bluuebunny/crossref_metadata_2025 huggingface dataset:
Preferred Orientation, Grain Sizes and Grain Boundaries of Chalcopyrite-Type Thin Films
Authors: Abou-Ras Daniel , Nichterwitz Melanie , Kaufmann Christian A. , Schorr Susan , Schock Hans-Werner
Published: April 2011

Chalcopyrite-type thin films - CuInS2, CuInSe2, CuGaSe2, and Cu(In,Ga)Se2 - in various completed solar cells were studied in cross-section by means of electron-backscatter diffraction (EBSD). Valuable information on grain sizes, local grain orientations, film textures, and grain boundaries were extracted from the EBSD linescans and maps. The grain-size distributions from the chalcopyrite-type thin films can be represented well by lognormal distribution functions. The EBSD measurements on CuGaSe2 thin film reveal a <110> fiber texture, in good agreement with x-ray diffraction texture analysis performed on the same sample. The EBSD maps from all samples studied exhibit considerable twinning in the chalcopyrite-type thin films. Indeed, the most frequent types of grain boundaries in these thin films are (near) Σ3 60°-<221> and 71°-<110> twins. It is shown that rotational 180°-<221> twins (which are symmetrically equivalent to 71°-<110>) are more frequently found than anion- or cation-terminated 60°-<221> twin boundaries.
Real-Time Investigations on the Formation of Cu(In,Ga)Se2 While Annealing Precursors Produced with a Combination of Sputtering and Thermal Evaporation
Authors: Jost Stefan , Hergert Frank , Hock Rainer , Purwins Michael
Published: April 2011

We have investigated the formation of Cu(In,Ga)Se2 thin films by real-time X-ray diffraction (XRD) experiments while annealing differently deposited and composed stacked elemental layer (SEL) precursors.

The in-situ measurements during the selenization of bi-layered Cu/In precursors reveal, that the semiconductor formation process is similar for precursors with thermally evaporated or sputtered indium. In both cases, the formation of binary copper and indium selenides is observed at temperatures around the melting point of selenium. After subsequent selenium transfer reactions, the chalcopyrite CuInSe2 is formed from the educt phases Cu2-xSe and InSe.

The addition of gallium leads to the formation of the intermetallic precursor phase Cu9Ga4, which reduces the overall amount of copper and gallium selenides at process temperatures above 500 K. This causes an ongoing selenization in the indium selenium subsystem, which results in the formation of CuInSe2 from the educt phases Cu2-xSe and the selenium richest indium selenide g-In2Se3.
Bandgap Engineering in Indium SulfideThin Films by Tin Mixing
Authors: Mathew Meril , Kartha C. Sudha , Vijayakumar K.P. , Elgin John , Hari Parameswar
Published: April 2011

In2S3 thin films appear to be a promising candidate for photovoltaic applications due to its stability, wide band gap and photosensitivity. The optical band gap value of Indium sulfide (In2S3) thin films reported in the literature varies from 2.0 eV to 2.4 eV following their synthesis process. These values are too small for an application as buffer layer in solar cells. In Present work, we report that incorporation of Sn using [SnCl4.5H2O] could increase the bandgap to wider ranges. In2S3/Sn thin films were deposited on soda lime glass substrate using chemical spray pyrolysis (CSP) technique. The spraying solution contained indium chloride (InCl3), thiourea [CS(NH2)2] and [SnCl4.5H2O]. Studies were done on films prepared using different Sn/In ratios. Depth profile using x-ray photoelectron spectroscopy showed that incorporation of Sn increased the concentration of oxygen in the samples. Band gap of the films increased with increase in Sn/In ratios. Depending on the ratios, bandgap could be varied from 2.72 eV to 3.78 eV. At lower mixing levels wide band gap low resistive In2S3/Sn films could be obtained which is highly useful for buffer layer applications. Low resistive buffer layer will decrease the series resistance of the cell and wider band gap will improve light transmission in the blue wavelength, both these factors help in increasing the short circuit current of the photovoltaic cell. Samples having higher Sn/In ratios showed wider band gap (up to3.78 eV).Though the samples had very high bandgap and high resistivity these samples were highly photosensitive [(IL-ID)/ID = 11,000]. The results proved that tin incorporation modified the band gap and electrical properties of the In2S3/Sn films favorably over wider ranges making it highly suitable for different optoelectronic applications.
Electron Spin Resonance and Ultra Violet (UV) Photoluminescence of Ge Implanted CuGaSe2 Thin Films Prepared by the CCSVT (Chemical Close-spaced Vapor Transport) Technique
Authors: Doka Serge , Hofstetter Jasmin , Rusu Marin , Arushanov Ernest , Klaus Lips , Schedel-Niedrig Thomas , Lux- Steiner Martha Ch.
Published: April 2011

Non-equilibrium ion implantation of Ge in p-type polycrystalline thin film CuGaSe2 (CGSe) prepared by Chemical Close-spaced Vapor Transport (CCSVT) has been performed with the goal to achieve n-type doping of this chalcopyrite semiconductor. Using Electron Spin Resonance (ESR) it is shown that Ge implantation induces a paramagnetic specie at g = 2.003. A model is proposed that assigns the ESR signal to electrons trapped by donor states that are electrically inactive. Moreover, UV photoluminescence of Ge implanted films has evidenced a new peak emission at 1.47 eV, which is resolved as a radiative recombination of a hole bound to the native copper vacancy and an electron bound to a deep donor with an ionization energy of ED =360±10 meV.
Influence of Deposition Parameters on the Morphology of CdTe Films and on the Performance of CdTe Solar Cells
Authors: Hädrich Mathias , Mack Sebastian , Metzner Heinrich , Reislöhner Udo , Witthuhn Wolfgang
Published: April 2011

