Piezo-spectroscopic determination of the ratio of electron—To phonon to hole—To phonon interaction in silicon

An investigation of the stress-dependence of the normalized wavelength-modulated absorption spectra of the TO-phonon assisted indirect transition in silicon at 77 K has yielded a value of 1.4 for the ratio of the electron-phonon to hole-phonon scattering matrix elements for the TO-phonon.     

Lattice and electronic properties and g-value of Pb1−xSnxTe

The lattice dielectric property and the band edge structure in Pb_1-xSn_xTe are investigated by magnetoplasma reflection using a strip-line technique with several submillimeter laser lines, which are in the Reststrahlen region in the vicinity of the TO-phonon energy. The TO-phonon frequency, the dielectric constant and the effective mass in PbTe and Pb_0.7Sn_0.3Te at 4.2K are obtained. The additional new fine structure in PbTe is identified as a spin flip combined resonance from which we determine the effective g-value and its angular dependence.     

Narrow luminescence linewidth of a silicon quantum dot

Single-dot luminescence spectroscopy was used to study the emission linewidth of individual silicon nanocrystals from low temperatures up to room temperature. The results show a continuous line narrowing towards lower temperatures with a linewidth as sharp as 2 meV at 35 K. This value, clearly below the thermal broadening at this temperature, proves the atomiclike emission from silicon quantum dots subject to quantum confinement. The low temperature measurements further reveal a approximately 6 meV replica, whose origin is discussed. In addition, an approximately 60 meV TO-phonon replica was detected, which is only present in a fraction of the dots.     

Soliton modulation-widths for Pb1−xSnxTe TO-ponons

Some new TO-phonon width data for Pb_1?xSn_xTe with strong temperature-dependence are explained in terms of a “modulation-effect” due to non-linear lattice modes. Reasonable values of the parameters provide very good agreement with the experimental widths.     

Dielectric constant and soft mode of Pb1−xSnxTe

We try to explain the large dielectric constant of Pb_1-xSn_xTe pseudobinary alloy system in terms of the softening of TO-phonon mode due to electron—phonon coupling. The order of magnitude estimation shows that the interband optical deformation potential of several electron volts is sufficient to explain the softening of phonon.     

Resistance anomaly due to displacive phase transition in SnTe

The effect of displacive phase transition on electrical transport properties is investigated in a p-type single crystal of SnTe with carrier concentration of 1.2 × 10²⁰/cm³ at 77 K. The resistivity vs temperature curve shows an anomalous increase in the vicinity of the transition temperature. An attempt is made to interpret the temperature dependence of the resistivity increment on the basis of the carrier-soft TO-phonon interaction.     

Raman scattering in LiB3O5 single crystals at 300 and 20 K

The Raman-scattering spectra of LiB₃O₅ single crystals at 300 and 20 K have been investigated in detail. The LO- and TO-phonon lines of different symmetries are separated and identified. The reasons for the change in the Raman spectra of LiB₃O₅ upon cooling to 20 K are studied. The intensity ratios for scattering with participation of LO and TO modes of the A ₁ symmetry are found in dependence on the observation geometry.     

Low-temperature photoluminescence in SiGe single quantum wells

1-x Ge_x single quantum wells (x=0.19) grown by rapid thermal chemical vapor deposition at 625 °C. A well-resolved strong excitonic luminescence with TO-phonon and no-phonon transitions with a full width at half-maximum as low as 6 meV is observed for a quantum well of 98 Å. The photoluminescence emission shows a significant blue shift and a broadening with excitation intensity. The results are analysed in terms of localization of photoinduced charge carriers at the heterointerfaces. Received: 11 September 1996/Accepted: 15 August 1997     

Raman scattering from soft to-phonon in IV–VI compound semiconductors

The soft TO-phonon modes were investigated below the cubic-rhombohedral transition temperature in Pb_1?xGe_xTe (x=0.05) and SnTe. We observed resolved Raman spectra from ordinary and extraordinary modes. The temperature dependence of the spectra was analyzed in terms of phonon-phonon interactions. We also discussed origins of extra Raman spectra which appear even in the high temperature phase. The energy gain of valence bonding electrons due to lattice distortions was estimated to be ≈10⁹erg/cm³ by analyzing anomalous temperature behavior of the optical dielectric constant. This is about two order of magnitude larger than the depth of the well of free energy.     

