bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of Twinning Elements in PST TiAl Single Crystal
Authors: Lu Lei , Pope David P.
Published: April 2011

Twinning is the major deformation mode at room temperature in TiAl polysynthetically twinned (PST) crystals (lamellar structure, TiAl is the major phase and Ti3Al is the minor phase). We present here the results of Atomic Force Microscope (AFM) observations of deformation twinning displacements measured on the free surfaces of PST single crystals. AFM is used in this experiment because of its very high resolution for topological measurements and its ability to measure surface displacements from very small twins.

Measurements were made on samples with different compression axes and surface orientations. When a twin intersects a free surface, a definite displacement is produced which is easily related to the twinning elements. The majority of the surface offsets observed correspond to those for ordinary twinning, within a very small deviation. Thus it is concluded that these are ordinary twins. The widths of the twinning bands are around 300nm, smaller than the widths of the TiAl lamellae. Slip bands are also observed. They are characterized by a much more irregular geometry than the twinning bands. At some places where twins intersect a domain boundary slip bands are produced in the adjacent domain.
Effect of Prestraining on the Brittle-To-Ductile Transition of NiAl Single Crystals
Authors: Shrivastava S. , Ebrahimi F.
Published: April 2011

The brittle-to-ductile transition (BDT) has been established for NiAl single crystals as evaluated by fracture toughness testing and also the effects of prestraining on the brittle-to-ductile transition temperature (BDTT) have been investigated. Specimens were prestrained to a 10% plastic strain level at 200°C under tension prior to toughness testing. The BDT of the prestrained specimens was compared to that of the as homogenized specimens. The results have revealed the occurrence of two competing effects upon prestraining: (1) an increase in dislocation sources causing a difficulty in micro-crack initiation and resulting in an increase in toughness at low temperatures, and (2) an increase in the flow stress resulting in an increase in BDT temperature. The crack initiation and propagation mechanisms were also analyzed and have been discussed.
Chemistry, Bonding and Fracture of Grain Boundaries in Ni3Si
Authors: Subramanian Shanthi , Muller David A. , Silcox John , Sass Stephen. L.
Published: April 2011

To obtain insight into the effect of dopants on the bonding and cohesive energy of gram boundaries in Ll2 intermetallic compounds, the chemistry and electronic structure at grain boundaries in B-free and B-doped Ni-23 at % Si alloys were examined, with electron energy loss spectroscopy (EELS) providing information on the former and energy dispersive X-ray spectroscopy (EDX) on the latter. Ni-enrichment was seen at large angle boundaries, both in the absence and presence of B. EELS of the Ni L3 edge showed that the bonding at Ni-rich grain boundaries was similar in both undoped and doped alloys. Comparison of the Ni L3 edge recorded at the grain boundary and in the bulk suggests that reduced hybridization and weaker bonding occurs at Ni-rich grain boundaries in both doped and undoped alloys. These changes in bonding are interpreted in terms of changes in the cohesive energy of the boundaries.
Mechanical Behavior of Reactively Hot-Pressed Aluminide Matrix Composites
Authors: Inoue M. , Suganuma K. , Niihara K.
Published: April 2011

FeAl and Ni3Al matrix composites containing various fine particles were fabricated successfully by reactive hot-pressing. The strength and the fracture toughness of these composites at ambient temperatures were evaluated. The addition of β-SiC particles was effective for strengthening of the Fe-40at%Al matrix, however, an extreme decrease of fracture toughness occurred due to the suppression of stress relaxation effect by plastic deformation at a crack tip. The fracture toughness of the reactively hot pressed Fe-40at%Al and its composites was also affected by the environmental embrittlement effect. TiB2 and ZrB2 particles in the Fe-40at%Al matrix composites were clarified to play a role in the reduction of the environmental effect. For the Ni-25at%Al matrix, higher flexural strength was achieved by the addition of TiB2, TiC and TiN particles. TiB2 particles reacted with the matrix during hot-pressing. The Ni-25at%Al/TiB2 composite had a fracture strength of 1.5 GPa in spite of large grain size of the matrix. TiC and TiN were the best choices as effective reinforcing matrials for the Ni3Al matrix among the chemical compatible ones.
Alloying Effect of Vanadium Upon Structure and Strength of σ-Phase Titanium Trialuminide
Authors: Takahashi Tohru , Iwami Kenji , Hasegawa TAdashi
Published: April 2011

The alloying effect of vanadium upon σ-phase titanium trialuminide has been investigated using materials whose compositions were of the type Al3(Ti,V). Six types of ternary aluminum-titanium-vanadium alloys, ranging from Al3Ti to Al3V at 5 atomic % intervals, have been prepared by arc melting. All the materials showed the D022 tetragonal structure, suggesting vanadium atoms substitute titanium atoms. The 0.2% proof stress increased with increasing vanadium content up to about 10 atomic %, and then decreased toward that of Al3V both at room temperature and at elevated temperatures. Such behavior can be interpreted as substitutional solid solution strengthening.
Investigation of Diblock Copolymer thin film Morphology for Nanolithography
Authors: Park Miri , Harrison Christopher , Chaikin Paul M. , Register Richard A. , Adamson Douglas , Yao Nan
Published: April 2011