For industrial CdTe solar cell production, thin, dense and pinhole-free films have to be deposited at high rates. Using a close-to-industrial close space sublimation (CSS) process, we deposited CdTe films at different temperatures and rates. The morphology of these films was analyzed by scanning electron microscopy (SEM) and x-ray diffraction (XRD). The measurements show the size, size distribution and orientation of the grains to strongly depend on deposition temperature and rate. A suitable combination of these parameters yields large grains of about 3 microns diameter even for deposition temperatures below 750 K and at high deposition rates of 3 microns per minute. The interplay of CdTe layer morphology and solar cell performance is elucidated employing a TCO-CdS-CdTe-Mo film sequence for complete solar cells.
Modelling of Nanoindentation of Compliant Layers on Stiffer Substrates using Finite Element Analysis
Authors: Clifford Charles A , Seah Martin P
Published: April 2011

Nanoindentation using an Atomic Force Microscope (AFM) or a nanoindenter was modelled using Finite Element Analysis (FEA). Force versus indentation depth data were taken for a system consisting of a compliant layer on a stiffer substrate. It was found that the FEA results may be expressed analytically by a simple function that describes the reduced modulus value obtained with Oliver and Pharr's method for any moduli values, thickness of layer or radius of the indenter tip. Initial results obtained by varying the Poisson's ratio of the layer and substrate are also presented.
Contribution of Solvothermal Processes to the Synthesis of Novel Nitrides and the Development of Shaping Processes
Authors: Demazeau Gerard , GOGLIO Graziella , LARGETEAU Alain
Published: April 2011

Solvothermal processes can be described as the reaction or the decomposition of precursor(s) in presence of a solvent in a close system at a temperature higher than the solvent boiling point. Consequently pressure parameter is involved. Such processes are mainly managed by two sets of parameters: (i) thermodynamical parameters and (ii) chemical parameters.

Solvothermal processes concern either supercritical or subcritical conditions, -homogeneous or heterogeneous systems, and thermodynamical parameters (P and T) play an important role. The main interest of solvothermal reactions is the improvement of the chemical reactivity, and in such a case the nature of the reagents and the physico-chemical properties of the solvent are important.

For the last 20 years, solvothermal processes have been developed in different research areas, such as:

- synthesis of new compounds (including in particular hybride systems),

- crystal growth of functional materials,

- preparation of nanocrystallites with well defined size and morphology,

- deposition of thin films,

- sintering in mild temperature conditions.

In particular, solvothermal reactions involve nitrides and derived materials either for preparing new compositions or shaping functional nitrides (single crystals, nanoparticles…).

In a first approach the synthesis of nitrides using solvothermal reactions will be described versus the nature of the precursors and the composition of the solvent. The nitriding process will be analyzed versus the chemical species, in particular N3−, N3−…Different illustrations will be described (transition metal nitrides, light elements-based nitrides…).

The second part will be devoted to the development of solvothermal processes for the preparation of single crystals or nanocrystallites.

As a conclusion, the potential developments of solvothermal nitriding processes either in basic research or industrial applications will be discussed.
Molecular Beam Epitaxy of Nonpolar Cubic AlxGa1−xN/GaN Epilayers
Authors: As Donat , Potthast Stefan , Schoermann Joerg , Tschumak Elena , de Godoy Marcio F. , Lischka Klaus
Published: April 2011

Cubic AlxGa1-xN films were grown by molecular beam epitaxy on freestanding 3C-SiC (001) substrates with an Al mole fraction of x=0 to 0.74. Using the intensity of a reflected high energy electron beam as a probe we find optimum growth conditions of c-AlGaN when a one-monolayer gallium coverage is formed at the growing surface. Clear reflection high energy electron diffraction oscillations during the initial growth of AlxGa1-xN/GaN layers were observed. The growth rate was about 177 nm/h. We find that the aluminium mole fraction is only determined by the aluminium flux, and that the AlxGa1-xN growth rate is independent on the aluminium content. Atomic force microscopy exhibits smooth surfaces with a RMS roughness of about 5 nm on 5×5 µm2 areas. Cathodoluminescence spectroscopy revealed clear band edge emission up to an aluminium mole fraction of x=0.52, showing a linear relation between the band gap energy and the Al composition.
Shock Wave Synthesis and Exploration of High-pressure Nitrides and Related Materials
Authors: Sekine Toshimori
Published: April 2011

We have successfully developed a method to manufacture spinel-type Si3N4 and also a chemical treatment method to separate the spinel-type phase from the low-pressure phases. Similar methods could be applied for the SiAlON systems. In order to explore high-pressure nitrides and oxynitrides, we extended toward the system Si3N4-AlN-Al2O3- SiO2. According to the results of in situ measurements of the high-pressure behavior up to pressures of 200 GPa, there appears to be post-spinel phase in the system. This is consistent with the results from the first principles calculations. However we could not obtain the post-spinel phase by the shock recovery experiments at present. We also carried out shock recovery experiments on carbon nitrides and related materials. Experimental results showed formation of a new carbon nitride, high stability of melamine up to a shock pressure of 37 GPa, and production of amorphous C-N materials with a highest N/C ration of 1.26 from the reaction between carbon tetrahalide and sodium dicyanoamide. We tried further to extend toward the systems C3N4-Si3N4 and Mg2SiO4-Si3N4, after taking into account the results on shock synthesis of spinel-type nitrides.
Characterization of Spectral Emissions from Laser Irradiated Titanium
Authors: Akarapu Ravindra Kumar , Dua Puneit , Campbell Alan , Scott Dana , Nassar Abdalla , Todd Judith , Copley Stephen
Published: April 2011

