Polycrystalline Substrates Research Articles

Methods for atomistic abrasion simulations of laterally periodic polycrystalline substrates with fractal surfaces

In this work we discuss a method to generate laterally periodic polycrystalline samples with fractal surfaces for use in molecular dynamics simulations of abrasion. We also describe a workflow that allows us to produce random lateral distributions of simple but realistically shaped hard abrasive particles with Gaussian size distribution and random particle orientations. We evaluate some on-the-fly analysis and visualization possibilities that may be applied during a molecular dynamics simulation to considerably reduce the post-processing effort. Finally, we elaborate on a parallelizable post-processing approach to evaluating and visualizing the surface topography, the grain structure and orientation, as well as the temperature distribution in large atomistic systems.

Characterization of Amorphous Oxide Nano-Thick Layers on 316L Stainless Steel by Electron Channeling Contrast Imaging and Electron Backscatter Diffraction.

Characterization of the topmost surface of biomaterials is crucial to understanding their properties and interactions with the local environment. In this study, the oxide layer microstructure of plasma-modified 316L stainless steel (SS316L) samples was analyzed by a combination of electron backscatter diffraction and electron channeling contrast imaging using low-energy incident electrons. Both techniques allowed clear identification of a nano-thick amorphous oxide layer, on top of the polycrystalline substrate, for the plasma-modified samples. A methodology was developed using Monte Carlo simulations combined with the experimental results to estimate thickness of the amorphous layer for different surface conditions. X-ray photoelectron spectroscopy depth profiles were used to validate these estimations.

Effect of Silver Modification on Glycerol Oxidation Reaction Activity of Palladium Electrode in Alkaline Medium

Introduction Biodiesel fuel (BDF) attracts attention as a carbon-neutral fuel as well as bioethanol. As the production of BDF increases, the production of the glycerol byproduct is also increasing. It is important to develop new uses for glycerol to cope with the mass production of BDF. The use of glycerol as a fuel for direct alcohol fuel cells is promising, because anodic oxidation of glycerol produced by bioprocesses occurs in carbon-neutral cycles and direct glycerol fuel cells are expected to produce electricity with a low environmental load and to be energy efficient. It is well-known that Pd is cheaper than Pt and Au, and Pd-based alloy electrodes are highly active for the oxidation of alcohols in alkaline media. We also have reported the PdAg alloys-loaded carbon exhibited higher glycerol oxidation reaction (GOR) activity and tolerance to poisoning species than Pd.1 The mechanism for GOR, however, is not so clear. In this study we prepared an Ag atomic layer-modified Pd model electrode, and investigated the potential dependence of GOR products by in situ infrared reflectance-absorption spectroscopy (IRAS). In addition, we discussed the GOR mechanism based on these data. Experimental The Ag atomic layer-loaded Pd (Ag/Pd) electrode was prepared by underpotential deposition of Cu (Cu-upd) on a Pt polycrystalline substrate and the following galvanic replacement with Ag. The coverage of Ag (θ Ag) on the Pd substrate was evaluated to be 0.5 from the charges for Cu-upd before and after the Ag modification. 1 M KOH and (1 M KOH + 0.5 M glycerol) solution were used for electrochemical measurements. In situ infrared reflection-absorption spectroscopy (IRAS) was used to qualitatively analyze the products of GOR on the Pd and Ag/Pd electrodes in alkaline solution. All electrochemical measurements were performed at room temperature. Results and Discussion The cyclic voltammograms of the Pd and Ag/Pd electrodes in a (1 M KOH + 0.5 M glycerol) solution is shown in Fig. 1. The Ag/Pd electrode had higher oxidation current and more negative onset potential of the oxidation current than the Pd electrode, clearly indicating that the GOR activity was enhanced by the modification of the Ag atomic layer. In addition, the peak potential of the oxidation current for the Ag/Pd electrode was more positive than that for the Pd electrode, suggesting that the former was superior in tolerance to poisoning species to the latter. IRAS spectra for the Pt electrode exhibited that the absorption peak at 1335 cm-1 assigned to the formation of dihydroxyacetone was mainly increased at lower potentials, but the absorption peak at 1310 cm-1 assigned to the formation of glycerate was increased at higher potentials. This suggests that the secondary OH group in a glycerol molecule is preferentially oxidized at smaller overpotentials, and the primary OH group is greatly oxidized at larger overpotentials. For the Ag/Pd electrode, the oxidation of the primary OH group occurred even at smaller overpotentials, and hydroxypyruvate was also formed at larger overpotentials. Acknowledgement This work was partially supported by JSPS KAKENHI Grant Number 15H04162. Reference 1 B. T. X. Lam, M. Chiku, E. Higuchi, H. Inoue, J. Power Sources, 297, 149 (2015). Figure 1

