Showing papers in "Materials Science & Engineering R-reports in 1998"
TL;DR: In this paper, the current knowledge on dislocation types and slip systems, the development of deformation substructures, factors controlling the mobility and multiplication of dislocations, interface related plasticity, solid solution and precipitate strengthening mechanisms as well as microscopic aspects of creep and fracture are addressed.
Abstract: During the past decade considerable research efforts have been directed towards achieving balanced engineering properties of two-phase γ-titanium aluminide alloys for future applications as structural materials. For optimization of mechanical properties such as yield and creep strengths, tensile ductility and fracture resistance, a basic understanding of the temperature dependent micromechanisms of plasticity and fracture, and their interplay with various microstructural constituents is required. In this review article, the current knowledge on dislocation types and slip systems, the development of deformation substructures, factors controlling the mobility and multiplication of dislocations, interface related plasticity, solid solution and precipitate strengthening mechanisms as well as microscopic aspects of creep and fracture will be addressed. These topics will be related to specific microstructures and associated engineering properties.
633 citations
TL;DR: In this article, the authors present the present knowledge on tantalum pentoxide (Ta 2 O 5 ) thin films and their applications in the field of microelectronics and integrated microtechnologies.
Abstract: This paper reviews the present knowledge on tantalum pentoxide (Ta 2 O 5 ) thin films and their applications in the field of microelectronics and integrated microtechnologies. Different methods used to produce tantalum oxide layers are described, emphazing elaboration mechanisms and key parameters for each technique. We also review recent advances in the deposition of Ta 2 O 5 in the particular field of microelectronics where high quality layers are required from the structural and electrical points of view. The physical, structural, optical, chemical and electrical properties of tantalum oxide thin films on semiconductors are then presented and essential film parameters, such as optical index, film density or dielectric permittivity, are discussed. After a reminder of the basic mechanisms that control the bulk electrical conduction in insulating films, we carefully examine the origin of leakage currents in Ta 2 O 5 and present the state-of-the-art concerning the insulating behaviour of tantalum oxide layers. Finally, applications of tantalum oxide thin films are presented in the last part of this paper. We show how Ta 2 O 5 has been employed as an antireflection coating, insulating layer, gate oxide, corrosion resistant material, and sensitive layer in a wide variety of components, circuits and sensors.
627 citations
TL;DR: In this paper, a promising approach is connected with the use of continuum mechanics, which has been successfully applied to the analysis of compaction of porous bodies, based upon the theories of plastic and nonlinear-viscous deformation of porous body.
Abstract: Theoretical concepts of sintering were originally based upon ideas of the discrete nature of particulate media. However, the actual sintering kinetics of particulate bodies are determined not only by the properties of the particles themselves and the nature of their local interaction with each other, but also by macroscopic factors. Among them are externally applied forces, kinematic constraints (e.g. adhesion of the sample's end face and furnace surface), and inhomogeneity of properties in the volume under investigation (e.g. inhomogeneity of initial density distribution created during preliminary forming operations). Insufficient treatment of the questions enumerated above was one of the basic reasons hindering the use of sintering theory. A promising approach is connected with the use of continuum mechanics, which has been successfully applied to the analysis of compaction of porous bodies. This approach is based upon the theories of plastic and nonlinear-viscous deformation of porous bodies. Similar ideas have recently been embodied in a continuum theory of sintering. The main results of the application of this theory for the solution of certain technological problems of sintering are introduced including their thermo–mechanical aspects.
581 citations
TL;DR: In this article, the authors reviewed the device structure, electrical and optical device physics, and the material properties of TFEL displays, focusing on the phosphor layer properties and the radiative recombination phenomenon that is responsible for luminescence.
Abstract: Thin film electroluminescent (TFEL) displays are complex optoelectronic devices with challenging material requirements. The multilayer device structure includes two electrodes (one metallic and one transparent), two insulators, and a semiconducting ‘phosphor’ layer. Each layer has unique electronic and optical properties that must be satisfied for device operation. In this article, we review the device structure, the electrical and optical device physics, and the material properties of TFEL displays. Particular attention is given to the phosphor layer properties and the radiative recombination phenomenon that is responsible for luminescence. The current status of the red, green, blue and white TFEL phosphors is also reviewed, and the current and future applications are discussed.
413 citations
TL;DR: In this paper, the interplay of diffusion and aggregation was studied by Monte Carlo simulations, and it was shown that reactive metals do not have any long-range mobility and are effective diffusion barriers, whereas isolated atoms of less reactive metals diffuse deep into polymers at elevated temperatures.
