bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enhanced Control of Porous Thin Film Morphology via Ion Bombardment
Authors: Fleischauer Michael D. , Sorge Jason B. , Joseph Robert A. , Brett Michael J. 
Published: April 2011

ABSTRACTIon bombardment was used during and after the deposition of controlled-porosity thin films produced using the Glancing Angle Deposition (GLAD) technique. Post-deposition ion bombardment was used to mill vertical-post morphology GLAD films, whose constituent columns varied in size due to competition effects. Smaller columns, although in the minority, can have a significant impact on the function of these films in a variety of optics applications, and can only be avoided by pre-selecting column location (i.e. seeding). Uniform milling eliminated smaller columns and left only remnants of the largest columns, which then acted as seeds during subsequent depositions. This simple, non-lithographic technique leads to more uniform column morphology. Column tilt angle can also be adjusted using ion bombardment. Methods to tune column tilt angle as a function of ion current using ion-assisted deposition are discussed, with an emphasis on improved square spiral photonic band gap crystal fabrication. Ion bombardment was found to increase the tilt angle of each spiral arm, moving the architecture closer to the theoretical optimum structure.
Laser-induced Dewetting Nanomorphologies in Single and Bilayer Metal Films
Authors: Krishna Hare , Favazza Christopher , Sureshkumar R. , Kalyanaraman R. 
Published: April 2011

ABSTRACTSpatially ordered patterns result under ns laser-induced dewetting of nanoscopic metallic films like Co and Ag on inert substrates like SiO2. In both cases, the observed ordering length scale is due to thin film hydrodynamic instability with spinodal-like character. However, the morphological pathway during dewetting is different for the two metals: occurring through development of bicontinuous structures in the case of Ag and by progression of cellular networks for Co. Dewetting in bilayer structures of Ag and Co on SiO2 show that the morphology evolution is dictated by the thicker of the two films in the bilayer structure. We applied linear stability analysis to predict the length scales in single and bilayer metal film. The experimental observations are in good agreement with theoretical predictions from the analysis. An important result was that the length scales for the bilayer film were significantly smaller than a single layer of the same thickness suggesting that further control of patterning length scales may be achieved through multilayer dewetting.
Control of Growth and Morphology of a Crystal Surface by Induced Spatio-Temporal Oscillations of Surface Temperature
Authors: Khenner Mikhail 
Published: April 2011

ABSTRACTThis paper presents the model for pattern formation in the course of thermodynamically stable and unstable crystal growth from vapor phase, which is influenced by rapid spatio-temporal variations of substrate and film temperature. In the model, such variations result from the interference heating of a substrate by weak pulsed laser beams. In the thermodynamically stable case the surface relaxational dynamics is influenced by surface diffusion mass transport from hot to cold regions of a substrate; this leads to accumulation of mass in cold regions and depletion in hot regions. In the thermodynamically unstable case the underlying faceting (spinodal) instability coupled to diffusion mass fluxes from hot to cold regions leads to formation of pyramidal surface structures. The scale of stationary coarsened structure increases as the separation distance of the adjacent interference fringes decreases (relative to the intrinsic faceting wave length, which is determined by the balance between the corner regularization energies and the surface energy anisotropy). On the other hand, the coarsening rates decrease with decreasing the separation distance, at least at particular typical deposition strength. The deposition strength and the separation distance of the interference fringes determine the transient and stationary pattern shape. By effectively redistributing adatoms on a substrate through the enhanced, spatially inhomogeneous diffusion, the interference heating mechanism delays, for large separation distances, the onset of spatiotemporal chaos as the growth rate increases.
Laser Irradiation of Atomic Chains: A Show-Case Study Based on the Density Functional Theory
Authors: Mazzone Anna M. , Bianconi Marco 
Published: April 2011

ABSTRACTThis study is motivated by recent applications of short laser pulses to the manipulation of atomic structures at the atomic scale and is based on the Density Functional Theory. The structures considered are linear monoatomic chains, formed by covalent and metallic atoms, and the calculations illustrate their evolution under laser irradiation. The calaculations show that the modification of the chain structure spans from a slight relaxation of the interatomic distances to fragmentation and illustrate the times and energies needed to induce those changes.
Surface Modification Energized by FIB: The Influence of Etch Rates & Aspect Ratio on Ripple Wavelengths
Authors: MoberlyChan Warren 
Published: April 2011

