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Abstract: This study reports successful deposition of high quantum efficiency (QE) bialkali antimonide K2CsSb photocathodes on graphene films. The results pave the way for an ultimate goal of encapsulating technologically relevant photocathodes for accelerator technology with an atomically thin protecting layer to enhance lifetime while minimizing QE losses. A QE of 17% at ≈3.1 eV (405 nm) is the highest value reported so far on graphene substrates and is comparable to that obtained on stainless steel and nickel reference substrates. The spectral responses of the photocathodes on graphene exhibit signature features of K2CsSb including the characteristic absorption at ≈2.5 eV. Materials characterization based on X‐ray fluorescence and X‐ray diffraction reveals that the composition and crystal quality of these photocathodes deposited on graphene is comparable to those deposited on a reference substrate. Quantitative agreement between optical calculations and QE measurements for the K2CsSb on free suspended graphene and a graphene‐coated metal substrate further confirms the high‐quality interface between the photocathodes and graphene. Finally, a correlation between the QE and graphene quality as characterized by Raman spectroscopy suggests that a lower density of atomistic defects in the graphene films leads to higher QE of the deposited K2CsSb photocathodes. [ABSTRACT FROM AUTHOR]

Photocathodes can benefit from a thin protection layer and attain long-term stability. Graphene is potentially a good candidate for such application. We report direct growth of single-layer graphene on single crystal Cu(110) photocathodes using chemical vapor deposition and the effective protection of copper photocathodes with graphene against degradation under atmospheric conditions. Due to the interaction and charge transfer between graphene and copper, the graphene-protected cathodes have 0.25 eV lower work function and 17% higher quantum efficiency at 250nm compared with bare Cu cathodes. The graphene coating can protect copper photocathodes from degradation for more than 20 min in an exposure to 200 Torr of air. The validation of graphene-photocathode compatibility opens a new route to the lifetime-extension for photocathodes. [ABSTRACT FROM AUTHOR]

Abstract: Capacitive photocurrent spectroscopy is used to probe the electronic states of graphene-oxide, and reduced graphene-oxide. Three peaks are observed whose intensities scale with the oxygen coverage. The energy of these peaks correlate with the luminescence spectra reported for graphene-oxide. Using a fitting procedure, the density of states for graphene oxide is extracted from the data. It consists of the π/π∗ states along with a distribution of mid-gap states centered at three different energies near the Dirac point. X-ray photoelectron spectroscopy measurements are used to identify the oxygen functional groups corresponding to the observed state distribution. [Copyright &y& Elsevier]

The fragmentation rate (FR) of two-dimensional layered materials (2DLMs) MoS 2 , WS 2 , and graphene in N- methyl-pyrrolidinone (NMP) was computed, where FR is a measure of the particle size reduction with ultrasonication time. For the 2DLMs, the highest FR generally occurred for sonication times t sonic = 30 min, with FR Graphite ∼ −1176.4 μm-hr−1, FR WS2 ∼ −32.4 μm-hr−1and FR MoS2 ∼ −3.8 μm-hr−1. This is in contrast to a non-layered material, Al nanoparticles, where FR Al ∼0 μm-hr−1 for t sonic = 30 min. Knowledge of the particle size as a function of t sonic has not been reported previously for 2DLMs, and is extremely important as these materials are integrated into additively manufactured platforms, such as ink-jet printing and three-dimensional (3D) printing. The treated materials were then infused with two types of polymers, flexible and stretchable polyisoprene, and an optically transparent acrylic, poly-methyl-methacrylate (PMMA) for opto-electro-mechanical strain-based sensing device applications. In particular, the hybrid composites of graphene with optically transparent and bendable PMMA revealed the potential of forming opto-mechanical filters, where optical filtering can be engineered through the graphene loading. The polyisoprene-graphene composites were piezoresistive with potential for wearable electronics, where mechanical strain, as induced at joint movements on a finger for example, modulates the current with joint displacement. Strain levels of up to 200% were observed and the gauge factor of these devices was measured to be ∼75 which is > 10X higher compared to conventional metal-foil based strain sensors. This work sheds fundamental insights into the role of sonication on the materials properties of 2DLMs in solution dispersions and shows their potential in hybrid composites for opto-electro-mechanical strain based sensing applications and in wearable electronics. [ABSTRACT FROM AUTHOR]