bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural, Magnetic Properties of the Electrochemically Deposited Arrays of Nickel Nanowires
Authors: Khan H.R. , Petrikowski K.
Published: April 2011

The room temperature structural, magnetization and magnetoresistive properties of Ni-nanowires of diameters 18, 30 and 78 nm and various lengths, fabricated by electrochemical deposition of Ni in the nanopores of anodic alumina, are investigated. The crystallographic orientation depends on the diameter of nanowires. Nanowires show perpendicular magnetic anisotropy and enhanced coercivity (Hc) and remanent magnetization (Mr) values of up to 500 Oe and 50% respectively. An electrodeposited Ni-layer (5 μm) on copper substrate shows in plane magnetic anisotropy and the Hc and Mr values are 97 Oe and 37%. Ni-nanowires and Ni-layer show an anisotropic magnetoresistive behaviour.
Crack Healing in an Alumina/Silicon Carbide Nanocomposite After Grinding and Annealing
Authors: Wu H.Z. , Titchmarsh J.M. , Roberts S.G. , Derby B.
Published: April 2011

Alumina/silicon carbide nanocomposites are known to show their highest strength levels after surface grinding followed by annealing. After annealing in flowing argon, nanocomposites with very coarsely ground surfaces have strengths exceeding those with a finely polished surface. Specimens with lapped surfaces also show a small improvement in strength on annealing. TEM investigations of annealed cross-sections show that the annealing process leads to surface crack healing. The chemical composition of the subsurface region has been studied, and reactive products on and close to the nanocomposite surface after annealing have been investigated by energy dispersive X-ray analysis in the STEM.
Transparent Monolithic Metal Ion Containing Nanophase Aerogels
Authors: Risen William M. , Hu Xiangjun , Ji Shuang , Littrell Kenneth
Published: April 2011

The formation of monolithic and transparent transition metal containing aerogels has been achieved through cooperative interactions of high molecular weight functionalized carbohydrates and silica precursors, which strongly influence the kinetics of gelation. After initial gelation, subsequent modification of the ligating character of the system, coordination of the group VIII metal ions, and supercritical extraction afford the aerogels. The structures at the nanophase level have been probed by photon and electron transmission and neutron scattering techniques to help elucidate the basis for structural integrity together with the small entity sizes that permit transparency in the visible range. They also help with understanding the chemical reactivities of the metal-containing sites in these very high surface area materials. These results are discussed in connection with new reaction studies.
Preparation of Submicron and Micron Size Cr (IV) Optical Composites
Authors: Isaacs L.L. , Petricevic V. , Wang BaoPing , Ying Jinpin , Alfano R.R.
Published: April 2011

Sol - gel technology is used to prepare sub-micron to micron size particles of Chromium (IV) doped materials. These materials show strong luminescence, as single crystals, in the 1-2 μm range. Such materials include; Cr (IV): (Ca2GeO4, Mg2SiO4, LiScGeO4). The optically active particles are dispersed into glassy matrixes to form optical composites. Ongoing research is aimed at, a) reducing the size and the size distribution of the optically active particles, and b) finding suitable matrix materials.
Quantum Confined Gallium Nitride in a Mesoporous Matrix of Mcm-41
Authors: Winkler H. , Fischer R. A. , Schmechel R. , von Seggern H.
Published: April 2011

We report the synthesis of a nanocomposite materials consisting of gallium nitride (GaN) confined in the well ordered mesoporous transparent matrix MCM-41 with the help of the metalorganic single source precursor triazido(trimethylamine)gallium using solution impregnation technique. The loading of the pores of MCM-41 with GaN was confirmed by chemical analysis, XRD, TEM, BET, NMR and optical spectroscopy (PL and PL-excitation spectroscopy). The composites exhibit a blue shift of the bandgap of GaN due to quantum confinement.
Soft Chemical Design of Transition-Metal-Oxide/Clay Layered Nanocomposites
Authors: Fuda Kiyitali , Narita Shuji , Kudo Shuji , Murakami Kenji , Matsunaga Toshiaki
Published: April 2011

Room-temperature synthesis of transition metal ( TM = Co, Ni and Mn ) oxide intercalated clays has been developed, which extends the potentiality of clay based materials for the design of electroactive nanophase. The structure was examined by using powder XRD - one-dimensional Fourier analysis, magnetic susceptibility measurement as well as conventional analytical methods. From the results, it was revealed that the oxidation by using NaClO as the oxidative reagent affords a new expanded layer structure with a basal spacing of about 1.96 nm wherein a conductive TM oxide sheetadjacent to two hydrated sodium ion layers resides in the gallery of the clay. The resultant sodium cobaltate interlayered smectite bears multi-functionality; an apparent bulk conductivity in the order of 10−5 Scm−1 and a cation exchange ability.
Catalytic Activity and Surface Characterization Study of Pd Supported on Nanocrystalline and Polycrystalline CeO2
Authors: Hoflund Gar B. , Li Zhenhua , Campbell Timothy J. , Epling William S. , Hahn Horst W.
Published: April 2011

The catalytic activity of polycrystalline and nanocrystalline CeO2-supported Pd (Pd/pCeO2 and Pd/nCeO2) has been determined as a function of temperature and Pd loading. While the untreated nCeO2 support gives 50% methane conversion at 420°C, the untreated pCeO2 support exhibits little activity under the conditions examined due to its low surface area. A Pd loading of 5 wt% increases the activity of pCeO2 to 50% conversion at 260°C, while a 40 wt% Pd loading on nCeO2 exhibits a relatively smaller activity increase, yielding 50% conversion at 240°C. On a mass basis the 40 wt% Pd/nCeO2 catalyst is the most active tested in this study, but it is less active than the 5 wt% Pd/pCeO2 catalyst on a surface-area basis. Furthermore, the activity of the 40 wt% Pd/nCeO2 catalyst does not decrease during 100 hrs of exposure to CH4 and O2 at 250°C.

