bluuebunny/crossref_metadata_2025 huggingface dataset:
Computational Modeling For Magnetic-Sensor-Based Three-Dimensional Visualization Of Microcracks
Authors: Muratov Leonid , Lederman David , Cooper Bernard R.
Published: April 2011

The presence of cracks, phase segregation, or even submicron-sized grain boundaries creates a disruption of the magnetic field response to an externally applied electrical current running through the material. These effects can be detected through the magnetic field leakage in the external near-surface region. Using a computer model of an array of magnetic tunnel junction detectors, magnetic “signatures” of various faults and/or material borders and domains have been calculated using finite element analysis and portrayed by icons. We have considered a number of typical cracks and flaws, of different dimensions and orientations, within the bulk of the component. The database of “signatures” thus generated allows fast recognition of faults and generation of their images in real time. Significant efforts have been made to provide an adequate three-dimensional visualization of the shape and distribution of microcracks, the magnetic field lines, and delineation of the position of the faults in relation to the surface.
Magneto-Resistance and Induced Domain Structure in Tunnel Junctions
Authors: Hehn M. , Lenoble O. , Lacour D. , Schuhl A. , Tiusan C. , Hrabovsky D. , Bobo J.F.
Published: April 2011

Magnetization reversals in sputtered Co electrodes of a magnetic tunnel junction are studied using transport measurements, magneto-optic Kerr magnetometry and microscopy. Using the tunnel magneto-resistive effect as a probe for micromagnetic studies, we first evidence the existence of an unexpected domain structure in the soft Co layer. This domain structure originates from the duplication of the domain structure of the hard Co layer template into the soft layer via ferromagnetic inter-electrode coupling. A detailed analysis of the kerr microscopy images shows that all features appearing in the variation of tunnel resistance as a function of the applied field are associated to the domain phase evolution of each electrode. By tailoring the magnetic properties of the hard Co layer, we have demonstrated that the appearance of the domain duplication is driven by the magnetic anisotropy of the hard layer. Finally, a brief theoretical description of the domain duplication process allows us to extract the main parameters governing the effect.
Multilevel Magnetoresistance in a Structure Consisting of two spin-valves
Authors: Li Kebin , Wu Yihong , Qiu Jinjun , Han Guchang , Guo Zaibing , Chong Towchong
Published: April 2011

The magnetic and electrical properties as well as the structural characteristics have been studied on a series of samples with structure substrate (Sub)/SV(1)/Al2O35nm/SV(2). Here, SV(1) is either CoFe/IrMn based spin-valve (SV) such as Ta5/NiFe2/IrMn8/CoFe2/Cu2.6/CoFe2/Ta5 (thicknesses are in nanometers) bottom SV or Ta5/NiFe2/CoFe1.5/Cu2.6/CoFe2/FeMn10/Ta5 top SV and SV(2) is Ta5/NiFe2/CoFe1.5(or 2)/Cu2.6/CoFe2/IrMn8/Ta5 top SV. SV(1) and SV(2) in the structure are decoupled by a Al2O3 layer with 5nm in the magnetic properties, however, they are in parallel connection in the electrical properties. In a sample with structure Sub/Ta5/NiFe2/IrMn8/CoFe2/Cu2.6/CoFe2/Ta5/Al2O35/Ta5/NiFe2/CoFe2/Cu2.6/CoFe2/IrMn8/Ta5, five magnetoresistance states which are related to five magnetization states have been observed after the sample was annealed at T=220 °C with a field strength of 1T under high vacuum because of different interlayer coupling fields (Hint) in the top and bottom CoFe/IrMn based SVs (Hint is about 12.21 Oe in the top CoFe/IrMn SV and 29.3 Oe in the bottom CoFe/IrMn based SV). In a sample with structure Sub/Ta5/NiFe2/CoFe1.5/Cu2.6/CoFe2/FeMn10/Ta5/Al2O35/Ta5/NiFe2/CoFe1.5/Cu2.6/CoFe2 /IrMn8/Ta5, since the blocking temperature of the CoFe/FeMn based SV (Tb is about 150 °C) is lower than that of CoFe/IrMn based SV (Tb is about 230 °C), the spins can be easily engineered and therefore various magnetoresistance states can be obtained when the sample is magnetically annealed at different temperatures in a proper annealing sequence. By properly selecting materials and controlling the magnetically annealing conditions, multilevel giant magnetoresistance (MR) magnetic random access memory (MRAM) cell can be realized, which will significantly improve the MRAM data storage density without increasing any additional processing complexity.
Microstructure and Magnetic Properties of Co-CoO Nanocomposite Films
Authors: Yi Jae-Young , Hirata G. A. , Rudee M. L.
Published: April 2011

The effect of exchange anisotropy on nanosize Co particles was studied in Co-CoO nanocomposite thin films for possible applications for magnetic storage media. XRD analyses showed nanosize hcp Co particles and (111) textured CoO phase. A broken columnar structure was observed in cross-section TEM images. Very large room temperature coercivity (∼1 kOe) was observed and believed to be due to a shape effect and possible local exchange coupling. Large exchange anisotropy at low temperatures and linear type temperature dependence were explained by finite size effects and thermal relaxation of the CoO particles. A slow decrease of thermoremanent moment (TRM) with temperature and large TRM at room temperature indicated that the exchange anisotropy significantly modified the anisotropy energy barrier of the Co crystallites in the CoO matrix. The results indicated that the exchange anisotropy could be used to stabilize nanosize ferromagnetic particles.
Modification of the magnetic properties of longitudinal thin-film media by ion-beam irradiation
Authors: Wright Jason D. , Krishnan Kannan M.
Published: April 2011

