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At least 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Oxidation of SnO to SnO{sub 2} thin films in boiling water at atmospheric pressure

We demonstrated that SnO is oxidized to SnO{sub 2} in boiling water. (001)-oriented SnO thin films were pulsed-laser deposited onto a glass substrate. The Sn valence number changed from (II) to (IV) by keeping SnO films in boiling water at atmospheric pressure for 5 h. Optical transparency of the obtained SnO{sub 2} films was greater than 95% in the visible light range. The SnO{sub 2} films possessed an amorphous structure, and exhibited dielectric properties. Atomic force microscopy and Fourier transform infrared spectroscopy revealed granular structures and the existence of –OH groups, which may account for the diffusion of oxidants within the film.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Surface smoothing effect of an amorphous thin film deposited by atomic layer deposition on a surface with nano-sized roughness

Previously, Lau (one of the authors) pointed out that the deposition of an amorphous thin film by atomic layer deposition (ALD) on a substrate with nano-sized roughness probably has a surface smoothing effect. In this letter, polycrystalline zinc oxide deposited by ALD onto a smooth substrate was used as a substrate with nano-sized roughness. Atomic force microscopy (AFM) and cross-sectional transmission electron microscopy (XTEM) were used to demonstrate that an amorphous aluminum oxide thin film deposited by ALD can reduce the surface roughness of a polycrystalline zinc oxide coated substrate.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Formation of H-type liquid crystal dimer at air-water interface

We have formed the Langmuir monolayer of H-shaped Azo linked liquid crystal dimer molecule at the air-water interface. Isocycles of the molecule showed hysteresis suggesting the ir-reversible nature of the monolayer formed. The thin film deposited on the silicon wafer was characterized using Atomic Force Microscopy (AFM) and Field Emission Scanning Electron Microscopy (FESEM). The images showed uniform domains of the dimer molecule. We propose that these molecules tend to take book shelf configuration in the liquid phase.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Formation of continuous metallic film on quartz studied by noncontact resonant ultrasound spectroscopy

Dynamics of continuous film formation of metallic films on quartz substrates is studied using an electrodeless resonance method. Bare quartz is used as a substrate, and a metallic film is deposited on it. We use antenna transmission technique to measure the evolution of resonance frequencies and internal friction of the substrate during and after deposition, and the morphological transition between discontinuous islands and a continuous film is detected. By comparison with atomic force microscopy images, we confirm that the frequency drop and the internal-friction peak that appear during deposition indicate this transition. We also find that Pt film shows unexpected morphology change after deposition.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Spin-dependent charge transmission through chiral 2T3N self-assembled monolayer on Au

In this study, a gold surface is functionalized by chemisorption of the enantiopure N,N'-bis-[2,2';5',2"]tert-thiophene-5-yl methylcyclohexane-1,2-diamine (2T3N), a chiral oligothiophene derivative, via overnight incubation in a 2T3N ethanol solution. The Au|2T3N interface is characterized by x-ray photoelectron circular dichroism and comparing x-ray photoemission spectroscopy and electro-desorption results. Charge transmission at the Au|2T3N| solution interface is characterized by recording the cyclic voltammetry of the Fe(III)/Fe(II) reversible redox couple, finding a charge transfer rate constant, k°, variation from 1 × 10 -1 to 3.3 × 10 -2 cm s -1 , when comparing the bare Au and the Au|2T3N interfaces, respectively. The “anomalous” high value of k° found for the chiral Au|2T3N interface can be rationalized on the basis of the chiral-induced spin selectivity effect, as further proved by magnetic–conductive atomic force microscopy measurements at room temperature. A spin polarization of about 30% is found.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Nanoindentation Studies Of Hard Nanocomposite Ti-B-N Thin Films

Titanium boron nitride (Ti-B-N) films were deposited by reactive magnetron sputtering using single Titanium diboride (TiB{sub 2}) target in different Ar-N{sub 2} gas mixtures. The influence of N{sub 2}:Ar ratio on the microstructure and mechanical properties of the deposited films have been investigated. Atomic force microscopy analysis indicated the grain size decreases with incorporation of nitrogen in the films. Nanoindentation studies have shown the hardness decreases with nitrogen incorporation.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Reconfigurable and non-volatile vertical magnetic logic gates