The microphase separated morphology of diblock copolymers can be used to generate well-ordered nanometer scale patterns over a large area. To achieve this goal, it is important to understand and control the behavior of diblock copolymer thin films on substrates, which can differ from the bulk behavior. We have investigated the morphologies and ordering in thin polystyrene-polybutadiene (PS-PB) diblock copolymer films on bare silicon and silicon nitride substrates, and also on polymethylmethacrylate (PMMA) coated substrates. The PS-PB copolymers are synthesized to form, in bulk, PB cylinders or spheres in a PS matrix. In thin films (10–60 nm thick), prepared by spin-coating, we observe that the morphology and ordering of the microdomains are affected by strong wetting constraints and a reduced chain mobility on the substrate. The thinnest self-assembled layer of the copolymer films shows no in-plane microphase separation on both types of substrates. The PS blocks wet the PMMA substrates whereas the PB blocks wet the bare substrates as well as the air interface. Hence, different film thicknesses are necessary on the two types of substrates to obtain a uniform film of the first self-assembled cylindrical or spherical microdomain layer. The first layer of the cylindrical copolymer can vary from cylindrical to spherical morphology with a few nanometer decrease in film thickness. In the case of spherical PS-PB diblock copolymer films, we observe that the ordering of the microdomains is improved in the films on the PMMA substrates, compared to those on the bare substrates. We also demonstrate a successful transfer of the microdomain patterns to silicon nitride substrates by a reactive ion etching technique.
Measuring Polymer Microstructure using Spatially-Resolved Eels in the Stem
Authors: Siangchaew K. , Arayasantiparb D. , Libera M.
Published: April 2011

Image contrast for the examination of multiphase polymers in the transmission electron microscope (TEM) usually requires differential staining by a heavy element (Os, Ru, U). Staining methods have provided a wealth of microstructural information in polymers, but there are situations, particularly where high resolution is needed, where staining is undesirable or impossible. This research has collected microstructural information from multiphase polymers without heavy-element stains using spatially-resolved electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). The technique is known as spectrum imaging. The principal problems facing spectrum imaging in polymer applications are: (1) the identification of spectral fingerprints distinguishing different polymer phases; and (2) the extraction of meaningful microstructural data from large data sets where the signal is weak due to instrumentation and materials constraints. This paper describes applications of spectrum imaging to PE/PS and HDPE/Nylon 6 blends. The aim is to identify adequate spectral features and establish data acquisition and extraction procedures for applications to general, unstained, multiphase polymers.
Ultra-High Resolution Small-Angle Neutron Scattering Investigations of Liquid-Liquid Phase Separation in Linear Low-Density Polyethylene
Authors: Agamalian M. M. , Alamo R. G. , Londono J. D. , Mandelkern L. , Spooner S. , Stehling F. C. , Wignall G. D.
Published: April 2011

Previous small-angle neutron scattering (SANS) studies [1] of heterogeneous ethylene-hexene linear low-density polyethylene (LLDPE) copolymers have confirmed the existence of a dispersed minority phase (volume fraction φ ∼ 10−2) consisting of highly branched, amorphous material. However, these experiments were conducted via a pinhole SANS spectrometer with an upper resolution limit ∼ 103 Å, whereas microscopy indicates that the dimensions of the disperse phase extend to the μm-range. We have therefore complemented these investigations via a Bonse-Hart ultra-small angle neutron scattering (USANS) instrument which increases the instrumental resolution in reciprocal space by a factor - 100, and thus particle size up to 30 μm can be resolved. The sensitivity of the USANS camera has recently been increased by two orders of magnitude by using the modified channel cut crystals [2], and the performance is therefore comparable to the best x-ray Bonse-Hart cameras. Xylene extraction removes the highly branched molecules and hence the volume fraction of the disperse phase is higher (φ ∼ 0.3) in the extracted material.
Effect of Additive Constraint on the Morphological and Mechanical Properties of Triblock Copolymer Blends
Authors: Kane L. , Norman D. A. , White S. A. , Spontak R. J.
Published: April 2011

While numerous studies have addressed the morphological characteristics of diblock copolymer blends either with a second copolymer or a parent homopolymer, relatively few have examined comparable blends containing a triblock copolymer. In this study, we investigate the role of mid-block bridging on the morphological and physical characteristics of blends composed of a poly(styrene-b-isoprene-b-styrene) (SIS) triblock copolymer with either an unconstrained homo-polyisoprene (hI) or an end-grafted SI diblock copolymer. Blend compositions and molecular weights of the hi, as well as the I-block of the copolymer, have all been systematically varied to elucidate the effect of additive constraint on the extent of nonideal intramicrodomain mixing. Blend morphologies are characterized using transmission electron microscopy, while blend properties have been measured by dynamic mechanical analysis.
Determination of Degree of Polymerization of Cellulose in Ligneous Papers
Authors: Kaminska E.
Published: April 2011

In the past, many attempts have been made to determine the degree of polymerization (DP) of cellulose in ligneous pulps or papers. Frequently, the methods employed caused severe depolymerization of the cellulose.