Titanium nitride (TiN) is a candidate material for hard and wear resistant coatings on metallic substrates such as titanium (Ti), stainless steel and aluminum. Coating processes include chemical vapor deposition, ion implantation, plasma and thermal nitriding under vacuum and controlled environments. The motivation for the present research is to develop a laser plasma process for high rate formation of TiN coatings on Ti substrates at near-atmospheric pressures. Laser induced plasma generated by a pulsed CO2 laser was used to excite a Ti substrate. The species in the vapor plume were characterized by optical emission spectroscopy. Spatially and temporally resolved spectral characterization was performed as a function of laser power, position of the substrate relative to the focal plane, pulse parameters, and shielding gases. These experiments are a first step in understanding laser assisted plasma deposition of nitride/oxy-nitride coatings on titanium metal under atmospheric conditions. Results indicate a window of optimal process parameters for developing titanium nitride coatings.
Mn charge states in GaMnN as a function of Mn concentration and co-doping
Authors: Malguth Enno , Hoffmann Axel , Gehlhoff Wolfgang , Kane Matthew H. , Ferguson Ian T.
Published: April 2011

In the context of the pursuit of a dilute magnetic semiconductor for spintronic applications, a set of GaMnN samples with varying Mn concentration and Si or Mg co-doping was investigated by optical and electron spin resonance spectroscopy. The results clearly demonstrate how the charge state of Mn is changed between 2+, 3+ and 4+ by Mg and Si co-doping. For p-type GaMnN we show that the introduction of the Mn3+/4+ donor can be compensated by Mg co-doping lowering the Fermi energy below the Mn3+/4+ level. While our results are in agreement with the hypothesis that the infrared photoluminescence appearing in GaMnN upon Mg doping originates from Mn4+, an unambiguous proof is still to be presented. Under this assumption, our measurements show that the Mn4+ center must be excited via an extra-center process at 2.54 eV.
Thermal Volatilisation Analysis – The Development of a Novel Technique for the Analysis of Conservation Artifacts
Authors: Lewicki James Pawel , Todd Deborah , Redon Perrine , Liggat John , Gibson Lorraine
Published: April 2011

Reported here is the development of a novel evolved gas analysis technique; Sub-Ambient Thermal Volatilization Analysis (SATVA) and its application in characterizing key analyte species from conservation artifacts. In this work SATVA has been applied to the study of volatiles evolution processes occurring in number of model conservation artifacts. The evolution of volatile species from cured formaldehyde resin, leather and metallic artifacts has been studied by SATVA. The specific analytes making up the total quantity of evolved material in each case have been separated and identified using sub-ambient differential distillation and a combination of online mass spectrometry, gas phase IR spectroscopy and GC-MS. The data gathered has been used to provide information on both the degradation processes occurring within the artifacts and the environmental history of the artifacts themselves.
Plasma-enhanced chemical vapor deposition of carbon nanotubes using alcohol vapor
Authors: Okita Atsushi , Suda Yoshiyuki , Maekawa Masayuki , Takayama Junichi , Oda Akinori , Sugawara Hirotake , Sakai Yosuke
Published: April 2011

We have successfully grown carbon nanotubes (CNTs) by alcohol plasma-enhanced chemical vapor deposition (PECVD). When 0.01 wt% ferrocene was added to alcohol, vertically-aligned CNTs could be grown using RF (= 13.56 MHz) plasma at 650°C. In contrast, no CNTs were obtained by pure alcohol PECVD. To understand the plasma properties for CNT growth, especially plasma species containing a gas phase of alcohol plasma, we analyzed the plasma using optical emission spectroscopy (OES) and quadrupole mass spectrometry (QMS). From the OES measurement, one could identify the emission peaks from the excitation states of CHO, CO, C2, O2, H, CH+, and H2O+, while the QMS measurement also showed the existence of CO, H2O, and CxHy (x≥2, y≥2). It is considered that such plasma species affect CNT growth by changing the oxidation state of the catalyst or by adjusting the amount of precursor species in the plasma. Comparing this PECVD experiment with thermal alcohol CVD (without plasma), only PECVD can be used to grow CNTs under the reported experimental conditions. It is considered that thermal alcohol CVD requires more energy to grow CNTs because 650°C is a little lower than the temperature required for CNT growth. These results indicate that in alcohol plasma, the active species produced by decomposition and recombination reactions have a possibility to promote/suppress CNT growth depending on the process conditions.
Rosette Nanotubes: Factors Affecting the Self-assembly of the Monobases Versus the Twin Base System
Authors: Hemraz Usha , Fenniri Hicham
Published: April 2011

Rosette Nanotubes (RNTs) are formed by the self-assembly of a guanine-cytosine motif (GΛC), a hybrid of the DNA bases guanine and cytosine, to give a six membered macrocycle maintained by 18 H-bonds. In theory, any moiety covalently attached to the GΛC base can be expressed on the nanotubes surface. However we anticipate that the self-assembly and stability of these functionalised RNTs will also be governed by steric effects. Herein we describe the synthesis and the self assembly of the Twin Base Lysine (TBL-K) and its monobase (MBL-K). While TBL-K self-assembles readily in water and methanol to give nanotubular structures, MBL-K does not form nanotubes. Various techniques were used to characterize the RNTs and the factors, preventing self-assembly in the case of MBL-K, were investigated.
Engineered large area fabrication of ordered InGaAs-GaAs nanotube arrays
Authors: Chun Ik Su , Verma Varun B , Li Xiuling
Published: April 2011