Electroless Deposition of High Quality Co Films on Cu Polycrystalline Substrate Assisted By Pb UPD Monolayer

In the last several decades, the electrochemical thin film growth was proven to be one of the enabling fabrication methods behind the train of hi-tech enterprise [[i],[ii]]. Today, the electro- and electroless- depositions are recognized as standard processing operations in magnetic disk drive [[iii],[iv]], and microprocessor and MEMS technologies [[v],[vi],[vii],[viii]]. The focus of our talk is the electroless growth of Co ultra-thin films on highly textured Cu substrate. The Co/Cu system has been already studied before using different deposition approaches [[ix]]. Although layer-by-layer growth was initially reported [[x],[xi]] it is now known that, at room temperature, the growth of cobalt on Cu(111) is dominated by island formation due to kinetically limited interlayer transport [[xii]]. The electrolyte for electroless growth of Co is based on CoSO4 as a metal salt and TiCl3 as a reducing agent [[xiii]]. Prior to deposition experiments, the Cu substrates are annealed at 270 ○C using reducing atmosphere containing H2+CO mixture. To improve the interlayer transport of Co during the growth, the monolayer (ML) of Pb is pre-deposited using electroless plating on Cu surface before the Co growth. [[xiv]]. The benefit of Pb ML presence on Co interlayer kinetics during the growth is evident by high quality of Co films obtained, Figure 1. They are characterized by large 2D grains having the width to height ratio in excess of 500. The ultrathin Co films are continuous, highly conformal and very smooth yielding a 2D-like appearance, Figure 1. The saturation roughness measured over the range of 10 x10 microns for 10 nm thick Co films is only 3 nm. The Co films show extremely soft properties and very high electrical conductivity which indicates a very small concentration of defects and high quality of the grain boundaries. The benefit and application of this Co deposition protocol is discussed emphasizing its simplicity, fidelity of control and low capital cost of equipment. The authors acknowledge the support from Lam Research Corporation and NSF Chemistry division under the contract # 0955922. REFERENCES [i] Nanomaterials: Synthesis, Properties and Applications. IOP Publishing, Bristol, (1996) UK. [ii] Nanostructures and Nanomaterials: Synthesis, Properties and Applications. Imperial College Press, London, UK (2004). [iii] E. Cooper et al. IBM J Res & Dev 49 103 (2005). [iv]S.R. Brankovic et al.. IEEE Trans Magn 42 132 (2006). [v]M. Data et al. J Electrochem. Soc. 142 3779 (1995). [vi]P. Andricacos, Electrochem. Soc. Interface 8 32 (1999). [vii] H. Deligianni, Electrochem. Soc. Interface 15 33 (2006). [viii] W. Ehrfeld, Electrochim Acta 48 2857 (2003). [ix] M.T. Kief and W.F. Egelhoff, Phys. Rev. B 47 10 785 (1993) [x] Gonzalez, R. Miranda, M. Salmeron, J.A. Verges, and F. Yndurain, Phys. Rev. B 24, 3245 (1981). [xi] 3Q. Chen, M. Onellion, and A. Wall, Thin Solid Films 196, 103 (1991). [xii] J. de la Figuera, J.E. Prieto, C. Ocal, and R. Miranda, Phys. Rev. B 47, 13 043 (1993). [xiii] Y. Dordi, A. Joi et al, US Patent application # 14/264,994 [xiv] N. Dimitrov et al, Electrochemistry Communications, 44 19 (2014). Figure 1

Tight comparison of Mg and Y thin film photocathodes obtained by the pulsed laser deposition technique

In this work Magnesium (Mg) and Yttrium (Y) thin films have been deposited on Copper (Cu) polycrystalline substrates by the pulsed laser ablation technique for photocathode application. Such metallic materials are studied for their interesting photoemission properties and are proposed as a good alternative to the Cu photocathode, which is generally used in radio-frequency guns. Mg and Y films were uniform with no substantial differences in morphology; a polycrystalline structure was found for both of them. Photoemission measurements of such cathodes based on thin films were performed, revealing a quantum efficiency higher than Cu bulk. Photoemission theory according to the three-step model of Spicer is invoked to explain the superior photoemission performance of Mg with respect to Y.

