C 1<Emphasis Type="Italic">s</Emphasis> photoemission investigation of substrate bias and annealing temperature influencing the microstructure of amorphous diamond films

The hybridization composition of amorphous diamond films deposited using a filtered arc has been investigated as functions of the substrate bias and the annealing temperature by the deconvolution of C 1s photoemission spectra. The chemical shift and the half width of the entire C 1s spectrum have demonstrated the clear regularities to the changing bias and temperature. The XPS C 1s core level spectra can provide a powerful way to follow the evolution of the sp³ bonding configurations. PACS 68.49.Uv; 79.60.-i; 61.43.Dq; 65.90.+i     

Scattering of electrons on the Cu(001) surface by Co adatoms

Excited electrons at surfaces can be scattered by adsorbate atoms or defects, which changes the energy or momentum. Such scattering processes can be studied by energy, time and angle-resolved two-photon photoelectron spectroscopy. In this article the influence of statistically distributed Co adatoms on a Cu(001) surface on the dynamics of electrons in image-potential states is investigated. Different scattering mechanisms, such as interband, intraband, and bulk scattering are identified and analyzed quantitatively. Cobalt adatoms cause mainly quasielastic scattering of electrons in image-potential states. Inelastic processes are due to interactions with electrons in the substrate and are not significantly increased by Co adatoms. The results are compared to previous experimental and theoretical work on Cu adatoms. PACS 73.20.At; 68.49.Jk; 79.60.Ht     

Co interaction on ZnO(000–1) investigated by scanning tunneling microscopy

The interaction of Co thin films on atomically flat ZnO(000–1) has been investigated by low energy electron diffraction (LEED), scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES). A high density of islands nucleates at the earliest stages of the growth and a subsequent Wolmer–Weber growth of these islands is observed. Upon annealing at 600 °C, an atomically flat surface (Zn,Co)O(000–1) is restored due to the diffusion of the Co into the semiconductor. PACS 68.37.Ef; 68.49.Uv; 68.47.Fg; 68.47.Gh; 68.55.Ac     

Electrical characterization of ZnO,including analysis of surface conductivity

Most current device applications of ZnO are hampered by the lack of control over the electrical conductivity. As-grown ZnO usually exhibits n-type conductivity, and the cause of this residual doping is heavily debated. We have performed temperature-dependent Hall measurements and material characterization by secondary ion mass spectroscopy on nominally undoped bulk ZnO crystals as well as on material doped with potential candidates for p-conductivity in order to explore the cause of the background doping and to study the impact of possible candidates for p-doping of ZnO. Also, this paper gives an overview about surface conductivity of high-resistivity ZnO bulk material and discusses how this property might impact the difficult search for p-type ZnO. We will demonstrate the effect of a surface conducting channel on homoepitaxial MgZnO layers grown by liquid-phase epitaxy. The detectability of such a surface layer on an epi sample indicates the high structural quality and low background doping of the layer. PACS 61.72.Vv; 68.49.Sf; 73.25.+i; 74.62.Dh; 81.15.Lm     

Interpretation of TOF–SIMS depth profiles from ultrashallow high-k dielectric stacks assisted by hybrid collisional computer simulation

The TRIDYN collisional computer simulation has been modified to account for emission of ionic species and molecules during sputter depth profiling, by introducing a power law dependence of the ion yield as a function of the oxygen surface concentration and by modelling the sputtering of monoxide molecules. The results are compared to experimental data obtained with dual beam TOF–SIMS depth profiling of ZrO₂/SiO₂/Si high-k dielectric stacks with thicknesses of the SiO₂ interlayer of 0.5, 1, and 1.5 nm. Reasonable agreement between the experiment and the computer simulation is obtained for most of the experimental features, demonstrating the effects of ion-induced atomic relocation, i.e., atomic mixing and recoil implantation, and preferential sputtering. The depth scale of the obtained profiles is significantly distorted by recoil implantation and the depth-dependent ionization factor. A pronounced double-peak structure in the experimental profiles related to Zr is not explained by the computer simulation, and is attributed to ion-induced bond breaking and diffusion, followed by a decoration of the interfaces by either mobile Zr or O. PACS 68.49; 79.20; 81.65; 82.80     