Strain induced self-rolling semiconductor micro and nanotubes and related structures represent a new class of building blocks of nanotechnology. They are formed when strained planar bilayers are released from the substrate by selectively removing the sacrificial layer. Compared to other nanotechnology building blocks, one of the main advantages is the precise positioning capability due to top down fabrication approach. In this article, we demonstrate the fabrication of perfectly aligned arrays of InGaAs/GaAs nanotubes and the dispersion of freestanding semiconductor nanotubes into solution and onto foreign substrates. In addition, we systematically investigate the crystal orientation dependence of the rolling direction by using a wheel configuration. Other aspects of formation process are also discussed.
Self-assembly of Silicon Nanotubes
Authors: Xie Ming , Wang Jiesheng , Lee Chee Huei , Yap Yoke Khin
Published: April 2011

The growth of silicon nanotubes (SiNTs) by a dual-RF-plasma treatment technique is reported here. These SiNTs are vertically aligned and self-assembled from Si substrates at 500 degree Celsius by the use of Cu catalysts. Their diameters are ∼50 to 80 nm with tubular wall thickness of ∼10-15nm. Cu vapors were found partially filled inside the SiNTs. This is a novel technique that can convert bulk materials into their nanostructures.
Low Temperature Synthesis of Carbon Nanotube on Si substrate Using Alcohol Gas Source in High Vacuum
Authors: Maruyama Takahiro , Tanioku Kenji , Naritsuka Shigeya
Published: April 2011

Conventional alcohol catalytic chemical vapor deposition (ACCVD) growth of carbon nanotubes (CNTs) have been carried out under ambient gases from 103 to105 Pa. These ambient gas pressures have prevented in situ observations using an electron beam during CNT growth, such as scanning electron microscopy (SEM), scanning tunneling microscopy (STM). Therefore, in order to realize the in situ observations and to clarify the growth mechanism of nanotube, CNT growth in a high vacuum is essential. In addition, the effects of residual gases also may be avoided in the growth under high vacuum. In this study, we carried out CNT growth under high vacuum using an alcohol gas source in an ultrahigh vacuum (UHV) chamber and we achieved CNT growth below 400°C without any excitation processes of carbon source. After deposition of Co catalyst of 1 nm in thickness on SiO2/Si substrate, ethanol gas was supplied to the substrate surface through a stainless steel nozzle in the UHV chamber. The growth temperature was monitored by a pyrometer during the growth, and set between 350 and 900°C. The supply of ethanol gas was controlled by monitoring an ambient pressure, which was varied from 1 ∼10-1 to 1 ∼10-4 Pa. The grown CNTs were characterized by SEM and Raman spectroscopy. The G/Si intensity ratio reached its maximum at 700°C, when the pressure was 1 ∼10-1 Pa. The maximum point of the G/Si peak intensity shifted to a lower temperature as the growth pressure decreased. When the pressure was 1 ∼10-4 Pa, the G/Si intensity ratio reached its maximum at 400°C, at which clear RBM peaks were observed in the Raman spectrum. From the RBM peaks, the CNT diameters were estimated to be between 0.9 to 1.7 nm, and CNTs of 1.2-1.4 nm in diameter were dominant at 1 ∼10-1 Pa, whereas thinner CNTs (diameter is below 1.0 nm) were increased with the reduction of the pressure. Our largest G/D ratio was about 40 for the sample grown at 1 ∼10-1 Pa, which is considerably larger than the reported value for the CNTs grown under low pressure. From these results, we conclude that the reduction of the growth pressure lowers the growth temperature. This technique can be applied to in situ observation, and may also be useful for low temperature growth of CNTs, which opens new possibilities for the fabrication of CNT based nanodevices.
Influence of Nanotubes and Other Nanofillers on the Properties of Thermoset:thermoplastic Blends for Composite Matrices
Authors: Kilbride Marianne , Pethrick Richard Arthur , Ward Steven , Harriman Mark
Published: April 2011

Recently there has been an increase in the use of composite materials for aircraft construction. Composites have significant production and application advantages, but generally suffer from being electrically insulating, and hence are unable to handle a lightening strike in the traditional way that aluminium would. A potential solution to this problem is sought through the use of carbon nanotubes and carbon nanographite. Achieving the correct dispersion of the conducting filler is critical to achieving the desired enhancement in conductivity. Two different methods have been explored to achieve the dispersions; – direct blending and solution dispersion, with a range of concentrations of nanographite being incorporated. In addition, the effect of directly blending graphite nanoplatelets and carbon nanotubes in order to create a hybrid nanocomposite material was studied. The carbon nanotubes were incorporated into a blend with the graphite nanoplatelets with the intention of utilizing their tube structure in order to bridge the gaps between the platelet sheets of nanographite, creating more effective and abundant conductive pathways throughout the composite. In all cases the electrical conductivity was measured using a four point probe technique.
A Study of Conformal GaAs on Si Layers by Micro-Raman and Spectral Imaging Cathodoluminescence
Authors: Martínez Oscar , Sanz Luis Felipe , Jiménez Juan , Gérard Bruno , Gil-Lafon Evelyn
Published: April 2011