ABSTRACTIon beams have been used to modify surface topography, producing nanometer-scale modulations (and even subnanometer ripples in this work) that have potential uses ranging from designing self-assembly structures, to controlling stiction of micromachined surfaces, to providing imprint templates for patterned media. Modern computer-controlled Focused Ion Beam tools enable alternating submicron patterned zones of such ion-eroded surfaces, as well as dramatically increasing the rate of ion beam processing. The DualBeam FIB/SEM also expedites process development while minimizing the use of materials that may be precious (Diamond) and/or produce hazardous byproducts (Beryllium). A FIB engineer can prototype a 3-by-3-by-3 matrix of variables in tens of minutes and consume as little as zeptoliters of material; whereas traditional ion beam processing would require tens of days and tens of precious wafers. Saturation wavelengths have been reported for ripples on materials such as single crystal silicon or diamond (∼200nm); however this work achieves wavelengths >400nm on natural diamond. Conversely, Be can provide a stable and ordered 2-dimensional array of <40nm periodicity. Also ripples <0.4nm are fabricated on carbon-base surfaces, and these quantized picostructures are measured by HR-TEM and electron diffraction. Rippling is a function of material, ion beam, and angle; but is also controlled by chemical environment, redeposition, and aspect ratio. Ideally a material has a constant yield (atoms sputtered off per incident ion); however, pragmatic FIB processes, coupled with the direct metrological feedback in a DualBeam tool, reveal etch rates do not remain constant for nanometer-scale processing. Control of rippling requires controlled metrology, and robust software tools are developed to enhance metrology. In situ monitoring of the influence of aspect ratio and redeposition at the micron scale correlates to the rippling fundamentals that occur at the nanometer scale and are controlled by the boundary conditions of FIB processing.
FIB Precise Prototyping and Simulation
Authors: Nellen Philipp M. , Callegari Victor , Hofmann Juergen , Platzgummer Elmar , Klein Christof 
Published: April 2011

ABSTRACTWe present a closed approach towards direct microstructuring and high precision prototyping with focused ion beams (FIB). The approach uses the simulation of the involved physical effects and the modeling of geometry/topography during milling while the ion beam is steered over the surface. Experimental examples are given including the milling of single spots, trenches, rectangles, and Fresnel lenses. Good agreements between simulations and experiments were obtained. The developed procedures can also be applied to other FIB prototyping examples.
Development of Block Co-Polymers as Self-Assembling Templates for Patterned Media
Authors: Warke Vishal , Curry Michael L , Bakker Martin Gerard , Hong Kunlun , Mays Jimmy , Britt Phillip , Li Xuefa , Wang Jin 
Published: April 2011

ABSTRACTBlock copolymers that self-organize are of interest as templates for patterned media, as they potentially provide a low cost fabrication route. Poly(styrene)-Poly(methylmethacrylate) block co-polymers (PS-b-PMMA) of appropriate block length and PS to PMMA ratio self-assemble into a 2-D hexagonal phase in which the PS majority phase is continuous and surrounds cylinders of the minority, PMMA phase. For application of this phase to patterned media it is necessary that the cylinders of the minority phase be oriented perpendicular to the substrate surface. This can be achieved by a number of methods, including appropriate choice of substrate and use of a random co-polymer underlayer. Appropriate substrates include H-terminated silicon, some carbon coatings and some ITO glasses. Use of an acetic acid wash causes the minority PMMA component can be induced to be rearranged, giving rise to pores perpendicular to the substrate. Electrodeposition of a metal into the pores produces a hardmask which can be used with ion-milling to transfer the block co-polymer pattern onto a magnetic thin film.
Template Fabrication Challenges for Patterned Media
Authors: Resnick Douglas , Schmid Gerard , Miller Mike , Doyle Gary , Jones Chris , LaBrake Dwayne 
Published: April 2011

