bluuebunny/crossref_metadata_2025_split huggingface dataset:
Laser Ablation Synthesis of Ceramic Powders
Authors: Fahrenholtz W. G. , Foltyn S. R. , Ott K. C. , Chadwick M. , Smith D. M. 
Published: March 2011

AbstractA pulsed excimer laser was used to ablate aluminum metal into an oxygen-containing atmosphere. The resulting fine powder was collected on a 0.1 μm filter and analyzed to determine structure and composition. Using a combination of TEM, EELS, and thermal analysis techniques, the product was found to be amorphous aluminum oxide, Al2O3. The morphology of the powders was investigated using SEM, TEM, and surface area measurements. The resulting powder was crystallized and examined by x-ray diffraction.
Plasma Dynamics During Pulsed Laser Evaporation of High TcSuperconductors
Authors: Singh Rajiv K. , Neifeld R. , Narayan J. 
Published: March 2011

AbstractWe have theoretically and experimentally investigated the dynamics of the evaporated material generated by nanosecond excimer laser irradiation of YBa2Cu3O7targets in vacuum. The velocity distribution and the ionization of the plasma were determined by the ion time of flight measurements. The excimer laser ablated species possessed very high velocities (> 106cm/sec) which increased non-linearly with energy density. The ionization/ volume of the evaporated material exhibited a weak dependence on energy density, thereby suggesting the role of nonthermal mechanisms in the ionization process. These experimental results have been correlated with the theoretical model analyzing the plasma dynamics during pulsed laser evaporation of materials. A new modification to the earlier theoretical model is developed which accurately predicts the terminal velocities and the effect of ionization on these velocities. Various factors including, evaporation rates, degree of ionization, and laser wavelength which affect the plasma velocities will also be discussed.
Photoemission Study of Low-Fluence, Non-Thermal Laser Damage of UHV-Cleaved Gallium Arsenide (110)
Authors: Goldenberg S. S. , Long J. P. , Kabler M. N. 
Published: March 2011

AbstractThe pulsed-laser induced photochemical production of metallic Ga islands on the surface of GaAs cleaved, irradiated, and studied in ultrahigh vacuum (UHV) is documented through photoelectron spectroscopy and subsequent scanning electron microscopy. Ga islands are detected for laser fluences as low as 1 mJ/cm2, far below those previously reported for modification of GaAs, and for which the temperature rise is negligible.
Structure-Process-Property Relations in Excimer Laser Surface Processed Ti-6Al-4V Alloy
Authors: Jervis T. R. , Zocco T. G. , Steele J. H. 
Published: March 2011

AbstractExcimer laser processing results in very rapid solidification of metal surfaces. In addition to mixing or segregation processes, rapid heat treatment can result in phase transformations which yield beneficial surface properties. We have investigated the effect of pulsed excimer laser radiation on the microstructure and surface hardness of Ti-6A1-4V. This material undergoes a well defined martensite transformation during rapid quenching from temperatures in the β phase field. The depth of the transformed layer is thus a marker for the temperature profile during processing. We find that the depth of the transformed layer agrees well with a simple 1-D calculation of heat flow following the laser pulse. As measured by the nanoindenter, we find that the surface martensite is softer than the mechanically polished alloy. Multiple pulse processing at high fluences results in an increase in surface hardness, but at a depth much less than that of the martensite, suggesting an independent mechanism.
Threshold Fluence UV Laser Ablation of Single Crystal Bi2Sr2Ca1Cu2O8: Product Population and Kinetic Energy Distributions of Ejected Ionic Species
Authors: Wiedeman Lawrence , Sook Kim Hyun , Helvajian Henry 
Published: March 2011

AbstractWe have conducted an experiment which measures the product population and kinetic energy (KE) distributions from the UV laser induced decomposition of crystalline Bi2Sr2Ca1Cu2O8. We have measured these distributions at two laser wavelengths 248, 351. At a third wavelength (355 nm) we have measured the photoejected mass spectra from both a single crystal Bi2Sr2Ca1Cu2O8 sample and a polycrystalline Bi2Sr2Ca2Cu3O10 sample. For all the experiments, the laser fluence is maintained near the threshold for ion formation. The laser fluences are well below the level for instigating a laser induced above surface plasma. Our results show that the ejected products are not the consequence of a laser surface evaporation process. We measure a wavelength dependence in the ejected species population distribution and the ejected kinetic energy distribution (< KE > = 5 ± 1 eV.2eV FWHM) is indicative of an electronic excitation process. The measured ion mass spectra show atomic, diatomic (e.g. Sr2+), and oxide (e.g. SrO+, CaO+) species with lesser quantities of the complex oxides (e.g. S2O+). Distinctly absent from the mass spectra are the oxide compounds BiO+, CuO+, and the atomic species O+. Furthermore, the mass spectrum shows that at 248 nm laser excitation, the Bi+ species is the abundant photopro-duct. However, for both the 351 nm and 355 nm excitations, the Sr+ and SrO+ ions are measured as more abundant. Also, comparing the 355 nm laser excitation of the single and polycrystalline samples, there is very little difference in the photoejected species mass spectrum.
In Situ Observations of Beam-Induced Effects During High-Resolution Electron Microscopy
Authors: Smith David J. , Lu Ping , McCartney M. R. , Sharma R. 
Published: March 2011

