Smoothening Effect Research Articles

Correlation of magnetotransport and structure in sputtered Co/Cu multilayers

Magnetic multilayer structures of Co/Cu prepared by dc magnetronsputtering are studied with respect to changing number of bilayers(N)for different thicknesses of the Cu spacer layer corresponding to different couplingconditions according to the oscillatory interlayer exchange coupling. X-ray reflectivityand diffuse scattering show that the multilayers become smoother with increasingN. Thegrowth exponent of the roughness is found to be lower for a multilayerthan for a single-layer film of similar thickness. The roughness ofsubsequent interfaces along the stack is conformal, and the lateralcorrelation does not change with the period number, but depends on thethickness of the spacer layers. The improved layer structure for largerN increasesthe antiferromagnetic coupling fraction as inferred from magneto-optic Kerr effectmeasurements and thereby increases the giant magnetoresistance (GMR) ratio up to 35%for N = 10.Thus, the first few bilayers do not contribute to the GMR but act as a buffer toimprove the growth conditions for the following bilayers. The first about fivebilayers can be replaced by a bottom Co layer of equivalent thickness which alsoimproves the layer structure for a subsequently deposited lower number of bilayerswithout much loss in the GMR ratio. This smoothening effect due to theincreasing of the thickness of the bottom-most layer is related to thesimultaneously decreasing grain size.

Effect of smoothening functions on the frequency response of an oscillator with clearance non-linearity

Effect of smoothening functions on the frequency response of an oscillator with clearance non-linearity

Femtosecond pulsed laser ablation with spatial filtering

With the rise in demand for miniaturized features with better acute edge acuity and negligible thermal damage zone, one of the key vital areas lies in the refinement of the quality of the laser beam itself. Spatial filter is routinely used in optical micromachining systems to smoothen the Gaussian profile of the machining spot in order to obtain a feature of the desired quality. However, its profile smoothening effect has never been investigated for femtosecond pulsed laser micromachining process since the extremely high peak power of femtosecond pulses will cause damage on the filtering aperture of spatial filter. During the development of an acousto-optical micromachining system using femtosecond pulses, we found that if the damage of the filtering aperture can be circumvented, spatial filter can improve the machining quality of femtosecond pulse ablation, especially when ablation is conducted at low-fluency range (just above the ablation threshold fluency). In this paper, we investigate and demonstrate both the improvement and potential that beam refinement can bring about. In our experiment, a series of test patterns were ablated with a 400 nm second-harmonic Ti:Sapphire femtosecond laser of 150 fs duration at varying pulse energy ranging from 31 to 39 nJ. The specimen used in the experiment is a platinum- (Pt) sputtered coating of 100 nm thickness on a quartz substrate. The results show a significant improvement in the constancy of the shape as well as the size of ablated feature, revealing an improved beam profile and beam energy distribution due to spatial filtering.

Asymptotic step profiles from a nonlinear growth equation for vicinal surfaces

We study a recently proposed nonlinear evolution equation describing the collective step meander on a vicinal surface subject to the Bales-Zangwill growth instability [O. Pierre-Louis et al., Phys. Rev. Lett. 80, 4221 (1998)]. A careful numerical analysis shows that the dynamically selected step profile consists of sloped segments, given by an inverse error function and steepening as sqrt[t], which are matched to pieces of a stationary (time-independent) solution describing the maxima and minima. The effect of smoothening by step-edge diffusion is included heuristically, and a one-parameter family of evolution equations is introduced that contains relaxation by step-edge diffusion and by attachment-detachment as special cases. The question of the persistence of an initially imposed meander wavelength is investigated in relation to recent experiments.