In this paper, we discuss the concept and prototype fabrication of reconfigurable and non-volatile vertical magnetic logic gates. These gates consist of two input layers and a RESET layer. The RESET layer allows the structure to be used as either an AND or an OR gate, depending on its magnetization state. To prove this concept, the gates were fabricated using a multi-layered patterned magnetic media, in which three magnetic layers are stacked and exchange-decoupled via non-magnetic interlayers. We demonstrate the functionality of these logic gates by conducting atomic force microscopy and magnetic force microscopy (MFM) analysis of the multi-layered patterned magnetic media. The logic gates operation mechanism and fabrication feasibility are both validated by the MFM imaging results.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2010

Photoluminescence properties of SrAl{sub 2}O{sub 4}:Eu{sup 2+},Dy{sup 3+} thin phosphor films grown by pulsed laser deposition

Thin films of SrAl{sub 2}O{sub 4}:Eu{sup 2+},Dy{sup 3+} phosphor were deposited on silicon [Si (100)] substrates using a 248 nm KrF pulsed laser. Deposition parameters, such as substrate temperature, pulse repetition rate, number of laser pulses, and base pressure, were varied during the film deposition process. Based on the x-ray diffraction data, all the films were amorphous but were emitting visible light when excited by a monochromatic xenon lamp. The chemical composition and the stoichiometry of the films determined by the Rutherford backscattering spectroscopy were consistent with the commercial SrAl{sub 2}O{sub 4}:Eu{sup 2+},Dy{sup 3+} powder used to prepare the films. Photoluminescence (PL) emission spectra of the films were characterized by major green emission with a maximum at {approx}520 nm and minor red emission with a maximum at 630 nm. The green and red photoluminescence at 520 and 630 nm are associated with the 4f{sup 6}5d{yields}4f{sup 7}({sup 8}S{sub 7/2}) and {sup 5}D{sub 0}-{sup 7}F{sub 2} transitions of Eu{sup 2+} and residual Eu{sup 3+} ions, respectively. Brighter films were shown to have relatively higher values of the root mean square surface roughness, which were determined from the atomic force microscopy data. The effects of processing parameters on the PL intensity are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Structure fragmentation of a surface layer of commercial purity titanium during ultrasonic impact treatment

The mechanisms of surface layer fragmentation of titanium specimens subjected to ultrasonic impact treatment is investigated by atomic force microscopy, transmission electron microscopy and electron backscatter diffraction. It is shown that the twin boundaries Σ7b and Σ11b are unable to be strong obstacles for propagation of dislocations and other twins.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Electrochemical characterization of organosilane-functionalized nanostructured ITO surfaces

The electroactivity of nanostructured indium tin oxide (ITO) has been investigated for its further use in applications such as sensing biological compounds by the analysis of redox active molecules. ITO films were fabricated by using electron beam evaporation at different substrate temperatures and subsequently annealed for promoting their crystallization. The morphology of the deposited material was monitored by scanning electron microscopy, confirming the deposition of either thin films or nanowires, depending on the substrate temperature. Electrochemical surface characterization revealed a 45 % increase in the electroactive surface area of nanostructured ITO with respect to thin films, one third lower than the geometrical surface area variation determined by atomic force microscopy. ITO surfaces were functionalized with a model organic molecule known as 6-(ferrocenyl)hexanethiol. The chemical attachment was done by means of a glycidoxy compound containing a reactive epoxy group, the so-called 3-glycidoxypropyltrimethoxy-silane. ITO functionalization was useful for determining the benefits of nanostructuration on the surface coverage of active molecules. Compared to ITO thin films, an increase in the total peak height of 140 % was observed for as-deposited nanostructured electrodes, whereas the same measurement for annealed electrodes resulted in an increase of more than 400 %. These preliminary results demonstrate the ability of nanostructured ITO to increase the surface-to-volume ratio, conductivity and surface area functionalization, features that highly benefit the performance of biosensors.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Formation and evolution of self-organized Au nanorings on indium-tin-oxide surface