Order parameters in a-Si systems

We have used Raman scattering to characterize the change in structural order for three types of a-Si materials: fluorinated, a-Si:F:H; hydrogenated, a-Si:H; and sputtered, a-Si (sput) under heat-treatment. The narrower TO linewidth, the higher TO-phonon frequency, the lower TA-phonon frequency, and the lower “crystallization temperature”, all indicate an increase in the local order in the amorphous phase for a-SiH, and particularly for a-Si:F:H. This improved structural order is consistent with the reduction of electronic gap-states.     

Determination of field profiles in semiconductors by electroabsorption

The experimental demonstration of the possibility of applying modulation spectroscopy techniques to the microscopic probing of nonuniform electric fields in semiconductors is given. A silicon bar is scanned by a highly focused monochromatic light beam. The sample is sandwiched between two gold electrodes that allow application of an ac field and formation of depletion layers extending over distances of the order of 1 mm. The field intensity is probed by measuring the transverse electroabsorption at a photon energy that is conveniently chosen to produce TO-phonon assisted transitions from the valence band to the n = 1 level of the exciton. At this energy, the modulated signal is proportional to the square of the field because the experiment is done in the limit of Stark perturbation. Mapping of the field is achieved over the whole length of the bar and the expansion of the depletion layer region is followed up to a punch-through condition.     

Far infrared reflection spectra due to lattice and free carrier in ZnxHg1−xSe

Far infrared reflection spectra of Zn_xHg_1−xSe with x = 0 to 0.4 showed characteristic of two TO-phonon modes behavior and the plasmon-LO phonon coupling in the region from 20 to 500 cm⁻¹ at 5 and 300 K. The composition dependence of TO modes on the frequency is linear for the HgSe-like mode TO₁ and constant for the ZnSe-like mode TO₂. The additional TO mode due to clustering effect is observed at 113 cm⁻¹. The plasmon-LO phonon coupled modes are explained well by our model taken into account the two-mode behavior and the contribution of interband transitions in dynamic dielectric function.     

Optical phonon damping in the ultrathin-layer GaAs/AlAs superlattices

We performed the precision measurements of the near-normal far-infrared reflection and transmission spectra of the MBE-grown (GaAs)_n/(AlAs)_n (n =  1, 2, 4) superlattices. The results obtained show a noticeable (almost twofold) increase in the AlAs-phonon damping when n is decreased from 4 to 1. We consider possible physical mechanisms of this increase and compare our results with those obtained by other authors. The main implication of the work is that the increase in the TO-phonon damping may be related to interface broadening whose role becomes more important when the superlattice period decreases.     

Interference effects in the electrical conductivity tensors of doped polar semiconductors

In this paper, we develop a general procedure, based on the Kubo formula, for finding the frequency- and wavevector-dependent electrical conductivity tensor for arbitrary polarizations of the applied electric field. This procedure gives careful consideration to both the electron and the ion contributions to the current density. We find that, in addition to the standard electron and ion contributions to the conductivity tensor, there are contributions arising from the quantum interference between the electrons and the ions. These interference effects, which will affect the infrared absorption of a material, are similar to the interference effects observed by Cerdeira, Fjeldly, and Cardona (Solid State Commun.13 (1973), 325–328; Phys. Rev. B8 (1973), 4734–4745; 9 (1974), 4344–4350) in Raman scattering from p-type Si. We then evaluate these cross terms for simple models of a variety of semiconductors. We find that these interference effects are finite-q effects, with the actual dependence of the cross terms on the wavevector q being sensitive to the symmetry of the crystal. We also find that, in principle, these cross terms may be quite large near the TO-phonon frequency ω_TO. The cross terms are evaluated for both n-type and p-type semiconductors, and it is suggested that they are probably most important for p-type materials. However, we also find that the basic structure of these terms is very similar in the two cases.     

