掺杂纳米硅薄膜中电子自旋共振研究

研究了掺杂纳米硅薄膜(nc∶Si∶H)中的电子自旋共振(ESR)及与之相关的缺陷态.样品是用等离子体增强化学气相沉积方法制成,为两相结构,即纳米晶粒镶嵌于非晶本体之中.对掺磷的nc-Si∶H样品,测量出其ESR信号的g值为1.9990—1.9991,线宽ΔH_pp为(40—42)×10^-4T,ESR密度Nss为10¹⁷cm^-3数量级.对掺硼的nc-Si∶H样品,其ESR信号的g值为2.0076—2.0078,ΔH_{关键词： 纳米硅薄膜 微结构 电子自旋共振}     

纳米NiAl的电子自旋共振研究

对纳米NiAl样品进行电子自旋共振(ESR)研究时发现晶粒尺寸效应产生的非磁-磁性转变.大块多晶NiAl合金的没有ESR信号,只有很弱的Pauli顺磁性.而粒径为8.6nm的纳米NiAl样品的ESR信号,随温度的增高而显著下降,其居里温度T_C为124K,在室温下ESR信号很弱.8.6nm的纳米NiAl样品经550℃和707℃退火处理后得到粒径分别为12nm和21nm的两个样品,它们在室温下都有较强的ESR信号,并能够被永磁体吸起。多晶NiAl合金与纳米NiAl之间存在非磁-磁性转变,     

晶粒易轴取向度对纳米晶永磁Pr2Fe14B磁性的影响

构造了立方和不规则形状晶粒的各向异性纳米晶单相Pr₂Fe₁₄B磁体 .利用微磁学的有限元法，模拟计算了样品的磁滞回线.计算结果表明，随着磁体晶粒易轴取向度的变差， 磁体的剩磁、矫顽力均随之下降.不同晶粒尺寸的纳米晶单相Pr₂Fe_{14B磁体，其磁 性能随取向度的变化快慢不同，原因在于磁体中的晶间交换作用 (IGEC) 的强弱不同.随着 晶粒取向度的提高，纳米晶单相磁体的矫顽力逐渐增加，这完全不同于烧结磁体. 关键词： 纳米晶磁体 矫顽力 剩磁}     

Ar+离子束轰击在石墨表面形成六方金刚石纳米晶的研究

在0.6keV Ar⁺高剂量(～10²²/cm²)辐照石墨表面,借助于高分辨透射电子显微镜(HRTEM),发现有六方金刚石纳米晶产生.它们的平均直径介于1—50nm之间,而且晶粒个数约随其直径的增大而直线减少.有趣的是,晶粒具有两种结构模式：直径小于10nm的晶粒为单晶结构,而直径大于10nm的为多晶结构.基于受离子轰击过程特点制约的六方金刚石晶粒成核和成长观点,讨论了这种双重结构的形成性质. 关键词： 离子轰击 六方金刚石纳米晶     

Ag离子注入非晶SiO2的光学吸收、拉曼谱和透射电镜研究

能量为200keV的Ag离子，以1×10¹⁶，5×10¹⁶，1×10¹⁷ cm^-2的剂量分别注入到非晶SiO₂玻璃，光学吸收谱显示：注入剂量为1×10¹⁶ cm^-2的样品的光吸收谱为洛伦兹曲线，与Mie理论模拟的曲线形状一致；注入剂量较大的5×10¹⁶，1×10¹⁷ cm^-2的谱线共振吸收增强，峰位红移并出现伴峰. 透射电镜观察分析表明，注入剂量不同的样品中形成的纳米颗粒的大小、形状、分布都不同，注入剂量较大的还会产生明显的表面溅射效应，这些因素都会影响共振吸收的峰形、峰位和峰强. 当注入剂量达到1×10¹⁷ cm^-2时，Ag纳米颗粒内部可能还形成了杂质团簇. 关键词： 离子注入 纳米颗粒 共振吸收 红移     

NdBa2Cu3-xMnxOy体系的结构和声子振动

利用X光衍射、红外光谱、电子顺磁共振等实验手段对多晶样品NdBa2Cu3-xMnxOy(0≤x≤0.3)的结构、声子振动和自旋关联情况进行了研究.结果表明:随着Mn掺杂浓度的增加,样品由四方结构转变为正交结构.红外谱的研究发现:所有样品在580cm-1附近都有一个峰,强度随着掺杂浓度的增加而增强,振动膜逐渐软化这和样品的微结构变化密切有关.ESR研究表明: NdBa2Cu3-xMnxOy体系在不掺杂或低掺杂浓度时只有很弱的自旋共振信号,进一步增加Mn含量,自旋信号增强,线宽降低,显示Mn掺杂浓度增加引起Mn离子的自旋局域化程度增强.本文讨论了掺杂对结构、红外谱和自旋关联的影响.     

