arXiv subjects

Masahiro Sasaki

Publications and source records attributed to Masahiro Sasaki.

3 recordsLinked to original sources

arXiv2026

Maskless Electron Beam-Induced Etching of Diamond in Air: A Secondary Electron-Driven Mechanism

We report a direct, maskless electron beam-induced etching (EBIE) process for diamond in air, enabling high-precision patterning without lithography or plasma processing. Through a comprehensive analysis of electron-gas, electron-diamond, and gas-surface interactions in the SEM environment, we demonstrate that etching is predominantly governed by low-energy secondary electrons, which drive gas dissociation and radical generation. The resulting oxygen- and nitrogen-based radicals chemisorb on the diamond surface, form volatile carbon-containing species, and desorb under continued electron irradiation, enabling controlled material removal. The process exhibits two distinct regimes: a molecule-limited regime governed by gas flux and an electron-limited regime controlled by current density. Etch depths up to 212 nm and lateral resolution down to 200 nm are achieved. Time-dependent anisotropy is observed, with (100) surfaces transitioning to (111)-faceted morphologies, enhancing etch yield. These results establish a general secondary electron-driven mechanism for EBIE in gas environments, providing a maskless, damage-free nanofabrication route for diamond semiconductor and other chemically inert materials.

cond-mat.mtrl-sci↗

arXiv2026

First Plasma Atomic Layer Etching of Diamond via O$_2$/Kr Chemistry

We report the first plasma atomic layer etching (ALE) process for diamond using a cyclic plasma sequence composed of two separated steps: oxygen surface modification and krypton ion removal. The process is implemented in an inductively coupled plasma reactor using alternating O$_2$ plasma exposure and low-energy Kr ion bombardment. This cyclic process exhibits the characteristic self-limiting behavior of ALE and enables controlled material removal with atomic-scale precision. An etch depth per cycle of \SI{6.85}{\angstrom} was achieved. Surface analysis reveals that the etched diamond surfaces exhibit lower roughness than the pristine material, while XPS confirms the preservation of the diamond bonding structure and indicates essentially damage-free etching. These results demonstrate that plasma ALE based on O$_2$/Kr chemistry provides a viable route toward damage-controlled nanoscale processing of diamond, opening new opportunities for advanced device fabrication in power electronics, photonics, quantum sensing and quantum computing technologies.

cond-mat.mtrl-sci↗

arXiv2023

Partial Hydrogenation of N-heteropentacene: Impact on molecular packing and electronic structure

Four-nitrogen-containing 5,6,13,14-Tetraazapentacene (BTANC) has attracted attention as a new n-type organic semiconductor with a rigid crystalline phase due to intermolecular CH-N hydrogen bonding. However, in the thin film transistor of BTANC, poor carrier transport properties and low stability in the ambient condition have been reported so far; thus further refining and understanding of the thin film of BTANC will be required. Here, by means of carefully-controlled vacuum deposition of BTANC in the narrow window of temperature avoiding impurity sublimation and thermal degradation of molecules, we produced a well-defined monolayer on Cu(111) for molecular-level investigations. Synchrotron photoemission of the monolayer revealed a noticeable alteration of the chemical state of N atoms, which is unexpected for the pure BTANC molecule. In addition, molecular imaging of the monolayer by scanning tunneling microscope (STM) revealed that the molecular packing structure in the monolayer significantly differed from that in the single crystal of BTANC. These observations can be interpreted as a result of the partial hydrogenation of N atoms in BTANC and the emergence of the NH-N type intermolecular hydrogen bonding in the monolayer. These findings will provide a general remark and strategy to control the molecular packing structure and electronic property in the molecular films of the nitrogen-containing acenes, by means of controlled hydrogenation.

cond-mat.mtrl-sci↗