The modification of conventional longitudinal recording media by ion-beam irradiation is of both scientific and technological interest. In particular, patterning by irradiation through a stencil mask at the 50 nm length scale may fulfill the promise of a commercially viable patterned media architecture. In this context, the magnetic properties and microstructural evolution of high-coercivity longitudinal thin film media were investigated after ion-beam irradiation. TRIM simulations were used to calculate the depth profiles and damage distributions as a function of energy and dose for carbon, nitrogen, and chromium ions and three different media (C, Cr, no capping layer). Corresponding implantations were carried out and hysteresis curves were measured using a vibrating sample magnetometer (VSM). Using chromium ion implantation at 20 keV, both remanence and coercivity were reduced to zero, i.e., rendering the ferromagnetic thin film paramagnetic, at doses as low as 1×1016 cm−2. For C+ implantation at 20 keV, remanence and coercivity were also reduced to varying extent up to doses of 5×1016 cm−2 after which further irradiation had no effect. Slight decreases in remanence and coercivity were observed for 20 keV N2+ irradiation. XRD measurements indicate that the hexagonal cobalt alloy phase remains intact after irradiation. The physical and magnetic domain structures at the surface were assessed by atomic force and magnetic force microscopy. Combined with the development of a suitable stencil mask, such chromium ion implantation can be used to develop a viable patterned media with nanoscale dimensions, consisting of locally defined ferromagnetic and paramagnetic regions. This work is in progress.
Chalcopyrite Magnetic Semiconductors: An AB–Initio Study of Their Structural, Electronic and Magnetic Properties
Authors: Picozzi S. , Continenza A. , Geng W. T. , Zhao Y. J. , Freeman A. J.
Published: April 2011

Stimulated by recent experimental observations of room{temperature ferromagnetism of MnxCd1−xGeP2, we investigate the structural, electronic and magnetic properties of these systems as a function of Mn concentration by means of first–principles density-functional-theory-based codes. Moreover, we investigate the effect of the anion substitution (P vs As) in Mn-rich chalcopyirites. Our calculations indicate that the antiferromagnetic alignment is the most stable ordering for all the systems studied, at variance with that experimentally reported. Moreover, we find that there is a slight reduction of the total magnetic moment per Mn atom from ∼5 µB in all the Cd-rich P-based chalcopyrites to ∼4 µB in the Mn–rich MnGeP2 and MnGeAs2 systems.
Ferromagnetic properties and Nanocrystallization behavior of Amorphous (Fe0.99Mo0.01)78Si9B13 Ribbons
Authors: Sun Xiang-Cheng , Toledo J. A. , Galindo S. , Sun W. S.
Published: April 2011

Ferromagnetic properties and nanocrystallization process of soft ferromagnetic (Fe0.99Mo0.01)78Si9B13 ribbons are studied by transmission electron microscope (TEM), X-ray diffraction (XRD), Mössbauer spectroscopy (MS), differential scanning calorimeters (DSC) and magnetization measurements. The Curie and crystallization temperature are determined to be TC=665K and Tx = 750K, respectively. The Tx value is in well agreement with DSC measurement results. X-ray diffraction patterns had shown a good reconfirm of two metastable phases (Fe23B6, Fe3B) were formed under in-situ nanocrystallization process. Of which these metastable phases embedded in the amorphous matrix have a significant effect on magnetic ordering. The ultimate nanocrystalline phases of α-Fe (Mo, Si) and Fe2B at optimum annealing temperature had been observed respectively. It is notable that the magnetization of the amorphous phase decreases more rapidly with increasing temperature than those of nanocrystalline ferromagnetism, suggesting the presence of the distribution of exchange interaction in the amorphous phase or high metalloid contents.
Characterization of Softmagnetic Thin Layers using Barkhausen Noise Microscopy
Authors: Hoffmann Jochen , Meyendorf Norbert , Altpeter Iris
Published: April 2011

Ferromagnetic materials are essential for data recording devices. For inductive or magnetoresistive (MR) sensors softmagnetic thin layer systems are used. Optimal performance of these layers requires homogeneous magnetic properties, especially a pronounced uniaxial magnetic anisotropy. Furthermore, microstructural imperfections and residual stresses influence the magnetic structure in the layer system.

Barkhausen Noise Microscopy enables the characterization of such thin layers. By cycling the magnetic hysteresis of ferromagnetic material electrical voltages (the Barkhausen noise) are induced in an inductive sensor. Miniaturization of the sensor and the scanning probe technique provides resolution down to few micrometers. Two materials were examined in terms of their structure, thickness, residual stresses and heat treatment condition: Sendust, used in inductive sensors and nanocrystalline NiFe, used in MR-sensors. In quality correlations to Barkhausen noise parameters were found. For representative sample a quantification of residual stress distribution could be established employing X-ray stress analysis.
Effect of Composition and Processing on the Microstructure and Magnetic Properties of 2:17 High Temperature Magnets
Authors: Tang W. , Zhang Y. , Goll D. , Kronmüller H. , Hadjipanayis G. C.
Published: April 2011

