Approach for growth of high-quality and large protein crystals

Three crystallization methods for growing large high-quality protein crystals, i.e. crystallization in the presence of a semi-solid agarose gel, top-seeded solution growth (TSSG) and a large-scale hanging-drop method, have previously been presented. In this study the effectiveness of crystallization in the presence of a semi-solid agarose gel has been further evaluated by crystallizing additional proteins in the presence of 2.0% (w/v) agarose gel, resulting in complete gelification with high mechanical strength. In TSSG the seed crystals are hung by a seed holder protruding from the top of the growth vessel to prevent polycrystallization. In the large-scale hanging-drop method, a cut pipette tip was used to maintain large-scale droplets consisting of protein-precipitant solution. Here a novel crystallization method that combines TSSG and the large-scale hanging-drop method is reported. A large and single crystal of lysozyme was obtained by this method.     

Applications of nano-polycrystalline diamond anvils to X-ray absorption spectroscopy under high pressure

ABSTRACT

Recently, nano-polycrystalline diamond (NPD) anvils have been widely applied in high pressure research using X-ray absorption spectroscopy (XAS). The nanometer-sized polycrystallization in NPD anvils enables us to obtain glitch-free X-ray absorption spectra. This advantage of NPD anvils drastically improves the experimental conditions of XAS, which has previously used conventional single-crystal diamond (SCD) anvils. Distorted spectra due to the glitches from the SCD anvils have been an inevitable problem of XAS. This paper reviews recent studies of XAS and related spectroscopic techniques using the NPD anvils, which have mainly been performed on BL39XU of SPring-8. We demonstrate how NPD anvils are useful when using XAS for high pressure research.     

Impurity effects on the laser-induced crystallization of thin amorphous silicon film on glass substrate

Crystallization of 100 nm thick amorphous silicon (a-Si) films deposited on glass substrates was carried out using a dual-green-laser method. Depending on a-Si deposition method, either low-pressure chemical vapor deposition (LPCVD) or plasma-enhanced chemical vapor deposition (PECVD), the density of impurities such as Al, K, and Na within the a-Si thin films significantly varied. For the high impurity case of LPCVD, grains of 200–300 nm in size were obtained, whereas for the PECVD case a maximum grain size of about 4 μm was achieved, satisfying the requirements for applications in commercial TFT devices. These results confirm that for the use of glass substrates in polycrystallization of a-Si, controlling the impurity density during substrate preparation is critical.     

Effect of lower growth temperature on C incorporation in GeC epilayers on Si(0 0 1) grown by MBE

Effect of lower growth temperature T_s on C incorporation to substitutional sites in Ge_1−xC_x/Si(0 0 1) grown by molecular beam epitaxy was investigated. To enhance the non-equilibrium growth condition, the temperature T_s was lowered from 600°C down to 300°C. The C incorporation into substitutional sites of GeC epilayers was very sensitive to T_s. X-ray diffraction (XRD) measurement indicated that the substitutional C composition x increased with decrease in T_s from 600°C to 400°C. At T_s350°C, the estimation of x by the XRD analysis was impossible because of polycrystallization. The Raman shift measurement enables to estimate x for T_s350°C, as consequently larger x than that grown at T_s=400°C was verified. The enhancement of non-equilibrium growth condition by decreasing T_s was important to increase x.     

Large single-crystal growth of RBa2Cu3O7−x by the flux method (R=Y and rare earths)

Il Nuovo Cimento D - In this work the thermal conditions required for single-crystal growth in RBa2Cu3O7−x systems (R=Y or rare earths apart from Ce and Tb) have been systematically revised...     

Large deviation function for the eden model and universality within the one-dimensional kardar-parisi-zhang class

It has been recently conjectured that for large systems, the shape of the central part of the large deviation function of the growth velocity would be universal for all the growth systems described by the Kardar-Parisi-Zhang equation in 1+1 dimension. One signature of this universality would be that the ratio of cumulants R(t)=[(c)](2)/[(c)(c)] would tend towards a universal value 0.415 17ellipsis as t tends to infinity, provided periodic boundary conditions are used. This has recently been questioned by Stauffer. In this paper we summarize various numerical and analytical results supporting this conjecture, and report in particular some numerical measurements of the ratio R(t) for the Eden model.     

Increased cubic–tetragonal phase transition temperature and resistivity hysteresis of surface vacuum annealed SrTiO3

Electrical properties of SrTiO₃ single crystal samples treated by an anisotropic surface annealing technique under reducing conditions have been investigated in the temperature range of 35 K–300 K. Optical and atomic force microscopy show that annealing gives rise to polycrystallization and the formation of colored dendritic structures. Carrier concentrations and mobilities determined by Hall measurements as well as resistivities detected by van der Pauw measurements show the expected metallic behavior due to oxygen vacancy doping. Moreover, the temperature dependent resistivities indicate a cubic-to-tetragonal phase transition, which to our knowledge has not been reported before. Additionally, the transition occurred up to 53 K above the known bulk transition temperature T _C at 105 K with a hysteresis up to a temperature of 220 K. Both phenomena possibly arise from dislocations and associated strain fields introduced by surface annealing that are assumed to lower the free energy of the tetragonal phase and simultaneously pin tetragonal domains. Thus, microregions of the tetragonal phase persist above T _C causing the hysteresis in resistivity up to ∼12%. This effect possibly provides new chances for future oxide based non-volatile data-storage devices.     