ABSTRACTThe Step and Flash Imprint Lithography (S-FILTM) process uses field-to-field drop dispensing of UV curable liquids for step and repeat patterning for applications where high-resolution mix-and-match overlay is desired. Several applications, including patterned media, photonic crystals and wire grid polarizers, are better served by a patterning process that prints the full wafer since alignment requirements are not so stringent. In this paper, a methodology for creating high resolution thin templates for full wafer (or disk) imprinting is described. The methods have been applied toward the imprinting of both patterned media and photonic crystal devices using a large area printing tool developed around the S-FIL process. Techniques for further enhancing the pattern density as well as a method for addressing feature image placement are described. Finally, a process for replicating a Master Template is discussed in detail.
Observation of Ge2Sb2Te5 thin film phase transition behavior according to the number of cycles using Transmission Electron Microscope and Scanning Probe Microscope
Authors: Kim Hyunjung , Choi Sikyung , Kang Sukhoon , Oh Kyuhwan , Kweon Soonyong 
Published: April 2011

ABSTRACTRecently, the development of information technology (IT) increases the demands of memory devices. Phase change random access memory (PRAM), based on the reversible phase change of the chalcogenide alloy, Ge2Sb2Te5, is widely regarded as a favourite candidate for the next generation memory. Because of PRAM has a simple cell structure with high scalability; it is non-volatile, has a relatively high read/write operation speed (Â50ns). The PRAM operation relies on the fact that chalcogenide-based materials can be reversible switched from an amorphous phase to a crystalline state by an external electrical current. It is important to study the electrical property with set/reset cycles, since film thickness shrinkage occurs with the phase transition.In this work, we fabricated the 100nm amorphous Ge2Sb2Te5 thin film on TiN/Ti/Si substrate using dc-magnetron sputtering. The 50X50§2 isolated Ge2Sb2Te5 cell was lithographed by the lift-off pattern and wet etching. And TiN top electrode was deposited using pattern align process at room temperature after the SiO2 insulator CMP. Phase transition behavior with the set/reset cycle was observed using I-V measurement and transmission electron microscope (TEM) on isolated Ge2Sb2Te5 cell. The set/reset programming was operated using tungsten SPM tip which was fabricated using focused ion beam (FIB) lithography. I-V curve which was observed by the I-V probe clearly showed that the phase transition was occurred by applying the electric field through the I-V probe. The resistivity difference between amorphous and crystal state was more than 102. After the phase transition, it was also demonstrated with transmission electron microscope (TEM) analysis. For the preparation of TEM specimen of the amorphous and crystalline cell, focused ion beam (FIB) lithography was adopted.
Nonvolatile Two-Terminal Molecular Memory
Authors: Snodgrass Jason , Kennedy Glen , Mei Wai-Ning , Sabirianov Renat 
Published: April 2011

ABSTRACTWe propose a nonvolatile two-terminal memory with two resistance states based on the molecular tunnel junctions. This tunnel junction is composed of one or few monolayers of polar molecules sandwiched between two electrodes made of materials with different screening length. As a prototype model system we study rare earth endohedral metallofullerene molecule with reversible dipole moment sandwiched by metal and semiconducting electrodes forming a double barrier junction. We use the Thomas-Fermi model to calculate the potential profile across the device. Calculated tunneling conductance through the proposed structure changes by order of magnitude upon the reversal of the dipole orientation (due to the applied voltage). This effect originates from the difference of potential profile seen by tunneling electrons for two opposite dipole orientations.
Sequential Stretching Lithography
Authors: Lin Haojing , Lima Ocelio V , Tan Li , Li Zheng , Li Jiangyu 
Published: April 2011

ABSTRACTWe developed an embossing/imprinting based nanofabrication technique, dubbed Sequential Stretching Lithography (SSL). In this process, a master pattern is imprinted into an elastomer containing a film of uncured elastomer. The elastomer is cured and then elongated to increase feature density and reduce feature size. Replication of this substrate yields a new master that can be used in further reduction steps. One-dimensional grating features with a pitch size below 200 nm were fabricated from 750 nm-pitch grating lines. This process gives us a faithful pattern miniaturization in all aspects and, as a result, a much effective control on density and dimension regulation.
GMR in Excess of 10% at Room Temperature and Low Magnetic Fields in Electrodeposited Cu/Co Nano-multilayer Structures
Authors: Pandya Dinesh K. , Gupta Priyanka , Kashyap Subhash C. , Chaudhary Sujeet 
Published: April 2011

