我们分别于1955年和1957年考入东北人民大学(后改名为吉林大学)物理系学习,后来又分别于1960年和1962年与曾琴,黄和鸾,邹广田和杨克大成为芶清泉老师固体物理研究方向的研究生.虽然毕业后,我们两人的科学研究方向偏离了原子分子物理和高压物理,但是在本科和研究生阶段与芶老师近距离的学习和研讨中,以及毕业后对物理前沿问题的交流中,对芶老师后期的科学研究思路和成果有进一步的较深入的了解和体会,在纪念芶老师诞辰一百周年之际,表达我们对芶老师的崇敬和感恩之情.

Titanium oxide ceramics doped with niobium is synthesized in reduced atmosphere at 1200 degrees C by conventional solid-state reaction technique. From their crystal structures determined by the powder X-ray diffraction (XRD), the samples have multiple-phase with low Nb concentration, but they have single tetragonal rutile phase when Nb content is larger than 0.02. The electrical conductivities, the Seebeck coefficients and the thermal conductivities of the samples with single phase are measured at a temperature range between room temperature and 900 K. The electrical conductivity and the Seebeck coefficient show non-metallic behaviors. According to the fitting, it is found that the samples show thermal-activation mechanism at low temperatures and small-polaron hopping conduction mechanism at high temperatures. Moreover, the analyses of XRD, electrical conductivity and Seebeck coefficient show that the concentration of oxygen vacancy decreases with Nb content increasing. Thermal conductivity decreases with temperature increasing, dominating by lattice thermal conductivity. In the measurement region, the figure of merit (ZT) reaches a highest value of 0.19 at 873 K in the Ti(0.98)Nb(0.02)O(2-delta) sample.

本文综述了重大研究计划"理论物理学及其交叉科学若干前沿问题"实施8年来所取得的成绩。列举了参加成员的创新成果和对解决核心科学问题的贡献。

This paper proposes a universal spin-dependent variable range hopping theoretical model to describe various experimental transport phenomena observed in wide-band-gap oxide ferromagnetic semiconductors with high transition metal concentration.The contributions of the ’hard gap’ energy,Coulomb interaction,correlation energy,and exchange interaction to the electrical transport are considered in the universal variable range hopping theoretical model.By fitting the temperature and magnetic field dependence of the experimental sheet resistance to the theoretical model,the spin polarization ratio of electrical carriers near the Fermi level and interactions between electrical carriers can be obtained.

We carried out first-principles calculations to explore the oxidative longitudinal unzipping of single-walled carbon nanotubes (SWCNTs) of different diameters and chiralities. We found that the initial attack leading to nanotube unzipping prefers to occur in the middle region for armchair tubes, and at the tube ends for zigzag tubes. Once the initial attack has taken place, by overcoming an energy barrier whose value decreases with increasing tube diameter, the subsequent breakage of C-C bonds parallel to the ones broken in the former process is barrierless. The energetically preferred unzipping path is parallel to the tube axis for armchair tubes, resulting in straight zigzag-edged graphene nanoribbons. For zigzag tubes, there are two energetically equivalent unzipping directions corresponding to the opening of two types of C-C bonds tilted towards the tube axis, giving rise to helical unzipping paths. This is disadvantageous for the production of straight graphene ribbons. A local curvature modulation procedure is proposed to efficiently control the location of the initial attack and thus the shape of the produced graphene nanoribbons.

Amorphous GaN (a-GaN) films on Si (111) substrates have been deposited by RF magnetron sputtering with GaN powder target. The growth process from amorphous GaN to polycrystalline GaN is studied by XRD, SEM, PL and Raman. XRD data mean that annealing under flowing ammonia at 850–950°C for 10min converts a-GaN into polycrystalline GaN (p-GaN). The growth mechanism can be mostly reaction process through N3− in amorphous GaN replaced by N3− of NH3. Annealing at 1000°C, the appearance of GaN nanowires can be understood based on the vapor–liquid–solid (VLS) mechanism. In addition, XRD, PL and Raman measurement results indicate that the quality of GaN films increases with increasing temperature. The tensile stress in the films obtained at 1000°C is attributable to the expansion mismatch between GaN and Si, with the gallium in the film playing a negligible role.

