Room temperature fabrication of silicon nanocrystals by pulsed laser deposition

Reaction of 10 nm gold nanoparticles (AuNPs) with a thiol-functionalized bipyridine copper(II) complex, Cu[(N-(6-mercaptohexyl)-2,2′-bipyridinyl-5-carboxamide)]Cl₂ (3), and (1-mercaptohex-6-yl)tri(ethylene glycol) (5) in different ratios resulted in mixed monolayer modified NPs with varying surface coverage of capping agent. The copper complex modified NPs were used for surface plasmon resonance (SPR) promoted homogeneous catalysis applied to the hydrolysis of the nerve agent methyl parathion (MeP) at pH 8.0. Low power green laser (532 nm) irradiation of solutions of modified AuNPs with MeP resulted in significant increase in the rate of phosphate ester hydrolysis which could not be attributed to a thermal process. Ratios of initial rates (laser/dark) at high substrate concentrations of MeP as a function of copper catalyst coverage were determined. A possible mechanism for catalytic enhancement involving dissociation of catalytically inactive hydroxy-bridged Cu(II) dimer is discussed.     

Theory of diluted magnetic semiconductor ferromagnetism

We present a theory of carrier-induced ferromagnetism in diluted magnetic semiconductors ( III1-xMnxV) which allows for arbitrary itinerant-carrier spin polarization and dynamic correlations. Both ingredients are essential in identifying the system's elementary excitations and describing their properties. We find a branch of collective modes, in addition to the spin waves and Stoner continuum which occur in metallic ferromagnets, and predict that the low-temperature spin stiffness is independent of the strength of the exchange coupling between magnetic ions and itinerant carriers. We discuss the temperature dependence of the magnetization and the heat capacity.     

Room temperature ferromagnetism in magic-sized Cr-doped CdS diluted magnetic semiconducting quantum dots

Manipulation of carrier spins in semiconductors for spintronics applications has received great attention driven by improved functionalities and higher speed operation. Doping of semiconductor nanocrystals by transition-metal ions pronounced as diluted magnetic semiconductors (DMS) has attracted tremendous attention. Such doping is, however, difficult to achieve in low-dimensional strongly quantum-confined nanostructures by conventional growth procedures. In the present case, magic-sized, pure, and Cr-doped CdS DM-QDs have been synthesized by solution phase chemistry (lyothermal method). Structural, optical, and magnetic investigation suggest an intrinsic nature of ferromagnetism with highly quantum-confined system. Optical and magnetic results of pure and doped QDs reveal major physical consequences of dopant localization within the capacity to engineer dopant-carrier exchange interactions introducing magnetic functionalities within the host semiconductor lattice. Unpaired Cr ions in Cd substitutional sites could create spin ordering and ferromagnetic coupling. The results presented herein illustrate some of the remarkable and unexpected complexities that can arise in doped QDs.     

Room temperature ferromagnetism of amorphous MgO films prepared by pulsed laser deposition

Amorphous MgO thin films were prepared by pulsed laser deposition (PLD) under various oxygen pressures. The structural, magnetic, and optical properties of the films were investigated. All as-deposited samples exhibit room temperature ferromagnetism, which depend strongly on oxygen pressure. It is found that the saturation magnetization (M _s) initially increases with the oxygen pressure, the maximum M _s of 8.57 emu/cm³ is obtained for the MgO film deposited under an oxygen pressure of 2 mTorr. However, the M _s significantly reduces at higher oxygen pressures. Further X-ray photoelectron spectroscopy and photoluminescence demonstrate that the long-range magnetic order in amorphous MgO films can be attributed to the nonstoichiometry effect and the presence of Mg vacancies.     

