bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of Novel Biomaterials in Colloidal Drug Delivery Systems
Authors: Garnett M.C. , Stolnik S. , Dunn S.E. , Armstrong I. , Lin Wu , Schacht E. , Ferutti P. , Vert M. , Davies M.C. , Illum L. , Davis S.S.
Published: August 2016

The development of biomaterials to treat, repair, or reconstruct the human body is an increasingly important component of materials research. Collaboration between materials researchers and their industrial and clinical partners is essential for the development of this complex field. To demonstrate the importance of these interactions, two articles in this issue focus on advances in biomaterials relating to the use of colloidal systems for transport, drug delivery, and other medical applications. These articles were coordinated by Dominique Muster (Université Louis Pasteur, Strasbourg) and Franz Burny (Hôpital Erasme, Brussels). The following is the second of these two articles.

There are two important objectives in drug delivery research. The first is to maximize the effectiveness of drugs by increasing the amount of drug reaching the target tissue while sparing other tissues the deleterious effects of the drug. The second is to control the release of a drug, so that the period of optimal drug concentration in the target tissue is maximized. A numbe r of different Systems have been investigated to achieve these objectives, including soluble polymeric delivery Systems and a range of colloidal drug delivery forms such as liposomes, emulsions, micelles, microcapsules, microparticles, and nanoparticles. This article focuses on polymeric materials for the production of micro- or nanoparticle Systems for dru g delivery by injection, and their characterization and Performance in vivo.

Colloidal particles have a number of advantages as drug delivery Systems; they are easy to prepare, have the potential for high drug loading, and release of the drug can be controlled. However, without surface modification, colloidal particles are difficult to target because they are directed largely to the liver and spieen after intravenous injection. The reasons for this can be found in the context of the body's defenses. In order to protect against disease, the body has a complex System to ensure that invading microorganisms are identified and neutralized at the earliest possible opportunity. Most parasitic or invading organisms which pose a threat are particulate in form, and thus any colloidal drug delivery System will have to evade detection by these mechanisms in order to reach its target.
Advances in the Creation of Filled Nanotubes and Novel Nanowires
Authors: Terrones M. , Grobert N. , Hsu W.K. , Zhu Y.Q. , Hu W.B. , Terrones H. , Hare J.P. , Kroto H.W. , Walton D.R.M.
Published: August 2016

Soon after the identification of carbon nanotubes, produced by arc-discharge techniques, the possibility of introducing metals into the inner core of the tubes was considered (Figure 1). This idea followed logically from the successful observation of fullerenes containing endohedral metals. The introduction of metals or metal carbides and oxides into multiwalled nanotubes [usually 2–70 nm outside diameter (OD), <60 microns in length] may significantly alter their conducting, electronic, and mechanical properties, arising from the internal framework within these structures. Early theoretical work predicted that all carbon open nanotubes could behave as “molecular straws.” In this context, Ajayan and lijima were the first to introduce Pb by heating the metal with open-ended nanotubes (sometimes in the presence of oxygen). Capillarity, wetting, and surface tension play an important role in the process; other elements such as Bi, Cs, S, and Se were also introduced into nanotubes in this way. Generally, the filling of open nanotubes by capillary action is confined to low surface-tension substances. Alternative methods of encapsulating other materials within nanotubes have now been developed, including chemical treatment, arc discharge, catalyzed hydrocarbon pyrolysis, and electrochemical techniques. In addition, carbon nanotubes can be used as reactive templates to generate novel metal carbide and nitride nanorods. These developments represent only the tip of the iceberg, because numerous noncarbon materials (e.g., Si, SiOx, SiC, MoS2, WS2, etc.) are able to form novel nanowires and fullerene-like morphologies. This review discusses methods for generating these fascinating structures and evaluates their possible applications in materials science and engineering.
Photonic Applications of Rare-Earth-Doped Materials
Authors: Steckl Andrew J. , Zavada John M.
Published: August 2016

The elements of the lanthanide series, from Ce (atomic number 58) to Yb (atomic number 70), form a group of chemically similar elements that have in common a partially filled 4f shell. These so-called “rare earth” (RE) elements usually take on a 3+ ionic state (RE3+). Because the 4f electronic-energy levels of each lanthanide ion are shielded from external fields by 5s2 and 5p6 outer-shell electrons, RE3+ energy levels are predominantly independent of their surroundings.

