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首页> 外文期刊>Chemistry: A European journal >Ordered Arrays of II/VI Diluted Magnetic Semiconductor Quantum Wires: Formation within Mesoporous MCM-41 Silica
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Ordered Arrays of II/VI Diluted Magnetic Semiconductor Quantum Wires: Formation within Mesoporous MCM-41 Silica

机译：II / VI稀释磁半导体量子线的有序阵列：在中孔MCM-41二氧化硅中的形成

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摘要

We present a novel way of synthesisig highly ordered arrays of hollow cd_(1-x)Mn_xS quantum wires with lateral dimensions of 3-4 nm separated by 1-2 nm SiO_2 barriers by forming Cd_(1-x)Mn_xS (0 <= x <= 1) semiconductors inside the pore system of mesoporous MCM-41 SiO_2 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 SiO_2. The X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS), electron paramagnetic 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 hybridization 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 Mn~(2+) 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.
机译：我们提出了一种新颖的合成中空cd_（1-x）Mn_xS量子线的新方法，该方法通过形成Cd_（1-x）Mn_xS（0 <= x <= 1）介孔MCM-41 SiO_2主体结构的孔系统内部的半导体。 X射线衍射和透射电子显微镜（TEM）研究揭示了这些阵列（空间群p6m）的六边形对称性，并确认了高度有序性。物理吸附测量表明，MCM-41 SiO_2的孔已充满。 X射线吸收近边缘结构（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客体的良好结晶质量。通过光致发光（PL）和PL激发光谱，以及在2-400 K的温度范围内通过SQUID和EPR测量，研究了减小横向尺寸对稀释的磁性半导体的磁和电子性能的影响。在导线中的激子中，观察到直接带隙增加了约200 meV。另外，与线中的Mn浓度有关的带隙的p-d杂交相关的弯曲比在主体中强得多。该效应与由于量子限制引起的带隙的增加有关，量子限制使p型价带边缘更接近价带中Mn的3d相关态。因此，增加了p-d杂交和带隙弯曲的强度。与块状（II，Mn）VI化合物相比，Mn〜（2+）离子的磁矩之间的反铁磁耦合更弱。对于具有高Mn浓度（x> 0.8）的样品，这会抑制Mn系统从顺磁性到反铁磁性的相变。可以通过以下事实解释这种效果：导线的横向尺寸小于反铁磁​​有序的磁长度标度。

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