The oxidation of Ge covered with graphene that is either grown on or transferred to the surface is investigated by X-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy. Graphene properly grown by chemical vapor deposition on Ge(100), (111), or (110) effectively inhibits room-temperature oxidation of the surface. When graphene is transferred to the Ge surface, oxidation is reduced relative to that on uncovered Ge but has the same power law dependence. We conclude that access to the graphene/Ge interface must occur via defects in the graphene. The excellent passivation provided by graphene grown on Ge should enhance applications of Ge in the electronic-device industry.
We established locally varying strain fields in unmodified MoS nanosheets. The approach relies on dry release in place of multilayer MoS on textured Si substrates. By this process we demonstrated intense photoluminescence, a ∼70 meV decrease of the transition energy, and exciton funneling in ∼4 nm-thick MoS films.
We demonstrate that wrinkled graphene on Ge with nanoscale period and amplitude holds the potential to generate cyclotron-like radiation in the THz range of the electromagnetic spectrum. We show nanoscale graphene wigglers fabricated by release and transfer of atomically thin sheets to one-dimensional Ge gratings. We present a simple time of flight and interference model to calculate the radiated frequency and output power for the fabricated devices. We establish, theoretically, that an output power of ∼ 0.1-7 mW can be obtained from graphene/Ge wigglers with period not exceeding 85 nm, and amplitude-to-period ratio in the range of 1.4 to 10.
We demonstrate thin-film GaSb solar cells which are isolated from a GaSb substrate and transferred to a Si substrate. We epitaxially grow ∼3.3 μm thick GaSb P on N diode structures on a GaSb substrate. Upon patterning in 2D arrays of pixels, the GaSb films are released via epitaxial lift-off and they are transferred to Si substrates. Encapsulation of each pixel preserves the structural integrity of the GaSb film during lift-off. Using this technique, we consistently transfer ∼4 × 4 mm2 array of pixelated GaSb membranes to a Si substrate with a ∼ 80%–100% yield. The area of individual pixels ranges from ∼90 × 90 μm2 to ∼340 × 340 μm2. Further processing to fabricate photovoltaic devices is performed after the transfer. GaSb solar cells with lateral sizes of ∼340 × 340 μm2 under illumination exhibit efficiencies of ∼3%, which compares favorably with extracted values for large-area (i.e., 5 × 5 mm2) homoepitaxial GaSb solar cells on GaSb substrates.
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