This work reports on the formation of Au nanoclusters and on their evolution in nanoring structures on indium-tin-oxide surface by sputtering deposition and annealing processes. The quantification of the characteristics of the nanorings (surface density, depth, height, and width) is performed by atomic force microscopy. The possibility to control these characteristics by tuning annealing temperature and time is demonstrated establishing relations which allow to set the process parameters to obtain nanostructures of desired morphological properties for various technological applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2011

Note: The intermodulation lockin analyzer

Nonlinear systems can be probed by driving them with two or more pure tones while measuring the intermodulation products of the drive tones in the response. We describe a digital lockin analyzer which is designed explicitly for this purpose. The analyzer is implemented on a field-programmable gate array, providing speed in analysis, real-time feedback, and stability in operation. The use of the analyzer is demonstrated for intermodulation atomic force microscopy. A generalization of the intermodulation spectral technique to arbitrary drive waveforms is discussed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Surface forces: Surface roughness in theory and experiment

A method of incorporating surface roughness into theoretical calculations of surface forces is presented. The model contains two chief elements. First, surface roughness is represented as a probability distribution of surface heights around an average surface height. A roughness-averaged force is determined by taking an average of the classic flat-surface force, weighing all possible separation distances against the probability distributions of surface heights. Second the model adds a repulsive contact force due to the elastic contact of asperities. We derive a simple analytic expression for the contact force. The general impact of roughness is to amplify the long range behaviour of noncontact (DLVO) forces. The impact of the elastic contact force is to provide a repulsive wall which is felt at a separation between surfaces that scales with the root-mean-square (RMS) roughness of the surfaces. The model therefore provides a means of distinguishing between “true zero,” where the separation between the average centres of each surface is zero, and “apparent zero,” defined by the onset of the repulsive contact wall. A normal distribution may be assumed for the surface probability distribution, characterised by the RMS roughness measured by atomic force microscopy (AFM). Alternatively the probability distribution may be defined by the histogram of heights measured by AFM. Both methods of treating surface roughness are compared against the classic smooth surface calculation and experimental AFM measurement.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Topological size effect in tin-dioxide cluster films produced by reactive sputtering

The optical properties of tin-dioxide nanofilms produced by reactive sputtering are studied by the internal reflection technique and modulation polarimetry. The angular and spectral characteristics of the reflection coefficients R{sub s}{sup 2} and R{sub p}{sup 2}are studied for linear-polarized radiations, for which the wave electric field is, correspondingly, orthogonal and parallel to the plane of incidence. The characteristics of the physical difference between the reflection coefficients, {rho} = R{sub s}{sup 2}-R{sub p}{sup 2}, are studied as well. From the experimental results, it follows that (i) the doping-induced finite conductivity of the film brings about the appearance of surface plasmon resonance; (ii) the shape of the spectral and angular characteristics of the parameter {rho} is indicative of the cluster structure of the film, which is in agreement with the phase topology data obtained by atomic force microscopy; and (iii) the nonspherical shape of the clusters is responsible for the splitting of resonances and for the dependence of their parameters on the angle of incidence, which defines the topological size effect.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Surface Topography and Optical Properties of Thin AlN Films Produced on GaAs (100) Substrate by Reactive Ion-Plasma Sputtering

A study of the surface topography and optical characteristics of thin AlN films used as passivating and antireflection coatings deposited on n-GaAs (100) substrates by reactive ion-plasma sputtering is reported. It was found that the process conditions affect the structure and the optical characteristics of the films, which makes it possible to obtain coatings with prescribed parameters. An analysis of the results furnished by ellipsometry and atomic-force microscopy of the surface shows that the refractive index of the films is correlated with the surface structure.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Effect of O{sub 2} gas partial pressure on mechanical properties of Al{sub 2}O{sub 3} films deposited by inductively coupled plasma-assisted radio frequency magnetron sputtering

