The lattice deformation and the energy of antiphase boundaries in Fe-Si alloys

The lattice deformation across the antiphase boundary and the energy of both types (a/2111 anda(100) of antiphase boundaries lying in {110} plane are calculated using a series of three interatomic potentials fitted to experimental data. It is shown that the relaxation of atomic planes in the vicinity of antiphase boundary is important for thea/2111 antiphase boundary and is negligible for a 100 antiphase boundary in the DO₃ structure.The author is grateful to Dr. F.Kroupa and to Dr. A.Gemperle for valuable discussions.     

Effect of bias field on the dielectric properties of 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 single crystals with different orientations

Microdomain-macrodomain transformations and phase transitions in 0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ single crystals were investigated by studying their relative permittivity under various dc bias at constant heating and cooling rates. The orientation dependence of the bias field effect was revealed by examining the temperature dependence of relative permittivity as a function of crystal orientation (the 111, 011 and 001 directions) and dc bias field. The crystals have a microdomain rhombohedral ferroelectric state in the ferroelectric phase under zero dc bias. External bias field could modulate the domain state and induce a macrodomain state in the crystals. Also, it is proposed that the dc bias applied along the 001 or 011 direction could induce a tetragonal ferroelectric phase or an orthorhombic ferroelectric phase, respectively, in an intermediate temperature range. PACS 77.80.-e; 77.22.-d; 81.40.-z     

Indium-hydrogen complexes in silicon and germanium under compression and tension

The response of hydrogen-acceptor complexes in silicon and germanium to the application of uniaxial mechanical stress was studied by means of the perturbed angular correlation technique. This hyperfine interaction technique is sensitive to the microscopic structure of the immediate lattice environment of the probe atom. For the measurements, the probe¹¹¹In was introduced into Si and Ge crystals by ion implantation at room temperature. After annealing, the radioactive probe atom¹¹¹In acts as an acceptor in the elemental semiconductors Si and Ge and as such can easily be passivated by hydrogen indiffusion. The resulting In-H complex was subsequently exposed to uniaxial compressive and tensile stress, which was produced by bending the crystals along the three major lattice directions 100, 110 and 111. It was found that the application of uniaxial mechanical stress causes no change in the population of the four equivalent bond centred H sites surrounding the In acceptor. Evidence was found for a large mismatch of the lattice parameters between the passivated In implanted layer and the surrounding pure Si.     

The growth of crystalline vapor deposited carbon-60 thin films

Thin films (25-2500 Å) of C₆₀ molecules have been deposited on both (001) NaCl and mica substrates at varying temperatures by resistive evaporation. Both electron diffraction and high resolution microscopy have been used to assess the degree of crystallinity, the orientational ordering and the nature of the defects present in these face-centered-cubic films. For NaCl, optimum conditions yielded polycrystalline films with a tendency towards a 110 orientation, while for mica, extended single crystal films have been fabricated which exhibit a 111 direction normal to the film surface.     

Investigation of nematic order by coherent neutron scattering

The mathematical relationship between the orientational order parameters and the coherent neutron scattering cross section for a nematic liquid crystal is given. For deuterated para-azoxyanisole the single-molecule part of the cross section is evaluated within the meanfield approximation and combined with experimental results to give information about molecular orientational order in terms of P ₂, P ₄ and P ₆. Both P ₂ and P ₄ are found necessary for describing the molecular order. Discrepancies between experimental and theoretical results are interpreted as possibly reflecting the inadequacy of the meanfield theory of Maier and Saupe.     

Improved bounds for the transition temperature of directed polymers in a finite-dimensional random medium

We consider the problem of directed polymers in a random medium of a finitedimensional lattice. In the high-temperature phase of this system it is known that the annealed and quenched free energies coincide. Upper bounds on the transition temperature to a low-temperature phase had previously been obtained by calculating the first two moments Z and Z² of the partition function. We improve these bounds by estimating noninteger moments Z for 1<<2.     

Molecular dynamics study of nematic liquid crystal orientation ordering

Molecular dynamics investigations of distribution functions of orientation, order parameters P ₂, P ₄ and selfdiffusion tensor components for nematic liquid crystal model were performed. Our results are in good agreement with experimental data for p-azoxyanisole (PAA). Applied molecular dynamics model is perspective for investigations of structure characteristics and transport coefficients of nematic phase.     

Ray theory of the impulse response of randomly bent multimode fibres

A ray theory based on the time-independent Fokker-Planck equation and the integration of time along ray trajectories provides analytical expressions for the average arrival time and spread of optical pulses propagating in randomly distorted, multimode, optical fibres. A clear physical picture emerges from the theory. The analytical expressions obtained for t and t ² coincide with the ones obtained by Olshansky from coupled-mode theory. The t ³ and t ⁴ moments of the impulse response are also calculated. Simple closed-form formulae are given for the step-index slab. The coupling between all modes is effectively taken into account in our ray theory.On leave of absence at the Laboratoire des Signaux et Systèmes.     

