bluuebunny/crossref_metadata_2025 huggingface dataset:
Credibility of European Monetary System Interest Rate Policies: A Markov Regime‐Switching Approach
Authors: Arestis Philip , Mouratidis Kostas
Published: February 2004

The Markov regime‐switching modelling framework, with time‐varying transition probabilities, is utilized to study the credibility of monetary policy in five member countries of the European Monetary System during the period 1979–98 (Austria, Belgium, France, Italy and the Netherlands). The output‐gap variability and the inflation variability variables are incorporated in the determination of the monetary policy preferences of the five countries. Empirical evidence is provided to show that although all the countries in our sample followed a credible monetary policy regarding price stability, they had different preferences regarding the trade‐off between the stabilization of output‐gap variability and inflation variability.
The Advertising of Credence Goods as a Signal of Product Quality
Authors: Hahn Sunku
Published: February 2004

The advertising of credence goods is analysed in a similar way to the way Milgrom and Roberts analysed the advertising of experience goods. The existing literature on credence goods has not considered the possibility that some consumers have the expertise to assess the product's quality and the possibility that the producer can advertise. I assume these two points and show that there exists a unique equilibrium that survives the ‘intuitive criterion’. Also, it is shown that through encouraging producers to accept new technologies advertising may increase social welfare instead of just being a pure social cost.
Interactions between Money, Lending and Investment in the UK Private Non‐Financial Corporate Sector
Authors: Brigden Andrew , Mizen Paul
Published: February 2004

In this paper we consider the additional information to be derived from modelling lending, investment and money in a jointly determined system of equations. We allow demand‐ and supply‐side effects to influence the money, investment and lending equations. Using UK corporate data, we find acceptable equilibrium equations for investment, lending and money with a causal chain running from money and lending to investment and money to lending in a dynamic model. There is clear support for ‘value added’ from a lending equation and support for interactions between financial variables and real economic activity.
Dangerous Work: The Gendered Nature of Bullying in the Context of Higher Education
Authors: Simpson Ruth , Cohen Claire
Published: February 2004

This article discusses results from a research project which set out to investigate gender differences in the nature and experience of bullying within the higher education sector. Gender differences emerged in the form and perception of bullying as well as in target responses. Results also indicate that, irrespective of gender, bullies can capture and subvert organizational structures and procedures (such as official hierarchies, mentoring systems and probationary reviews) to further their abuse of the target and to conceal their aggressive intent. These outcomes are discussed in relation to gendered assumptions behind management practices and in relation to the masculinist ethic that underpins many higher education management initiatives. Overall, results indicate that bullying cannot be divorced from gender and that such behaviour needs to be seen in a gendered context.
Chronic Presenteeism: The Multiple Dimensions to Men's Absence from Part‐Time Work
Authors: Sheridan Alison
Published: February 2004

While there is considerable debate in the popular press about the changing roles of men and women, labour force statistics suggest that there has been little change in the work patterns of men and women. Despite the increasing availability of part‐time work, men in professional and managerial roles are not considering part‐time as an option for them. Rather, there are increasing organizational pressures for men to be working long hours in the paid workforce. In this paper, men's absence from part‐time work is considered from a multidisciplinary perspective. Factors operating at the individual, social and organizational levels are identified and explored in terms of their impact on men's working patterns. A model is presented that characterizes men's absence from part‐time work as a result of the mutually reinforcing nature of these factors.
Problem‐solving tasks in a foreign language: the importance of the L1 in private verbal thinking
Authors: Centeno‐Cortés Beatriz , Jiménez Jiménez Antonio F.
Published: February 2004

The objective of the study is the analysis of private verbal thinking (PVT) during problem‐solving activities carried out in a second language, as well as the study of the role that both the L1 and the L2 play in this process. PVT is defined as a particular type of private speech that surfaces during the reasoning process as a tool used in the resolution of problem‐solving tasks. This study is based on the comparison of the PVT produced by three different groups of speakers: intermediate‐level students of Spanish as an L2, advanced‐level speakers of Spanish as an L2, and native speakers of Spanish. In addition to analyzing the general characteristics of this phenomenon, special attention is paid to the use that each of these groups made of their L1 in relation to their L2 during the resolution of a battery of logical, mathematical, and spatial questions. The ultimate goal of this study is to contribute to clarifying the importance of the L1 in an L2 language classroom, as it was found that the L1 manifested itself as a key factor in the process of reasoning.
Private speech: a study of language for thought in the collaborative interaction of language learners
Authors: DiCamilla Frederick J. , Antón Marta
Published: February 2004

This article analyzes the speech of English‐speaking college students of Spanish working in pairs to produce compositions in Spanish. Although there was considerable variability in the frequency of private speech from one dyad to another, the main goal of the study was to analyze those instances of private speech that could be clearly identified by both linguistic and paralinguistic evidence. Eight such excerpts are analyzed and discussed here. The analysis reveals that private speech of the participants facilitated two fundamental cognitive operations: focusing of attention and the creation of psychological distance. That is, private speech enabled the participants to concentrate on the task at crucial moments and to distance themselves from the problems they encountered, thereby achieving a perspective that in turn helped them to gain control in the performance of the task. It is argued that private speech that occurs in a social context can be identified and analyzed, and ultimately distinguished from social speech.
On calculating scanning capacitance microscopy data for a dopant profile in semiconductors
Authors: Marchiando J. F. , Kopanski J. J.
Published: February 2004

