Search

Phase transformations between amorphous and crystalline states induced by irradiation of pulsed laser deposition grown GeTe thin films with nanosecond laser pulses at 248 nm and pulse duration of 20 ns are studied. Structural and optical properties of the Ge-Te phase-change films were studied by X-ray diffraction and optical reflectivity measurements as a function of the number of laser pulses between 0 and 30 pulses and of the laser fluence up to 195 mJ/cm2. A reversible phase transition by using pulse numbers ⩾5 at a fluence above the threshold fluence between 11 and 14 mJ/cm2 for crystallization and single pulses at a fluence between 162 and 182 mJ/cm2 for amorphization could be proved. For laser fluences from 36 up to 130 mJ/cm2, a high optical contrast of 14.7% between the amorphous and crystalline state is measured. A simple model is used that allows the discussion on the distribution of temperature in dependency on the laser fluence. [ABSTRACT FROM AUTHOR]

The temporal shape evolution in glancing angle deposition was examined for a-Ge nanocolumns on honeycomb templates. The column shape formation is closely related to the particular stage of deposition and two shape regions were observed. (1) A broadening shape develops in the initial stage. Interdistance deposits were found to result from insufficient shadowing of the early nanostructures. On top of the nanocolumns, a characteristic cap is observed, which results from next-neighbor shadowing. (2) When the equilibrium cross-section shape is reached, a columnar region with parallel border planes follows. The shape of the cross-section can be tuned from triangular to hexagonal/round by adjusting the honeycomb lattice periodicity and the deposition angle. Based on quantitative investing on the axial sizes of the shape regions, conclusions regarding the influencing growth processes in glancing angle deposition on pre-patterned substrates are drawn. [ABSTRACT FROM AUTHOR]

We report on the experimental and theoretical investigation of the magnetization reversal in magnetic nanotubes that have been synthesized by a combination of glancing angle and atomic layer deposition. Using superconducting quantum interference device magnetometry the angular dependence of the coercive fields is determined and reveals a nonmonotonic behavior. Analytical calculations predict the crossover between two magnetization reversal modes, namely, the movement of different types of domain boundaries (vortex wall and transverse wall). This transition, already known in the geometrical dependences of the magnetization reversal in various nanotubes, is found within one type of tube in the angular dependence and is experimentally confirmed in this work. [ABSTRACT FROM AUTHOR]

Regular arrays of Si nanorods with a circular cross section in hexagonal-closed-packed and triangular cross section in honeycomblike arrangements were grown using glancing angle deposition on Si(100) and fused silica substrates that were patterned with Au dots using self-assembled mono- and double layers of polystyrene nanospheres as an evaporation mask. The Au dots were used as an etching mask for the underlying silica substrates in a reactive ion beam etching process, which greatly enhanced the height of the seeding spaces for the subsequent glancing angle deposition. An elongated shadowing length l of the prepatterned nucleation sites and less growth of Si structures between the surface mounds could be achieved this way. Differences in form, height, and diameter of the Si nanorods grown on either hcp or honeycomb arrays are explained by purely geometrical arguments. Different seed heights and interseed distances are found to be the main reasons for the strong distinctions between the grown nanorod arrays. [ABSTRACT FROM AUTHOR]

Nanostructured Ti thin films are fabricated by oblique angle deposition (OAD) in combination with electron beam evaporation in an ultrahigh vacuum chamber at room temperature on thermally and natively oxidized Si(100) substrates. The incidence angle θOAD of the incoming particle flux with respect to the substrate normal is varied between 70° ≤ θOAD ≤ 84°. This highly oblique deposition geometry leads to the formation of highly porous, thin, crystalline films consisting of separated Ti columns that are oriented toward the incoming particle flux. The influence of the incidence angle on the texture, morphology, and columnar tilt angles of these Ti thin films is investigated. It is found that the texture depends on the angle θOAD of the incoming particle flux. High-resolution transmission electron microscopy reveals that highly oblique deposited Ti columns tend to grow with single crystalline morphology. The orientation of the lattice planes in the Ti columns with respect to the substrate normal changes remarkably as the incidence angle is varied. Moreover, the orientation of the lattice planes differs from the growth direction of the columns. The samples are analyzed using x-ray diffraction measurements such as in-plane pole figure measurements and θ-2θ x-ray diffraction patterns, as well as by using transmission electron microscopy and scanning electron microscopy. [ABSTRACT FROM AUTHOR]

In this work, a synthesis method for the growth of low-defect large-area graphene using carbon ion beam implantation into metallic Cu foils is presented. The Cu foils (1 cm² in size) were preannealed in a vacuum at 950 °C for 2 h, implanted with 35 keV carbon ions at room temperature, and subsequently annealed at 850 °C for 2 h to form graphene layers with the layer number controlled by the implantation fluence. The graphene was then transferred to SiO2/Si substrates by a PMMA-free wet chemical etching process. The obtained regions of monolayer graphene are of ~900 µm size. Raman spectroscopy, atomic force microscopy, scanning electron microscopy, and optical microscopy performed at room temperature demonstrated a good quality and homogeneity of the graphene layers, especially for monolayer graphene. [ABSTRACT FROM AUTHOR]

