Confinement in self-assembled InAs/InP quantum wires studied by magneto-photoluminescence

We studied two InAs/InP quantum wire samples with different growth conditions. The photoluminescence of the first sample reveals up to six distinct peaks, while the second has only two pronounced photoluminescence peaks that are attributed to flat wires with heights that differ by exactly one monolayer. Despite the large band offsets in this system, the photoluminescence energy shift of these peaks with a magnetic field applied in the plane of the wires shows that the extent of the exciton wave function in the growth direction is much larger than the wire height, i.e. the wave function spills over into the InP. Moreover, the exciton wave function shrinks for increasing wire height. The wave function spill-over is qualitatively confirmed in the first quantum wire sample.     

Recent developments in the stereological analysis of particles

Recent developments in the stereological analysis of particles are reviewed. The trend has been towards methods which are applicable without specific assumptions about particle shape. Geometric samples of a local 3-d character are used. Stereological estimators of particle intensity, particle size distribution and particle interaction are presented and discussed.An earlier version of this article was presented at the Symposium on the Analysis of Statistical Information held in the Institute of Statistical Mathematics, Tokyo during December 5–8, 1989.     

Moving eccentric crack in a piezoelectric strip bonded to elastic materials

Summary  The steady-state of a propagation eccentric crack in a piezoelectric ceramic strip bonded between two elastic materials under combined anti-plane mechanical shear and in-plane electrical loadings is considered in this paper. The analysis based on the integral transform approach is conducted on the permeable crack condition. Field intensity factors and energy release rate are obtained in terms of a Fredholm integral equation of the second kind. It is shown for this geometry that the crack propagation speed has influence on the dynamic energy release rate. The initial crack branching angle for a PZT-5H piezoceramic structure is predicted by the maximum energy release rate criterion. Received 23 January 2001; accepted for publication 18 October 2001     

原子发射光谱内标法测量误差的研究

证明了原子发射光谱内标法的测量误差。当分析线和内标线的相对强度等于1时，测量误差最小。     

超快速COSY类2D NMR实验弛豫假峰的抑制

在脉冲梯度场基础上研究了进一步缩短COSY类2D NMR实验数据采集时间的新方法.利用主动屏蔽梯度场线圈的梯度场恢复时间仅为100μs数量级这一特点,提出一类基于脉冲梯度场消除弛豫假峰的脉冲序列.并以DQF-COSY脉冲序列为例加以验证.实验结果表明:采用文中的方法,取序列重复时间远小于T₁和T₂是切实可行的;梯度场技术能很好地抑制弛豫假蜂以达到2D NMK数据的快速采集.     

四端光纤补偿网络的理论分析

强度干扰是阻碍强度调制光纤传感器发展及应用的关键问题.研究表明,光纤网络补偿方法对抑制强度干扰是一种行之有效的方法.作者经过深入的研究,提出了一种先进的四端光纤补偿网络结构.本文对四端光纤补偿网络进行了全面、系统的分析,揭示了网络的特性.这对于强度调制光纤传感器的发展及应用具有重要的意义.同时,对于强度调制光学测量系统也具有一定的意义.     

Bending wave intensity in a thick beam

I.IntroductionMeasurementSofbendingwaveintensityinoneortwodimensi0na1structuresbecomequitepopularandgetavarietyofindustria1app1icati0ns.Theexistingintensitytheory['-']wasderivedbasedontheclassicaIBernou11i-Eu1ertheorywhichisanapproximatetheoryforana-lyzingstructuralvibration.Inthe1ow-frequencylimitwherebendingwavelengthsaremuchlongincomparisonwiththethicknessofthestructurealongwhichtheypr0pagate(i.e.,thinstructurcs),theuse0ftheclassica1theorywi1lresu1tinanegligiblyerro/`].Forshortwave-1ength…     