Evolution of grain structure during laser additive manufacturing. Simulation by a cellular automata method

We have developed a two-dimensional numerical model to simulate the evolution of grain structure observed during the laser additive manufacturing process. A cellular automata method is used to describe grain growth. The Goldak heat source model is adopted to calculate the heat input during laser melting. A selective laser melting process which involves sequential deposition of powder layers on a polycrystalline substrate followed by their melting is examined. The influence of the heat source parameters on the evolution of grain structure is discussed. The simulation results are shown to be consistent with the experimental data describing the main characteristics of the grain structure.

Large-Area Deposition of MoS2 by Pulsed Laser Deposition with In Situ Thickness Control.

A scalable and catalyst-free method to deposit stoichiometric molybdenum disulfide (MoS2) films over large areas is reported, with the maximum area limited by the size of the substrate holder. The method allows deposition of MoS2 layers on a wide range of substrates without any additional surface preparation, including single-crystal (sapphire and quartz), polycrystalline (HfO2), and amorphous (SiO2) substrates. The films are deposited using carefully designed MoS2 targets fabricated with excess sulfur and variable MoS2 and sulfur particle size. Uniform and layered MoS2 films as thin as two monolayers, with an electrical resistivity of 1.54 × 10(4) Ω cm(-1), were achieved. The MoS2 stoichiometry was confirmed by high-resolution Rutherford backscattering spectrometry. With the method reported here, in situ graded MoS2 films ranging from ∼1 to 10 monolayers can be deposited.

Investigation of dendritic growth and liquation cracking in laser melting deposited Inconel 718 at different laser input angles

Nickel-baresulting in the higher sed Inconel 718 (IN718) superalloy is deposited on a polycrystalline substrate by laser melting deposition. The effects of the laser input angle on the dendritic microstructure, crystal orientation and heat-affected zone (HAZ) liquation cracking tendency are studied by optical microscopy, scanning electron microscopy, and electron backscatter diffraction. Larger laser input angles improve the lateral temperature gradient, enhance growth of secondary dendrites, and establish firm interconnections among secondary dendrites in the interdendritic regions, resulting in the formation of a “cross-band” morphology inside the grains, especially laser input angles of 10° and 20°. Larger laser input angles also improve the homogeneity of heat dissipation flow during solidification in laser deposition as well as the resulting in the higher crystal orientation. The enhanced interdendritic bonding improves the cracking resistance of the crystal inner grain and attributed to the decrease in the grain boundary misorientation, the stability of liquation film at the grain boundaries reduces. Owing to these two reasons, the susceptibility to HAZ liquation cracking is effectively depressed when using larger laser input angles in laser deposition.

The multicomponent doping of surface layers of materials under the influence of ion beams with a broad energy spectrum

The paper discusses the various factors that influence the efficiency of ion mixing. It was found that in the base of penetration of atoms multilayer films in polycrystalline substrate is the process of energy transfer from ions and primary knocked-on atom (PKA) of films to subsequent displacement cascade. At the same time the penetration of implanted atoms to great depths determined by the density of defects, radiation-stimulated migration of interstitial atoms and their physico-chemical interaction with the atoms of the matrix, which can be described by the model of an isotropic mixing. It is shown that doping atoms of the multilayer films, possibly the formation of gradient layers, which are determined by radiation traces in the substrate implanted atoms and their migration under irradiation by the ion beam with a broad energy spectrum.

Oriented thin films of Na 0.6CoO 2 and Ca 3Co 4O 9 deposited by spin-coating method on polycrystalline substrate

Thin film of two thermoelectric materials, NaxCoO2 (x~0.6) and Ca3Co4O9, was deposited using the sol–gel spin-coating method on a polycrystalline yttria-stabilized zirconia (YSZ) substrate. Despite the polycrystalline character of the substrate, the c-axis preferred orientation was obtained, suggesting self-assembly growth mechanism. The deposition procedure used offers several benefits, namely simplicity, high deposition rate, low fabrication cost as well as low price of the substrate, and low thermal conductivity of the substrate suitable for characterization of thermoelectric properties and for applications. The thermoelectric properties of the thin films are comparable with bulk materials. The samples exhibit power factor 0.23-0.26×10-3W⋅m-1⋅K-2 at 750K.