An attempt to deposit a high quality epitaxial thin film of a two-dimensionally bonded (layered) chalcogenide material with van-der-Waals (vdW) epitaxy is of strong interest for non-volatile memory application. In this paper, the epitaxial growth of an exemplary layered chalcogenide material, i.e., stoichiometric Sb2Te3 thin films, is reported. The films were produced on unreconstructed highly lattice-mismatched Si(111) substrates by pulsed laser deposition (PLD). The films were grown by vdW epitaxy in a two-dimensional mode. X-ray diffraction measurements and transmission electron microscopy revealed that the films possess a trigonal Sb2Te3 structure. The single atomic Sb/Te termination layer on the Si surface was formed initializing the thin film growth. This work demonstrates a straightforward method to deposit vdW-epitaxial layered chalcogenides and, at the same time, opens up the feasibility to fabricate chalcogenide vdW heterostructures by PLD. [ABSTRACT FROM AUTHOR]

The article discusses a study on direct imaging of crystal structure of chalcogenide (GST) thin films by using quantitative aberration-corrected scanning transmission electron microscopy. It mentions that the study included X-ray diffraction (XRD), analysis of crystallization behavior of amorphous GST thin film, and X-ray spectroscopy studies.

In this report, we show that an annular dark-field detector in an aberration-corrected scanning transmission electron microscope allows the direct observation of light element columns in crystalline lattices. At specific imaging conditions, an enhancement of the intensities of light element columns in the presence of heavy element columns is observed. Experimental results are presented for imaging the nitrogen and carbon atomic columns at the GaN-SiC interface and within the GaN and SiC compounds. The crystal polarity of GaN at the interface is identified. The obtained findings are discussed and are well supported by image simulations. [ABSTRACT FROM AUTHOR]

Si sculptured thin films consisting of spiral-, screw-, and columnlike-shaped nanostructures were grown by ion beam-induced glancing angle deposition of Si on rotating bare Si[001] substrates at different substrate rotational speeds and substrate temperatures ranging from room temperature to (360±10)°C. For rotational speeds leading to the growth of nanoscrews at room temperature, morphology changes are observed with increasing temperature, such as an increase of the critical height at which single spiral fibers start merging to screws, thus giving the possibility to grow separated nanospirals with diameters of about 30 nm over a large thickness range. A decrease of the overall film thickness, indicating a change in the film density, is also observed with increasing the substrate temperature. For deposition conditions leading to the growth of vertical columns at room temperature, the substrate temperature influences the total number of columns, the column diameter, and the total structure height. The temperature-related changes in structure morphology show that surface diffusion effects play an important role in the morphological evolution of sculptured thin films consisting of helicoidal and columnlike structures during their growth by glancing angle deposition. [ABSTRACT FROM AUTHOR]

Various silicon nanostructures (twofold chevrons and three- and fourfold spirals) were grown on silicon [111] substrates prepatterned with a two-dimensional square lattice of blocks with different block size and periodicity via ion beam induced glancing angle deposition at room temperature, in combination with a controlled substrate rotation. Top view and cross-section scanning electron microscopy pictures reveal that form, size, and periodicity of the structures are strongly dependent on the size and periodicity of the seeding space and differ widely from structures grown on plain substrates. It is shown that the growth of periodically arranged nanostructures, which is important for many possible applications, including photonic crystals, on prepatterned substrates is only possible if the periodicity of the seeding spaces matches the natural lateral dimensions of the structures grown on bare substrates. [ABSTRACT FROM AUTHOR]

Surface-enhanced fluorescence from porous, metallic sculptured thin films (STFs) was demonstrated for sensing of bacteria in water. Enhancement factors larger than 15 were observed using STFs made of silver, aluminum, gold, and copper with respect to their dense film counterparts. The STFs used are assemblies of tilted, shaped, parallel nanowires prepared with several variants of the oblique-angle-deposition technique. Comparison between the different films indicates that the enhancement factor is higher when the tilt is either small (<30 deg) or large (>80 deg); thus, the enhancement is higher when only a single resonance in the nanowires is excited. [ABSTRACT FROM AUTHOR]

Hydrogen preimplantation performed in addition to helium implantation efficiently shrinks the width of the gettering layer in Si and increases the empty volume fraction as well as the internal surface area per unit volume. The gettering efficiency for oxygen is significantly enhanced compared to the single helium implantation, and the helium implantation dose can be strongly reduced. The gas-filled bubble layer induced by the coimplantation of hydrogen and helium has the highest gettering efficiency for the oxygen accumulation. Direct evidence for oxygen gettering at the internal wall of the cavity is demonstrated by cross-sectional transmission electron microscopy. [ABSTRACT FROM AUTHOR]

Growth of Ge2Sb2Te5 phase-change films on flexible polyimide substrates by pulsed laser deposition (PLD) is demonstrated. The effect of annealing temperature on the crystalline nature of the films was studied. A decrease of (200) lattice plane distance with the increase of annealing temperature was revealed for the films grown on both polyimide and Si substrates, which was related to tensile stress in the crystallized films. Optical reflectivity measurements showed a high reflectivity contrast between full crystalline and amorphous films. The results indicate an excellent potential for applications of these PLD-deposited Ge2Sb2Te5 films on flexible polyimide substrates in optical data storage. [ABSTRACT FROM AUTHOR]