bluuebunny/crossref_metadata_2025 huggingface dataset:
Deposition of Ru Thin Films by MOCVD Using Direct Liquid Injection System
Authors: Kang Sang Y. , Hwang Cheol S. , Kim Hyeong J.
Published: April 2011

Ru thin films were deposited on SiO2/Si and (Ba,Sr)TiO3 [BST]/Pt/TiO2/SiO2/Si substrates using Ru(C2H5C5H4)2 [Ru(EtCp)2] by metal-organic chemical vapor deposition (MOCVD). To determine the effects of the solvent, C4H8O [tetrahydrofuran: THF], it was injected into the reaction chamber by the Direct Liquid Injection (DLI) system while Ru(EtCp)2 was input through the bubbler system. Also, Ru thin films were deposited using a liquid source, Ru(EtCp)2 dissolved in THF, delivered by the DLI system. The surface of the Ru thin films deposited on the BST substrate using only Ru(EtCp)2 through the bubbler system was very rough and milky, but the addition of THF made the surface of the films smooth and clean. In addition, Ru films deposited at 325°C using Ru(EtCp)2 dissolved in THF through the DLI system have a dense and smooth microstructure with resistivity as low as 15µωcm.
The Laser-Mössbauer Method for Surface Evolution and Thin Film Microstructure
Authors: Sorescu Monica
Published: April 2011

Using amorphous Fe81B13.5Si3.5C2, Fe40Ni38Mo4B18, Fe66Co18B15Si1 and Fe72.6Cr22Al4.8Si0.3Y0.3 as model systems, we apply the laser-Mössbauer method in order to obtain metallic glasses with novel properties. As shown by transmission Mössbauer spectroscopy, the bulk magnetic texture was modified in a rational manner by applying a varying number of excimer laser pulses per spot (λ=248 nm, τ=8 ns). As shown by conversion electron Mössbauer spectroscopy, this process left the surface magnetic texture unchanged and induced a distribution of magnetic moment directions throughout the thickness of the foil. A similar dependence of the magnetic texture upon the number of applied laser pulses was obtained in metallic glasses irradiated with a Nd:YAG laser (λ=532 nm, τ=8 ns). However, in this case we observed the onset of surface crystallization in the hyperfine magnetic field distributions extracted from the CEMS spectra. When a pulsed alexandrite laser was used (λ=750 nm, τ=60 μs), the onset of crystallization was found to be accompanied by bulk oxidation and the formation of magnetite particles in the irradiated system. Finally, a crucial experiment was performed in order to demonstrate the role played by the magnetostriction constant in the onset of crystallization.
Epitaxial NiO-Co exchange-biased bilayers grown on MgO single crystals Influence of the substrate orientation on the film morphology, the Co structure and the magnetic behavior
Authors: Warot B. , Snoeck E. , Ousset J.C. , Casanove M.J. , Dubourg S. , Fert A.R. , Bobo J.F.
Published: April 2011

Co/NiO bilayers have been grown on MgO(001), MgO(110) and MgO(111) substrates in an ultra high vacuum sputtering chamber. Growth mode and surface morphology are investigated by X-ray diffraction, Reflection High Energy Electron Diffraction (RHEED), Atomic Force Microscopy (AFM) and High Resolution Transmission Electron Microscopy (HRTEM). NiO layers grow epitaxially whatever the substrate orientation. Flat surfaces are observed on NiO/MgO(001) whereas on MgO(110) the NiO surface exhibits a roof-like morphology consisting in (100) and (010) facets elongated along the [001] direction. On MgO(111), the NiO surface presents pyramids with {100} facets. A temperature dependence of the cobalt layer structure is observed: on NiO(001) at room temperature it grows in its high temperature face-centered cubic structure (fcc), whereas it has the hexagonal close-packed structure (hcp) when deposited at slightly higher temperatures.
Low Temperature Deposition of ZnO SiO2 Thin Films on Polymer Surfaces by Plasma Enhanced CVD
Authors: Anma Hidetaka , Yoshimoto Yuuji , Tanaka Mariko , Takatsuka Hiroyuki , Hatanaka Yoshinori
Published: April 2011

ZnO and SiO2 thin films coated on plastic materials were investigated for the protection against solar ultraviolet (UV) radiation and the hard coating. Using diethylzinc (DEZ) as the organic zinc material, we attempt to deposit ZnO thin films on polycarbonate (PC) resin at room temperature by the cathode deposition technique of the plasma enhanced (PE) CVD method. It was found that the rf power and the substrate temperature intensively influenced on the deposition rate. The deposition rate increased with the rf power up to 100W, but decreased with the RF power above 100W, and also decreased with increasing the substrate temperature. In a xenon arc weatherability test, the ZnO-coated PC plates exhibited remarkable protection characteristics against UV radiation. They kept a smooth surface and no- coloring even if UV light irradiated for 1000 hours. Moreover, SiO2film deposited from tetraethoxysilane (TEOS) was over-coated on the ZnO film / PC plates. These films showed a drastic improvement in the hardness. Therefore, these films are expected as the UV-cut and hard coating for the automotive parts.
Luminous efficiency of AC Plasma Display Panels with MgO–TiO2
Authors: Kim Younghyun , Kim Rakhwan , Lee Yonguk , Jung Seonghoon , Park Jong-Wan
Published: April 2011