Spectral imaging cathodoluminescence and micro-Raman spectroscopy studies of GaAs layers grown on Si substrates by the conformal method allow to reveal a great variety of physical features of the layers, such as the complete stress distribution, self-doping effects, or the incorporation of dopants. We present herein the characterization of GaAs conformal layers grown by hydride vapor phase epitaxy, where the main issues concerning the distribution of defects and stresses are revealed. Also, intentionally doped layers were analyzed, revealing the main aspects of the incorporation of dopant impurities during growth.
Simulation of Forescattered Electron Channeling Contrast Imaging of Threading Dislocations Penetrating SiC Surfaces
Authors: Twigg Mark E. , Picard Yoosuf N. , Caldwell Joshua D. , Eddy Charles R. , Neudeck Philip G. , Trunek Andrew J. , Powell J. Anthony
Published: April 2011

The interpretation of ECCI images in the forescattered geometry presents a more complex diffraction configuration than that encountered in the backscattered geometry. Determining the Kikuchi line that is the primary source of image intensity often requires more than simple inspection of the electron-channeling pattern. This problem can be addressed, however, by comparing recorded ECCI images of threading screw dislocations in 4H-SiC with simulated images. An ECCI image of this dislocation is found to give the orientation of the dominant Kikuchi line, greatly simplifying the determination of the diffraction simulation. In addition, computed images of threading screw dislocations in 4H-SiC were found to exhibit channeling contrast essentially identical to that obtained experimentally by ECCI and allowing determination of the dislocation Burgers vector.
MOVPE Growth and Characterization of AlInN FET Structures on Si(111)
Authors: Hums Christoph , Gadanecz Aniko , Dadgar Armin , Bläsing Jürgen , Witte Hartmut , Hempel Thomas , Dietz Annette , Lorenz Pierre , Krischok Stefan , Schaefer Jürgen Alois , Christen Jürgen , Krost Alois
Published: April 2011

In this work metalorganic chemical vapor phase epitaxy (MOVPE) growth and characterization of AlInN in the whole compositional range and the impact on the development of field effects transistors (FET) structures will be presented. Due to the large difference in the lattice parameters of the binaries AlN and InN the growth of AlInN with high indium concentrations is ambitious, and first the growth conditions for the alloy will be discussed. An experimental phase diagram and corresponding theoretical calculations will be displayed. The critical layer thickness of AlInN on GaN has been experimentally determined. Relaxation of the AlInN-layer has a strong influence on the sample morphology. At indium concentration exceeding 30% an polarization induced hole gas is expected at the AlInN/GaN interface from theoretical calculations, but no p-channel conductivity could be confirmed. The absence of the two dimensional hole gas will be discussed.
Impact of the High-Temperature Process Steps on the HfAlO Interpoly Dielectric Stacks for Nonvolatile Memory Applications
Authors: Ruiz Aguado Daniel , Govoreanu Bogdan , Favia Paola , De Meyer Kristin , Van Houdt Jan
Published: April 2011

This work reports on the performance of different Hafmiun aluminate (HfAlOx)-based interpoly dielectrics (IPD) for future sub-45nm nonvolatile memory (NVM) technologies. The impact of the thermal budget during the fabrication process is studied. The good retention and large operating window shown by this material, can be compromised by a high temperature activation anneal (AA) after the gate deposition. The AA step may induce phase segregation of the HfAlOxand outdiffusion of the Hf (Al) towards the floating gate/IPD and IPD/gate interfaces and subsequent formation of Hf (Al) silicates. These findings are supported by the low field leakage analysis, which shows large device to device dispersions. However, the effect of the spike anneal can be minimized if the HfAlOxlayer is crystallized prior to the AA. Devices with polysilicon or TiN gate are compared in terms of memory performance and reliability.
Ferroelectric and Electrical Properties of BaZrO3 Doped Sr0.8Bi2.2Ta2O9 Thin Films
Authors: Bozgeyik Mehmet S. , Cross J. S. , Ishiwara H. , Shinozaki K.
Published: April 2011

BaZrO3 (BZO) doped Sr0.8Bi2.2Ta2O9 (SBT), a new modified SBT, thin films were prepared and related ferroelectric and electrical properties were evaluated.
Organic Single Crystal Transistors Gated by Electric Double Layers in Ionic Liquid
Authors: Hirahara R. , Ono S. , Seki S. , Tominari Y. , Takeya J.
Published: April 2011

Gating organic transistors with electric double layers (EDL) of electrolytes is advantageous in injecting high-density carriers with the application of minimum gate voltage. The drawback of such devices, however, has been that commonly used polymer electrolytes suffer relatively slow ionic diffusion before forming the EDLs. In this report, we disclose a new class of EDL devices incorporating low-viscosity room temperature ionic liquid as the electrolyte layer, so that the rapid ionic diffusion allows MHz operation for the transistor performance. We fabricate a well structure using an elastomeric rubber stamp of poly-dimethylsiloxane to hold the ionic liquid 1-ethyl 3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide, known for high ionic conductivity. The transistor performs without hysteresis with the carrier mobility of 5 cm2V−1s−1, realizing the highest sheet transconductance ever achieved.
Synthesis and Characterization of Structured Metal/Silica Clusters
Authors: Patil A.N. , Otsuka N. , Andres R.P.
Published: April 2011

