Capabilities
Capabilities
Surface Analysis Cluster Tool
Laboratory
National Renewable Energy Laboratory (NREL)Capability Expert
Glenn TeeterClass
BenchmarkingCharacterization
Node Readiness Category
2: High-Temperature Electrolysis (HTE)1: Low-Temperature Electrolysis (LTE)
1: Photoelectrochemical (PEC)
2: Solar Thermochemical (STCH)
Description
The NREL surface analysis cluster tool integrates deposition, processing, and characterization capabilities with an ultrahigh vacuum sample transfer system, as illustrated in Figure 1. A dedicated glovebox facilitates air-free sample transfer into and out of the system. Key analytical capabilities include:
- X-ray and ultraviolet photoelectron spectroscopies (XPS/UPS): XPS/UPS quantifies near-surface compositions (~1 atomic % composition and above) and chemical states, and correlates these with surface valence-electronic structure and interfacial band alignments. Additional capabilities being developed include in operando XPS (opXPS) as illustrated in Figure 2 and Figure 3 for applications in lithium-ion-battery and photovoltaics materials research, respectively.
- Auger electron spectroscopy (AES); scanning Auger microscopy (SAM); scanning electron microscopy (SEM): The instrument combines an SEM with an electron energy analyzer that measures the kinetic energies of Auger electrons. Auger electron spectroscopy (AES) provides surface-sensitive compositional measurements and depth profiling of matrix elements (~1 atomic % composition and above). Scanning Auger microscopy (SAM) measurements permit compositional imaging with spatial resolutions down to ~50 nm, as well as correlations between composition maps and SEM images of the sample morphology, as illustrated in Figure 4.
- Omicron surface-science platform: This instrument is geared toward fundamental studies of materials using techniques including XPS/UPS, low-energy electron diffraction (LEED), scanning-tunneling and atomic-force microscopies (STM/AFM), and ion-scattering spectroscopy (ISS).
Capability Bounds
NREL currently has three fully operational XPS/UPS systems for conventional measurements of surface chemical states, valence-electronic structure, and compositions, as well as Ar+-ion sputter depth profiling. Two of these XPS instruments are coupled to an ultrahigh vacuum transfer system (Figure 1) that incorporates extensive characterization and in situ/controlled-ambient processing capabilities. One of the XPS/UPS instruments on the NREL cluster tool is configured for in operando measurements including combinations of light and voltage bias, and includes an atomic hydrogen source. A third XPS tool is part of NREL's integrated Process Development and Integration Laboratory (PDIL), which combines an array of processing and characterization tools that share a standardized sample form factor, and are configured to enable controlled-ambient sample transfers through vacuum pods. The NREL PDIL XPS/UPS system can handle samples up to 150 mm x 150 mm in size, can perform highly automated mapping experiments, and includes parallel-imaging capabilities with spatial resolutions down to ~10 mm. The AES instrument can accommodate sample sizes up to 25 mm x 25 mm, with spatial resolutions down to ~50 nm. The Omicron platform can accommodate samples up to ~10 mm x 10 mm.
Unique Aspects
These instruments are coupled to an ultrahigh vacuum cluster tool that enables preparation and study of sample surfaces under controlled-ambient conditions. This collection of tools is ideally suited to identification and quantification of surface species due to surface modification processes, or for understanding processes such as photocorrosion, etc. Additionally, the XPS/UPS instruments include capabilities for in situ and in operando studies of surfaces and interfaces, including the effects of light, voltage, and/or current bias, as well as high-throughput combinatorial mapping capabilities, and parallel imaging capabilities with spatial resolution down to ~10 mm.
Availability
These capabilities are available for use within the HydroGEN consortium effort with no significant restrictions. NREL staff members are available to perform measurements and can also host visitors to NREL.
Benefit
The capabilities for preparing and transferring samples under controlled ambient conditions provide unique opportunities for studying processes related to topics of interest to HydroGEN. The in operando XPS capabilities that have been developed recently at NREL (Figures 2 and 3) enable novel measurements of interfacial processes occurring in solar cell and battery materials and device structures. Variations on these techniques could be developed for studying issued related to hydrogen generation.
Images
Figure 1. Schematic of NREL surface-science cluster tool, including capabilities for sample preparation and transfer under controlled-ambient conditions
Figure 2. In operando XPS capability developed at NREL for studying issues related to lithium-ion battery interfaces
Figure 3. In operando XPS capability developed at NREL for studying solar cell interfaces and junction formation
Figure 4. Sequence of SEM images and corresponding SAM maps illustrating the evolution of surface morphology and elemental composition of a CdTe single crystal sample at various stages of processing with Cu. a) Deposition of elemental Cu followed by in-vacuum heating results in reaction of Cu with the CdTe surface to form CuxTe precipitates. b) Additional annealing causes Cu to diffuse into the bulk of the CdTe substrate (as confirmed by SIMS measurements). c) Extensive annealing results in substantial changes to sample morphology, coupled with Cu surface segregation on and stabilization of the CdTe(111) facets.