mechanical properties of that material—hence, this 

region is of extreme importance.

Our techniques use ions, electrons, and X-ray or ultraviolet photons 

in high vacuum to probe surfaces and interfaces of a material. We 

map the elemental and chemical composition of specimens, study 

impurities and grain boundaries, gather bonding and chemical-state 

information, measure surface electronic properties, and perform 

depth profiles to determine doping and elemental distributions. We 

have analyzed a wide range of materials, including photovoltaics, 

microelectronics, polymers, and biological specimens.

We work collaboratively with you to solve materials- and devicerelated R&D problems. This sheet describes our major technique 

capabilities. 

Field Emission Auger Electron Spectroscopy (FE-AES) 

with Scanning Auger Microscopy (SAM)

In Auger electron spectroscopy (AES), a sample surface is 

bombarded with a focused beam of high-energy (2- to 10-kV) 

electrons. The incident electrons lose energy to the sample atoms, 

generating Auger electrons that have discrete kinetic energies 

characteristic of the emitting atoms.

This technique is particularly useful for determining the elemental 

composition of the surface because Auger electrons have a limited 

escape depth. A key capability of the FE-AES is its ability to focus the 

electron beam to a small spot, with resolutions similar to an electron 

microscope. By scanning the electron beam across the surface, we can 

generate both element-specific Auger maps and secondary-electron 

microscope (SEM) images from the same region of the sample.

Applications

Elemental surface analysis. Identifies and quantifies elemental 

compositions of solid surfaces, with a sensitivity to 0.5 at.% for 

elements from lithium to uranium.

Depth profiling. Argon ions are used to remove successive 

layers, thus allowing elemental analysis as a function of depth. 

Especially useful for quantitative bulk and volumetric analysis 

of thin-film materials, and for exploring impurities and diffusion 

present at junctions and grain boundaries.

Small-feature analysis. The field-emission electron source 

produces a small spot size (> ~25 nm) that can be used to 

explore the composition and structure of small particles or 

intricate features, such as those found in microelectronics or 

polycrystalline thin-films.

Imaging. By using raster scanning with a highly focused electron 

beam ≥ 25 nm in diameter, SEM micrographs can be obtained 

with up to 20,000x magnification. Using the same raster scan, 

SAM can produce elemental composition maps of a surface.

X-Ray and Ultraviolet 

Photoelectron Spectroscopy (XPS/UPS)

Photoemission techniques use either X-rays or ultraviolet photons 

to bombard the surface of a sample. The incident photons cause 

the emission of electrons (photoelectrons) from atoms in the nearsurface region (about the top 4 nm) of the sample.

In XPS, the photoelectrons have energies characteristic of the 

atom they came from, thus allowing elemental and chemical 

determinations to be made. Ultraviolet photons used for UPS have 

lower energies and probe the electrons in the outermost valence 

levels of the surface atoms, yielding surface electronic structure 

information such as work function and valence band-edge.

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Analytical

Technique

Auger electron 

spectroscopy

X-ray and

ultraviolet 

photoelectron

spectroscopy

Dynamic SIMS

Static 

TOF SIMS

Instrumentation

Physical

Electronics

PHI 670

Physical

Electronics

PHI 5600

Cameca IMS5F & IMS-3F

IONTOF TOF 

SIMS IV

Typical 

Applications

Elemental surface 

analysis, smallfeature analysis

Elemental and 

chemical surface 

analysis, surface 

electronic properties

Trace-element 

contaminant and 

dopant analysis

Surface elemental 

and molecular 

information

Probing

species

Electrons

X-ray or 

ultraviolet 

photons

Ions

(Cs, O, Ar)

Ions

(Ga, Ar, O)

Signal

Detected

Auger

electrons

Photoemitted

electrons

Ions (+/-)

Ions (+/-)

Elements

Detected

Li to U

Li to U

H to U and 

all isotopes

H to U, all 

isotopes, 

mass range 

>1000 amu

Detection

limit

0.5–1 at.%

0.5–1 at.% 

(XPS)

ppm–ppb

(cm-1)

ppm–ppb

(cm-2)

Lateral

Resolution

25 nm

50 μm 

(XPS)

1 μm

0.5 μm

Depth Profiling/

Resolution

Yes, 10 nm

Yes, limited, 

100 nm both

Yes, <10 nm

Yes, <5 nm

Mapping?

Yes

Limited

Yes

Yes

Organic

Info.?