The synthesis of two component clusters of Au/SiO2, Ag/SiO2 and Cu2O/SiO2 is described. These heteronuclear clusters are synthesized as metal/silicon clusters of controlled composition and controlled size using a novel gas aggregation source and by means of gas phase annealing are transformed into ‘structured’ particles. The final metal/oxide and oxide/oxide clusters are formed by air exposure. The structure of these nanostructured particles is determined by electron diffraction and transmission electron microscopy (TEM). The clusters exhibit two distinct structural forms: (1) clusters consisting of a metal rich core surrounded by a silicon rich skin and (2) clusters having a metal rich domain and a silicon rich domain separated by a sharp interface.
Tem Studies on the Morphology, Size Distribution and Structure of Nanocrystalline Iron Particles Using a Formvar Embedded Preparation Technique
Authors: Ni Hengfei , Bi Xiangxin , Stencel John M.
Published: April 2011

A new, simple and effective method was developed for preparing specimens of Fecarbide ultrafine particles (UFP), by suspending them in Formvar films. Various samples of Fe-carbide UFP's were obtained by a laser pyrolysis process by varying the process parameters. The UFP samples were mixed with different concentrations of Formvar in ethylene dichloride solution. The sample particles were embedded in ultra-thin Formvar films with thickness of 20 nm or more and mounted on the 200 mesh copper TEM grids. The influences of the concentration of the Formvar solution and the amount of sample powder on the UFP distribution in the micrographs were investigated to determine the optimal film-making parameters. The different sizes and same spherical morphology for the various UFP samples were revealed, indicating the main diameters to be between 5–20 nm. Compared with the size values obtained by using XRD, the UFP size measurements by the new process are in good agreement. The crystalline features and the surface of the UFP's are presented and confirmed by micro-diffraction studies.
Challenges and Opportunities in Magnetic Resonance Force Microscopy
Authors: Sidles John A. , Garbini Joseph L.
Published: April 2011

Recently the first experiments in magnetic resonance force microscopy (MRFM) have been conducted. In these experiments a force microscope cantilever is used to detect the magnetic force exerted by electrons and nuclei in a sample. The magnetization of the sample is modulated at the resonant frequency of the cantilever, using standard magnetic resonance techniques. The resulting excitation of the cantilever is detected optically. This article reviews the present status of MRFM technology, emphasizing the physical principles involved and the opportunities for further research and development. Particular emphasis is placed on single spin detection by MRFM and potential applications in biomolecular imaging.
Microstructural Imaging of Localized Chemical Reactions using Valence Photoelectrons
Authors: Liang S. , Ray-Chaudhuri A.K. , Ng W. , Cerrina F.
Published: April 2011

We have utilized scanning soft X-ray photoelectron spectromicroscopy-MAXIMUM to investigate the microstructural evolution induced by localized corrosion in the Al-Cu-Si alloy thin films. We present energy-specific photoelectron micrographs showing the distribution of Cu-rich precipitates and corrosion products for the thin films after corrosion. Microspectroscopy performed across a corrosion site reveals that the O 2p valence band shifts in energy with location and the amount of shift can be related to the degree of corrosion. The photoelectron micrographs also show that the Cu-rich phase precipitates near the surface region and grows with annealing temperature.
Electromigration Characteristics of Cu and Al Interconnections
Authors: Shingubara S. , Fujiki K. , Sano A. , Sakaue H. , Horiike Y.
Published: April 2011

Electromigration activation energies (Ea) of Al and Cu interconnections are strongly dependent on the grain boundary morphology, and it is pointed out that Ea of bamboo-like Al interconnection is not less than Ea of small grain Cu interconnections. Small resistance oscillatory changes caused by electromigration, which are classified into three categories; oscillation, downward spikes, and upward spikes, are investigated in detail. It seems most likely that oscillations correspond to annihilation and formation of the one void. It is also pointed out that downward spikes are local, while upward spikes are non-local. Dislocation dynamics such as generation, rapid transport and subsequent annihilation are considered to be origins of spikes.
Measurement of Adhesion at Film -Substrate Interfaces by Constant Depth Scratch Testing
Authors: Dutta I. , Lascurain D. P. , Secor E. D.
Published: April 2011

Quantitative tests for interfacial adhesion between films and substrates are of criticalimportance in micro-electronic applications. However, many of the available tests are applicable to a limited array of materials systems, or are experimentally complex. In thispaper, a constant depth scratch test, which has been designed to circumvent the limitations associated with currently available tests, is presented along with theoretical developments for the quantification of interfacial shear strength. Because of a fixed scratchgeometry, the test is amenable to straightforward analytical formulations unlike other versions of scratch tests. It is unique in its experimental simplicity, and allows evaluation of interface strength as function of position on the sample. Sample outputs from the test based on Cr films on glass substrates are presented.
Excess Conductance of MOS Diodes Suffered Current Stress and Elucidation of Induced Interface States
Authors: Inoue Masao , Shirafuji Junji
Published: April 2011

The ac conductance-voltage (G–V) characteristics at various frequencies have been measured in MOS diodes which suffered constant current stress by Fowler–Nordheim (F–N) electron injection from Si substrate.It is found that a double-peak structure appears in G–V curve and grows continuously with proceeded current stress.The growth of two kinds of interface states is elucidated after subtracting the effect of oxide capacitance and substrate resistance by a simple equivalent circuit analysis.
Epitaxial Solid-Solution Films of Immiscible MgO and CaO
Authors: Hellman E. S. , Hartford E. H.
Published: April 2011