A comprehensive and systematic study has been made on Sm(CobalFevCuyZrx)zmagnets to completely understand the effects of composition and processing on their magnetic properties. The homogenized Sm(Co,Fe,Cu,Zr)z magnets have a featureless microstructure. A cellular/lamellar microstructure develops after 2-3 hours of aging at 800-850°C, but the coercivity increases only after a subsequent slow cooling to 400°C. During cooling, diffusion takes place and Cu is concentrated in the 1:5 cell boundaries and Fe in the 2:17R cells. This dilutes the magnetic properties of the 1:5 phase and causes domain wall pinning/nucleation at the cell boundaries. Higher ratio z leads to larger cells as expected due to the larger amount of the 2:17 phase. For a fixed Cu content, this translates to a larger amount of Cu in the 1:5 cell boundaries, and therefore, to a higher coercivity. Magnets without Cu but with Zr have a lamellar and a cellular like microstructure. In Zr free samples, however, a larger amount of Cu is needed to form the cellular microstructure. This cellular microstructure is unstable with prolonged isothermal aging. A uniform and stable cellular/lamellar microstructure is only observed in alloys containing both Cu and Zr. A higher aging temperature Tag leads to larger cells and higher coercivity as explained above. The results of all these studies clearly show that the amount of Cu in the 1:5 cell boundaries controls both the coercivity and its temperature dependence leading to positive and negative temperature coefficients of coercivity in low and high Cu content alloys, respectively.
Magnetic and Microstructural Aspects of the Bulk Metallic Glassy Materials Nd60Fe30Al10
Authors: Dan N. H. , Phuc N. X. , Ky V. H. , Hong N. M. , Chau N. , Luong N. H. , Huu C. X. , Mccallum R. W. , Kramer M. J. , O'Connor A. S. , Dennis K. W. , Lewis L. H. , Tung L. D.
Published: April 2011

The ferromagnetic bulk metallic glass (BMG) Nd60Fe30Al10system exhibits extremely large coercivities at low temperature and moderate coercivities near room temperature. The magnetic hardness, as best evidenced by the onset of magnetic irreversibility, was studied in bulk suction-cast and melt-spun alloys with the nominal composition Nd60Fe30Al10. Systematic x-ray diffraction studies of the degree of crystallinity performed as a function of position within the bulk suction-cast samples is found to correlate with the variation in the room-temperature magnetic hysteresis character. X-ray diffraction data clearly shows the presence of both crystallites and amorphous material on the samples' outmost surfaces; the amorphous phase content increases with distance into the cast sample. These results underscore the importance of solidification conditions and attendant nanophase selection, on the resultant magnetic properties of this class of alloys.
Investigations on the Magnetic Properties of High-Coercivity (Nd1−xFex)90Al10 Bulk Amorphous Alloys
Authors: Lupu N. , Chiriac H. , Takeuchi A. , Inoue A.
Published: April 2011

Bulk rods with diameters up to 3 mm prepared by suction casting and respectively mould casting and melt-spun amorphous ribbons with thicknesses in the range 25 – 150 μm with compositions Nd90−xFexAl10 (x = 35; 40; 45; 50) were investigated by XRD, DSC and magnetic measurements in the temperature range 5 – 600 K. The microstructure and magnetic properties are strongly dependent on the cooling rate, preparation process and Fe content. The large values of the coercive field, which amount to 320 kA/m in the as-cast state as well as the increase with decrease of the temperature and cooling rate result from the formation of very small metastable or nonequilibrium magnetic clusters.
Influence of Domain Structure on Magnetoresistance in Perovskite Manganite Grain Boundary Junctions
Authors: Gunnarsson Robert , Kadigrobov Anatoli , Ivanov Zdravko
Published: April 2011

We have been able to deduce a temperature dependence of the built-in potential in La2/3Sr1/3MnO3 grain boundary junctions. This has been performed by trimming a single grain boundary down to 1μm width with a focused ion-beam. We can thereby see the impact of single domain walls on the magnetoresistance and the current-voltage characteristics. We have also demonstrated the effect of averaging as we increased the number of junctions.
Magnetic Properties of Self-Assembled Fe Nanoparticle Arrays
Authors: Farrell D. , Yamamuro S. , Majetich S. A.
Published: April 2011

The magnetic properties of multilayer arrays of Fe nanoparticles were compared with those of frozen, dilute suspensions of the same particles. The array sample displayed larger coercivity in both hysteretic and remanent magnetization measurements. However, the derivative of the remanent magnetization curve shows a much broader switching field distribution for the arrays than for the dilute sample. Magnetic relaxation measurements show the convergence of the time dependent properties of the samples at large times, and much more rapid relaxation in the arrays at short times.
Stability of Magnetic States in Patterned Materials
Authors: Pardavi-Horvath Martha
Published: April 2011

The stability of the individual elements of a two-dimensional (2D) regular array of single domain particles is investigated. The variance in the statistical distribution of up- and down switching fields of the elements leads to premature switching for the low coercivity particles, and incomplete overwriting for the high end of the distribution. The distribution of the interaction fields from surrounding elements on a 2D array depends the saturation magnetization of the elements, their packing density, and the recorded information. The non-ellipsoidal shape of the elements leads to reduced switching fields as a result of non-collinear magnetization around the corners and edges. The thermal stability of 2D arrays, switching by (incoherent) rotation of the magnetization, is enhanced compared to bulk/contiguous media, due to the lack of low energy barrier domain wall motion processes. However due to the fast decrease of the anisotropy, stability at elevated temperatures is still a problem. Experimental data for a model 2D square array of single crystalline, strongly uniaxial, single domain garnet particles illustrate the effects on stability of statistics, shape, and thermal excitation.
Synthesis and Self-Assembly of Films Containing FeCoPt Nanoparticles
Authors: Chen Min , Nikles David E.
Published: April 2011