In order to improve both the operating voltage and the luminous efficiency of the protective layer for AC Plasma Display Panels, controlled amount of TiO2 was added to the pure MgO. The effect of the TiO2 addition on both the electrical properties (firing voltage & sustain voltage) and the luminous efficiency of the Mg2−2xTixO2 films deposited by e-beam evaporation was investigated. By addition of a proper amount of TiO2 to MgO, the dielectric constant of protective layer was increased to the 11, which has higher than that of bulk MgO. When the composition of Ti in the thin films was about 2.45at%, firing and sustain voltages were very low. With this composition, the luminous efficiency characteristics were much better than that of any other protective layer. When compared to that of the conventional MgO protective layer, the luminous efficiency showed an increase by 28%.
Microstructruture of Heteroepitaxially Grown TiO2 Films by Magnetron Sputtering
Authors: Yamagishi Makiko , Song Pung Keun , Shigesato Yuzo
Published: April 2011

Titanium dioxide (TiO2) films were deposited on (a) non-alkali glass, (b) MgO (100) and (c) SrTiO3 (100) single crystals by rf reactive magnetron sputtering using a Ti metal target. X-ray diffraction and a pole figure analysis revealed that TiO2 films on the (a) were anatase polycrystals with <101> preferred orientation, whereas heteroepitaxial growth of anatase TiO2 was observed on the (b) and the (c) substrates. FE-SEM analyses on the crystal habit of the firm surfaces showed that the substrate temperature during the deposition (Ts) heavily affected the microstructure and surface morphology of the heteroepitaxially grown films, which could be clearly explained in terms of “Thornton's zone model” or “epitaxial growth model of 2-dimensional ledge or kink modes” considering the normalized Ts by the phase transition temperature from anatase to rutile.
Growth of compound semiconductors in nanometer sized channels of polymers
Authors: Engelhardt R. , Könenkamp R.
Published: April 2011

We report about the electrodeposition of a transparent, p-type semiconductor in etched channelsof a thin polyester foil. The embedded semiconductor columns are robust against mechanical stress exerted on the foil, as the soft polyester matrix exerts only small forces on the embedded material. Dissolving the polyester results in freestanding semiconductor columns with height-to-diameter ratios in excess of 100.
Detection of Pinholes in Ultrathin Films by Magnetic Coupling
Authors: Egelhoff W. F. , Gan L. , Chen P. J. , Powell C. J. , Mcmichael R. D. , Fry R. A. , Beach G. , Martien D. , Berkowitz A. E.
Published: April 2011

When two magnetic films are separated by a nonmagnetic film, pinholes in the nonmagnetic film can allow direct contact and, thereby, direct magnetic exchange coupling between the two magnetic films. We have studied this coupling by having one of the magnetic films pinned and leaving the other free to switch at low field. The pinning is accomplished with test structures based on exchange bias and synthetic antiferromagnetic layers. Since the pinning strength increases sharply at low temperatures but orange-peel coupling does not, low-temperature (77 K) measurements appear to identify whether an observed coupling arises primarily from magnetic coupling through pinholes or primarily from orange-peel roughness. Our measurements appear to indicate that the observed coupling arises primarily from magnetic coupling through pinholes for Cu films less than 2.1 nm thick and for Al2O3films less than 0.6 nm thick but primarily from roughness-induced (orange-peel) magnetostatic coupling for larger thicknesses.
Laser ablated pure non-crystalline Co thin films for inductors for ultra-high frequencies
Authors: Madurga V. , Vergara J. , Favieres C.
Published: April 2011

Non-crystalline Co thin films have been prepared by pulsed laser ablation deposition. From the M-H hysteresis loops measurements, a soft magnetic behavior is observed. Néel type magnetic domain walls are observed in the as-deposited films. The spontaneous magnetization, Ms(T = 300 K), is ≍ 860 emu/cm3. After annealing at 500 oC, Ms(T = 300 K) is ≍ 1460 emu/cm3. The extrapolated to zero K resistance decreases almost two orders of magnitude from the as deposited samples to the crystallized heated at 500 °C ones. A trilayer Co/Cu/Co has shown a real part magnetic susceptibility of 120 at 100 MHz. In the 100 MHz to 1 GHz frequency range, a perpendicular bias magnetic field increased this value up to 270, remaining almost constant for all range.
Iron Manganites Synthesis by the Soft Chemistry Method
Authors: Coradin Herve , Guillemet-Fritsch Sophie , Agnoli Fabrice , Tailhades Philippe , Rousset Abel
Published: April 2011

The iron manganites FexMn(3−x)O4 synthesis by soft chemistry method have been studied. The main difficulty is to obtain single phase spinel with high Mn content (0.4< x < 1.3). Oxalate precursor powders of these materials with controlled shape and nanoscopic size have been prepared. The precursors are then heat treated with a H2/H2O/N2 gas mixture at low temperature. The resulting stoechiometric spinels are metastable phases with high specific surface area and are highly reactive toward oxygen. Therefore, these oxide can be oxidized in air at low temperature in order to produce mixed valence defect manganites FexMn(3−x)O4+δ with a good reproducibility on the oxygen content. Although, some problems persist for the higher Mn contents, as the oxygen partial pressure for the reduction must be controlled precisely in order to produce the stoechiometric spinel at low temperature. The development of a low temperature reduction system, with oxygen partial pressure controlled by oxygen electrochemical pumping, is in progress.
Magnetic Permeability and Relaxation Frequency in High Frequency Magnetic Materials.
Authors: Rosales M.I. , Montiel H. , Valenzuela R.
Published: April 2011