The characteristic energy levels of 4f electrons of the trivalent RE elements have been investigated in detail by Gerhard Heinrich Dieke and co-workers and were reported approximately 30 years ago. The Dieke diagram showing RE3+ energy levels is a familiar tool of scientists and engineers working with RE elements. However, the history of RE elements goes back to the year 1787 in the small Swedish town of Ytterby near Stockholm and to the gifted amateur mineralogist and military man Lt. Carl Axel Arrhenius. Arrhenius discovered an unusual black mineral in Ytterby (perceived initially as much rarer in occurrence and in concentration than the common ores or earths of aluminum, calcium, etc.). Many new elements were discovered by various chemists upon analysis of this black stone and others like it. The names given to these elements are variations of the location where the first discovery was made: yttrium, ytterbium, terbium, and erbium. The history of RE elements is fascinating and involves many other famous names in science: Berzelius, Gadolin, Bunsen.

The properties of these elements and their multifaceted applications to science and industry are equally fascinating and have remained important to this day. Commercial applications of RE elements began after World War II, when their available quantity and purity were greatly enhanced by improved separation techniques developed as a part of the Manhattan Project. Until fairly recently, the main industrial application of RE elements has been in permanent magnets. The unpaired 4f electrons result in some RE elements having the highest magnetic moments of any element. The development and applications of RE magnets are reviewed in a very interesting article by Livingston3 in a previous MRS Bulletin issue. In this issue of MRS Bulletin, we have taken as our aim to review some of the properties and applications of RE elements relevant to photonics.
Antisite Defects and Nonequilibrium Phase Transition in Intermetallics
Authors: Martin G. , Bellon P.
Published: August 2016

Among the many point defects in crystalline solids, antisite defects play a key role in the stability of intermetallics. Such defects are either thermal equilibrium defects or are introduced by some external forcing.

There are, indeed, many examples where intermetallics or compound semiconductors are “driven,” i.e., sustained in nonequilibrium configurations by external forcing. Good examples include the following:

∎ Intermetallics in alloys under irradiation, like FeZr2 in Zircalloy used as a cladding material in pressurized water nuclear reactors, or any of the compounds produced by ion implantation or ion beam mixing (atoms are continuously forced to change lattice sites because of replacement collsions). See, for example, Reference 1.

∎ Intermetallics in superalloys under cyclic fatigue (γ′ precipitates in persistent slip bands undergo sustained shearing, and sometimes redissolves).

∎ Intermetallics during high-energy ball milling, a promising technique to stabilize nonequilibrium phases.

∎ Ordered compounds when formed by vapor phase deposition.

In such compounds, atoms are forced to leave their optimum local surroundings by nuclear collisions, shearing, fracturing, and welding respectively, or land on a surface at a random position, while thermal jumps tend to restore some degree of local atomic order. For simplicity, we call such compounds “driven systems” or “driven intermetallics.” Indeed, such systems are driven away from the usual thermodynamic equilibrium by a permanent dynamical forcing (nuclear collisions, plastic shear, etc.).
Overview of Biomedical Materials
Authors: Helmus Michael N.
Published: August 2016

Biomedical materials are synthetic polymers, metals, ceramics, inorganics, and natural macromolecules (biopolymers), that are manufactured or processed to be suitable for use in or as medical devices or prostheses. These materials typically come in contact with cells, proteins, tissues, organs, and organ systems. They can be implanted for long-term use, e.g., an arrtificial hip, or for temporary use, e.g., an intravenous catheter. Except in isolated cases when a material is used by itself, such as collagen injections for filling soft tissue defects, biomedical materials are used as a component in a medical device. The form of the material (perhaps a textile) how it interfaces (blood contacting, for instance), and its time of use will determine its required properties. A material's use needs to be viewed in the context of the total device and its interface with the body. One material property alone is unlikely to lead to a successful and durable device, but the failure to address a key property can lead to device failure. Until recently, medical-grade polymers, ceramics, inorganics, and metals were purified versions of commercial-grade materials. A variety of polymers, biopolymers, and inorganics is now being specifically developed for medical applications. Table I summarizes the types of biomedical materials.
Bioceramics
Authors: Hench Larry L. , Wilson June
Published: August 2016

The innovative use of specially designed ceramics to repair and reconstruct diseased or damaged parts of the body has improved the quality of life, and in some cases the length of life, for thousands of people. Ceramics used for this purpose are termed “bioceramics” and can be single crystals (sapphire), polycrystalline (alumina or hydroxylapatite), glass (Bioglass®), glass-ceramics (Ceravital® or A/W glassceramic), or composites (stainless-steel fiber-reinforced Bioglass or polyethylene-hydroxylapatite).

