Field Of Materials Research Research Articles

Oriented Film Growth of Organic Semiconductor Sexithiophene on Artificial Periodic Grooves and Electrical Conduction Properties of the Films

ABSTRACTFilm growth of organic semiconductor α-sexithiophene (6T) was studied using substrates with artificial periodic grooves. The grooves were fabricated on thermally oxidized silicon substrates by electron beam lithography. Based on the orientation analysis by atomic force microscopy and grazing-incidence x-ray diffraction, part of the 6T grains grew having the in-plane orientational relationship with the artificial grooves. This phenomenon corresponds to “ggraphoepitaxy” which has been well known in inorganic materials research field. As well as the in-plane preferred orientation, one-dimensional structure consisting of connected 6T grains was observed. The electrical conduction properties of the films were also evaluated.

Defect reduction in sublimation grown SiC bulk crystals

Abstract For several years the major focus of material issues in SiC substrates was laid on the reduction of macroscopic defects like polytype inclusions, low angle grain boundaries and micropipes. Although significant improvements have been achieved, there are still shortcomings in material quality that have to be overcome. Since it is clear that dislocations are the main reason for degradation in power devices the prevailing attention has shifted to that field of material research. The aim of our work was to investigate the mechanisms that affect the generation of macroscopic and microscopic defects during sublimation growth. Intense studies were utilized on dislocation and stacking fault formation. For this reason we systematically varied parameters of the growth process and applied several methods for the characterization to evaluate material properties most precisely, e.g. KOH-defect-etching, X-ray-diffraction, electron microscopy and optical microscopy. The investigations were accompanied by failure analysis of devices of the Schottky type. We found out that for the improvement of substrate quality emphasis has to be laid on the reduction of thermoelastic stress in the growing crystal. From results of numerical calculations we were able to derive moderate growth conditions with reduced temperature gradients prevailing during the growth process. As a consequence we succeeded in decreasing the defect concentration. The best value so far achieved for the sum of both BPD and TED was 7×103 cm−2.

Multi purpose research reactor

At present Dhruva and Cirus reactors provide the majority of research reactor based facilities to cater to the various needs of a vast pool of researchers in the field of material sciences, physics, chemistry, bio sciences, research & development work for nuclear power plants and production of radio isotopes. With a view to further consolidate and expand the scope of research and development in nuclear and allied sciences, a new 20 MWt multi purpose research reactor is being designed. This paper describes some of the design features and safety aspects of this reactor.

Design and development of soft nanomaterials from biobased amphiphiles.

Design and development of different forms of soft matter from renewable (biomass) feedstocks is gaining attention in current research. This highlight summarizes our continuing efforts towards the effective utilization of renewable resources for new chemicals, fuels and soft materials, and selected successful stories in that direction. Cashew nut shell liquid, an industrial by-product, was used as a raw material to synthesize aryl glycolipids which upon self-assembly generated an array of soft materials such as lipid nanotubes, twisted/helical nanofibers, low-molecular-weight hydro/organogels and liquid crystals. These soft architectures were fully characterized by using different techniques. In another example, amygdalin, a by-product of the apricot industry, was used to develop novel amphiphiles, which showed unprecedented gelation properties in a wide range of solvents. To take these soft nanomaterials to a second level, we successfully demonstrated the utility of these hydrogels as drug delivery vehicles. Intriguingly, enzyme catalysis was used as a tool to make and break the hydrogels, which apparently triggered controlled drug delivery. We believe these results and this highlight will motivate us and others in the field of biobased materials research, green chemistry and soft material development through self-assembly processes, to design and develop new functional materials from plant/crop-based renewable resources, otherwise underutilized.

Carbon nanotubes for science and technology

The discovery of the fullerene molecule C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</inf> by Kroto, Heath, and Smalley in 1985 and the subsequent discovery of carbon nanotubes by Iijima in 1991 have launched entirely new fields of materials research and development. Carbon nanotubes are single molecules that can extend to lengths approaching 0.01 mm, and they are particularly important since they bridge the nanoscopic and macroscopic length scales. The physical properties that derive from this extended one-dimensional system have changed the way we think about materials for R&D activities as diverse as quantum transport in one-dimension and functionalizing structural materials in automobiles. Here we review the key developments of the science of carbon nanotubes and outline promising technology areas.