One scanning probe method that holds great promise for two-dimensional dopant profiling in semiconductors is scanning capacitance microscopy (SCM). The usual way to calculate the SCM signal (the derivative capacitance) for a dopant profile is to use the finite-element method to solve Poisson’s equation. The domain region includes the doped semiconductor substrate region, the oxide layer region, and the air region bordering the metallic probe-tip of the SCM. The bias between the probe and sample is determined by using Dirichlet boundary conditions along the boundary of the probe-tip and the grounded plane deep within the doped semiconductor substrate. Managing this mesh-object (domain geometry and boundary conditions) requires sophisticated software. To help simplify these calculations, it is proposed that the SCM signal be found by using the areal capacitance distribution of the oxide and the air near the probe-tip to specify a natural boundary condition along the probed surface of the doped semiconductor sample, so that only the doped semiconductor substrate region needs to be meshed. For this configuration, it is found that linear finite-elements can give inaccurate results, and that cubic finite-elements can give accurate results. To help speed the calculations, it is proposed that a reasonably coarse mesh may be used, as well. The method is applied to a model one-dimensional ion-implanted dopant profile in a two-dimensional geometry, and the results of calculation for the forward problem are compared with that of using Dirichlet boundary conditions along the probe-tip.
{311} defect evolution in ion-implanted, relaxed Si1−xGex
Authors: Crosby Robert , Jones K. S. , Law M. E. , Larsen A. Nylandsted , Hansen J. Lundsgaard
Published: February 2004

Si-implanted, unstrained Si1−xGex layers of various Ge concentrations ranging from 0% to 50% were grown by molecular beam epitaxy on top of a Si substrate. The samples were subjected to a 750 °C anneal for 180 min to explore the subsequent defect structure. Plan-view transmission electron microscopy was implemented to investigate the evolution of defects. The Si1−xGex samples with ⩽5% Ge exhibit {311} defect formation and dissolution, and these defects ripen throughout the course of the anneal. Increasing the Ge content has an adverse effect on the growth of {311} defects. The samples with Ge contents ⩾25% demonstrated only dislocation loop formation. Dislocation loop formation and the observed impedance of {311} defect growth is facilitated by increasing the Ge content due to the weak bonding associated with the Ge atoms.
Ultrashallow junction formation by point defect engineering
Authors: Shao Lin , Thompson Phillip E. , van der Heide P. A. W. , Patel Sanjay , Chen Quak. Y. , Wang Xuemei , Chen Hui , Liu Jiarui , Chu Wei-Kan
Published: February 2004

We demonstrated that formation of sub-10 nm junctions can be realized by the technique of point defect engineering (PDE). The approach was based on the fact that high-energy ion bombardment with silicon can spatially separate the distribution of interstitials and vacancies, with a vacancy-rich region formed near the surface region. Effects of PDE on the boride-enhanced diffusion (BED) were systematically investigated by using boron superlattices grown by molecular-beam epitaxy. We observed that a high-energy implant provides an effective method to suppress BED. Furthermore, PDE can also (1) increase the stability of highly doped junction, (2) retard boron diffusion to a rate much less than normal diffusion, (3) sharpen the dopant profile, and (4) enhance boron activation.
Simulation of scanning capacitance microscopy measurements on ultranarrow doping profiles in silicon
Authors: Giannazzo F. , Goghero D. , Raineri V. , Mirabella S. , Priolo F. , Liotta S. F. , Rinaudo S.
Published: February 2004

Scanning capacitance microscopy (SCM) has been performed both in cross-sectional and in angle-beveling configurations on ultranarrow B spikes with a full width at the half maximum smaller than the SCM probe diameter. A relevant improvement in the SCM response has been observed passing from the cross section to ten times magnification, but a peculiar asymmetric shape characterizes all the profiles on the beveling configuration and broadening and peak lowering are observed for the narrowest spikes. Accurate two-dimensional simulations allowed us to reproduce the experimentally observed peculiar phenomena.
Analytical damage tables for crystalline silicon
Authors: Chan H. Y. , Benistant F. , Srinivasan M. P. , Erlebach A. , Zechner C.
Published: February 2004

Tables describing the damage profiles created after ion implantation are presented for a wide range of impurities at three tilts and twists (7°/22°, 0°/0°, and 45°/45°), showing the tilt and rotational effects on the damage profiles. While postimplantation damage is well understood in amorphous silicon, damage tables suitable for crystalline silicon, in which channeling effects are dominant, were not yet available. The impurities of concern are B, C, P, N, F, Si, As, Ga, Ge, In, and Sb. Energy ranges from 0.1 to 1000 keV. The Monte Carlo simulations are performed by the binary collision code CRYSTAL-TRIM implemented in DIOS utilizing its full cascade capability. The coefficients are extracted by a technique, called sampling calibration of profiles, which allows any damage profiles between two energies to be predicted by interpolation. This technique overcomes the limitations plaguing some of the most common analytical impurity and damage models.
PSPICE analysis of a scanning capacitance microscope sensor
Authors: Buh G. H. , Tran Chi , Kopanski J. J.
Published: February 2004