An investigation of the frequency behavior of polycrystalline ferrites is presented. It is shown that the low frequency dispersion (f < 10 MHz) of permeability is associated with the bulging of pinned domain walls, and has a mixed resonance-relaxation character, closer to the latter. It is also shown that there is a linear relationship between the magnetocrystalline anisotropy constant, K1, and the relaxation frequency. The slope of this correlation depends on the grain size. Such a relationship could allow the determination of this basic parameter from polycrystalline samples.
Effect of Iron Substitution on the High-temperature Properties of Sm(Co,Cu,Ti)z Permanent Magnets
Authors: Zhou Jian , Skomski Ralph , Sellmyer David J. , Tang Wei , Hadjipanayis George C.
Published: April 2011

Recently, Ti-substituted Sm-Co permanent magnets have attracted renewed attention due to their interesting high-temperature coercivity. Our presentation deals with the effect of iron substitutions on the magnetic properties of the materials. X-ray diffraction shows that the investigated Sm(Co,Fe,Cu,Ti)z materials (z = 7.0 - 7.6) are two-phase magnets, consisting of 1:5 and 2:17 regions. The iron content affects both the coercivity and the magnetization. Depending on composition and heat treatment, some samples show a positive temperature coefficient of the coercivity in the temperature range from 22 °C to 550 °C. Moderate amounts of iron enhance the room-temperature coercivity. For example, the room-temperature coercivity of Sm(Co6.0Fe0.4Cu0.6Ti0.3) is 9.6 kOe, as compared to 7.6 kOe for Sm(Co6.4Cu0.6Ti0.3). At high temperatures, the addition of Fe has a deteriorating effect on the coercivity, which is as high as 10.0 kOe at 500 °C for Sm(Co6.4Cu0.6Ti0.3). The room-temperature magnetization increases on iron substitution, from 73 emu/g for Sm(Co6.4Cu0.6Ti0.3) to 78 emu/g for Sm(Co6.0Fe0.4Cu0.6Ti0.3). The observed temperature dependence is ascribed to the preferential dumbbell-site occupancy of the Fe atoms.
Advances in the Low Temperature Preparation and Structural Characterization of Lanthanum Strontium Manganite Powder
Authors: Guillemet-Fritsch Sophie , Coradin Hervé , Barnabé Antoine , Calmet Christophe , Tailhades Philippe , Rousset Abel
Published: April 2011

Perovskite oxides of formula La1−xSrxMnO3 have been obtained by the thermal decomposition of precursor powders. Two different kinds of precursors, carbonates and citrates have been prepared by low temperature, i.e., “chimie douce” technique. The careful control of the chemical and the hydrodynamic parameters during the synthesis process allows obtaining nice homogeneous and small size particles (80 nm for the ex-carbonates and 30 nm for ex-citrates). Pure perovskite phase is observed after a low temperature thermal treatment, from 550 °C. The structure of these oxides is either rhombohedral or cubic and depends on the strontium content, the temperature and the partial pressure of oxygen during the thermal treatment. The Mn-O distances and the Mn-O-Mn angles are directly related to the amount of Mn4+ content.
Observation of Patterns by Magnetic Force Microcopy in Fe-alloys with Shape Memory Effect
Authors: Silva M. I.N. da , González J. C. , Andrade M. S.
Published: April 2011

In this study, we investigated the magnetic domains of a FeMnSiNiCr stainless steel sample using Magnetic Force Microscope (MFM). We compared the magnetic patterns obtained by scanning the sample with three coated probes with different magnetic properties: Medium magnetic moment (MM), low magnetic moment (LM), and low coercivity (LC). The probe-surface separation was varied between 25 to 300 nm in order to quantify the magnetic microstructure of the sample. A simple model for the probe-sample interaction was used to interpret the contrast change as a function of the probe-surface separation. The experiment showed that the average maximum frequency decreases with the probe-surface separation and the intensity of the frequency is the strongest for the MM probe. X ray diffraction experiments were used to identify the different phases present in the sample. The X-ray diffraction experiments together with the MFM showed that α-phase islands surrounded by a γ-phase matrix are responsible for the magnetic properties of the sample.
Phase-Change Media for High-Density Optical Recording
Authors: Borg Herman , Lankhorst Martijn , Meinders Erwin , Leibbrandt Wouter
Published: April 2011

Rewritable optical-storage systems are quickly gaining market share in audio, video and data- storage applications. The development of new rewritable optical-storage formats with higher capacity and data rate critically depends on innovations made to the recording media incorporating so-called phase-change materials. These materials allow reversible switching between a low and high reflective state induced by laser heating. In this paper, we highlight phase-change media aspects as optical and thermal design, sputter-deposition, materials optimization, and the development of new recording strategies. Focus is on the speed race in optical recording.
Analysis of Multipulse Strategies for High Data Rate Phase Change Optical Recording
Authors: Sheila Aparna C. , Schlesinger T.E.
Published: April 2011

Multipulse strategies for two disk rotation velocities of the same phase change optical disk, were analyzed using simulations, at red and blue wavelengths. Results showed that at either wavelength, lower pulse duty cycles are needed at lower velocities to reduce recrystallization and higher duty cycles are needed at higher velocities. Optimal erase powers and cooling width for minimal overwrite jitter were also found.
A Novel Approach to Obtain GeSbTe-Based High Speed Crystallizing Materials for Phase Change Optical Recording
Authors: Lee Tae-Yon , Cheong Byung-ki , Lee Taek Sung , Park Sung Jin , Kim Won Mok , Lee Kyung Seok , Kim Ki-Bum , Kim Soon Gwang
Published: April 2011

