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1.
Reliable and precise knowledge about the strain and composition effects on the band structure properties is crucial for the optimization of InGaN based heterostructures for electronic and optoelectronic device applications. AlInGaN as quaternary barrier material permits to control the band gap and the lattice constant independently. Using the model solid theory and the multi-band k.p interaction model, we investigate the composition effects on band offsets and band structure for pseudomorphic Ga1−xInxN/AlzInyGa1−yzN (0 0 1) heterointerfaces having zinc-blende structure. The results show that both conduction and valence band states are strongly modified while varying In and Al contents in the well and barrier materials. Furthermore, it is found that using AlInGaN as the barrier material allows the design of heterostructures including InGaN wells with tensile, zero or compressive strain. Such results give new insights for III-nitride compounds based applications and especially may guide the design of white-light emission diodes.  相似文献   
2.
A commonly used technique for frequency locking a laser is dithering the laser frequency and monitoring the first derivative of the laser transmission through an absolute reference. In semiconductor lasers, this frequency dithering can be obtained easily by dithering the injection current. However, this dithering also modulates the laser output power. Here we show that this modulation of the laser output power results in an offset of the locked laser frequency from the reference frequency. We derive analytical expressions for these frequency offsets for semiconductor lasers frequency-locked to a Fabry-Perot transmission peak, a Gaussian absorption line, and a Lorentzian absorption line.  相似文献   
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4.
Optimal control in NMR spectroscopy: Numerical implementation in SIMPSON   总被引:2,自引:2,他引:0  
We present the implementation of optimal control into the open source simulation package SIMPSON for development and optimization of nuclear magnetic resonance experiments for a wide range of applications, including liquid- and solid-state NMR, magnetic resonance imaging, quantum computation, and combinations between NMR and other spectroscopies. Optimal control enables efficient optimization of NMR experiments in terms of amplitudes, phases, offsets etc. for hundreds-to-thousands of pulses to fully exploit the experimentally available high degree of freedom in pulse sequences to combat variations/limitations in experimental or spin system parameters or design experiments with specific properties typically not covered as easily by standard design procedures. This facilitates straightforward optimization of experiments under consideration of rf and static field inhomogeneities, limitations in available or desired rf field strengths (e.g., for reduction of sample heating), spread in resonance offsets or coupling parameters, variations in spin systems etc. to meet the actual experimental conditions as close as possible. The paper provides a brief account on the relevant theory and in particular the computational interface relevant for optimization of state-to-state transfer (on the density operator level) and the effective Hamiltonian on the level of propagators along with several representative examples within liquid- and solid-state NMR spectroscopy.  相似文献   
5.
We discuss the interactions of adsorbates with the organic ferroelectric copolymer poly(vinylidene fluoride (PVDF)–trifluoroethylene (TrFE)). Range of molecular adsorbates is discussed from the smaller polar molecules like water, which is small enough to both adsorb and absorb, to the larger macrocyclic metal–organic metal phthalocyanines. The changes in local dipole orientation may affect the strength of the coupling between adsorbate or absorbate and the copolymer poly(vinylidene fluoride–trifluoroethylene). The interface dipole interactions may also affect device properties. The dipole interactions are implicated at the interface between copper phthalocyanine and poly(vinylidene fluoride with trifluoroethylene) affecting the band offsets and the diode properties.  相似文献   
6.
为了对GaN/AlN异质结电子结构有更为深入的认识,采用超原胞模型,对其进行了基于密度泛函理论的第一性原理计算.结果发现GaN/AlN为突变同型异质结,价带顶带阶为0.62eV,与实验值很接近.通过使用常用的平均键能法、平均势法和芯态法三种近似方法对GaN/AlN带阶的计算,比较得出,超原胞法虽然计算量较大,但能够给出异质结界面附近更为详细的信息,这一点其他三种近似方法无法得到,但他们也能够得出与实验值基本一致的带阶参量.  相似文献   
7.
汪建军  方泽波  冀婷  朱燕艳  任维义  张志娇 《物理学报》2012,61(1):17702-017702
利用分子束外延系统在Si (001) 衬底上制备了单晶Tm2O3薄膜, 利用X射线光电子能谱研究了Tm2O3相对于Si的能带偏移. 得出Tm2O3相对于Si的价带和导带偏移分别为3.1 eV± 0.2 eV和1.9 eV± 0.3 eV, 并得出了Tm2O3的禁带宽度为6.1 eV± 0.2 eV. 研究结果表明Tm2O3是一种很有前途的高k栅介质候选材料. 关键词: 2O3')" href="#">Tm2O3 X射线光电子能谱 能带偏移  相似文献   
8.
吴鹏  郭华 《波谱学杂志》2016,33(4):539-548
自适应重建(Adaptive Reconstruction,AR)算法被广泛应用于磁共振图像的多通道合并问题上.AR算法不需要直接采集各个线圈的灵敏度信息,而是通过通道间信号及噪声相关矩阵,估算出各个通道的灵敏度,从而保证了合并的幅值图像具有较高的信噪比(Signal-to-Noise Ratio,SNR).然而,由于AR算法没有针对相位图像的合并问题进行优化,导致重建出的相位图像具有不确定性.另外,受各通道之间相位偏移及低信噪比相位图像的影响,重建结果可能包含伪影.该文提出了一种改进型AR算法,估算并移除了各通道之间的相位偏移,同时对多通道数据的相位进行质量评估及通道重排,用以进行后续自适应重建.仿体及在体实验表明,该方法可以有效提升AR算法稳定性、消除重建图像中存在的伪影,同时保持合并后幅值图像及相位图像的高信噪比.  相似文献   
9.
C.F. Cai  J.X. Si  Y. Xu 《Applied Surface Science》2010,256(20):6057-6059
The band offset at the interface of PbTe/Ge (1 0 0) heterojunction was studied by the synchrotron radiation photoelectron spectroscopy. A valence band offset of ΔEV = 0.07 ± 0.05 eV, and a conduction band offset of ΔEC = 0.27 ± 0.05 eV are concluded. The experimental determination of the band offset for the PbTe/Ge interface should be beneficial for the heterojunction to be applied in new optoelectronic and electronic devices.  相似文献   
10.
曲线、曲面的广度Offset及其性质   总被引:1,自引:0,他引:1  
陈雪娟 《数学研究》2003,36(1):63-70
针对广义offset在实际中的广泛应用,给出一种曲线、曲面的广义offset的定义,并讨论它们的性质.  相似文献   
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