The present paper provides a detailed procedure of DP determination of cellulose for both lignin-free and ligneous papers. The proposed method is based on viscosity measurements of cadoxen solutions of cellulose. Prior to dissolution in cadoxen, ligneous samples are partially delignified by a modified chlorite method, under conditions preventing any substantial depolymerization of cellulose. Results of preliminary experiments carried out on groundwood newsprint papers provide strong evidence of reliability of DP values so determined.
Point Defects, Diffusion and Gettering in Silicon
Authors: Gösele U. , Conrad D. , Werner P. , Tong Q.-Y. , Gafiteanu R. , Tan T. Y.
Published: April 2011

The status of our knowledge on intrinsic point defects and diffusion mechanisms is reviewed. Special attention is given to the question of the possible role of carbon in influencing effective diffusivities of intrinsic point defects and the resulting consequences for the values of vacancy and self-interstitial thermal equilibrium concentrations and diffusivities. It is pointed out that we might have to deal with the unfortunate situation that the effective diffusivities of intrinsic point defects might be influenced already by a carbon concentration which is below the detection limit and therefore not amenable to measurement and control. Whereas dopant diffusion processes have been modeled and simulated for a long time the first attempts to quantitatively simulate various gettering processes have just started as will be described in the paper. Finally, the subject of microcrack formation in hydrogen implanted silicon will be dealt with as used for the so-called “smart-cut” process for fabricating silicon-on-insulator (SOI) substrates with thin and uniform silicon layers by wafer bonding. Presently no quantitative treatment of this fascinating hydrogen agglomeration phenomenon is available.
Point Defect Injection Kinetics by N2O Oxidation of Silicon
Authors: Tsamis C. , Kouvatsos D. N. , Tsoukalas D.
Published: April 2011

The influence of N2O oxidation of silicon on the kinetics of point defects at high temperatures is investigated. Oxidation Stacking Faults (OSF) are used to monitor the interstitials that are generated during the oxidation process. We show that at high temperatures (1050°-1150°C) the supersaturation of self-interstitials in the silicon substrate is enhanced when oxidation is performed in an N2O ambient compared to 100% dry oxidation. This behavior is attributed to the presence of nitrogen at the oxidizing interface. However, at lower temperatures this phenomenon is reversed and oxidation in N2O ambient leads to reduced supersaturation ratios.
Formation and Binding Energies of Vacancy Clusters in Silicon
Authors: Colombo L. , Bongiorno A. , Diaz De La Rubia T.
Published: April 2011

We critically readdress the problem of vacancy clustering in silicon by perform large-scale tight-binding molecular dynamics simulations. We also compare the results of this quantum-mechanical approach to the widely used model-potential molecular dynamics scheme based on the Tersoff and Stillinger-Weber interatomic potentials.
Effect of Annealing Under Uniform Stress on Photoluminescence, Electrical and Structural Properties of Silicon
Authors: Misiuk A. , Karwasz G. P. , Cazzanelli M. , Jung W. , Pavesi L.
Published: April 2011

Effect of increased pressure (up to 1.5GPa) during annealing of Cz-Si on creation of thermal donors (at 720 - 1000K) and visible luminescence (peaking at 1.7- 2.2eV for samples annealed at up to 1420K) is reported. The observed phenomena are related to stress - stimulated oxygen clustering / precipitation in Cz-Si resulting in creation of specific defects.
The Effect of Oxygen on The Electrical Activation and Diffusion of Ion-Implanted Boron
Authors: Kyllesbech Larsen K. , Stoik P. A. , Privitera V. , van Berkum J. G. M. , de Boer W. B. , Marinino G. , Cowern N. E. B. , Huizing H. G. A.
Published: April 2011

Transient enhanced diffusion (TED) and electrical activation (EA) of ion-implanted boron during rapid thermal annealing has been investigated using three types of boron doped p-type Si (100) substrates: (a) Cz 20 Ωcm, (b) 3 μm thick 20 Ωcm epitaxial Si layer (epi-layer) grown on a 20 Ωcm Cz substrate, and (c) 3 μm thick 20 Ωcm epi-layer grown on a 5 mΩcin Fz substrate. The level of oxygen is known to decrease from material type (a) to (c). The samples were implanted with 20 keV, 5×1013cm−2boron and subjected to rapid thermal annealing (RTA) at various temperatures and times. The EA and TED were studied using spreading resistance profiling (SRP) and secondary ion mass spectrometry (SIMS), respectively. Although the amount of TED is almost identical for the three substrates, the EA is found to be significantly higher in the epi-layers compared to Cz substrates. It is speculated that the trapping of vacancies by oxygen in the ion-damaged region leads to an increase in the interstitial supersaturation during annealing, which then results in enhanced boron clustering and reduced electrical activation in the peak of the implanted profile.
Chemical and Electrochemical Staining for Two-Dimensional Dopant Concentration Profiling on ULSI Silicon Devices
Authors: Spinella C.
Published: April 2011

We discuss the sample preparation technique for the two-dimensional dopant concentration profiling in silicon based on chemical staining and transmission electron microscopy analysis. The capability of characterizing ULSI silicon devices is demonstrated by showing an example of failure analysis performed on a high speed bipolar transistor. The high spatial resolution of the technique allows to reveal many details which are not detectable by other techniques. The limitations of this method concern the impossibility to simultaneously delineate n and p-type regions on the same sample, and the need to have a p+n junction for delineating a boron profile with an acceptable sensitivity. We demonstrate that these limitations can be overcome by developing a novel electrochemical staining procedure based on anodic oxidation of silicon.
Monte Carlo simulation of Boron diffusion during low energy implantation and high temperature annealing
Authors: Caturla M.-J. , Diaz de la Rubia T. , Zhu J. , Johnson M.
Published: April 2011