Ceramics and glasses have long been used in the health care industry for eye glasses, diagnostic instruments, chemical ware, thermometers, tissue culture flasks, and fiber optics for endoscopy. Insoluble porous glasses have been used as carriers for enzymes, antibodies, and antigens. Ceramics are also widely used in dentistry as restorative materials, gold porcelain crowns, glass-filled ionomer cements, and dentures.

This review describes bioceramics used as implants to repair parts of the body, usually hard tissues such as bones or teeth, but also to replace heart valves. Dozens of ceramic compositions have been tested, but few have achieved human clinical application. Clinical success requires the simultaneous achievement of a stable interface with tissue and a match of the mechanical behavior of the implant with the tissue to be replaced.

The mechanism of tissue attachment depends on the type of tissue response at the implant interface (Table I).
Elastic Anomalies in Superlattices
Authors: Schuller Ivan K. , Fartash A. , Grimsditch M.
Published: August 2016

The presence and origin of elastic anomalies in superlattices, interfaces, composites, and nanocrystalline materials has been a subject of much interest and controversy in recent years. In particular, superlattices are being used as model systems to study the effect of interfaces on the mechanical properties of novel materials. Early claims of anomalously large enhancements of the biaxial and flexural moduli of Au/Ni and Cu/Ni superlattices (“supermodulus effect”) created considerable controversy and contradictory reports in the experimental and theoretical literature. To understand the mechanical properties of superlattices and their implication for other types of nanofabricated materials, it is important to look critically at the field.

Superlattices have been fabricated in different laboratories by a variety of preparation methods and have been characterized structurally and elastically to various degrees. Because of this, before addressing any sophisticated theoretical issues regarding elastic anomalies, it is important to understand in detail the experimental techniques and the possible pitfalls in the experimental determination of mechanical properties of thin films. Once the presence or absence of the effect is ascertained, the need arises to understand any possible experimental correlations with other structural and/or physical properties. These correlations can be used to address issues regarding the possible origins of the effect and their theoretical basis. It will be apparent from this article that slight changes in structural properties are correlated with relatively large elastic anomalies. Consequently, this points to the importance of precise, comprehensive, and detailed structural characterization. With our present understanding of the physics of superlattices, qualitative studies are no longer sufficient!
Effects of Atomic-Level Disorder at Solid Interfaces
Authors: Phillpot Simon R. , Wolf Dieter , Yip Sidney
Published: August 2016

The importance of interface materials is based largely on their inherent inhomogeneity, i.e., that the chemical composition and physical properties at or near an interface can differ dramatically from those of the nearby bulk material. For example, the propagation of a crack along an interface — rather than through the surrounding bulk material — indicates a different mechanical strength near the interface. Also, the elastic response and thermal behavior near an interface can be highly anisotropic in an otherwise isotropic material, and can differ by orders of magnitude from those of the adjacent bulk regions. Typically, these gradients extend over only a few atomic distances.

Because relatively few atoms control the properties in the interfacial region, the inherent difficulty in the experimental investigation of buried interfaces is actually an advantage in the atomic-level study of solid interfaces by means of computer-simulation techniques. While the limitations of such simulations are well known, this article will attempt to demonstrate the unique insights they can provide on some aspects of the mechanical behavior of both buried and thin-film interfaces. While to date, relatively little simulation work has focused directly on the observation of crack extension, we will discuss two types of phenomena with particular relevance in the fracture behavior of interface materials, namely their elastic and high-temperature properties. We will conclude with an outlook, too optimistic perhaps, on how the complementary capabilities of continuum-elastic theory, atomic-level computer simulation, and experiment could (and probably should) be combined in a new strategy for tackling the difficult problem of interface fracture to elucidate the underlying complex interplay between elasticity, plasticity, and temperature.
Fine Particles Part II: Formation Mechanisms and Applications
Authors: Matijević Egon
Published: August 2016

The original intention was to publish one special issue on the materials science of fine particles. As a Guest Editor, I approached a number of specialists with specific interests in this field, soliciting contributions. Normally, an editor expects a number of requests to be declined. In this particular instance the response was overwhelming, which indicated both the enthusiasm of the people active in fine particle science and the timeliness of the topics. Thus, the MRS BULLETIN decided to dedicate two issues to this subject, December 1989 and January 1990.

