The Systematics of Muonium Hyperfine Constants

The hyperfine constants for muonium in elemental and binary inorganic solids suggest formation of three different families of defect centre, with distinct electronic structures. The overall range of values, spanning nearly five orders of magnitude, and their correlation with host properties such as band gap and electron affinity, reveal a deep-to-shallow instability which has profound implications for the electrical properties of hydrogen impurity in electronic materials, both semiconducting and dielectric.     

Hyperfine Parameters for Muonium in Copper (I), Silver (I) and Cadmium Oxides

Muonium centres in Cu₂O, Ag₂O and CdO show hyperfine parameters spanning four orders of magnitude. They exemplify the three different categories of hydrogen defect centre in semiconducting and dielectric solids, with very different electronic structure and electrical activity, namely quasi-atomic (possibly deep acceptor), deep donor and shallow donor.     

Recent Progress in the Study on Muonium Centers in Semiconductors

The electronic structures and the locations of muonum centers (Mu) were investigated in single crystalline ZnO. Mu centers with extremely small hyperfine parameters have been observed below 40 K. It is inferred from their small ionization energy and hyperfine parameters that these centers behave as shallow donors, strongly suggesting that hydrogen is one of the primary origins of n type conductivity in as-grown ZnO. This revised version was published online in August 2006 with corrections to the Cover Date.     

Static and Intermittent Hyperfine Coupling for the Muoniated Radical in Tellurium

The hyperfine constant for muonium defect centres in elemental tellurium, measured spectroscopically at low temperature, corresponds to 7% of the free-atom value. The centres are tentatively identified as the diatomic species TeMu, analogous to the hydroxyl radical, OH. Their spectrum disappears as the centres ionize around 80 K but the muon spin response indicates that the same centres form and reionise, rapidly and repeatedly, above 200 K. The capture and loss of charge carriers provide a model for the electrical activity of hydrogen impurity in this low-gap semiconductor.     

Muonium/muonic hydrogen formation in atomic hydrogen

The muonium/muonic hydrogen atom formation in μ^±−H collisions is investigated, using a two-state approximation in a time dependent formalism. It is found that muonium cross-section results are similar to the cross-section results obtained for positronium formation in e⁺-H collision. Muonic hydrogen atom formation cross-sections in μ^--H collision are found to be significant in a narrow range of energy (5 eV–25 eV).     

First-Principles Theory of Muon and Muonium Trapping in the Protein Chain of Cytochrome c and Associated Hyperfine Interactions

The microscopic details of the electron transfer in cytochrome c (cyt c) are being investigated by the Muon Spin Relaxation (μSR) technique. We are using the Hartree–Fock Cluster Procedure to determine the most likely trapping sites for μ⁺ and muonium (Mu) in the protein chain, and have performed extensive calculations in single amino acid molecules of the protein chain of cyt c. The double-bonded oxygen atom of the carboxyl group was identified as the trapping site for both μ⁺ and Mu. Utilizing the wave functions we obtained from the Hartree–Fock calculations, we have determined the hyperfine field that the μ⁺ in Mu experiences while the latter is trapped at the oxygen. This revised version was published online in September 2006 with corrections to the Cover Date.     

Comparative Theoretical Study of Hyperfine Interactions of Muonium in A- and B-Form DNA

Muon Spin Relaxation (μSR) experiments in A- and B-form DNA have shown evidence for an enhanced electron mobility in the more closely-packed A-form. Besides dynamic effects (electronic diffusion) that could cause the observed difference in muon spin relaxation, one should also carefully examine the difference in the strengths of the hyperfine interactions of the muon (μ ⁺) with the moving electron in the two forms of DNA, since this could contribute to the observed difference in the muon spin relaxation rates as well. We have therefore investigated the (static) trapping properties of muon and muonium (μ ⁺ e ⁻) in A-form and B-form DNA from first-principles with the aim to understand how the different structural geometries of A- and B-form DNA can influence the hyperfine interaction of trapped muonium.     

Excited states of muonium in atomic hydrogen

Muonium formation in excited states in muon-hydrogen charge-exchange collision is investigated using a method developed in a previous paper. Differential cross-section results are found to resemble positronium formation cross-section results of positron—hydrogen charge-exchange problem. Forward differential and integrated cross-sections are computed for muon energy of 2 keV and higher. Total muonium formation cross-sections are computed using Jackson and Schiff scaling rules. Muonium formation cross-section results obtained from proton—hydrogen charge-exchange cross-section results, using velocity scaling are compared with the results of the present calculation     

Hyperfine Interaction of Metamict Zircon Studied by PAC Spectroscopy

Zircon (ZrSiO₄) is a common accessory mineral found in igneous and metamorphic rocks and is generally in an amorphous state due to self-irradiation from radioactive impurities. The crystalline structure may be recovered by annealing. We have studied the annealing behavior of a nearly fully metamict zircon specimen by perturbed angular correlation spectroscopy and powder X-ray diffraction. Our results are consistent with accepted damage accumulation models and point to a two-stage recovery process for the transition from metamict to crystalline zircon. In all of our experiments PAC overestimates the amorphous fraction as compared to that determined by diffraction experiments, and we propose an explanation for this discrepancy. This revised version was published online in September 2006 with corrections to the Cover Date.     