We use a kinetic Monte Carlo model to simulate the implantation of low energy Boron in Silicon, from 0.5 to 1 keV, at high doses, 1015 ions/cm2. The damage produced by each ion is calculated using UT-Marlowe, based on a binary collision approximation. During implantation at room temperature,, silicon self-interstitials, vacancies and boron interstitials are allowed to migrate and interact. The diffusion kinetics of these defects and dopants has been obtained by ab initio calculations as well as Stillinger Weber molecular dynamics. Clustering of both self-interstitials, vacancies and boron atoms is included. We also model the diffusion of the implanted dopants after a high temperature annealing in order to understand the transient enhanced diffusion (TED) phenomenon. We observe two different stages of TED During the first stage vacancies are present in the lattice together with interstitials and the diffusion enhancement is small. The second stage starts after all the vacancies disappear and gives rise to most of the final TED.
Effect of End-of-Range Defects, Arsenic Clustering and Precipitation on Transient Enhanced Diffusion in As+ Implanted Si
Authors: Krishnamoorthy V. , Venables D. , Moeller K. , Jones K. S. , Jackson J.
Published: April 2011

(001) CZ silicon wafers were implanted with As at lOOkeV to a dose of 1×1015/cm2. The implant was amorphizing in nature and the peak As concentration was below the As clustering threshold. Subsequently, a second As+or Ge+ implant at 30keV at doses of 2×1015/cm2, 5×1015/cm2 and 1×1016/cm2 were performed, respectively, into the as-implanted samples. The samples with a double arsenic implant induce As clustering at the lower doses and As precipitation at the highest dose at the projected range. However, the samples with the Ge do not induce clustering or precipitation. The samples were annealed at 700°C for various times to regrow the amorphous layer and to cause enhanced arsenic diffusion beyond the end-of range region. These samples wereanalyzed by SIMS and TEM. The difference in the defect evolution at the end-of-range region and TED beyond the end-of-range region between the As and Ge implanted samples was used to isolate the effects of As clustering and precipitation.
Nucleation and Growth of {113} Defects and {111} Dislocation Loops Insilicon-Implanted Selicon
Authors: Pan G. Z. , Tu K. N.
Published: April 2011

Plan-view and cross-sectional transmission electron microscopy have been used to study the microstructural characterization of the nucleation and growth behavior of {113} rodlike defects, as well as their correlation with {111} dislocation loops in silicon amorphized with 50 keV, 36×1014 Si/cm2, 8.0 mAand annealed by rapid thermal anneals at temperatures from 500 °C to 1100 °C for various times. We found that the nucleations of the {113} rodlike defects and {111} dislocation loops are two separate processes. At the beginning of anneals, excess interstitials accumulate and form circular interstitial clusters at the preamorphous/crystalline interface at as low as 600 °C for 1 s. Then these interstitial clusters grow along the <110> direction to form {113} rodlike defects. Later, while the {113} defects have begun to grow and/or dissolve into matrix, the {111} faulted Frank dislocation loops start to form. We also found that the initial interstitial clusters prefer to grow along the <110>directions inclined to the implantation surface.
Point Defect Properties from Metal Diffusion Experiments — What Does the Data Really Tell Us?
Authors: Chakravarthit Srinivasan , Dunham Scott T.
Published: April 2011

Point defect properties, including diffusivities and equilibrium concentrations for both interstitials and vacancies, are commonly extracted from metal diffusion experiments, and these values are widely used in process simulation software. However, in many cases, these parameter values were extracted using oversimplified models which ignore interactions between interstitial and vacancy diffusion mechanisms. Questions about the accuracy of these parameters have come from ab-initio defect calculations which conclude that vacancies diffuse faster than interstitials, in contrast with published reports on metal diffusion which find vacancies diffuse much more slowly than interstitials. We have reanalyzed published data for zinc and platinum diffusion and find that it is possible to match all of the data using fast vacancy diffusivity. The most direct evidence for slow vacancy diffusion (and a high equilibrium concentration) comes from platinum diffusion experiments. However, we are able to reproduce these results with fast V diffusion and carbon/interstitial clustering, using carbon concentrations typical of Czochralski and float zone silicon (1016cm−3). We evaluate the effectiveness of metal diffusion experiments in determining point defect parameters, and find that it is not possible to reliably determine both diffusivities and equilibrium concentrations for both interstitials and vacancies from metal diffusion results.
Self-Diffusion as A Limiting Factor of a-SiGe Crystallization
Authors: Edelman F. , Raz T. , Komem Y. , Werner P. , Beyer W. , Butz R. , Zeindl H. , Zaumseil P.
Published: April 2011

Highly doped (∼1018 to 1021cm−3) polycrystalline Si1-xGex films, crystallized from amorphous (a) state at relative low temperatures, are prospective materials in a variety of applications, such as liquid-crystal displays, solar cells and integrated thermoelectric sensors on large-area glass substrates. Since the nature of the grains in the crystallized film defines properties such as carrier mobility, the nucleation and growth process of the a-SiGe films is of fundamental interest. We have studied the crystallization of undoped and highly doped (B or Ga) amorphous SiGe films. The films were deposited by RFCVD or molecular beam on oxidized (001)Si and for TEM study on cleaved NaCl. The incubation time and grain growth rate were studied by means of in situ TEM using a heating stage. The crystallization process in undoped SiGe followed Avrami relationship. An average grain size between 0.1 and 2μm was observed. However, the highly p-doped (with B or Ga) SiGe films crystallized to a stable nanocrystalline structure (grain size <10nm). The process of the a-SiGe crystallization is explained on the basis of self-diffusion. During the first stage, the nucleation of crystals is accompanied with nonequilibrium vacancy generation at the amorphous/crystalline interface. During the second stage, the growth of crystals takes place by vacancy outdiffusion which is hindered by B and Ga interaction with vacancies.
Anomalous Diffusion of Ultra low Energy Boron Implants in Silicon
Authors: Webb R. P. , Foad M A , Gwilliam R M , Knights A P , Thomas G.
Published: April 2011