The December 1989 issue dealt essentially with the procedures and principles for preparing finely dispersed matter consisting of particles of different chemical composition, shape, and size. This issue treats the problems of the mechanisms of formation of well-defined dispersions and offers examples of applications in two areas — ceramics and adhesion. Only the limitations in space prevented the editor from including other topics relevant to fine particle science and technology, which are both fascinating and useful.
Chemical Synthesis of Fine Powders
Authors: Livage J. , Henry M. , Jolivet J.P. , Sanchez C.
Published: August 2016

Interest in the synthesis of submicron monodispersed powders is increasing. Such powders find applications in the ceramic industry when high performance materials are required. Sintering time and temperature can be significantly reduced with powders of narrow particle-size distribution. Fine colloidal particles can be made by a variety of methods, from the vapor phase or the liquid phase.

The sol gel process offers new approaches to the synthesis of fine powders. Starting from molecular precursors, such as metal alkoxides or aqueous solutions, an oxide network is obtained via inorganic polymerization reactions. These reactions occur in solution, and the term “sol-gel processing” is often used to describe the synthesis of inorganic oxides by wet chemical methods. It offers many advantages compared to the conventional powder route. One unique advantage is the ability to go all the way from the molecular precursor to the solid material, permitting better control of the entire process and allowing synthesis of “tailor-made” powders.
Behavior of Block Copolymers in Thin Films
Authors: Russell T.P. , Deline V.R. , Wakharkar V.S. , Coulon G.
Published: August 2016

The uses of polymeric materials in today's world are vast. Polymers are finding applications in the microelectronics industry as dielectric insulators and photoresists, in the aerospace and automobile industry as lightweight substitutes for metals, and in biotechnology as replacement components for bone, heart, and other organs. These are just a few of the many end uses of polymers.

Often, a polymer may have a particular, desirable property but processing of the polymer is difficult or the polymer's surface characteristics are undesirable. To circumvent such shortcomings there are several options. The first is to synthesize a new material, which is quite costly and time consuming. Alternatively, two polymers with complimentary properties can be mixed. Unfortunately, most polymer pairs are immiscible unless there are specific interactions (e.g., hydrogen bonding) between the two components. Consequently, coarse phase separation is often observed, leading to an ill-defined material. Finally, two chemically distinct homopolymers can be joined together at one point, forming a block copolymer. While phase separation may occur, the scale of the domains is restricted to the sizes of the individual homopolymers, which is typically on the tens of nanometers scale. The added advantage of this approach is that the size of the different blocks can be altered, varying the concentration of the different components. For copolymers that “microphase” separate, this variation in composition leads to a variation of the morphology of the microdomains ranging from spherical to cylindrical to lamellar.
Magnetic and Magneto-Optical Properties of Interfaces and Superlattices
Authors: Engel Brad N. , Falco Charles M.
Published: August 2016

The ability to study, and to some extent control, the magnetic properties of surfaces and interfaces is an extremely interesting development in the field of magnetism. Along with experimental advances in techniques to accurately prepare magnetic structures by such methods as sputtering and molecular beam epitaxy (MBE) have been theoretical and computational advances in the ability to calculate properties of realistic model systems. At the same time, increasingly sophisticated characterization techniques have become available (e.g., intense synchrotron sources, pulsed sources for magnetic neutron scattering, polarized electron microscopy, scanning tunneling microscopy, etc.), which enable sample characterization at a level not before possible.

In recent years, the study of magnetism near surfaces and interfaces has been driven by the observation of significant differences from bulk behavior.1 An understanding of these phenomena is fundamentally important to the field of magnetism and provides the potential for technological applications.2 Although the real situation is more complicated, for the purposes of the discussion here, it is convenient to think about the causes of the observed physical effects at interfaces and in superlattices as falling into two categories: “dimensionality effects,” due to the reduced coordination of the magnetic atoms; and “substrate effects,” due to interactions between the differing materials at an interface. An ultrathin film on an insulator, or the free surface of a bulk crystal, are examples of the first category. However, the magnetic atoms at an interface between two different materials are affected both by the reduced number of similar neighboring atoms (i.e., the dimensionality) and by the crystal and electronic structure of the neighboring layer (i.e., the substrate).
Silver Halides in Photography
Authors: Tan Yen T.
Published: August 2016

Since their first use about 150 years ago, silver halides have remained the primary photosensing materials in an image capturing process known as photography. Silver halides have retained their pre-eminent role despite numerous attempts to replace them with other materials. Even in the present era of electronics, conventional photography remains the most popular format for recording still images. When compared with electronic imaging, silver halide photography retains an edge in resolution, latitude, and convenience.

