Capabilities

Looking to collaborate on a H₂ generation project? See my node through the HydroGEN: Advanced Water Splitting Materials project and email me.

Other collaborations and inquiries and be addressed to Jason Cooper at: jkcooper@lbl.gov

Synthesis

Reactive Sputtering

Oxide, nitrides, and metallic thin films with up to 4 element compositions on a variety of substrates such as conductive glass, quartz, silicon wafers, SiN membrane windows. Used for the production of Mo:BiVO₄, CuBi₂O₄, Cu, and CuFeO₂.

Chemical Vapor Annealing

Used for the fabrication of Cu₃N and H₂ annealing of BiVO₄, the tube furnace has process gasses including: Ar, O₂, NH₃, and H₂

Characterization

Transient Absorption Spectroscopy

Pump-probe spectroscopy driven by Coherent Libra and Coherent OPerA Solo allow characterization of photocarrier dynamics continuously from sub-ps to us time scales and over probe wavelengths from UV-NIR spectral ranges (350 – 1600 nm) and in transmission or reflection geometry. Measurement cells for operando spectroscopy are compatible with all setups and can be coupled to a dedicated potentiostat, thereby enabling direct probes of excited state spectra and their evolution to the ground state under electrochemical bias. In ex-situ configuration, measurements can be performed as a function of temperature from 10 K to 500 K.

Photoluminescence Spectroscopy

Steady state and time resolved photoluminescence, by TCSPC, measurements can be performed with photoexcitation over the visible range and detection from the UV to IR spectral range. Continuous wave laser sources at 100 mW include 405, 488, and 532 nm. Measurements can be performed under operational photoelectrochemical conditions, allowing for characterization of radiative band-to-band and sub-gap defect recombination. Photoluminescence quenching due to charge extraction and interface recombination can be probed as a function of electrochemical bias or, in ex situ configuration. Temperature control using a closed loop liquid helium cryostat from 10 to 500 K.

Photoelectrochemical Stations

Using 1-sun AM1.5G solar simulators, electrodes are tested under various electrochemical conditions to measure the current-voltage behavior, current transients with chopped illumination, impedance, and stability under long-term operating conditions. Similarly, we also use a high power 365 nm LED to simulate solar flux up to 10 suns.

Raman Spectroscopy

Confocal Raman spectrometer is equipped with Teflon-coated immersion lenses and an electrochemical cell for probing chemical transformations of electrochemical and photoelectrochemical systems under operational conditions. Raman mapping under ex situ conditions is suited for analyzing phase segregation, as well as localized failure, of (photo)electrochemical systems.

Variable Angle Spectroscopic Ellipsometry

Under ex situ condition, this capability is suited for determining optical functions of newly discovered materials (semiconductors, catalysts, protective coatings, membranes) and thicknesses of thin films, from the UV to the NIR spectral range (200-1600 nm). A heating and cooling stage (77-773 K) is available for tracking materials during thermal processing, thereby allowing in situ evaluation of the impacts of phase transformations, composition evolution, and interfacial reactions on optical characteristics and thicknesses. This capability can also be used as an environmental cell to characterize water uptake in membranes as a function of temperature and humidity and thermal reduction and oxidation reactions of solid state materials. A (photo)electrochemical cell provides opportunity to probe optical and physical property changes of electrified solid/electrolyte interfaces in quasi-darkness or under bias illumination, thereby allowing electrochromic, (photo)corrosion, and phase transformations to be characterized. Data collection times of ~1s mean that transient changes of materials as a function of bias and illumination can be established. Data from these measurements can aid in understanding of mechanisms associated with transduction of solar to chemical energy, as well as for identifying spectral features from other optical probes.

Photothermal Deflection Spectroscopy

Custom built system capable of measuring absorption spectra from 250 – 2500 nm with high sensitivity of thin-film samples. Absorption coefficients from 100 – 1×10⁵ cm^-1 have been determined. This technique is sensitive to absorption processes that decay through non-radiative recombination thus resulting in sample heating, therefore scattering and reflection do not contribute to the absorption spectrum. Due to the high sensitivity, it is also particularly well suited for measuring sub-gap absorption due to defects.

X-Ray Photoelectron Spectroscopy

Kratos Axis Ultra DLD system with monochromatized Al K-alpha, nonmonochromatic Al and Mg emission, and UPS He-I and He-II. He-ion scattering spectroscopy. Ar-ion sputtering. Heated / cooling stage. Variable sample angles from 0 – 60 degrees.

X-Ray Diffraction with In-Situ Reactive Annealing

Rigaku x-ray diffration with 2D hypix detector, in-plane mode for ultra-thin film characterization, and Eulerian cradle. ReactorX – in-situ characterization of thermal processing of materials in air, Ar, NH₃, and O₂ up to 800 C.