Abstract: First information on metal diffusion in polymers resulted from surface spectroscopies which mainly provided insight into chemical interactions of metals at polymer surfaces and into their growth mode. Medium energy ion scattering, electron microscopy, atomic force microscopy, and second-harmonic generation revealed a strong tendency of metals of low and intermediate reactivity to form clusters when deposited onto polymers. The interplay of diffusion and aggregation was also studied by Monte Carlo simulations. Metal diffusivities were obtained from radiotracer and Rutherford backscattering measurements. The available results show that reactive metals do not have any long-range mobility and are effective diffusion barriers. In contrast, isolated atoms of less reactive metals diffuse deep into polymers at elevated temperatures. However, the very pronounced aggregation tendency of these metals effectively impedes diffusion unless they are deposited at rates of the order of monolayers per minute or lower. Nevertheless, traces of noble metals always diffuse into polymers during the early stages of metal deposition, whereas no significant diffusion occurs from a continuous metal film. Even noble metal diffusivities are many orders of magnitude smaller than diffusivities of non-reactive gas molecules and largely decoupled from polymer dynamics. This is attributed to a pronounced reduction in the local chain mobility near metal atoms, e.g., by temporary metal-atom-induced crosslinking.
235 citations
TL;DR: In this paper, a self-monitoring (or intrinsically smart) structural material including concrete containing short carbon fibers, and polymer-matrix and carbon-carbon composites containing continuous carbon fibers were reviewed.
Abstract: Self-monitoring (or intrinsically smart) structural materials, including concrete containing short carbon fibers, and polymer-matrix and carbon-matrix composites containing continuous carbon fibers, were reviewed. Each material is capable of monitoring its own reversible strain and damage through the effects of these on the electrical resistance of the material. This capability is valuable for structural control and structural health monitoring. Among these three materials, the concrete gives the highest strain sensitivity or gage factor (up to 700), while the carbon-carbon composite gives the highest damage sensitivity (i.e., sensitivity even to the damage after the first cycle of tensile loading within the elastic regime). The origin of the self-monitoring ability differs among the three materials. For the concrete, it is related to slight fiber pull-out during strain and fiber and matrix fracture during damage. For the polymer-matrix composite, it is related to the increase in the degree of fiber alignment and reduction of fiber pre-stress during tension in the fiber direction and to fiber fracture and delamination during fatigue. For the carbon-carbon composite, it is related to dimensional changes during strain and fiber and matrix fracture during damage. © 1998 Elsevier Science S.A.
228 citations
TL;DR: Many compounds with general chemical formula A 2 BB′X 6 and with tolerance factor value t have been found in the literature, see as mentioned in this paper for a complete list of compounds and their tolerance factors.
Abstract: Many compounds with general chemical formula A 2 BB′X 6 and with tolerance factor value t
198 citations
TL;DR: In this article, the optical properties of nanometer-sized composite particles with a core-shell structure have been reviewed, and it was found that a strong chemical affinity between the metal salt and the polar head group of amphiphilic molecules and the anisotropic structure of microemulsion systems play a premier role in the growth.
Abstract: By using self-assembly molecules as a template, nanometer-sized plate-like metal oxide and semiconductor particles can be obtained by confined growth inside the lamellar bilayers of microemulsion systems. It was found that a strong chemical affinity between the metal salt and the polar head group of amphiphilic molecules and the anisotropic structure of microemulsion systems play a premier role in the anisotropic growth. Nanometer-sized composite particles (nano-composites) with a core-shell structure have been prepared by arrested precipitation of metal or semiconductor clusters in reverse micelles, followed by hydrolysis and condensation of organometallic precursors in the microemulsion matrices. Temporally discrete nucleation and growth at elevated temperature (70 °C) give the resulting particles a narrow size distribution and defined crystallinity. Both the size of the core particles and the thickness of the coating layers can be varied by controlling processing parameters such as the ratio of water to surfactant and the ratio of water to organometallic precursors. By controlling the pH conditions and aging temperatures, a transparent gel composing the nanometer-sized inorganic clusters has been obtained. Optical properties of nanometer-sized composite particles are reviewed. For silver metal clusters and nano-composites, the shift of the absorption peak at the surface-plasmon resonance frequency due to the classical limited mean-free path of the conduction electrons or quantum size effects has been observed. The enhanced third-order non-linear susceptibility of the silver nano-composites results from the local-field enhancement and size effects, which has been experimentally demonstrated by the optical phase-conjugation technique.
172 citations
TL;DR: In this article, the motivation for shallow junctions, specific requirements for shallow junction used in deep sub-micron dimension metal-oxide-semiconductor field effect transistors (MOSFETs), current understanding of implant and diffusion processes, and the state-of-the-art in low energy implantation and a number of alternate doping technologies, including plasma implantation, gas-immersion laser (GILD) doping, rapid vapor-phase doping (RVD), ion shower doping, and decaborane (B10H14) implantation.