The current superiority and popularity of conventional photography stem from an unusual confluence of properties found in the silver halides. The ensuing articles will discuss the properties that make silver halides particularly well suited for photography. The article by L.M. Slifkin discusses the improbability of any one material having the characteristics of the silver halides. F.C. Brown describes the special electronic properties, and P.W.M. Jacobs covers ionic characteristics. C.R.A. Catlow gives us some insight into the nature of the silver halides based on their interatomic potentials. This introductory article presents an overview of the photographic process.

The theory of the photographic process has its roots in the Gurney-Mott model of latent image formation. Since it was first proposed over 50 years ago, this model has formed the basis of mechanistic thinking about photography.
Crystal Growth of High Temperature Superconductors
Authors: Scheel H.J. , Licci F.
Published: August 2016

The discovery of high temperature superconductivity (HTSC) in oxide compounds has confronted materials scientists with many challenging problems. These include the preparation of ceramic samples with critical current density of about 106 A/cm2 at 77 K and sufficient mechanical strength for large-scale electrotechnical and magnetic applications and the preparation of epitaxial thin films of high structural perfection for electronic devices.

The main interest in the growth of single crystals is for the study of physical phenomena, which will help achieve a theoretical understanding of HTSC. Theorists still do not agree on the fundamental mechanisms of HTSC, and there is a need for good data on relatively defect-free materials in order to test the many models. In addition, the study of the role of defects like twins, grain boundaries, and dislocations in single crystals is important for understanding such parameters as the critical current density. The study of HTSC with single crystals is also expected to be helpful for finding optimum materials for the various applications and hopefully achieving higher values of the superconducting transition temperature Tc than the current maximum of about 125 K. It seems unlikely at present that single crystals will be used in commercial devices, but this possibility cannot be ruled out as crystal size and quality improve.
High Resolution Imaging of Magnetization
Authors: Pierce D.T. , Unguris J. , Celotta R.J.
Published: August 2016

In 1907 Weiss postulated that a ferro-magnet has many small regions or domains that are spontaneously magnetized below the Curie temperature. In an unmagnetized ferromagnetic specimen the domains form so as to minimize the free energy, which includes contributions from the exchange energy, crystal and shape anisotropy energy, magnetostrictive energy, and so on. The actual size and shape of domains can only be calculated for the simplest geometries and for idealized materials. To investigate magnetic microstructure and how it determines macroscopic magnetic properties, we want to be able to see domain configurations and understand how the magnetic microstructure is changed by external influences and varying material properties. The observation of microscopic domain configurations can aid in engineering magnetic materials with desired magnetic properties.

Domains were first observed using the Bitter method in which fine magnetic particles collect on the surface of a specimen in the field gradients at domain walls. Domains can also be observed by electron microscopy, with scanning electron microscopy, or at higher resolution with transmission electron microscopy. Specimens must be thinned to about 100 nm for use in the TEM. This, in turn, changes their magnetic properties. The magneto-optic Kerr effect has the advantage that the signal is directly related to the magnetization of the specimen and not just to the leakage fields or internal magnetic fields as in the methods mentioned above. This technique has the disadvantage of being limited to an optical resolution of typically 1μm.
Characterization of Thin Organic and Polymeric Films by Spectroscopic Methods
Authors: Rabolt J.F.
Published: August 2016

Much of the anisotropic mechanical and thermal behavior exhibited by materials can be attributed to anisotropic orientation at the molecular level. In self-supporting thin films (5–10 microns) and those (0.01–1.0 microns) deposited on solid substrates, the role of molecular orientation is even more important since it will critically determine their two-dimensional behavior and their structural integrity as well. These two aspects are extremely important because if thin organic and polymeric films are to be competitive with existing materials for such diverse applications1 as chemical sensors and integrated optics, they must be mechanically robust and, ideally, defect free. These stringent constraints dictate that sophisticated characterization techniques, which can interrogate at the molecular level, be developed or refined so as to have the sensitivity to address these critical issues.

The development of nondestructive techniques for studying thin organic films has certainly lagged behind those developed for metallic and semiconductor films. Unfortunately, many of these same techniques cannot be simply applied to organic films because they are “invasive” and often alter the structure of the system they were designed to probe. This is especially so in organic and polymer films, and this awareness within the materials science community has led to the adaptation of many photon intensive techniques to the study of thin films. A number of these will be discussed in later sections with their relative merit put in perspective.