A new approach is proposed to obtain fast crystallizing materials based on a conventional GeSbTe alloy for rewritable phase change optical data storage. By means of co-sputtering, Ge1Sb2Te4alloy was mixed with Sn1Bi2Te4alloy so as to form pseudo-binary alloys (Ge1Sb2Te4)1-x(Sn1Bi2Te4)x (x is a mole fraction). From structural and optical analyses of the co- sputtered and annealed alloy films, the formation of stable crystalline single phases was observed along with a Vegard's law behavior, suggesting a homogeneous mixing of the two alloys. By use of a 4 layered disk with (Ge1Sb2Te4)0.85(Sn1Bi2Te4)0.15 recording layer, a preliminary test of writing and erasing was carried out and the results were compared with the case of the disk with Ge1Sb2Te4recording layer. The (Ge1Sb2Te4)0.85(Sn1Bi2Te4)0.15 recording layer was found to yield markedly higher erasibility, especially with increasing disk linear velocity.
Microscopic studies of fast phase transformations in GeSbTe films
Authors: Detemple Ralf , Friedrich Inés , Njoroge Walter , Thomas Ingo , Weidenhof Volker , Wöltgens Han-Willem , Ziegler Stefan , Wuttig Matthias
Published: April 2011

Vital requirements for the future success of phase change media are high data transfer rates, i.e. fast processes to read, write and erase bits of information. The understanding and optimization of fast transformations is a considerable challenge since the processes only occur on a submicrometer length scale in actual bits. Hence both high temporal and spatial resolution is needed to unravel the essential details of the phase transformation. We employ a combination of fast optical measurements with microscopic analyses using atomic force microscopy (AFM) and transmission electron microscopy (TEM). The AFM measurements exploit the fact that the phase transformation from amorphous to crystalline is accompanied by a 6% volume reduction. This enables a measurement of the vertical and lateral speed of the phase transformation. Several examples will be presented showing the information gained by this combination of techniques.
Super-Resolution Readout for Magneto-Optical Disk by Optimizing the Deposition Condition of Non-Magnetic Mask Layer
Authors: Shima Takayuki , Kim Johoo , Fuji Hiroshi , Atoda Nobufumi , Tominaga Junji
Published: April 2011

Super-resolution near-field structure (Super-RENS) was prepared by a heliconwave-plasma sputtering method to improve the disk property that is combined with a magneto-optical (MO) recording disk. Antimony and silver-oxide mask layers were prepared by the method and refractive indices were measured. Recording and retrieving of signals beyond the resolution limit (<370 nm) were achieved for both mask cases. Attempts to optimize the disk structure were also made using a conventional sputtering method. The smallest mark size was around 200 nm and the highest carrier-to-noise ratio (CNR) was 30 dB for 300-nm mark and 22 dB for 250-nm, when using a laser wavelength of 780 nm and a numerical aperture of 0.53. We have found that there is a competing super-resolutional mechanism besides Super-RENS that appears when high readout laser power is applied. This mechanism played rather an important role at least in the mark-size range of 200-370 nm.
Materials Development for Thermally-Assisted Magnetic Recording Media
Authors: Brucker C.F. , McDaniel T.W.
Published: April 2011

We have carried out a combined experimental and computer simulation study to specify and identify candidate films to support high areal density, thermally-assisted magnetic recording. The motivation of this work is to utilize the enhanced writability of very high coercivity materials that thermal assistance can provide. Media with high coercivity (and anisotropy Ku) are known to be essential to achieve a sufficiently high ratio of KuV/kBT necessary to maintain magnetic stability at temperature T in media switching units (grains; single domains) of volume V. Nominally, we expect V ∝ D−3/2, where D is the medium bit density per unit area in recording. A micromagnetic recording simulation tool with a capability of representing realistic grain size distributions, temperature-dependent magnetic properties, and spatially-varying imposed temperature distributions was employed to study the interplay of thermal and magnetic field gradients in the recording process. In addition, a simple LLG-based thermomagnetic switching model supplemented the micromagnetics model. We fabricated improved Co/X multilayer media for recording evaluation, and performed standard materials characterization.
Integrated Surface Emitting Laser Arrays with Flat-Tip Microprobes for the Near-Field Optical Data Storage
Authors: Kim Young-Joo , Ye Shu-Ying , Suzuki Kazuhiro , Goto Kenya
Published: April 2011

Current optical data storage is challenging to increase its memory capacity and data transfer rate for realizing high-quality image and rapid service in the coming digital, multimedia and network era. To actualize more effective and simple data storage, a novel parallel near-field optical system has been proposed using vertical cavity surface emitting laser (VCSEL) microprobe arrays. The new parallel optical system is based a multibeam recording head consisting of a VCSEL array with apertures of nanometer size as a near-field wave exit. We have developed some candidates for the parallel recording head, including the direct aperture formation on the VCSEL emitting surface and the preparation of microprobe arrays with flat-tip structure. The new flat-tip microprobe array has advantages for improving the optical efficiency and stabilizing the contact head system with optical media since it is prepared from semiconductor materials of high refractive index. Silicon nano-aperture probe array has been prepared successfully with the aperture size of 150 to 500nm using micro-fabrication techniques. We have also investigated the integrated microprobe array by the direct fabrication of flat-tip probes on the substrate of bottom emitting VCSEL arrays. Finally the reading mechanism has been studied theoretically using a finite difference time domain (FDTD) simulation and an optical feedback effect of semiconductor lasers for the integrated microprobe VCSEL array. We believe this nano-aperture VCSEL probe array is sufficiently effective to be applied to the parallel recording head for the near-field optical data storage of a high data capacity and fast transfer rate.
Human Brain Like Memory Behavior in the Magnetic Domain Expansion Type Magneto-Optical Disk
Authors: Ota Norio , Awano Hiroyuki , Tani Manabu , Imai Susumu
Published: April 2011

Magnetic Amplifying Magneto-Optical System (MAMMOS) shows human brain like memory behavior. Magnetic field and laser power have threshold to recover the stored memory like the human response of remembering. MAMMOS also has a feature to amplify very small recorded signals like our recovery of memory, e.g. fifty years ago episode.