A detailed analysis of the capacitance sensor from a scanning capacitance microscope (SCM) is presented. PSPICE circuit simulations are compared with experimental results. The general behavior of the SCM sensor and practical aspects of the sensor-tuning curve are described. It is found that stray capacitances of the magnitude encountered in a conventional SCM measurement configuration are large enough to significantly decrease measurement sensitivity and sensor high-frequency voltage across the tip sample. We have also calculated and measured the delocalized dC/dV caused by stray capacitance, revealing that this background dC/dV must be accounted for in order to obtain the true localized dC/dV.
Silicon deposition from BCl3/SiH4 mixtures: Effect of very high boron concentration on microstructure
Authors: Herner S. B. , Clark M. H.
Published: February 2004

The microstructures of in situ boron-doped silicon films deposited by low-pressure chemical vapor deposition using SiH4 and BCl3 source gases on SiO2 substrates have been characterized. As-deposited films have a decreasing sheet resistance with increasing boron concentration up to 3.1±0.6×1021/cm3, and are polycrystalline. As the boron concentration exceeds 3.1±0.6×1021/cm3, the sheet resistance increases dramatically. It is shown that as the boron concentration in the silicon film exceeds 3.1±0.6×1021/cm3, the films transition from a completely polycrystalline phase to a combination of polycrystalline and amorphous phases as deposited. The amorphous phase has a higher boron concentration than the polycrystalline phase, as shown by selective Auger electron spectroscopy and secondary ion mass spectrometry. The relative fraction of amorphous phase can be controlled by boron concentration.
Physical and electrical properties of ultrathin HfO2/HfSixOy stacked gate dielectrics on compressively strained-Si0.74Ge0.26/Si heterolayers
Authors: Maikap S. , Lee Je-Hun , Kim Doh-Y. , Mahapatra R. , Ray S. K. , Song Jae-Hoon , No Y. S. , Choi Won-Kook
Published: February 2004

The physical properties of HfO2/HfSixOy stacked gate dielectric films deposited on compressively strained-Si0.74Ge0.26/Si heterolayers have been investigated using Rutherford backscattering spectrometry, high-resolution transmission electron microscopy, time-of-flight secondary ion mass spectroscopy, and Auger electron spectroscopy measurements. Polycrystalline HfO2 film with physical thickness of ∼4.0 nm and an amorphous interfacial layer with a physical thickness of ∼4.5 nm has been observed. Secondary ion mass spectroscopy and Auger electron spectroscopy analyses show the formation of an amorphous Hf-silicate interfacial layer between the oxide deposited and SiGe films. The electrical properties in terms of capacitance–voltage (C–V), conductance–voltage, hysteresis, current density-electric field, and shift in gate voltage under constant current stress have been studied using a metal–oxide–semiconductor structure. Dielectric constants of 26 for HfO2 and 8.0 for the interfacial Hf-silicate layer have been calculated from the high frequency C–V (100 kHz) characteristics. These dielectrics show an equivalent oxide thickness as small as 0.6 nm for HfO2 and 2.2 nm for the interfacial silicate layer. The fixed oxide charge density and interface state density are found to be 1.5×1012 cm−2 and 5.5×1011 cm−2 eV−1, respectively, for HfO2 with the interfacial layer and those values are found to be 3.5×1012 cm−2 and 1.3×1012 cm−2 eV−1 for the Hf-silicate interfacial layer, respectively. The metal–oxide–semiconductor capacitor shows low hysteresis of 0.08 V, low leakage current density of ∼10−7 A/cm2 at −1.0 V, and breakdown field of 6.5 MV/cm for HfO2 with interfacial layer. Significant improvement of the charge trapping properties under Fowler–Nordheim constant current stress in HfO2 with the interfacial layer has been observed.
Formation mechanism and Coulomb blockade effect in self-assembled gold quantum dots
Authors: Hu S. F. , Yeh R. L. , Liu R. S.
Published: February 2004

Nanometer-scale Au quantum dots have been assembled on SiO2 by controlling the reaction of raw materials to form a citrate Au sol and aminosilane/dithiol treated patterned Si wafer. Details of the formation mechanism have been studied. Three gold colloidal particles (∼15 nm), aligned in a chain to form a one-dimensional current path, were bridged on an 80 nm gap between the source and drain metal electrodes. The device exhibited a Coulomb blockade effect at 33 K.
Characterization of scratches generated by a multiplaten copper chemical–mechanical polishing process
Authors: Teo T. Y. , Goh W. L. , Lim V. S. K. , Leong L. S. , Tse T. Y. , Chan L.
Published: February 2004

Copper (Cu) chemical–mechanical polishing (CMP) using a multiplaten approach is a key process in the fabrication of Cu interconnects. It is customary to employ different slurries on each platen in a bid to optimize the performance of the Cu CMP process. These slurries generally contain abrasive particles that aid in the removal of material during CMP, but their presence is likely to result in the formation of scratches. In this article, a defect source analysis (DSA) technique was employed to identify the different types of scratches that were generated progressively by the three platens of an Applied Materials Mirra CMP polisher. In addition, the DSA technique also allowed tracking of the scratches from one platen to the next. Our results showed that scratches due to platen 1 were likely to result in more damage, and this was attributed to the use of alumina abrasive particles on platen 1.
Fabrication of InP-based two-dimensional photonic crystal membrane
Authors: Xing Aimin , Davanco Marcelo , Blumenthal Daniel J. , Hu Evelyn L.
Published: February 2004