Room temperature growth and properties of ZnO films by pulsed laser deposition

ZnO thin films were prepared by pulsed laser deposition at room temperature on glass substrates with oxygen pressures of 10-30 Pa. The structural, electrical, and optical properties of ZnO films were studied in detail. ZnO films had an acceptable crystal quality with high c-axis orientation and smooth surface. The resistivity was in the 10² Ω cm order for ZnO films, with the electron concentration of 10¹⁶-10¹⁷ cm⁻³. All the films showed a high visible transmittance ∼90% and a high UV absorption about 90-100%. The UV emission ∼390 nm was observed in the photoluminescence spectra. The oxygen pressures in the 10-30 Pa range were suitable for room temperature growth of high-quality ZnO films.     

基于电子回旋共振-等离子体增强金属有机物化学气相沉积技术生长GaMnN稀磁半导体的研究

利用电子回旋共振-等离子体增强金属有机物化学气相沉积 (ECR-PEMOCVD)方法，采用二茂锰(Cp₂Mn)作为Mn源，高纯氮气作为氮源，三乙基镓(TEGa)作为Ga源，在蓝宝石(α-Al₂O₃)(0001)衬底上外延生长GaMnN稀磁半导体薄膜.反射高能电子衍射(RHEED)、X射线衍射(XRD)、原子力显微镜(AFM)表征了GaMnN薄膜的晶体结构和表面形貌.GaMnN薄膜均表现出良好的(0002)择优取向，表明制备的薄膜倾向于     

基于电子回旋共振-等离子体增强金属有机物化学气相沉积技术生长GaMnN稀磁半导体的研究

利用电子回旋共振-等离子体增强金属有机物化学气相沉积 (ECR-PEMOCVD)方法,采用二茂锰(Cp₂Mn)作为Mn源,高纯氮气作为氮源,三乙基镓(TEGa)作为Ga源,在蓝宝石(α-Al₂O₃)(0001)衬底上外延生长GaMnN稀磁半导体薄膜.反射高能电子衍射(RHEED)、X射线衍射(XRD)、原子力显微镜(AFM)表征了GaMnN薄膜的晶体结构和表面形貌.GaMnN薄膜均表现出良好的(0002)择优取向,表明制备的薄膜倾向于 关键词： GaMnN薄膜 稀磁半导体 铁磁性 居里温度     

Excitonic effects in diluted magnetic semiconductor nanostructures

Excitonic properties and the dynamics are reported in quantum dots (QDs) and quantum wells (QW) of diluted magnetic semiconductors. Transient spectroscopies of photoluminescence and nonlinear-optical absorption and emission have been made on these quantum nanostructures. The Cd_1−x Mn_xSe QDs show the excitonic magnetic polaron effect with an increased binding energy. The quantum wells of the Cd_1−x Mn_xTe/ZnTe system display fast energy and dephasing relaxations of the free and localized excitons as well as the tunneling process of carriers and excitons in the QWs depending on the barrier widths. The observed dynamics and the enhanced excitonic effects are the inherent properties of the diluted magnetic nanostructures. Fiz. Tverd. Tela (St. Petersburg) 40, 846–848 (May 1998) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Phase diagram of diluted magnetic semiconductor quantum wells

The phase diagram of diluted magnetic semiconductor quantum wells is investigated. The interaction between the carriers in the hole gas can lead to first-order ferromagnetic transitions, which remain abrupt in applied fields. These transitions can be induced by magnetic fields or, in double-layer systems, by electric fields. We make a number of precise experimental predictions for observing these first-order phase transitions.     

ZnCoO稀磁半导体的室温磁性

采用固相反应法，将ZnO和Co₂O₃粉末按不同的成分配比混合，制备了稀磁半导体Zn_1-xCo_xO (x=0.02,0.06,0.10)材料.并使用H₂气氛退火技术对样品进行了处理，得到了具有室温铁磁性的掺Co氧化锌稀磁半导体.利用全自动X射线衍射仪、X射线光电子能谱仪、高分辨透射电子显微镜和超导量子干涉器件磁强计对样品的结构、晶粒的尺寸、微观形貌以及磁性等进行了测量和标度. 关键词： 稀磁半导体 氧化锌 掺杂 固相反应法     