AbstractA variety of electron-beam-induced effects, including oxidation, reduction and surface rearrangements are observed to occur at surfaces of oxides, fluorides and compound semiconductors during electron irradiation within the electron microscope. The extent and type of surface modifications observed are shown to depend upon the irradiation level, the residual microscope vacuum and the specimen temperature. For example, ex situ annealing of compound semiconductors leads to different end-products compared with in situ irradiation, thus showing that residual gas components can have a strong influence on the surface reactions. Electron irradiation of rutile during annealing at high temperature under ultrahigh vacuum conditions caused the rapid development of well-facetted holes without the usual intermediary phase seen at room temperature in conventional vacuum.
Angular and Energy Distributions of RH Atoms Desorbed in an Excited State from Ion-Bombarded Rh{100}
Authors: Maboudian Roya , El-Maazawi M. , Postawa Z. , Winograd N. 
Published: March 2011

AbstractMultiphoton resonance ionization spectroscopy has been used to determine the polar-angle and the kinetic-energy distributions of rhodium atoms desorbed from ion-bombarded Rh{100} surface in the fine-structure components of the a 4Fj (J=9/2 and 7/2) ground-state multiplet. The peak in the energy distribution of the metastable level (4F7/2 with excitation energy of 0.2 eV) is found to occur roughly at the same value as the ground-state (4F9/2) distribution but decays more gradually at higher energies. The measured spectra have been used to investigate the dependence of the excitation probability on the takeoff angle (θ) as well as the emission velocity (v). It is shown that the excitation probability depends strongly on these parameters, approaching an exponential dependence on l/[v cos(θ)] at higher velocities (> 5×l05cm/sec).
Sputtering of Molecules From ZnS, CdS, and FeS2
Authors: Nikzad S. , Calaway W. F. , Pellin M. J. , Young C. E. , Gruen D. M. 
Published: March 2011

It has been the general consensus in the sputtering community that molecules are sputtered from a clean metal surface in much smaller quantities than atoms. Some of the existing models further suggest that the sputter yield of molecules should be even lower from a compound than from a pure metal when the constituents of the molecule do not reside on neighboring sites in the solid.In our experiments, neutral species sputtered from single crystals of ZnS, CdS, and FeS2by a 3 keV Ar+beam have been observed by laser photo-ionization followed by time-of-flight mass spectrometry. While the atomic metal (Fe, Zn, Cd) and S2were the predominant species observed, substantial amounts of S, FeS, Zn2, ZnS, Cd2, and CdS were also detected. The experimental results demonstrate that molecules represent a larger fraction of the sputtered yield than was previously believed from secondary ion mass spectrometry experiments. In addition, our data suggest that the sputtered molecules are not necessarily formed from adjacent atoms in the solid. The applicability of various sputtering models will be discussed in the light of these results.
Phase Separation During Film Deposition
Authors: Atzmon M. , Adams C. D. , Cheng Y.-T. , Srolovitz D. J. 
Published: March 2011

ABSTRACTWe report a study of the microstructure and surface morphology of co-deposited Al-Ge films. At 200 °C and above, the terminal solid solutions are obtained, whereas at lower temperatures, metastable amorphous or crystalline phases coexist with the Al-rich terminal phase. For film thickness below 200 nm, lateral phase separation is observed with surface grooving which reflects the bulk microstructure. Analysis of the data with a model for the diffusion process shows that the results are consistent with a surface diffusion mechanism. For thicker films, there is a transition into a layered microstructure in which Al segregates to the surface. This transition is explained in terms of the surface and interfacial energies of the phases.
The Nucleation and Growth of Polycrystalline Silicon Carbide
Authors: Sheldon Brian W. , Besmann Theodore M. 
Published: March 2011