Fe49Co7Pt44 and Fe40Co17Pt43nanoparticles were synthesized by simultaneous chemical reduction of platinum acetylacetonate and cobalt acetylacetonate and thermal decomposition of iron pentacarbonyl. As-prepared the particles had a disordered face-centered cubic lattice with an average diameter of 3.2 nm and were superparamagnetic. These particles were well dispersed in a 50/50 mixture of hexane and octane. The particles self-assembled into ordered superlattices when deposited onto carbon coated Cu TEM grids or onto single crystal Si (100) substrates. After vacuum annealing (from 500°C to 700 °C), the particles transformed to the tetragonal phase. The coercivity of the film strongly depended on the composition and annealing temperature. For the Fe49Co7Pt44film, coercivity of 8700 Oe and a squareness of 0.75 after annealing at 700 °C for 30 minutes. XPS shows existance of oxidized iron and cobalt on the surface of film.
Effects of Substrates on the Self-Assembling of FePt Nanocrystals
Authors: Chen Min , Nikles David E.
Published: April 2011

Fe48Pt52 nanoparticles were synthesized by the simultaneous chemical reduction of platinum acetylacetonate and thermal decomposition of iron pentacarbonyl. As-prepared the particles were spherical with an average diameter of 3 nm and a polydispersity of less than 5%. The particles were superparamagnetic and had a fcc structure. Highly ordered self-assembled supercrystals of particles were formed in TEM grids by deposition from dispersions in hydrocarbon solvents. Nanoparticles deposited on amorphous carbon-coated and SiO2-coated Cu grids tend to assemble into small domains of hexagonal arrays. Larger domains of hexagonal arrays formed on Si3N4 membrane TEM grids. For thin multilayers, the FePt nanoparticles tends to assemble into hexagonal close-packed lattices (ABABAB stacking). For the thicker multilayers, ABCABC stacking was observed. Small angle X-ray reflectivity of the particles on a Si (100) substrate show highly ordered multiplanar structure with d-spacing of 6.2 nm. The coercivity of self-assembled FePt films strongly depended on the annealing temperature. After annealing at 700°C for 30 minutes, the particles transformed from FCC to “FCT” phase and the coercivity of film increased up to 11570 Oe. However, the particle size increased to 16 nm due to sintering.
Optical absorption spectroscopy in the metastable state SI of Na2[Fe(CN)5NO]·2H2O
Authors: Schaniel Dominik , Schefer Jürg , Delley Bernard , Imlau Mirco , Woike Theo
Published: April 2011

The metastable state SI in single crystals of orthorhombic Na2[Fe(CN)5NO]2H2O (sodiumnitroprusside, SNP) was investigated by absorption spectroscopy. The development of the spectra with increasing population of SI was monitored and a new band in the red spectral range was assigned to SI. By comparing with density functional theory (DFT) calculations we were able to assign the band to the electronic transition 2b2→7e. In addition we found that very strong holographic light scattering influences the absorption spectra measured with light polarization along the a- or b-axis of the crystals.
Investigations of Sputtered Silver Oxide Deposits for the SUPER–RENS High Density Optical Data Storage Application
Authors: Büchel Dorothea , Mihalcea Christophe , Fukaya Toshio , Atoda Nobufumi , Tominaga Junji
Published: April 2011

Thin silver oxide films used as mask layers in super-Resolution Nearfield Structure (super-RENS) disks for high density optical data storage were reactively sputter-deposited and their composition was determined by spectroscopic means. We found that the stoichiometry of the films changed with the oxygen content in the sputtering gas atmosphere. With a stepwise increase in the percentage of O2 from 0 - 100%, the corresponding layers consist of Ag, mixtures of Ag and Ag2O, Ag2O, mixtures of Ag2O and AgO and AgO. Laser activation of such oxidic phase containing deposits results in the decomposition of the material and excitation of strong local plasmons in the remaining silver clusters. This was confirmed by acquiring surface enhanced Raman spectra (SERS) of benzoic acid (BA), copper phthalocyanine (CP) and internal carbon impurities on silver oxide substrates. From this data, we conclude that the sub-wavelength resolution obtained in super-RENS disks is mediated by local surface plasmons on small silver particles forming in the mask layer.
A Study on Batch Method of Thermal Fixing for Multiplexed Holographic Recordings
Authors: Jiang Zhuqing , Meng Gang , Liu Guoqing , Tao Shiquan
Published: April 2011

We have investigated the batch method of thermal fixing for multiplexed holograms. The batch fixing process is pictured and analyzed, for the first time to our knowledge. The batch procedure of thermal fixing includes optical erasure of electronic gratings by subsequent recordings both in the same batch and in different batches, ionic compensation during thermal fixing in one batch, smoothing of ionic gratings during thermal fixing of subsequent batches, and revealing of ionic gratings. The inter-batch optical erasure time constants of LiNbO3:Fe:Ce crystals are measured in experiment.
External Chemical Reactivity of Fullerenes and Nanotubes
Authors: Park Seongjun , Srivastava Deepak , Cho Kyeongjae
Published: April 2011

The external chemical reactivity of graphene sheet, fullerenes and carbon nanotubes has been investigated. The total reaction energy is analyzed with several contributing terms and formulated as a function of the pyramidal angles of C atoms. We have determined the parameters for the formulae from ab initio simulation of graphene. We have applied them to predict hydrogenation energy of several nanotubes and C60, and demonstrated that the predicted total reaction energies are very close to the results of total energy pseudo-potential density functional theory calculations. This analysis can be used to predict the reaction energy and local bonding configuration of a reactant with diverse fullerenes and nanotubes within 0.1 eV accuracy.
Acoustic Microscopy and Surface Brillouin Scattering of Amorphous Carbon Pressure-Synthesized From C60
Authors: Zinin Pavel V. , Manghnani Murli. H. , Tkachev Sergey , Zhang Xinya , Lyapin Alexander G. , Brazhkin Vadim V. , Trojan Ivan A.
Published: April 2011