The effect of O{sub 2} partial pressure on the mechanical properties of Al{sub 2}O{sub 3} films is studied. Using films prepared by inductively coupled plasma-assisted radio frequency magnetron sputtering, the deposition rate of Al{sub 2}O{sub 3} decreases rapidly when oxygen is added to the argon sputtering gas. The internal stresses in the films are compressive, with magnitude decreasing steeply from 1.6 GPa for films sputtered in pure argon gas to 0.5 GPa for films sputtered in argon gas at an O{sub 2} partial pressure of 0.89 Multiplication-Sign 10{sup -2} Pa. Stress increases gradually with increasing O{sub 2} partial pressure. Using a nanoindentation tester with a Berkovich indenter, film hardness was measured to be about 14 GPa for films sputtered in pure argon gas. Hardness decreases rapidly on the addition of O{sub 2} gas, but increases when the O{sub 2} partial pressure is increased. Adhesion, measured using a Vickers microhardness tester, increases with increasing O{sub 2} partial pressure. Electron probe microanalyzer measurements reveal that the argon content of films decreases with increasing O{sub 2} partial pressure, whereas the O to Al composition ratio increases from 1.15 for films sputtered in pure argon gas to 1.5 for films sputtered in argon gas at O{sub 2} partial pressures over 2.4 Multiplication-Sign 10{sup -2} Pa. X-ray diffraction measurements reveal that films sputtered in pure argon gas have an amorphous crystal structure, whereas {gamma}-Al{sub 2}O{sub 3} is produced for films sputtered in argon gas with added O{sub 2} gas. Atomic force microscopy observations reveal that the surface topography of sputtered Al{sub 2}O{sub 3} films changes from spherical to needlelike as O{sub 2} partial pressure is increased. Fracture cross sections of the films observed by scanning electron microscopy reveal that the film morphology exhibits no discernible features at all O{sub 2} partial pressures.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Autophagy induction by silver nanowires: A new aspect in the biocompatibility assessment of nanocomposite thin films

Nanomaterials and their enabled products have increasingly been attracting global attention due to their unique physicochemical properties. Among these emerging products, silver nanowire (AgNW)-based thin films are being developed for their promising applications in next generation nanoelectronics and nanodevices. However, serious concerns remain about possible health and safety risks they may pose. Here, we employed a multi-modal systematic biocompatibility assessment of thin films incorporating AgNW. To represent the possible routes of nanomaterial entry during occupational or environmental exposure, we employed four different cell lines of epithelial, endothelial, gastric, and phagocytic origin. Utilizing a cell-based automated image acquisition and analysis procedure in combination with real-time impedance sensing, we observed a low level of cytotoxicity of AgNW, which was dependent on cell type, nanowire lengths, doses and incubation times. Similarly, no major cytotoxic effects were induced by AgNW-containing thin films, as detected by conventional cell viability and imaging assays. However, transmission electron microscopy and Western immunoblotting analysis revealed AgNW-induced autophasosome accumulation together with an upregulation of the autophagy marker protein LC3. Autophagy represents a crucial mechanism in maintaining cellular homeostasis, and our data for the first time demonstrate triggering of such mechanism by AgNW in human phagocytic cells. Finally, atomic force microscopy revealed significant changes in the topology of cells attaching and growing on these films as substrates. Our findings thus emphasize the necessity of comprehensive biohazard assessment of nanomaterials in modern applications and devices and a thorough analysis of risks associated with their possible contact with humans through occupational or environmental exposure. Highlights: ► Thin films containing nanomaterials are subject to increasing contact with humans. ► This study provides multi-modal biohazard assessment of AgNW-based thin films. ► Thin films containing AgNW affect human cell topology and attachment. ► AgNW toxicity depends on cell type, nanowire length, dose, and exposure time. ► AgNW can induce the process of autophagy in phagocytic cells.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

Damage of multilayer optics with varying capping layers induced by focused extreme ultraviolet beam

Extreme ultraviolet Mo/Si multilayers protected by capping layers of different materials were exposed to 13.5 nm plasma source radiation generated with a table-top laser to study the irradiation damage mechanism. Morphology of single-shot damaged areas has been analyzed by means of atomic force microscopy. Threshold fluences were evaluated for each type of sample in order to determine the capability of the capping layer to protect the structure underneath.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