arXiv subjects

M. C. Hersam

Publications and source records attributed to M. C. Hersam.

3 recordsLinked to original sources

arXiv2025

Comparison of Nb and Ta Pentoxide Loss Tangents for Superconducting Quantum Devices

Superconducting transmon qubits are commonly made with thin-film Nb wiring, but recent studies have shown increased performance with Ta wiring. In this work, we compare the resonator-induced single photon, millikelvin dielectric loss for pentoxides of Nb (Nb2O5) and Ta (Ta2O5) in order to further understand limiting losses in qubits. Nb and Ta pentoxides of three thicknesses are deposited via pulsed laser deposition onto identical coplanar waveguide resonators. The two-level system (TLS) loss in Nb2O5 is determined to be about 30% higher than that of Ta2O5. This work indicates that qubits with Nb wiring are affected by higher loss arising from the native pentoxide itself, likely in addition to the presence of suboxides, which are largely absent in Ta.

quant-ph↗

arXiv2015

Gate-tunable Memristive Phenonmena Mediated by Grain Boundaries in Single Layer MoS2

Continued progress in high speed computing depends on breakthroughs in both materials synthesis and device architectures. The performance of logic and memory can be enhanced significantly by introducing a memristor, a two terminal device with internal resistance that depends on the history of the external bias voltage. State of the art memristors, based on metal insulator metal (MIM) structures with insulating oxides, such as TiO2, are limited by a lack of control over the filament formation and external control of the switching voltage. Here, we report a class of memristors based on grain boundaries (GBs) in single-layer MoS2 devices. Specifically, the resistance of GBs emerging from contacts can be easily and repeatedly modulated, with switching ratios up to 1000 and a dynamic negative differential resistance (NDR). Furthermore, the atomically thin nature of MoS2 enables tuning of the set voltage by a third gate terminal in a field-effect geometry, which provides new functionality that is not observed in other known memristive devices.

cond-mat.mes-hall↗

arXiv2006

Saturated Hydrocarbons on Silicon: Quantifying Desorption with Scanning Tunneling Microscopy and Quantum Theory

Electron stimulated desorption of cyclopentene from the Si(100)-2x1 surface is studied experimentally with cryogenic UHV STM and theoretically with transport, electronic structure, and dynamical calculations. Unexpectedly for a saturated hydrocarbon on silicon, desorption is observed at bias magnitudes as low as 2.5 V, albeit the desorption yields are a factor of 500 to 1000 lower than previously reported for unsaturated molecules on silicon. The low threshold voltage for desorption can be attributed to hybridization of the molecule with the silicon surface, which results in low-lying ionic resonances within 2-3 eV of the Fermi level. These resonances are long-lived, spatially localized and displaced in equilibrium with respect to the neutral state, resulting, upon excitation, in symmetric (positive ion) or asymmetric (negative ion) motion of the silicon dimer atoms. This study highlights the importance of nuclear dynamics in silicon-based molecular electronics and suggests new guidelines for the control of such dynamics.

cond-mat.mes-hall↗