Design, Fabrication, and Measurement of Two-Dimensional Photonic Crystal Slab Waveguides

Two-dimensional photonic crystal slab waveguides on SOI wafer are designed and fabricated. Photonic band gap, band gap guided mode, and index guided mode are observed by measuring the transmission spectra. The experimental results are in good agreement with the theoretical ones.     

Graphite nanosheets doped with Fe, Ni, and N, synthesized in one step, and their unique magnetic performance

Graphite nanosheets (GNs) doped with N, Fe, or Ni were synthesized by pyrolysis of metal tetrapyridinoporphyrazine (MPTpz, M=Fe²⁺, and Ni²⁺) and a mixture of MPTpzs in a chemical vapor deposition furnace. The products obtained were characterized by scanning and transmission electron microscopy, and X-ray photoelectron spectroscopy. The magnetic properties of the GNs obtained were investigated at room temperature using a vibrating sample magnetometer with an applied field of −10 000-10 000 Gs. The results show the GNs obtained are terrace-like and ultra-thin, with very high aspect ratio. Fe, Ni and N atoms have been doped to the GNs successfully. There are two types of N atom that are introduced into pure carbon systems: pyrinidic and graphitic N atoms. The GNs obtained exhibit ferromagnetic behavior at room temperature. Sample S1, obtained by pyrolysis of a mixture of MPTpzs (M=Fe²⁺ and Ni²⁺), have the highest coercivity force. The saturation magnetization (M_s), remanent magnetization (M_r), and coercivity (H_c) values of sample S1 are 24.51 emu g⁻¹, 3.95 emu g⁻¹, and 207.34 Gs, respectively.     

Duality, phase structures, and dilemmas in symmetric quantum games

Symmetric quantum games for 2-player, 2-qubit strategies are analyzed in detail by using a scheme in which all pure states in the 2-qubit Hilbert space are utilized for strategies. We consider two different types of symmetric games exemplified by the familiar games, the Battle of the Sexes (BoS) and the Prisoners’ Dilemma (PD). These two types of symmetric games are shown to be related by a duality map, which ensures that they share common phase structures with respect to the equilibria of the strategies. We find eight distinct phase structures possible for the symmetric games, which are determined by the classical payoff matrices from which the quantum games are defined. We also discuss the possibility of resolving the dilemmas in the classical BoS, PD, and the Stag Hunt (SH) game based on the phase structures obtained in the quantum games. It is observed that quantization cannot resolve the dilemma fully for the BoS, while it generically can for the PD and SH if appropriate correlations for the strategies of the players are provided.     

Growth of thin, crystalline oxide, nitride, and oxynitride films on NiAl and CoGa surfaces

At 300 K, an amorphous Al-oxide film is formed on NiAl(001) upon oxygen adsorption. Annealing of the oxygen-saturated NiAl(001) surface to 1200 K leads to the formation of thin well-ordered θ-Al₂O₃ films. At 300 K, and low-exposure oxygen atoms are chemisorbed on CoGa(001) on defects and on step edges of the terraces. For higher exposure up to saturation, the adsorption of oxygen leads to the formation of an amorphous Ga-oxide film. The EEL spectrum of the amorphous film exhibits two losses at ≈400 and 690 cm^-1. After annealing the amorphous Ga-oxide films to 550 K thin, well-ordered β-Ga₂O₃ films are formed on top of the CoGa(001) surface. The EEL spectrum of the β-Ga₂O₃ films show strong Fuchs-Kliewer (FK) modes at 305, 455, 645, and 785 cm^-1. The β-Ga₂O₃ films are well ordered and show (2×1) LEED pattern with two domains, oriented perpendicular to each other. The STM study confirms the two domains structure and allows the determination of the two-dimensional lattice parameters of β-Ga₂O₃. The vibrational properties and the structure of β-Ga₂O₃ on CoGa(001) and θ-Al₂O₃ on NiAl(001) are very similar. Ammonia adsorption at 80 K on NiAl(111) and NiAl(001) and subsequent thermal decomposition at elevated temperatures leads to the formation of AlN. Well-ordered and homogeneous AlN thin films can be prepared by several cycles of ammonia adsorption and annealing to 1250 K. The films render a distinct LEED pattern with hexagonal [AlN/NiAl(111)] or pseudo-twelve-fold [AlN/NiAl(001)] symmetry. The lattice constant of the grown AlN film is determined to be a_AlN= 3.11 Å. EEL spectra of AlN films show a FK phonon at 865 cm^-1. The electronic gap is determined to be E_g= 6.1±0.2 eV. GaN films are prepared by using the same procedure on the (001) and (111) surfaces of CoGa. The films are characterized by a FK phonon at 695 cm^-1 and an electronic band gap E_g= 3.5±0.2 eV. NO adsorption at 75 K on NiAl(001) and subsequent annealing to 1200 K leads to the formation of aluminium oxynitride (AlON). An oxygen to nitrogen atomic ratio of ≈2:1 was estimated from the analysis of AES spectra. The AlON films shows a distinct (2×1) LEED pattern and the EEL spectrum exhibits characteristic Fuchs-Kliewer modes. The energy gap is determined to be E_g= 6.6±0.2 eV. The structure of the AlON film is derived from that of θ-Al₂O₃ formed on NiAl(001). Received: 21 March 1997/Accepted: 12 August 1997     

