Zengming Zhang

Thickness Dispersion of Surface Plasmon of Ag Nano-thin Films: Determination by Ellipsometry Iterated with Transmittance Method

Effective optical constants of Ag thin films are precisely determined with effective thickness simultaneously by using an ellipsometry iterated with transmittance method. Unlike the bulk optical constants in Paliks database the effective optical constants of ultrathin Ag films are found to strongly depend on the thickness. According to the optical data two branches of thickness dispersion of surface plasmon energy are derived and agreed with theoretical predication. The thickness dispersion of bulk plasmon is also observed. The influence of substrate on surface plasmon is verified for the first time by using ellipsometry. The thickness dependent effective energy loss function is thus obtained based on this optical method for Ag ultrathin films. This method is also applicable to other ultrathin films and can be used to establish an effective optical database for ultrathin films.

High pressure photoluminescence of CdZnSe quantum dots : Alloying effect

The pressure dependence of photoluminescence of wurtzite 5.5nm CdZnSe alloy quantum dots (QDs) was studied and compared with that of the wurtzite 3.5nm CdSe QDs. The direct Γ energy gaps of wurtzite QDs were found to increase with the pressure, and the pressure coefficients were gained as 35.4meV∕GPa for CdZnSe and 28.4meV∕GPa for CdSe QDs. The authors attributed the high value of pressure coefficient for CdZnSe alloy QDs to the alloying effect with strengthening the anion-cation s‐s orbital coupling and weakening p‐d orbital coupling in the alloy. The result demonstrates that the alloying process has a dominant role in the electronic state and structure transition under high pressure.

Laser effects on phase transition for cubic Sb2O3 microcrystals under high pressure

The effects of laser irradiation and high pressure on the phase transition of cubic phase antimony trioxide microcrystals have been investigated. In situ Raman spectroscopy was performed at high pressure up to 45 GPa in a diamond anvil cell. The results indicated that two pressure-induced isostructural phase transitions occurred at 4.5 GPa and 11.3 GPa and were independent of laser irradiation. The Sb2O3 sample started transforming into a high density amorphous phase at 25 GPa and completed at more than 35 GPa. After irradiation for 7 minutes by 514.5 nm laser with 8 mW, the required pressure of the complete phase transition reduced to 27 GPa. On releasing pressure to ambient pressure, the samples reverse partly to the cubic phase, which takes days for the complete transition. This transition duration was reduced to seconds after irradiation by laser. It was also found that the residual amorphous phase at ambient pressure was of low density and medium-range order, which was not similar to the one that was observed at more than 25 GPa. The mechanism of laser irradiation boosting up the process of phase transitions was studied. Combining the cut-off wavelength of laser irradiation and absorption spectra, the photothermal effect induced via laser irradiation was found to dominate phase transition.

Structure transformation and remarkable site-distribution modulation of Eu3+ ions in CaMoO4 : Eu3+ nanocrystals under high pressure

High-pressure behaviors of scheelite-type CaMoO4 : Eu3+ nanocrystals with an average size of 30 nm have been investigated by using Raman and luminescence spectroscopy at pressures of up to 21 GPa in a diamond anvil cell (DAC). Under the loading of pressure, the softening of the external T(Bg) mode before 10.8 GPa and the appearance of new Raman peaks suggest a phase transformation around this pressure from scheelite to fergusonite structure. When the pressure is released, the scheelite phase recovers due to the small difference in bond strength between scheelite and fergusonite structures. The transformation pressure is slightly enhanced in nanosized CaMoO4 : Eu3+ as compared to the bulk due to the difference in surface energy between the two samples of different sizes. Moreover, it is identified that the Eu3+ ions occupy both the bulk and the surface sites in CaMoO4 : Eu3+ nanocrystals at ambient pressure by the site-selective excitation, emission and lifetime spectra. As an effective site probe, the red-to-orange luminescence intensity ratio of Eu3+ ions, I(5D0 → 7F2)/I(5D0 → 7F1), is found to exhibit remarkable changes with pressure, which indicates a large variation of the distribution and the local symmetry of Eu3+ ions.

Facile fabrication of infrared photodetector using metastable vanadium dioxide VO2 (B) nanorod networks

Photodetectors find important military and civilian applications, commonly requiring expensive components and exhibiting complex designs. Herein, we report a simple and cost-effective infrared photodetector fabricated using metastable vanadium dioxide VO2 (B) nanorod (NR) networks and exhibiting high photosensitivity, stability, and reproducibility under ambient conditions. We discuss electron transfer processes in NR networks and elucidate the mechanisms of photocurrent generation as well as performance-affecting factors, revealing that the fabricated device can be used as a high-performance infrared light photodetector.Photodetectors find important military and civilian applications, commonly requiring expensive components and exhibiting complex designs. Herein, we report a simple and cost-effective infrared photodetector fabricated using metastable vanadium dioxide VO2 (B) nanorod (NR) networks and exhibiting high photosensitivity, stability, and reproducibility under ambient conditions. We discuss electron transfer processes in NR networks and elucidate the mechanisms of photocurrent generation as well as performance-affecting factors, revealing that the fabricated device can be used as a high-performance infrared light photodetector.

Pressure-induced topological phase transitions and structural transition in 1T-TiTe2 single crystal

High pressure in situ Raman scattering and electrical resistivity measurements were performed to investigate the phase transitions in a semimetal 1T-TiTe2 single crystal up to 17 GPa. Combining anomalous experimental results with the electronic band structures and Z2 topological invariants in calculations, two topological phase transitions and one structural phase transition were confirmed at 1.7 GPa, 3 GPa, and 8 GPa, respectively. These two topological transformations are due to the enhanced orbital hybridization followed by a few of band inversions near the Fermi level, and the further parity analysis manifested that the phases II and III correspond to a strong topological state and a weak topological state, respectively. The rich topology variation of 1T-TiTe2 under high pressure provides a potential candidate for understanding the relevant topology physics and probable applications. The current results also demonstrate that Raman spectroscopy and electrical transport measurements are efficient tools to detect the topological phase transition under high pressure.High pressure in situ Raman scattering and electrical resistivity measurements were performed to investigate the phase transitions in a semimetal 1T-TiTe2 single crystal up to 17 GPa. Combining anomalous experimental results with the electronic band structures and Z2 topological invariants in calculations, two topological phase transitions and one structural phase transition were confirmed at 1.7 GPa, 3 GPa, and 8 GPa, respectively. These two topological transformations are due to the enhanced orbital hybridization followed by a few of band inversions near the Fermi level, and the further parity analysis manifested that the phases II and III correspond to a strong topological state and a weak topological state, respectively. The rich topology variation of 1T-TiTe2 under high pressure provides a potential candidate for understanding the relevant topology physics and probable applications. The current results also demonstrate that Raman spectroscopy and electrical transport measurements are efficient tools ...