The fabrication process of a InP-based two-dimensional photonic crystal membrane structure is developed. The process includes a well-calibrated electron-beam (e-beam) lithography and InGaAsP/InP etching using methane–hydrogen–argon reactive ion etching. The photonic crystal blocks with ten rows of a hexagonal array of holes with various lattice constants and filling factors are successfully fabricated and characterized by optical transmission measurement. The sensitivity of the band gap to the systematic fabrication error is determined.
Resolution-limiting factors in low-energy electron-beam proximity projection lithography: Mask, projection, and resist process
Authors: Yoshizawa Masaki , Oguni Kumiko , Nakano Hiroyuki , Amai Keiko , Nohama Shoji , Moriya Shigeru , Kitagawa Tetsuya
Published: February 2004

The resolution-limiting factors in low-energy electron-beam proximity projection lithography were analyzed quantitatively using the blur of a Gaussian-shaped latent image (σQBP) as the resolution index. σQBP is the square root of the sum of squares of the factors, such as electron scattering and resolution performance of resist. The resolution limit of 45 nm for isolated patterns and the resolution of 70 nm for practically used periodic patterns with 10% exposure latitude were achieved at σQBP of 49 nm. Eliminating a crossover in the electron optics decreased the factor depending on the gap between a mask and a wafer to 19 nm at a 40 μm gap. Because of the intensive studies on multilayer processes, the factor attributed to the resolution performance of thin resist dropped from 58 to 26 nm. Reduction in the blur due to electron scattering, 34 nm in the case of a 70-nm-thick resist film and 2 keV electrons, must be considered for the 45 nm technology node.
Nanofabrication using nanotranslated stencil masks and lift off
Authors: Racz Zoltan , He Jianli , Srinivasan Srivatsan , Zhao Wei , Seabaugh Alan , Han Keping , Ruchhoeft Paul , Wolfe Jack
Published: February 2004

We propose and demonstrate a technique for forming nanometer-scale metal features based on evaporation onto a substrate through a stencil mask. In this work, the stencil mask is laterally translated by a piezoflexure stage, between evaporations of different metals. The metals are chosen based on their etch chemistry to allow one material to be lifted off with respect to another. In this way, sidewall features are formed with dimensions and spacings controlled by moving the translational stage, which has 1 nm resolution.
Analysis of the two-dimensional-dopant profile in a 90 nm complementary metal–oxide–semiconductor technology using scanning spreading resistance microscopy
Authors: Eyben P. , Alvarez D. , Jurczak M. , Rooyackers R. , De Keersgieter A. , Augendre E. , Vandervorst W.
Published: February 2004

In this study we demonstrate the capabilities of scanning spreading resistance microscopy (SSRM), which is an atomic force microscope based technique, for two-dimensional (2D) carrier profiling with nanometer spatial resolution, high quantification accuracy, and high concentration sensitivity. As a test vehicle we discuss the application of SSRM on devices obtained from a 90 nm node complementary metal–oxide–semiconductor technology. Transistors processed in this technology, and with poly-gate lengths down to 70 nm have been analyzed using SSRM. Dedicated quantification software has been used to calculate carrier concentration profiles. The source/drain implants and the halo- and threshold voltage adjustment implants have been analyzed for different gate sizes in order to understand their impact on the 2D channel carrier profile. The SSRM results have been compared to the results of calibrated process simulators.
Assessing the performance of two-dimensional dopant profiling techniques
Authors: Duhayon N. , Eyben P. , Fouchier M. , Clarysse T. , Vandervorst W. , Álvarez D. , Schoemann S. , Ciappa M. , Stangoni M. , Fichtner W. , Formanek P. , Kittler M. , Raineri V. , Giannazzo F. , Goghero D. , Rosenwaks Y. , Shikler R. , Saraf S. , Sadewasser S. , Barreau N. , Glatzel T. , Verheijen M. , Mentink S. A. M. , von Sprekelsen M. , Maltezopoulos T. , Wiesendanger R. , Hellemans L.
Published: February 2004

This article discusses the results obtained from an extensive comparison set up between nine different European laboratories using different two-dimensional (2D) dopant profiling techniques (SCM, SSRM, KPFM, SEM, and electron holography). This study was done within the framework of a European project (HERCULAS), which is focused on the improvement of 2D-profiling tools. Different structures (staircase calibration samples, bipolar transistor, junctions) were used. By comparing the results for the different techniques, more insight is achieved into their strong and weak points and progress is made for each of these techniques concerning sample preparation, dynamic range, junction delineation, modeling, and quantification. Similar results were achieved for similar techniques. However, when comparing the results achieved with different techniques differences are noted.
Selective growth of carbon nanotube on scanning probe tips by microwave plasma chemical vapor deposition
Authors: Pan F. M. , Liu Y. B. , Chang Y. , Chen C. Y. , Tsai T. G. , Chang M. N. , Sheu J. T.
Published: February 2004

We have selectively grown carbon nanotubes on the probe tip of an atomic force microscope by microwave plasma chemical vapor deposition. The catalyst domain was defined on the tip apex of an Si based scanning probe by local electric field induced oxidation of a TiN cap layer, under which the cobalt catalyst layer was predeposited on the probe surface. High resolution atomic force microscopy images of an SiO2 trench pattern are demonstrated using the carbon nanotube tip. The nanotube tip fabrication method is simple and compatible with existing thin film process technology.
Compositional effects on electrical and mechanical properties in carbon-doped oxide dielectric films: Application of Fourier-transform infrared spectroscopy
Authors: Andideh Ebrahim , Lerner Michael , Palmrose Gerald , El-Mansy Safaa , Scherban Tracey , Xu Guanghai , Blaine Jeanette
Published: February 2004