We perform first-principle calculations to study the geometric and electronic structures of cobalt silicide (CoSi2) nanosheet and nanotubes. The structure of layered CoSi2 is characterized by a CoSi2 nanosheet, analogous to the (111) surface of CoSi2 crystal. The strain energy involved in rolling up a CoSi2 nanosheet to CoSi2 nanotubes is very low. Both the CoSi2 nanosheet and nanotubes are energetically stable. CoSi2 nanotubes prefer to form bundles to further release strain energy. All CoSi2 nanotubes exhibit uniformly metallicity and steady work functions, independent of tube chirality.

The band structure and equi-frequency contours for the holographical photonic crystals (PhCs) were calculated by using plane wave extension method, and the conditions for negative refraction in PhCs were analyzed as well as the frequency band. The finite-difference time-domain method was used to verify the conclusion, and it is shown that negative refraction can be clearly observed in the holographical PhCs within a wide frequency band and a large incident angle scope. The research on the negative refraction in holographical PhCs will provide a new idea for the design and fabrication of the left-handed negative-index materials.

The possibility of forming cascading energy levels in SrTiO 3 by doping Bi and Cu as an example is analyzed by using the density-functional-theory based first principles calculations of the electronic structure. The results show that both Bi doping and Cu doping can introduce a defect level in the forbidden band，and Co-doping of Bi and Cu can introduce two defect levels in the forbidden band. Electrons at the top of valence band can transit to the bottom of conduction band through a cascade transition process. Using the nonradiative transition model，we point out that the probability of electronic transition from the valence band to the conduction band through a cascade transition is much higher than that of direct transition from the valence band to the conduction band. The cascade transitions can effectively increase the carrier concentration in the conduction band.

Centerline of nose is extracted by Hessian matrix parameters to segment the matched region.Direction of gradient and eigenvector corresponding to the largest eigenvalue are combined to detect nose pore.The proposed method achieves an identification correct rate of 88.07% on a database of 103 persons.The experimental results show that nose pore feature can be used as one of the most efficient biometric features in recognition.

Hydrogen interstitials-mediated ferromagnetism in MnxGe1-x magnetic semiconductors was studied by first-principles calculations. It was found that the H:1s state in Mn–H–Mn complexes can strongly hybridize with the valence states of Mn and change the spin polarization of Mn atoms. Although the doped Mn atoms tend to form the nearest-neighbor Mn atomic pairs with antiferromagnetic coupling in Mn-doped Ge without H, the asymmetrical configurations of Mn–H–Mn complexes show the ferromagnetic (FM) ground state in Mn-doped Ge with H interstitials. Therefore, Mn-doped Ge with H interstitials is predicted to be an FM semiconductor with higher Curie temperature and larger magnetization than Mn-doped Ge without H.

A four channel photonic crystal filter is designed using 2-D photonic crystal.The condition of achieving 100% channel coupling is educed using CMT(coupling mode theory).Four-channel filter is designed based on the condition,and results are simulated using FDTD(finite difference time domain).The coupling efficiency of every channel is higher than 96% from simulation results.Frequency of the four-channel is from 1520 nm to 1 580 nm when lattice constant is 570 nm,and interval of every channel is less than 20 nm.The crosstalk interference of every channel is very small.

<span id="ChDivSummary" name="ChDivSummary" class="abstract-text">利用电子显微分析技术对高Co含量的室温铁磁性半导体Zn_1-xCo_xO_1-δ进行了微观表征.证明了氧含量是决定Zn_1-xCo_xO_1-δ薄膜微观结构和磁性能的重要因素.在缺氧环境下,薄膜由含有大量氧缺位的纤锌矿结构的Zn_1-xCo_xO_1-δ纳米晶（直径约5 nm）和填充其间的Zn-Co-O非晶相组成,两相对薄膜宏观磁性均有贡献;在富氧的环境下,非晶Zn-Co-O相消失,出现了CoO反铁磁相,纤锌矿结构Zn_1-xCo_xO_1-δ中的氧缺位大量减少,晶粒长大到10—20 nm,室温铁磁性逐渐减弱,直至消失.</span>