X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) have been used to characterize the surfaces of both bare supports and Pd-containing catalysts before and after exposure to reactor conditions. The XPS results reveal that the Pd surface concentration is more than an order of magnitude higher for 5 wt% Pd/pCeO2 than for 5 wt% Pd/nCeO2 due to the larger surface area of nCeO2 and that the 40 wt% Pd/nCeO2 catalyst has a lower Pd loading on a surface-area basis than the 5 wt% Pd/pCeO2 catalyst. Most of the supported Pd is in the form of PdO, but higher PdO2/PdO ratios are observed for both CeO2 supports compared to Pd supported on ZrO2 or CO3O4. Furthermore, a significant amount of metallic Pd forms on Pd/nCeO2 but not on Pd/pCeO2 during reaction. The nanocrystalline and polycrystalline CeO2 behave differently chemically which is consistent with the fact that the nanocrystalline catalysts are less active on a surface-area basis. Accumulation of H20 on the Pd/pCeO2 surface during reaction is significant but not on the Pd/nCeO2 surface. This suggests that the rate limiting step may be H2O desorption on Pd/pCeO2 while for Pd on nCeO2 adsorption of methane appears to be the slow step. The ISS data indicate that the outermost atomic layer of Pd/nCeO2 consists mostly of O and C, which is not the case for Pd/pCeO2. Site blockage by these species may also contribute to the lower activity on a surface-area basis of Pd/nCeO2 compared to Pd/pCeO2.
Electrical Resistivity as a Characterization Tool for Nanocrystalline Metals
Authors: McCrea J.L. , Aust K.T. , Palumbo G. , Erb U.
Published: April 2011

The electrical resistivity as a function of temperature (4K to 673K) of several electrodeposited nanocrystalline materials (Ni, Ni-Fe, Co) has been examined. The contribution of the grain boundaries to the electrical resistivity was quantified in terms of a specific grain boundary resistivity, which was found to be similar to previously reported values of specific grain boundary resistivity for copper and aluminum obtained from studies involving polycrystalline materials. In the high temperature range, the resistivity of the nanocrystalline samples was monitored as a function of time. The observed time dependence of the resistivity at elevated temperatures was correlated to microstructural changes in the material. The study has shown that electrical resistivity is an excellent characterization tool for nanocrystalline materials giving useful information regarding grain size and degree of thermal stability, as well as some insight into the grain growth kinetics at various temperatures.
Synthesis and Characterization of Manganese Vanadium Oxides as Cathodes in Lithium Batteries
Authors: Zhang Fan , Zavalij Peter , Whittingham M. Stanley
Published: April 2011

Our research on new cathode nano-materials for advanced lithium batteries has focused on the hydrothermal method for synthesis. We have synthesized two novel manganese vanadium oxides using the hydrothermal reactions of vanadium (V) pentoxide, [N(CH3)4]MnO4, and MnSO4 with an organic templating cation at 165°C. The 6-type [N(CH3)4]zMnyV2O5*nH2O has a monoclinic structure, a= 11.66(2)Å, b=3.610(9)Å, c= 13.91(4)Å, β= 108.8(2)°. It has a disordered V2O5 double layer and the Mn and N(CH3)4 ions reside between the layers. The γ-type MnV2O5 is orthorhombic, belongs to the space group Pnma, a=9.7585(2) Å, b=3.5825(l)Å, c= 11.2653(2) Å. These compounds were also characterized by electron microprobe, FTIR and TGA. They reacted readily with lithium, and their electrochemical behavior in lithium cells was determined.
Nanoporous Alumina Coatings for Medical Implants and Stents - Radiotherapy, Drug Delivery, Biological Compatibility
Authors: Sawitowski T. , Brandau W. , Fischer A. , Heilmann A. , Schmid G.
Published: April 2011

The body implant interaction is strongly affected by the implant surface structure and chemistry [1,2]. Thus by applying a nanoporous coating to metallic implants the implant surface can be adjusted to different needs. Compared to biological molecules the size of the pores is so small (between 5 nm and 250 nm) that the cellular response to this surface modification is not affected by the structure itself. Nevertheless by loading the pores with bioactive molecules it is possible to achieve a new kind of active implants surfaces for soft and hard tissue implants. With this coating it is possible to irreversibly bind radioactive isotopes like 99mTc, 186/188Re, 103Pd, and many more for local radiotherapy onto soft tissue implants like stents or seeds.
Microstructural and Magnetic Properties on Graphitic Encapsulated Ni Nanocrystals and Pure Ni Nanoparticles with NiO Layer
Authors: Suns Xiangcheng , Yacamana M. Jose , Morales F.
Published: April 2011