Abstract: The fabrication of thin, sub-40 nm doped layers in Si with high concentrations of electrically active dopants and box-like profiles is a major technological challenge. Making these regions without introducing residual defects in the material and without affecting the properties of other material regions in the device is even more difficult. The need to control these properties of doping profiles in ultra-large-scale integrated (ULSI) circuits has driven the study of low energy implantation, transient enhanced diffusion (TED), and focused the search fornew shallow junction doping techniques. In this article, wereview the motivation for shallowjunctions, specific requirements for shallow junctions used in deep sub-micron dimension metal-oxide-semiconductor field effect transistors (MOSFETs), current understanding of implant and diffusion processes, and the state-of-the-art in low energy implantation and a number of alternate doping technologies, including plasma implantation, gas-immersion laser (GILD) doping, rapid vapor-phase doping (RVD), ion shower doping, and decaborane (B10H14) implantation.
123 citations
TL;DR: In this paper, a vibrational model for thermal expansion of refractory body centered cubic (BCC) metals has been proposed and the properties of these elements are evaluated in terms of models that interrelate the thermophysical properties, self diffusion, and high temperature thermal defects.
Abstract: Thermophysical properties at high temperatures and pressures are difficult to measure. Many reviews have approximated experimental data with empirical polynomial functions. In the case of thermal expansion and molar volume, extensive results for refractory body centered cubic (BCC) metals have been published. A critical evaluation of these experimental data is essential for many other studies. We provide this evaluation in terms of models that interrelate the thermophysical properties, self diffusion, and high temperature thermal defects. Experimental and theoretical methods for measuring and representing thermal expansion and the limitations of such methods are also briefly reviewed. Results for V, Nb, Ta, Mo, and W fall into two distinct subgroups relating to their elemental positions in the periodic table. The thermal expansions for these elements are analyzed within the constraints of a simple vibrational model and its equation of state. This approach represented the thermal expansion as the contributions from a perfect crystal and the crystal's high temperature anharmonicity as well as its thermal defects. Quantitative expressions, neglecting electronic contributions, are provided for the coefficient of thermal expansion and the expansivities for these five BCC metals from near 20°K to their melting temperatures. Vacancy formation enthalpies and entropies are also estimated. Our vacancy thermodynamic results are compared with earlier predictions and results from positron annihilation, thermal expansion, and specific heat measurements.
122 citations
TL;DR: In this paper, a review of low dielectric constant materials for interlayer dielectrics in ultralarge-scale integrated circuit (ULSI) multilevel interconnections is presented.
Abstract: This paper reviews low dielectric constant materials for interlayer dielectric films in ultralarge-scale integrated circuit (ULSI) multilevel interconnections. The trends of ULSIs in the last decade were briefly described first. Then, the requirements for interlayer dielectric film properties and their formation techniques were explained. They are: (1) a low dielectric constant, (2) a surface planarity, (3) a gap-filling capability, and (4) a low residual stress. In contrast with the requirements, the interlayer dielectric films and related technologies developed in the last decade were reviewed. In the requirements, the low dielectric constant materials are strongly required because the device performance has been limited by signal propagation time and cross-talk in the multilevel interconnections. Furthermore, the low dielectric constant is also required for reduction of power consumption in ULSI operation. Finally, the low dielectric constant materials were summarized, and future trends of the low dielectric constant interlayer dielectric film technologies are discussed.
TL;DR: A review of the literature on substitutions and their effect on the properties of the 90 K superconductor YBa 2 Cu 3 O δ (YBCO) can be found in this paper.
Abstract: The 90 K superconductor, YBa 2 Cu 3 O δ (YBCO), has proved to be highly adaptable chemically as it can accommodate a wide variety of cationic and anionic substitutions. Indeed, the majority of the chemical elements, excluding noble gases and actinides, have been reported to substitute to some extent into the YBCO structure. This review covers the literature on such substitutions and their effect on the properties of YBCO. Reported solubility limits are given, together with crystal symmetry and trends in unit cell parameters with dopant concentration. The dopant site is considered; this is additionally complex in the case of copper substitution because of the two distinct copper sites in the crystal structure. The effect of the dopant on the critical temperature, T c , is reviewed; the literature is often contradictory due to the dual effects of variable oxygen content and the nature of the dopant. Preparation methods appear to have an effect on solubility limits, crystal symmetry and T c , Also, the methods used to determine solubility limits are often imprecise which can lead to contradictions. The magnetic properties of doped materials are reviewed; for some dopants, particularly the magnetic lanthanides, antiferromagnetism and superconductivity co-exist. The related RBa 2 Cu 3 O δ phases (R = lanthanide), their structure, properties and behaviour on doping are reviewed in a similar way. For the larger rare earths, the related systems R 1+ x Ba 2- x CU 3 O δ , are reviewed; as x increases, the transition temperature decreases and compositions R 1.5 Ba 1.5 Cu 3 O δ are semiconducting. The upper and lower solubility limit changes with R, and for R = Dy, the upper limit is x = 0 composition, LaBa 2 Cu 3 O δ , cannot be prepared in air since substitution of La onto the Ba site occurs, forming the Ba-deficient solid solutions. The discovery of superconductivity above liquid nitrogen temperatures in YBa 2 Cu 3 O 7 , has generated a vast quantity of research; to date, > 20 000 papers have appeared on the 123 materials (source: BIDS). This review, therefore, cannot be comprehensive, but attempts to highlight important substitutions, their effect on the properties of YBCO and any contradictions in the literature.