We performed spin-polarized density functional calculations to study the stable configurations, energetics and electronic structures of Co-doped single-walled silicon nanotubes (CoSi2NTs) with the stoichiometry of CoSi2. We found that the incorporation of Co atoms into the wall of SiNTs not only effectively stabilizes the tubes but also tunes their electronic properties. The formation energies of the CoSi2NTs are much lower than those of pristine SiNTs, indicating the plausibility of these tubes. The electronic structures of the CoSi2NTs display the characters of metals. This provides a promising synthetic route to stable SiNTs which may find potential applications in building nanoscale devices.

Fe/In2O3 granular films have been prepared by RF sputtering method.The susceptibility measurements manifest that the blocking temperature is 50 K.At a certain freezing temperature Tf about 10 K,the film transits from ferromagnetic state to particle-spin-cluster state.A maximum GMR ratio up to 506% is obtained at the metal-semiconductor transition temperature about 2.2 K.The mechanism of this GMR is related to the interaction with the impurities influencing the local magnetization,which is quite different to spin-dependent tunneling effect at room temperature.The magnetic field aligns the particle-spin-clusters and increases the mobility of the electron's hopping between these clusters which causes the magnetoresistance effect to increase significantly.

We investigate the variations from as-deposited Zn1−xCoxO magnetic semiconductors to the post-annealed Co–ZnCoO granular composite. The as-deposited Zn1−xCoxO magnetic semiconductor deposited under thermal non-equilibrium conditions is composed of Zn1−xCoxO nanograins of high Co concentration. The room-temperature ferromagnetism with high magnetization and large negative magnetoresistance are found in the as-deposited samples. By annealing, the samples become of granular composite consisting of the Co metal grains and the remanent Zn1−xCoxO matrix. Although the magnetization is enhanced after annealing, the spin-dependent negative magnetoresistance disappears at room temperature. The magnetoresistance observed in the annealed samples in the high field region has no relation with the ferromagnetism, which in turn indicates that the room-temperature ferromagnetism and large negative magnetoresistance observed in the as-deposited are the intrinsic properties of the Zn1−xCoxO magnetic semiconductor.

The finite-difference time-domain (FDTD) method was introduced into the simulation of the physics phenomena of the negative refractive index materials (NIM).The numerical formulation of the FDTD method for TM wave in the NIM materials was presented,and the perfectly matched layer (PML) was used in the absorption boundary condition.The Drude model was introduced,in order to avoid instability of the leapfrog in time domain,and the perfect lens phenomenon proposed by Pendry was simulated.The simulation results show the perfect lens only occur when the nslab=-1,otherwise,the paraxial focusing of the wave energy occurs.

研究了制备态和退火态Zn1-xCoxO非匀质磁性半导体的极向克尔谱,发现通过调制样品成分和退火处理,可以大幅度调制极向克尔谱。退火后样品的磁光克尔旋转角得到显著增强,克尔角最大值达到0．72°,这是由于退火后样品变成了Co颗粒和Zn1-xCoxO磁性半导体的纳米复合体系。

High quality Co-doped ZnO thin films are grown on single crystalline Al2O3(0001) and ZnO(0001) substrates by oxygen plasma assisted molecular beam epitaxy at a relatively lower substrate temperature of 450°C. The epitaxial conditions are examined with in-situ reflection high energy electron diffraction (RHEED) and ex-situ high resolution x-ray diffraction (HRXRD). The epitaxial thin films are single crystal at film thickness smaller than 500 nm and nominal concentration of Co dopant up to 20%. It is indicated that the Co cation is incorporated into the ZnO matrix as Co2+ substituting Zn2+ ions. Atomic force microscopy shows smooth surfaces with rms roughness of 1.9 nm. Room-temperature magnetization measurements reveal that the Co-doped ZnO thin films are ferromagnetic with Curie temperatures TC above room temperature.