Mean Square Surface Roughness Research Articles

Precision aspherization of the surface of optical elements by ion-beam etching

Ion-beam methods are developed for forming supersmooth aspherical optical surfaces of polished fused quartz with a precision on the level of 3 nm relative to the standard deviation and 0.2–0.3 nm for the mean-square surface roughness in the range of spatial frequencies of 0.01–100 μm−1.

High-Performance Flexible Bottom-Gate Organic Field-Effect Transistors with Gravure Printed Thin Organic Dielectric.

Gravure-printed dielectric films are presented, which are 100-nm thick, have about 1-nm root mean-square surface roughness and show high electric field strength (>300 MV/m). This dielectric is combined with an ultra-thin—less than 10 nm—layer of poly(α-methylstyrene) on top which gives state-of-the-art field-effect mobility in transistors with thermally-evaporated pentacene (0.6 cm2/Vs) and zone-cast TIPS-pentacene (0.3 cm2/Vs).

Effects of withdrawal speed on the structural and optical properties of sol–gel derived ZnO thin films

Nanostructured zinc oxide (ZnO) of hexagonal wurtzite crystal structure was successfully prepared on corning glass substrates by sol–gel method using dip coating technique. The effects of withdrawal speed (WS) on the crystalline structure, morphology and optical properties of the pure ZnO thin films were investigated using x-ray diffraction (XRD), atomic force microscopy (AFM) and optical transmittance measurements. It was found that, the WS significantly affects the crystalline structure, morphology and optical properties of the films. All ZnO films were observed to grow along the c-axis with a preferential orientation of (0 0 2). The lower the withdrawal speed of the substrate the higher the tendency toward preferred orientation along (0 0 2) plane. The surface roughness mean square (RMS) of the films as estimated from AFM measurements rises from 6 to 19 nm, when the withdrawal speed increased from 20 to 80 mm/min, respectively. The optical transmittance of the films within the visible and near infrared region was found to be about 80%. The optical constants of the films such as refractive index (n) and extinction coefficient (k) were determined using spectroscopic ellipsometer (SE) technique. The optical constants (n and k) were fitted according to Cauchy model.

Experimental characterization of the inner surface in micro-drilling of spray holes: A comparison between ultrashort pulsed laser and EDM

Abstract In this research, the inner surface characteristics of micro-drilled holes of fuel injector nozzles were analyzed by Shear Force Microscopy (SHFM). The surface texture was characterized by maximum peak-to-valley distance and periodicity whose dimensions were related to the adopted energy. 180 µm diameter holes were drilled using ultrashort pulsed laser process using pulse energies within the range of 10–50 µJ. Laser ablated surfaces in the tested energy range offer a smooth texture with a peculiar periodic structure with a variation in height between 60 and 90 nm and almost constant periodicity. The Scanning Electron Microscopy (SEM) photograph of the Laser Induced Periodic Surface Structure (LIPSS) showed the co-existence of Low Spatial Frequency LIPSS (LSFL) and High Spatial Frequency LIPSS (HSFL). A comparative analysis was carried out between the highest laser pulse energy in the tested range energy laser drilling which enables the shortest machining time and micro-Electrical Discharge Machining (µ-EDM). On the contrary, results showed that surfaces obtained by electro-erosion are characterized by a random distribution of craters with a total excursion up to 1.5 µm with a periodicity of 10 µm. The mean-squared surface roughness ( R q ) derived from the scanned maps ranges between 220 and 560 nm for µ-EDM, and between 50 and 100 nm for fs-pulses laser drilling.

Characteristics of Al-doped TiO<SUB align="right">2 thin films grown by pulsed laser deposition

Al-doped TiO2 (TiO2:Al) thin films were deposited at 450oC onto glass substrates using pulsed laser deposition method. X-rays diffraction spectra showed that the obtained films are polycrystalline of anatase structure with preferential orientation of (101) direction. AFM images, nanoparticles size and surface roughness mean square values showed that the surfaces of TiO2:Al films are smoother than that of undoped TiO2 films. A blue shift in the absorption edge of TiO2 with increasing Al concentration in the film is noteworthy as it leads to increase in the width of the optical transmission. The optical waveguiding performances of the TiO2:Al films were demonstrated by using the m-lines spectroscopy technique and the results were correlated to the structural properties. Spectroscopic ellipsometry was used to extract the optical constants of the films. The determined band gap of undoped and Al doped films varies from 3.43 to 3.61 eV, which is in accordance to Burstein-Moss shift.