ABSTRACTElectrodeposition has emerged as a novel economically viable technique with large-scale production capabilities in modern day micro technologies. The current trends are to extend the potential of the electrodeposition to nano fabrication. We have successfully electrodeposited Cu/Co multilayers, exhibiting appreciably high GMR, on ITO as well as on Cu/Si substrates. Multilayer stacks with films in thickness range 1 – 10 nm were deposited. The Co layers have different mechanisms of growth on these substrates, thus resulting in different microstructure and topography of the electrodeposited films. This leads to different GMR behavior of the multilayers in both these cases. Room temperature GMR values of 15% at low fields are obtained on ITO substrate and higher values are possible on Cu/Si substrate.
Formation and Characterization of Striped Nano-Channel Structure on the Functional Oxide Thin Film
Authors: Kasahara Masayasu , Matsuda Akifumi , Akita Yasuyuki , Hara Wakana , Kobayashi Keisuke , Kobayashi Kazuyoshi , Suzuki Toshimasa , Yoshimoto Mamoru 
Published: April 2011

ABSTRACTThe striped nano-channel structure (about 10nm in depth) was formed on the NiO film surface by thermal annealing of the film deposited on the sapphire(0001) substrate with periodic straight atomic steps. The interval of each nano-channel was about 100nm in average and well corresponding to the separation of atomic steps on the used sapphire(0001) substrate. Effects of annealing temperature and impurity doping into NiO upon the nanochannel formation were examined in order to control the depth. The depth of nano-channels formed on the alkali-metal(Li or Na) doped NiO films were found to be larger than that of nano-channels on the non-doped NiO films and enlarged with increasing annealing temperature in the range of 500∼900°C. Atomic-scale cross sectional structure of the nano-channel was characterized by transmission electron microscopy with focused on the film/substrate interface.
Structural and Morphological Characterization of Nanostructured Cobalt Ferrite Thin Films by Pulsed Laser Deposition
Authors: Kant K. Mohan , Ramachandra Rao M.S. 
Published: April 2011

ABSTRACTCobalt ferrite (CoFe2O4) thin films were deposited on quartz and single crystalline MgO(001) substrates using pulsed laser deposition (PLD) technique. The orientation of the as-deposited films were investigated as a function of substrate temperature (TS) in the range 200°C – 750°C. Films grown on MgO at higher substrate temperature were found to be (001) oriented while the films grown at lower substrate temperature were polycrystalline in nature. Magnetic measurements reveal that films deposited at lower substrate temperature had lower magnetic moment compared to that of films grown with higher substrate temperature, indicating the correlation between magnetic order and crystallinity. This is attributed to the presence of ordered magnetic domains in the oriented films even though the microstructure remains the same.
The Heating Effects of Dextran Coated Iron Oxides
Authors: Zeng Qi , Baker Ian , Hoopes Jack 
Published: April 2011

ABSTRACTThe structural and quasi-static magnetic behaviors and the temperature rises of three Dextran-coated maghemite nanoparticles subjected to alternating magnetic field (AMF) were investigated for potential use in magnetic hyperthermia treatments. In order to elucidate the effect of the hydrodynamic particle size on the specific absorption rate, the temperature rises for various hydrodynamic particle sizes were investigated in AMFs of various strengths and frequencies. Structural characterization was performed using a TEM and a SEM as well as by dynamic light scattering, and the quasi-static magnetic hysteresis loops were measured using a VSM. The heating behavior is discussed in relation to the magnetic behavior and particle size. While it was found that the heating mechanism for the ferromagnetic particles was mainly magnetic hysteresis losses, Brownian relaxation losses also contributed to the heating.
Microemulsion Synthesis of Nd0.5Ca0.5MnO3 and Nd0.5Sr0.5MnO3 Nanoparticles
Authors: Wang Z. Q. , Yin K. B. , Gao F. , Wang K. F. , Ren Z. F. , Liu J. -M. 
Published: April 2011

ABSTRACTNd0.5Ca0.5MnO3 (NCMO) and Nd0.5Sr0.5MnO3 (NSMO) nanoparticles have been synthesized using microemulsion synthesis method, with hexamethylene alkyl, a mixture of OP and 1-hexanol, NaOH as oil phase, surfactant, and precipitating agent, respectively. The phase formation of NCMO and NSMO nanoparticles was examined. The final NCMO and NSMO nanoparticles have average particle size of 24 and 50 nm, respectively, and present high-quality crystallinity. Measurements of the magnetic properties suggest that the charge-order state favored for bulk NCMO phase collapses in NCMO nanoparticles. The spin freezing behavior for both NCMO and NSMO nanoparticles was identified.
Guiding And Confining Light In Nanoporous Cu4O3-C Composite Thin Films
Authors: Das Mahua , Shivashankar S. A. 
Published: April 2011