The optical properties of solar cells before and after encapsulation

In this work we investigate how the optical properties of monocrystalline silicon and polycrystalline silicon wafers are affected by texturing techniques and encapsulation. For monocrystalline wafers, the KOH etching is better than acid etching while reactive ion etching (RIE) is proven to be preferred compared to acid etching for polycrystalline wafers. The differences in reflectance (R) between two textures are apparent before encapsulation, but when the textured wafers are encapsulated with glass especially antireflectance coated (ARC) glass, the difference can be reduced from about five percentage points to below a percentage point. More important, the optical losses caused by reflectance (R) losses and parasitic absorption losses (A) for four types of commercial monocrystalline and polycrystalline silicon module are quantified and compared. Analyses are carried out for eight configurations using a stratified model consisting of solar cell wafers as well as cover glass and ethylene vinyl acetate (EVA). The model is to first obtain the external reflectance (R) and transmittance (T) in each layer, and the spectrally parasitic absorption loss associated with the cover glass and EVA is calculated with the aid of R and T measurements, which allows us to do a complete optical loss analysis for the solar module. The results show that the KOH texture with ARC glass encapsulation may be better choice for monocrystalline wafers, which gives a 94.04% of effective light collected by silicon. The RIE technique with ARC glass is suitable for polycrystalline substrates with excellent light trapping of 94.14%. After all, reflectance from glass surface and silicon surface accounts for over 70% of total loss, while the absorption of glass and EVA accounts for the rest and less loss.

Formation of Al/Au Bimetallic Interface Studied by Angle-Resolved X-Ray Photoelectron Spectroscopy (ARXPS)

ARXPS (Angle-resolved X-ray photoelectron spectroscopy) measurements were performed on the thin aluminum films deposited on the gold polycrystalline substrate kept at the temperature of liquid nitrogen in order to characterize the interdiffusion process during early stages of Al/Au interface formation. The intermixing of Al and Au elements at Al/Au bimetallic interface occurred already at temperature of liquid nitrogen leading to the formation of the well-resolved component on the high binding energy side of Au(4f) core line corresponding to AlAu intermetallic phase. The formation of initial AlAu phase at Al/Au interface in our experimental conditions can be explained on the base of its thermodynamic stability. The sample annealing resulted in the growth of the amount of AlAu intermetallic compound formed at liquid nitrogen temperature with subsequent decomposition of the parent alloy phase and formation of AlAu2 intermetallics richer in Au atoms. Tikhonov regularization method was used to extract the aluminum in-depth concentration profile from the measured ARXPS intensities. L-curve analysis was applied to determine the regularization parameter.

Estudio de estructuras de cis- y trans-estilbeno mediante microscopiade fuerza atómica

RESUMENLa nanotecnología es un área multidisciplinaria que ha tenido un gran auge en los últimos años, principalmente debido al desarrollo de instrumental que permite "ver", estudiar y manipular la materia a nivel atómico y molecular. El estilbeno y algunos de sus derivados son moléculas orgánicas de origen natural, que presentan una estructura química de interés en la fabricación de nanoestructuras y bloques constituyentes de máquinas moleculares (potencialmente aplicables en tecnología de nanosensores, almacenamiento de datos, liberación controlada de fármacos, entre otros). Sin embargo todavía no han sido ampliamente exploradas como nanomateriales. El interés en este tipo de sistemas reside en sus aplicaciones en medicina, farmacia y biotecnología.Este trabajo presenta los primeros resultados obtenidos al estudiar formas isoméricas de estilbeno: cis- y trans-estilbeno, líquido y sólido a temperatura ambiente, respectivamente, con el objetivo de explorar sus propiedades, al estar las mismas en contacto con superficies policristalinas de oro (Au/mica) y grafito (HOPG).Se encontró que la inmovilización de trans-estilbeno sobre una superficie puede modificar el proceso de cristalización de estas moléculas orgánicas, cuya morfología depende del sustrato. Mientras que el trans-estilbeno forma "clusters" que originan cristales de forma pseudo-romboide sobre HOPG, sobre la superficie de Au/mica forma estructuras dendríticas con ramificaciones en ángulos a 90 º.Por otra parte, se observó que el cis-estilbeno a escala nanométrica forma también "clusters" sobre HOPG, comportándose de manera similar al trans-estilbeno. Un paulatino incremento en la cantidad de cis-estilbeno conlleva al crecimiento de dichos "clusters" y a su coalescencia en una fase amorfa. Por el contrario, la interacción molécula-sustrato de cis-estilbeno sobre Au/mica es más lábil que sobre HOPG y ya no resulta posible observar centros de nucleación o nanoestructuras estables. Un aumento en la cantidad de cis-estilbeno sobre Au/mica resulta en una especie de película delgada líquida.