Time-Resolved X-Ray Scattering Study of Co Surface Evolution during Low-Energy Ion Irradiation

AbstractThe sputter-erosion of hcp Co (0001) single crystal with Ar+ ions in the 100 to 700 eV energy range was investigated using in-situ time-resolved x-ray scattering. At temperatures above 300°C the surface remains relatively smooth, erosion evolving through a layer-by-layer or step flow mechanism. In this regime the ions have a smoothening effect on the surface and the resulting roughness decreases with increasing ion energy. Below 300°C the surface develops a pattern of mounds or pits with a characteristic wavelength. The time, ion energy and temperature dependence of this wavelength were studied in detail. Epitaxial Co thin films thermally evaporated on sapphire were also sputtered through in order to synthesize self-assembled arrays of Co nanoclusters with a narrow size distribution. The degree of local order within the Co dot arrays was examined using atomic force microscopy.

Real time measurements of surface growth evolution in magnetron sputtered single crystal Mo/V superlattices using in situ reflection high energy electron diffraction analysis

The use of video recording of reflection high energy electron diffraction (RHEED) patterns for assessing the dynamic evolution of the surface morphology and crystallinity during growth was evaluated. As an example, Mo/V(001) superlattices with varying layer thickness (with periods Λ of 2.5 to 8.9 nm and a constant Mo:V ratio of 1:1) were examined. During the deposition, changes from two- to three-dimensional growth were observed in situ. From prior transmission electron microscopy (TEM) and X-ray diffraction (XRD) studies, it is known that this transition is associated with a critical thickness and concurrent roughening of the V layer. Video recording and subsequent image and data processing allowed the surface morphology to be continuously followed during growth. Post-growth analyses of the recorded data provided the evolution of surface lattice parameters and short range [1–2 monolayer (ML)] surface roughnesses with a time resolution of 200–400 ms (0.02–0.04 nm thickness resolution). During growth of Mo, a smoothening effect could be observed while the growth of V evidently increased the surface roughness from 1 to 2 ML. Furthermore, the onset of coherency strain relaxation of the topmost growing layers was observed to occur at 2.0–2.5 nm layer thicknesses for both materials, which is in qualitative agreement with theoretical predictions.

Big islands in dispersing billiard-like potentials

We derive a rigorous estimate of the size of islands (in both phase space and parameter space) appearing in smooth Hamiltonian approximations of scattering billiards. The derivation includes the construction of a local return map near singular periodic orbits for an arbitrary scattering billiard and for the general smooth billiard potentials. Thus, universality classes for the local behavior are found. Moreover, for all scattering geometries and for many types of natural potentials which limit to the billiard flow as a parameter ϵ→0, islands of polynomial size in ϵ appear. This suggests that the loss of ergodicity via the introduction of the physically relevant effect of smoothening of the potential in modeling, for example, scattering molecules, may be of physically noticeable effect.

Direct current bias applied to hot flame diamond deposition produces smooth low friction coatings

As-deposited diamond coatings generally have a high surface roughness which results in a high friction coefficient and extensive wear of the counter material in sliding contact. Therefore several methods for smoothening diamond coatings have been proposed, such as laser polishing, molten metal etching, thermochemical polishing and mechanical polishing. All these methods have some disadvantage e.g. long processing time or high processing temperature. Furthermore, they are all post-deposition treatments i.e. the manufacture of these coatings requires at least two processing steps, deposition and smoothening. With the present method which combines d.c. bias with hot flame diamond deposition, a smooth diamond surface is produced during the actual growth of the film. No post-deposition treatment is necessary. The surface roughness is not dependent on the coating thickness which means that thick coatings with smooth surface can be produced. In fact, the method has a smoothening effect, i.e. rough surfaces can be made smooth. The method is comparable to conventional hot flame deposition of diamond as to growth rate and cost of producing the coatings. The coatings have a nano-crystalline structure and a surface roughness of Ra = 25 nm, and result in a friction coefficient of 0.1 or less in dry sliding and about 0.05 in water-lubricated sliding against cemented carbide. Their wear resistance is virtually the same as that of conventional diamond films.