Velocity dependence of metal cluster deposition on an insulating surface

We present a detailed study of the deposition of small sodium clusters on a NaCl surface. To that end, we use a microscopic model based on the Time-Dependent Local Density Approximation (TDLDA) for electrons, coupled to classical Molecular Dynamics (MD) for ions. We discuss in particular the deposition mechanism for different initial cluster velocities and demonstrate that extremely slow velocities are necessary to ensure a cluster deposition without damaging the original cluster.Received: 13 March 2004, Published online: 11 May 2004PACS: 36.40.Cg Electronic and magnetic properties of clusters - 36.40.Sx Diffusion and dynamics of clusters - 68.49.Fg Cluster scattering from surfaces     

Scattering by Cu adatoms between image-potential bands on Cu(001)

With the increasing resolution and sensitivity of photoelectron spectroscopy, the influence of defects is becoming more and more obvious. Scattering processes induced by adsorbate atoms can be studied by time- and angle-resolved two-photon photoemission. We have examined the dynamics of electrons in image-potential states on the Cu(001) surface for statistically distributed Cu adatoms and have identified different scattering mechanisms. Scattering of electrons from the second (n=2) to the bottom of the first (n=1) image-potential band is observed, which we attribute to inelastic interband scattering with electrons in the bulk. At energies above the bottom of the n=2 band, resonant interband scattering from the n=2 to the n=1 image-potential band is found. The rate for these processes can be determined by modeling the time-resolved measurements via optical Bloch equations of a four-level system. Comparison of the transition and decay rates reveals that the decay rate of the n=2 electrons is almost exclusively changed by additional resonant interband-scattering processes upon adsorption. PACS 73.20.At; 79.60.Ht; 68.49.Jk     

Investigation of Cl corrosion products of iron archaeological artefacts using micro-focused synchrotron X-ray absorption spectroscopy

Synchrotron-based micro-X-ray absorption spectroscopy is used in the present study to obtain chemical information at the microscopic scale such as coordination and oxidation state of Fe atoms in phases constituting corrosion products within archaeological iron artefacts buried in soil. This technique is required in order to answer questions about the iron corrosion process related to the presence of chloride, particularly for restoration and conservation of metallic artefacts of the cultural heritage. The samples available for X-ray microprobe analyses are cross sections from corroded iron archaeological objects. Previously, complementary techniques have been used such as μXRD and μRaman. This specific study applies micro-X-ray absorption spectroscopy to determine the spatial variation of the predominant Fe oxidation state and to identify the corresponding crystallographic phase. The analyses performed at Fe and Cl K-edges (μXANES) reveal the correlation between the valence distribution in the corrosion products and the evolution of the chloride concentration. In addition to the presence of the well-known iron oxyhydroxide β-FeOOH: akaganeite, we highlight the presence of another important phase, the β-Fe₂(OH)₃Clhydroxychloride. These important findings help to gain new insights concerning the influence of such phases in the iron corrosion mechanism within their precise characterization. PACS 61.10.Ht; 61.10.-i; 68.49.Uv     

Formulation and characterisation of drug-loaded antibubbles for image-guided and ultrasound-triggered drug delivery

The aim of this study was to develop high load-capacity antibubbles that can be visualized using diagnostic ultrasound and the encapsulated drug can be released and delivered using clinically translatable ultrasound.The antibubbles were developed by optimising a silica nanoparticle stabilised double emulsion template.We produced an emulsion with a mean size diameter of 4.23 ± 1.63 µm where 38.9 ± 3.1% of the droplets contained a one or more cores. Following conversion to antibubbles, the mean size decreased to 2.96 ± 1.94 µm where 99% of antibubbles were <10 µm. The antibubbles had a peak attenuation of 4.8 dB/cm at 3.0 MHz at a concentration of 200 × 10³ particles/mL and showed distinct attenuation spikes at frequencies between 5.5 and 13.5 MHz. No increase in subharmonic response was observed for the antibubbles in contrast to SonoVue®. High-speed imaging revealed that antibubbles can release their cores at MIs of 0.6. In vivo imaging indicated that the antibubbles have a long half-life of 68.49 s vs. 40.02 s for SonoVue®. The antibubbles could be visualised using diagnostic ultrasound and could be disrupted at MIs of ≥0.6. The in vitro drug delivery results showed that antibubbles can significantly improve drug delivery (p < 0.0001) and deliver the drug within the antibubbles. In conclusion antibubbles are a viable concept for ultrasound guided drug delivery.     

