Applied Physics A Solids and Surfaces

The Monte Carlo Simulation Program TRIM is used to calculate particle and energy reflection coefficients as well as energy and angular distributions of reflected H, D, and T. To account for binding effects at the target surface a planar potential is applied. This binding potential reduces the reflection below an energy of a few eV.

An optical backplane based on a meshed polymer waveguide architecture enabling high-speed board-to-board optical interconnection is presented. This planar array of multimode polymer waveguides can provide passive strictly non-blocking links between server line cards fitted with optical transmitter and receiver arrays. This architecture offers a scalable and low-cost solution to the bandwidth limitations faced by electrical backplanes and is suitable for PCB integration. The reported backplane demonstrator uses a matrix of 100 waveguides each capable of 10 Gb/s operation to interconnect 10 cards for a total capacity of a terabit per second aggregate data rate in multicast mode. Characterisation of the backplane demonstrator reveals low link losses of 2 to 8 dB for a multimode fibre input and crosstalk values below −35 dB. Error free data transmission at 10 Gb/s is achieved with a power penalty of only 0.2 dB at a bit-error-rate of 10−9. Additionally, lossless operation of a Gigabit Ethernet link over the backplane is achieved even when using the worst-case highest loss links.

The study of ancient mortars is an important aspect of building conservation: the choice of the materials has varied according to historical period, regional habits, and their specific function in the structure. Ancient mortars are composites, comprising hydraulic or aerial binding materials, and aggregates, passive or active, which may react with binding material. Moreover, they were modified during setting, hardening, and aging, according to processes not yet well known. In this paper, we present a study of ancient mortars from the Villa of Pollio Felice of Sorrento (Naples). The analysis has been performed by conventional techniques (grain-size distribution, lime-percentage analysis, optical and electron microscopy, and X-ray diffraction) and by means of a laboratory X-ray microdiffractometer equipped with an image plate detector. This system, applied for the first time to archaeological studies, can reach a spatial resolution of a few tenths of microns and it allows us to obtain separate phase identification of binder and filler particles.

Laser-induced multilevel spallation in diamond-like carbon films is observed and studied for a wide range of laser parameters (λ=539, 800, 1064, and 1078 nm; τ=100 fs, 300 ps, 10 ns, and 150 ns; E>0.1 J/cm2). Laser irradiation causes the detachment and removal of material layers, whose lateral size is comparable with the irradiated area and whose thickness of 10–200 nm is much less than the DLC film thickness. The influence of the laser parameters on the thickness, size, and number of removed layers is examined. A qualitative explanation of laser-induced spallation in DLC films is proposed, which is based on the fact that the absorbed laser pulse produces a rapidly expanding surface layer of modified structure and reduced density.

The contribution of curvature dependent sputtering and mass redistribution to ion-induced self-organized formation of periodic surface nanopatterns is revisited. Ion incidence angle-dependent curvature coefficients and ripple wavelengths are calculated from 3-dimensional collision cascade data obtained from binary collision Monte Carlo simulations. Significant modifications concerning mass redistribution compared to the model of Carter and Vishnyakov and also models based on crater functions are introduced. Furthermore, I find that curvature-dependent erosion is the dominating contribution to pattern formation, except for very low-energy irradiation of a light matrix with heavy ions. The major modifications regarding mass redistribution and ion-induced viscous flow are related to the ion incidence angle-dependent thickness of the irradiated layer. A smaller modification concerns the relaxation of inward-directed mass redistribution. Ion-induced viscous flow in the surface layer also depends on the layer thickness and is thus strongly angle dependent. Simulation results are presented and compared to a variety of published experimental results. The simulations show that in most cases curvature-dependent erosion is the dominant contribution to surface instability and ripple pattern formation and also determines the pattern orientation transition. The simulations predict the occurrence of perpendicular ripple patterns at larger ion incidence angles, in agreement with experimental observations. Mass redistribution causes stabilization of the surface at near-normal ion incidence angles and dominates pattern formation only at very low ion energies.

The dependence of ferroelectric phase transition temperature as a function of strontium substitution in lead titanate zirconate thin films (referred here as PSZT) on platinum-coated silicon substrates was investigated. The dielectric study reveals that the material undergoes a diffuse type ferroelectric phase transition that depends on the substitution of Sr for Pb in PZT. At 100 kHz, the phase transition temperatures were 633, 613 and 516 K for PSZT10, PSZT20 and PSZT30 thin films, respectively. On the other hand, the results showed that the dependence of the dielectric constant upon the frequency does not reveal any relaxor behavior. The diffusivity increases with increasing Sr contents in the studied composition range. The experimental data obtained from measurements of the dielectric constant as a function of temperature and frequencies showed a classical behavior of ferroelectric phase transition in PSZT thin films, rather than a relaxor ferroelectric phase transition. The transition temperature decreases with increasing Sr contents due to the decrease in grain size, lattice decrease and local structural disorder.

Following a phenomenological approach an expression for the nonlinear current density in a plasma in the presence of an amplitude-modulated two-dimensional Gaussian (in space) electromagnetic beam has been derived. This expression has been used to study the nonstationary self focusing and resulting self distortion of the beam. The amplitude maxima/minima of the beam are focused by different amounts giving rise to a moving periodic focus and an overmodulation of the beam. The effect of finite values of relaxation times, involved in the nonlinearity, is to shift the amplitude envelope on the time scale.

p +/n + In0.53Ga0.47As tunnel diodes were prepared by liquid phase epitaxy and their electrical properties were characterized. These devices exhibit large forward conductances (2.59×103 Ω−1 cm−2), high peak current densities (793 A/cm2) and large peak to valley current ratios (16.2). These devices offer great promise as intercell ohmic contacts (IOCs) for InP-based, onolithic multijunction solar cells.