arXiv subjects

Xuezhe Zhou

Publications and source records attributed to Xuezhe Zhou.

4 recordsLinked to original sources

arXiv2018

High pressure, high temperature molecular doping of nanodiamond

The development of color centers in diamond as the basis for emerging quantum technologies has been limited by the need for ion implantation to create the appropriate defects. We present a versatile method to dope diamond without ion implantation, by synthesis of a doped amorphous carbon precursor and transformation at high temperatures and high pressures. To explore this bottom-up method for color center generation, we rationally create silicon-vacancy defects in nanodiamond and investigate them for optical pressure metrology. In addition, we show that this process can generate noble gas defects within diamond from the typically-inactive argon pressure medium, which may explain the hysteresis effects observed in other high pressure experiments and the presence of noble gases in some meteoritic nanodiamonds. Our results illustrate a general method to produce color centers in diamond, and may enable the controlled generation of designer defects.

cond-mat.mtrl-sci↗

arXiv2017

Photothermal effects during nanodiamond synthesis from a carbon aerogel in a laser-heated diamond anvil cell

Nanodiamonds have emerged as promising materials for quantum computing, biolabeling, and sensing due to their ability to host color centers with remarkable photostability and long spin-coherence times at room temperature. Recently, a bottom-up, high-pressure, high-temperature (HPHT) approach was demonstrated for growing nanodiamonds with color centers from amorphous carbon precursors in a laser-heated diamond anvil cell (LH-DAC) that was supported by a near-hydrostatic noble gas pressure medium. However, a detailed understanding of the photothermal heating and its effect on diamond growth, including the phase conversion conditions and the temperature-dependence of color center formation, has not been reported. In this work, we measure blackbody radiation during LH-DAC synthesis of nanodiamond from carbon aerogel to examine these temperature-dependent effects. Blackbody temperature measurements suggest that nanodiamond growth can occur at 16.3 GPa and 1800 K. We use Mie theory and analytical heat transport to develop a predictive photothermal heating model. This model demonstrates that melting the noble gas pressure medium during laser heating decreases the local thermal conductivity to drive a high spatial resolution of phase conversion to diamond. Finally, we observe a temperature-dependent formation of nitrogen vacancy centers and interpret this phenomenon in the context of HPHT carbon vacancy diffusion using CBΩ theory.

cond-mat.mtrl-sci↗

arXiv2016

Recovery of Si-IV nanowires from extreme GPa pressure

We use Raman spectroscopy in tandem with transmission electron microscopy and DFT simulations to show that extreme (GPa) pressure converts the phase of silicon nanowires from cubic (Si-I) to hexagonal (Si-IV) while preserving the nanowire's cylindrical morphology. In situ Raman scattering of the TO mode demonstrates the high-pressure Si-I to Si-II phase transition near 9 GPa. Raman signal of the TO phonon shows a decrease in intensity in the range 9 to 14 GPa. Then, at 17 GPa, it is no longer detectable, indicating a second phase change (Si-II to Si-V) in the 14 to 17 GPa range. Recovery of exotic phases in individual silicon nanowires from diamond anvil cell experiments reaching 17 GPa is also shown. Raman measurements indicate Si-IV as the dominant phase in pressurized nanowires after decompression. Transmission electron microscopy and electron diffraction confirm crystalline Si-IV domains in individual nanowires. Computational electromagnetic simulations suggest that heating from the Raman laser probe is negligible and that near-hydrostatic pressure is the primary driving force for the formation of hexagonal silicon nanowires.

cond-mat.mtrl-sci↗

arXiv2015

Cold Brownian motion in aqueous media via anti-Stokes photoluminescence

Advances in cryogenic sciences have enabled several observations of new low-temperature physical phenomena including superconductivity, superfluidity, and Bose-Einstein condensates. Heat transfer is also critical in numerous applications including thermal management within integrated microelectronics and the regulation of plant-growth and development. Here we demonstrate that single-beam laser-trapping can be used to induce and quantify the local refrigeration of aqueous media through analysis of the cold Brownian dynamics of individual Yb3+-doped yttrium lithium fluoride (YLF) crystals in an inhomogeneous temperature field via forward light scattering and back-focal-plane interferometry. A tunable, NIR continuous-wave laser is used to optically trap individual YLF crystals with an irradiance on the order of 1 MW/cm2. Heat is transported out of the crystal lattice (across the solid / liquid interface) by anti-Stokes photoluminescence following upconversion of Yb3+ excited states mediated by optical-phonon absorption. The cold Brownian motion (CBM) analysis of individual YLF crystals indicates local cooling by >21 C below ambient conditions suggesting a range of potential future applications.

cond-mat.mes-hall↗