Advanced Materials Research Vols. 415-417

Abstract: Theoretical calculation indicates that the large exponential-doping GaAs photocathodes have a much narrower electron energy distribution than traditional GaAs NEA cathodes, and the excellent performance attributes to the special structure characters of the band-bending region and lower negative electron affinity of the new-type GaAs photocathodes. The effects of surface doping concentration and work function on the energy distribution are discussed in details, and the FWHM of the energy distribution is less than 100meV. The simulation results indicate that the large exponential-doping mode further improves the features of the electron energy spreads for GaAs photocathodes, which may meet the further demand of next generation of electron guns.

Abstract: The model of thermal effect for liquid crystal director was built. The temperature field of liquid crystal was numerically studied. The effects of laser irradiation time and the crystal size on the thermal effect were analyzed and compared. With the increase of laser irradiation time, the temperature field became stable.

Abstract: A new type of amino resin nanocomposite(THPS-OMMT-MDFP) was synthesized from amino resin(MDFP), Tetra-hydroxymethyl phosphonium sulfate(THPS) and Organ-montmorillonite (OMMT)by intercalation compounding method. It was characterized by FT-IR，XRD and TG/DTG and applied to the preparation of flam-retardant leather. The flame retardant performance was characterized by Oxygen index (OI) test. The results showed that the nanocomposite was obtained as expected and had effective flame retardant performance.

Abstract: The low temperature magnetizations of TbGG have been systematically investigated from the average effect of the nonequivalent crystal sites. Our calculated results show that the different nonequivalent crystal sites have the different contributions to the magnetization. The step-like appearance of the low temperature magnetization curves in TbGG originates from the average effect of the magnetizations of six nonequivalent crystal sites, not from the near-crossing of the lowest energy levels of Tb³⁺ ions.

Abstract: The pH-dependent properties of carbon dots (CDs), decorated with surface carboxylic acid functional groups, are described. Absorption, fluorescence emission measurements were used to study the reversible pH-dependent spectral response. The pH-dependent emissions of CDs demonstrate a strong dependence on the excitation wavelengths and make the as-prepared CDs a good ratiometric pH-sensor candidate. This green material CDs-based probe shows promising potential for probing pH in real sample and in vivo intracellular imaging.

Abstract: In order to investigate the performance of silicon single crystal depended on the annealing temperature, the minority carrier lifetime, the resistivity and oxygen concentration after different temperature annealing in Ar ambient were examined. And the effect of oxygen and related defects formed during annealed on the minority carrier lifetime were analyzed by microwave photoconductivity method, Fourier transform infrared spectrometer and four-probe measurement. The results indicate that after 450°C annealing for 30h, the resistivity and minority carrier lifetime of silicon increase significantly, while the concentration of interstitial oxygen decreases. After the annealing at 650°C, oxygen donor can be removed and the resistivity and the minority carrier lifetime decrease. During the high-temperature (above 650°C) annealing, the oxygen precipitation can decrease the minority carrier lifetime silicon.

Abstract: Al_0.22Ga_0.78As/In_0.18Ga_0.82As/Al_0.22Ga_0.78As double heterojunction high electron mobility transistors (DH-HEMTs) with gate structures of traditional planar gate (PG), one-stage gamma-gate (1SΓG) and two-stage gamma-gate (2SΓG) formed by using the Al_0.22Ga_0.78As/In_0.49Ga_0.51P etch-stop layers (ESL) are simulated and presented in this work. Based on this proposed ESL structure design, the fabrication and implementation of studied DH-HEMT device with 1SΓG and 2SΓG could be expected. Both ΓG-structure devices show the better electric field property compared to PG-device. Simulated results reveal that there are no significant differences in common-source voltage-current characteristics among all studied devices. The obtained drain current density and transconductance of all studied devices are about 220 mAmm^-1 and 265 mSmm^-1. However, the current stability of ΓG-devices with larger bias operation would be improved due to its edge-effect of ΓG extended-region. In addition, the electric field intensity under the gate-footprint is effectively reduced by both studied ΓG structures. The electric field peak value of PG-device is 498 kV cm^-1, and it would be reduced down to about 210 kVcm^-1 and 178 kVcm^-1 for 1SΓG- and 2SΓG-device, respectively. On the other hand, some frequency property dropping is observed from studied device with 1SΓG or 2SΓG due to the side-edge extension of ΓG-device would create the additional parasitic capacitance. The obtained cut-off frequencies are 15 GHz, 10.5 GHz and 10 GHz for PG-, 1SΓG- and 2SΓG-device (at V_GS=+5 V and V_GS=-0.75 V), respectively.

Abstract: The Y₄MgSi₃O₁₃:Tb³⁺,Ce³⁺green phosphors are synthesized by sol-gel method, the preparation temperature, reduction atmosphere and luminescence characteristics of Y₄MgSi₃O₁₃ doped with single Ce³⁺ ions and Ce³⁺,Tb³⁺ ions have been studied. The excitation and emission spectra of phosphors is determined by fluorescence spectrophotometer. The results show that: luminous intensity of Y₄MgSi₃O₁₃:Tb³⁺phosphors increased after doped with Ce³⁺ ions and the optimal doping concentration of Ce³⁺ is 0.04. Y^3.94MgSi³O¹³: 0.02Tb³⁺,0.04Ce³⁺ green phosphor has the best luminescence characteristics under reduction atmosphere(H₂:N₂=1:3) at 1000°C, the phosphor gives intense green emission at 550nm originating from the ⁵D₄→⁷F₅ transition of Tb³⁺ ions.

Abstract: Since a two-level resonant atomic system can be simulated by a simple circuit, three- and four-level electromagnetically induced transparency (EIT) that occur due to light-atom interaction can find its classical counterpart in circuit analog. As the optical response of an EIT atomic medium (including atomic vapors and semiconductor-quantum-dot dielectrics) can be controlled via tunable quantum interference induced by applied external control fields, in the scheme of circuit analog, such a controllable manipulation is achieved via capacitor coupling, where two loops are coupled by a capacitor that can represent the applied control fields in atomic EIT. Both numerical simulation and experimental demonstration of three- and four-level EIT were performed based on such a scenario of circuit analog. The classical “coherence” relevant to quantum interference among transitions pathways driven by both probe and control fields in EIT atomic systems has been manifested in the present circuit analog of EIT.

Abstract: Absorption coefficient is an important parameter of the absorption function of the absorption material. Traditional measurement methods of absorption coefficient are standing wave tube and reverberation which have some shortcomings. In this paper, phase of the sound pressure measured by two equal distance microphones placed in the front of the absorption material is delayed in order to attain the absorption coefficient. At the last, an experiment for one absorption material is carried out, the experiment results compare with the results of the other methods above mentioned that denotes that the theory is correct and practicable.