TL;DR: A review of the approaches that have been used for silicon, aluminum, SiO2 and polymeric materials to suppress etching reactions at microstructure sidewalls is presented in this article.
Abstract: A prerequisite of successful microstructure fabrication in electronic materials using plasma-based etching methods is the ability to maximize the ratio of ion-enhanced etching reactions relative to spontaneous etching reactions. To produce vertical etching profiles, the rate of the etching reaction in line-of-sight of the plasma has to be large, whereas the lateral etching rate should vanish. We present a review of the approaches that have been used for silicon, aluminum, SiO2 and polymeric materials to suppress etching reactions at microstructure sidewalls. These approaches include the judicious choice of the primary etching gas, adding certain gases to the main etching gas, lowering the substrate temperature, mask material redeposition, or alternate etch and deposition cycles. Our knowledge of the sidewall chemistry resulting from these approaches, e.g. the production of sidewall passivation layers, and experimental methods that have been employed to study these, are reviewed. The impact of sidewall chemistry on the etching profiles of the final microstructure is also discussed.
TL;DR: A systematic overview of the work carried out in the area of pulsed laser deposition (PLD), characterization and device application aspects of high temperature superconducting YBCO thin films can be found in this article.
Abstract: This article presents a systematic overview of the work carried out in the area of pulsed laser deposition (PLD), characterization and device application aspects of high temperature superconducting YBCO thin films. The theoretical and experimental aspects of the pulsed laser deposition process for the synthesis of YBCO thin films have been described in detail. The deposition technique has emerged as a very powerful method to make composition and microstructure controlled superconducting YBCO films. Some unique features of this process are due to the rapid heating and evaporation of the target and the interaction of the laser beam with the evaporated materials leading to the formation of a high temperature plasma. Major advantages of PLD process are congruent evaporation and crystallinity due to the presence of high energy evaporants and fast response time. It has the potential to encompass a wide scope of physical vapor-deposition techniques from thermal evaporation to sputtering and MBE. The electrical and structural studies performed on laser deposited YBCO films have shown that films produced by PLD are superior than films produced by other thin film growth techniques. The major technical obstacle of particulates emission, encountered initially with PLD, has now greatly been solved. Some new developments with PLD technology such as large-area and nonplanar substrates coatings and growth of novel superconductors as oriented films have been demonstrated.
TL;DR: In this article, a review of recent developments in scanning probe microscopy (SPM) on organic materials are reviewed with selected examples, including instrumentation and particularities in connection with SPM imaging on soft organic materials.
Abstract: In this paper recent developments in scanning probe microscopy ( SPM ) on organic materials are reviewed with selected examples. Presented subjects include instrumentation and particularities in connection with SPM imaging on soft organic materials. Exemplary cases of structure-properties investigations with SPM in organic materials science including amorphous polymers, polymer crystal growth effects, interface structure and stability, spinodal decomposition effects, copolymer and liquid crystal (LC) nanophase separation, LC phase transitions on a molecular scale, molecular manipulation as well as structure and properties of other organic materials are presented. Naturally, this paper cannot review all papers published about SPM on organic materials. Rather, main principles and problems as well as the strategy of probe microscopy on organic materials is elucidated with selected examples. SPM is shown to be an effective and forceful organic materials analytic tool for the materials scientist.
TL;DR: In this article, the authors review aspects of carrier dynamics concerning semiconductor quantum wells in the picosecond and femtosecond regime with emphasis on tunneling and spin relaxation which they were experimentally involved in.
Abstract: This article reviews aspects of carrier dynamics concerning semiconductor quantum wells in picosecond and femtosecond regime with emphasis on tunneling and spin relaxation which we were experimentally involved in. We refer to recent significant developments in the field. We also pick up intriguing aspects of quantum dots on possible applications to both electronic and photonic devices related to the carrier dynamics.