Two kinds of different nickel nanoparticles with distinct morphological properties, Ni(C) and Ni(O), are studied. Magnetization measurements for the assembly of two kinds of Ni nanoparticles show, a larger coercivity and remanence as well as the deviation between the zero field cooling (ZFC) and the field cooling (FC) magnetization have been observed in the Ni(O) particles. This deviation may be explained as a typical cluster glass-like behavior due to ferromagnetic interaction among the assembly of Ni(O) particles. However, Ni(C) particles exhibit superparamagnetism at room temperature. The average blocking temperature (TB) is determined to around 115K. We also observe gradual decrease in saturation magnetization, which is attributed to the nanocrystalline nature of the encapsulated particles.
Chemical Reactions on the Surface of SnO2 Nanosized Powders at the Origin of the GaS Sensing Properties: FTIR Investigation
Authors: Baraton M.-I. , Merhari L.
Published: April 2011

The surface chemical reactions at the origin of the CO detection by SnO2-based sensors are investigated by Fourier transform infrared spectrometry for two different SnO2 particle sizes. Knowing that the variations of the infrared energy transmitted by the sample versus surrounding gases are related to the variations of the electrical conductivity, correlation of surface chemical reactions with the sensor response is established and discussed.
Morphological Stability of Ni(Al)/Ni3Al Nanolaminate Composites
Authors: Fain Jason P. , Banerjee Rajarshi , Josell Daniel , Anderson Peter M. , Fraser Hamish , Tymiak Natalia , Gerberich William
Published: April 2011

This manuscript discusses the morphological instability observed when multilayered samples with alternating layers of Γ-Ni(Al)/γ-Ni3Al are exposed to 800C for approximately 100 hours. Samples with 20nm/20nm or 120nm/120nm layer thickness and <001> or  crystal orientation to the interface normal were tested. Pinching off of layers is strongly affected by crystal orientation and layer thickness. Corresponding modeling suggests that the stability of this system is sensitive to fluctuations in the volume fraction of the two phases, the aspect ratio of columnar grains in the layers, and whether coherent or semi-coherent interfaces are present.
Measuring the Dielectric Properties of Nanostructures using Optical Reflection and Transmission: Bismuth Nanowires in Porous Alumina
Authors: Black M. R. , Lin Y. M. , Dresselhaus M. S. , Tachibama M. , Fang S. , Rabin O. , Ragot F. , Eklund P. C. , Dunn Bruce
Published: April 2011

This paper develops a method to deduce the dielectric function of nanostructures smaller than the chosen wavelength of light. It modifies the Maxwell - Garnett Effective Medium Theory equations to calculate the dielectric function of a metal embedded inside a dielectric. Specifically, reflection and transmission measurements of an array of bismuth nanowires in an anodized porous alumina template are used to calculate the frequency - dependent di-electric function of the nanowires. The spectra are taken using Fourier transform infrared spectroscopy covering the 500 to 4000 cm−1 frequency range. These data are used to determine the real and imaginary parts of the dielectric function of the composite materials. Next, the percentage of the total volume occupied by either Bi or air in the porous alumina (the “filling factor”) was found by scanning electron microscopy. The modified Maxwell-Garnett (M-G) equations specify how to use the filling factor and the dielectric function of the composite material to calculate the dielectric function of the alumina. Finally, the modified M-G equations are used a second time to calculate the dielectric function of Bi nanowires using the dielectric function of alumina, the dielectric function of the filled template, and the filling factor. The resulting dielectric function of Bi nanowires is then compared to theoretical predictions.
Colossal Hopping Magnetoresistance of GaAs/ErAs Nanocomposites
Authors: Petukhov A. G. , Foygel M. , Chantis A.
Published: April 2011

A theory of bound magnetic polaron (BMP) hopping, driven by thermodynamic fluctuations of the local magnetization, has been developed. It is based on a two-site model of BMP's. The BMP hopping probability rate was calculated in the framework of the “Golden Rule” approach by using the Ginzburg-Landau effective Hamiltonian method. The theory explains the main features of hopping resistivity observed in a variety of experiments in dilute magnetic semiconductors and magnetic nanocomposites, namely: (a) negative giant magnetoresistance, the scale of which is governed by a magnetic polaron localization volume, and (b) low magnetic field positive magnetoresistance, which usually preceeds negative magnetoresistance.
Magnetic Hardening Induced by Exchange Coupling in Mechanically Milled Antiferromagnetic - Ferromagnetic Composites
Authors: Sort J. , Nogués J. , Amils X. , Suriñach S. , Muñoz J.S. , Baró M.D.
Published: April 2011

Mechanical milling has been used to synthesize ferromagnetic (FM, Co) - antiferromagnetic (AFM, NiO) composites. The coercivity, HC, and energy product, BHMax, of these composites can be enhanced at room temperature after appropriate heat treatments above the Néel temperature of the AFM, TN. Although the maximum Hcis achieved for the (NiO)1: 1 (Co) weight ratio, BHMaxis further enhanced for the (NiO)2:3(Co) ratio, where higher saturation magnetization is obtained due to the larger amount of FM. Exchange coupling, responsible for these effects, decreases as the temperature is increased and vanishes close to TN. The thermal stability of the coercivity enhancement remains rather insensitive to the somewhat broad distribution of blocking temperatures of this system.
Study of the Luminescence of Eu-Doped Nanocrystalline Si/SiO2 Systems Prepared by RF Co-Sputtering
Authors: Nery G.A. , Mahfoud A. , Fonseca L.F. , Liu H. , Resto O. , Weisz S.Z.
Published: April 2011

