Thermodynamic behaviour of Rashba quantum dot in the presence of magnetic field

The thermodynamic properties of an In Sb quantum dot have been investigated in the presence of Rashba spin–orbit interaction and a static magnetic field. The energy spectrum and wave-functions for the system are obtained by solving the Schrodinger wave-equation analytically. These energy levels are employed to calculate the specific heat, entropy,magnetization and susceptibility of the quantum dot system using canonical formalism. It is observed that the system is susceptible to maximum heat absorption at a particular value of magnetic field which depends on the Rashba coupling parameter as well as the temperature. The variation of specific heat shows a Schottky-like anomaly in the low temperature limit and rapidly converges to the value of 2kB with the further increase in temperature. The entropy of the quantum dot is found to be inversely proportional to the magnetic field but has a direct variation with temperature. The substantial effect of Rashba spin–orbit interaction on the magnetic properties of quantum dot is observed at low values of magnetic field and temperature.     

PHOTOLUMINESCENCE STUDY OF InAs/GaAs SELF-ORGANIZED QUANTUM DOTS WITH BIMODAL SIZE DISTRIBUTION

We have investigated the temperature dependence of the photoluminescence (PL) spectrum of self-organized InAs/GaAs quantum dots. A distinctive double-peak feature of the PL spectra from quantum dots has been observed, and a bimodal distribution of dot sizes has also been confirmed by scanning tunneling microscopy image for uncapped sample. The power-dependent PL study demonstrates that the distinctive PL emission peaks are associated with the ground-state emission of islands in different size branches. The temperature-dependent PL study shows that the PL quenching temperature for different dot families is different. Due to lacking of the couple between quantum dots, an unusual temperature dependence of the linewidth and peak energy of the dot ensemble photoluminescence has not been observed. In addition, we have tuned the emission wavelength of InAs QDs to 1.3 μm at room temperature.     

Internal quantum efficiency drop induced by the heat generation inside of light emitting diodes （LEDs）

The reasons for low output power of AlGaInP Light Emitting Diodes (LEDs) have been analysed. LEDs with AlGaInP material have high internal but low external quantum efficiency and much heat generated inside especially at a large injected current which would reduce both the internal and external quantum efficiencies. Two kinds of LEDs with the same active region but different window layers have been fabricated. The new window layer composed of textured 0.5 μm GaP and thin Indium-Tin-Oxide film has shown that low external quantum efficiency (EQE) has serious impaction on the internal quantum efficiency (IQE), because the carrier distribution will change with the body temperature increasing due to the heat inside, and the test results have shown the evidence of LEDs with lower output power and bigger wavelength red shift.     

Abnormal Energy Dependence of Photoluminescence Decay Time in InGaN Epilayer

We employ photoluminescence (PL) and time-resolved PL to study exciton localization effect in InGaN epilayers.By measuring the exciton decay time as a function of the monitored emission energy at different temperatures,we have found unusual behaviour of the energy dependence in the PL decay process. At low temperature, the measured PL decay time increases with the emission energy. It decreases with the emission energy at 200K, and remains nearly constant at the intermediate temperature of 12OK. We have studied the dot size effect on the radiative recombination time by calculating the temperature dependence of the exciton recombination lifetime in quantum dots, and have found that the observed behaviour can be well correlated to the exciton localization in quantum dots. This suggestion is further supported by steady state PL results.     

Hexapole State-Selection and Beam Focus of Linear Triatomic Molecules

The state selection and beam focus of linear triatomic molecules （OCS, HCN, ClCN, BrCN and ICN） with doubling states in a hexapole electric field have been numerically realized. The method is based on a quantum mechanical treatment of the molecular Stark energy and a classical mechanical treatment for the molecular trajectory in the field. In linear molecules with doubling states, the second-order Stark effect can be neglected and the doubling states have the same value of J and M. The influences of the molecular properties, state energies, and the apparatus parameters such as molecular beam temperature and length of the hexapole, on the role of state selection and focus have been discussed. The method established here can be taken as a guide for hexapole experiment of orientation of polar molecules.     

Effect of dichroic azo-dye doped on ferroelectric liquid crystals

In order to study the effect of mixing dye in ferroelectric liquid crystal （FLC） materials, the phase transition temperature and electro-optical properties of azo dye doped FLC samples have been investigated. All the properties have been found to be changed drastically. The results have revealed that not only the SmC^＊- SmA^＊ transition temperature decreased markedly by the addition of azo-dye, but also dye-doped FLC had lower threshold voltage and saturation voltage than the pure FLC.     