On the zigzagging causility model of EPR correlations and on the interpretation of quantum mechanics

Being formalized inside the S-matrix scheme, the zigzagging causility model of EPR correlations has full Lorentz and CPT invariance. EPR correlations, proper or reversed, and Wheeler's smoky dragon metaphor are respectively pictured in spacetime or in the momentum-energy space, as V-shaped, A-shaped, or C-shaped ABC zigzags, with a summation at B over virtual states |B B|. An exact correspondence exists between the Born-Jordan-Dirac wavelike algebra of transition amplitudes and the 1774 Laplace algebra of conditional probabilities, where the intermediate summations |B) (B| were over real hidden states. While the latter used conditional (or transition) probabilities (A|C) = (C|A), the former uses transition (or conditional) amplitudes A|C = C|A*. The formal parrallelism breaks down at the level of interpretation because (A|C) = |A|C|². CPT invariance implies the Fock and Watanabe principle that, in quantum mechanics, retarded (advanced) waves are used for prediction (retrodiction), an expression of which is | U | = | U = U|, with | denoting a preparation, | a measurement, and U the evolution operator. The transformation | = |U or | = |U^–1 exchanges the preparation representation and the measurement representation of a system and is ancillary in the formalization of the quantum chance game by the wavelike algebra of conditional amplitude. In 1935 EPR overlooked that a conditional amplitude A|C = A|BB|C between the two distant measurements is at stake, and that only measurements actually performed do make sense. The reversibility A|C = C|A* implies that causality is CPT-invariant, or arrowless, at the microlevel. Arrowed causality is a macroscopic emergence, corollary to wave retardation and probability increase. Factlike irreversibility states repression, not suppression, of blind statistical retrodiction—that is, of final cause.Dedicated to Professor David Bohm, proponent of the EPRB version of nonseparability.     

Static and Vibrational Properties of Transition Metals

A model pseudopotential depending on an effective core radius but otherwise parameter free is proposed to study the equation of state by incorporating the s-d hybridization effects. Very recently proposed screening function due to Sarkar et al has been used to obtain the screened form factor. The equations of state for Cu, Ta, Mo, W and Pt have been studied up to the pressure of 1000 GPa. The vibrational properties such as phonon dispersion curves (in q and r space), phonon density of states, mode Grüneisen parameters, maximum frequency _max, mean frequency , ^21/2 = (/ ^-1)^1/2 and fundamental frequency ² and static properties such as dynamical elastic constants of rhodium and iridium are also calculated. The theoretical results are compared with experimental findings wherever possible. A good agreement between theoretical investigations and experimental findings has confirmed our formulation.     

Mixing properties,differentiability of the free energy and the central limit theorem for a pure phase in the Ising model at low temperature

For the Ising model with nearest neighbour interaction it is shown that the spin correlations _{A B} - _{A B} decrease exponentially asd(A, B) in a pure phase when the temperature is well belowT _c. This is used to prove that the free energyF(,h) is infinitely differentiable in and has one sided derivatives inh of all orders forh=0. The bounds are also used to prove that the central limit theorem holds for several variables such as e.g. the total energy and the total magnetization of the system, the limit distribution being gaussian with variances determined by the second derivatives ofF(,h).     

Thermal oxidation of cobalt disilicide

The thermal oxidation kinetics of cobalt disilicide on Si substrates have been investigated in the temperature range of 650–1100 °C in dry oxygen and wet oxygen. A surface layer of SiO₂ grows parabolically with time. The growth rate is independent of the substrate orientation (111 or 100) and thickness of the CoSi₂ layer. We surmize that the oxidation mechanism is dominated by the diffusion of an oxidant through the growing SiO₂. Activation energies for the dry and wet oxidation are 1.49±0.05 eV and 1.05±0.05 eV, respectively. The kinetics is exactly the same as for NiSi₂ oxidation which suggest that the same mechanism controls the oxidation of these two similar suicides.     

Compressible Flow: Turbulence at the Surface

In a study of compressible flow, we have tracked the motion of particles that float on a turbulent body of water. The second moment of longitudinal velocity differences scales as in incompressible flow. However the separation R ²(t) of particle pairs does not vary in time according to the Richardson–Kolmogorov prediction R ²(t)t ³. As expected, the self diffusion d ²(t) shows a crossover between ballistic motion d ²(t)t ² at small t and uncorrelated motion d ²(t)t in the longtime limit.     

Random walk with persistence

The exact analytic result is obtained for the Fourier transform of the generating functionF(R,s)= _n=0 s ⁿ P(R,n), whereP(R,n) is the probability density for the end-to-end distanceR inn steps of a random walk with persistence. The moments R ²(n), R ⁴(n), and R ⁶(n) are calculated and approximate results forP(R,n) and R ^–1(n) are given.     