Mediated Electrochemical Deposition of Copper and Silver Thin Films for Improved Resistivity, Grain Size and Intrinsic Stress

INTRODUCTION Copper interconnects are typically grown electrochemically as electrodeposition provides a means of depositing large amounts of material over complex geometries and is easily scalable. However, electrodeposition generally results in film microstructures that adversely affect resistivity and electromigration properties. Electromigration rates increase due to surfaces and grain boundaries, and this problem may worsen as smaller device scales lead to larger surface area to volume ratios. Chemical additives are typically used in electrolytes in order to mitigate these problems. Several additives often must be used to manufacture a high quality film, and the relative concentrations of additives can have significant impact on the microstructure of the film. Unfortunately these additives are poorly understood, and their effects are complex and empirically derived, which slows improvements in electrodeposition processes that rely on these additives. Mediating electrochemical deposition with under potentially deposited (UPD) monolayers of another elemental metal provides a controllable means of affecting the microstructure of the deposited film. The technique requires only one additive to the deposition solution, the mediating metal. This mediator must meet only a few characteristics. The mediating element must be less noble than, exhibit under potential deposition on, and not alloy with the deposited metal. The technique has been previously demonstrated for silver deposition on a single crystal gold substrate. [1,2] In this study, we extend the process to electrodeposition of silver and copper on industrially relevant polycrystalline substrates. RESULTS AND DISCUSSION We investigated UPD mediated electrodeposition of silver and copper films on polycrystalline substrates using lead as the mediating element. We varied the deposition potential to change the coverage of the UPD metal during electrodeposition, and this change in coverage caused a change in the growth mechanism of the depositing film. Silver films were deposited on polycrystalline gold films from 0.1M perchloric acid, 0.01M lead perchlorate and 0.5 mM silver perchlorate solutions. Copper films were deposited on Si substrates with polycrystalline copper seed films from 0.01M lead perchlorate and 0.01M copper perchlorate solutions. The copper films were deposited on silicon substrates as blanket films and patterned lines. We present resistivity data that demonstrate improvement over unmediated growth. In situ stress measurements of the growing films indicate UPD deposition significantly reduces the intrinsic stresses of deposited films. Atomic force microscopy images of the films are presented to show the effects of UPD on growth mechanism, surface roughness and grain sizes. We present Rutherford backscattering data to show the purity of the deposited films. Finally, we report the filling characteristics of UPD mediated deposition of Cu films on patterned Si substrates. Based on experimental results, we discuss how mediated deposition can be applied to improve the quality of electrodeposited copper for interconnect applications to improve electrical resistivity. We also discuss how this deposition technique might be applied to other film/substrate systems to tailor resistivities, intrinsic stresses, and microstructures of electrodeposited films. We also propose that the demonstrated correlation between intrinsic film stress, grain size and resistivities might be used for qualitative characterization of deposited films. The authors gratefully acknowledge materials support from Dr. Qiang Huang of IBM T. J. Watson Research Center. The authors gratefully acknowledge the support of NSF Award Number 1309849. 1. K. Sieradzki, S.R. Brankovic, and N. Dimitrov, Electrochemical Defect-Mediated Thin-Film Growth, Science, Vol. 284, pp. 138-141 (1999). 2. S.R. Brankovic, N. Dimitrov, K. Sieradzki, Surfactant Mediated Electrochemical Deposition of Ag on Au(111), J. Electrochem. Soc., Vol. 2, pp. 443-445 (1999). Figure 1

Surface properties of atomically flat poly-crystalline SrTiO3.