Ultra low energy boron implants (0.2 to 3 keV) have been carried out on Si (100) at doses between 1×1014cm−2 and 1×1015cm−2 using xRLEAP. The samples were annealed at temperatures between 900°C and 1050°C. The atomic profiles of these samples was measured using SIMS. Monte Carlo and diffusion simulations were performed using the SSupreme code. Comparisons between the simulations and experimental measurements show interesting differences these are discussed.
High Silicon Self-Interstitial Diffusivity as Revealed by Lithium Ion Drifting
Authors: Knowlton W. B. , Walton J. T. , Wong Y. K. , Mason I. A. , Haller E. E.
Published: April 2011

We report on the use of lithium ion (Li+) drifting1 as a sensitive means to study Si self-interstitial (SiI) diffusion.2 Li+ properties in silicon are well known from extensive ion drift studies and Li+ interactions with dopants and point defects.3 We have used this low temperature (∼100°C) technique in combination with Si1 injection from oxides to delineate, identify and eliminate D defects4 in certain p-type floating zone (FZ) Si single crystals.5 Our results suggest Si1 diffusion occurs to a depth of at least 10 mm into the bulk during phosphorus (P) diffusion with oxidation (i.e., POCI3 process) at 950°C for 100 min. Process modeling of this lower bound SiI diffusion using SUPREM-IV9 results in a Sii diffusivity of 3.5×10−6 cm2/s at 950°C.
An Examination of the Crystalline Quality of 200mm Diameter Silicon Substrates using X-ray Topography
Authors: Curley J. , McNally P. J. , Reader A. , Tuomi T. , Taskinen M. , Rantamäki R. , Danilewsky A. , Schropp B.
Published: April 2011

The continued decrease in critical dimensions and increasing integration levels in Si CMOS technology is imposing ever tighter constraints on quality control parameters for the IC manufacturing industry. One very important issue is the need to ensure a uniform, high quality Si substrate, i.e. minimise defect/dislocation densities and eliminate strain distributions in the starting wafer material. A comprehensive Synchrotron X-Ray Topography (SXRT) study was applied to commercially supplied 200mm diameter Si wafers. These wafers, which all included a surface Si epilayer growth were supplied from manufacturers from around the globe. The study revealed not only differences in the overall quality of the wafers, but also differences in the quality of the individual Silicon epilayers and substrates. In all wafers the substrate quality varied dramatically with position across the wafer, as measured by the distribution of oxygen precipitates and stacking faults in the wafer. This distribution also varied significantly from manufacturer to manufacturer. The strain fields induced by the growth of lightly doped Si epilayers were also observed to qualitatively vary with location on a wafer, together with (as expected) thickness of the epilayers. The results clearly indicate that optimal quality control for such commercial wafers has not yet been achieved.
Twinning Mechanism in PrCo2Cx Magnetic Phase
Authors: Wu Lijun , Bian Weimin , Zhu Yimei
Published: April 2011

A magnetic rhombohedral PrCo2Cx (x=0.05∼0.25) phase (space group R3m), which is heavily twinned along the {110} and {211} planes, was identified. The twinning mechanism was explored by analyzing the reduction of crystal symmetry due to the cubic-rhombohedral phase transformation. The origin of the twinning and the formation of four twin variants were attributed to the insertion of carbon interstitials into Co4 tetrahedrons along the 3 axis in the rhombohedral lattice, which corresponds to one of the four equivalent <111> axes of its parent PrCo2 cubic-lattice.
Origins of Contrast in Near-Field Scanning Optical Microscopy Photovoltage Images of Cu(In,Ga)Se2 Solar Cells
Authors: McDaniel A. A. , Hsu J. W. P.
Published: April 2011

Photovoltage images of Cu(In,Ga)Se2 solar cells taken using near-field scanning optical microscopy (NSOM) show reduction of photoresponse along grain boundaries. Two factors might be responsible for this contrast. The first is that the topographic changes associated with the grains could cause the NSOM tip to move further from the sample, resulting in a reduction in photoresponse. The second possibility is that the contrast is due to real physical properties of the sample, e.g. higher recombination velocities near grain boundaries. We show convincing evidence that the major contribution to the contrast in the photovoltage images is due to the latter.
Preparation and Residual Stress Characterisation of Polycrystalline Silicon Germanium Films Grown by Atmospheric Pressure Chemical Vapour Deposition
Authors: Fiorini P. , Sedky S. , Caymax M. , Baert C.
Published: April 2011

Polycrystalline silicon-germanium alloys (poly-SiGe) are deposited by chemical vapour deposition at atmospheric and reduced pressure. The stress, as well as its profile along the growth direction, are measured. Depending on the deposition pressure the stress can be compressive or tensile, the profile of the stress is in both cases rather uniform. The behaviour of the stress as a function of annealing temperature is also investigated. Films which are compressive as grown can be made tensile by annealing, films which are tensile as grown remains tensile even after high temperature annealing.
Electromigration and 1/f Noise in Single-Crystalline, Bamboo and Polycrystalline Al Lines
Authors: Van Den Homberg Marc J.C. , Alkemade P.F.A. , Verbruggen A.H. , Dirks A.G. , Ochs E. , Radelaar S.
Published: April 2011

The relation between electromigration and microstracture for three types of Al lines with different microstructures has been studied. The lines were made by recrystallization of Al in a SiO2 groove pattern. They were either truly bamboo with grains of on average 3 μm long or distorted (i.e. with dislocations) single-crystals. In addition, conventional, polycrystalline Al lines with grains of on average 230 nm were made. The lines were lifetime-tested (200 °C,j=2, 5 and 8 MA/cm2) and subjected to 1/f noise measurements (from 200 to 500 K).