Organosilicate glasses, also known as carbon-doped oxides (CDO), have been studied for application as interlayer dielectrics in microprocessors. Fourier-transform infrared (FTIR) spectroscopy is used here to monitor CDO film compositions prepared by plasma-enhanced chemical vapor deposition of dimethyldimethoxysilane. The Si–CH3/Si–O peak area ratios represent the relative content of these functional groups within the films, and indicate compositional changes in the films produced. Additionally, a close inspection of the C–H stretching modes shows a large peak at 2962 cm−1 due to the CH3 asymmetric stretch and a smaller shoulder to the right, made up of up to three other C–H stretching modes. The shoulder intensity divided by the asymmetric stretch intensity provides another metric that tracks compositional changes in the film. Product compositions indicated by FTIR also correlate well with physical properties such as dielectric constant, hardness, bulk modulus, and cohesive strength.
Exploring the ultimate resolution of positive-tone chemically amplified resists: 26 nm dense lines using extreme ultraviolet interference lithography
Authors: Golovkina V. N. , Nealey P. F. , Cerrina F. , Taylor J. W. , Solak H. H. , David C. , Gobrecht J.
Published: February 2004

Interference lithography (IL) [Yen et al., Appl. Opt. 31, 2972 (1992)] based on reflective optics, and utilizing extreme ultraviolet (EUV) light from an electron storage ring, can be used to pattern structures with periods below 70 nm [Solak et al., Appl. Phys. Lett. 75, 2328 (1999); Ali et al., Microelectron. Eng. 65, 454 (2003)]. Previously achromatic interferometers with EUV transmission diffraction gratings were also used for this purpose [Wei et al., J. Vac. Sci. Technol. B 12, 3648 (1994)], and recently we have printed sub-50 nm high quality periodic structures in poly(methylmethacrylate) exposed with transmission-grating EUV interference lithography (EUV-IL) [Solak et al., Microelectron. Eng. 61, 77 (2002); Solak et al., ibid. 67-68, 56 (2003)]. With this technique, two-dimensional patterns are easily achievable using multiple diffraction gratings. Both types of EUV-IL have been implemented on one of the undulator beam lines at the University of Wisconsin-Madison Synchrotron Radiation Center electron storage ring because this undulator source provides a tunable and coherent beam of radiation well suited for IL studies. In this article, both exposure methods were applied to explore the ultimate resolution of two positive-tone chemically amplified resists supplied by the Shipley Corporation. We have demonstrated the printing of features as small as 26 nm line and space in Shipley XP9947W-100 resist. The present results demonstrate the fine quality of the above-mentioned EUV-IL techniques to test resist formulations for high-resolution patterning, and we provide the experimental setup and discuss the observed results.
Secondary defect formation in bonded silicon-on-insulator after boron implantation
Authors: Saavedra A. F. , King A. C. , Jones K. S. , Jones E. C. , Chan K. K.
Published: February 2004

Silicon-on-insulator (SOI) has proven to be a viable alternative to traditional bulk silicon for fabrication of complementary metal–oxide–semiconductor devices. However, a number of unusual phenomena with regards to diffusion and segregation of dopants in SOI have yet to be explained. In the present study, SOITEC wafers were thinned to 700 and 1600 Å using oxidation and etching. Ion implantation was performed into SOI and bulk silicon wafers using B+11 ions at 6.5 and 19 keV with a dose of 3×1014 cm−2. Thermal processing occurred in a furnace at 750 °C for times ranging from 5 min to 8 h under an inert ambient. Using quantitative transmission electron microscopy it was observed that the concentration of trapped interstitials and density of {311} defects was significantly reduced in SOI compared to the bulk. Hall effect was used to monitor the activation process of boron in SOI and bulk silicon. Significantly less activation was observed in SOI compared to the bulk and was dependent on the surface silicon thickness. For the first time, a decrease in the trapped interstitial concentration is observed in SOI even with minimal dose loss to the buried oxide. It is hypothesized that the formation of boron–interstitial clusters may be more pronounced in SOI, leading to a reduction in the trapped interstitial population and {311} defect density.
Nondestructive dopant profile measurement and its quantitative analysis using the nanocapacitance–voltage method
Authors: Kang Eu-Seok , Hwang Ho-Jung , Lee Gyoo-Yeong
Published: February 2004

We propose a new method that can quantitatively extract the dopant profile in a nondestructive manner using scanning capacitance microscopy (SCM) or a nanocapacitance–voltage (nano-C–V) system. The method is based on a nanotip capacitor model, and not the common parallel-plate capacitor model. For the first time, we have physically analyzed a nanotip capacitor by considering the interaction between the air and a semiconductor and have calculated the full C–V curves and the rate of capacitance change with bias (dC/dV). We calculated the local dC/dV curve that was matched to the experimental dC/dV data. This quasi-three-dimensional modeling illustrates that the C–V characteristics derived from the nanotip model are different from those of a conventional parallel-plate method. We found that the increase in capacitance in the inversion region (characterized by a double peak in the dC/dV curve) is due to the quasispherical characteristics of the depleted layer generated by the nanotip located in the air. These results enable the quantification of dopant profiles in a step-by-step process using a one-dimensional inversion algorithm, and their subsequent comparison with a secondary ion mass spectroscopy profile.
Nanoimprint lithography of chromophore molecules under high-vacuum conditions
Authors: Pisignano Dario , Melcarne Angelo , Mangiullo Diego , Cingolani Roberto , Gigli Giuseppe
Published: February 2004