Here, we report successful measurements by surface Brillouin scattering (SBS) and scanning acoustic microscopy (SAM) of the elastic properties of small specimens of amorphous carbon obtained from C60 under high pressure and temperature. The superhard phases of amorphous carbon were synthesized from C60 at pressure 13 – 13.5 GPa and temperature 800–900°C. Two types of acoustic waves have been detected by SBS in superhard samples: surface Rayleigh wave and bulk longitudinal wave. The longitudinal velocity (νL) in the hardest sample is slightly lower than longitudinal wave velocity in diamond in [110] direction. Simultaneous measurements of the Rayleigh and longitudinal wave velocities make it possible to determine shear and bulk elastic moduli of the specimens. Obtained elastic properties for amorphous carbon synthesized under pressure 13.5 GPa and temperature 900°C are close to those for diamond, indicating that bonds among amorphous carbon network are diamond bonding dominated.
Raman and Eels Studies on Nanocrystalline Diamond Prepared in a Low Pressure Inductively Coupled Plasma
Authors: Okada Katsuyuki , Kimoto Koji , Komatsu Shojiro , Matsumoto Seiichiro
Published: April 2011

Nanocrystalline diamonds with several hundred nm in diameter have been prepared in a 13.56 MHz low pressure inductively coupled CH4/H2 or CH4/CO/H2 plasma. The bonding structures were investigated by Raman spectroscopy and electron energy loss spectroscopy (EELS). Visible (514 nm) and UV (325, 244 nm) excited Raman spectra with CO additive exhibit peaks at ∼1150 cm-1 assigned to sp3 bonding and at 1332 cm-1 due to zone center optical phonon mode of diamond, respectively. It indicates that the UV excitations are possibly sufficient to excite the σ state of both sp2- and sp3-bonded carbon. The high resolution EELS (HREELS) spectra with CO additive show peaks at ∼1100 cm-1 assigned to C-C stretching vibration of sp3 bonding and at ∼700 cm corresponding to the bending vibration of sp3 bonding. It is qualitatively agreement with the Raman spectra. Furthermore the EELS spectrum without CO additive exhibits two peaks at 284 eV and at 292 eV corresponding to π* states and σ* states, respectively, and is similar to that of graphite rather than that of sp2-rich amorphous carbon. The EELS spectrum with CO additive, on the other hand, shows a peak at 292 eV due to σ * states and is similar to that of diamond. A slight peak appears at ∼285 eV corresponding to π* states. It consequently implies that the particles almost consist of sp3 bondings and that the small amount of sp2 bondings are considered to exist in grain boundaries. The EESL spectra are consistent with the results of Raman scattering and HREELS.
Synthesis of Vertically Aligned Carbon Nanofiber Films by RF Magnetron Sputtering
Authors: Lee K. -Y. , Fujimoto K. , Ohkura S. , Honda S. , Katayama M. , Hirao T. , Oura K.
Published: April 2011

The aligned carbon nanofibers were synthesized on Si substrates using RF magnetron sputtering with a hot filament. The hot filament was made of tungsten wire and its temperature was up to 2000°C during the deposition. Nitrogen was used as the sputter gas at a relatively low pressure of 2×10-2 Torr. The sputtering deposition was carried out at a substrate temperature of 700°C. The nanofibers were grown vertically on the substrates. The diameters and the density of the fibers were about 30–45 nm and 109 cm-2, respectively.
Ab initio Study of Metal Atoms on SWNT Surface
Authors: Peng Shu , Cho Kyeongjae
Published: April 2011

Interactions of metal atoms (Al, Ti) with semiconducting single walled carbon nanotube (SWNT) are investigated using first-principles pseudopotential calculations. Six different adsorption configurations for aluminum and titanium atoms are studied. Comparison of the energetics of these metal atoms on (8,0) SWNT surface shows significant differences in binding energy and diffusion barrier. These differences give an insight to explain why most of metal atoms (such as Al) form discrete particles on nanotube while continuous nanowires are obtained by using titanium in the experiment.
From Diamond to Carbon Nanotube Field Emitter
Authors: Gröning O. , Nilsson L-O. , Gröning P. , Schlapbach L.
Published: April 2011

In this paper we review the physics and the expectations that were put into the negative electron affinity (NEA) mediated field emission of chemical vapor deposition CVD diamond films and how the emitter technology made possible by this mechanism could have challenged the classical metal micro-tip field emitter arrays. We discuss the dependency between emitter performance of micro-tip emitter arrays and feature size (size of the field enhancing tip) and due to this to the connection between emitter performance and fabrication costs.