Self-similarity, small-world, scale-free scaling, disassortativity, and robustness in hierarchical lattices

In this paper, firstly, we study analytically the topological features of a family of hierarchical lattices (HLs) from the view point of complex networks. We derive some basic properties of HLs controlled by a parameter q: scale-free degree distribution with exponent γ=2+ln 2/(ln q), null clustering coefficient, power-law behavior of grid coefficient, exponential growth of average path length (non-small-world), fractal scaling with dimension d_B=ln (2q)/(ln 2), and disassortativity. Our results show that scale-free networks are not always small-world, and support the conjecture that self-similar scale-free networks are not assortative. Secondly, we define a deterministic family of graphs called small-world hierarchical lattices (SWHLs). Our construction preserves the structure of hierarchical lattices, including its degree distribution, fractal architecture, clustering coefficient, while the small-world phenomenon arises. Finally, the dynamical processes of intentional attacks and collective synchronization are studied and the comparisons between HLs and Barabási-Albert (BA) networks as well as SWHLs are shown. We find that the self-similar property of HLs and SWHLs significantly increases the robustness of such networks against targeted damage on hubs, as compared to the very vulnerable non fractal BA networks, and that HLs have poorer synchronizability than their counterparts SWHLs and BA networks. We show that degree distribution of scale-free networks does not suffice to characterize their synchronizability, and that networks with smaller average path length are not always easier to synchronize.     

Optical phonon frequencies and damping in AlAs, GaP, GaAs, InP, InAs and InSb studied by oblique incidence infrared spectroscopy

The transverse (TO) and longitudinal (LO) optical phonons in AlAs, GaP, GaAs, InP, InAs and InSb have been measured at room temperature by infrared spectroscopy using an oblique incidence reflectance method. The spectra obtained were then fitted using a novel approach to determine the TO and LO phonon frequencies and damping. The results obtained are found to be more precise than in earlier reflectivity measurements using near-normal angles of incidence and provide information on the damping of both phonons. Apart from the GaAs LO mode, the observed damping parameters are found to be quite different from those predicted by theory. From these results the Lowndes condition governing the relative magnitudes of the TO and LO phonon line widths is found to be violated for all these zincblende semiconductors.     

Synthesis, integration, and electrical properties of individual single-walled carbon nanotubes

High-quality single-walled carbon nanotubes (SWNTs) are synthesized by chemical vapor deposition (CVD) of methane on silicon-dioxide substrates at controlled locations using patterned catalytic islands. With the synthesized nanotube chips, microfabrication techniques are used to reliably contact individual SWNTs and obtain low contact resistance. The combined chemical synthesis and microfabrication approaches enable systematic characterization of electron transport properties of a large number of individual SWNTs. Results of electrical properties of representative semiconducting and metallic SWNTs are presented. The lowest two-terminal resistance for individual metallic SWNTs (≈5 μm long) is ≈16.5 kΩ measured at 4.2 K. Received: 17 May 1999 / Accepted: 18 May 1999 / Published online: 14 July 1999     

