The
In this work, we report a simplified method to measure thermal conductivity from the typical Raman thermometry method by employing a much simpler dispersion relationship equation and the Debye function, instead of solving the heat equation. Unlike the typical Raman thermometry method, our new method only requires monitoring of the temperature-dependent Raman mode shifting without considering laser power-dependent Raman mode shifting. Thus, this new calculation method offers a simpler way to calculate the thermal conductivity of materials with great precision. As a model system, the
- Award ID(s):
- 1809077
- Publication Date:
- NSF-PAR ID:
- 10199547
- Journal Name:
- Nano Express
- Volume:
- 1
- Issue:
- 3
- Page Range or eLocation-ID:
- Article No. 030010
- ISSN:
- 2632-959X
- Publisher:
- IOP Publishing
- Sponsoring Org:
- National Science Foundation
More Like this
-
β -Ga2O3nanomembrane (NM)/diamond heterostructure is one of the promising ultra-wide bandgap heterostructures that offers numerous complementary advantages from both materials. In this work, we have investigated the thermal properties of theβ -Ga2O3NM/diamond heterostructure with three different thicknesses ofβ -Ga2O3nanomembranes (NMs), namely 100 nm, 1000 nm, and 4000 nm thickβ -Ga2O3NMs using Raman thermometry. The thermal property—temperature relationships of theseβ -Ga2O3NM/diamond heterostructures, such as thermal conductivity and interfacial thermal boundary conductance were determined under different temperature conditions (from 100 K to 500 K with a 40 K interval). The result provides benchmark knowledge about the thermal conductivity ofβ -Ga2O3NMs over a wide temperature range for the design of novelβ -Ga2O3-based power electronics and optoelectronics. -
Abstract This work reports on the correlation between structure, surface/interface morphology and mechanical properties of pulsed laser deposited (PLD)
β -Ga2O3films on transparent quartz substrates. By varying the deposition temperature in the range of 25 °C–700 °C, ∼200 nm thick Ga2O3films with variable microstructure and amorphous-to-nanocrystalline nature were produced onto quartz substrates by PLD. The Ga2O3films deposited at room temperature were amorphous; nanocrystalline Ga2O3films were realized at 700 °C. The interface microstructure is characterized with a typical nano-columnar morphology while the surface exhibits the uniform granular morphology. Corroborating with structure and surface/interface morphology, and with increasing deposition temperature, tunable mechanical properties were seen in PLD Ga2O3films. At 700 °C, for nanocrystalline Ga2O3films, the dense grain packing reduces the elastic modulus Erwhile improving the hardness. The improved crystallinity at elevated temperatures coupled with nanocrystallinity, theβ -phase stabilization is accounted for the observed enhancement in the mechanical properties of PLD Ga2O3films. The structure-morphology-mechanical property correlation in nanocrystalline PLDβ -Ga2O3films deposited on quartz substrates is discussed in detail. -
Abstract We report on structural, microstructural, spectroscopic, dielectric, electrical, ferroelectric, ferromagnetic, and magnetodielectric coupling studies of BiFeO3–GdMnO3[(BFO)1–
x –(GMO)x ], wherex is the concentration of GdMnO3(x = 0.0, 0.025, 0.05, 0.075, 0.1, 0.15, and 0.2), nanocrystalline ceramic solid solutions by auto-combustion method. The analysis of structural property by Rietveld refinement shows the existence of morphotropic phase boundary (MPB) atx = 0.10, which is in agreement with the Raman spectroscopy and high resolution transmission electron microscopy (HRTEM) studies. The average crystallite size obtained from the transmission electron microscopy (TEM) and x-ray line profile analysis was found to be 20–30 nm. The scanning electron micrographs show the uniform distribution of grains throughout the surface of the sample. The dielectric dispersion behavior fits very well with the Maxwell-Wagner model. The frequency dependent phase angle (θ ) study shows the resistive nature of solid solutions at low frequency, whereas it shows capacitive behavior at higher frequencies. The temperature variation of dielectric permittivity shows dielectric anomaly at the magnetic phase transition temperature and shifting of the phase transition towards the lower temperature with increasing GMO concentration. The Nyquist plot showed the conduction mechanism is mostly dominated by grains and grain boundary resistances. The ac conductivity of all the samples follows the modifiedmore » -
Abstract We report polarization dependent photoluminescence studies on unintentionally-, Mg-, and Ca-doped
β -Ga2O3bulk crystals grown by the Czochralski method. In particular, we observe a wavelength shift of the highest-energy UV emission which is dependent on the pump photon energy and polarization. For 240 nm (5.17 eV) excitation almost no shift of the UV emission is observed betweenE ||b andE ||c , while a shift of the UV emission centroid is clearly observed for 266 nm (4.66 eV), a photon energy lying between the band absorption onsets for the two polarizations. These results are consistent with UV emission originating from transitions between conduction band electrons and two differentially-populated self-trapped hole (STH) states. Calcuations based on hybrid and self-interaction-corrected density functional theories further validate that the polarization dependence is consistent with the relative stability of two STHs. This observation implies that the STHs form primarily at the oxygen atoms involved in the original photon absorption event, thus providing the connection between incident polarization and emission wavelength. The data imposes a lower bound on the energy separation between the self-trapped hole states of ~70–160 meV, which is supported by the calculations. -
We report the effect of extended duration electron beam exposure on the minority carrier transport properties of 10 MeV proton irradiated (fluence ∼1014cm−2) Si-doped
β -Ga2O3Schottky rectifiers. The diffusion length (L ) of minority carriers is found to decrease with temperature from 330 nm at 21 °C to 289 nm at 120 °C, with an activation energy of ∼26 meV. This energy corresponds to the presence of shallow Si trap-levels. Extended duration electron beam exposure enhancesL from 330 nm to 726 nm at room temperature. The rate of increase forL is lower with increased temperature, with an activation energy of 43 meV. Finally, a brief comparison of the effect of electron injection on proton irradiated, alpha-particle irradiated and a reference Si-dopedβ -Ga2O3Schottky rectifiers is presented.