Chiral tunneling in trilayer graphene

We study the effect of chiral-tunneling in Bernal and Rombhohedral stacked trilayer-graphene (3LG). Based on the chirality of the electronic bands, at the K-point, (Rombhohedral) Bernal-3LG exhibits 100% (50%) transparency across a heterojunction. Utilizing this property, we further investigate the effect of electron collimation in 3LG. Due to the difference in the Berry's phase, we show that, Rombhohedral-3LG is a better electron collimator, compared to monolayer and Bernal-bilayer graphene. Since, Bernal-3LG can be decomposed into two separate channels consisting of a monolayer and a modified Bernal-bilayer graphene; the Bernal-3LG is weaker electron collimator, compared to Rombhohedral-3LG.Comment: APL, 2012; http://dx.doi.org/10.1063/1.370375

Plasmonic behaviour of sputtered Au nano island arrays

Je demonstrována specifikace formování naprášených Au nano-ostrůvkových polí (NOP) na skleněných substrátech, anebo na tenkých vrstvách ZnO dopovaných galiem. Statistická analýza morfologie zobrazení SEM a AFM ukázala normální rozdělení velikosti nano-částic na dlouhou vzdálenost - jejich modus AM se měnil z 8 na 328 nm2 v závislosti na hustotě výkonu naprašování, který definoval nominální tloušťku vrstvy v rozpětí 2-8 nm. Přednostní orientace krystalitů Au NOP ve směru [111] kolmém k podložce se zvyšuje s vyšší hustotou výkonu naprašování a po tepelném zpracování vrstev. Příčně lokalizovaná povrchová plazmonická rezonance (LPPR vyhodnocená pomocí transmisní UV-Vis spektrofotometrie) ukázala „rudý“ posun extinkčního maxima (l ≤ 100 nm) se zvýšením nominální tloušťky a „modrý“ posun (≤ -65 nm) po žíhání Au NOP. Plazmonické vlastnosti Au NOP byly popsány modifikací velikostně škálovacího univerzálního modelu použitím nominální tloušťky vrstvy jako technologického škálovacího parametru. Naprášením mezilehlé ultra-tenké vrstvy titanu mezi sklo a zlato se zlepší adheze zlatých nano-ostrůvků, jakož i podpora formování lépe definované struktury Au NOP menší dimenze.The specificity of the formation of Au sputtered nanoisland arrays (NIA) on a glass substrate or on a ZnO thin film doped by Ga is demonstrated. Statistical analysis of morphology images (SEM, AFM) exhibited the Log-normal distribution of the size (area) of nanoislands—their modus AM varied from 8 to 328 nm2 depending on the sputtering power density, which determined the nominal thicknesses in the range of 2–8 nm. Preferential polycrystalline texture (111) of Au NIA increased with the power density and after annealing. Transverse localised surface plasmonic resonance (LSPR; evaluated by transmission UV–vis spectroscopy) showed the red shift of the extinction peaks (l ≤ 100 nm) with an increase of the nominal thickness, and the blue shift( ≤ −65 nm) after annealing of Au NIA. The plasmonic behaviour of Au NIA was described by modification of a size-scaling universal model using the nominal thin film thickness as a technological scaling parameter. Sputtering of a Ti intermediate adhesive ultrathin film between the glass substrate and gold improves the adhesion of Au nanoislands as well as supporting the formation of more defined Au NIA structures of smaller dimensions

Molecular dynamics simulations of Ni/NiAl interfaces

Molecular dynamics simulations are used to study brittle/ductile interfaces Ni/B2-NiAl under mechanical loading. Uniaxial tensile tests perpendicular to the interface are performed. It is shown that interfaces have influence on strain induced material failure by nucleation of defects. Crack propagation in the interface is investigated by applying load via fixed displacement boundary conditions. Determined crack velocities in the interface are found to be clearly above those in each of the materials

The effect of clay on foaming and mechanical properties of glass foam insulating material

In the current study, the main composition was prepared using soda-lime glass with dolomite [CaMg(CO3)(2)] as a foaming agent. The clay powder was added to the main composition in different ratios, and then, the mixtures were shaped by one-axial pressing. Differential thermal analysis (DTA) was used for the determination of crystallization temperatures, and the samples were heated according to the DTA results. Furthermore, heating microscopy was employed for studying the high-temperature behaviours of the mixtures. The samples were characterized using scanning electron microscopy, X-ray diffraction analysis, and comprehensive strength testing. Porosity and bulk density were measured to assess the foaming capability of the mixtures. The results showed that clay addition has a positive role on the mechanical properties of glass foam