By adding the meaningful information on the magnetic field pattern, we can get some correlation between our memory and external stimulation. Such scheme is named as “the Active readout MAMMOS” which is analogues to the human process of remembering the memory.

If the applied field pattern and timing phase just coincide with stored information, there occurs the coherent amplification of MAMMOS signal. We can utilize such phenomena as the trigger of “Memory Association”.
Chiroptical Molecular Memory of Amorphous Azopolymer using Light Handedness
Authors: Kim Mi Jeong , Kim Dong-Yu
Published: April 2011

For chirooptic molecular memory system, induced chirality on an azobenzene-containing amorphous polymer film was investigated using circularly polarized Ar+ laser with various ellipticity. High intense CD spectrum proved that optical-induced chirality on the amorphous film. Additionally, elliptically polarized light induced much higher chirality than circularly polarized light.
C60Clusters Self-Assembly in One-beam Optical Trap
Authors: Eugene Collins W. , Lu Weijie , Morgan Steven , Zavalin Andrey
Published: April 2011

C60aggregated clusters up to 20 um length were created on a glass surface within a solution inside of a gradient one-beam optical trap. It was possible to grow rod-shaped structures by motion of an optical trap parallel to the surface of the substrate. After the deposited structures became stable, the solution was dried. By AFM measurements of the stable dried structures, it was shown, that aggregations have typical sizes of 5–15 um X 1.5–2 um, and thickness near 1.5 um. The aggregations consist of thinner (30–100 nm diameter) rods, bundled together.
Effect of Metal Back Contacts on Tetrahedral Amorphous Carbonc Films Grown Using the Cathodic Arc Process.
Authors: Satyanarayana B.S. , Takahashi H. , Narusawa T. , Hiraki A.
Published: April 2011

Reported here is a study on the effect of different metal back contacts onthe electrical and structural properties of the tetrahedral amorphous carbon (ta-C). The films were grown using a pulsed cathodic arc system. Ta-C films were deposited simultaneously on silicon substrate, precoated with the following metals, namely aluminium (Al), gold (Au), chromium(Cr), molybdenum (Mo), copper (Cu), tungsten (W) and titanium(Ti). The electrical measurements and Raman response show that the back contact does influence the properties of ta-C films. These results are analysed with respect to our earlier report regarding the influence of back contacts on field emission from similar ta-C films.
X-Ray Reflectivity of Ultra-Thin Diamond-Like Carbon Films
Authors: Tanner B. K. , LiBassi A. , Ferrari A. C. , Robertson J.
Published: April 2011

Grazing incidence x-ray reflectivity has been employed to investigate ultra-thin films of tetrahedral amorphous carbon (ta-C) grown with an S-bend filtered cathodic vacuum arc. The results indicate that x-ray reflectivity can be used as a metrological tool for thickness measurements on films as thin as 0.5 nm, which is lower than the range required for carbon overcoats for magnetic hard disks and sliders if they are to reach storage densities of 100 Gbits/in2. The density of the films was derived from the best-fit to simulated reflectivity profiles from models for the structural parameters. In such thin films, the x-rays are reflected mainly at the film substrate interface, rather than the outer surface, so that the film density is derived from analysisof the oscillations of the post-critical angle reflectivity.
Preferential Growth of Carbon Nanotubes/Nanofibers Using Lithographically Patterned Catalysts
Authors: Teo K. B. K. , Chhowalla M. , Amaratunga G. A. J. , Milne W. I. , Pirio G. , Legagneux P. , Wycisk F. , Pribat D.
Published: April 2011

In order to utilise the full potential of carbon nanotubes/nanofibers, it is necessary to be able to synthesize well aligned nanotubes/nanofibres at desired locations on a substrate. This paper examines the preferential growth of aligned carbon nanofibres by PECVD using lithographically patterned catalysts. In the PECVD deposition process, amorphous carbon is deposited together with the nanotubes due to the plasma decomposition of the carbon feed gas, in this case, acetylene. The challenge is to uniformly nucleate nanotubes and reduce the unwanted amorphous carbon on both the patterned and unpatterned areas. An etching gas (ammonia) is thus also incorporated into the PECVD process and by appropriately balancing the acetylene to ammonia ratio, conditions are obtained where no unwanted amorphous carbon is deposited. In this paper, we demonstrate high yield, uniform, ‘clean’ and preferential growth of vertically aligned nanotubes using PECVD.
Inorganic Nanocrystals with Dendrimer Templates: Mesoscopic Model System and Route to New Nanocomposites
Authors: Gröhn Franziska , Bauer Barry J. , Amis Eric J.
Published: April 2011

We investigate nanostructures that are formed when dendrimers act as hosts. Poly(amidoamine) (PAMAM) dendrimers can be used as templates for inorganic nanocrystals, both in aqueous solution1-3 and in a polymeric matrix4. SANS, SAXS and TEM are used to characterize the resulting hybrid structures. Different inorganic colloids like noble metal and cadmium sulfide colloids are studied1,2. With increasing dendrimer generation, we observe a transition from low molecular colloid stabilizing to an effective polymer templating in terms of a “host-guest nanoscale synthesis”. For these higher generation dendrimers, inorganic colloids are formed inside single dendrimer molecules and the size of the nanocrystal can precisely be controlled by the dendrimer generation (“fixed loading law”). Hydrophobically modified dendrimers in organic solvent represent a further, different kind of host system that we have investigated using scattering methods5.
Designing Molecular Assemblies in the Solid-State: Induced-Stacking by a Rebek Cleft
Authors: MacGillivray Leonard R. , Siebke Michelle M.
Published: April 2011