ABSTRACTNanoporous Cu4O3 – C composite thin films with spherical and bicontinuous elongated pore structure have been grown on stainless steel substrates by metalorganic chemical vapour deposition technique using a single source tetranuclear metalorganic complex as precursor. The guiding and confinement of light in these quasi-periodic structures has been investigated by glancing incidence (75°) infrared spectroscopy at room temperature. The transmittance spectra of these films between wave number 10000 – 400 cm−1 reveal light confinement modes in photonic band gap between 6127-8839 cm−1 and propagation modes between 5094-400 cm−1.
Structural and Magnetic Properties of Nanogranular BaTiO3-CoFe2O4 Thin Films Deposited by Laser Ablation on Si/Pt Substrates
Authors: Barbosa José , Almeida Bernardo , Mendes Jorge A. , Rolo Anabela G. , Araújo João P. , Sousa João B. 
Published: April 2011

ABSTRACTThin film nanogranular composites of cobalt ferrite (CoFe2O4) dispersed in a barium titanate (BaTiO3) matrix were deposited by laser ablation with different cobalt ferrite concentrations (x). The films were polycrystalline and composed by a mixture of tetragonal-BaTiO3and CoFe2O4with the cubic spinnel structure. A slight (111) barium titanate phase orientation and (311) CoFe2O4phase orientation was observed. As the concentration of the cobalt ferrite increased, the grain size of the BaTiO3phase decreased, from 91nm to 30nm, up to 50% CoFe2O4concentration, beyond which the BaTiO3grain size take values in the range 30-35nm. On the other hand the cobalt ferrite grain size did not show a clear trend with increasing cobalt ferrite concentration, fluctuating in the range 25nm to 30nm. The lattice parameter of the CoFe2O4phase increased with increasingx. However, it was always smaller than the bulk value indicating that, in the films, the cobalt ferrite was under compressive stress that was progressively relaxed with increasing CoFe2O4concentration. The magnetic measurements showed a decrease of coercive field with increasingx, which was attributed to the relaxation of the stress in the films and to the increase of particle agglomeration in bigger polycrystalline clusters with increasing cobalt ferrite concentration.
Microwave Responce from La- and Dy- doped BiFeO3 Thin Films
Authors: Petrov Peter Kr. , Palkar Vaijayanti R , Alford Neil McN , Tagantsev Alexander K , Prashanthi K , Chien Hsin-I , Axelsson Anna-Karin , Bhattacharya S 
Published: April 2011

ABSTRACTThe dielectric response of La- and Dy- doped BiFeO3 thin films to electric- and magnetic fields was measured at microwave frequencies (up to 12GHz) in a temperature range from 25 °C to 300 °C. Interesting phenomena were observed. Significant oscillations in the C(f) characteristic which were unaffected by the electric field or by elevated temperature but which were dampened by a magnetic field. We also observed ‘N’-type I-V characteristics. A possible explanation for this mesoscopic response is the presence of structural features that cause resonance (e.g. grains, grain-boundaries, domains, domain walls etc), with a contribution strong enough to be averaged by the system. The exact origin of these features is unknown at present.
Control of Ferroelectric Phases by 4f Magnetic Moments in Multiferroic RMnO3 Crystals
Authors: Kuwahara Hideki , Noda K. , Akaki M. , Nakamura F. , Akahoshi D. 
Published: April 2011

ABSTRACTWe have investigated the magnetoelectric (ME) properties of the orthorhombic RMnO3 (R=mixed rare earth ions) crystals with and without the 4f magnetic moments, while keeping an average ionic size of R. In the presence of the magnetic contribution from the R ions ((Eu,Ho)MnO3), we have observed the ferroelectric polarization along the c axis (Pc) in a zero field, which arises from the bc spiral structure stabilized by the anisotropic exchange interaction between the R and Mn sublattices like TbMnO3. The Pc phase can be transferred to Pa by application of fields of ∼1.5 T parallel to the b axis. The observed decrease of transition field compared with TbMnO3 suggests that the magnetic contribution and the local distortion of the R ions are key factors for governing the ME properties.