Silicon Surface Treatments and Their Impact on Chemical Composition and Morphology

The smoothness of silicon wafer surfaces is defined by polishing. Subsequent cleaning steps take account of surface conditioning of the wafer and meet the demands for low metal surface contamination as well as low particle level. Wet chemical treatments, however, can also influence surface morphology. The coexistence of oxidation and etching of the Si surface has a pronounced feedback on the resulting surface roughness. This holds in particular for SC1 cleaning solutions and modified HF treatments. Buffered HF enhances surface roughness of the technological important Si (100) surface, in contrast to a smoothening effect on Si (111). The same holds for other modifications of HF treatments with an enhanced oxidation behaviour involved, like HF-H2O2 solutions. In parallel with the change of surface morphology and with the increase of surface roughness an increase in Light Point Defect (LPD) densities is also found. Small LPDs are predominantly not particle related, depend on the respective silicon substrate material and were not found to influence gate oxide integrity.

Thin-film coalescence in hydrogenated amorphous silicon probed by spectroscopic ellipsometry with millisecond-scale resolution.

New developments in spectroscopic ellipsometry (1.5\ensuremath{\le}h\ensuremath{\nu}\ensuremath{\le}4.3 eV) now provide quantitative information on thin films with a time resolution of 16 ms. We report submonolayer sensitivity to a surface smoothening effect associated with nuclei coalescence in the early stages of hydrogenated amorphous silicon (a-Si:H) preparation by plasma-enhanced chemical vapor deposition. An investigation of a-Si:H prepared on c-Si and Cr substrates under different conditions of substrate temperature and plasma power discloses a clear correlation between the magnitude of this effect and the ultimate bulk properties of the material.

Ion etching of thin W layers: enhanced reflectivity of W-C multilayer coatings

Thin layers of tungsten were deposited on carbon films by electron beam evaporation and subsequently ion etched by bombardment with Ar + ions of 200 eV. We used an in-situ soft X-ray reflection monitor as a diagnostic tool and observed a consistently higher reflectivity for a given thickness of the W layer after ion etching than as-deposited. We ascribe the difference to a considerable decrease of the surface roughness induced by the ion bombardment process. This smoothening effect occurred mainly during etching of the first 1.5 nm. Since the interface roughness is an important parameter influencing the efficiency of X-ray reflecting optics, we applied ion etching to each tungsten layer in a W(1.3 nm)-C(1.5 nm) multilayer coating of 10 periods: We deposited tungsten layers having a thickness of 2.8 nm and subsequently removed about 1.5 nm using ion etching. For comparison we deposited an identical coating without ion etched tungsten layers. We report a relative increase of the reflectivity at the N Kα emission line by a factor 3 for the multilayer coating having ion etched tungsten layers.

Hydrogen ion beam smoothening of Ge(001)

Low-energy hydrogen ion beams are shown to clean and rapidly smoothen Ge(001) surfaces that have been subjected to severe oxygen roughening. Characteristic smoothening times of 1000 s are found at 500 °C for 200 to 600 eV hydrogen ion beams at fluxes of 200 nA/cm2. By comparing hydrogen and noble gas ion bombardment at various temperatures, we show that the hydrogen ion smoothening effect consists of both physical and chemical mechanisms which act to free pinned surface sites of contaminants and enable subsequent thermal smoothening of the germanium surface. Such oxygen roughened surfaces can be recovered to a state suitable for epitaxial growth without resorting to high-temperature annealing, keV ion sputtering or additional growth.

Kinetics of Molecular Beam Epitaxy: Effect of Ion-Induced Sputtering

ABSTRACTSteady state roughness of surfaces growing by molecular beam epitaxy is investigated by Monte Carlo simulations under conditions where an ion beam is also present which sputters adatoms off the surface. If the sputtering is random, it only increases the roughness. But if the sputtering probability is strongly dependent on the binding energy of an adatom within a cluster or island, the ions can have a smoothening effect. Physical arguments are given in support of the results.

On Airflow Boundary Layer above the Profile of Long Waves

Experiments were performed on the airflow boundary layer over pre-existing long waves. The latter were verified to have smoothening effects on the wind-disturbed water surface. The wind stress was found to be modulated, with a larger stress on the windward face of long waves.