Hyperfine Spectroscopy with Nuclear Resonant Scattering of Synchrotron Radiation

Since its observation in 1985 nuclear resonant scattering of synchrotron radiation has become an excellent tool to study hyperfine interactions in solids. It combines the advantages of both local probe experiments and scattering techniques and gives valuable information on magnetic and electronic structures in case of NFS experiments. Experiments benefit from the outstanding beam quality of 3rd generation synchrotron radiation sources, as the small beam size and divergence. This revised version was published online in August 2006 with corrections to the Cover Date.     

Long Lifetime State of Shallow Donor Centres for Silicon Based THz Sources

Impurity centres in high purity silicon with ionization energies 38.32 and 40.09meV are observed by photothermal ionization spectroscopy measurements. Their typical shallow donor characteristics are approved by good agreement with theoretic evaluation under varying magnetic fields. The 2p0 state lifetime of one donor centres are more than 3 times longer than that of phosphorus in the same silicon sample. Compared to phosphorus which has been already successfully exploited to produce silicon-based THz radiations, this shallow donor centre has a pronounced enhancement on lifetime and quality factor of population inversion level. Hence, silicon with this donor centre would be a potential excellent candidate to develop improved silicon-based THz sources.     

钠磷酸盐精细结构的拉曼光谱解析

构建了钠磷酸盐精细结构团簇,应用量子化学从头计算方法,采用闭壳层Hatree-Fock(RHF)方法和6-31G(d, p)基组优化构型,进行了拉曼光谱的模拟计算。引入SIT应力指数标识磷酸盐局部微观精细结构,讨论和分析了磷酸盐在高频区的非桥氧对称伸缩振动的特征谱峰。结果表明SIT值与相应结构特征谱峰的拉曼位移呈良好相关性。采用高温拉曼光谱仪测定了Na₅P₃O₁₀固态及熔体的变温拉曼光谱,观察到了Na₅P₃O₁₀在873～1 073 K间的相变。Na₅P₃O₁₀晶体的微结构单元为Q2₁与Q11₂, 其理论含量比例为2∶1。随着温度升高,Na₅P₃O₁₀的主要峰包中心向低频移动,熔融后体系中出现了Q₀,Q1₁,Q2₁,Q11₂,Q12₂,Q22₂等多种精细结构单元,导致其拉曼光谱的展宽与不对称性的出现。这些概念的建立和运用为磷酸盐熔体及玻璃的拉曼光谱的定量分析奠定了基础。     

Submillimeter wave photoconductivity observation of shallow donors in In0.53Ga0.47As

The hydrogen like 1s 2p (m=–1,0,+1) transitions of two donors have been observed in high intensity magnetic fields up to 8.5T. The m=–1 transitions ocurred between 2 cm^–1 and 25 cm^–1. The signature curves for donors in ternary semiconductor In_0.53Ga_0.47As have now been established.Work supported by the U.s. Air Force Office of Scientific Research under Contract # AFOSR-78-3708-DSupported by the National Science Foundation     

荧光法测定镧原子高激发态的超精细结构

在Ｌａ空心阴极灯中，用荧光法测定了二级跃迁（１６８５６ｃｍ＾－１→３４２７２ｃｍ＾－１），（２００８２ｃｍ＾－１→２６８５３ｃｍ＾－１）和（２００８２ｃｍ＾－１→３７５４４ｃｍ＾－１）的超精细结构光谱，得到了３４２７２ｃｍ＾－１，３６８５３ｃｍ＾－１和３７５４４ｃｍ＾－１能级的Ａ常数，这些镧原子高激发态超精细结构数据是首次报道。     

Hyperfine Interactions of 181Ta in Zr2Ni Observed Using PAC Spectroscopy

We have measured nuclear electric–quadrupole interactions (EQI) at ¹⁸¹Ta impurities substituted as Hf atoms into the Zr site in Zr₂Ni. Using perturbed-angular-correlation (PAC) spectroscopy, we measured the EQI over temperatures ranging from 10 to 1200 K. Over the entire range of temperature, the Zr₂Ni crystal has a bct Al₂Cu structure that includes a single Zr site. The crystal field symmetry surrounding this site is rather low, giving rise to a highly asymmetric electric-field gradient tensor. At 10 K, the EQI is characterized by an angular frequency ω₀=601(3) Mrad s⁻¹, and an asymmetry parameter η=0.835(2). At 1200 K, ω₀ decreases to 516(3) Mrad s⁻¹, and η also decreases to 0.790(4). Although weak, the temperature dependence of ω₀ is consistent with a (1−BT ^3/2) power law, in which B=6×10⁻⁶ K^−3/2. The EQI also manifests a very narrow linewidth. We observed no evidence either for magnetic ordering or for structural phase transitions in the temperature range covered by this experiment. Moreover, the sharpness of the EQI indicates that the samples as prepared are remarkably free of strain and defects. These results indicate that the Zr₂Ni structure does not promote the formation of defects and that the power-law dependence of ω₀ on T is insensitive to the asymmetric nature of the crystal. This revised version was published online in September 2006 with corrections to the Cover Date.     