The bamboo and single-crystalline Al lines showed the same, although weak, 1/f noise. This observation demonstrates that other mechanisms than thermal motion of atoms at grain boundaries can cause noise. It is suggested that dislocations are the sources for noise in our samples. The measured activation energy (0.8 eV) is in agreement with the activation energy for pipe diffusion along dislocation lines.

The lifetime-tests showed significantly higher times to failure for the single-crystalline and bamboo lines as compared to polycrystalline lines. Preliminary results indicate slightly higher lifetimes for the bamboo than for the single-crystalline lines. It is concluded that interface diffusion is the main mechanism for electromigration in truly bamboo or single-crystalline lines. Our measurements demonstrated that dislocations are important in the formation of 1/f noise and interfaces in the formation of electromigration damage.
The Fiber Texture Growth and the Surface Roughness of ZNO Thin Films
Authors: Anna Selvan J. A. , Keppner H. , Kroll U. , Cuperus J. , Shah A. , Adatte T. , Randall N.
Published: April 2011

Zinc Oxide (ZnO) is one of the important Transparent Conducting Oxides (TCO) for thin film photovoltaic cells with respect to performance and cost reduction. When used in photovoltaic cells, the surface roughness of ZnO is required in order to increase the amount of light going inside the cells (Light Trapping). In this paper we present the surface morphology in connection with the fiber texture of ZnO films at different experimental conditions. The structural properties of the ZnO films grown by the method of radio frequency sputtering and Chemical Vapour Deposition (CVD) with the special effort to make surface roughness (Surface Texturing) are presented. The influence of the control over the fiber texture, surface mobility of the adatoms and the dissociation of water vapour during growth are explained.
Evolution of Texture and Microstructure in Rough Polycrystalline Silicon for Advanced Dram Applications
Authors: Banerjee A. , Wise R. L. , Crenshaw D. L. , Khamankar R. B. , Edwards Hal
Published: April 2011

This study investigates the morphology, roughness and electrical performance of rough polysilicon films deposited by LPCVD process. The deposition duration was varied over a broad range to study the evolution of microstructural texture in terms of nuclei formation, growth and grain coalescence. The area enhancement factor (AEF) of rough polysilicon film, expressed as the ratio of cell capacitance incorporating textured film to that of a smooth polysilicon film is observed to range from 1.4 to 2.4 for the above conditions. It is observed that the AEF shows a strong dependence on the microstructural texture and correlates with the surface roughness. A model for electrical AEF based on grain morphology attributes from AFM is included. The dependence of rough polysilicon nucleus cluster density on silane flow rate and deposition temperature is also presented.
Growth and Structure of Ti2O3and TiO2Thin Films on (0001) α-Al2O3Substrates
Authors: Wagner T. , Agarwal M.
Published: April 2011

Titanium oxide thin films were grown at different temperatures on (0001) α-Al2O3substrates by molecular beam epitaxy (MBE). The films grown at room temperature were amorphous. Annealing at 1223K of 6 nm thick films led to the formation of TiO2with an epitaxial orientation relationship (100)<001>TiO2∥ (0001)<01101>Al2O3with the substrate. However, on similar heat treatment, thicker 100 nm films formed polycrystalline TiO2. At a deposition temperature of 1223K epitaxial Ti2O3films with orientation relationship (0001)<2110>Ti2O3∥ (0001)<21101>Al2O3were formed. The lattice mismatch between Ti2O3and α-Al2O3was accomodated by a regular arrangement of misfit dislocations at the Ti2O3/α-Al2O3interface. By comparing the microstructural evolution of the annealed films with that of those films grown at high temperature, mechanisms governing grain growth in polycrystalline titanium oxide films were discussed.
Electrical Characterization of Ultra-Thin Oxides Grown on
Silicon Surfaces Cleaned in Ultra-High Vacuum
Authors: Petersen C. L. , Grey F.
Published: April 2011

We have investigated the oxidation of clean reconstructed silicon surfaces
in-situ using a fourpoint probe technique. The measured conductance
variations, on Si(111) and Si(100) surfaces as a function of oxygen exposure
are markedly different. On Si(100) surfaces, the conductance displays a
rapid fall during the first 100 L exposure to O2, followed by a
slower steady decrease at higher oxygen exposures. This behavior is similar
for both n-type arid p-type silicon. The conductance of Si(111) surfaces
increases significantly at the onset of the oxidation. This conductance
increase is found on both n-type and p-type Si(111) samples. We interpret
this as being due to the molecular precursor which is known to form in the
peroxy bridge position.
Native Oxide Growth Behavior on Silicon Surface with Various
Resistivity in Ultrapure Water and CuF2 Solution
Authors: Sekine Katsuyuki , Choi Geun-Min , Saito Yuji , Ohmi Tadahiro
Published: April 2011

We have studied native oxide growth behavior on silicon surface with various
resistivity in ultra pure water (UPW), SPM (sulfuric acid-hydrogen peroxide
mixture, H2SO4:H2O2 = 4:1)
cleaning and UPW contaminated with CuF2 by X-Ray photoelectron
spectroscopy (XPS). The results show that the native oxide growth behavior
in UPW is different from that in UPW contaminated with CuF2 and
that grown by SPM cleaning. Native oxide thickness grown in UPW depends on
resistivity. Native oxide thickness grown during SPM cleaning has the
relationship of steric hinderance effect. However, in CuF2
solution, native oxide thickness is more influenced by the redox reaction
between Cu ions and silicon atoms.
Utilizing Bath/Wafer Contamination Correlation to Validate a
Pre-Gate Cleaning Strategy
Authors: Gilton Terry , Higdon Clarence , Copsey Kate
Published: April 2011