Nonlinear-Ion-Acoustic-Wave Instability, Threshold, Half Width of Trapped Region and Transition Region

Nonlinear Landau damping of ion acoustic wave (IAW) is one of the most important phenomena in the ionosphere and in space and laboratory plasma as well. The instability growth rate of the IAW with electron drift, the amplitude threshold for exciting the nonlinear effects, the half widths of the trapped region with the trapped electrons are studied experimentally. Under the experimental conditions, it is shown that there is a frequency range of 140--160 kHz, within which the growth rate has the largest value of about 6×10⁴--1.5×10⁵ s^-1. We obtain the transitional region width caused by collisions theoretically and experimentally, for the first time to our knowledge. The experimental results are in good agreement with the theoretical prediction.     

Structural, elastic and electronic properties of transition metal carbides TMC (TM=Ti, Zr, Hf and Ta) from first-principles calculations

The structural, elastic and electronic properties of TiC, ZrC, HfC and TaC have been investigated by first-principles calculations using the plane-wave pseudopotential method. Different exchange-correlation functionals regarding the local density approximation and the PBE, RPBE and PW91 forms of generalized gradient approximation are taken into account. The NaCl-type cubic structures of TMC (TM=Ti, Zr, Hf and Ta) are optimized and confirmed to be mechanically stable. The elastic properties such as the elastic constants, bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio of TMC are investigated, and the performances of LDA and GGA are discussed. The electronic density of state, electron charge density and Mulliken population analysis have been explored to discuss the electronic properties and bonding behaviors of TMC. The present calculation results compare satisfactorily with the experimental data and previous theoretical calculations.     

Spectroscopic studies of laser-produced plasmas formed in CO and CO2 using 193, 266, 355, 532 and 1064 nm laser radiation

The wavelength dependence of laser-produced breakdown in air, CO and CO₂ has been studied using the four Nd:YAG harmonics (266 nm, 355 nm, 532 nm and 1064 nm) and the ArF-excimer laser (193 nm). Breakdown thresholds at these wavelengths are reported for air, CO and CO₂. A significant reduction in the breakdown thresholds for both CO and CO₂ is apparent when comparing 193 nm with the four Nd:YAG harmonics. This reduction is attributed to the resonance-enhanced two-photon ionization of metastable carbon atoms generated in the laser focus at the ArF-laser wavelength. In addition to reporting breakdown thresholds, the laser-produced plasmas in CO and CO₂ are characterized in terms of plasma temperatures and electron densities which are measured by time-resolved emission spectroscopy. Electron densities range from 9 × 10¹⁷ cm^–3 to 1 × 10₁₇ cm^–3. Excitation temperatures range from 22 000 K at 0.2 µs to 11 000 K at 2 µs. Ionization temperatures range from 22 000 K at 0.1 µs to 16 000 K at 2 µs. Evidence is presented to indicate that, like ArF-laser-produced plasmas, Nd:YAG-laser-produced plasmas formed in CO and CO₂ are in or near a state of Local Thermodynamic Equilibrium (LTE) soon after their formation.     

A comparison of hydrogen incorporation and effusion in doped crystalline silicon,germanium, and gallium arsenide

The incorporation of deuterium into crystalline silicon, germanium, and gallium arsenide from a plasma source is investigated as a function of sample temperature during the plasma treatment. The total amount of incorporated deuterium and its bonding states are characterized by the thermal effusion (TE) technique for different dopants and doping levels. In all samples investigated, we find a strong influence of the passivation temperature on these quantities; however, there are large differences between different semiconductors and for different doping levels or dopants. The results are discussed in terms of plasma-induced defects, dopant-deuterium complexes, and surface effects.Dedicated to H.-J. Queisser on the occasion of his 60th birthday     

Ab-initio investigation of electronic properties and magnetism of half-Heusler alloys XCrAl (X=Fe, Co, Ni) and NiCrZ (Z=Al, Ga, In)

