Interfacial and Surface Science
NREL researchers have developed an integrated set of experimental capabilities to address a broad range of fundamental and applied issues in surface and interfacial science that are critical for advancing sustainable-energy technologies.
Surface and interface phenomena often control the opto-electronic, chemical, or mechanical properties of materials and device structures used in energy-harvesting and storage applications such as photovoltaics, fuel cells, and batteries.
Direct and Inverse Photoemission
Capabilities include X-ray/ultraviolet photoelectron spectroscopy (XPS/UPS) and inverse photoemission spectroscopy (IPES). XPS/UPS quantifies near-surface compositions and chemical states, and correlates these with surface valence-electronic structure and interfacial band alignments. The complementary technique IPES provides direct information on conduction-band density-of-state at surfaces and interfacial conduction-band alignments. Our XPS/UPS instruments include capabilities for 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.
Secondary Ion Mass Spectroscopy
Secondary ion mass spectrometry (SIMS) is a powerful analytical technique useful for measurements of dopants and impurities in semiconductors and other materials.
Magnetic-Sector SIMS, also known as dynamic SIMS (DSIMS), provides the ultimate in low detection limits for all species in the periodic table. Depending on the matrix and element of interest, quantification can be as low as 5×1012 atoms/cm3. High-lateral-resolution (≥300 nm) imaging is possible at low or high mass resolution.
Time-of-flight SIMS (TOF-SIMS) provides surface spectroscopy of both inorganic and organic materials, and is capable of detection limits in the sub-ppm range. High-lateral-resolution (>100 nm) chemical imaging is also possible; recent TOF-SIMS work at NREL has focused on understanding grain-boundary segregation effects in materials such as thin-film polycrystalline CdTe via high-resolution 3-D tomography.
Auger Electron Spectroscopy
Auger electron spectroscopy (AES) measurements provide compositional mapping and depth profiling of matrix elements (~1 atomic % composition and above). A typical application is compositional profiling of a material such as Cu(In,Ga)Se2 (CIGS) to determine compositional and hence optical bandgap variations in a thin-film PV material, or compositional mapping to identify impurity phases.
Chalcogenide Deposition Chamber
This tool enables deposition of inorganic chalcogenides and for basic material and device studies, and for in situ interface formation for band-offset studies. Recent work has focused on thin-film growth and surface/interface studies of the novel Earth-abundant thin-film PV absorber Cu2ZnSnS4 (CZTS).
Omicron Surface Science Platform
This surface science platform includes the following suite of instruments: XPS/UPS/IPES, scanning tunneling microscopy (STM), atomic force microscopy (AFM), temperature-programmed desorption (TPD), low-energy electron diffraction (LEED), and ion scattering spectroscopy (ISS). These integrated capabilities support comprehensive and detailed surface-science studies of energy-relevant materials, interfaces and device structures.
Atomic, Molecular, and Nanocrystal Deposition Apparatus
Called AMANDA, this novel deposition tool is configured to deposit a variety of materials used in third-generation PV and related technologies. Examples include novel thin-film absorbers based on organometallic lead halide perovskites and semiconductor quantum dots.
The Materials Science Center is part of the Materials, Chemical, and Computational Science directorate, led by Associate Lab Director Bill Tumas.