脉冲磁场下水热法制备Cr掺杂ZnO稀磁 半导体晶体

本文以ZnCl₂, CrCl₃. 6H₂O和氨水缓冲溶液为原料, 在4T脉冲磁场下水热法制备了Cr掺杂ZnO稀磁半导体晶体, 通过X射线衍射分析、扫描电子显微镜观察及采用振动样品磁强计进行磁性分析等, 探讨了脉冲磁场对其微观结构及磁性能的影响. 结果表明: Cr掺杂ZnO稀磁半导体晶体仍保持ZnO的六方纤锌矿结构, 脉冲磁场具有促进晶粒生长及取向排列的作用, 4T脉冲磁场条件下合成的Cr掺杂ZnO稀磁半导体具有良好的室温铁磁性, 其饱和磁化强度(M_s)为0.068 emu/g, 而无脉冲磁场情况下制备的样品室温下呈顺磁性, 并且, 脉冲磁场下制备将稀磁半导体的居里温度提高了16 K.     

Structural and magnetic studies on Zr doped ZnO diluted magnetic semiconductor

In this study, Zirconium doped Zn_1−xZr_xO (with x = 0.00–0.10) samples have been prepared by formal solid-state reaction technique. The Zr doped ZnO samples annealed at 1100 °C and characterized by different characterization techniques, such as X-ray diffraction (XRD), Scanning electron microscope (SEM), Vibrating sample magnetometer (VSM) and Fourier transform infrared spectroscopy (FTIR). The X-ray diffraction (XRD) used to study the structural properties. XRD pattern showed that lattice parameters, “a”, “c”, unit cell volume and Zn–O bond length increase with doping content (x ≤ 0.04) where as these decrease with x > 0.04. On the other hand, reverse trend observed with lattice distortion. The crystallite size decreases with increasing doping content of Zr. FTIR employed to investigate functional chemical bonding properties of different elements and compounds present in materials. The low, medium and high frequency absorption bands observed at 630, 1500 and 3435 cm⁻¹, which were the common features of Zn–O, H–O–H and O–H bond respectively. SEM used to study surface morphology and measured grain size of specimen. The surface becomes dense and grain size decreases with increasing degree of Zr contents. The SEM micrograph also shows the presence of spherical micro size particles and formation of pores in samples. Magnetic properties were obtained using VSM. The samples exhibit room temperature ferromagnetism. The magnetic hysteresis loops show variation in the value of magnetic parameter. The saturation magnetization (M_s) and coercivity (H_c) decrease, while remanence magnetization (M_r) shows gradually increasing trend with Zr content. VSM measurement reveals that sample Zn_0.96Zr_0.4O show better result as compared to x = 0.06–0.10.     

稀释磁性半导体Sn1-xMnxO2的室温铁磁性

采用固相反应法,制备了不同成分的稀释磁性半导体Sn1-xMnxO2(x=0.02,0.04,0.06).利用x射线衍射和傅里叶变换红外光谱法证明了锰均匀地掺杂到二氧化锡中.在室温下研究了掺锰二氧化锡基稀释半导体的磁性,发现它具有明显的铁磁性,同时对磁性的强弱与锰的含量和烧结温度的关系作了研究.     

Laser induced ultrafast demagnetization in diluted magnetic semiconductor nanostructures

We present a dynamical model that reproduces the observed time evolution of the magnetization in diluted magnetic semiconductor films after weak laser excitation. Based on a many-particle expansion of the exact p–d exchange interaction, our approach goes beyond the usual mean-field approximation. Numerical results demonstrate that the hole spin relaxation plays a crucial role for explaining the ultrafast demagnetization processes observed experimentally. The influence of the laser power on the magnetization dynamics is also investigated.     