The correlation of contaminants in a process bath with contaminants on a
silicon wafer prepared in the bath is important information when developing
a cleaning strategy. In this paper, we present such a correlation focused on
contaminants in dilute HF (1:100) and in SC1 (1:1:5 and 1:1:80 at 50°C and
65°C). We have limited the contamination levels to between 0 and 150 ppb. We
have also limited the contaminants studied to those that are most likely to
be a problem (Fe, Al, Mg, Ca, Cu, Zn, and Na). The bath concentrations are
measured using ICPMS and the wafer surface concentrations are measured using
both VPD/TXRF and VPD/ICPMS.

We demonstrate that Fe and Ca at the levels studied do not deposit from
dilute HF, while Cu deposits, showing a linear dependence on bath
concentration. We also demonstrate that in the SCl bath, both concentration
and temperature are important variables in the contamination of wafers for a
given bath contamination level. Al and Zn contaminate wafers most strongly,
with Al being the largest contributor at the higher concentration of SC1 and
Zn being the largest contributor in the lower concentration. Finally, we
demonstrate that a dilute HF clean can remove everything deposited in a
highly contaminated SC1 bath.
The Role of HO2− in SC-1 Cleaning Solutions
Authors: Verhaverbeke Steven , Parker Jennifer W. , McConnell Chris F.
Published: April 2011

The RCA Standard Clean, developed by W. Kern and D. Puotinen in 1965 and
disclosed in 1970 [1] is extremely effective at removing contamination from
silicon surfaces and is the defacto industry standard.[2]. The RCA clean
consists of two sequential steps: the Standard Clean 1 (SC-1) followed by
the Standard Clean 2 (SC-2). The SC-1 solution, consisting of a mixture of
ammonium-hydroxide, hydrogen-peroxide, and water, is the most efficient
particle removing agent found to date. This mixture is also referred to as
the Ammonium- Hydroxide/Hydrogen-Peroxide Mixture (APM). In the past, SC-1
solutions had the tendency to deposit metals on the surface of the wafers,
and consequently treatment with the SC-2 mixture was necessary to remove
metals. Ultra-clean chemicals minimize the need for SC-2 processing. SC-I
solutions facilitate particle removal by etching the wafer underneath the
particles; thereby loosening the particles, so that mechanical forces can
readily remove the particles from the wafer surface. The ammonium hydroxide
in the solution steadily etches silicon dioxide at the boundary between the
oxide and the aqueous solution (i.e., the wafer surface). The hydrogen
peroxide in SC-I serves to protect the surface from attack by OH" by
re-growing a protective oxide directly on the silicon surface (i.e., at the
silicon/oxide interface). If sufficient hydrogen peroxide is not present in
the solution, the silicon will be aniostropically etched and surface
roughening will quickly occur. On the other hand, hydrogen peroxide readily
dissociates and forms water and oxygen. If the concentration of the
resulting oxygen is too high, bubbles will appear in the solution. The gas
liquid interfaces that result from the bubble formation act as a “getter”
for particles that can re-deposit on the wafer surface if a bubble comes in
contact with the wafer.
The Formation of Water Marks on Both Hydrophilic and Hydrophobic
Wafers
Authors: Park Jin-Goo , Han Jeung-Hoon , Kim Seung-Hwan , Lee Sang-Ho
Published: April 2011

The purpose of this paper is to explore the formation of water residues on
wafers during drying. To investigate this DI water droplets were
intentionally placed on the surface of substrates with various wettabilities
and then left to dry in both N2 and O2 atmospheres. It
was found that both hydrophobic and hydrophilic surfaces created the water
mark in N2 and O2. The size and dry time of residues
were dependent on the wettability of surfaces. Auger analysis of residues
showed that the oxidation of surface in water might be one of causes of
water mark formation. Considering the pore size of final filters in DI water
generation is 0.05 μn, a large number of particles less than 0.05 μm ay be
in DI water. In order to investigate the effect of small particles less than
0.05 μm on water mark formation, PSL particles less than 0.05 μm were added
to DI water. DI water containing particles was left to dry as a function of
particle concentrations. The size of water marks was dependent on the
concentration of particles in DI water after they reached a critical
concentration.
Surface Treatment with UV-Excited Radicals for Highly-Reliable
Gate Dielectrics
Authors: Ito Takashi , Sugino Rinji , Nakanishi Toshiro , Ohkubo Satoshi , Tamura Yasuyuki , Takasaki Kanetake
Published: April 2011

The UV-excited chlorine radical treatment effectively removed trace metal
contaminants from Si ans SiO2 surfaces. We have found that this
is predomonantly attributed to reactions between metal and chlorine, and
metal oxides and silicon chloride, respectively. The former process was
subjected to identify a breakdown spot on a thin gate dielectric film. After
dielectric breakdown, a silicon crystallized filament as small as a few
nanometers in diameter was formed and was selectively etched with chlorine
radicals revealing a successively-etched region of the Si substrate.
Nonuniformities of native exides on silicon were also detected using the
same method. Gettering and etching wi:h a poly Si layer showed a possibility
to make a gate dielectric film damage free and contamination free.
Densification of native oxides formed after conventional wet cleaning of
silicon was made with UV-excited oxygen radicals. Electrical characteristics
of gate dielectrics treated with UV-excited chlorine and oxygen radicals
showed high reliability.
Development of BI-SB-TE Ternary Alloy with Compositionally Graded Structure
Authors: Yamamoto A. , Ohta T.
Published: April 2011