We introduce the concept of the field enhancement distribution function f(β) for a useful characterization of the field emission properties of thin film emitter and show how this distribution function can be measured by scanning anode field emission microscopy. Using f(β) measured on a thin film of randomly oriented multiwalled carbon nanotubes we show that even these kinds of low cost emitters can show a field emission performance comparable to micro-tip arrays, yet that the large spread in field enhancement values between the individual emitter prevent this performance to be fully exploited. This because the field range in which such thin film emitters can be operated is limited due to emitter disruption and triggering of vacuum arcs. Simulations show how resistor-limited emission can solve these limitations.
Three-dimensional calculation of field emission from carbon nanotubes using a transfermatrix methodology
Authors: Mayer Alexandre , Miskovsky Nicholas M. , Cutler Paul H.
Published: April 2011

We present simulations of field emission from carbon nanotubes, using a transfer-matrix methodology. By repeating periodically a basic unit of the nanotubes in the region preceding that containing the extraction field, specific band-structure effects are included in the distribution of incident states, i.e. those entering the field region. The structures considered are the metallic (5,5) and the semiconducting (10,0) single-wall carbon nanotubes. The total-energy distributions of incident states show the gap of the (10,0) and the expected flat region for the (5,5) nanotube. The field-emitted electron energy distributions contain peaks, which are sharper for the (10,0) structure. Except for peaks associated with van Hove singularities in the distribution of incident states or with the Fermi level in the case of a metallic structure, all peaks are shifted to lower energies by the electric field.
Field Emission Site Densities of Nanostructured Carbon
Authors: Cui J B , Robertson J , Milne W I
Published: April 2011

The field emission properties of nanostructured carbon films deposited by cathodic vacuum arc in a He atmosphere have been studied by measuring the emission currents and the emission site density. The films have an onset field of ∼3 V/μm. The emission site density is viewed on a phosphor anode and it increases rapidly with applied field. It is assumed that the emission occurs from surface regions with a range of field enhancement factors but with a constant work function. The field enhancement factor is found to have an exponential distribution.
Effects of Sulfur Concentration on the Electron Field Emission Properties of Nanocrystalline Carbon Thin Films
Authors: Gupta S. , Weiner B. R. , Weiss B. L. , Morell G.
Published: April 2011

The electron field emission properties of sulfur-assisted nanocrystalline carbon (n-C: S) thin films grown on molybdenum substrates by hot-filament CVD technique using methane-hydrogen (CH4/H2) and hydrogen sulfide-hydrogen (H2S/H2) gas mixtures were investigated. The field emission properties of the S-assisted films are reported as a function of sulfur concentration. The incorporation of S caused structural and microstructural changes that were characterized with SEM, AFM and Raman spectroscopy (RS). The S-assisted films show smoother surfaces and smaller grains than those grown without. The lowest turn-on field measured was around 4.5 – 5.0 V/μm films grown with 500 ppm of hydrogen sulfide and at 900 °C. The electron field emission properties of S-assisted films were also compared to those grown without sulfur (i.e., intrinsic). An inverse correlation between the threshold field (Ec) and sulfur concentration was found. These finding are attributed to defect induced states within the electronic band structure.
Studies on the Interaction of Water-Soluble Fullerols with BSA and the Effects of Metallic Ions
Authors: Bingshe Xu , Xuguang Liu , Xiaoqin Yan , Jinli Qiao , Weijun Jin
Published: April 2011

The interaction of water-soluble C60 derived fullerols with bovine serum albumin (BSA) in physiological environment was studied in detail by the fluorescence method. Experiments showed that the interaction of fullerols with BAS is mainly in the manner of non-covalent hydrogen bond. Based on the measurements of fluorescence intensity, the apparent binding constant K and the binding site number n were obtained with K=4000 and n=1, and the energy transfer efficiency in the reaction is 0.63. Besides, the effects of metallic ions such as Cu2+, Fe3+ and Cr(VI) on the interaction of fullerols with BSA were investigated. It was found that the effects of the metallic ions are quite different from each other. Low concentrations of Cu2+ can promote the interactions between fullerols and BSA, while high concentrations of Fe3+ or Cr(VI) favorite the interactions between fullerols and BSA.
Effect of Crystalline Structure and Impurity Content of C60 Thin Films on the Order/Disorder Phase Transition
Authors: Katz Eugene A. , Faiman David , Shtutina Svetlana , Isakina Aleksandra P. , Yagotintsev Konstantin A.
Published: April 2011

Near the temperature of 260 K, C60 crystal is known to undergo a first order phase transition, associated with changes in molecular rotations. The present paper reports the effect of the crystalline structure and impurity content of C60 thin films on their structural behavior near this phase transition. Polycrystalline C60 films with different grain sizes and oxygen content were obtained by varying the conditions of their vacuum deposition and post-grown exposure. Temperature-resolved X-ray diffraction in the range 300 – 15 K was used to determine the lattice parameter and its changes near the phase transition temperature. Decrease in grain sizes and increase in oxygen content of the films are found to lead to a gradual reduction in the discontinuity in lattice parameter and the transition temperature.
Characterizations of HgTe nanocrystals induced by controlled precipitation in PbTe-4HgTe semiconductor alloys
Authors: Lee Manjong , Kim Choong-Un
Published: April 2011

This paper reports the observation of HgTe precipitate formation and its subsequent evolution in a PbTe semiconductor matrix containing 4 mol. % HgTe (PbTe-4HgTe) produced by a controlled precipitation process. The controlled precipitation process is being developed as a new way to produce a large number of quality semiconductor nanocrystals more simply than the conventional methods. Characterization of the HgTe precipitates resulting from application of controlled precipitation to the PbTe-4HgTe alloy system provides evidence that this method is effective in generating nanocrystals. Transmission electron microscopy of the processed alloys reveals that HgTe precipitates are extremely small in size, maintain a coherent interface, and experience a unique shape evolution with aging.
AFM-Based Nanomechanical Properties and Storage of Dentin and Enamel
Authors: Habelitz Stefan , Balooch Mehdi , Marshall Grayson W. , Breunig Thomas M. , Marshall Sally J.
Published: April 2011