Comparison between single- and the poly-crystalline structures provides essential information on the role of long-range translational symmetry and grain boundaries. In particular, by comparing single- and poly-crystalline transition metal oxides (TMOs), one can study intriguing physical phenomena such as electronic and ionic conduction at the grain boundaries, phonon propagation, and various domain properties. In order to make an accurate comparison, however, both single- and poly-crystalline samples should have the same quality, e.g., stoichiometry, crystallinity, thickness, etc. Here, by studying the surface properties of atomically flat poly-crystalline SrTiO3 (STO), we propose an approach to simultaneously fabricate both single- and poly-crystalline epitaxial TMO thin films on STO substrates. In order to grow TMOs epitaxially with atomic precision, an atomically flat, single-terminated surface of the substrate is a prerequisite. We first examined (100), (110), and (111) oriented single-crystalline STO surfaces, which required different annealing conditions to achieve atomically flat surfaces, depending on the surface energy. A poly-crystalline STO surface was then prepared at the optimum condition for which all the domains with different crystallographic orientations could be successfully flattened. Based on our atomically flat poly-crystalline STO substrates, we envision expansion of the studies regarding the TMO domains and grain boundaries.

Characterization of dielectric layers grown at low temperature by atomic layer deposition

Dielectric films, such as hafnium dioxide (HfO2), aluminum oxide (Al2O3), zirconium dioxide (ZrO2), titanium dioxide (TiO2) and their composite layers are deposited on polycrystalline and amorphous substrates by the atomic layer deposition (ALD) method. We demonstrate that the use of this technology guarantees a uniform and controlled surface coverage in the nanometer scale at low temperatures (in our case, below 100°C). Modification of the composition of oxide layers allows the deposition of materials with quite different absorption coefficients, refractive indexes and dielectric constants. In particular, we demonstrate structural, electrical and optical properties of dielectric layers and test metal-oxide-semiconductor structures with these oxide materials. Our good quality dielectric layers, obtained at low-temperature ALD, are characterized by a high dielectric constant (above 10), very smooth surface, wide energy gap (above 3eV), low leakage current (in the range of 10−8 A/cm2 at 1V), high dielectric strength (even 6 MV/cm) and high refractive indexes (above 1.5 in the visible spectral range).

Raman studies on the effect of multiple-energy ion implantation on single-crystal hexagonal boron nitride

Single energy ion implantation of hexagonal boron nitride (h-BN) at various fluences and keV energies has shown that there is a change in the local symmetry of the crystal from hexagonal to the cubic (c-BN) symmetry. These conclusions have been primarily based on Raman scattering (RS) and Fourier transform infrared spectroscopy. Transmission electron microscopy (TEM) analyses have been a challenge because the sample preparation for cross-sectional study of both the polycrystalline substrates and single-crystal material used in the study presented problems that were difficult to circumvent. A multiple-energy implant with different fluence fractions has been used to create a uniform implanted layer in the material from the surface to the end of range of the implant in this study. We report on the initial RS studies on these samples.

Oxide nanofilms on copper and silver: anodic synthesis and semiconducting properties

Structure-sensitive properties of oxide nanofilms anodically formed on single crystals and polycrystalline silver and copper were determined by photoelectrochemical methods and scanning electron microscopy. At transition from polycrystalline substrate to single crystals the structural disordering decreases for Ag(I) oxide and increases for Cu(I) oxide in accordance with morphological modification.

Three-dimensional whispering gallery modes in InGaAs nanoneedle lasers on silicon

As-grown InGaAs nanoneedle lasers, synthesized at complementary metal–oxide–semiconductor compatible temperatures on polycrystalline and crystalline silicon substrates, were studied in photoluminescence experiments. Radiation patterns of three-dimensional whispering gallery modes were observed upon optically pumping the needles above the lasing threshold. Using the radiation patterns as well as finite-difference-time-domain simulations and polarization measurements, all modal numbers of the three-dimensional whispering gallery modes could be identified.

Additive manufacturing of nickel-based superalloy Inconel 718 by selective electron beam melting: Processing window and microstructure

Abstract