Certainly the origins of anisotropic structure in bulk materials are manyfold, but the spatial constraints in 2-D can lead to even more complex causes of orientation. In thin films on substrates the role of the surface is important in determining the ordering and orientation of the individual molecular segments which come into intimate contact with it. The extent of this orientation and order is still somewhat controversial but there is general agreement that it probably differs depending on the nature of the substrate.
New Directions in Auger Microanalysis
Authors: Browning R.
Published: August 2016

Scanning Auger microscopy is a developing field which has by no means reached its limits either in instrumentation or methodology. Two areas of progress in the microanalysis of materials are the quantification of micro-area spectra and the collection and analysis of Auger images. For microanalysis, some strategies for the quantification of spectra depend on determining the shape of the secondary electron background. Developments in the method of linearized secondary-electron cascades give promise to achieving this. Analyses of materials by multispectral Auger imaging show that it is possible to give a meaningful and quantifiable representation of the inhomogeneities across a surface in the form of color-coded statistically significant images.
Molecular-Scale Mlcroporous Superlattices
Authors: Deckman H.W. , Abeles B. , Dunsmuir J.H. , Roxlo C.B. , Moustakas T.D.
Published: August 2016

We have been interested in fabricating structures which can have dimensions on the scale of molecules (˜10 Å). By producing lithographic structures on the molecular-scale length, we obtain a new class of materials with unusual chemical properties. The materials contain pores which have been shown to restrict the mobility and adsorption of molecules. This restriction is the basis of size- and shape-selective chemistry which is used in many modern separation and catalytic processes.

Features in our materials are significantly smaller than the smallest nano-structures produced with electron beam lithography. To date 20–50 Å features have been produced with electron beam lithography which uses ionization from beam-solid interactions to drive radiation chemistry in a resist layer. These dimensions are near fundamental limits which come from beam-solid interactions and the response of the resist system. Further limitations occur when the nanostructural pattern must be transferred from the resist layer into a useful metal or semiconductor structure. Methods have not been devised to fully exploit the accuracy with which resist patterns can be defined, and the smallest useful transferred structures have dimensions of ˜80–100 Å.

To produce the smallest of all lithographic structures, we use a new method for pattern generation. Instead of using radiation chemistry to define a pattern, we use the organization of layers in deposited superlattices.
Electron Beam Bombardment Induced Decrease of Cathodoluminescence Intensity from GaN Not Caused by Absorption in Buildup of Carbon Contamination
Authors: Campo Eva M. , Cargill III G. S. , Pophristic Milan , Ferguson Ian
Published: August 2016

Monochromatic CL imaging, CL spectra, WDS spectra, and EDS spectra and imaging demonstrate that electron beam bombardment of LEO-GaN causes decrease of near band edge cathodoluminescence intensity that cannot be attributed to absorption in a growing carbon contamination layer. An alternative explanation is needed, such as generation of defects, or charge injection and buildup of internal electric fields, caused by electron beam bombardment.
The growth rate evolution versus substrate temperature and V/III ratio during GaN MBE using ammonia
Authors: Alexeev A.N. , Borisov B.A. , Chaly V.P. , Demidov D.M. , Dudin A.L. , Krasovitsky D.M. , Pogorelsky Yu.V. , Shkurko A.P. , Sokolov I.A. , Stepanov M.V. , Ter-Martirosyan A.L.
Published: August 2016

The growth rate evolution versus V/III ratio and substrate temperature was studied by means of optical reflectivity during MBE of GaN layers using NH3 as nitrogen source. The GaN desorption becomes observable at temperatures above 800°C and causes the reduction of growth rate accompanied with the surface roughening at temperatures above 850-870°C. Unlike GaAs, which evaporates in accordance with the action mass law, the desorption rate of GaN is found to be almost independent of V/III ratio within the N-rich growth conditions. The activation energy for GaN desorption during the growth is found to be (3.2±0.1)eV. This value is very close to the activation energy for free evaporation. At V/III ratio values exceeding 200 the GaN growth rate reduction caused by violation of the molecular flow regime is observed. The Mg-doped samples grown under these extreme conditions tend to have improved acceptor activation and thus p-type conductivity.
Photoluminescence measurements on GaN/AlGaN modulation doped quantum wells
Authors: Dalfors J. , Bergman J. P. , Holtz P.O. , Monemar B. , Amano H. , Akasaki I.
Published: August 2016