ABSTRACTSilicon carbide was deposited from methyltrichlorosilane onto polished polycrystalline SiC substrates at reduced pressure, and the resultant surface morphology was characterized by analyzing the angular spectrum of scattered light which was generated with a He-Ne laser. Light-scattering analyses incorporating specific nucleation and growth models were developed. With these methods, it was possible to analyze the angular scattering spectra and directly measure the nucleation and growth rates. These results were verified by using image analysis to quantify the number and size distribution of surface features that were observed with scanning electron microscopy. The nucleation and growth rates that were obtained by fitting the models to the image-analysis results were in good agreement with the rates obtained from the light-scattering.
Thermal Spike Model of Ion-Induced Grain Growth
Authors: Alexander Dale E. , Was Gary S. 
Published: March 2011

ABSTRACTA thermal spike model has been developed to describe the phenomenon of ion irradiation-induced grain growth in metal alloy thin films. In single phase films where the driving force for grain growth is the reduction of grain boundary curvature, the model shows that ion-induced grain boundary mobility, Mion, is proportional to the quantity FD2/ΔHcoh3, where FD is the ion and recoil energy deposited in nuclear interactions and ΔHcoh is the cohesive energy of the element or alloy. Experimental grain growth results from ion irradiated coevaporated binary alloy films compare favorably with model predictions.
Structural Characterization of Laser-Annealed Sputtered Poly-Si Films for High Mobility Tfts
Authors: Okamoto Akio , Shirai Seiiti , Suyama Shiro , Serikawa Tadashi 
Published: March 2011

ABSTRACTA high mobility of 390 cm2/Vs was successfully obtained for sputtered films, compared with 100 cm2/Vs for CVD films. Then, structural characterization of laser-annealed sputtered silicon films were performed, and compared with that of CVD films. TEM observations show a structural difference between the two film types. In sputtered films, many fine grain-like regions which have slightly different crystal orientation from surrounding regions are observed. On the other hand, in the CVD films, defects are widely spread over the film. X-ray diffraction, Raman scattering, and SIMS yield almost the same results in both films. The above-mentioned structural difference is thought to be essential to obtain high mobility.
Microstructure of BaTiO3 Thin Films Grown by Reduced-Pressure CVD
Authors: Van Buskirk Peter C. , Gardiner Robin , Kirlin Peter S 
Published: March 2011

ABSTRACTPolcrystalline BaTiO3 films have been grown on NdGaO3 [100], SrTiO3 [100] and Si [100] substrates by reduced pressure CVD. The substrate temperature was 1000°C and the total pressure during growth was 4 torr. X-ray diffraction measurements indicate highly textured films on the NdGa03 substrate. The orientation was predominantly [100], accompanied by small quantities of various TiO crystalline phases.
Microstructural Changes During Processing of Laser-Deposited BaTiO3 and Pzt Thin Films
Authors: Cook L. P. , Vaudin M. D. , Schenck P. K. , Wong-Ng W. , Chiang C. K. , Brody P. S. 
Published: March 2011

ABSTRACTThin films of BaTiO3 and PZT (lead zirconate titanate, 47%PbTiO3, 53%PbZrO3) have been produced by laser irradiation of the appropriate ceramic targets and deposition of the ejected and vaporized material on planar substrates. The microstructural changes during thermal processing of these films have been studied by scanning electron microscopy/energy dispersive x-ray spectrometry (SEM/EDX), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), x-ray diffraction (XRD), and by measurement of electrical properties. Films have been deposited using both Nd/YAG and excimer lasers and on unheated as well as heated substrates. Excimer films are considerably smoother than the Nd/YAG films, and the uniformity of the as-deposited microstructures is promoted by substrate heating. However, ferroelectric hysteresis loops were only observed for the considerably less smooth Nd/YAG PZT films; thermal treatment did little to improve the smoothness of these films. An excimer BaTiO3 film deposited on a heated substrate showed crystallographic alignment and had a dielectric constant of −100. Efforts are underway to combine the best features of films produced by both methods.
The Effects of Substrate Conditions on the Microstructural Evolution of Thin Diamond-Like Films
Authors: Cuomo J. J. , Bruley J. , Doyle J. P. , Pappas D. L. , Saenger K. L. , Liu J. C. , Batson P. E. 
Published: March 2011

