Observation of new quantum interference effect in solids

In order to achieve quantum interference of free electrons inside a solid, we have modified the geometry of the solid so that de Broglie waves interfere destructively inside the solid. Quantum interference of de Broglie waves leads to a reduction in the density of possible quantum states of electrons inside the solid and increases the Fermi energy level. This effect was studied theoretically within the limit of the quantum theory of free electrons inside the metal. It has been shown that if a metal surface is modified with patterned indents, the Fermi energy level will increase and consequently the electron work function will decrease. This effect was studied experimentally in both Au and SiO2 thin films of special geometry and structure. Work function reductions of 0.5 eV in Au films and 0.2 eV in SiO2 films were observed. Comparative measurements of work function were made using the Kelvin Probe method based on compensation of internal contact potential difference. Electron emission from the same thin films was studied by two independent research groups using Photoelectron Emission Microscopy (PEEM).Comment: 11 pages, 5 figure

Thermionic emission microscopy of scandium thin film dewetting on W(100)

© 2018 Author(s). Scandium thin films of 5-30 nm thickness deposited on clean W(100) surfaces de-wet from the tungsten surface when heated to temperatures \u3c 0.5 Tmelt. The dewetting temperature and the resulting droplet size are a function of the initial scandium film thickness

Band-gap Engineering in Sputter Deposited Amorphous/Microcrystalline Sc(x)Ga(1-x)N

Reactive sputtering was used to grow thin films of Sc(x)Ga(1-x)N with scandium concentrations of 20%-70% on quartz substrates at temperatures of 300-675 K. X-ray diffraction (XRD) of the films showed either weak or no structure, suggesting the films are amorphous or microcrystalline. Optical absorption spectra were taken of each sample and the optical band gap was determined. The band gap varied linearly with increasing Ga concentration between 2.0 and 3.5 eV. Ellipsometry was used to confirm the band gap measurements and provide optical constants in the range 250-1200 nm. ScN and GaN have different crystal structures (rocksalt and wurzite, respectively), and thus may form a heterogeneous mixture as opposed to an alloy. Since the XRD data were inconclusive, bilayers of ScN/GaN were grown and optical absorption spectra taken. A fundamental difference in the spectra between the bilayer films and alloy films was seen, suggesting the films are alloys, not heterogeneous mixtures

Thermionic emission microscopy of scandium thin film dewetting on W(100)

© 2018 Author(s). Scandium thin films of 5-30 nm thickness deposited on clean W(100) surfaces de-wet from the tungsten surface when heated to temperatures \u3c 0.5 Tmelt. The dewetting temperature and the resulting droplet size are a function of the initial scandium film thickness

Monitoring Phase Separation and Dark Recovery in Mixed Halide Perovskite Clusters and Single Crystals Using <i>In Situ</i> Spectromicroscopy

Mixed halide perovskites (MHPs) are a group of semiconducting materials with promising applications in optoelectronics and photovoltaics, whose bandgap can be altered by adjusting the halide composition. However, the current challenge is to stabilize the light-induced halide separation, which undermines the device’s performance. Herein we track down the phase separation dynamics of CsPbBr1.2I1.8 MHP single cubic nanocrystals (NCs) and clusters as a function of time by in situ fluorescence spectromicroscopy. The particles were sorted into groups 1 and 2 using initial photoluminescence intensities. The phase separation followed by recovery kinetics under dark and photo blinking analysis suggests that group 1 behaved more like single NCs and group 2 behaved like clusters. Under the 0.64 W/cm2 laser illumination, the phase shifts for single NCs are 3.4 ± 1.9 nm. The phase shifts are linearly correlated with the initial photoluminescence intensities of clusters, suggesting possible interparticle halide transportation

Effect of Temperature and Gold Nanoparticle Interaction on the Lifetime and Luminescence of NaYF₄:Yb³⁺:Er³⁺ Upconverting Nanoparticles

In this paper, we measured the temperature dependence in the temporal response of the green emission for both the H band (²H_11/2 → ⁴I_15/2 transition) and the S band (⁴S_3/2 → ⁴I_15/2 transition) for β-NaYF₄ nanocrystals and β-NaYF₄ nanocrystals decorated with 10 nm gold nanoparticles and found that the emission is quenched with temperature. We measured the time-resolved green emission intensity for decorated upconverting nanoparticles (UCNPs) and observed a biexponential decay that has a dominant decay time of ∼30 μs and a longer decay time of ∼300 μs that is similar to the single-exponential decay observed for the undecorated UCNPs. The temperature dependence in the green emission for β-NaYF₄ nanocrystals has a nonradiative quenching rate modeled with activation energy of 700 cm^–1 assigned to multiphonon relaxation to Er³⁺ lower energy levels. We measured the steady-state emission from the H and S bands for temperatures between 300 and 450 K and obtained a linear relationship between calculated and measured temperatures