Co-crystallization of 2,7-di-tert-butyl-9,9-dimethyl-4,5-xanthenedicarboxylic acid (1), a Rebek cleft, with 1,2-trans-bis(4-pyridyl)ethylene 2 yields a four-component molecular assembly, 2(1)·2(2), that is held together by four O-H…N hydrogen bonds. The cleft organizes the bipyridine such that two molecules of 2 lie in a stacked arrangement.
Characterization of Wet-Chemically Nanostructured Stainless Steel Surfaces
Authors: Buescher R. , Jennissen H. P. , Chatzinikolaidou M. , Fischer A.
Published: April 2011

A novel surface modification process is presented, which creates a macroscopically smooth and a nanoscopically rough surface on an austenitic stainless steel. The chemical structure of the oxide layer is changed due to the acid treatment, whereas the thickness is not increased. An altered chromiumoxide content in the passive layer connected with a high bonding strength to the substrate material suggests the use of these wet chemically modified steels in biomedical applications.
Tunable Magnetic Properties in Metal Ceramic Composite Thin Films
Authors: Kumar D. , Narayan J. , Sharma A. K. , Kvit A. , Jin C. , Sankar J.
Published: April 2011

We have developed a novel thin film processing method based upon pulsed laser deposition to process nanocrystalline magnetic materials with accurate size and interface control. Using this method, single domain nanocrystalline Fe and Ni particles in 5-10 nm size range embedded in amorphous as well as crystalline alumina have been produced. Magnetization measurements of these layered thin films as function of field and temperature were carried out using a superconducting quantum interference device magnetometer. Hysteresis below blocking temperature have been found to be consistent with the Stoner-Wohlfarth type behavior. The size of Fe and Ni nanodots measured using transmission electron microscopy and calculated using magnetic data are in excellent agreement with each other.
Silver Nanowires Eelectrodeposited from Reverse Hexagonal Liquid Crystals
Authors: Huang Limin , Wang Huanting , Wang Zhengbao , Mitra Anupam , Yan Yushan
Published: April 2011

A novel, simple and efficient procedure was developed to electrodeposit one-dimensional Ag nanowires from reverse hexagonal liquid crystalline phases by using their one-dimensional cylindrical aqueous microdomains as space-confined reactors. Using this soft-template approach, flexible Ag nanowire arrays with wire diameter of 15-30 nm, high aspect ratio over 1000, and high wire densities over 1011 wires/cm2 were obtained. The Ag nanowire arrays can be easily collected by simply washing. The nanowires obtained can be used either in high-density bundle form or as single wires after dispersion by untrasonication.
Development of Quantum dot Reporters for Immunoassay Applications
Authors: Speckman D. M. , Jennings T. L. , LaLumondiere S. D. , Moss S. C.
Published: April 2011

Multi-pathogen biosensors that take advantage of sandwich immunoassay detection schemes usually rely on spatial resolution patterns of capture antibodies on a detector plate for pathogen recognition, and typically utilize fluorescent, organic dyes as optical labels to identify captured pathogens. An immunoassay-based, fiber optic detector that utilizes varying sized fluorescent semiconductor quantum dots (QDs) as the reporter labels for different antibodies would have the ability to detect multiple pathogens within a single fiber, using a single excitation source. Such a detector requires that QDs be attached to antibody proteins, such that the specificity of the antibody is maintained. We have been involved in efforts to develop a reproducible method for attaching QDs to antibodies for use in such a biosensor.

We synthesized CdSe/ZnS core-shell QDs of differing size, functionalized their surfaces with several types of organic groups for water solubility, and covalently attached these functionalized QDs to rabbit anti-ovalbumin antibody protein. We also demonstrated that these labeled antibodies exhibit selective binding to ovalbumin antigen. We characterized the QDs at each step in the overall synthesis by UV-VIS absorption spectroscopy and by picosecond (psec) transient photoluminescence (TPL) spectroscopy. TPL spectroscopy measurements indicate that QD lifetime depends on the size of the QD, the intensity of their optical excitation, and whether or not they are functionalized and conjugated to antibody. We describe details of these experiments and discuss the impact of our results on our biosensor program.
Tuning the Optical Properties of Large Gold Nanoparticle Arrays
Authors: Kim Beomseok , Tripp Steven L. , Wei Alexander
Published: April 2011

Gold nanoparticles in the mid-nanometer size regime can undergo self-organization into densely packed monoparticulate films at the air-water interface under appropriate passivation conditions. Films could be transferred onto hydrophilic Formvar-coated Cu grids by horizontal (Langmuir-Schaefer) deposition or by vertical retraction of immersed substrates. The latter method produced monoparticulate films with variable extinction and reflectance properties. Transmission electron microscopy revealed hexagonally close-packed arrays on the micron length scale. The extinction bands of these arrays shifted by hundreds of nanometers to near-infrared wavelengths and broadened enormously with increasing periodicity. Large particle arrays also demonstrated extremely high surface-enhanced Raman scattering (SERS), with enhancement factors greater than 107. Signal enhancements could be correlated with increasing periodicity and are in accord with earlier theoretical and experimental investigations involving nanoparticle aggregate structures.
The characterisation and reactivity of nanostructured cerium-copper-oxide composites for environmental catalysis
Authors: Adamopoulos Othon , Zhang Yu , Croft Mark , Zakharchenko Igor , Tsakalakos Thomas , Muhammed Mamoun
Published: April 2011