Detailed study of NBTI characterization in 40-nm CMOS process using comprehensive models

The impact of negative bias temperature instability(NBTI) can be ascribed to three mutually uncorrelated factors, including hole trapping by pre-existing traps(?V_(HT)) in gate insulator, generated traps(?V_(OT)) in bulk insulator, and interface trap generation(?V_(IT)). In this paper, we have experimentally investigated the NBTI characteristic for a 40-nm complementary metal–oxide semiconductor(CMOS) process. The power-law time dependence, temperature activation, and field acceleration have also been explored based on the physical reaction–diffusion model. Moreover, the end-of-life of stressed device dependent on the variation of stress field and temperature have been evaluated. With the consideration of locking effect, the recovery characteristics have been modelled and discussed.     

Origin of Electron and Hole Charging Current Peaks in Nanocrystal-Si Quantum Dot Floating Gate MOS Structure

The nanocrystal-Si quantum dot （nc-Si QD） floating gate MOS structure is fabricated by using plasma-enhanced chemical vapour deposition （PECVD） and furnace oxidation technology. The capacitance hysteresis in capacitancevoltage （C - V） measurements confirm the charging effect of nc-Si QDs. Asymmetric charging current peaks both for electrons and holes have been observed in current-voltage （I - V） measurements at room temperature for the first time. The characteristic and the origin of these current peaks in this nc-Si QD MOS structure is in- vestigated systematically. Moreover, the charge density （10^-7 C/cm^2） calculated from the charging current peaks in the I - V measurements at different sweep rates shows that each quantum dot is charged by one carrier. The difference of charging threshold voltages between the electrons and holes charging peaks, △VG, can be explained by the quantum confinement effect of the nc-Si dots in size of about 3.5 nm.     

Study on the nitridation of β-Ga_2O_3 films

Single-crystal GaN layers have been obtained by nitriding β-Ga_2O_3 films in NH_3 atmosphere. The effect of the temperature and time on the nitridation and conversion of Ga_2O_3 films have been investigated. The nitridation process results in lots of holes in the surface of films. The higher nitridation temperature and longer time can promote the nitridation and improve the crystal quality of GaN films. The converted Ga N porous films show the single-crystal structures and lowstress, which can be used as templates for the epitaxial growth of high-quality GaN.     

Room—Temperature Dual Excitonic Emission from Amorphous ZnO

Optical properties of amorphous ZnO have been investigated at room temperature.It is demonstrated that the ultraviolet emission components due to the recombination of two different excitons were verifield by examining their relative energy positions and ultraviolet integrated photoluminescence intensity dependece on reaction time.The dual excitonic emissions are derived from amorphous ZnO and crystallized ZnO nanocrystallite,respectively.On the optimized condition,the photoluminescence spectrum of amorphous ZnO shows a strong ultraviolet emission while the visible emission is almost fully quenched.The enhanced ultraviolet emission is attributed to quantum confinement effect.     

Out-of-time-ordered correlation in the anisotropic Dicke model

Out-of-time-ordered correlation (OTOC) functions have been used as an indicator of quantum chaos in a lot of physical systems. In this work, we numerically demonstrate that zero temperature OTOC can detect quantum phase transition in the anisotropic Dicke model. The phase diagram is given with OTOC. The finite-size effect is studied. Finally, the temperature effect is discussed.     

Experimental simulation of the Unruh effect on an NMR quantum simulator

The Unruh effect is one of the most fundamental manifestations of the fact that the particle content of a field theory is observer dependent. However, there has been so far no experimental verification of this effect, as the associated temperatures lie far below any observable threshold. Recently, physical phenomena, which are of great experimental challenge, have been investigated by quantum simulations in various fields. Here we perform a proof-of-principle simulation of the evolution of fermionic modes under the Unruh effect with a nuclear magnetic resonance(NMR) quantum simulator. By the quantum simulator, we experimentally demonstrate the behavior of Unruh temperature with acceleration, and we further investigate the quantum correlations quantified by quantum discord between two fermionic modes as seen by two relatively accelerated observers. It is shown that the quantum correlations can be created by the Unruh effect from the classically correlated states. Our work may provide a promising way to explore the quantum physics of accelerated systems.     