Raman spectroscopy of fullerenes and fullerene-nanotube composites.

The discovery of fullerenes in 1985 opened a completely new field of materials research. Together with the single-wall carbon nanotubes (SWCNTs) discovered later, these curved carbon networks are a playground for pure as well as applied science. We present a review of Raman spectroscopy of fullerenes, SWCNTs and composite materials. Beginning with pristine C(60), we discuss intercalated C(60) compounds and polymerized C(60), as well as higher and endohedral fullerenes. Concerning SWCNTs, we show how the diameter distribution can be obtained from the Raman spectra and how doping modifies the spectra. Finally, the Raman response of C(60) encapsulated into SWCNTs (C(60) peapods) is discussed.

Internet-Accessible Electronic Materials Database System

The Electronic Materials Database System described in this paper incorporates the Diagramma Database (phase diagrams of semiconductor systems) and the Kristall Database (substances with special acous- tooptic, electrooptic, and nonlinear optical properties). The database system is available in the Internet on the Web site http://phase.imet.ac.ru. The technology of integrating dissimilar databases of substances and materials is discussed, and the possibilities of using database systems in the fields of inorganic chemistry and materials research are examined.

Recent developments in positron research

Positrons are proving to be powerful analysis tool in the field of materials research and development. Due to positrons' highly interactive nature and how they affect their surroundings when they become trapped in a defect, positron spectroscopy is a fast growing field. Positron spectroscopy may be utilized to detect and analyze defects on and near the surfaces of many materials used in engineering applications today. This spectroscopy technique is very useful in the silicon and semiconductor industry for locating and analyzing the low amount of defects present in those materials. The research in this field is growing every year, with more types of positron sources being developed and more complete systems being operated. This article attempts to provide a recent review of the research in the positron fields of materials analysis and spectroscopy research.

Combinatorial study for ceramics powder by X-ray diffraction

Application of ceramics powder synthesis through solid and liquid processes to combinatorial chemistry is thought to be of much importance to expansion of material research field. Combinatorial robot system developed in our laboratory has the possibility of performing combinatorial synthesis through a liquid process. The robot system has an automatic arm. Automatic micropipette, attached to the arm, measures and mixes raw materials. Mixed samples were injected and carried to a pallet with many holes where the samples were sucked. The pallet filled with samples was heated in an electrical furnace. In this study, combinatorial powder XRD equipment with position-sensitive proportional counter (PSPC) was developed, which was able to measure a sample in only 2 min. Furthermore, combinatorial robot system and combinatorial X-ray diffraction clarified the influence of dopants on the structural phase transformation temperature of maghemite to hematite in case of using nanoparticle slurries as starting materials. Consequently, it was clarified that the structural phase transformation temperature of maghemite to hematite increased with increasing the adding amount of yttria nanoparticles and the temperature increased from ca. 540 to 820 °C by 2 at.% yttria addition.

New Directions in Photopolymerizable Biomaterials

AbstractThis article is based on the Outstanding Young Investigator Award presentation given by Kristi S. Anseth at the 2001 MRS Spring Meeting on April 17, 2001, in San Francisco. Anseth was recognized for “innovative work in polymeric biomaterials for drug delivery, bone and cartilage repair, and tissue engineering, and for outstanding leadership potential in this interdisciplinary field of materials research.”Photopolymerization provides many advantages as a technique for the fabrication of biomaterials. Temporal and spatial control, along with the diversity in material properties found with photopolymerizable materials, are advantageous in the biomaterials industry. For instance, multifunctional anhydride monomers form highly cross-linked surface-eroding networks directly in bone defects. These networks have good mechanical properties that are maintained with degradation and have the potential to restore tissue-like properties to bone during the healing process. Additionally, cartilage-forming cells photoencapsulated in hydrogel networks secrete an extracellular matrix as the hydrogel is resorbed and may provide a treatment alternative for cartilage defects that do not heal spontaneously. Finally, transdermal polymerization (photopolymerization through the skin) of multifunctional monomers is a noninvasive technique that is being developed for tissue regeneration and wound-healing applications.