We prepared Eu-doped films of Si nanoparticles embedded in SiO2 using pellets of Eu2O3 by sputtering. We studied their photoemission, transmission and fluorescence to obtain data about their composition and particle size and the Eu interaction characteristics. We were able to incorporate Eu(III) into the Si nanoparticle / SiO2 host. We also found we obtained Eu(II) in the process. We found a lowering of photoluminescence intensity with lowering of temperature. An as yet unanswered question is the reason for the intense whitish luminescence found in some regions of the samples. Some involvement with Eu(II) is suspected. Eu(IIl) related peaks were only observed where the size distribution peak of the nanoparticles was lower than 1.3nm. Whitish luminescence was related to peak sizes ranging from 1.1nm to 1.4nm. Annealing the samples had clear effects upon their photoluminescence, but did not necessarily involve changes in particle sizes, nor were these size changes necessary to increase luminescence. The Eu doping has a tendency to halt the annealing effects on size and, when changes did occur, the particles generally became smaller.
Can We Determine the Barrier Resistance for Electron Transport in Ligand Stabilized Nanoparticles from Integral Conductance Measurements?
Authors: Simon U.
Published: April 2011

By means of integral temperature dependent conductance measurements, the effective capacitance of ligand stabilized nanoparticles, arranged in dense packings or networks, can be deduced from the activation energy of the charge transport, for which the use of the Landauer formula is proposed. According to this, the barrier resistance in ligand stabilized nanoparticle arrangements depends predominantly on the inter particle spacing rather than on the chemical composition of the molecules. Comparison with data of the single molecule resistance determined by local probe techniques or by theoretical methods shows remarkable aggreement.
Stoichiometry Control in Molecular Beam Deposited Nanocrystalline SnO2 and TiO2 Thin Films
Authors: Hoche H. , Hahn H. , Edelman F. , Nagel R. , Werner P.
Published: April 2011

Molecular beam deposition (MB) of thin film metal oxide is prospective for application in gas sensor technology due to the well-controlled oxide molecular fluxes during creation of multi-oxide structures with improved characteristics. However, the MB process leads to some oxygen deficiency in the oxide. Further application of the MB technology (and, in general, the e-beam oxide deposition in vacuum) for processing of sensor structures needs the control and correction of the oxygen stoichiometry by adding in-situ atomic oxygen to the growing material or via the thin film oxidation after deposition.

Thin films (50 to 500 nm) of SnOx and TiOx were deposited on SiO2/(001)Si substrates at 100°C by MB from SnO2 and TiO2 sources. The film stoichiometry in the as-deposited state and after annealing in vacuum and in oxygen is characterized by XRD, TEM and RBS. Oxygen annealing transformed the strongly non-stoichiometric SnO (Romarchite) in the as-deposited state to Cassiterite, SnO2. Structure transformations in the TiO2 films during annealing are also discussed.
Structure and Magnetic Property Correlation in Nanocrystalline SmFe9
Authors: Djega-Mariadassou C. , Bessais L.
Published: April 2011

SmxFe100−x samples with x = 7.6, 10.5 and 12.5 were prepared by high energy ball-milling and subsequent annealing at various temperature Ta, 600 < Ta < 1200 °C. Rietveld analysis coupled to Curie temperature measurements and M6ssbauer spectroscopy revealed for 600 < Ta < 900 °C an hexagonal phase P6/mmm derived from TbCu7 with stoichiometry SmFe9. At Ta > 900 °C, the ordered R3m Sm2Fe17 structure is obtained so that SmFe9 appears as the out-of-equilibrium precursor of Sm2Fe17. The Curie temperature and hyperfine field augmentation found for SmFe9 results from an increase of the interatomic distance in the Fe-Fe dumbbell, responsible for a reduction of the negative exchange interaction.
Pulsed Magnetic Field Induced 3-D Islanding of Oxygen Contained Clusters in Cz-Si Crystals
Authors: Levin M. N. , Zon B. A.
Published: April 2011

Effect of pulsed magnetic field induced self-organized generation of 3-D spatially regular structures of oxygen-vacancy contained clusters of nanometer scale has been observed in silicon crystals grown by Czochralski method (Cz-Si). The effect has been studied by means of ultra-soft X-ray spectroscopy, scanning tunneling microscopy and potential probe measurements. Mechanisms responsible for the effect have been discussed.
Growth and Decay of Germanium Islands on Silicon Studied by High Temperature Stm
Authors: Kästner M. , Voigtländer B.
Published: April 2011

We use a scanning tunneling microscope (STM) capable of imaging the growing layer at high temperature during molecular beam epitaxy (MBE) to study the epitaxial growth of Germanium on Silicon and the decay of Ge islands. The periodicity of the (2×N) reconstruction of two-dimensional Ge layers on Si(001) is measured as function of the Ge coverage. Strain energy drives the formation of the (2×N) reconstruction and Si/Ge intermixing. A comparison to total energy calculations predicting the periodicity of the (2×N) reconstruction is used to estimate the amount of Si-Ge intermixing near the surface. The evolution of the size and shape of individual “hut clusters” is measured and explained by kinetically self-limiting growth. The relaxation of kinetically a determined morphology towards equilibrium is followed for a Ge layer on Si(111). Strained two-dimensional as well as partially relaxed three-dimensional islands dissolve and are soaked up by larger three-dimensional islands which are dislocated and therefore fully relaxed.
In Situ Measurements of Stress Relaxation During Strained Layer Heteroepitaxy
Authors: Chason E. , Yin J. , Tetz K. , Beresford R. , Freund L. B. , Gonzalez M. Ujue , Floro J. A.
Published: April 2011