Structure and properties of p-phenylenevinylene-p-xylylene copolymers prepared by vapor-deposition polymerization

Films based on the p-phenylenevinylene-p-xylylene precursor are prepared via vapor-deposition polymerization during the pyrolysis of α, α′-dichloro-p-xylene on a copper grid in vacuum at substrate temperatures −196, 25, and 50°C. Subsequent annealing of the precursor at 250°C yields the final material: the copolymer of p-phenylenevinylene and p-xylylene. The structure, surface morphology, and optical properties of the copolymer are studied at different substrate temperatures and copper amounts in the pyrolysis zone. It is found that p-phenylenevinylene units mostly occur in trans configurations. The thermal treatment of the precursor is accompanied by an increase in the mean-square surface roughness and a decrease in roughness coefficient α from 0.84 ± 0.05 to 0.79 ± 0.05. As the content of copper in the pyrolysis zone increases, the concentration of p-xylylene fragments in the copolymer tends to increase; the band gap increases from −2.5 to 3.1 eV. Depending on synthesis conditions, the copolymer is characterized by a shift of the fluorescence spectrum maximum that achieves 150 nm in the visible spectral region.

Structural and electrical characteristics of InGaAsN layers grown by LPE

Crystallographic and transport properties of nominally undoped and Sn-doped InGaAsN layers grown by low-temperature LPE have been studied and related to the growth conditions.In the case of lattice matching, flat and uniform mirror-like layers of 8–10μm in thickness are obtained. The compositions of the layers under study have been determined by combination of X-ray microanalysis and X-ray diffraction methods to be In0.035Ga0.065As0.086N0.014. The lattice mismatch between layer and substrate Δal/as calculated from X-ray diffraction curves is less than−7×10−4 for all samples. The layers grown at lower epitaxy temperatures exhibit the highest crystalline quality, better lattice match and better homogeneity. This is in good agreement with the results of morphological study by atomic force microscopy which show root mean-square surface roughness of 0.18nm for the best layers.CV and Hall measurements reveal that intentionally undoped InGaAsN layers are n-type with free carrier concentration about one order of magnitude higher in comparison to layers not containing nitrogen and high electron mobility values over 2000cm2/Vs. A dramatic reduction in the free carrier concentration and slightly increase in mobility are observed for Sn-doped InGaAsN layers.

The transparence comparison of Ga- and Al-doped ZnO thin films

The Ga-doped ZnO (GZO) and Al-doped ZnO (AZO) thin films were grown on quartz glass substrates by pulsed laser deposition under different oxygen partial pressures ( P O 2 ) . The transparent performances of films versus properties of structure and conductivity were discussed. With the increase of P O 2 , the transmittance of both GZO films and AZO films increased to maximum and then decreased which were in according with the change of crystallization quality. The transmittance of GZO films was higher than that of AZO films, which were not dominated by the impurity ions induced by doping. AFM images and surface roughness mean square coefficients showed that the surfaces of GZO films were smoother than that of AZO films, which were due to the dopant Ga acting as the surfactant and smoothed the GZO films surface.

Ion-beam engineering of Co/TiO2 multilayer nanostructures

Multilayer structures consisting of Co/TiO2 bilayers with partial layer thicknesses varied within several nanometers and a total thickness of up to 100 nm were obtained using the ion-beam sputter deposition method and studied using a combination of analytical techniques. It is shown that, in [Co(2 nm)/TiO2(2 nm)]15, [Co(2 nm)/TiO2(4 nm)]15, and [Co(4 nm)/TiO2(4 nm)]12 structures, the mean-square surface roughness does not exceed 0.9 nm, all partial layers are continuous, all interfaces are plane-parallel and sharp, and the characteristics of each layer are close to those of the corresponding bulk material. The [Co(2 nm)/TiO2(4 nm)]15 structure is characterized by the maximum transparency (exceeding 7% in he visible spectral range. The properties of these multilayer films are promising for applications in magnetooptics and spintronics. The surfaces of [Co(4 nm)/TiO2(2 nm)]15 and [Co(6 nm)/TiO2(2 nm)]12 structures have mean-square roughnesses above 1 nm and exhibit percolations with a surface density of up to 5 × 107 cm−2. A decrease in the partial layer thickness below 2 nm leads to the mixing of layers, while an increase in the thickness of individual TiO2 layers above 6 nm leads to significant differences of the optical transmission spectrum from that of the anatase form of TiO2 and to a decrease in the transparency.

Structure and optical characteristics of poly(p-phenylenevinylene) prepared by vapor deposition polymerization

Films based on poly(p-phenylenevinylene) are prepared by pyrolitic polymerization of α,α′-dichloro-p-xylene. During monomer precipitation, the temperature on a substrate is 25, 50, or −196°C. Subsequent annealing of the precursor at 250°C yields the final product: the copolymer of p-phenylenevinylene and p-xylylene with an approximate composition of 4: 1. The surface morphology, structure, and optical characteristics of the polymer are studied. The mean-square surface roughness of the precursor is 5 nm. Thermal treatment increase the samples’ roughness up to 10 nm. When the precursor is transformed into poly(p-phenylenevinylene), the roughness coefficient decreases from 0.85 ± 0.05 to 0.74 ± 0.05 owing to the formation of a rougher surface. Characterization of the optical characteristics of the synthesized poly(p-phenylenevinylene) shows that the maximum effective conjugation chain length achieves 12 units in the copolymer prepared when the temperature on the substrate is −196°C. As the temperature on the substrate increases, the conjugation length decreases to 8 units upon precipitation. Luminescence analysis reveals the effective excitation-energy transfer from short chain fragments of poly(p-phenylenevinylene) to long chain fragments. Electron parameters of the material are estimated: i.e., the band gap, the Huang-Rhys factor, the Stokes shift, and the oscillation energy of molecules.