Amplification of the induced ferromagnetism in diluted magnetic semiconductor

Magnetic properties of the planar structure consisting of a ferromagnetic metal and the diluted magnetic semiconductor are considered (by the example of the structure Fe/Ga(Mn)As, experimentally studied in [F. Maccherozzi, M. Sperl, G. Panaccione, J. Mina'r, S. Polesya, H. Ebert, U. Wurstbauer, M. Hochstrasser, G. Rossi, G. Woltersdorf, W. Wegscheider, C.H. Back, Phys. Rev. Lett. 101 (2008) 267201]). In the framework of the mean field theory, we demonstrate the presence of the significant amplification of the ferromagnetism, induced by the ferromagnetic metal in the near-interface semiconductor area, due to the indirect interaction of magnetic impurities. This results in the substantial expansion of the temperature range where the magnetization in the boundary semiconductor region exists, that might be important for possible practical applications.     

EPR and ferromagnetism in diluted magnetic semiconductor quantum wells

Motivated by recent measurements of electron paramagnetic resonance spectra in modulation-doped CdMnTe quantum wells [Phys. Rev. Lett. 91, 077201 (2003)]], we develop a theory of collective spin excitations in quasi-two-dimensional diluted magnetic semiconductors. Our theory explains the anomalously large Knight shift found in these experiments as a consequence of collective coupling between Mn-ion local moments and itinerant-electron spins. We use this theory to discuss the physics of ferromagnetism in (II,Mn)VI quantum wells and to speculate on the temperature at which it is likely to be observed in n-type modulation-doped systems.     

脉冲磁场对水热法制备Mn掺杂ZnO稀磁半导体的影响

本文以Zn(CH₃COO)₂·2H₂O, Mn(CH₃COO)₂·4H₂O和氨水缓冲溶液为原料, 在4 T脉冲磁场下利用水热法制备了Mn掺杂ZnO稀磁半导体晶体, 通过X射线衍射、 扫描电子显微镜、透射电子显微镜、拉曼光谱、荧光分光光度计及振动样品磁强计等对样品的微观结构及磁性能等进行了表征, 结果表明: Mn掺杂ZnO稀磁半导体晶体仍保持ZnO六方纤锌矿结构, 4 T脉冲磁场下合成的Mn掺杂ZnO稀磁半导体晶体具有明显的室温铁磁性, 其饱和磁化强度(M_s)为0.028 emu/g, 比无脉冲磁场下制备的样品提高一倍以上, 且4 T 脉冲磁场将样品的居里温度提高了15 K.     

脉冲激光沉积法制备的Ni1-xFexO稀磁半导体的结构和磁性研究

利用脉冲激光沉积方法制备出了具有室温铁磁性的Ni1-1-xFexO(x=0.02,O.05)稀磁半导体.X射线衍射(XRD)结果表明Ni,1-xFexO的品体结构为Nacl结构,并且在Fe含量较高的Ni095Fe0.05O中出现了少量的a-Fe2O3物相.X射线吸收近边结构谱(XANFS)和X射线光电子能谱(XPs)进一步表明了掺杂的Fe原子替代Ni0日格中Ni原子,并且样品中不存在能够诱导室温磁性的第二相.这些研究结果表明Ni1-xFexO的室温铁磁性是本征的.     

II-VI族稀磁半导体微纳结构中的激子磁极化子及其发光

自旋是基本粒子（电子、光子）角动量的内在形式.固体中体现自旋特征的集体电子行为如拓扑绝缘体等是当前凝聚态物理领域关注的焦点,是基态行为.激子作为电子空穴对的激发态且寿命很短,可复合发光,它是否能体现自旋极化主导的行为?对此人们的认识远不如针对基态的电子.激子磁极化子（exciton magnetic polaron,EMP）是由磁性半导体微结构中铁磁自旋耦合态与自由激子相互作用形成的复合元激发,但其研究很有限.本文概述了我们在稀磁半导体微纳米结构中的EMP及其发光动态学光谱、自旋极化激子凝聚态的形成方面取得的一些进展,展望了未来可能在自旋光电子器件、磁控激光、光致磁性等量子技术方面的潜在应用.