Photoluminescence spectra were measured for 100 Å wurtzite GaN AlGaN modulation doped quantum wells. Three well-resolved peaks originate from the quantum well. The theoretically calculated confinement energies have been compared to the experimental energy positions and found to be in good agreement with the data, assuming that the piezoelectric field is largely screened by the electron gas. The highest energy transition may originate from the Fermi edge, consistent with the temperature dependence of the photoluminescence. Decay times for the different transitions indicate that the photoexcited holes are localized.
Heterostructure for UV LEDs Based on Thick AlGaN Layers
Authors: Sakharov A. V. , Lundin W. V. , Usikov A. , Ushakov U. I. , Kudriavtsev Yu A. , Lunev A.V. , Sherniakov Y.M. , Ledentsov N.N.
Published: August 2016

Thick AlGaN layers and GaN/AlGaN heterostructures were grown by low pressure MOCVD on (0001) sapphire substrates utilizing a low temperature AlGaN buffer layer. The distribution of Al in the thick AlGaN layers was observed to be non-uniform as a function of depth. The Al content gradually increases from the substrate towards the epilayer surface. Moreover, fluctuations of Al content are also noticeable. The saturation of impurity-related emission with increasing current density was observed in EL spectra of LEDs consisting of AlGaN/GaN/AlGaN DH sandwiched by a 2 μm-thick bottom layer of GaN:Si and 0.5 μm-thick layer of GaN:Mg. The dominant near-band edge emission of the GaN active layer was found to be strongly absorbed in the thick bottom layer. Utilizing a 2 μm-thick AlGaN bottom layer instead of the GaN one allowed the absorption edge to be shifted towards higher energies. A single peak at 362 nm with FWHM of 14 nm was observed in this type of LED. Luminescence properties of various types of heterostructures are also discussed.
X-ray reciprocal lattice mapping and photoluminescence of GaN/GaAlN Multiple Quantum Wells; strain induced phenomena.
Authors: Langer R. , Simon J , Konovalov O. , Pelekanos N. , Barski A. , Leszczy˜ski M.
Published: August 2016

Structural properties of GaN/GaAlN multiple quantum wells (MQW) grown by nitrogen plasma assisted MBE on MOCVD-grown GaN/sapphire (GaN pseudosubstrates) have been characterised by X-ray reciprocal lattice mapping to determine the strain and composition of ternary alloys. The results clearly demonstrate that the barriers of GaAlN with up to 17% of aluminium content grown by plasma assisted MBE on GaN are fully strained. Optical properties have been characterised by low temperature photoluminescence. Photoluminescence emission peaks corresponding to the GaN/GaAlN MQW structures revealed strong red-shift with respect to the GaN energy gap. This can be explained by a strong internal electric field present in the QW's which is attributed to a transfer of piezoelectric field due to Fermi-level alignment.
Interfacial Reactions and Electrical Properties of Ti/n-GaN Contacts
Authors: Cordes Holger , Chang Y. A.
Published: August 2016

The phase equilibria in the ternary Ti-Ga-N have been investigated. Interfacial reactions in Ti/GaN contacts have been studied by diffusion couple experiments. The ternary phase Ti2GaN was confirmed by x-ray diffraction in bulk samples as well as in massive Ti/GaN diffusion couples and annealed Ti thin films on GaN. The diffusion path in samples, annealed at 850°C in Ar gas, is GaN/TiN/Ti2GaN/Ti3Ga/Ti. A planar TiN layer forms in direct contact to GaN and governs the electrical properties of annealed Ti/GaN contacts. Thin film contacts were fabricated by sputtering Ti on MOVPE grown n-GaN (5×1017cm−3) and subsequent rapid thermal annealing in an Argon atmosphere. Initially non-linear current-voltage characteristics become ohmic after annealing and a specific contact resistance of approximately 10−2 Ωcm2, measured with the circular transmission line method, was found after annealing at 9000C for 1 min.
Photoluminescence excitation spectroscopy of GaN thin layers as a function of temperature
Authors: Guénaud C. , Deleporte E. , Voos M. , Delalande C. , Beaumont B. , Leroux M. , Gibart Pierre , Faurie J. P.
Published: August 2016