We present real-time measurements of stress relaxation kinetics during epitaxial growth obtained using a wafer-curvature-based technique optimized for in situ studies. Depending on the temperature and misfit strain, different mechanisms of stress relaxation are observed. In heterolayers of InGaAs grown on GaAs (001) substrates, relaxation occurs by a dislocationmediated mechanism. In SiGe layers grown on Si (001) substrates at elevated temperature, relaxation occurs by the formation of islands on the surface. These islands elastically relax misfit stress without the introduction of dislocations at the island-substrate interface.
Spontaneous Formation of Arrays of Strained Islands: Thermodynamics Versus Kinetics
Authors: Shchukin V. A. , Ledentsov N. N. , Bimberg D.
Published: April 2011

Options are discussed which allow to distinguish equilibrium arrays of strained islands from kinetically-controlled arrays. Finite-temperature thermodynamic theory is developed for equilibrium arrays of two-dimensional monolayer-high islands in heteroepitaxial systems at submonolayer coverage. It is shown that the entropy contribution to the Helmholtz free energy of the system favors formation of small islands and results in the shrinkage of the islands with increasing temperature. The average size of islands decreases tremendously with respect to zero-temperature size at temperatures far below the characteristic energy of island formation. Such a temperature dependence can be the basis for decisive experiments aimed to distinguish between thermodynamic and kinetic effects on the formation of arrays of 2D islands. The theory is able to explain results of high-resolution electron microscopy of submonolayer arrays of InAs/GaAs(001) islands. Their formation is predominantly influenced by thermodynamics.
CuPt-B Ordered Microstructures in GaInP and GaInAs Films
Authors: Ahrenkiel S. P. , Jones K. M. , Matson R. J. , Al-Jassim M. M. , Zhang Y. , Mascarenhas A. , Friedman D. J. , Arent D. J. , Olson J. M. , Hanna M. C.
Published: April 2011

We examine CuPt-B atomic sublattice ordering in Ga0.51In0.49P (GaInP) and Ga0.47In0.53As (GaInAs) III-V alloy films grown by atmospheric- and low-pressure metalorganic chemical vapor deposition on singular and vicinal (001) substrates. The influences of growth conditions and substrate miscut on double- and single-variant ordered microstructures are investigated using transmission electron microscopy (TEM). Relatively thick (>1–2 litm) double-variant ordered GalnP and GaInAs films show complementary superdomain formation. Single-variant ordered films on <111>B-miscut substrates contain single-phase domains, separated by antiphase boundaries (APBs). The appearance of APBs in TEM dark-field images is anticipated from electron diffraction theory.
Single and Double Variant Cupt-B Ordered GalnAs
Authors: Forrest R. L. , Meserole E. D. , Nielsen R. T. , Goorsky M. S. , Zhang Y. , Mascarenhas A. , Hanna M. , Francoeur S.
Published: April 2011

Nominally lattice-matched GaInAs layers grown by metal organic vapor phase epitaxy on InP substrates have been studied using high-resolution x-ray diffraction (HRXRD) to determine the growth conditions under which ordering is introduced. HRXRD provides an independent means to quantify the order parameter of semiconductor heterostructures as well as the ordering on different {111} planes, i.e., double variant ordering. This independent means to determine ordering provides for a better understanding of the effects of ordering on the electronic and optical properties. Double variant ordering was observed for epitaxial layers grown on exact (001) InP substrates, with an order parameter of about 0.1 in both variants. For substrates that were miscut by 6 degrees, single variant ordering was detected. In these cases, an order parameter as high as 0.66 was measured for certain growth conditions. The layers grown on vicinal substrates are all of high crystalline quality, those on (001) substrates exhibit some mosaic spread.
Local Order of Te Impurity Atoms in Heavily Doped GaAs:Te and Accompanying Electron Localization Effect
Authors: Slupinski T. , Zielinska-Rohozinska E.
Published: April 2011

We show the results of joined studies of the free electron concentration and x-ray diffuse scattering from heavily doped GaAs:Te single crystal as a function of controlled annealings at high temperatures 700–1200°C and Te concentration 1018− 2 1019 cm−3 from the range, where the free electron concentration saturates. Changes of electron concentration caused by annealings are accompanied by structural changes, both being in a high coincidence and reversible versus annealing temperature On a basis of the microscopic model of x-ray diffuse scattering from a solid solution, newly proposed here, we argue that impurity atom pairs arise, locally in a crystal, when the free electron concentration is lowered by annealing. We suppose that the electron localization is caused by impurity atom pairs, supporting recently published results.
The Initial Stages of Growth of Ordered GaInP and GaInAs Grown by Metal Organic Vapor Phase Epitaxy
Authors: Hanna M. C. , Mascarenhas A. , Cheong Hyeonsik M.
Published: April 2011