—

Yes

—

Yes

Spot

Size

25 nm

50 μm

(XPS), 

1 mm 

(UPS)

1 to 

200 μm

To

0.3 μm

MAJOR INSTRUMENTATION FOR SURFACE ANALYSIS
Applications

Chemical state. Evaluate bonding environments of surface 

layers via XPS, and valence states via UPS. Ultrahigh vacuum 

facilitates sample cleanliness. Aluminum, magnesium, and 

monochromated Al Ka radiation allow a variety of analytical 

conditions. A high-resolution electron energy analyzer minimizes 

the spread of photoelectrons, allowing accurate 

determination of energies and enhanced 

peak separation for accurate chemical 

identifications.

Elemental analysis. Quantitative identification 

of elements from lithium to uranium by XPS, 

with detection levels down to 0.5 at.%.

Depth profiling. Argon ion gun equipped for 

sputter cleaning of the surface and for limited 

compositional depth profiles of layers 

<1 μm thick.

Polymers. Especially valuable for analyzing 

functional groups in polymers and other 

organic materials. Particularly useful in this 

regard when used as a complementary tool 

with static SIMS analysis.

Versatile sample capabilities. Accommodates 

standard semiconductor materials, but also, 

insulators, powders, irregular geometries, 

polymers, catalyst particles, and biological and 

cell materials.

Non-destructive depth profiling. Using angleresolved photoelectron spectroscopy (ARPES), 

photoelectron spectroscopy is performed from 

a variety of angles—from normal to the surface 

to nearly parallel to it—changing the sampling 

depth for photoelectrons. This yields a nondestructive method for producing depth profiles 

of near-surface regions.

Variable-temperature manipulator. Allows 

the acquisition of XPS and UPS data at variable 

temperatures (-50° to +800°C). Useful for 

in-situ cleaning of sample surfaces and 

temperature-programmed XPS/UPS studies.

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Surface Analysis Cluster Tool (includes AES, XPS/

UPS, UHV Deposition System, TDMS, inert-atmosphere 

glovebox)

This cluster system is a newly developed tool stemming from the 

need for integrated analysis, growth, and processing capabilities, 

such as will be available in NREL’s new Science and Technology 

(a) (b) (c)

(a) SEM and (b) SAM images of a surface defect in Cu(In,Ga)SeS. SAM analysis shows the defect to be an In-rich region (b), indicating that the likely origin was an 

“In-spit” during precursor deposition that was subsequently selenized during downstream processing (b,c).

Schematic diagram and photograph of the surface analysis cluster tool.
Facility. We developed and built a unique tool for the in-situ study of 

surface chemical changes that occur during growth and processing 

of materials under various conditions. In addition, using this tool, 

we developed capabilities to study reactions and kinetic processes 

at surfaces. We joined our previously stand-alone XPS/UPS and 

AES instruments to a custom ultrahigh-vacuum thin-film deposition 

system and a nitrogen-ambient glovebox, via a UHV trolley system, 

to form an ultrahigh-vacuum cluster tool.

The cluster tool greatly enhances the capabilities of our stand-alone 

tools by allowing controlled surface modification and processing, 

as well as adding the new analysis tools of thermal desorption 

mass spectrometry (TDMS), reflection high-energy electron 

diffraction (RHEED), and low-energy electron diffraction (LEED), 

and the capability for in-situ spectroscopic ellipsometry during film 

deposition. In addition, our variable-temperature manipulator for the 

photoemission system allows us to monitor chemical and electronic 

properties during temperature-programmed experiments.

Our expert staff is available to discuss how this tool and our 

experience in surface science experimental design can aid you in 

understanding issues related to surfaces and interfaces of your 

materials. 

Dynamic Secondary-Ion Mass Spectrometry (SIMS)

Dynamic SIMS uses a continuous, focused beam of primary ions 

to remove material from the surface of a sample by sputtering. 

The fraction of sputtered material that is ionized is extracted into a 

double-focusing mass spectrometer, which uses electrostatic and 

magnetic fields to separate the ions according to their mass-tocharge ratio. Ions of different mass-to-charge ratios are selected 

by adjusting the strength of the magnetic field. Dynamic SIMS 

is extremely sensitive—able to detect fractions in the range of 

parts per million to parts per billion—and is used to determine the 

elemental composition and levels of trace impurities and dopants in 

solid materials. 

Applications

Elemental analysis. Identifies all elements or isotopes present 

in a material, from hydrogen to uranium. Different primary-ion 

sources (cesium and oxygen) allow the choice of conditions for 

the best analytical sensitivity across the Periodic Table, down to 

parts per billion for many elements. High mass resolution (M/ΔM 

of up to 6000) allows the separation of nominally identical masses 

(e.g., 31P from 30SiH). This is the only surface analysis technique 

for directly detecting hydrogen and deuterium in materials.

