Metal-assisted chemical etching (MACE) is a versatile anisotropic etch for silicon although its mechanism is not well understood. Here we propose that the Schottky junction formed between metal and silicon plays an essential role on the distribution of holes in silicon injected from hydrogen peroxide. The proposed mechanism can be used to explain the dependence of the etching kinetics on the doping level, doping type, crystallographic surface direction, and etchant solution composition. We used the doping dependence of the reaction to fabricate a novel etch stop for the reaction.

Engineered optoelectronic surfaces must control both the flow of light and the flow of electrons at an interface; however, nanostructures for photon and electron management have typically been studied and optimized separately. In this work, we unify these concepts in a new hybrid metal-semiconductor surface that offers both strong light absorption and high electrical conductivity. We use metal-assisted chemical etching to nanostructure the surface of a silicon wafer, creating an array of silicon nanopillars protruding through holes in a gold film. When coated with a silicon nitride anti-reflection layer, we observe broad-band absorption of up to 97% in this structure, which is remarkable considering that metal covers 60% of the top surface. We use optical simulations to show that Mie-like resonances in the nanopillars funnel light around the metal layer and into the substrate, rendering the metal nearly transparent to the incoming light. Our results show that, across a wide parameter space, hybrid metal-semiconductor surfaces with absorption above 90% and sheet resistance below 20 Ω/□ are realizable, suggesting a new paradigm wherein transparent electrodes and photon management textures are designed and fabricated together to create high-performance optoelectronic interfaces.

We demonstrate a novel atom chip trapping system that allows the placement and high-resolution imaging of ultracold atoms within microns from any 100 µm-thin, UHV-compatible material, while also allowing sample exchange with minimal experimental downtime. The sample is not connected to the atom chip, allowing rapid exchange without perturbing the atom chip or laser cooling apparatus. Exchange of the sample and retrapping of atoms has been performed within a week turnaround, limited only by chamber baking. Moreover, the decoupling of sample and atom chip provides the ability to independently tune the sample temperature and its position with respect to the trapped ultracold gas, which itself may remain in the focus of a high-resolution imaging system. As a first demonstration of this new system, we have confined a 700-nK cloud of 8 × 10 4 87 Rb atoms within 100 µm of a gold-mirrored 100-µm-thick silicon substrate. The substrate was cooled to 35 K without use of a heat shield, while the atom chip, 120 µm away, remained at room temperature. Atoms may be imaged and retrapped every 16 s, allowing rapid data collection.Ultracold gases trapped near cryogenic surfaces using atom chips 1 can serve as elements of hybrid quantum systems for quantum information processing, e.g., by coupling quantum gases to superconducting qubits 2 , or as sensitive, high-resolution, and wide-area probes of electronic current flow 3 , electric ac and patch fields 4 , and magnetic domain structure 5 and dynamics. Previous experiments have succeeded in trapping and imaging ultracold thermal and quantum gases of alkali atoms around carbon nanotubes 6 , near superconductors 7 at 4 K, microns from room-temperature gold wires 8 , and within a He dilution refrigerator 9 .

We demonstrate gate control of the electronic g tensor in single and double quantum dots formed along a bend in a carbon nanotube. From the dependence of the single-dot excitation spectrum on magnetic field magnitude and direction, we extract spin-orbit coupling, valley coupling, and spin and orbital magnetic moments. Gate control of the g tensor is measured using the splitting of the Kondo peak in conductance as a sensitive probe of Zeeman energy. In the double-quantum-dot regime, the magnetic field dependence of the position of cotunneling lines in the two-dimensional charge stability diagram is used to infer the real-space positions of the two dots along the nanotube.

Double‐sided metal‐oxide‐semiconductor field‐effect‐transistor processing is demonstrated for the first time on an ultrathin crystalline silicon substrate of 6‐20 μm in a 100 mm diameter wafer format without a carrier wafer, the thinnest free‐standing silicon wafers ever fabricated. The compatibility of the flexible material with conventional semiconductor processing tools is enabled by supporting an interior ultrathin silicon with a surrounding thicker ring of silicon. Current‐voltage characteristics of transistors on ultrathin silicon show performance as expected from bulk silicon, with electron mobility ~1500 cm2 V−1 second−1. Mechanical measurements quantify the handleability.image