基于拉曼光谱-模式识别方法对奶粉进行真伪鉴别和掺伪分析

奶粉的真伪和掺伪近年来受到广泛的关注,研究一种操作便捷,能准确、快速、全面鉴定奶粉品牌并实现奶粉掺假鉴别的新方法对于奶粉的质量控制具有重要的意义。为实现奶粉的真伪鉴别,采集三种品牌奶粉贝因美、飞鹤和雀巢的拉曼光谱,并利用拉曼谱图特征峰结合最近邻算法(nearest neighbor,NN)的模型对三种品牌奶粉进行识别,在10次交叉验证的基础上,平均识别率为99.56%。为实现奶粉的掺伪分析,将飞鹤奶粉与雀巢奶粉按不同质量比(0∶1,1∶3,1∶1,3∶1,1∶0)混合成五种掺伪奶粉,提取掺伪奶粉中的脂肪,采集脂肪样本的拉曼光谱,分别使用拉曼谱图特征峰结最近邻算法的模型和核主成分分析(kernel principal components analysis,KPCA)结合最近邻算法的模型对五种脂肪样本进行识别,10次交叉验证下的平均识别率分别为93.33%和98.89%,平均运算时间分别为0.085和0.104 s。实验证明：特征峰结合NN的算法可以快速实现对奶粉真伪的判别,但此算法不能很好的区分掺伪奶粉;拉曼光谱-KPCA-NN模型可以为奶粉的掺伪检测提供一种简便、准确、快速的方法。     

不同溶胶体系对纳米氧化锌发光特性的影响

采用溶胶-凝胶工艺制备ZnO纳米粉体,研究了两种不同溶剂下制备的纳米ZnO的荧光特性。实验结果表明两种氧化锌样品有相同的晶型和能带结构,其紫外发光相似,但其带间的可见发射表现出了巨大差异,其原因在于两溶剂的极性不同导致两体系凝胶、烧结的微过程不同,从而使两种ZnO样品的表面态结构和布局发生变化。     

Estimation of Conduction as Well as Donor Electron Density Through Far-Infrared Resonant Faraday Effect

We have investigated resonant Faraday effect (RFE), so-called nonlinear Faraday effect, caused by conduction and donor electrons in n-InSb and n-GaAs. Experiments were carried out with using the magneto-optical spectroscopic system combined with two linear polarizers put in before and behind a sample. The rotation angle and the ellipticity for the far-infrared light with elliptical polarization transmitted through the sample were analyzed on the basis of spectra obtained under different experimental configuration for angles between the axes of the polarizer and the analyzer. We have observed some characteristic features associated with RFE in spectra of two samples. Tapping into these features, we could successfully determine the relaxation times and the densities of conduction and donor electrons in the semiconductors.     

显微红外反射光谱法快速鉴别珍珠粉真伪

珍珠是名贵的装饰品和中药材,在我国对其已有2000多年的应用历史。研究发现,贝壳内层的化学组成与珍珠相似,主要含有碳酸钙和各种氨基酸。贝壳粉也可在临床上做药用,但其药用价值远低于珍珠粉。然而,珍珠粉和贝壳粉外观特性极为相似,元素组成和形貌检测无法对其进行有效地鉴别。由于贝壳粉的成本低,常常冒充珍珠粉流入市场,侵害了消费者的利益。本研究通过珍珠粉和贝壳粉在不同温度下煅烧一定时间后显微红外反射光谱的差异实现珍珠粉真伪鉴别。实验结果表明,在一个大气压下经过400 ℃煅烧30 min后,珍珠粉中文石型碳酸钙部分转化为方解石型,而贝壳粉中文石型碳酸钙完全转化为方解石型。这种不同的相转变过程可以被显微红外反射光谱很好的区别。因此,可在此条件下利用红外反射光谱鉴别珍珠粉和贝壳粉相变差异。和传统的透射式红外光谱法相比,这种显微反射红外光谱法无需压片制样、快速灵敏。本研究也讨论了该方法针对其他常见伪品的适用性,如牡蛎粉和石决明粉,结果表明该方法能够简单、高效和准确地鉴别珍珠粉真伪。