Sub-millimolar determination of formalin by pulsed amperometric detection

Formalin, formaldehyde in the presence of methanol, was determined by pulsed amperometric detection (PAD). A triple waveform using E_det=−0.3 V (t_det=30 ms), E_oxd=+0.8 V (t_oxd=200 ms), and E_red=−0.8 V (t_red=350 ms) versus Ag/AgCl was applied at a Au electrode for detection in a flow injection (FI) system. The approach was rapid and yielded a sub-millimolar detection limit (0.0129 mM) with a dynamic range up to 100 mM. A precision of 8.8% R.S.D. at 1.0 mM for two hundred repetitive injections by the FI-PAD was obtained, whereas holding at a constant potential (−0.3 V versus Ag/AgCl) for anodic oxidation of formaldehyde caused the response to decrease dramatically after a few measurements. The method developed was used to analyze the formalin contents of water from rinsed samples of vegetables and fruit and ice-melt from seafood, and the method showed good agreement with the liquid chromatography (LC) method.     

High resolution laser spectroscopy of the titanium monohalides, TiCl and TiBr

The electronic spectra of the titanium monohalides, TiCl and TiBr, have been investigated in the blue-violet region using a laser ablation molecular beam spectrometer. Five subbands assigned as ⁴Γ_5/2-X⁴Φ_3/2 (0, 0), ⁴Γ_5/2-X⁴Φ_3/2 (1, 1), ⁴Γ_5/2-X⁴Φ_5/2 (0, 0), ⁴Γ_7/2-X⁴Φ_5/2 (0, 0) and ⁴Γ_7/2-X⁴Φ_7/2 (0, 0) were observed and recorded at both low and high-resolution for titanium monochloride. A Hund’s case (a) rotational analysis has been carried out for the ⁴⁸Ti³⁷Cl and ⁴⁸Ti³⁵Cl isotopic species, and polynomial analyses for these, as well as the ⁴⁶Ti³⁵Cl, ⁴⁷Ti³⁵Cl, ⁴⁹Ti³⁵Cl, and ⁵⁰Ti³⁵Cl isotopologues have been completed. The same spectral region yielded several molecular transitions for titanium monobromide, 10 of which were recorded at high resolution. Six of these have been attributed to a ⁴Γ-X⁴Φ electronic transition at 23 484 cm⁻¹, while the remaining four have been assigned to a second ⁴Γ-X⁴Φ electronic transition at 23 613 cm⁻¹. A Hund’s case (a) global analysis has been carried out for the ⁴⁸Ti⁷⁹Br and ⁴⁸Ti⁸¹Br isotopologues.     

High-resolution transmission electron microscopy investigation of the nanostructure of undoped and Pt-doped nanocrystalline pulsed laser deposited SnO2 thin films

Pulsed laser deposition (PLD) was used to grow nanocrystalline SnO₂ thin films onto alumina substrates. The reactive PLD process was carried out at different substrate deposition temperatures (T_d) between 20 and 600 °C under an oxygen background pressure of 150 mtorr. The same PLD technique was used to produce SnO₂ films in situ-doped with Pt (at the level of ∼2 at. %) through the concomitant ablation of both SnO₂ target and Pt strips. Conventional and high-resolution transmission electron microscopy (HRTEM) observations have revealed that the microstructure of the PLD SnO₂ films is highly sensitive to their deposition temperature. Indeed, its changes from a porous granular structure with extremely fine equiaxed grains (∼4 nm diameter), at T_d=20 °C to a very compact and textured columnar structure characterized by SnO₂ columns (∼25 nm diameter) composed of grains of ∼12 nm of diameter, at T_d=600 °C. In addition, the PLD SnO₂ films were found to exhibit the highest nanoporosity at T_d=300 °C which also coincides with the granular-to-columnar microstructural transition. On the other hand, the microstructure of the Pt-doped SnO₂ films, deposited at 300 °C, was found to contain a high density of defects, such as twin boundaries and edge dislocations. By combining HRTEM and EDS microanalysis, we were able to show that the Pt-dopant self-organizes into spherical nanoparticles (1-2 nm diameter) randomly distributed at the SnO₂ grain boundaries. Finally, doping the films with such platinum nanoclusters is found to affect the SnO₂ nanostructure by particularly reducing the SnO₂ mean grain size (from ∼10 nm when undoped to ∼6 nm for the doped films).