Temperature dependence of static and dynamic properties of an anisotropic ferrimagnet

The temperature dependences of the magnetizations of sublattices and the spectra of elementary excitations of an anisotropic ferrimagnet have been investigated. It has been shown that, in the anisotropic ferrimagnet, even a weak single-ion anisotropy induces the quantum spin reduction effect and, as a consequence, changes the behavior of the magnetizations of the sublattices. This gives rise to a new branch of magnetic excitations with the purely longitudinal dynamics of the average value of the spin due to the quantum spin reduction effect.     

Oscillations of the superconducting transition temperature in aluminum films

Oscillations of the superconducting transition temperature of thin Al-films have been observed during deposition of siliconmonoxide SiO. Friedel oscillations as well as the quantum size effect may account for the observations.     

Fano effect and Andreev bound states in T-shape double quantum dots

In this Letter, we investigate the transport through a T-shaped double quantum dot coupled to two normal metal leads left and right and a superconducting lead. Analytical expressions of Andreev transmission and local density of states of the system at zero temperature have been obtained. We study the role of the superconducting lead in the quantum interferometric features of the double quantum dot. We report for first time the Fano effect produced by Andreev bound states in a side quantum dot. Our results show that as a consequence of quantum interference and proximity effect, the transmission from normal to normal lead exhibits Fano resonances due to Andreev bound states. We find that this interference effect allows us to study the Andreev bound states in the changes in the conductance between two normal leads.     

Quantum interference effect in few-layered transition metal dichalcogenide

Van der Waals layered transition metal dichalcogenides (TMDCs), as atomically flat two-dimensional materials, have been studied extensively in both fundamental science and application fields in recent years. The reduced-dimensional properties of TMDCs not only provide a route for the fabricating of efficient field effect transistors and optoelectronic devices but also suggest the possibility of the devices that utilize quantum coherency. In this work, we characterize the electron transport properties of ReS₂, one of the TMDCs, at both room temperature and low temperature. Of particular note, we measured strong quantum conductance oscillations as a function of the gate voltages and source-drain voltages at reduced temperature, which is evidence of quantum coherent transport. This work unambiguously establishes ReS₂ as a promising candidate for future quantum materials.     

Thermal modulation in Zeno and anti-Zeno effects on quantum measurement

We have proposed the mathematical formulations of quantum Zeno and anti-Zeno effects at non-zero temperature on vibrational population transfer and dissociation of a diatomic system. The proposed formulation has been tested for diatomic systems HBr⁺ and HI using time-dependent Fourier grid Hamiltonian method. The effect of temperature on the dynamics is incorporated through the population distribution at different vibrational states following Boltzmann distribution formula. It has been found that with increase in temperature Zeno effect increases and anti-Zeno effect decreases in case of survival probability on ground vibrational state. In case of dissociation, with increase in temperature Zeno effect increases while anti-Zeno effect remains almost same.     

Preparation of Group IIB Selenide Nanoparticles Using Soft-Hard Dual Template Method

Using a celloidin membrane as template, the uniform Group IIB selenide nanoparticles were inductively synthesized at room temperature and ambient pressure. The nanoparticles are cubic ZnSe quantum dots, hexagonal CdSe quantum dots and cubic HgSe nanoparticles with average diameters of 3.1, 2.0 and 44nm, respectively. In the ultraviolet-visible spectra, their absorption peaks are at about 360, 480 and 440nm individually, and have large blue shifts due to quantum size effect. The corresponding photoluminescence peaks individually showed at 367, 438 and 440nm. In addition, the preparation conditions and formation mechanism have been explored.     

Electron capture and intra-band relaxation by means of Auger processes in colloidal semiconductor nanocrystals

The electron relaxation dynamics in combination with LO phonon-assisted electron capture and intra-dot Auger scattering processes in a spherical quantum dot embedded in non-polar matrix is presented theoretically. The electron capture efficiency is investigated as a function of the lattice temperature and quantum dot radius for a deferent injected electron concentration, taking into account the confinement effect of the polar optical phonons in spherical quantum dots. Exact numerical calculations for the phonon-assisted electron capture rate as well as for the Auger scattering rate in colloidal CdSe quantum dot have been carried out. These calculations are consistent with experiment.     

Effect of finite energy of intravalley acoustic phonons on the temperature of non-equilibrium electrons in a quantum surface

The effect of finite energy of intravalley acoustic phonons on the electric field dependence of the temperature of the non-equilibrium carriers in a quantum surface has been studied here. The calculations have been made, for a rather pure material, at low lattice temperature. Numerical results are obtained for GaAs and Si. The results are interesting being significantly different from what one obtains by neglecting the phonon energy.