Nanophase Ce-Cu-O powder has been synthesised via co-precipitation approach, whereas computer-assisted thermodynamic modelling was used to predict the optimum experimental criteria. The properties of Ce-Cu-O composite (10 mol% CuO) have been extensively investigated by a variety of techniques. The obtained materials show different morphology compared to other doped ceria salts, with uniform distribution of Ce and Cu throughout the powder. Detailed XRD study does not show the formation of solid solution and the composites consist of two separate metal oxides. X-ray absorption spectroscopy study shows a variation of the existence of Cu and Ce in several oxidation states. Copper oxide seems to exist evenly distributed along the surfaces and boundaries of the crystal grains of CeO2 on the nanoscale. The temperature-programmed reduction indicated that Ce-Cu-O composite has an enhanced oxygen storage capacity compared to CeO2 or pure copper oxide.
Low-Temperature Solvothermal Route to GaN Nanoparticles
Authors: Wang Jianjun , Grocholl Luke , Gillan Edward G.
Published: April 2011

We report a straightforward, non-aqueous solvothermal method for the production of nanoscale gallium nitride structures. Nanoparticles with spherical and rod-like morphologies are produced via in situ gallium azide precursor synthesis and decomposition in superheated toluene or THF. The solution reaction between gallium chloride and sodium azide produces an insoluble azide precursor that is then solvothermally decomposed to GaN at temperatures below 260 °C. The resulting products are poorly crystalline but thermally stable and crystallize to hexagonal GaN upon annealing at 750 °C. Product morphologies include spherical particles (ca. 50 nm) and nanorods. Upon annealing, the nanoparticles coalesce into larger organized crystalline structures with hexagonal facets.
Investigation of Epitaxial Overgrowth on Germanium Quantum Dots
Authors: Greve David W. , Zhao Qian
Published: April 2011

We report on the characterization of germanium quantum dots grown on silicon (001) substrates by ultra-high vacuum chemical vapor deposition (UHV/CVD). In many applications small and uniform quantum dots are required which must be overgrown by a silicon epitaxial layer. We report here on the effect of carbon predeposition from methylsilane on the dot size and uniformity. In addition, we use reciprocal space mapping to evaluate the qualityof epitaxial layers which overgrow the quantum dots. The results show some differences from previous reports on MBE-grown dots.
Processing and Magnetic Properties of Ni-Fe Alloy Dispersed Alumina Nanocomposites
Authors: Lee Jai-Sung , Oh Sung-Tag , Namkung Seok
Published: April 2011

An optimum route to fabricate the Al2O3/Ni-Fe alloy nanocomposites with sound microstructure and magnetic propertieswas investigated. The composites were fabricated by the hot pressing of powder mixtures of Al2O3 and nano-sized Ni-Fe alloy, in which the alloy was prepared by solution-chemistry routes using Ni- and Fe-nitrate powders and a subsequent hydrogen reduction process. Microstructural observation of reduced powder mixture revealed that the Ni-Fe alloy particles of about 20 nm in size were homogeneously surrounded Al2O3, forming nanocomposite powder. The hot-pressed composite showed improved mechanical properties and magnetic response. The properties are discussed in terms of microstructural characteristics such as the distribution and size of Ni-Fe dispersion.
Resonant Tunnelling Behaviour in Multilayered Cold Cathodes Made of Nanoseeded Diamond and Nanocluster Carbon
Authors: Satyanarayana B.S. , Hiraki A.
Published: April 2011

Multilayered cold cathodes made of spin coated nanocrystalline diamond and cathodic arc process grown nanocluster carbon films, were studied. The nanocrystalline diamond was first coated on to the substrate. The nanocluster carbon films were then deposited on the seeded nanocrystalline diamond coated substrates using the cathodic arc process at room temperature. Theresultant hetrostructured microcathodes were observed to exhibit electron emission currents of 1μA/cm2 at fields as low as 1.2 V/μm. Further some of the samples seem to exhibit I-V characteristics witha negative differential resistance region at room temperature conditions. This negative differential resistance or the resonant tunneling behaviour was observed to be dependent on the nanoseeded diamond size and concentration for a given nanocluster carbon film.
Spray and Inkjet Printing of Hybrid Nanoparticle-Metal-Organic Inks for Ag and Cu Metallizations
Authors: Curtis C. J. , Schulz D. L. , Miedaner A. , Alleman J. , Rivkin T. , Perkin J. D. , Ginley D. S.
Published: April 2011

Metal-organic and hybrid metal-organic/metal nanoparticle inkswere evaluated for use in the inkjet printing of copper and silver conducting lines. Pure, smooth, dense, highly conductive coatings were produced by spray printing with (hexafluoroacetylacetonato)copper(I)-vinyltrimethylsilane Cu(hfa)·VTMS) and (hexafluoroacetylacetonato)silver(I)(1,5-cyclooctadiene) (Ag(hfa)COD) metal-organic precursors on heated substrates. Good adhesion to the substrates tested, glass, Kapton tape and Si, has been achieved without use of adhesion promoters. The silver metal-organic ink has also beenused to print metal lines and patterns with a commercial inkjet printer. Hybrid inks comprised of metal nanoparticles mixed with the metal-organic complexes above have also been used to deposit Cu and Ag films by spray printing.This approach gives dense, adherent films that are much thicker than those obtained using the metal-organic inks alone. The conductivities of the silvercoatings obtained by both approaches are near that of bulk silver (2 μΩ·cm). The copper coatings had conductivities at least an order ofmagnitude less than bulk.
Imaging of gold dendrimer nanocomposites in cells
Authors: Eichman Jonathan D. , Khan Mohamed K. , Lee Inhan , Baker James R. , Lawrence Theodore S. , Sorenson Dorothy R. , Edwards Chris A. , Balogh Lajos
Published: April 2011