We report on high-vacuum nanoimprint lithography onto chromophore dye molecules embedded in optically inert polymer matrices. A specifically designed high-vacuum (10−5–10−6 mbar) chamber to perform nanoimprint lithography at temperatures up to 300 °C and pressures up to 105 psi on areas of more than 25 cm2 allows us to imprint in principle any class of thermoplastic molecules without loss of functionality. We tested our system by imprinting different polymers and polymer/dyes blends, demonstrating that the photoluminescence efficiency of light-emitting molecules is preserved in the lithography process.
Method of control of nitrogen content in ZnO films: Structural and photoluminescence properties
Authors: Ma J. G. , Liu Y. C. , Mu R. , Zhang J. Y. , Lu Y. M. , Shen D. Z. , Fan X. W.
Published: February 2004

In this article, nitrogen doped ZnO thin films with various nitrogen concentrations were obtained by thermal processing of zinc oxynitride alloy films prepared by radio frequency reactive magnetron sputtering. X-ray photoelectron spectroscopy study shows that varying the annealing temperature can modulate the concentration of nitrogen in ZnO. X-ray diffraction and Raman scattering measurements were employed to investigate the structural changes of ZnO films induced by the introduction of nitrogen. The results of the temperature-dependent photoluminescence measurements suggest that the optical properties of ZnO thin films are strongly influenced by nitrogen incorporation. With this technique, the binding energy of the nitrogen acceptor is also estimated.
Negative resist image by dry etching as a surface imaging process using focused ion beams
Authors: Arshak Khalil , Mihov Miroslav , Arshak Arous , McDonagh Declan , Sutton David , Newcomb Simon B.
Published: February 2004

Focused ion beam (FIB) lithography has significant advantages over the electron beam counterpart in terms of resist sensitivity, backscattering, and proximity effects. However, combining the FIB lithography with top surface imaging (TSI) will extend its advantages by allowing anisotropic processing of thicker resist layers. This article reports the development of novel single layer lithography process by combining focused Ga+ ion beam (Ga+ FIB) lithography, silylation, and oxygen dry etching. The negative resist image by dry etching is a TSI scheme for DNQ/novolak based resists and can result in either positive or negative resist images depending on the extent of the ion beam exposure dose. Results show that the Ga+ ion beam dose in the range of 1–50 μC/cm2 at 30 keV can successfully prevent silylation of the resist, thus resulting in the formation of a positive image after the dry etching. A negative image can be formed by using a second Ga+ ion beam exposure with a dose higher than 900 μC/cm2 at 30 keV to pattern lines into the original exposed resist area. It was observed that resist regions exposed to such high doses can effectively withstand oxygen dry development, thus giving formation of negative resist image. In this study, nanometer resist patterns with a high aspect ratio up to 15 were successfully resolved due to the ion beam exposure and anisotropic dry development. This novel TSI scheme for ion beam lithography could be utilized for the fabrication of critical complementry metal–oxide–semiconductor process steps, such as deep isolation trench formation and lithography over substantial topography.
Silicon–germanium spherical quantum dot infrared photodetectors prepared by the combination of bottom-up and top-down technologies
Authors: Lin Tse-Chi , Lee Si-Chen , Cheng Hung-Hsiang
Published: February 2004

By combining a bottom-up, i.e., thermal evaporation method, and the top-down technologies, i.e., molecular beam epitaxy, the spherical SiGe quantum dot infrared photodetectors (QDIP) have been successfully fabricated for the first time. The thermal evaporation method was chosen to synthesize spherical SiGe nanoparticles. They are treated with methanol containing alumina powders in the ultrasonic bath to form a single SiGe dot layer with density about 1.6×1011 cm−2. The QDIP exhibits two response regions, i.e., 1–3.5 and 14–20 μm. The peak responsivity of QDIP is 5.4 mA/W at 2 μm and about 0.6 mA/W at 17 μm at a bias of 200 mV. This QDIP also exhibits photovoltaic response, a short circuit current exists at zero bias. This device is capable of operating up to 240 K with good performance.
Specific contact resistance of Ti/Al/Pt/Au ohmic contacts to phosphorus-doped ZnO thin films
Authors: Ip K. , Heo Y. W. , Baik K. H. , Norton D. P. , Pearton S. J. , Ren F.
Published: February 2004

The carrier concentration dependence of Ti/Al/Pt/Au ohmic contact resistance on P-doped n-type ZnO thin films is reported. Ti (200 Å)/Al (800 Å)/Pt (400 Å)/Au (800 Å) was deposited by electron-beam evaporation on ZnO thin films grown by pulsed laser deposition on (0001) sapphire substrates using a ZnO:P0.02 source. Postgrowth annealing from 30 to 600 °C resulted in carrier concentrations of 7.5×1015 cm−3–1.5×1020 cm−3 in the ZnO. After metal deposition, the specific contact resistances were measured at temperatures in the range 30–100 °C prior to alloying annealing at 200 °C and at 30–200 °C after this anneal. The lowest specific contact resistance of 8.7×10−7 Ω cm2 for nonalloyed ohmic contacts was achieved in the sample with carrier concentration of 1.5×1020 cm−3 when measured at 30 °C. In the annealed samples, minimum specific contact resistances of 3.9×10−7 Ω cm2 and 2.2×10−8 Ω cm2 were obtained in samples with carrier concentrations of 6.0×1019 cm−3 measured at 30 °C and 2.4×1018 cm−3 measured at 200 °C, respectively. Auger electron spectroscopy detected Ti–O interfacial reaction and intermixing between Al and Pt at 200 °C.
Alteration of Cu conductivity in the size effect regime
Authors: Rossnagel S. M. , Kuan T. S.
Published: February 2004