ABSTRACTWe report on a study of hard amorphous carbon thin films prepared by condensing streams of energetic carbon species, onto a range of substrates maintained at different temperatures. The carbon vapor is generated either by ion sputtering, laser ablation or e-beam evaporation. Spatially resolved electron-energy-loss spectra reveal variations in the films′ microstructure brought about by altering the deposition conditions. We estimate that the density of the different films varies between 2.0 and 3.26 g/cm3. We observe an evolution towards denser films upon increasing incident beam energy, reducing substrate temperature, and increasing substrate thermal conductivity. Low density films contain a predominance of trigonally bonded sp2-hybridized carbon (i.e graphitic carbon) and the highest density films contain a high fraction (∽ 80%) of tetr-ahedral sp3-bonded carbon (i.e. diamond-like).
The Growth and Characterisation of Ir Silicide Films on (111)Si
Authors: Lawn M.A. , Elliman R.G. , Ridgway M.C. , Leckey R. , Riley J.D. 
Published: March 2011

ABSTRACTA study of the growth of thin Ir silicide films on (111)Si substrates has been undertaken. Thin (2.0nm) ir films deposited onto Si substrates under ultra-high vacuum conditions have been observed to display remarkable film continuity and fine grain structure (lnm). In situ annealing at 1000°C resulted in the formation of large regions (>10µm) of epitaxial IrSi3 islands (∼1µm) with identical epitaxial orientations. By means of annealing an as-deposited (2.0nm) Ir film stepwise to 1000°C within a transmission electron microscope the evolution of Ir silicide phases and morphologies were observed. The epitaxial growth of the semiconducting IrSi1.75 phase is reported along with the formation of Ir silicide islands at temperatures between 700°C and 800°C.
Effects Of Ar+ Ion Bombardment on the Nucleation and Growth of Ag Thin Films
Authors: Cotell C.M. , Sprague J.A. , Gossett C.R. 
Published: March 2011

ABSTRACTThin films of Ag were grown on amorphous C and <111= Si substrates with simultaneous Ar+ bombardment at energies ranging from 50–40,000 eV. For deposition of Ag on amorphous C, ion beam bombardment induced no changes in film nucleation behavior relative to evaporation (henceforth referred to as physical vapor deposition, PVD). Film growth was affected at the highest energy (40 keV); the grain size of the Ag films was increased by a factor of three. Rutherford Backscattering (RBS) measurements on Ag films on <111=Si bombarded with Ar+ at 1.5 keV showed that the Ag sputtering yield at film thicknesses <1.5 nm was less than for bulk Ag, in agreement with TRIM calculations. At 40 keV there was evidence for an additional effect of the ion beam due to recoil implantation or ion mixing. Electron diffraction from Ag fdms grown on <111= Si substrates with simultaneous Ar+ bombardment at either 1.5 keV or 40 keV showed evidence for only the expected phases: single crystal Si, polycrystalline Ag, and an amorphous phase that likely resulted from ion damage to the substrate.
Structure Determination of the Nisi2(111) Surface Using Medium Energy Ion Scattering with Monolayer Resolution
Authors: Vrijmoeth J. , Zagwijn P.M. , Frenken J.W.M. , van der Veen J.F. 
Published: March 2011

ABSTRACTThe surface structure of epitaxial NiSi2 films grown on Si (111) has been determined using a new method. The backscattering signals from subsequent Ni layers in the NiSi2 (111) surface are resolved.The topology of the NiSi2 (111) surface is concluded to be bulklike, i.e., it is terminated by a Si – Ni – Si triple layer.
GaAs(100) Surface Modifications at Elevated Temperatures, Studied By In-Situ Spectroscopic Ellipsometry
Authors: Yao Huade , Snyder Paul G , Woollam John A 
Published: March 2011

ABSTRACTSpectroscopic ellipsometric (SE) measurements of GaAs (100) were carried out in an ultrahigh vacuum (UHV) chamber, without arsenic overpressure, at temperatures ranging from room temperature (RT) to ∼610°C. Surface changes induced at elevated temperatures were monitored by in-situ spectroscopic ellipsometry. The SE data clearly displayed in real time the process of desorption of the GaAs-surface-oxide overlayer at ∼580°C. In addition, changes in the near-surface region were observed before and after the oxide desorption. The near-subsurface region (top 50–100 Å) became less optically dense after being heated to 540°C or higher. For comparison, a pre-arsenic-capped molecular-beam-epitaxy (MBE)-grown GaAs surface was also studied. After the arsenic cap was evaporated off at ∼350°C, this surface remained smooth and clean as it was heated to higher temperatures.
Microstructural Evolution of Epitaxial LiNbO3 Thin Films Derived From Metal Alkoxide Solutions
Authors: Nashimoto Keiichi , Cima Michael J. , Rhine Wendell E. 
Published: March 2011