The electronic structures and magnetism of the half-Heusler alloys XCrAl (X=Fe, Co, Ni) and NiCrZ (Z=Al, Ga, In) have been investigated to search for new candidate half-metallic materials. Here, we predict that NiCrAl, and NiCrGa and NiCrIn are possible half-metals with an energy gap in the minority spin and a completely spin polarization at the Fermi level. The energy gap can be attributed to the covalent hybridization between the d states of the Ni and Cr atoms, which leads to the formation of bonding and antibonding peaks with a gap in between them. Their total magnetic moments are 1μ_B per unit cell; agree with the Slater-Pauling rule. The partial moment of Cr is largest in NiCrZ alloys and moments of Ni and Al are in antiferromagnetic alignment with Cr. Meanwhile, it is also found that FeCrAl is a normal ferromagnetic metal with a magnetic moment of 0.25μ_B per unit cell and CoCrAl is a semi-metal and non-magnetic.     

Iodine hyperfine structure and absolute frequency measurements at 565, 576, and 585 nm

The hyperfine structure splittings of the P(10)14-1, R(15)14-1, and R(99)15-1 transitions at 585 nm, P(62)17-1 at 576 nm, and P(80)21-1 at 565 nm in ¹²⁷I₂ are measured by heterodyne spectroscopy using two dye lasers. In addition, the absolute frequencies of the hyperfine components P(10)14-1 a₁₅ and P(80)21-1 a₁₀ are determined using a self-referenced frequency comb. These frequencies are used in an experiment testing relativistic time dilation by laser spectroscopy on a fast ion beam.     

Theoretical study of resonant tunneling in rectangular double-, triple-, quadruple-, and quintuple-barrier structures

The transmission coefficient and the resonance condition in the one-dimensional rectangular double-, triple-, quadruple-, and quintuple-barrier structures are derived theoretically under the assumption of the constant tunneling effective mass. It is found that the resonance energies are different from the eigenvalues in the quantum well due to coupling between wells in the multiple-barrier (much more than triple-barrier) structures. It is confirmed that the transmission spectrum is a Lorentzian near to energies of resonance.     

Combined raman elastic-backscatter LIDAR for vertical profiling of moisture,aerosol extinction,backscatter, and LIDAR ratio

A combined Raman elastic-backscatter lidar has been developed. A XeCl excimer laser is used as the radiation source. Inelastic Raman backscatter signals are spectrally separated from the elastic signal with a filter or grating polychromator. Raman channels can be chosen to register signals from CO₂, O₂, N₂, and H₂O. Algorithms for the calculation of the water-vapor mixing ratio from the Raman signals and the particle extinction and backscatter coefficients from both elastic and inelastic backscatter signals are given. Nighttime measurements of the vertical humidity distribution up to the tropopause and of particle extinction, backscatter, and lidar ratio profiles in the boundary layer, in high-altitude water and ice clouds, and in the stratospheric aerosol layer are presented. Daytime boundary-layer measurements of moisture and particle extinction are made possible by the improved daylight suppression of the grating polychromator. Test measurements of the CO₂ mixing ratio indicate the problems for the Raman lidar technique in monitoring other trace gases than water vapor.     

First-principles study on the crystal, electronic structure and mechanical properties of hexagonal Al3RE (RE = La, Ce, Pr, Nd, Sm, Gd) intermetallic compounds

The structural properties, elastic properties and electronic structures of hexagonal Al₃RE intermetallic compounds are calculated by using first-principles calculations based on density functional theory. Since there exists strong on-site Coulomb repulsion between the highly localized 4f electrons of RE atoms, we present a combination of the GGA and the LSDA+U approaches in order to obtain the appropriate results. The GGA calculated lattice constants for the hexagonal Al₃RE intermetallic compounds are in good agreement with available experimental values. The results of cohesive energy indicate that these compounds can be stable under absolute zero Kelvin and the stability of Al₃Gd is the strongest in all of the hexagonal Al₃RE compounds. The densities of states for GGA and LSDA+U approaches are also obtained for the Al₃RE intermetallic compounds. The mechanical properties are calculated from the GGA method in this paper. According to the computed single crystal elastic constants, Al₃La, Al₃Sm and Al₃Gd are mechanically unstable, while Al₃Ce, Al₃Pr and Al₃Nd are stable. The polycrystalline elastic modulus and Poisson’s ratio have been deduced by using Voigt-Reuss-Hill (VRH) approximations, and the calculated ratio of bulk modulus to shear modulus indicates that Al₃La compound is ductile material, but Al₃Ce, Al₃Pr, Al₃Nd, Al₃Sm and Al₃Gd are brittle materials.     