Studies on the high-frequency properties of 〈111〉, 〈110〉 and 〈100〉 oriented GaAs IMPATT diodes

High-frequency analysis has been carried out to predict the rf performance of 111, 110 and 100 oriented p ⁺ nn ⁺, n ⁺ pp ⁺ (single drift region) and n ⁺ npp ⁺ (double drift region) GaAs IMPATT diodes for opertion at 35 and 60 GHz. The microwave performance is observed to be highly sensitive to crystal orientation in case of p ⁺ nn ⁺ and n ⁺ npp ⁺ diodes whereas orientation of the substrate has negligible effect on n ⁺ pp ⁺ avalanche diodes. The calculation shows that 111 oriented GaAs IMPATT diode would provide the largest magnitude of negative resistance and negative conductance for both SDR p ⁺ nn ⁺ and DDR n ⁺ npp ⁺ diodes which indicates that high microwave power with high conversion efficiency can be realised from these 111 oriented GaAs devices. This result can be explained from the experimental data of electron and hole ionization rates for different orientations in GaAs.     

Damage created by high-current-density implants of phosphorus into 〈100〉 and 〈111〉 silicon wafers

The damage left by high-current-density, 9 A/cm², implants of 120 keV phosphorus into 100 and 111 silicon oriented substrates was investigated as a function of the fluence in the range 4×10¹⁵–1.5×10¹⁶/cm². The samples were analyzed by 2 MeV He⁺ channeling and transmission electron microscopy. Initially a buried amorphous layer forms at low fluences until the wafer temperature saturates at 450 °C at a fluence of 4.5×10¹⁵/cm². As the fluence is further increased ion-assisted regrowth of this initial buried amorphous layer takes place and is 2 to 2.5 times faster (with respect to ion fluence) for 100 substrates than for 111 substrates. At higher fluences, most of the residual damage is located at a depth equal to the sum of the projected range and of the straggling. In the regrown layers twins are found in both orientations, and in some cases a hexagonal silicon phase is present at high fluences. The results are compared with the ion assisted regrowth of amorphous layers at well defined temperatures in the 250°–400 °C range.     

Investigation of nematic order by coherent neutron scattering

The mathematical relationship between the orientational order parameters and the coherent neutron scattering cross section for a nematic liquid crystal is given. For deuterated para-azoxyanisole the single-molecule part of the cross section is evaluated within the meanfield approximation and combined with experimental results to give information about molecular orientational order in terms of P ₂, P ₄ and P ₆. Both P ₂ and P ₄ are found necessary for describing the molecular order. Discrepancies between experimental and theoretical results are interpreted as possibly reflecting the inadequacy of the meanfield theory of Maier and Saupe.     

Ultra-high piezoelectric response in 〈<Emphasis Type="Bold">110</Emphasis>〉- oriented polydomain Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>- PbTiO<Subscript>3</Subscript> single crystals

The piezoelectric constant and electromechanical coupling coefficients of 110-oriented polydomain0.71Pb(Mg_1/3Nb_2/3)O₃-0.29PbTiO₃ single crystals were determined experimentally by using resonance methods. It was confirmed that the single-crystal system has large electromechanical coupling coefficients k₃₃ (91%), k₃₃ (83%), and k₃₁ (81%), and piezoelectric constant d₃₃ (1400 pC/N), which are comparable to those of 001-oriented crystals, and we also found that the values of k₃₃ and k₃₁ are sensitive to the cuts of the crystals. X-ray-diffraction measurements on 110-oriented crystals have shown that the origin of the high piezoelectric response should be attributed to the orthorhombic distortion. Our results show that the 110-oriented crystals are also promising for a wide range of electromechanical transducer applications, since the 110-oriented crystals can be grown from 110-oriented seed crystals in the modified Bridgman technique. PACS 77.80.Bh; 77.84.Dy; 77.65.Bn     

Thes-f model with Coulomb repulsion: Thermodynamics of two atomic cluster. Spin 1/2

A cluster of two atoms described by thes-f model with Coulomb repulsion has been considered. The interaction between localized 4f electrons (S=1/2) is taken in the molecular field approximation. The thermodynamic quantities like magnetization, specific heat and correlation functions n , n , S ^z n , S ^z n , S ^z (n –n ), n n and S ⁺ a ⁺ a as functions of temperature are presented for different band fillingN=0, 0.5, 1, 1.5, 2. The dependence of Curie temperature onN is calculated. The phase diagram forN=1 (T=0K) shows the possibility of existence of two phases: paramagnetic and ferromagnetic.The Curie temperature and the specific heat as functions ofN exhibit similar trends as found in experiments on doped magnetic semiconductors.     

Compatibility stresses in deformed bicrystals

Compatibility stresses have been calculated in the model of a bicrystal composed of two semi-infinite crystals. The elastic anisotropy of the component crystals is fully taken into account. Various particular cases chosen for the cubic bicrystals with the 100 and 110 rotation axes commonly used in experiments are discussed in detail. The effects of elastic and plastic deformation have also been compared. The model provides compatibility stresses as functions of grain boundary geometrical parameters and of the loading axis orientation.