Metastable solid-solutions in the MgO-CaO system grow readily on MgO at 300°C by molecular beam epitaxy. We observe RHEED oscillations indicating a layer-by-layer growth mode; in-plane orientation can be described by the Matthews theory of island rotations. Although some films start to unmix at 500°C, others have been observed to be stable up to 900°C. The Mgl-xCaxO solid solutions grow despite a larger miscibility gap in this system than in any system for which epitaxial solid solutions have been grown. We describe attempts to use these materials as adjustable-lattice constant epitaxial building blocks
Implications of Interfacial Coupling and Strain on the Magnetic and Structural Ordering of Fe3O4/NiO Superlattices
Authors: Lind David M.
Published: April 2011

Here we review recent work on the preparation and characterization of magnetically ordered oxide Fe3O4/NiO superlattices. The materials were prepared by oxygen plasma-assisted molecular beam epitaxy. Their structural ordering was studied by x-ray, neutron, and RHEED electron diffraction techniques, and the superlattices are found to form as highly coherent strained-layer modulated single crystals. The magnetic ordering studies, using SQUID magnetometry, ferromagnetic resonance, and neutron diffraction, indicated strong interfacial coupling between the ferrimagnetic Fe3O4 layers and the antiferromagnetic NiO layers, with the magnetic ordering in each layer altered by the proximity to the magnetic moments in the adjacent layer. Strain and other layer-thickness effects are also evident in these magnetic layered structures. The special influence of interlayer coupling and strain on the Fe3O4 Verwey transition are discussed.
Microstructural Studies of Ferroelectric Bi2VO5.5 Thin Films With LaNiO3 Electrodes
Authors: Beesabathina D. Prasad , Salmanca-Riba L. , Hegde M. S. , Satyalakshmi K. M. , Prasad K. V. R. , Varma K. B. R.
Published: April 2011

Thin films of Bi2VO5.5 (BVO), a vanadium analog of the n = I member of the Aurivillius family, have been prepared by pulsed laser deposition. The BVO films grow along the [001] direction on LaNiO3(LNO) and YBa2Cu3O7 (YBCO) electrode buffer layers on LaA- IO3(LAO) substrates as obtained from X-ray diffraction studies. The microstructure of the films and of the interfaces within the film and between the film and the substrate were characterized using transmission electron microscopy. The in-plane epitaxial relationship of the rhombohedral LNO on perovskite LAO was [100] LNO // [100] LAO and [001] LNO // [001] LAO. High resolution lattice images showed a sharp interface between LNO and LAO. However, the LNO film is twinned with a preferred orientation along the growth direction. The BVO layer is single crystalline on both LNO/LAO and YBCO/LAO with the caxis parallel to the growth direction except for a thin layer of about 400 Å at the interface which is polycrystalline.
Silicon Oxynitride and Oxide-Nitride-Oxide Gate Dielectrics by Combined Plasma-Rapid Thermal Processing
Authors: Ma Y. , Hattangady S.V. , Yasuda T. , Niimi H. , Gandhi S. , Lucovsky G.
Published: April 2011

We have used a combination of plasma and rapid thermal processing for the formation of thin gate-dielectric films. The bulk dielectric films investigated include silicon oxide, oxynitride and multilayer oxide-nitride-oxide heterostructures formed by plasma-assisted oxidation, remoteplasma-enhanced chemical-vapor deposition (remote-PECVD) followed by post-deposition rapid thermal annealing (RTA). Auger electron spectroscopy (AES) and infrared absorption spectroscopy (IR) have been used to study the chemistry of interface formation and the bulk dielectric chemical bonding, respectively. Electrical characterization of MOS capacitor structures incorporating these dielectrics was performed by conventional capacitance and current voltage techniques, C-V and I-V, respectively.
In-Situ Multiprocessing of Ultrathin Silicon Nitride Capacitors for Advanced Dram Cells
Authors: Thakur Randhir P.S. , Hawthorne Rick , Mathews Viju K. , Fazan Pierre C. , Werkhoven Chris J. , Granneman Ernst , Wilhelm Rudy
Published: April 2011

Ultrathin silicon nitride capacitors were fabricated using in-situ multiprocessing technology. In this paper we present comparative studies of capacitor formation using standard furnace processing, rapid thermal processing (RTP), and cluster tool processing of ONO dielectric films. We show that, due to better interface control using cluster tool processing, higher capacitance can be obtained for a fixed leakage level for the same thickness of dielectric film when compared to furnace and rapid thermal processing. We discuss the structural and electrical properties of these films and show that, due to an oxide-free interface, the improved film quality results in lower leakage current density and higher reliability.
Ripple Pyrometry for Rapid Thermal Annealing
Authors: Fiory A. T. , Nanda A.K.
Published: April 2011

Ripple pyrometry was proposed by Accufiber as a method for measuring wafer temperature in lamp-heated ovens. The technique obtains the wafer temperature from the wafer emittance radiation by simultaneously determining the effective emittance of the wafer and suppressing the interference from reflected lamp radiation. This paper reviews the technique for rapid thermal annealing and presents experimental results on silicon wafers instrumented with thermocouples and on processing blanket-film monitor wafers.
Optical Properties of Thermally Oxidized Silicon
Authors: Russo O.L. , Ravindra N.M. , Grow J.M. , Dumas K.A.
Published: April 2011