Commissioning of electron cooling in CSRe

The 400 MeV/u 12C6+ion beam was successfully cooled by the intensive electron beam near 1 A in CSRe.The momentum cooling time was estimated near 15 s.The cooling force was measured in the cases of different electron beam profiles,and the different angles between the ion beam and electron beam.The lifetime of the ion beam in CSRe was over 80 h.The dispersion in the cooling section was confirmed as positive close to zero.The beam sizes before cooling and after cooling were measured by the moving screen.The beam diameter after cooling was about 1 mm.The bunch length was measured with the help of the signals from the beam position monitor.The diffusion was studied in the absence of the electron beam.     

Study of molecular mobility of fluid in zeolite NaX.

The self-diffusion of n-decane in zeolite NaX was studied by NMR PFG method. The situation when the liquid was only in the crystalline channels was studied in details. The restricted molecular motion of liquid in the crystalline channels was observed. The reasons of the anomalous self-diffusion of n-decane in zeolite bed were stated. The technique of the determination of the genuine self-diffusion coefficient in such porous systems was proposed. The genuine self-diffusion coefficients for system NaX/n-decane were obtained.     

微波消解-氢化物发生-原子荧光光谱法测定大米中痕量汞

采用微波消解 氢化物发生 原子荧光光谱法对大米中痕量汞进行了消解、测定。以微波消解为样品前处理方法 ,建立了大米微波消解的最佳分析条件。确定了原子荧光光谱仪的参数设置 ,最佳氢化反应条件以及影响汞测定的相关环境参数。检测限 0 0 0 5ng·mL-1 ,测定大米中汞成分分析标准物质 (GBW 0 85 0 8)中汞的含量 ,其结果与证书值相吻合 ,精密度 2 1 % ,回收率 95 2 %～ 1 0 6 4 %。     

铜(Ⅱ)-新铜试剂-谷胱甘肽-乙醇体系显色反应研究

本文研究铜（Ⅱ）－新铜试剂－谷胱甘肽－乙醇体系的显色反应,探讨了反应条件。试验中发现乙醇可以使吸光度增加１３．８％,提高提高了显色反应的灵敏度。该方法用于测定大豆提取液中谷胱甘肽的含量,取得了满意结果。     

河鳗中恶喹酸残留量测定方法的改进

样品用二氯甲烷提取,除去溶剂后,残渣用稀盐酸溶液和正己烷处理以除去脂肪,然后用二氯甲烷萃取,挥干,残留物溶于甲醇水溶液中,用高效液相色谱荧光检测器测定.该方法的测定低限为0.005mg/kg,方法的回收率范围为82.7%-89.4%.     

SrS∶Eu,Sm光存储机理的研究

采用高温固相反应法在还原气氛下制备了SrS:Eu,Sm样品,利用荧光光谱仪测量了这种光存储材料的激发光谱和发射光谱.将样品用紫外灯(265 nm)照射激发饱和后,再用980 nm的红外激光器激励,利用荧光光谱仪测试得到了峰值位于599 nm的光激励发光光谱.此外还利用热释光谱仪测试了样品的热释光谱.探讨了SrS:Eu,Sm的光存储机理,认为引入的稀土离子在SrS的带隙中形成分裂能级.当用紫外光照射材料时,Eu的电子从基态被激发到激发态或基质材料的导带,其中一部分电子被辅助激活剂Sm的陷阱俘获,实现信息写入.当材料被与陷阱深度相当的红外光激励时,电子陷阱Sm2 俘获的电子才可能跃出俘获能级,与空穴在Eu的激发态和基态能级上复合,多余的能量以可见光的形式释放出来,实现信息读出.