Fatigue life prediction of bolted joints in vehicle structures by the lethargy coefficient

Mechanical fastened joints are widely used for joining structural parts. In estimating the reliability of a bolted joint in vehicle structures, the prediction of failure life is the most important failure mode to be considered. This paper presents a method for determining the fatigue life of bolted SAPH45 steel structures used extensively in truck vehicle frames. First, the fastening torque on bolted joints in the structure is determined by a vibration test. Under such torque, the fatigue life of the bolted joint can be estimated using the lethargy coefficient as the total defect estimation coefficient and the stress distribution factor. The lethargy coefficient is based upon previous applications of molecular dynamics in materials research field. In this paper, it is obtained from a simple tensile test and is measured by complete fracture time and ultimate stresses.

Extraction of domain structure information from small-angle scattering patterns of bulk materials

A method is presented that permits the extraction and visualization of topological domain structure information contained in small-angle scattering (SAS) patterns without complex pretreatment. Multi-dimensional noisy raw data can be processed. Such data are, for instance, accumulated in the field of materials research from short-exposure-timein situsmall-angle X-ray scattering (SAXS) experiments with synchrotron radiation. The result is a multi-dimensional intersect or chord distribution, which is defined as the Laplacian of the correlation function. Moreover, it is equivalent to the autocorrelation of the gradient of the electron density. The procedure is, in particular, adapted to the analysis of the nanoscale structure of samples with fibre symmetry, such as polymer fibres or strained elastomers. Multi-dimensional relations among morphological components become apparent in real space and help to elucidate the nature of the processes governing formation and change of structure on the nanometre scale. Utilizing digital signal processing tools, the algorithm is based on spatial frequency filtering of the raw data. The background to be subtracted from the small-angle scattering pattern is formed from its own low spatial frequencies. Noise may be removed by suppressing high spatial frequencies. In the frequency band between these low and high spatial frequencies, the domain structure information of the studied nanocomposite appears.

Generation and use of parametric X-rays with an electron linear accelerator

Parametric X-ray radiation (PXR) at energies from 15 to 30 keV was produced by a 45 MeV electron linear accelerator (LINAC) using a silicon (Si) single crystal. The appropriate conditions for generation of good monochromatic hard X-ray fields by PXR were obtained with the LINAC by theoretical calculations and experiments. The PXR intensity increased approximately linearly with the electron energy in the electron energy range of several tens of MeV. The PXR energy increased linearly with the crystal rotation angle that depended on the reflection plane and the observation angle and did not depend on the electron energy. The obtained counts of PXR increased at large observation angles although the energy decreased. The experiments used Si plates with thicknesses of 200, 300, 400, 500, 530, and 625 μm. Differences in angular distribution by the thickness of the Si plates were established. The possibility for PXR applications to material research and other fields is discussed. The off angle of the polished (cut) plane of the crystal was accurately determined using the PXR and the attenuation coefficient around the K-shell absorption edge of Zr, Nb and Mo were measured.

Impact analysis of the materials research programmes “Matfo” and “MaTech” of the German Federal Ministry of Education and Research—BMBF Extended summary of a study published in September 1999

The study presents the findings of an impact Key words Impact analysis of public support by the German Federal Ministry of Education and Research, BMBF, in the field of materials research. The Project Management Organization New Materials and Chemical Technologies, NMT, at Forschungszentrum Jülich GmbH is acting on behalf of the BMBF. More than 350 projects with industrial participation have been analysed to determine the effectiveness of the project funding in application-oriented materials research. In addition some projects were assessed in depth to provide case studies for various areas of materials science. The scientific and technical success as well as the commercial, ecological and sociological (job-market effects) impacts of projects finished for at least one year have been investigated by means of a questionnaire addressed to the industrial participants with the following results:• More than 75% of the projects, which responded, were estimated to be a scientific and technical success.• 25% provided results, which had been commercialized at this time (spin-offs included).• Furthermore, for 29% of the projects started before 1994 (programme “Matfo”) and for 42% of the projects in the “MaTech” programme (running since 1994) commercialization is expected within the next few years.• Almost 40% of the projects achieved a positive impact on employment.• More than two-thirds of all commercialized projects led to positive ecological effects by applications of new materials in technological products or processes.