Giant SALR cluster reproduction,with implications for their chemical evolution

ABSTRACT

Particles with SALR (short-range attraction and long-range repulsion) interactions are common to many physical systems, especially biological and soft matter, yet their behaviour is still not completely understood. Using Monte Carlo simulations and a thermodynamic model, it is shown here that giant SALR clusters can grow and reproduce in these fluids. Giant cluster growth and reproduction should therefore be common to a wide range of natural and synthetic systems under suitable conditions. If, in addition, cluster fitness selection occurs then chemical evolution of giant SALR cluster might be observed in suitable systems.     

A Density Functional Theory Study of Codoping Characteristics of Sulfur with Alkaline Earth in Delafossite CuAlO_2

The structural,electronic properties and formation energies of sulfur and alkaline earth codoped delafossite CuAlO_2 have been investigated using the first-principles density functional theory calculations.Our results reveal that the volume of codoping systems increases with the increasing atomic radius of metal atoms.The formation energies under different growth conditions have been calculated,showing that the codoping systems are formed easily under O-rich growth conditions.Electronic band structures and density of states have been obtained.The decreased bandgaps,enhanced covalence and appearance of electron acceptors after codoping are all good for p-type conductivity.     

Growth and Properties of Ferromagnet-SemiconDuctor Hetero-Structures for Spin Injection

Molecular-beam epitaxial growth and interface formation is investigated and optimized for the material systems Fe-on-GaAs(001) and MnAs-on-GaAs(001), which represent model systems for the integration of magnetic materials with semiconductors and the investigation of spin injection. In view of interface reactions as a key problem for the first system and in order to optimize the surface morphology, the Fe films are grown at reduced temperature. For MnAs-on-GaAs, an abrupt interface with an anisotropic lattice-mismatch accommodation mechanism is observed, which explains the unexpected high quality of the films. It is shown that the phase transition between paramagnetic g MnAs and ferromagnetic f MnAs during cooling after growth plays an important role and leads, at appropriate conditions, to strain-mediated self-organized structures. Electrical injection of spin polarized electrons through the ferromagnet-semiconductor interfaces is observed by analyzing the electroluminescence signal of GaAs/(In, Ga)As light emitting diodes capped with Fe or MnAs.     

Effects of temperature and oxygen pressure on binary oxide growth using aperture-controlled combinatorial pulsed-laser deposition

In pulsed-laser deposition (PLD), there are many processing parameters that influence film properties such as substrate-target distance, background reactive gas pressure, laser energy, substrate temperature and composition in multi-component systems. By introducing a 12.7-mm diameter circular aperture in front of a 76.2-mm silicon wafer and rotating the substrate while changing conditions during the PLD process, these parameters may be studied in a combinatorial fashion, discretely as a function of processing conditions. We demonstrate the use of the aperture technique to systematically study the effects of oxygen partial pressure on the film stoichiometry and growth rate of VO_x, using Rutherford backscattering spectrometry (RBS). In another example, we discuss the effect of growth temperature on TiO₂ films characterized by X-ray diffraction and Fourier transform far-infrared (Terahertz) absorption spectroscopy. We demonstrate that we have considerable combinatorial control of other processing variables besides composition in our combi-PLD system. These may be used to systematically study film growth and properties.     

InAs/GaAs自组织量子点的DLTS谱

将DLTS用于对InAs/GaAsQD结构样品的测量,测定了QD能级发射载流子的热激活能;获得了QD能级俘获电子过程伴随有多声子发射(MPE)、QD能级存在一定程度的展宽、以及在某些特定的生长条件下,存在亚稳生长构形的实验证据.结果表明:DLTS在QD体系的研究中有其特有的功能     

A study of void size growth in nonequilibrium stochastic systems of point defects

We study properties of voids growth dynamics in a stochastic system of point defects insolids under nonequilibrium conditions (sustained irradiation). It is shown thatfluctuations of defect production rate (external noise) increase the critical void radiuscomparing to a deterministic system. An automodel regime of void size growth in astochastic system is studied in detail. Considering a homogeneous system, it is found thatexternal noise does not change the universality of the void size distribution function;the mean void size evolves according to classical nucleation theory. The noise increasesthe mean void size and spreads the void size distribution. Studying dynamics of spatiallyextended systems it was shown that vacancies remaining in a matrix phase are able toorganize into vacancy enriched domains due to an instability caused by an elastic latticedeformation. It is shown that dynamics of voids growth is defined by void sinks strengthwith void size growth exponent varying from 1/3 up to 1/2.     