退火温度对硼掺杂纳米金刚石薄膜微结构和p型导电性能的影响

采用热丝化学气相沉积法制备硼掺杂纳米金刚石 (BDND) 薄膜, 并对薄膜进行真空退火处理, 系统研究退火温度对BDND薄膜微结构和电学性能的影响. Hall效应测试结果表明掺B浓度为5000 ppm (NHB) 的样品的电阻率较掺B浓度为500 ppm (NLB) 的样品的低, 载流子浓度高, Hall迁移率下降. 1000 ℃退火后, NLB和NHB 样品的迁移率分别为53.3和39.3 cm²·V^-1·s^-1, 薄膜的迁移率较未退火样品提高, 电阻率降低. 高分辨透射电镜、紫外和可见光拉曼光谱测试结果表明, NLB样品的金刚石相含量较NHB样品高, 高的硼掺杂浓度使薄膜中的金刚石晶粒产生较大的晶格畸变. 经1000 ℃退火后, NLB和NHB薄膜中纳米金刚石相含量较未退火时增大, 说明薄膜中部分非晶碳转变为金刚石相, 为晶界上B扩散到纳米金刚石晶粒中提供了机会, 使得纳米金刚石晶粒中B浓度提高, 增强纳米金刚石晶粒的导电能力, 提高薄膜电学性能. 1000 ℃退火能够恢复纳米金刚石晶粒的晶格完整性, 减小由掺杂引起的内应力, 从而提高薄膜的电学性能. 可见光Raman光谱测试结果表明, 1000℃退火后, Raman谱图中反式聚乙炔 (TPA) 的1140 cm^-1峰消失, 此时薄膜电学性能较好, 说明TPA减少有利于提高薄膜的电学性能. 退火后金刚石相含量的增大、金刚石晶粒的完整性提高及TPA含量的大量减少有利于提高薄膜的电学性能. 关键词： 硼掺杂纳米金刚石薄膜 退火 微结构 电学性能     

纳米晶永磁材料晶间交换耦合作用的模拟计算研究

利用微磁学有限元法，模拟计算了单相和复相各向同性纳米晶磁体的起始磁化曲线、退磁曲线和回复曲线.验证了用δm(H)曲线的正峰值来衡量纳米晶磁体晶间交换耦合作用的有效性.计算 结果表明，纳米晶单相和复相磁体的晶间交换耦合作用都随晶粒尺寸的增加而降低，当晶粒尺寸过大时 复相磁体表现出两相行为，其δm(H)曲线出现了两个正峰值.分析表明，外场较小的正峰值是软磁相与硬磁相晶粒之间交换耦合作用的结果，而外场较大的正峰值是硬磁相晶粒之间交换耦合作用的结果. 关键词： 纳米晶永磁 晶间交换耦合 δm(H)曲线     

牙齿化石中由辐照产生的陷阱电子的热稳定性研究

本文对周口店北京猿人遗址的动物牙齿化石进行了辐照产生的陷阱捕获电子的热稳定性研究和釉质样品及牙质样品的热稳定性对比实验。得到釉质样品中g=2.0016 ESR峰的寿命为7.1×10⁶年(20℃)。说明了取该峰进行ESR年代测定的可信性和用釉质样品进行ESR年代测定的必要性。     

Fe/[NiFe/Cu]30多层膜线列阵的铁磁共振研究

用铁磁共振(FMR)技术研究Fe/［NiFe/Cu］₃₀多层膜线列阵的特性,线列阵采用激光全息光刻和离子束刻蚀技术加工,线密度为250线/mm和500线/mm.线列阵样品的FMR谱在稍高于主峰（声学峰）的共振场下有光学峰出现,相当层间交换耦合为反铁磁型.光学峰与声学峰的峰位间距沿易轴小于沿难轴.又,来自非磁Cu夹层的顺磁共振峰的幅度远大于原始的连续膜,说明线列阵加工致使层结构退化. 关键词：     

Magnetic Resonance Study of Fe-Implanted TiO<Subscript>2</Subscript> Rutile

Single-crystal (100) and (001) TiO₂ rutile substrates have been implanted with 40 keV Fe⁺ at room temperature with high doses in the range of (0.5–1.5) × 10¹⁷ ions/cm². A ferromagnetic resonance (FMR) signal has been observed for all samples with the intensity and the out-of-plane anisotropy increasing with the implantation dose. The FMR signal has been related to the formation of a percolated metal layer consisting of close-packed iron nanoparticles in the implanted region of TiO₂ substrate. Electron spin resonance (ESR) signal of paramagnetic Fe³⁺ ions substituting Ti⁴⁺ positions in the TiO₂ rutile structure has been also observed. The dependences of FMR resonance fields on the DC magnetic field orientation reveal a strong in-plane anisotropy for both (100) and (001) substrate planes. An origin of the in-plane anisotropy of FMR signal is attributed to the textured growth of the iron nanoparticles. As result of the nanoparticle growth aligned with respect to the structure of the rutile host, the in-plane magnetic anisotropy of the samples reflects the symmetry of the crystal structure of the TiO₂ substrates. Crystallographic directions of the preferential growth of iron nanoparticles have been determined by computer modeling of anisotropic ESR signal of substitutional Fe³⁺ ions.     

