Smooth Multilayers Research Articles

Quantum Linear Magnetoresistance and Shubnikov De-Haas Oscillation in Suspended Wrinkled and Smooth Multilayer Graphene

Quantum Linear Magnetoresistance and Shubnikov De-Haas Oscillation in Suspended Wrinkled and Smooth Multilayer Graphene

Structural and Mechanical Properties of Zirconia Film Deposited by Plasma Focus Device

Nano-crystalline ZrO2/ZrSiO4 composite films are deposited on Si by the irradiation of energetic oxygen ions by plasma focus operation. The XRD patterns confirm the development of different phases (ZrO2 and ZrSiO4) which grow along various orientations and their peak intensities strongly depend on increasing focus shots and sample angular positions. The average crystallite size of the films deposited at 0° angular position is increased with increasing focus shots while it is decreased for the films deposited at 10° angular position. The dislocation density in ZrSiO4 (2 0 4) plane is increased from 3.51 × 10−5 to 8.67 × 10−5 (nm)−2 while it is decreased from 8.85 × 10−5 to 0.011 × 10−5 (nm)−2 in m-ZrO2 (1 2 3) plane when the samples are treated at 0° and 10° angular positions for five focus shots respectively. The FESEM analysis confirms the formation of rounded nano-particles, complicated network of nano-rods, formation of compact, uniform and smooth multi-layers. The EDS analysis confirms the presence of Si, Zr and O in the composite films deposited for different focus shots and sample angular positions. The maximum microhardness of the composite film deposited for 25 focus shots is found to be 10.56 ± 0.51 GPa which definitely will improve the life time of the coated material.

Wrinkles enhance the diffuse reflection from the dragonfly Rhyothemis resplendens.

The dorsal surfaces of the hindwings of the dragonfly Rhyothemis resplendens (Odonata: Libellulidae) reflect a deep blue from the multilayer structure in its wing membrane. The layers within this structure are not flat, but distinctly 'wrinkled', with a thickness of several hundred nanometres and interwrinkle crest distances of 5 µm and greater. A comparison between the backscattered light from R. resplendens and a similar, but un-'wrinkled' multilayer in the damselfly Matronoides cyaneipennis (Odonata: Calopterygidae) shows that the angle over which incident light is backscattered is increased by the wrinkling in the R. resplendens structure. Whereas the reflection from the flat multilayer of M. cyaneipennis is effectively specular, the reflection from the wrinkled R. resplendens multilayer spans 1.47 steradians (equivalent to ±40° for all azimuthal angles). This property enhances the visibility of the static wing over a broader angle range than is normally associated with a smooth multilayer, thereby markedly increasing its conspicuousness.

Fabrication of laser deposited high-quality multilayer zone plates for hard X-ray nanofocusing

Abstract Recently, we demonstrated unprecedented sub-5 nm point focusing of hard X-rays (at 7.9 keV) based on the combination of a high gain Kirkpatrick–Baez (KB) mirror system and a high resolution W/Si multilayer zone plate (MZP). This MZP was prepared by the combination of pulsed laser deposition (PLD) and focused ion beam (FIB). Despite the small focus size, the MZP's quality suffered from sufficient but comparatively low efficiency (2%). In this paper we discuss how to overcome limitations of MZP fabrication by PLD by investigating the material systems W/Si, W/ZrO2, and Ta2O5/ZrO2. We give a detailed description on the optimization processes for the deposition of smooth multilayers with highly precise layer thicknesses on a rotating wire. Furthermore, we present our latest results regarding a Ta2O5/ZrO2 MZP, which has been proven already to be a system of high potential in the very first experiments as the efficiency reached 6.9% (at 18 keV).