We have used atomic force microscopy (AFM) and Raman spectroscopy to investigate the development of the surface morphology of (001) direct and vicinal GaInP and GaInAs grown under conditions to produce strong CUPtB ordering. Raman spectroscopy provided direct evidence of CuPtB ordering in layers as thin as 10 nm for GaInP and 5 nm for GaInAs. We find that the morphology of GaInP and GaInAs on (001)6B substrates consists of ridges, which are aligned predominately along the [110] direction (A-direction). These ridges are well developed even at layer thicknesses of 2 nm, and their sides consist of step-bunches and near (001) terraces. On (001) direct substrates, the GaInP morphology is similar to that obtained on 6B substrates, although the step bunches have no preferential orientation, while GaInAs (001) growth proceeds by a combination of 2D-island and step flow growth. We discuss possible reasons for the differences in the morphology of ordered GaInP and GaInAs. The results of this work suggest it may be difficult to produce abrupt heterointerfaces in structures containing ordered GalnP and GaInAs alloys.
The Nature and Origin of Lateral Composition Modulations in Short-Period Strained-Layer Superlattices
Authors: Norman A. G. , Ahrenkiel S. P. , Moutinho H. R. , Ballif C. , Al-Jassim M. M. , Mascarenhas A. , Follstaedt D. M. , Lee S. R. , Reno J. L. , Jones E. D. , Mirecki-Millunchick J. , Twesten R. D.
Published: April 2011

The nature and origin of lateral composition modulations in (AlAs)m(InAs)nshort-period strained-layer superlattices grown by molecular beam epitaxy on InP substrates have been investigated by x-ray diffraction, atomic force microscopy, and transmission electron microscopy. Strong modulations were observed for growth temperatures between ≈ 540 and 560° C. The maximum strength of modulations was found for SPS samples with InAs mole fraction x (= n/(n+m)) close to ≈ 0.50 and when n≈m≈2. The modulations were suppressed at both high and low values of x. For x > 0.52 (global compression), the modulations were along the <100> directions in the (001) growth plane. For x < 0.52 (global tension), the modulations were along the two <310> directions rotated ≈ ±27° from [110] in the growth plane. The remarkably constant wavelength of the modulations, between ≈ 20–30 nm, and the different modulation directions observed, suggest that the origin of the modulations is due to surface roughening associated with the high misfit between the individual SPS layers and the InP substrate. Highly uniform unidirectional modulations have been grown by control of the InAs mole fraction and growth on suitably offcut substrates, which show great promise for application in device structures.
Formation of Direct Energy Gap Group IV Semiconductor Alloys and Quantum Dot Arrays in SnxSi1−x /Si and SnxGe1−x/Ge Alloy Systems
Authors: Atwater Harry A. , Ragan Regina , Min Kyu S.
Published: April 2011

The narrow gap semiconductor alloys SnxGe1−x, and SnxSi1−x offer the possibility for engineering tunable direct energy gap Group IV semiconductor materials. For pseudomorphic SnxGe1−x, alloys grown on Ge (001) by molecular beam epitaxy, an indirect-to-direct bandgap transition with increasing Sn composition is observed, and the effects of misfit on the bandgap analyzed in terms of a deformation potential model. Key results are that pseudomorphic strain has only a very slight effect on the energy gap of SnxGe1−x, alloys grown on Ge (001) but for SnxGe1−x alloys grown on Ge (111) no indirect-to-direct gap transition is expected. In the SnxSi1−x system, ultrathin pseudomorphic epitaxially-stabilized α-SnxSi1−x alloys are grown on Si (001) substrates by conventional molecular beam epitaxy. Coherently strained oa-Sn quantum dots are formed within a defect-free Si (001) crystal by phase separation of the thin SnxSi1−x layers embedded in Si (001). Phase separation of the thin alloy film, and subsequent evolution occurs via growth and coarsening of regularly-shaped α-Sn quantum dots that appear as 4–6 nm diameter tetrakaidecahedra with facets oriented along elastically soft [100] directions. Attenuated total reflectance infrared absorption measurements indicate an absorption feature due to the α-Sn quantum dot array with onset at ˜0.3 eV and absorption strength of 8 × 103 cm−1, which are consistent with direct interband transitions.
Self-Assembled Iii-Phospide Quantum Dots Grown by Metalorganic Chemical Vapor Deposition
Authors: Ryou Jae-Hyun , Chowdhury Uttiya , Dupuis Russell D. , Reddy Chavva V. , Narayanamurti Venkatesh , Mathes David T. , Hull Robert
Published: April 2011

We report InP self-assembled quantum dots embedded in In0.51Al0.49P grown by metalorganic chemical vapor deposition. Growth parameters are altered to study the InP quantum-dot growth characteristics under various growth conditions. Quantum-dot morphology is characterized using atomic-force microscopy. Also, photoluminescence studies of the light-emitting properties are performed. Direct-bandgap ternary InxAlI−xP (x=˜0.7, ˜0.85) self-assembled quantum dots are also grown and compared with InP quantum dots.
Shape Reversal of Ge/Si Domes to Pyramids Via Si-Ge Intermixing and Strain Reduction
Authors: Henstrom William L. , Liu Chuan-Pu , Gibson J. Murray
Published: April 2011

At 650°C, Si freely intermixes with Ge in the dome islands causing a reduction in the strain of the islands and an increase in island size. The shape reversal of Ge/Si domes to pyramids is investigated by analysis of the strain and size changes that occur on an island by island basis. This was carried out for anneal times of 0, 20, 40 and 60 minutes. Transition islands were observed consistent with previous work[1], which are partially domes and partially pyramids. These islands demonstrated a strain gradient, having a slightly lower strain on the side that has transformed to a pyramid. Cross-sectional STEM was then used to show that this strain gradient is associated with a non-uniform Si intermixing in the islands.
Systematic Studies of Fullerene Derivative Electron Beam Resists
Authors: Robinson A. P. G. , Palmer R. E. , Tada T. , Kanayama T. , Shelley E. J. , Philp D. , Preece J. A.
Published: April 2011