This study evaluated the affects of 2 different solutions, e. g. deionized water and Hanks' Balanced Salt Solution (HBSS), on nanohardness and elastic modulus of dentin and enamel from human third molars at storage times of 0, 1, 7, 14 and 28 days using a modified AFM (Triboscope). The pH values of the solutions were monitored throughout the test periods. Storing the specimens in deionized water resulted in a large decrease of mechanical properties, e.g. the reduced elastic modulus of dentin decreased from 24.0 ±1.5 GPa to 21.0 ±1.6, 8.6 ±1.1 and 5.2 ±1.1 GPa for storage times of 1, 7 and 14 days, respectively. Mechanical properties of dentin and enamel dropped by more than 12% after one day and more than 50% after a week when stored in deionized water. The observed changes in mechanical response were attributed to a superficial demineralization process during storage. In contrast, storing teeth in HBSS did not significantly alter the mechanical properties of dentin or enamel over the time studied.
Surface Initiated Polymerization (SIP) on Nanoparticle Surfaces: Demonstration of First Principles and Preparation of Nanocomposite Materials
Authors: Advincula Rigoberto , Zhou Qingye , Mays Jimmy
Published: April 2011

To investigate the grafting of polymer chains onto nanoparticles (metal, semi-conductor, inorganic, etc) and nanostructured (patterned) surfaces, we have investigated anionic surface initiated polymerization (SIP) on a variety of surfaces. Understanding the surface chemistry issues involved is critical for future applications and protocols. SIP of polystyrene from Silicate and clay nanoparticles surfaces have been made by the living anionic polymerization method with 1,1-diphenylethylene (DPE) initiation sites attached to nanoparticle surfaces using chlorosilane and amino functional groups. Model studies were initially done on flat Si-wafer surface and recently with Au surfaces. For the nanoparticles, the grafted polymers were cleaved and characterized by FTIR, NMR, AFM, TGA and SEC. Polymers grafted from nanoparticle surfaces show higher polydispersity and lower molecular weight than those formed in solution. We observed that diffusion of the monomer, stability of the initiator attachment to the surface, and aggregation of the particles controls the properties of the grafted polymers on particle surfaces. On the other hand, the use of the anionic polymerization method on surfaces allows the possibility of combining a variety of polymers (organic) with various nanoparticle and surfaces (inorganic) for the preparation of hybrid nanocomposite materials.
Sub-10 nm Gold Nanoarrays for Tethering Single Molecules
Authors: Chan Vanessa Z-H. , Codd Sarah L. , van der Helm Mark J. , Spatz Joachim P. , Röcker Carlheinz , Ulrichs Nienhaus G. , Levi Stefano , van Veggel Frank C. J. M. , Reinhoudt David N. , Möller Martin
Published: April 2011

Nanometer sized gold patterns were produced with controlled spacings using the combination of a top-down (e-beam lithography) and a bottom-up (macromolecular chemistry) technique. Sub-10 nm nanoparticle arrays on silicon consisting of gold nano particles separated by micro meter spacings were fabricated with this approach. Using electron beam lithography, templates comprising of 150 nm to 1 μm sized trenches, holes and aperiodic patterns were made in an electron-beam resist. Block copolymer micelles were then patterned into this template by spincoating. The micelles acted as positioners for a nanometer sized gold precursor that is sequestered within its core. Subsequent removal of the resist layer left an array of Au loaded organic micelles ordered according to the pattern of the template. Exposure of this substrate to a hydrogen plasma removed the organic block copolymer and resulted in an array of sub-10 nm gold nanoparticles/nanoclusters with micron separations. The gold was then used as an anchor point for the tethering of functional molecules in order to localize fluorescent molecules.
Study of Catalytic Methane Oxidation Over Pd Supported on Nanocrystalline CeO2: Effects of Calcination and Pd Loading
Authors: Oh Seung H. , Everett Michael L. , Hoflund Gar B. , Seydel Johannes , Hahn Horst W.
Published: April 2011

The catalytic oxidation of methane was studied over palladium supported on nanocrystalline ceria. Three palladium weight loadings (1, 5, and 10 wt%) were tested after calcining at 500 °C, at 280 °C and after no calcination at all. For the 5 and 10 wt% loadings, the 280 °C-calcined and non-calcined catalysts exhibit enhanced activity after several heating and cooling cycles. Calcining these same catalysts at 500 °C results in a systematic decline in activity. For all pretreatments the 1 wt% Pd catalyst exhibits decreasing activity. For the 5 and 10 wt% Pd loadings, the non-calcined catalysts are more active than the 280 °C-calcined catalysts, which are more active than the 500 °C-calcined catalysts. For the 1 wt% Pd catalyst, the opposite is true. The catalyst activity improves as the Pd loading is increased.
Charge-influenced structural properties of electrically connected platinum nanoparticles
Authors: Viswanath R. N. , Weissmüller J. , Würschum R. , Gleiter H.
Published: April 2011

We present results of a study motivated by the recent suggestion that the properties of nanocrystalline materials with a large surface-to-volume ratio can be tuned by inducing spacecharge regions at interfaces by means of an applied voltage. As an example, we investigate the reversible variation of the lattice constant of platinum nanoparticles immersed in an aqueous 1M KOH electrolyte as a function of applied potential. It is found that a reversible volumetric strain of up to 1.2 % can be induced, corresponding to pressures of up to 3.2 GPa. We present the experimental set-ups for in-situ X-ray diffraction with an electrochemical cell. The variation of the space charge at the metal-electrolyte interface results in a variation of the surface stress f as a function of the applied potential, which is not an electrocapillary effect.
Superparamagnetism and Microstructural Properties of Carbon Encapsulated Ni nanoparticle Assemblies
Authors: Sun Xiang-Cheng , Dong Xinglong , Toledo J. A. , Yacaman M. J.
Published: April 2011

Carbon encapsulated Ni nanoparticles (Ni(C)) were synthesized by modified arc-discharge reactor under methane atmosphere. The presence of carbon encapsulation is confirmed by HR-TEM imaging, and Nano-diffraction. The average particle radius is typically 10.5 nm with spherical shape. The intimate and contiguous carbon fringe around these Ni nanoparticles is good evidence for complete encapsulation by carbon shell layers.