Dendrimer nanocomposites (DNC) are hybrid nanoparticles formed by the dispersion and immobilization of guest atoms or small clusters in dendrimer matrices. They have a great potential in biomedical applications due to their controlled composition, predetermined size, shape and surface functionalities. In this work, nanocomposites of gold and poly(amidoamine) dendrimers {Au(0)n-PAMAM} have been selected to demonstrate this nanoparticle based concept. {Au(0)n-PAMAM} gold dendrimer nanocomposites with a well-defined size have been synthesized and imaged by TEM both in vitro and in vivo. Dendrimer nanocomposites have also the potential to be used as drug delivery vehicles either utilizing bioactive guests or incorporating radioactive isotopes. Radioactive dendrimer nanocomposites, e.g. {198-Au}, can be delivered to the tumor either by means of injecting the active nanoparticles directly into the tumor microvasculature or by intravenous injection. Both specific or non-specific targeting can be utilized in this process to achieve appropriate transfer.
Boundary conditions for dislocation dynamics simulations and stage 0 of BCC metals at low temperature
Authors: Tang Meijie , Kubin Ladislas P.
Published: April 2011

In order to study the dislocation density evolution of body centered cubic (bcc) crystals at low temperature by dislocation dynamics (DD) simulations, we investigated carefully three different boundary conditions (BC) for DD, i.e., the quasi-free surface BC, the flux-balanced BC, and the periodic BC. The latter two BCs can account for the dislocation loss from the boundary of the finite simulation box. PBC can also eliminate the influence of surfaces and improve the line connectivity. We have found that the PBC provides a convenient and effective boundary condition for DD simulations and have applied it to the study of dislocation density evolution of bcc metals during stage 0 deformation at low temperature.
Concurrent Multiscale Modeling of Embedded Nanomechanics
Authors: Rudd Robert E.
Published: April 2011

We discuss concurrent multiscale simulations of dynamic and temperature-dependent processes found in nanomechanical systems coupled to larger scale surroundings. We focus on the behavior of sub-micron Micro-Electro-Mechanical Systems (MEMS), especially micro-resonators. The coupling of length scales methodology we have developed for MEMS employs an atomistic description of small but key regions of the system, consisting of millions of atoms, coupled concurrently to a finite element model of the periphery. The result is a model that accurately describes the behavior of the mechanical components of MEMS down to the atomic scale. This paper reviews some of the general issues involved in concurrent multiscale simulation, extends the methodology to metallic systems and describes how it has been used to identify atomistic effects in sub-micron resonators.
Lattice parameter dependence versus composition in semiconductor alloys: the InGaAs case
Authors: Ferrari C. , Villaggi E. , Armani N. , Carta G. , Rossetto G.
Published: April 2011

Following recent works that report a non linear dependence of the lattice parameter versus composition in some semiconductor alloys the InGaAs/InP system has been investigated. The lattice parameter and the composition of InGaAs/InP lattice matched heterostructures have been independently determined by measuring the high resolution X-ray diffraction profile and the absorption of the X-ray beam diffracted from the InP substrate. In contrast with previous results that stated a linear dependence of the lattice parameter with composition, a 6% larger In content in the InGaAs/InP lattice matched alloy is found. Such result has been confirmed by the analysis of the X-ray fluorescence induced by an electron beam on the layer and on standards made of InAs and GaAs fine ground crystals. The result is in good agreement with the predictions of models based on the elasticity theory applied on a microscopic scale.
Diffusion in the Presence of Grain Boundaries: a Variable Length Scale Simulation Method
Authors: Belova Irina V , Murch Graeme E
Published: April 2011

In this paper we introduce a Monte Carlo method for numerical analysis of the problem of tracer diffusion in the presence of isolated grain boundaries with a variable mesh in the direction perpendicular to the grain boundary plane. A number of isoconcentration contour profiles were studied. Two different expressions for the angle between the isoconcentration contours and the grain boundary were derived for the instantaneous tracer source following procedures analogous to Fisher's and Whipple's approximations for the constant tracer source. Comparison with the numerical data was made. Both these approximations overestimate the grain boundary diffusivity.
Modeling of Sol-Gel Transition with Loop Network Formation and its Implications on Mechanical Properties
Authors: Ma Hang-Shing , Prévost Jean-H. , Jullien Rémi , Scherer George W.
Published: April 2011

Certain classes of sol-gel transition have been modeled as diffusion-limited cluster-cluster aggregation (DLCA), but it produces excessive dangling branches on the resulting network that underestimates the rigidity of gels. The “dangling bond deflection” (DEF) model was developed to simulate spatial fluctuation of the dangling branches under thermal energy. Collision and sticking of two dangling branches within the same cluster turns these branches into a loop. Combination of the DLCA and DEF models creates network that possesses extensive loop structure and negligible dangling mass. The networks are substantially stiffened by the loop structure, and successfully reproduce the empirical scaling relationship between linear elastic modulus and density exhibited by real aerogels. The gel structure can be represented by the “blob-and-link” model, in which blobs refer to dense, rigid collections of particles, interconnected by tenuous links of particle chains. When the network is deformed, only these few weak links contribute to the stiffness, leaving the blobs unstrained. The gel modulus drops significantly as porosity increases because more particles reside in the blobs and fewer particles carry the strain.