ABSTRACTThe evolution of the microstructure of sol-gel derived LiNbO3 thin films was investigated to understand the growth of epitaxial films. LiNbO3 films were prepared from a precursor solution of lithium ethoxide and niobium pentaethoxide. Prehydrolysis promoted the development of polycrys-talline LiNbO3 films, whereas nonhydrolysis produced solid-state epitaxial growth of LiNbO3 films on sapphire substrates. Although the films looked smooth after annealing at 400°C, the morphology of the films changed, depending on substrates and precursors, due to grain growth at high annealing temperature. Prehydrolysis of the alkoxides caused a decrease in the temperature at which grain growth occurred, whereas the film prepared from the nonhydrolyzed precursor on a sapphire substrate showed denser texture and contained abnormally large domains that appeared to be single phase.
Deposition of Highly Transparent and Conductive Fluorine Doped Zinc Oxide Films
Authors: Hu Jianhua , Gordon Roy G. 
Published: March 2011

ABSTRACTZinc oxide films have been deposited from dimethyl zinc and oxygen in an atmospheric pressure laminar flow reactor at temperatures ranging from 300°C to 450°C. Highly oriented, conductive and transparent films were obtained at temperatures above 400°C by doping the films with fluorine. The crystallite sizes increase with increasing deposition temperature. From electron microprobe analysis, the doped films usually contained 0.5% to 2% fluorine atoms. Hall coefficient and resistance measurements at room temperature gave electron concentrations above 1020cm−3 and resistivities around 10−3 Ωcm. The doped films had mobilities varying from 20 to 40 cm2/V-s depending on the deposition temperature and fluorine concentration. These are the highest mobilities reported for zinc oxide films. The experimental results were then compared with those obtained from a simple resistivity network model which includes the effects of impurity and grain boundary scattering. Films with a sheet resistance of 5 Ω/square have visible absorption of about 5 to 10%. These properties are very suitable for applications as transparent electrodes for flat-panel displays and other electro-optical devices.
Growth and Characterization of Heteroepitaxial Nickel Films on Diamond Substrates
Authors: Humphreys T. P. , Jeon Hyeongtag , Nemanich R. J. , Posthill J. B. , Rudder R. A. , Malta D. P. , Hudson G. C. , Markunas R. J. , Hunn J. D. , Parikh N. R. 
Published: March 2011

ABSTRACTIn the present study epitaxial Ni(001) films have been grown on natural C(001) substrates (type la and Ha) and homoepitaxial C(001) films. Two deposition techniques including electron-beam evaporation of Ni in a molecular beam epitaxy (MBE) system and evaporation of Ni from a resistively heated tungsten filament have been employed. As evidenced by scanning electron microscopy (SEM), the Ni films deposited by electron-beam evaporation were found to replicate the very fine, unidirectional scratches present on the as polished C(001) substrates. Indeed, the coverage and uniformity of the deposited films would imply a two-dimensional (2-D) growth mode. In comparison, the thermal evaporation of Ni on C(001) substrates results in a highly textured and faceted surface morphology indicative of three-dimensional (3–D) nucleation and growth. Moreover, Rutherford backscattering/channeling measurements have demonstrated that the Ni(001) films deposited by electron-beam evaporation are of superior crystalline quality. Differences in the observed microstructure and apparent growth modes of the epitaxial Ni(001) films have been attributed to the presence of oxygen incorporation in those layers deposited by thermal evaporation.
Relaxation of Capped Strained Layers Via the Formation of Microtwins
Authors: Hwang D. M. , Schwarz S. A. , Ravi T. S. , Bhat R. , Chen C. Y. 
Published: March 2011

ABSTRACTA new strain relief mechanism in epitaxial layers of lattice mismatched face-centered cubic materials is identified using transmission electron microscopy. For an embedded strained layer near its critical thickness, we find that the primary strain-relaxation channel is through the formation of microtwins. A monolayer microtwin (a stacking fault) spanning the strained layer can form when a pair of partial dislocations of the <112> /6 type with antiparallel Burgers vectors are generated inside the strained layer and glide to the opposite interfaces. A series of partial dislocations can result in a microtwin several monolayers thick. For embedded strained layers of materials with small stacking fault energy, the formation of partial dislocation pairs is an energetically-favored strain relaxation channel, as compared to the formation of perfect dislocation pairs in the conventional double-kink model. Therefore, the mechanism proposed here poses fundamental limitations for strained layer device structures.