We report systematic studies of the response of C60 derivatives to electron beam irradiation. Films of fourteen different mono, tris and tetra adduct methanofullerene C60 derivatives were produced by spin coating on hydrogen terminated silicon substrates. Exposure of the films to a 20 keV electron beam substantially altered the dissolution rate of the derivative films in organic solvents such as monochlorobenzene. All of the derivatives exhibited negative tone resist behaviour with sensitivities between ∼ 8.5 × 10-4 and ∼ 4 × 10-3 C/cm2 107, much higher than that of C60. Features with widths of ∼ 20 nm were produced using these compounds, and the etch ratios of the compounds were found to be more than twice those of a standard novolac based resist (SAL601).
A New High Performance CA Resist for E-beam Lithography
Authors: Kwong Ranee , Huang Wu-Song , Moreau Wayne , Lang Robert , Robinson Christopher , Medeiros David R. , Aviram Ari , Guarnieri Richard C. , Angelopoulos Marie
Published: April 2011

Three major lithographic applications have emerged for electron beam exposure tools: optical mask fabrication, direct writing for device fabrication, and more recently projection e-beam printing. The traditional mask making process uses poly(butenesulfone) resist. A wet etch process was adopted to generate patterns on chrome. Recently, shrinking dimensions, optical proximity correction features, and the complexity of phase shift masks have forced the industry to a chrome dry etch process. ZEP, a poly(methyl α-chloroacrylate-co-α-methylstyrene) based resist, has been well accepted for most of the >180 nm device mask making. The acceptance of ZEP comes in spite of its low contrast, marginal etch resistance, organic solvent development, and concerns of resist heating associated with its high dose requirements. These issues have spawned interest in using chemically amplified resist (CAR) systems for direct write and mask making applications. We have developed a high contrast resist based on ketal protecting groups, KRS-XE, which is robust against airborne contamination and can be used for all forms of e-beam exposure in both chrome mask and silicon processing. This high contrast resist is processed with aqueous base developer and has a wide bake latitude. The development of KRS-XE has provided the capability of fabricating chrome masks for future generation (< 180 nm) devices and has potential for use with projection beam exposure systems.
Photo and Scanning Probe Lithography Using Alkylsilane Self-Assembled Monolayers
Authors: Sugimura H. , Hanji T. , Takai O. , Fukuda K. , Misawa H.
Published: April 2011

An organic film of a few nm in thickness was applied as a resist for photolithography and scanning probe lithography. This resist film was prepared on an oxide-covered Si substrate through chemisorption and spontaneous organization of organosilane molecules, e.g., n-octadecyltrimethoxysilane. The film belongs to a class of materials referred to as self-assembled monolayer (SAM). A SAM/Si sample was irradiated through a photomask with vacuum ultraviolet (VUV) light at a wavelength of 172 nm. The photomask image was transferred to the SAM through the decomposition of the SAM. Furthermore, we demonstrate nano-scale patterning of the SAM using an atomic force microscope (AFM) with an electrically conductive probe. The SAM was electrochemically degraded in the region where the AFM probe had been scanned. Both the photo-printed and AFM-genereated patterns were successfully transferred into the Si substrates based on wet chemical etching or on dry plasma etching. At present, using these VUV and AFM-based lithographies, we have succeeded in fabricating minute features of 2 μm and 20 nm in width, respectively.
Improved Algorithm to Extract Force-distance Curves from Scanning Force Microscope Data
Authors: Eppell Steven J. , Todd Brian A. , Zypman Fredy R.
Published: April 2011

Physically meaningful near-surface force fields are used to calculate simulated scanning force microscope cantilever deflection data. The simulated data is used to evaluate the ability of a few models to calculate forces from cantilever deflections. The conventional simple harmonic oscillator model is shown to be significantly inaccurate in converting deflections to forces. A bending beam model is developed which accurately converts deflections to forces. This model is shown to be necessary for accurate assignment of physical meaning to the calculated forces under high force gradient conditions.
Ion Projection Lithography for Nano Patterning
Authors: Heuberger A. , Bruenger W.
Published: April 2011

As a result of continuous improvement of the resist process, the experimental ion projector in the Fraunhofer Institute in Berlin (manufactured by Ion Microfabrication Systems, IMS, Vienna) has been able to print 75 nm lines and spaces into 180 nm thick standard DUV resist UV II HS without pattern collapse. A new wafer flow process for more reliable open stencil mask making was developed by IMS –Chips, Stuttgart (Germany), based on SOT wafers. Resistless direct surface modification by He and Xe ions has been tested on metallic and magnetic films in the Berlin projector. This method opens up a new possibility for the production of patterned media for future magnetic storage disks.
Direct-write Electron Beam Lithography: History and State of the Art
Authors: Carr Dustin W. , Tiberio Richard C.
Published: April 2011

Direct-write electron beam lithography is a patterning technique that has rapidly evolved over the last 40 years. For many years it has been possible to use electrons to pattern lines with widths as narrow as 10 rum. Recent advances in resist materials, electron sources, and system integration have further enhanced the capabilities. High-sensitivity resists provide substantial increases in the throughput without sacrificing resolution. Thermal field-emission sources improve the stability and reduce the minimum attainable spot size. Modem lithography systems integrate the electron beam column with advanced control electronics, making a system capable of nanometer-scale placement accuracy. In addition to these improvements, the technology is more accessible now than ever before, thanks to the proliferation of lithography systems consisting of modified scanning electron microscopes.
Optimization of the Broadband Reflectance of Graded Multilayers for Hard X-Ray Mirrors
Authors: Ivana Adrian , Brunia Ricardo , Byuna Kyung , Gorensteina Paul , Romaine Suzanne
Published: April 2011