The effect of furnace grown SiO2 layers on the optical properties of p- on p+ (100) Si substrates are investigated. The real part, n, of the complex refractive index n* = n + ik is calculated for radiation measured in the infra-red (IR) region between 3000 and 8000 cm−1 where the extinction coefficient, k, is negligible. The expression for n is obtained using the Fresnel coefficients for a three medium air-oxide-Si model. Strain in the silicon, which affects n, and caused by the stress in the SiO2 layer, increases with oxide thickness. X-ray diffraction (XRD) was used to measure the strain in Si for oxides layers ranging from native to 5124Å. The data showed a monotonically increasing normal compressive strain, εN (up to 0.47%) with oxide thickness, however, the corresponding change in n due to strain was not well defined. The effect of strain on the direct optical gap, Ed, at 3.46 eV when determined from results of other investigators by electroreflectance, suggests an average shift in Ed of about 25 meV.
Tunneling Current in Thin Silicon Dioxide Films
Authors: Zafar Sufi , Poler J. C. , Irene E. A. , Xu X. , Haines G. , Kuehn R. , Wortman J. J.
Published: April 2011

Tunneling currents through thin silicon dioxide films on p-type silicon are measured at electric fields greater than 5 MV/cm. At the onset of the Fowler-Nordheim tunneling, oscillations in the current are observed. These oscillations are used for characterizing oxide films grown by three different processes: rapid thermal chemical vapor deposition, rapid thermal oxidation and thermal oxidation. We have explored the correlation between the oscillatory tunneling currents and the breakdown fields, and find a low field dc component to correlate with the breakdown fields and obscure the oscillations.
Electrical Activation of Boron in B+ + C+ Implanted Si during RTA with Different Heating Rates
Authors: Boudinov H. , Souza J.P. de
Published: April 2011

Silicon samples were single implanted with B+ (5 x 1014 cm−2, 50 keV) or co-implanted with C+ (5 x 1015 cm−2, 55 keV). Rapid thermal annealing (RTA) with heating rates (HR) of 1°C/s and 100°C/s with dwell time duration from 2 s to 15 min was used for B activation and the results compared with those provided by conventional furnace annealing (FA) for 30 min. In single implanted samples it was found that below 600°C or above 800°C the activation always increases with the annealing time. However, in the temperature range of 600-800°C and annealing times longer than 60 s a fraction of the initially activated B concentration deactivates. For temperatures in the range of 700-800°C the deactivation is followed again by another activation period. There is no noticeable difference between the activation yields after RTA with high HR for 15 min or FA for 30 min. In the C co-implanted samples the activation of boron saturates after few minutes. In addition the deactivation process is significantly reduced. A model assuming interaction of the B atoms with point defects and the C atoms with Si self- interstitial atoms is proposed to explain the results.
RTP Modeling for CVD and Thermal Oxidation
Authors: Sorrell F.Y. , Fordham M.J. , Yu Seungil , Neto A.J. Silva
Published: April 2011

A methodology for predicting the spatial and temporal distribution of film thickness is given for Chemical Vapor Deposition (CVD), and for thermal oxidation in Rapid Thermal Processor (RTP) systems, e.g. RTPCVD and RTO. The methodology is based on a wafer thermal model for the heat transfer to, from and within the wafer, a geometric ray trace algorithm to predict the radiant heat transfer from the lamps and reflectors to the wafer, a process model for the deposition or oxidation, and a gas flow model to predict the flow field in the RTP chamber. The CVD process is based on the Arrhenius deposition model, and thermal oxidation is based on a parallel diffusion model. The methodology has been validated by comparison of measured and predicted final film thickness from a cylindrical RTP system. The methodology is based on physical principles, with a minimum reliance on empirical relations and experimental data. As such it can be used for optimization of existing RTP designs and for the evaluation of proposed RTP configurations, such as new or novel lamp, reflector or chamber geometry.
In-Situ Doped Multi-Layer Epitaxial Structures with Abrupt Doping Transitions by Ultra High Vacuum Rapid Thermal Chemical Vapor Deposition (UHV-RTCVD)
Authors: ÅztÖjrk Mehmet C. , Muhsin S. , Ban Ibrahim , Harris Gari , Sanganeria Mahesh K. , Violette Katherine E. , Lee Archie
Published: April 2011

In this work, we have studied boron doped multi-layer epitaxial structures as active regions of deep submicron (< 0.25 gtm)metal oxide silicon field effect transistors (MOSFETs).The structures were formed by ultra high vacuum chemical vapor deposition (UHV-RTCVD) using Si2H6 and B2H6 as the source gases and H2 as the carrier gas at 750°C - 800°C and at a total pressure of 80 mTorr. With the high growth rates provided by Si2H6, thermal budgets were kept below the limit of boron diffusion in Si resulting in extremely abrupt doping transitions pushing the depth resolution limits of secondary ion mass spectroscopy. The structures consist of three epitaxial layers with thicknesses ranging from 100 A to 625 T. The top layer on which the gate oxide is formed is lightly doped (lxl016 cm-3) to minimize vertical electrical field and ionized impurity scattering for higher MOSFET channel mobility. The second layer is doped to lx1018 cm-3 for suppression of punchthrough short channel effects and finally the third layer is doped to lx 1017 cm-3 to decrease the parasitic source/drain junction capacitance that will result from the relatively high doping density of the intermediate layer. To minimize dopant diffusion in Si, low temperature (or low thermal budget) processes were employed for gate oxidation and polysilicon implant activation. A typical source/drain activation anneal was also included in sample preparation in order to simulate complete MOSFET fabrication assuming remaining steps could be carried out at lower temperatures with little contribution to dopant diffusion. Our results indicate that after all process steps a lightly doped region can still be obtained under the gate oxide with sufficient thickness to contain the MOSFET inversion layer. In these structures, the threshold voltage is determined by the doping density and thickness of the top two layers and can be easily tailored to the desired value by optimizing these parameters. With the range of parameters used in this study, our measurements show threshold voltages within the range desired for 0.1 µm MOSFETs.