Superparamagnetic property studies were performed using SQUID magnetometer for the assemblies of Ni(C) nanoparticles. The blocking temperature (TB) is determined to around 115K at 1000Oe applied field. Above TB, the magnetization M (H, T) can be described by the classical Langevin function L using the relation, M/Ms(T=0) = coth(μH/kT)- kT/μH. The particle radius can be inferred from Langevin fit (particle moment μ) and blocking temperature theory (TB), which values are a little bigger than HR-TEM observations. It is suggested, these assemblies of carbon encapsulated Ni nanoparticles have been showed typical single-domain, field-dependent superparamagnetic relaxation properties.
Optical And Structural properties of Vertical Aligned Self-Assembled InAs Quantum Dots Multilayers
Authors: González J. C. , da Silva M. I. N. , Rodrigues W. N. , Matinaga F. M. , Magalhaes-Paniago R. , Moreira M. V. , Oliveira A. G. de , Ugarte D.
Published: April 2011

In this work, we report optical and structural properties of vertical aligned self-assembled InAs quantum dots multilayers. The InAs quantum dots samples were grown by Molecular Beam Epitaxy. Employing Atomic Force Microscopy, Transmission Electron Microscopy, and Gracing Incident X-ray Diffraction we have studied the structural properties of samples with different number of periods of the multiplayer structure, as well as different InAs coverage. The optical properties were studied using Photoluminescence spectroscopy.
Biomedical application of ferrofluids containing magnetite nanoparticles
Authors: Kim D. K. , Voit W. , Zapka W. , Bjelke B. , Muhammed M. , Rao K.V.
Published: April 2011

Ferrofluids containing superparamagnetic Fe3O4 nanoparticles have been prepared by a controlled co-precipitation method.The aggregation of the particles was prevented by using a polymeric starch network as a coating agent. Structural and magnetic measurements reveal a particle size of around 6 nm, with a clear evidence of a uniform particle coating. The ferrofluids have been used as a contrast agent for MR imaging in biological tissue.
Direct Electronic Control of Biomolecular Systems: Using Nanocrystals as Antennas for Regulation of Biological Activity
Authors: Hamad-Schifferli Kimberly , Schwartz John J. , Santos Aaron T. , Zhang Shuguang , Jacobson Joseph M.
Published: April 2011

We report a means of directly controlling DNA dehybridization by radio frequency magnetic field coupling to a nanometer scale antenna covalently linked to the DNA. The method of control relies on induction heating of an Au nanocrystal, which raises the temperature of a biomolecule to which it is covalently bound, while leaving surrounding molecules relatively unaffected. Because heat dissipation in biomolecules in solution is rapid(<50 picoseconds[1]) this switching is reversible. This technique is specific, reversible, and non-optical. Since it can be used in solution, it has the potential to be extended to systems in vivo. The ability to differentially control local temperature forms the basis of control of properties such as hybridization and enzyme activity, and has the potential of controlling many biological processes.
A Combined Density Functional and Monte Carlo Study of Polycarbonate
Authors: Jones R. O. , Ballone P.
Published: April 2011

Density functional computations have been performed to investigate the structure, potential en- ergy surface and reactivity for organic systems closely related to bisphenol-A-polycarbonate(BPA- PC). The results provide the basis for the construction of two different empirical models, the first extending the atomistic simulations into the mesoscopic range (104–105 atoms and 0.01–0.1 μs), the second providing an idealized description of polymerization in BPA-PC. The combination of models and computational techniques focusing on different length and time scales provides a route to determine mechanical and thermal properties of materials without experimental input.
Electronic and Optical Properties of Si/SiO2 Superlattices from First Principles: Role of Interfaces.
Authors: Carrier Pierre , Abramovici Gilles , Lewis Laurent J. , Dharma-wardana M. W. C.
Published: April 2011

The observation of intense luminescence in Si/SiO2 superlattices (SLs) has lead to new theoretical research on silicon-based materials. We have performed first-principles calculations using three Si/SiO2 SL models in order to examine the role of interfaces on the electronic structure and optical properties. The first two models are derived directly from crystalline structures and have simple interfaces. These models have been studied using the full-potential, linearized-augmented-plane-wave method, in the local-density-approximation (LDA). The optical absorption within the interband transition theory (excluding excitonic effects) have been deduced. The Si(001)-SiO2 interface structure is shown to affect the optical behaviour. Following these observations, we have considered a more realistic, fully-relaxed model. The projector-augmented-wave method under the LDA is used to perform the structural relaxation as well as band structure and optical calculations. The role of confinement on the energy gap is studied by inserting additional silicon slabs into the supercell. Direct energy gaps are observed and the energy gap is found to decrease with increasing silicon slab thickness, as observed experimentally. The role of the interface has been considered in more details by studying the contribution to the energy gap of Si atoms having different oxidation patterns; partially oxidized Si atoms at the interface, as well as Si atoms inside the Si layer, are shown to contribute to the transitions at the energy gap.