Comparison of surface morphology in pulsed laser deposited Sm 1+ xBa 2− xCu 3O 6+ δ (0⩽ x⩽0.12) thin films

We have fabricated Sm 1+ x Ba 2− x Cu 3O 6+ δ (SmBCO) thin films by means of the pulsed laser deposition technique, using the stoichiometric and the Sm-rich SmBCO ( x=0.08 and 0.12) composition laser targets. In this work, the influence of the Sm–Ba substitution on the film surface morphology in the SmBCO system was investigated using the atomic force microscopy. With the increase of the Sm–Ba substitution, it was found that the surface of SmBCO thin films was very smooth and highly stable in the air. It is observed that Sm-rich SmBCO thin films using laser targets of x=0.08 and 0.12 have a root mean-square surface roughness in a 2×2 μm 2 area of about 2.1 and 1.7 nm, respectively. It was concluded that the Sm–Ba substitution influences the smoothness and the stability on the surface of the SmBCO thin films. We speculate that the surface morphology of the SmBCO thin films is influenced by the Sm–Ba substitution and the migration potential.

X-ray scattering studies of low-T Ag(001) and Cu(001) homoepitaxy: Vacancy trapping and surface morphology evolution

ABSTRACTWe have used synchrotron x-ray diffraction to study the low-T homoepitaxial growth on Ag(001) and Cu(001) surfaces. For both systems, we found that a large, temperature-dependent vacancy concentration is incorporated in films grown below 160K. The vacancy trapping occurs concomitantly with substantial changes in the surface morphology, where a non-monotonic temperature dependence of the mean-square surface roughness has been previously observed. For Cu/Cu(001) we also found that the concentration of vacancies incorporated at 110K evolves, upon heating, according to the vacancy annealing behavior well-known from radiation damage studies of bulk copper and it is consistent with the activation energy for vacancy mobility.

Modeling of spray-formed plates using an X-Y moving substrate

A mathematical model, incorporating the thermal component of sticking efficiency (SEt) into the calculation of shape evolution, is formulated to predict the evolution and final geometry of plates. The plates are spray formed using a moving substrate displaced in a two-dimensional (i.e., X-Y) plane. By using this model, the effects of the substrate movement parameters, such as the acceleration, time required to complete a stroke in the reciprocal movement direction (X-axis), and the velocity in the uniform movement direction (Y-axis), on the shapes of the plates are investigated. The processing parameters are evaluated by minimizing the values of the mean-squared (MS) surface roughness. On the basis of the evaluation, the optimal combinations of processing parameters are found.

Transfer by direct photo etching of poly(vinylidene flouride) using X-rays

A direct pattern transfer method has been developed by photo etching poly(vinylidene fluoride) (PVDF) using X rays (1-16 keV) from a synchrotron storage ring. The ability to pattern thin film of PVDF, a piezoelectric, pyroelectric and ferroelectric polymer, has potential applications in the areas of MEMS, nonlinear optics, and nonvolatile ferroelectric random access memory technology. Without the use of any reactive chemical gas, a maximum etched depth in excess of 9 /spl mu/m is achieved. The etched depth for a given photon energy approaches saturation with respect to exposure time. An in situ mass spectrometry revealed the evolution of hydrogen, fluorine, and hydrogen fluoride species. The etched regions turned dark in color indicating a possible increase in the fraction of carbon atoms. The X-ray transmittance of photo etched PVDF approached that of a pure carbon as the exposure time is increased. Upon etching the root mean-square surface roughness of the etched portion increased by more than a factor of two. The rate of etching increased at elevated sample temperatures.

Monte Carlo simulations of Si(001) growth and reconstruction during molecular beam epitaxy

A Monte Carlo simulation of Si(001) crystal growth and surface reconstruction during molecular beam epitaxy is described. The simulation is based on the solid-on-solid model and depicts the diamond lattice and surface reconstructions explicitly. Si deposition, surface diffusion, and the formation and reorientation of surface dimer pairs are accounted for. The results indicate that surface dimer formation plays an important role in determining the crystal growth kinetics, which is observed to be a combination of step propagation and two-dimensional island nucleation modes. At least 5 diffusion events per deposited atom and second nearest neighbor interaction energies E 2 ≳ kT were required to yield films with mean-square surface roughnesses of ≲ 0.7 monolayer. Decreasing either the diffusion rate or E 2 yielded increasingly rough surfaces. Ordered (2 × 1) rows of dimer pairs were observed when a term accounting for the subsurface strain energy interaction between dimers was included. First-order reflected electron intensity calculations for the simulated surfaces showed strong intensity oscillations with a period of 1 monolayer.