A novel room temperature electron beam ion trap for atomic physics and materials research

Highly charged ions are used in basic investigations to study problems in atomic and plasma physics. Further on, the application of highly charged ions in materials research and other fields as nanomechanics and information techniques grew significantly in the last years. In the present paper, we report on results derived with a warm electron beam ion trap (WEBIT) that works without any cryogenic equipment. A special source construction allows to generate dense electron beams at room temperature with a current density of up to 240 A cm −2 and an acting ionization factor of (2⋯5)×10 21 cm −2 . Ions like Ar 17+, Xe 44+ and Ir 65+ were detected by X-ray spectroscopy. A charge capacity of about 8×10 7 elementary charges of the trap is estimated.

Test methods for polymeric insulating materials for outdoor HV insulation

The paper describes an analysis of standardized and non-standardized test methods for polymeric insulating materials, either suitable or applied for, outdoor HV insulation. The analysis particularly considers the increasing use of silicone elastomers for composite insulators. In the first part, test methods covering erosionltracking performance and hydrolysis phenomena are discussed. These are inclined plane test (IPT)a nd arc test (AT) for the evaluation of the tracking and erosion behavior as well as boiling water test (BWT) for the evaluation of the HV diffusion. breakdown-strength. These tests have a long tradition in the field of material research. Secondly, the resistance of hydrophobicity under accelerating aging conditions using simultaneous moisture and voltage stress is considered. Results from the rotating wheel dip test (RWDT) are presented and related to results from an equivalent salt-fog test. The third part of the paper deals with the regeneration of hydrophobicity after sample exposure to moisture and corona discharges. Recovery includes also the transfer of hydrophobicity into pollution layers, which is quantified by measurement of dynamic contact angle.

Magnetism And Micro Structure: Advances In Electron-Optical Characterization

Tremendous progress has been made in the field of magnetic materials research and technology over the past few years. Superior properties and novel scientific questions arise due to our ability to either synthesize artificial structures or to tailor microstructures at the appropriate length scales. Microstructure, generally defined as the morphological arrangement of crystallites with similar or different phase constitutions and of the crystal defects, is controlled by the processing, which in turn affects the phases present, their topology and their dispersion. There are two key length scales that determine the magnetic behavior of materials. One is the characteristic length scale associated with the dimensional characteristics of the magnetic phenomenon under consideration. The second is the size of the microstructural feature of interest - grain size, shape, isolation, interfaces, inter-granular phases etc. It is important to identify the range where these two length scales overlap, for it is there that novel properties and phenomenon are usually observed.

The fabrication and morphology of niobium carbide crystal with solid cage shape

The fabrication of inorganic materials with complicated shape is one of hottest research topics in the field of materials research. Here, the fabrication and morphology of micrometer niobium carbide crystals with solid cage shapes will be reported. These results may reveal one method or approach or strategy to fabricate high temperature inorganic materials with complicated shape and lead to deeper research about the morphology of crystal growth.

The tensile behavior of Ti 36Ni 49Hf 15 high temperature shape memory alloy

Recently, ternary Ti-Ni-Hf alloys have attracted great interest in the field of high temperature shape memory materials research and development. Extensive studies have been made on its manufacture process, constitutional phases, phase transformation behavior, the structure, substructure and interface structure of martensite and the precipitation behavior during ageing. Yet up to date there is no report about the fundamental mechanical properties of Ti-Ni-Hf alloys, such as the stress-strain data, the variation laws of the yield strength and elongation with the temperature. In the present study, tensile tests at various temperatures are employed to investigate the mechanical behavior of Ti-Ni-Hf alloy with different matrix structures, from full martensite to full parent phase structure, with the corresponding deformation mechanism discussed.

Properties of an optical fluid filter: Theoretical evaluations and measurement results

The DLR solar furnace in Cologne has been working successfully since 1994 to allow high flux tests in the field of solar chemistry and materials research. Sophisticated measurement technique like the Flux and Temperature Measurement System (FATMES) and the High Flux Spectrometer (HIS) support the evaluation of measurement results. The efficiency of the DLR measurement equipment is demonstrated by means of determination optical properties of a fluid filter. Additionally obtained measurement results are compared with theoretical calculations. The fluid filter was designed, constructed and tested to absorb undesired radiation before entering photochemical reactors. As a first application the filter was filled with water to absorb the IR part of the solar spectrum. Due to the changes in the spectral content of the concentrated radiation the flux measurement system had to be calibrated especially for the employment of the water filter. Each filter thickness requires its own calibration. This lead to an intensive measurement campaign to determine the optical properties of the fluid filter and the efficiency of the measurement equipment.