Compositionally graded p-type Bi-Sb-Te thermoelectric material was synthesized by PIES (Pulverized and Intermixed Elements Sintering) method. The materials consisted of three segmented regions of different alloy composition, i.e. y = 0.8/0.825/0.9 in (Bi2Te3)1−y(Sb2Te3)ysystem. It was found that the electrical power output of the compositionally graded material was larger than that of the best single composition material when the temperature difference was the designed value.
Microstructure, Mechanical Properties, and Thermoelectric Properties of Hot-Extruded P-Type Te-Doped Bi0.5Sb1.5Te3 Compounds
Authors: Park K. , Seo J. , Lee C.
Published: April 2011

The p-type Bi0.5Sb1.5Te3 compounds with Te dopant (4.0 and 6.0 wt%) and without dopant were fabricated by hot extrusion in the temperature range of 300 to 510 °C under an extrusion ratio of 20:1. The undoped and Te doped compounds were highly dense and showed high crystalline quality. The grains contained many dislocations and were fine equiaxed (˜ 1.0 μm) owing to the dynamic recrystallization during the extrusion. The hot extrusion gave rise to the preferred orientation of grains. The bending strength and the figure of merit of the undoped and Te doped compounds were increased with increasing the extrusion temperature. The Te dopant significantly increased the figure of merit. The values of the figure of merit of the undoped and 4.0 wt% Te-doped compounds hot extruded at 440 °C were 2.11×10−3/K and 2.94×10−3/K, respectively.
Thermoelectric Properties of M2Mo6Se6 (M=TI, In)
Authors: Verebelyi D. T. , Payne J. E. , Tessema G. X. , Mengistu E.
Published: April 2011

We have measured the thermal conductivity of TI2Mo6Se6, a quasi-one dimensional conductor which belongs to the family of M2Mo6X6 linear chain compounds. Using these results and our measurements of the Seebeck coefficient and the electrical conductivity we estimate the dimensionless figure of merit to be of the order of 0.08. This result suggest that this compound and other related compounds are good potential TE.
Rare Earth Thermoelectrics
Authors: Mahan G. D.
Published: April 2011

A review is presented of the thermoelectric properties of rare earth compounds. A discussion is presented of the prospects for future improvements in the figure of merit.
The Thermoelectric Process
Authors: Vining C. B.
Published: April 2011

The efficiency of thermoelectric technology today is limited by the properties of available thermoelectric materials and a wide variety of new approaches to developing better materials have recently been suggested. The key goal is to find a material with a large ZT, the dimensionless thermoelectric figure of merit. However, if an analogy is drawn between thermoelectric technology and gas-cycle engines then selecting different materials for the thermoelements is analogous to selecting a different working gas for the mechanical engine. And an attempt to improve ZT is analogous to an attempt to improve certain thermodynamic properties of the working-gas. An alternative approach is to focus on the thermoelectric process itself (rather than on ZT), which is analogous to considering alternate cycles such as Stirling vs. Brayton vs. Rankine etc., rather than ‘merely’ considering alternative ‘gases’. Focusing on the process is a radically different approach compared to previous studies focusing on ZT. Aspects of the thermoelectric process and alternative approaches to efficient thermoelectric conversion are discussed.
Thermal Conductivity and Heat Transfer in Superlattices
Authors: Chen G. , Neagu M. , Borca-Tasciuc T.
Published: April 2011

Understanding the thermal conductivity and heat transfer processes in superlattice structures is critical for the development of thermoelectric materials and devices based on quantum structures. This work reports progress on the modeling of thermal conductivity of superlattice structures. Results from the models established based on the Boltzmann transport equation could explain existing experimental results on the thermal conductivity of semiconductor superlattices in both in plane and cross-plane directions. These results suggest the possibility of engineering the interfaces to further reduce thermal conductivity of superlattice structures.
Multivalent Acceptor-Doped Germanium Lasers: a solid-state tunable source from 75 to 300 μm
Authors: Chamberlin D. R. , Dubon O. D. , Bründermann E. , Haller E. E. , Reichertzl L. A. , Sirmain G. , Linhart A. M. , Röser H. P.
Published: April 2011

We report on the performance of far-infrared hole inversion lasers made from germanium doped with the multivalent acceptors beryllium and copper. Commonly used hole inversion lasers are made from Czochralski-grown Ga-doped Ge single crystals and show emission from 75 to 125 and 170 to 300 μm. The emission gap between 125 and 170 μm, originating from absorption of the far-infrared light due to internal hole transitions in the neutral Ga acceptor, is absent in the new Be and Cu-doped lasers. We also find a mechanism for inversion depopulation through neutral Ga which hinders lasing at low electric fields. This same mechanism is shown to cause population inversion in the Be-doped laser and allows lasing at lower fields. This reduces the power input into the germanium crystal and has allowed us to increase the duty cycle up to 2.5% which is one order of magnitude higher than the maximum duty cycle reported for Ga-doped Ge lasers. These new lasers may offer an opportunity for achieving continuous-wave operation.

In addition we have performed preliminary studies on the effect of uniaxial stress on the lasing in these new materials. We demonstrate that small uniaxial stress increases laser action in Ge:Cu. We propose that this is due to an increased population inversion because under these conditions two separate mechanisms cause heavy holes to enter the light hole band.