Depth profiling. Sputtering into a material generates a profile 

of the concentration of impurities or dopants as a function of 

depth. Depth resolution of better than 10 nm is possible, and the 

technique can be quantitative with standards.

Interface analysis. By sputter-removing material from the 

sample, dynamic SIMS determines the changes in composition 

or the diffusion of impurities from layer to layer. Variable primaryion conditions allow depth resolutions of <10 nm.

Image analysis. Raster scanning or the unique direct-imaging 

capability of the instruments can produce secondary-ion images 

for detecting the lateral distribution of trace impurities. Image 

analysis, combined with depth profiling, produces threedimensional maps of elemental distributions.

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High-resolution XPS spectra of carbon 1s from polyethylene terephthalate 

backsheet material, showing excellent quantitative agreement between 

measured and predicted peak area ratios. Subtle differences in polymer 

functionality are assessed by deviations from stoichiometry.

SIMS depth profiles of hydrogen for a series of a-Si films undergoing solid-phase 

recrystallization at different temperatures. Hydrogen loss is greater for higher 

temperatures. However, the rate of loss for a given temperature is also affected by 

the type of dopant and proximity to the surface.
Static Time-of-Flight Secondary-Ion

Mass Spectrometry (TOF SIMS)

Static SIMS uses a pulsed primary-ion beam to sputter-remove 

material from the top monolayer of a sample. Secondary ions are 

collected and focused into a reflectron time-of-flight (TOF) mass 

spectrometer. The combination of low primary-ion density (low 

surface damage) and high transmission of the TOF analyzer (high 

sensitivity) makes the technique extremely useful for studying 

the top monolayer of a surface. The large mass range of the TOF 

analyzer makes the instrument well suited for detecting trace 

levels of organic contaminants on surfaces. Depth profiling is also 

possible in combination with high-current, low-energy cesium 

and argon sputter sources. Information on chemical structure is 

especially useful when combined with XPS analysis.

Applications

Surface sensitive. Low doses of primary ions ensure that below 

the static limit, every secondary ion comes from an undisturbed 

region of the surface. High vacuum promotes a clean specimen 

surface. Multiple ion sources (liquid-metal gallium and argon) 

promote analytical flexibility.

Elemental and molecular analysis. Performs mass analysis to 

determine the elemental and/or molecular composition of the top 

monolayer of a material’s surface. Can distinguish elements and 

molecules whose masses range from 1 to >10,000 amu. High 

mass resolution (M/∆M > 7000) allows precise differentiation of 

secondary-ion species.

Wide range of materials. Can be used for a wide range of 

organic and inorganic materials, including thin films, solid-state 

materials, ceramics, polymers, biological samples, and catalyst 

particles.

Imaging. Using a rastered probe, we can generate images 

to determine the lateral distribution of surface elemental and 

molecular species, with spot sizes down to 0.5 μm for the 

gallium liquid-metal ion source. Collecting a complete spectrum 

at every pixel allows for retrospective analysis of the image data.

Depth profiling. Low-energy cesium, and argon or oxygen 

sputter guns for depth profiling provide high-resolution depthprofiling capabilities. Collecting an entire spectrum for each 

point allows for retrospective analysis of depth-profile data.

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National Renewable Energy Laboratory

1617 Cole Blvd., Golden, CO 80401

NREL is a national laboratory of the U.S. Department of Energy,

Energy Efficiency and Renewable Energy,

operated by Midwest Research Institute • Battelle

Measurements and Characterization is within the

National Center for Photovoltaics at NREL

Web site: www.nrel.gov/pv/measurements

Phone: (303) 384-6675 • Fax: (303) 384-6604

Contract No. DE-AC36-99-GO10337

NREL/BR-520-40122 • June 2006 Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste

NOTICE—This report was prepared as an account of work sponsored by an agency of the United States government. Neither the 

United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes 

any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process 

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endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of 

authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.

We used the high mass resolution and mass accuracy of TOF SIMS to study surface 

cleanliness of tin-oxide-coated glass after different types of isolation scribes 

and cleaning processes. Not all processes were equal. As-received tin oxide was 

heavily contaminated with silicone oils (not shown). An acidic wash resulted in 

contamination by Fe and other metals. Without high mass accuracy, the CaO signal 

might be mistaken for Si2 , or Fe mistaken for CaO.