Feasibility of radiation sterilization and dosimetric features of ampicillin: an electron spin resonance study

In the present work, it was aimed to identify radical species produced by gamma irradiation (3–34?kGy) of solid ampicillin, to determine its spectroscopic, dosimetric, stability and kinetic behavior, and to investigate feasibility of the radiation sterilization feature of ampicillin by using electron spin resonance (ESR) spectroscopy. ESR experiments were performed at low and high temperatures (130–400?K) to examine the characteristic properties of the radical intermediates that are produced in ampicillin by gamma radiation treatment. Unirradiated ampicillin presented no ESR signal but irradiated samples exhibited ESR spectra with four resonance peaks spread over a magnetic field range of 8?mT. The spectral parameters of the central resonance line of the spectrum are g?=?2.0044 and ΔH_pp?=?0.08?mT. An exponential growth function of the applied dose was found to describe best the experimental dose–response data and it was found that ampicillin did not exhibit the feature of a good dosimetric material as its ESR intensity was relatively weak even for the samples irradiated at high level of doses. G_mean value of gamma-irradiated ampicillin was found to be 4.6?±?0.9?×?10^?9?mol/J, which is very small compared to irradiated alanine solid sample. However, the discrimination of irradiated ampicillin from unirradiated one was possible even ～3 months after storage at normal conditions. The simulation calculations indicated that gamma irradiation created two different radical species in solid ampicillin. Decay activation energy of the radical species which is mostly responsible from central intense resonance line is calculated to be 55.6?±?3.2?kJ/mol by using the signal intensity decay data derived from annealing studies. It was concluded that ampicillin could be sterilized by gamma radiation and ESR spectroscopy can be used as a potential technique to monitor its radiosterilization process.     

蓝宝石(α-Al_2O_3:Fe~(3+))体系基态分裂与局域晶格畸变的研究

2002年Scholz和Buzaré对蓝宝石晶体中Fe3+离子的基态分裂重新进行了EPR实验测量和研究,他们的初步分析表明在蓝宝石晶体中Fe3+离子的6A1基态分裂有可能同时与两个方向的畸变角(θ和φ)有关.本文采用对角化d5组态在C3点群对称下的252×252完全能量矩阵的方法,对蓝宝石晶体中Fe3+离子的光谱和EPR谱进行了系统的研究.计算结果表明蓝宝石体系中Fe3+离子的6A1基态分裂确实将明显依赖于两个方向的畸变角θ和φ,这一理论结果与Scholz和Buzaré等的实验相符合.同时,通过拟合Fe3+离子在蓝宝石体系中的实验光谱和EPR参量,确定了蓝宝石晶体中(FeO6)9团簇局域晶格畸变角θi的范围.     

Paramagnetic centers in nonmetallic amorphous polyphthalocyanines

Electron paramagnetic resonance (EPR) spectra of nonmetallic amorphous polyphthalocyanines are investigated in the temperature range 295–500 K. The EPR spectrum of nonmetallic amorphous polyphth-alocyanine samples at room temperature prior to heating is a narrow singlet of approximately Lorentzian shape with a linewidth ΔH_pp ≈ 1.7 Oe, a splitting factor g=2.00, and an intensity I_EPR ≈ 10¹⁷ spins/g. It is found that the intensity and linewidth of the EPR spectrum increase with increasing temperature. Beginning with a characteristic temperature T₁, both parameters, ΔH_pp and I_EPR, become dependent on time (under isothermal conditions). Computer calculations of the spectra demonstrate that the EPR spectrum can be represented as a superposition of two lines with substantially differing parameters whose dependences on the temperature and micro-wave power also differ significantly. The possible reasons for the existence of electron paramagnetic resonance centers of two types with different degrees of delocalization of a charge carrier with a magnetic moment in nonmetallic amorphous polyphthalocyanines are discussed.     