Thermal properties and structures of chlorocadmate, bromocadmate, and bromochlorocadmate glasses

Glass transition temperatures (T_g), crystallization temperatures (T_x), and ¹¹³Cd magic-angle spinning (MAS) NMR spectra of the chlorocadmate, bromocadmate, and bromochlorocadmate glasses and the CdCl₂, CdBrCl, and CdBr₂ crystals have been measured. The T_g and T_x, and thermal stabilities (T_x−T_g) decreased with increasing Br-content. No enhancement of (T_x−T_g) of bromochlorocadmate glasses by anion-mixing was observed. The CdCl₂ and CdBr₂ crystals gave the isotropic chemical shifts of 183 and −24 ppm, which are assigned to the CdCl₆ and CdBr₆ octahedra, respectively. The isotropic chemical shifts of CdBrCl crystal (186, 166, 135, 101, 63, 25 and −21 ppm) were assigned to CdBr_nCl_(6−n) (n=0-6) octahedra, respectively. It was found that the Br and Cl atoms in CdBrCl randomly occupy chlorine sites in the CdCl₂ structure. The ¹¹³Cd MAS NMR spectra revealed that the chlorocadmate, bromocadmate, and bromochlorocadmate glasses are composed of the CdCl₆, CdBr₆ and CdBr_nCl_(6−n) octahedra (n=0-6), respectively, and that the Cd²⁺ in all the bromochlorocadmate glasses was more preferentially bonded to Br⁻ than Cl⁻. The relationship between the thermal properties and the anion coordination environments around Cd²⁺ in these glasses is discussed.     

Gas flow sputtering: Versatile process for the growth of nanopillars, nanoparticles, and epitaxial thin films

Gas flow sputtering is a sputter-deposition method that enables soft and high-rate deposition even for oxides or nitrides. It involves sputtering at a high pressure of around 100 Pa and hollow cathode discharge in a tubular or parallel plate target with forced Ar flow. Depending on the sputtering conditions, various structures of magnetic materials are obtained, and some examples are shown in this paper. Co-Pt and Fe nanopillars are fabricated using a tubular target with a large inner diameter (6-40 mm). Fe nanoparticles with diameters ranging from a few nanometers to 150 nm are fabricated using a tubular target with a small inner diameter (5 mm). Magnetite epitaxial thin films are fabricated on MgO and GaAs substrates by substrate heating.     

Electronic structure,phase stability,and vibrational properties of Ir-based intermetallic compound IrX (X=Al,Sc, and Ga)

The phase stability and mechanical properties of B2 type IrX (X=Al, Sc and Ga) compounds are investigated. Self-consistenttotal-energy calculations in the framework of density functional theory using the Generalized Gradient Approximation (GGA) to determine the equations of state and the elastic constants of IrX (X=Al, Sc, and Ga) in the B2 phase have been performed. The calculations predicted the equilibrium lattice constants, which are about 1% greater than experiments for IrAl, 1.81% for IrGa, and 0.71% for IrSc compound. IrAl is shown to be the least compressible, and it is followed by IrGa and the IrSc compound. The phase stability of the studied compounds is checked. The brittleness and ductility properties of IrX (X=Al, Sc, and Ga) are determined by Poisson's ratio σ criterion and Pugh's criterion. IrGa compound is a ductile material; however, IrAl and IrSc show brittleness. The band structure and density of states (DOS), and phonon dispersion curves have been obtained and analyzed. The position of the Fermi level and the contribution of d electrons to the density of states near E_F is studied and discussed in detail. We also used the phonon density of states and quasiharmonic approximation to calculate and predict some thermodynamic properties such as constant-volume specific heat capacity of the B2 phase of IrX (X=Al, Sc and Ga) compounds.