Orientation dependence of void growth at triple junction of grain boundaries in nanoscale tricrystal nickel film subjected to uniaxial tensile loading

Molecular dynamics simulation was performed in order to investigate the dependence of void growth on crystallographic orientation at the triple junction of grain boundaries in nanoscale tricrystal nickel film subjected to uniaxial tensile loading. The nucleation, the emission and the transmission of Shockley partial dislocations play a predominant role in the growth of void at the triple junction of grain boundaries. The orientation factors of various slip systems are calculated according to Schmid law. The slip systems activated in a grain of tricrystal nickel film basically conform to Schmid law which is completely suitable for a single crystal. The activated slip systems play an important role in plastic deformation of nanoscale tricrystal nickel film subjected to uniaxial tensile loading. The slip directions exhibit great difference among the activated slip systems such that the void is caused to be subjected to various stress conditions, which further leads to the difference in void growth among the tricrystal nickel films with different orientation distributions. It can be concluded that the grain orientation distribution has a significant influence on void growth at the triple junction of grain boundaries.     

Role of the Metal/Semiconductor interface in quantum size effects: Pb /Si(111)

Self-organized islands of uniform heights can form at low temperatures on metal/semiconductor systems as a result of quantum size effects, i.e., the occupation of discrete electron energy levels in the film. We compare the growth mode on two different substrates [Si(111)- (7x7) vs Si(111)- Pb(sqrt[3]xsqrt[3] )] with spot profile analysis low-energy electron diffraction. For the same growth conditions (of coverage and temperature) 7-step islands are the most stable islands on the (7x7) phase, while 5-step (but larger islands) are the most stable islands on the (sqrt[3]xsqrt[3] ). A theoretical calculation suggests that the height selection on the two interfaces can be attributed to the amount of charge transfer at the interface.     

Formation of pyramid-like nanostructures in MBE-grown Si films on Si(001)

The growth of Si homoepitaxial layers on Si(001) substrates by molecular beam epitaxy is analyzed for a set of growth conditions in which diverse nanometer-scale features develop. Using Si substrates prepared by exposure to HF vapor and annealing in ultra-high vacuum, a rich variety of surface morphologies is found for different deposited layer thicknesses and substrate temperatures in a reproducible way, showing a critical dependence on both. Arrays of 3D islands (truncated pyramids), percolated ridge networks, and square pit (inverted pyramid) distributions are observed. We analyze the obtained arrangements and find remarkable similarities to other semiconductor though heteroepitaxial systems. The nanoscale entities (islands or pits) display certain self assembly and ordering, concerning size, shape, and spacing. Film growth sequence follows the ‘islands–coalescence–2D growth’ pathway, eventually leading to optimum flat morphologies for high enough thickness and temperature.     

Scale-invariance underlying the logistic equation and its social applications

On the basis of dynamical principles we i) advance a derivation of the Logistic Equation (LE), widely employed (among multiple applications) in the simulation of population growth, and ii) demonstrate that scale-invariance and a mean-value constraint are sufficient and necessary conditions for obtaining it. We also generalize the LE to multi-component systems and show that the above dynamical mechanisms underlie a large number of scale-free processes. Examples are presented regarding city-populations, diffusion in complex networks, and popularity of technological products, all of them obeying the multi-component logistic equation in an either stochastic or deterministic way.     

Cluster growth processes by direct simulation monte carlo method

Thin films obtained by cluster deposition have attracted strong attention both as a new manufacturing technique to realize high-density magnetic recording media and to create systems with unique magnetic properties. Because the film’s features are influenced by the cluster properties during the flight path, the relevant physical scale to be studied is as large as centimeters. In this paper, a new model of cluster growth processes based on a combination of the Direct Simulation Monte Carlo (DSMC) method and the cluster growth model is introduced to examine the effects of experimental conditions on cluster growth by an adiabatic expansion process. From the macroscopic viewpoint, we simulate the behavior of clusters and inert gas in the flight path under different experimental conditions. The internal energy of the cluster, which consists of rotational and vibrational energies, is limited by the binding energy which depends on the cluster size. These internal and binding energies are used as criteria of the cluster growth. The binding energy is estimated by surface and volume terms. Several types of size distribution of generated clusters under various conditions are obtained by the present model. The results of the present numerical simulations reveal that the size distribution is strongly related to the experimental conditions and can be controlled. Received: 23 January 2001 / Accepted: 3 May 2001 / Published online: 30 August 2001     

Anisotropic growth and “layer-by-layer” epitaxy

It is proposed and justified that systems that grow epitaxially, but in which there is a lateral growth anisotropy, will grow with a smaller interface width than systems in which the growth is isotropic. An example in which this may be true is the growth of Si on Si(100). Scanning tunneling micrographs of the growth of Si on Si(100) are presented.     

Influence of a circulating current on the thermal conductivity of heterogeneous systems

An approach describing the influence of thermoelectric effects and boundary conditions on the thermal conductivity of heterogeneous systems is developed. At a certain configuration of a heterogeneous system, circulating electric currents appearing in the system are shown to influence markedly the effective thermal conductivity. The maximum growth of the thermal conductivity is to be expected in heterogeneous semiconductors and semimetal systems with opposed thermoelectromotive forces.