Formation of Smooth, Conformal Molecular Layers on ZnO Surfaces via Photochemical Grafting

We have investigated the photochemical grafting of organic alkenes to atomically flat ZnO(10 ̅10) single crystals and ZnO nanorods as a way to produce functional molecule-semiconductor interfaces. Atomic force microscopy shows that photochemical grafting produces highly conformal, smooth molecular layers with no detectable changes in the underlying structure of the ZnO terraces or steps. X-ray photoelectron spectroscopy measurements show that grafting of a methyl ester-terminated alkene terminates near one monolayer, while alkenes bearing a trifluoroacetamide-protected amine form very smooth multilayers. Even with multilayers, it is possible to deprotect the amines and to link a second molecule to the surface with excellent efficiency and without significant loss of molecules from the surface. This demonstrates that the use of photochemical grafting, even in the case of multilayer formation, enables multistep chemical processes to be conducted on the ZnO surface. Photoresponse measurements demonstrate that functionalization of the surface does not affect the ability to induce field effects in the underlying ZnO, thereby suggesting that this approach to functionalization may be useful for applications in sensing and in hybrid organic-inorganic transistors and related devices.

The effect of surfactants on the growth of Co/Cu multilayers

The effect on the interface structure of multilayers of a pre-deposited ultrathin film of Bi and Pb surfactants introduced into Co/Cu multilayers has been studied. The [Co(1 nm)/Cu(2 nm)] multilayers were thermally evaporated at very low deposition rates with a small amount of Bi and Pb surfactant (about 0.2 ML) introduced at each Cu layer. Auger spectra were taken after subsequent steps of evaporation of Co and Cu, and also after evaporation of surfactants. The evolution of Auger peaks showed that on both Co and Cu surfaces a surfactant peak was always visible. Its intensity continuously increased with the number of Co/Cu repetitions. This shows that the surfactant already segregates to the surface of Co/Cu multilayers during the deposition process. The structure of Co/Cu multilayers with added surfactant has been studied using low-angle X-ray reflectivity. We have found that surfactant addition leads to well-ordered structures with small roughness (a few Å). The results demonstrate that the application of a surfactant during deposition process allows the fabrication of atomically smooth multilayers via a surface segregation mechanism.

Heteroepitaxial Growth Mode Transitions in the Presence of a Schwoebel Barrier at an Island Edge

AbstractA recently developed model for homoepitaxial growth on a singular surface in the presence of a Schwoebel barrier at an island edge is extended to the case of heteroepitaxy (without lattice mismatch) by introducing different adatom mobilities in the first layer (heterodiffusion) and in all the next ones (self-diffusion).The model consists of an infinite set of rate equations for adatom and 2D island areal densities and coverage in successive layers. Growth behaviour depending on the model parameters is studied with emphasis on the transient growth regimes: layer-by-layer (LL) to a smooth multilayer (SML) and SML to a rough 3D growth. It is shown that a slower heterodiffusion relative to the self-diffusion leads to a smoother initial growth and thus retards the LL → SML growth trasition, whereas a faster heterodiffusion leads to a rougher initial growth and assists that transition and especially SML → 3D growth transitition at a higher Schwoebel barrier. It is found also that in a smooth growth regime nucleation kinetics eventually acquires a universal scaling form and the corresponding exponents are determined.

The influence of brighteners on the friction and wear of electrodeposited multilayer films

Electrodeposited Cu/Ni multilayer alloy films were prepared on a beryllium bronze substrate by a single bath technique. The tribological behavior of the films was investigated with a DF-PM apparatus which is capable of measuring both the static and kinetic friction coefficients. The effect of the concentration of brighteners on the tribological behavior of Cu/Ni multilayer films was also examined using the same friction and wear apparatus. The surface roughness, crystal orientation, and stress of Cu/Ni multilayers were analyzed with emphasis on revealing the relationship between the structure of the films and their tribological behavior. The results showed that the electrodeposited Cu/Ni multilayer film obtained from the bath containing 0.5 ml l −1 brightener exhibited a low friction coefficient and excellent anti-wear properties. The microstructural observation of the films indicated that highly compact and smooth multilayers were obtained in this case. The results from X-ray diffractometer analysis showed that the orientation of Cu/Ni multilayer films changed from the (200) plane to the (111) plane which is parallel to the surface when the content of the brighteners in the bath increased from 0 to 0.5 ml l −1. Moreover, multilayers with a low level of compressive stress were obtained at a brightener concentration of 0.5 ml l −1. It was supposed that the compactness and smoothness of the Cu/Ni multilayer films, the change in the crystal orientation of the Cu/Ni multilayer films from the (200) plane to the (111) plane, and the low compressive stress of the films jointly contributed to the low friction coefficient and excellent anti-wear properties.