Common Surface Analysis Techniques

Why This Matters

Surface science sits at the heart of modern materials research, catalysis, semiconductor manufacturing, and nanotechnology. When you're analyzing a thin film, characterizing a catalyst, or investigating why a coating failed, you need techniques that can probe just the top few atomic layers—where all the interesting chemistry happens. The techniques in this guide aren't just tools to memorize; they represent fundamentally different approaches to answering questions about what's there, how it's arranged, and how it behaves.

You're being tested on more than technique names and acronyms. Exams will ask you to select the right technique for a given problem, explain why one method works better than another for a specific application, and interpret the kind of data each produces. The key is understanding the underlying physics: electron emission, diffraction, tunneling, ion scattering, and thermal desorption each reveal different aspects of surface character. Don't just memorize what each technique does—know what physical principle it exploits and what questions it can answer.

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Electron Emission Techniques

These methods detect electrons ejected from surfaces after excitation by photons or electrons. The kinetic energy of emitted electrons carries information about elemental identity, chemical bonding, and electronic structure.

X-ray Photoelectron Spectroscopy (XPS)

• Core-level electron emission—X-rays eject photoelectrons whose kinetic energies reveal binding energies specific to each element and its chemical state
• Chemical state sensitivity allows identification of oxidation states, bonding environments, and functional groups through characteristic binding energy shifts
• Sampling depth of 1–10 nm makes XPS the workhorse technique for thin film composition and surface contamination analysis

Auger Electron Spectroscopy (AES)

• Three-electron process—a core hole is filled by an outer electron, transferring energy to eject a second (Auger) electron with element-specific kinetic energy
• Nanometer-scale spatial resolution enables compositional mapping of small features, grain boundaries, and localized defects
• Chemical state information available through peak shape analysis, though less straightforward than XPS chemical shifts

Ultraviolet Photoelectron Spectroscopy (UPS)

• Valence band probing—UV photons (typically 21.2 eV from He I) excite valence electrons, mapping the density of states near the Fermi level
• Work function measurements and band alignment studies are critical for understanding electronic interfaces in devices
• Surface-sensitive to ~1 nm due to the short mean free path of low-energy photoelectrons

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Diffraction-Based Structural Techniques

Electrons scatter from periodic atomic arrangements, producing diffraction patterns that encode surface symmetry and atomic positions. The wavelength of low-energy electrons matches interatomic spacings, making them ideal surface structure probes.

Low-Energy Electron Diffraction (LEED)

• Surface crystallography—electrons with energies of 20–500 eV diffract from the topmost atomic layers, producing spot patterns that reveal surface periodicity
• Surface reconstructions and superstructures appear as additional diffraction spots, indicating atomic rearrangements from bulk-terminated structures
• Quantitative analysis through intensity-voltage (I-V) curves enables determination of atomic positions with ~0.1 Å precision

Reflection High-Energy Electron Diffraction (RHEED)

• Grazing incidence geometry—high-energy electrons (10–30 keV) strike the surface at ~1–3°, ensuring extreme surface sensitivity despite high electron energy
• Real-time growth monitoring during molecular beam epitaxy (MBE) through oscillations in diffraction intensity that track layer-by-layer deposition
• Surface reconstructions and roughness are immediately visible in the diffraction pattern, enabling in-situ process control

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Scanning Probe Techniques

A sharp tip scans across the surface, measuring local interactions to build real-space images with atomic or near-atomic resolution. These techniques provide direct visualization rather than averaged spectroscopic signals.

Scanning Tunneling Microscopy (STM)

• Quantum tunneling current—electrons tunnel between a sharp metallic tip and the sample when separated by ~1 nm, with current exponentially sensitive to tip-sample distance
• Sub-angstrom vertical resolution enables imaging of individual atoms, surface defects, and electronic density of states on conducting surfaces
• Atom manipulation capabilities allow construction of nanoscale structures by pushing, pulling, or depositing individual atoms

Atomic Force Microscopy (AFM)

• Force-based imaging—a cantilever deflects in response to tip-sample forces (van der Waals, electrostatic, capillary), enabling topographic mapping
• Works on insulators, biological samples, and liquids—unlike STM, no conductivity requirement, vastly expanding the range of accessible materials
• Mechanical property mapping through force spectroscopy measures local stiffness, adhesion, and elastic modulus at nanometer scales

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Ion-Based Techniques

Ions interact with surfaces through sputtering or scattering, providing compositional information with extreme surface sensitivity or depth resolution. Ion-surface collisions transfer momentum and energy in ways that reveal atomic identity and arrangement.

Secondary Ion Mass Spectrometry (SIMS)

• Sputter and detect—a primary ion beam ejects secondary ions from the surface, which are mass-analyzed to determine elemental and isotopic composition
• Parts-per-billion sensitivity for many elements makes SIMS the technique of choice for trace impurity detection and dopant profiling
• Depth profiling by continuous sputtering reveals concentration gradients through layered structures with nanometer depth resolution

Ion Scattering Spectroscopy (ISS)

• Binary collision model—low-energy noble gas ions (0.5–5 keV) scatter elastically from surface atoms, with energy loss determined by target atom mass
• True top-layer sensitivity—only the outermost atomic layer contributes significantly, providing the most surface-specific elemental analysis available
• Surface segregation studies reveal which elements preferentially occupy the topmost layer in alloys and compounds

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Thermal and Reaction-Based Techniques

Temperature-dependent measurements reveal how molecules bind to and desorb from surfaces. Activation energies and binding site populations are encoded in desorption kinetics.

Temperature Programmed Desorption (TPD)

• Desorption peaks vs. temperature—as a surface is heated at a controlled rate, adsorbates leave at temperatures related to their binding energies via the Redhead equation
• Multiple binding sites appear as distinct desorption peaks, revealing surface heterogeneity and adsorbate-adsorbate interactions
• Catalysis fundamentals—TPD characterizes how reactants bind to catalytic surfaces, informing mechanistic understanding and catalyst design

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Quick Reference Table

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Self-Check Questions

1. You need to determine the oxidation state of iron in a thin oxide film. Which technique would you choose, and what spectral feature would you analyze?

2. Compare XPS and AES: both detect electrons from surfaces, but what fundamental difference in their excitation/emission processes affects their spatial resolution capabilities?

3. A researcher wants to image individual DNA molecules on a mica substrate. Why would AFM be preferred over STM for this application?

4. You're growing a semiconductor heterostructure by MBE and need real-time feedback on layer completion. Which diffraction technique is appropriate, and what signal would indicate complete monolayer formation?

5. Compare SIMS and ISS: both use ion beams, but how do their sampling depths differ, and what types of problems is each best suited to solve?