The resistivity of thin Cu films depends on film thickness as the dimensions approach the electron mean-free-path for Cu of 39 nm. The key size-dependent contributions are from electron–surface scattering, grain boundary scattering, and surface roughness-induced scattering. Measurements with pseudoepitaxial Cu films deposited on Si have been undertaken to reduce effects of grain boundaries and surface roughness and suggest an electron-scattering parameter of p=0.12. Overlayers of metal films on the Cu generally increase the resistivity for Ta and Pt overlayers, and may reduce the resistivity for Au and Al. The resistivity increase may also be reversed if the overlayer oxidizes.
Initiation and evolution of phase separation in GaP/InP short-period superlattices
Authors: Shin B. , Chen W. , Goldman R. S. , Song J. D. , Kim J. M. , Lee Y. T.
Published: February 2004

We have investigated the initiation and evolution of lateral phase separation in GaP/InP short-period superlattices (SPSs). Cross-sectional scanning tunneling microscopy reveals lateral contrast modulations within the SPS region, presumably due to alloy phase separation. The wavelength of the modulations appears to be constant throughout the entire SPS structure. Interestingly, the wavelength is dependent on the thickness of the constituent layers of the superlattice, and is likely to be affected by an observed significant concentration of group V vacancies. Together, these results suggest that phase separation is initiated by compositional nonuniformities from excess surface adatoms due to incomplete coverage of the constituent layers of the superlattice, and that the phase separation process is assisted by In–Ga interdiffusion via P vacancies.
Effect of nitride sidewall spacer process on boron dose loss in ultrashallow junction formation
Authors: Kohli P. , Jain Amitabh , Bu H. , Chakravarthi S. , Machala C. , Dunham S. T. , Banerjee S. K.
Published: February 2004

A nitride spacer with an underlying deposited tetraethoxysilane oxide, that behaves as a convenient etch stop layer, is a popular choice for sidewall spacer in modern complementary metal–oxide–semiconductor process flows. In this work we have investigated the effect of the silicon nitride spacer process on the boron profile in silicon and the related dose loss of B from the Si into the silicon dioxide. This is reflected as a dramatic decrease in the junction depth. We find that the silicon nitride influences the concentration of hydrogen in the silicon dioxide during the final source/drain anneal. The presence of H enhances the diffusivity of B in the silicon dioxide and thereby results in a significant dose loss from the Si into the silicon dioxide. In this work we have shown this dose loss can be lowered by altering the silicon nitride stoichiometry.
Accuracy of scanning capacitance microscopy for the delineation of electrical junctions
Authors: Stangoni Maria , Ciappa Mauro , Fichtner Wolfgang
Published: February 2004

In this work, we investigate the theoretical and the experimental accuracy limits of the delineation of pn junctions by scanning capacitance microscopy. We compare three different techniques basing both on experimental data and on one- and two-dimensional simulations of scanning capacitance measurements of epitaxial and shallow junctions.
Nanomanipulator and actuator fabrication on glass capillary by focused-ion-beam-chemical vapor deposition
Authors: Kometani Reo , Morita Takahiko , Watanabe Keiichiro , Hoshino Takayuki , Kondo Kazushige , Kanda Kazuhiro , Haruyama Yuichi , Kaito Takashi , Fujita Jun-ichi , Ishida Masahiko , Ochiai Yukinori , Matsui Shinji
Published: February 2004

Three-dimensional (3D) nanostructures on a glass capillary have a number of useful applications such as manipulators, actuators, and sensors in the various microstructures. We observed a phenomenon that two diamondlike-carbon pillars on a tip of glass capillary fabricated by 30 keV Ga+ focused-ion-beam-chemical vapor deposition (FIB-CVD) with a precursor of phenanthrene vapor was able to work as a manipulator during FIB irradiation. It became clear that it was caused by electronic charge repulsion between two pillars, which accumulated electric charge by FIB irradiation. By applying this moving mechanism, we have developed a 3D nanomanipulator and actuator on a tip of glass capillary by FIB-CVD. Furthermore, in situ observations of movement for a 3D nanomanipulator and actuator have been demonstrated by applying voltage onto a Au-coated glass capillary.
Isotropic/anisotropic growth behavior and faceting morphology of Si epitaxial layer selectively grown by cold wall ultrahigh vacuum chemical vapor deposition
Authors: Lim Seung-Hyun , Song Sukchan , Yoon Euijoon , Lee Jong-Ho
Published: February 2004