Autocompensation doping in light-soaked and in radiation-damaged a-Si:H

n-type a-Si:H films have been irradiated with light, electrons, protons and heavy ion beams. It is shown that the non-thermal creation of dangling-bond defects activates significant densities of previously inactive phosphorus dopants. The relevance of these results is discussed with respect to equilibration phenomena in doped material and with respect to degradation phenomena in a-Si:H solar cells.     

强激光条件下5CB液晶中的激光诱导衍射环现象

强激光经5CB液晶传播时会产生非线性自相位调制现象,利用532 nm和1 064 nmCW激光研究了强激光条件下5CB液晶中的激光诱导衍射环现象,并对强激光在5CB液晶中产生自相位调制的现象和机理进行了讨论.当532 nm激光和1 064 nm激光功率密度分别大于10 kW/cm2和300 W/cm2时,接收白屏上有较明显的衍射环现象|当激光分别持续作用数十毫秒和数百毫秒量级时间时,接收屏上的衍射环现象消失.分别利用基尔霍夫衍射积分公式的菲涅耳近似和夫朗和费近似形式对5CB中激光自相位调制和激光诱导衍射环进行了数值模拟,数值结果与实验结果符合的较好.基于热传导理论定性分析了5CB液晶在不同波长和入射条件下的三阶非线性系数.结果表明：在强激光入射条件下,热效应是自相位调制的主要原因,这种三阶非线性系数除了与液晶的吸收系数和作用时间相关,还与激光作用面积甚至激光诱导指向矢转动过程相关.     

Magnetic relaxation in superfluid<Superscript>3</Superscript>He-B at very low temperatures

Main properties of the spin supercurrents and coherent precession of magnetization in the superfluid³He-B in hydrodynamic regime seem to be very well understood now. But recently surprisingly new unpredicted phenomena such as, for example, “catastrophic” relaxation, persistent spin precession, very strong magnetic relaxation, etc., have been observed in³He-B at ultralow temperatures in so-called non-hydrodynamic regime using both pulse and cw-NMR techniques. This paper deals with some of these new phenomena (a “linear term” in magnetic relaxation and a reduction of magnetization of coherent precession with magnetic field gradient) observed by cw-NMR technique, compares these results with new effects found by pulse NMR and speculates about the nature of these new phenomena.     

Threshold phenomena in R-matrix theory

An R-matrix treatment of threshold phenomena in nuclear reactions is developed. It results, in addition to cusp phenomena, in a class of threshold anomalies induced by a resonance located at the threshold of the opening channel. The influence of compound nucleus and single-particle resonances and of direct interaction on threshold phenomena is discussed for s- and p- waves.     

A thermodynamic discussion of the possibility of singular yield conditions in plasticity theory

A generalization is given of the author's theory for plasticity phenomena. The generalization leads to the possibility that the yield surface has singularities. From the theory a formula may be derived which is analogous to a formula proposed by Koiter for plastic flow in media with singular yield surfaces. The possibility of elastic relaxation phenomena in the preplastic range is included in the developed formalism.     

Critical phenomena studied via nuclear techniques

Since pioneering NMR studies of magnetic critical phenomena in MnF₂ by Heller, a range of hyperfine techniques, particularly Mössbauer effect and perturbed angular correlations, have been successfully applied to the problem. When optimally designed, these methods provide experimental approaches that are in some ways more successful than magnetic neutron scattering. Although the number of hyperfine results now number in the hundreds, only a few are sufficiently asymptotic to provide clearcut tests of theory. In this paper we outline the theoretical framework used to describe the modern theory of critical phenomena, discuss the strengths and weakness of various experimental methods, and provide a selection of the best experiments that test the theory. Whereas we emphasize hyperfine interaction studies, we also describe the principles and results of other methods where appropriate. Particular topics include: (1) static critical phenomena in chemically ordered systems studied as a function ofn andd, the spin and lattice dimensionality; (2) static critical phenomena in magnetically disordered systems studied as a function of the type of disorder; and (3) dynamic critical phenomena in chemically ordered systems.     