Multilayer structures with depth graded spacing can present a high reflectivity in a broad energy bandpass for hard X-rays (>20 keV) if the interface roughness/diffuseness is controlled and minimized. We present an optimization study of several multilayer systems deposited by DC magnetron sputtering on <111> silicon wafer substrates. The material combinations presented in this work are W/Si, W/C, Wsi2/Si, Pt/C, Ni/C, and Mo/Si.
Engineering the Interfacial Chemistry in Metal/Oxide Systems
Authors: PrüBner K. , Pint B. A. , Hou P. Y. , Alexandert K. B. , Tortorellit P. F.
Published: April 2011

Alloys designed for high-temperature applications need to form a protective oxide scale to withstand further degradation by oxidation. The importance of the interfacial chemistry for the adhesion of the protective scale was demonstrated in experiments with β-NiAl, iron-aluminides, NiCrAlYs and Ni-based superalloys. Interfaces between alloys both with and without thermal barrier coatings and their thermally grown alumina scales were studied as well as interfaces between alloys and deposited alumina coatings. It was found, that in all cases improved oxidation performance and scale adhesion could be achieved by doping the alloys with reactive elements. The improvement was shown to be due to interfacial segregation of the reactive element. Segregation of sulfur to internal interfaces on the other hand caused scale spallation.
Interface Multiplication Through the Combination of Interface and Lattice Diffusion-Controlled Transformations in Alloys
Authors: Solórzano I. G. , Cohn J. A. , Andrade R. M.
Published: April 2011

A procedure for obtaining interface and grain boundary multiplication, without externally applied deformation, in alloy systems is described. It is shown that an essential prerequisite is the occurrence of, and the possibility of controlling, discontinuous precipitation (DP) reactions in the alloy. Several alloy systems have been studied and experimentally generated, in a controlled volume fraction, DP lamellar products in the following model alloys: Al%Ag; Al-22at%Zn; Cu-7at%In and Ni-8at%Sn. The resulting microstructures have been observed in detail through conventional and analytical electron microscopy, confirming that DP is a transformation controlled by solute diffusion along moving grain boundaries. Although the precipitates correspond to the equilibrium phase, the transformation, as a whole, does not reach thermodynamic equilibrium since high-resolution microanalysis of aged and quenched microstructures reveal that a significant amount of supersaturation is retained in the depleted lamellar matrix. In addition, TEM observations have revealed that the DP product, besides generating a high density of interfaces, is able to incorporate a significant amount of strain energy. On the other hand, the dissolution of the lamellar microstructures has been observed to proceed in both continuous and discontinuous fashions. The former, dominating at high dissolution temperatures, is controlled by volume diffusion and gives rise to the development of new microstructures in the original DP colonies: the generation of dislocations and their dynamic re-arrangement into a cellular sub-structure in Al – base alloys; the formation of new grains, in Cu-In and in Ni-Sn alloys. Operating mechanism are proposed and the nature of the driving force for the observed phenomena is discussed in terms of its chemical, interfacial and strain energy components.
Interface Related Strength Phenomena in Two-Phase Titanium Aluminides
Authors: Christoph U. , Oehring M. , Appel F.
Published: April 2011

Phase equilibria and transformations in near-equiatomic titanium aluminides lead to the formation of a lamellar structure comprising of the intermetallic phases α2(Ti3Al) and γ(TiAl). Due to the differences in lattice parameters and crystal structure, coherency stresses and mismatch structures occur at various types of semicoherent interfaces present in the material. The present paper reports an electron microscope study of the atomic structure of the interfaces. The residual coherency stresses present at the interfaces were determined by analysing the curvature of dislocation loops which were emitted from the network of interfacial dislocations. The implication of these stresses on creep will be discussed.
Indentation-Induced Debonding of Ductile Films
Authors: Volinsky Alex A. , Clift W. Miles , Moody Neville R. , Gerberich William W.
Published: April 2011

Thin film adhesion can be measured by means of the nanoindentation technique [1]. In the case of a ductile film (Cu, Al, Au, etc.) well adhered to a brittle substrate, plastic deformation in the film acts as an energy dissipation mechanism, preventing film debonding. Depositing a brittle layer of W (about 1 micron thick) on top of the film of interest increases the driving force for delamination, thus solving the problem [2]. Indentation produces circular delaminations (blisters), sometimes two orders of magnitude bigger than the indenter contact radius. Thin film adhesion was shown to scale with the film thickness, approaching the true work of adhesion of 0.8 J/m2for Cu films less than 100 nm thick [3].

Conceptually it is important to know along what interface the fracture occurs during the blister formation. Auger electron spectroscopy (AES) has been used to determine where fracture occurs for different film systems. Cu films on SiO2failed along the Cu/SiO2interface. Fracture of Cu films with a 10 nm adhesion-promoting Ti underlayer occurred along the Ti/Cu interface. Significantly, Ti increased the thin Cu film adhesion by a factor of ten. Blisters were removed from the substrate, and the fracture surface was analyzed. In the case of thin Cu films, crack arrest (fiducial) marks were found upon blister removal, and represent the shape of the crack tip [4]. AFM has been used to determine the geometry of the marks. The main component of the arrest marks is carbon, which comes either from the diamond tip or from the hydrocarbons adsorbed on the newly formed surfaces in the indentation process.