Si epitaxial layers were selectively grown on local oxidation of silicon patterned Si (100) substrates by the cold wall ultrahigh vacuum chemical vapor deposition under various growth conditions. The isotropic/anisotropic growth behavior and the faceting morphology of Si epitaxial layers were systematically investigated. As the growth temperature increased and the Si2H6 flow rate decreased, the lateral overgrowth of Si was reduced, and subsequently the anisotropic selective epitaxial growth (SEG) of Si was enhanced. Depending on growth conditions, the lateral overgrowth was not initiated until the layer thickness exceeded a critical value, and the degree of lateral overgrowth was changed with the layer thickness. These observations strongly imply that the mass transport and accumulation processes on facet surfaces play an important role in the SEG morphological change. Taking both surface mass transport and free energy change into account, a model is proposed to explain our experimental observations, and the detailed discussion is provided. Finally, we confirmed the proposed model through the experimental and theoretical analysis of the Si growth rate change on the (111) facet plane with facet length, which highlights the strong dependence of the mass transport and accumulation processes on the difference between facet length and surface diffusion length.
Large Shifts in Pathogen Virulence Relate to Host Population Structure
Authors: Boots M. , Hudson P. J. , Sasaki A.
Published: February 2004

Theory on the evolution of virulence generally predicts selection for an optimal level of virulence determined by trade-offs with transmission and/or recovery. Here we consider the evolution of pathogen virulence in hosts who acquire long-lived immunity and live in a spatially structured population. We show theoretically that large shifts in virulence may occur in pathogen populations as a result of a bistability in evolutionary dynamics caused by the local contact or social population structure of the host. This model provides an explanation for the rapid emergence of the highly virulent strains of rabbit hemorrhagic disease virus.
48,000 Years of Climate and Forest Change in a Biodiversity Hot Spot
Authors: Bush Mark B. , Silman Miles R. , Urrego Dunia H.
Published: February 2004

A continuous 48,000-year-long paleoecological record from Neotropical lower montane forest reveals a consistent forest presence and an ice-age cooling of ∼5° to 9°C. After 30,000 years of compositional stability, a steady turnover of species marks the 8000-year-long transition from ice-age to Holocene conditions. Although the changes were directional, the rates of community change were no different during this transitional period than in the preceding 30,000-year period of community stability. The warming rate of about 1°C per millennium during the Pleistocene-Holocene transition was an order of magnitude less than the projected changes for the 21st century.
Selective D2 Receptor Actions on the Functional Circuitry of Working Memory
Authors: Wang Min , Vijayraghavan Susheel , Goldman-Rakic Patricia S.
Published: February 2004

Prefrontal neurons engaged by working memory tasks express a sequence of phasic and tonic activations linked to a train of sensory, mnemonic, and response-related events. Here, we report that the dopamine D2 receptor selectively modulates the neural activities associated with memory-guided saccades in oculomotor delayed-response tasks yet has little or no effect on the persistent mnemonic-related activity, which is instead modulated by D1 receptors. This associates the D2 receptor with a specific component of working memory circuitry and fractionates the modulatory effects of D1 and D2 receptors on the neural machinery of a cognitive process.
Rheology and Microscopic Topology of Entangled Polymeric Liquids
Authors: Everaers Ralf , Sukumaran Sathish K. , Grest Gary S. , Svaneborg Carsten , Sivasubramanian Arvind , Kremer Kurt
Published: February 2004

The viscoelastic properties of high molecular weight polymeric liquids are dominated by topological constraints on a molecular scale. In a manner similar to that of entangled ropes, polymer chains can slide past but not through each other. Tube models of polymer dynamics and rheology are based on the idea that entanglements confine a chain to small fluctuations around a primitive path that follows the coarse-grained chain contour. Here we provide a microscopic foundation for these highly successful phenomenological models. We analyze the topological state of polymeric liquids in terms of primitive paths and obtain parameter-free, quantitative predictions for the plateau modulus, which agree with experiment for all major classes of synthetic polymers.
Global Mapping of the Yeast Genetic Interaction Network
Authors: Tong Amy Hin Yan , Lesage Guillaume , Bader Gary D. , Ding Huiming , Xu Hong , Xin Xiaofeng , Young James , Berriz Gabriel F. , Brost Renee L. , Chang Michael , Chen YiQun , Cheng Xin , Chua Gordon , Friesen Helena , Goldberg Debra S. , Haynes Jennifer , Humphries Christine , He Grace , Hussein Shamiza , Ke Lizhu , Krogan Nevan , Li Zhijian , Levinson Joshua N. , Lu Hong , Ménard Patrice , Munyana Christella , Parsons Ainslie B. , Ryan Owen , Tonikian Raffi , Roberts Tania , Sdicu Anne-Marie , Shapiro Jesse , Sheikh Bilal , Suter Bernhard , Wong Sharyl L. , Zhang Lan V. , Zhu Hongwei , Burd Christopher G. , Munro Sean , Sander Chris , Rine Jasper , Greenblatt Jack , Peter Matthias , Bretscher Anthony , Bell Graham , Roth Frederick P. , Brown Grant W. , Andrews Brenda , Bussey Howard , Boone Charles
Published: February 2004

A genetic interaction network containing ∼1000 genes and ∼4000 interactions was mapped by crossing mutations in 132 different query genes into a set of ∼4700 viable gene yeast deletion mutants and scoring the double mutant progeny for fitness defects. Network connectivity was predictive of function because interactions often occurred among functionally related genes, and similar patterns of interactions tended to identify components of the same pathway. The genetic network exhibited dense local neighborhoods; therefore, the position of a gene on a partially mapped network is predictive of other genetic interactions. Because digenic interactions are common in yeast, similar networks may underlie the complex genetics associated with inherited phenotypes in other organisms.