Brieler Felix J, Fröba Michael, Chen Limei, Klar Peter J, Heimbrodt Wolfram, Von NiddaHans-AlbrechtKrug, Loidl Alois
Institute of Inorganic and Analytical Chemistry, Justus-Liebig-University Giessen, Germany.
Chemistry. 2002 Jan 4;8(1):185-94. doi: 10.1002/1521-3765(20020104)8:1<185::aid-chem185>3.0.co;2-l.
We present a novel way of synthesising highly ordered arrays of hollow Cd(1-x)Mn(x)S quantum wires with lateral dimensions of 3-4 nm separated by 1-2 nm SiO2 barriers by forming Cd(1-x)Mn(x)S (0 < or = x < or = 1) semiconductors inside the pore system of mesoporous MCM-41 SiO2 host structures. X-ray diffraction and transmission electron microscopy (TEM) studies reveal the hexagonal symmetry of these arrays (space group p6m) and confirm the high degree of order. Physisorption measurements show the filling of the pores of the MCM-41 SiO2. The X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS), electron paramagentic resonance (EPR), and Raman studies confirm the good crystalline quality of the incorporated (Cd,Mn)S guest. The effects of reducing the lateral dimensions on the magnetic and electronic properties of the diluted magnetic semiconductor were studied by photoluminescence (PL) and PL excitation spectroscopy and by SQUID and EPR measurements in the temperature range 2-400 K. Due to the quantum confinement of the excitons in the wires, an increase of about 200 meV in the direct band gap was observed. In addition, the p-d hybridisation-related bowing of the band gap as a function of Mn concentration in the wires is much stronger than in the bulk. This effect is related to the increase in the band gap due to quantum confinement, which shifts the p-like valence band edge closer to the 3d-related states of Mn in the valence band. Thus, the p-d hybridisation and the strength of the band gap bowing are increased. Compared to bulk (II,Mn)VI compounds, antiferromagnetic coupling between the magnetic moments of the Mn2+ ions is weaker. For the samples with high Mn concentrations (x > 0.8) this leads to a suppression of the phase transition of the Mn system from paramagnetic to antiferromagnetic. This effect can be explained by the fact that the lateral dimensions of the wires are smaller than the magnetic length scale of the antiferromagnetic ordering.
我们提出了一种新颖的方法来合成高度有序的中空Cd(1 - x)Mn(x)S量子线阵列，其横向尺寸为3 - 4纳米，被1 - 2纳米的SiO2势垒隔开，通过在介孔MCM - 41 SiO2主体结构的孔系统内形成Cd(1 - x)Mn(x)S（0≤x≤1）半导体来实现。X射线衍射和透射电子显微镜（TEM）研究揭示了这些阵列的六方对称性（空间群p6m）并证实了高度有序性。物理吸附测量表明MCM - 41 SiO2的孔被填充。X射线吸收近边结构（XANES）、扩展X射线吸收精细结构（EXAFS）、电子顺磁共振（EPR）和拉曼研究证实了掺入的（Cd,Mn）S客体具有良好的晶体质量。通过光致发光（PL）和PL激发光谱以及在2 - 400 K温度范围内的超导量子干涉仪（SQUID）和EPR测量，研究了减小横向尺寸对稀磁半导体的磁性和电子性质的影响。由于量子线中激子的量子限制作用，观察到直接带隙增加了约200毫电子伏特。此外，与量子线中Mn浓度相关的带隙的p - d杂化相关弯曲比体材料中要强得多。这种效应与量子限制导致带隙增加有关，这使得类p价带边缘更靠近价带中与Mn相关的3d态。因此，p - d杂化和带隙弯曲强度增加。与体相（II,Mn）VI化合物相比，Mn2 +离子磁矩之间的反铁磁耦合较弱。对于高Mn浓度（x > 0.8）的样品，这导致Mn系统从顺磁到反铁磁相变的抑制。这种效应可以通过量子线的横向尺寸小于反铁磁有序化的磁长度尺度这一事实来解释。
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