Dopant Spin States and Magnetic Interactions in Transition Metal (Fe3+)-Doped Semiconductor Nanoparticles: An EMR and Magnetometric Study

In this work, electron magnetic resonance (EMR) spectroscopy and magnetometry studies were employed to investigate the origin of the observed room-temperature ferromagnetism in chemically synthesized Sn_1?x Fe _x O₂ powders. EMR data clearly established the presence of two different types of signals due to the incorporated Fe ions: paramagnetic spectra due to isolated Fe³⁺ ions and broad ferromagnetic resonance (FMR) spectra due to magnetically coupled Fe³⁺ dopant ions. EMR data analysis and simulation suggested the presence of high-spin (S = 5/2) Fe³⁺ ions incorporated into the SnO₂ host lattice both at substitutional and at interstitial sites. The FMR signal intensity and the saturation magnetization M _s of the ferromagnetic component increased with increasing Fe concentration. For Sn_0.953Fe_0.047O₂ samples, well-defined EMR spectra revealing FMRs were observed only for samples prepared in the 350–600°C range, whereas for samples prepared at higher annealing temperatures up to 900°C, the FMRs and saturation magnetization were vanished due to diffusion and eventual expulsion of the Fe ions from the nanoparticles, in agreement with data obtained from Raman and X-ray photoelectron spectroscopy.     

Electron spin resonance properties of semiconductor/granular film heterostructures with cobalt nanoparticles in millimeter waveband

Ferromagnetic resonance spectra (FMR) on heterostructures of amorphous silicon dioxide films containing cobalt nanoparticles, (SiO₂)_100−xCo_x, grown on GaAs and Si substrates have been investigated over a frequency range of 37–41 GHz at room temperature. The FMR linewidth and saturation magnetization dependencies on the cobalt concentration have been analyzed. The impact of the semiconductor type on the FMR linewidth ΔH and a sharp increase in ΔH with a decreasing concentration of cobalt nanoparticles have been noted. The effect of considerable FMR linewidth broadening has been accounted for by the spin-polarized relaxation mechanism.     

Effect of temperature and high pressure on Mn2+ EPR spectra in K3H(SO4)2 fast-proton conductor

The linewidth ΔH _pp and spin-Hamiltonian parameters under temperature and high hydrostatic pressure by X-band continuous wave electron paramagnetic resonance in the K₃H(SO₄)₂ crystal were studied. Spin-Hamiltonian parameters, direction cosines and coordination of Mn²⁺ ion were determined at room temperature. The pressure at 300?MPa leads to the change of hydrogen bond potential and the transition from double well to single well potential moves about 10?K towards a higher temperature.     

Electron spin resonance study of a CuIr2S4 single crystal

A spinel sulphide CuIr₂S₄ single crystal, which exhibits an orbitally induced Peierls phase transition at ～230?K, is investigated by electron spin resonance (ESR) spectroscopy. The phase transition is clearly manifested on the ESR spectra. It is suggested that the ESR signals are produced by a few non-dimerized Ir⁴⁺ ions. Moreover, an extra ESR spectrum appears at low temperature in addition to the paramagnetic ESR signals of Ir⁴⁺ ions, which is suggested to be caused by the Jahn–Teller effect of the non-dimerized Ir⁴⁺ ions. From the ESR results, it is found that the Jahn–Teller splitting energy ΔE _JT is much smaller than the spin-dimerization gap.     

High-frequency tunable EPR spectroscopy of Cr3+ in synthetic forsterite

The electron paramagnetic resonance spectra of isolated and dimer impurity centers of trivalent chromium ions in the octahedral Ml sites in synthetic forsterite are studied in the frequency range of 65–90 GHz. The measurements are performed at 4.2 K in magnetic field from ?0.04 to 0.3 T. The zero-field splitting between spin doublets of the isolated Cr³⁺ ion Δ_s = 66.7 GHz and between spin sublevels of the Cr³⁺-Cr³⁺ dimer Δ_d1 = 71.5 GHz and Δ_d2 = 73.0 GHz is measured directly at zero field. The analysis of the spin Hamiltonian parameters shows that the dimer center consists of a pair of Cr³⁺ ions with an Mg²⁺ vacancy between them replacing three Mg²⁺ ions situated in a quasi-one-dimensional chain aligned parallel to the crystal c-axis. It is found that the exchange interaction in the dimer is ferromagnetic with parameters J_z = 0.47 GHz and J_t = 0.79 GHz.     

High frequency characteristics of NiO/(FeCo/NiO)10 multilayers with exchange anisotropy

[NiO/Fe₆₅Co₃₅]₁₀ exchange-coupled multilayer films for high frequency applications are fabricated, and their static magnetic property and microwave permeability are studied systematically. Both exchange bias field and ferromagnetic resonance frequency of the multilayers increase with decreasing Fe₆₅Co₃₅ thickness, which means that the microwave properties such as permeability and FMR frequency can be controlled by changing Fe₆₅Co₃₅ thickness in the exchange-coupled films. Ferromagnetic resonance frequencies beyond 7 GHz of the films are measured and reported for the first time.