Puzzles in astrophysics in the past and present

About 400 years have passed since the great discoveries by Galileo, Kepler, and Newton, but astronomy still remains an important source of discoveries in physics. They start with puzzles, with phenomena difficult to explain, and phenomena which in fact need new physics for explanation. Do such puzzles exist now? There are at least three candidates: absence of absorption of TeV gamma radiation in extragalactic space (violation of Lorentz invariance?), absence of GZK cutoff in the spectrum of ultrahigh-energy cosmic rays (new particle physics?), tremendous energy (up to 10⁵⁴ erg) released in gamma ray bursts on a time scale of a second (collapsing stars or sources of a new type?). Do these puzzles really exist? A critical review of these phenomena is given.     

Negative capacitance phenomena depending on the wake-up effect in the ferroelectric Si:HfO2 film

Negative capacitance (NC) phenomena is recently suggested as a breakthrough that can lead to the improved transistor by decreasing the subthreshold swing. To understand the NC phenomena, we investigated the effects of the ferroelectric properties such as the remnant polarization depending on the switching cycles in Si-doped HfO₂ thin film capacitor. The ferroelectric properties were controlled by using the wake-up effect, in which the remnant polarization enhances as the number of switching cycles increase. The relation between the wake-up effect and the voltage drop region with the negative differential capacitance were elucidated. The dynamic hysteresis loops were fitted based on Landau-Khalatnikov equation, and the free energy as a function of polarization was obtained. The Landau coefficients showed that the double-well feature of the free energy becomes more apparent due to the wake-up. Based on the wake-up effect on NC phenomena, we show that the NC phenomena is well described by Landau-Ginzburg theory of ferroelectrics.     

Soliton-induced supercontinuum generation in liquid-filled photonic crystal fibre

We aim to study the nonlinear optical phenomena with ultra-broadband radiation in photonic crystal fibre (PCF). While PCFs with cores made from different glasses are well studied in previous works, in this paper, it is planned to investigate the dynamics of nonlinear processes of supercontinuum generation (SCG) in liquid-filled PCF (LCPCF) to understand the physical phenomena of femtosecond pulse propagation, particularly, the temporal and spectral changes of the pulse propagating through specific PCFs. Since the CS₂-filled LCPCF has complex nonlinear phenomena, we intend to analyse the role of saturable nonlinear response and slow nonlinear response on SCG in detail. For the physical explanation, soliton fission and modulational instability techniques will be implemented to investigate the impact of slow nonlinear response and saturable nonlinear response respectively, in SCG process.     

Phase equilibria in the system LiOH–H<Subscript>2</Subscript>O at 350–425°C

The system LiOH—H₂O is characterized by immiscibility phenomena both in equilibrium with vapor and solid saturated solutions or without the solid phase. The solubility of LiOH increases as a result of immiscibility phenomena at ~355°C and further increases above this temperature up to the melting point. The immiscibility region (g–l₁–l₂) is terminated by the critical phenomena (g = l₁–l₂) at ~390°C. A separation of liquid phases is observed at elevated pressures (at ~39 MPa) and temperatures up to 425°C.     

UV laser desorption of nitric oxide from semiconducting C<Subscript>60</Subscript>/Cu(111)

The desorption of NO from a well-characterized, epitaxially grown semiconducting C₆₀ surface is reported. Two different channels are identified in the laser desorption. Both channels yield a comparably high desorption cross section of σ₁=7.0×10^-17 cm² and σ₂=5.5×10^-17 cm² for the first and second channel, respectively. The laser desorbed NO molecules are detected with rovibrational state selectivity by (1+1) REMPI in the -bands. In the first channel the desorbing molecules are highly excited with an average kinetic energy of 〈E_kin〉=174 meV. The rotational population distribution can be fitted by a rotational temperature of T_rot=800 K. A rotational–translational coupling is observed, with velocities ranging from 1000 m/s for low to 1300 m/s for high rotational states. The vibrationally excited population is estimated to be less than 1% of the ground state. The second channel yields less excited molecules and an almost Boltzmann distributed rotational population with a temperature of T_rot=280 K. The apparent velocity distribution derived from the pump-probe delay yields molecules much too slow to be explained by even a thermal desorption. This desorption is probably caused by a long-lived electronic excitation in the substrate for which a lifetime of τ≈160 μs is estimated. PACS 42.62.Fi; 34.50.Dy; 68.49.Df; 68.43.Tj; 79.20.La