We report on photoluminescence and photoluminescence excitation experiments performed on hexagonal GaN layers grown on a Sapphire substrate. Information about extrinsic and intrinsic optical properties have been obtained. We show that, at low temperature, the fundamental A excitons are preferentially involved in the relaxation towards the neutral donor bound exciton photoluminescence line, while electron-hole pairs rather participate in the relaxation towards D0−A0 emission and the yellow band. The relaxation from the A exciton towards the yellow band and D0−A0 emission is made easier by temperature. The band structure of the GaN layers has been determined from temperature dependent photoluminescence excitation spectroscopy: A and C excitons and A continuum band gap have been identified up to 210K.
Temperature behaviour of the yellow emission in GaN
Authors: Seitz R. , Gaspar C. , Monteiro T. , Pereira E. , Leroux M. , Beaumont B. , Gibart Pierre
Published: August 2016

Even in good quality undoped GaN samples, as assessed by the intense excitonic emission, the yellow band is present. This band has been attributed either to a shallow donor to deep double donor pair recombination [1], to a deep donor to a shallow acceptor [2] or to a shallow donor and a deep state [3]. However, its origin is not yet clear. We present data on time resolved spectroscopy compared with steady state results. These results indicate that there is no difference in band shape between steady state and time resolved spectra at all temperatures. However, in some samples there is an increase in intensity of the yellow band. It is concluded that besides a fast emission, due to prompt excitation of the centre, an indirect path from a trap 13.7 meV below the shallow donor is responsible for the long component of the decay and the intensity increase. An emission with a lifetime of ca. 300 ms is also present with a maximum at 2.35 eV.
GaN Based p-n Structures Grown on SiC Substrates
Authors: Dmitriev V.A.
Published: August 2016

Wide band gap nitrides(InN, GaN, AlN) have been considered promising optoelectronics materials for many years [1]. Recently two main technological problems in the nitrides were overcome: (1)high quality layers has been grown on both sapphire and SiC substrates and(2) p-type GaN and AlGaN material has been obtained. These achievements resulted in the fabrication of bright light emitters in the violet, blue and green spectral regions [2].First injection laser has been demonstrated [3]. This paper reviews results obtained over the last few years on nitride p-n junctions, particularly on GaN based p-n junctions grown on SiC substrates. We will consider GaN p-n junctions, AlGaN p-n junctions, GaN and AlGaN p-i-n structures, and, finally, GaN/SiC p-n structures.
Consultório na Rua em uma capital do Nordeste brasileiro: o olhar de pessoas em situação de vulnerabilidade social
Authors: Ferreira Cíntia Priscila da Silva , Rozendo Célia Alves , Melo Givânya Bezerra de
Published: August 2016

Resumo: O objetivo deste estudo foi avaliar a estratégia do Consultório na Rua em Maceió, Alagoas, Brasil, com base na perspectiva de seus usuários. Pesquisa de abordagem qualitativa, cujo cenário foram os campos de atuação da estratégia Consultório na Rua em Maceió, Alagoas. Os sujeitos da pesquisa foram 18 pessoas em situação de rua atendidas pela estratégia, sendo dez homens e oito mulheres, com idades entre 20 e 40 anos. A coleta de dados se deu entre setembro de 2014 e fevereiro de 2015, sendo empregada a técnica de entrevista semiestruturada. Os dados foram analisados por meio da técnica de análise de conteúdo e apontaram duas categorias: a primeira, Consultório na Rua como ele é, revelou os nós críticos, desafios e potencialidades dessa estratégia; a segunda, Consultório na Rua: suporte social, afeto e perspectiva de mudança, para quem se encontra em situação de rua. Os resultados demonstraram que a estratégia é avaliada positivamente e que se constitui como suporte social não apenas em questões relativas à saúde-doença, mas também em aspectos da vida cotidiana.
Ser trabalhadora remunerada ou dona de casa associa-se à qualidade de vida relacionada à saúde?
Authors: Senicato Caroline , Lima Margareth Guimarães , Barros Marilisa Berti de Azevedo
Published: August 2016

Resumo: Considerando que não há estudos brasileiros que avaliem a relação entre a inserção no mercado de trabalho e a qualidade de vida relacionada à saúde (QVRS) de mulheres, objetivou-se com a presente pesquisa verificar se existe associação entre ter ou não trabalho remunerado e a QVRS das mulheres, e, se o estrato socioeconômico modifica esta associação. Trata-se de estudo transversal de base populacional com amostra de 668 mulheres de 18 a 64 anos do Inquérito de Saúde de Campinas (ISACamp 2008/2009), utilizando-se o SF-36 para avaliar a QVRS. Ser dona de casa esteve associado à pior QVRS, sobretudo nos aspectos mentais, mas esta associação é modificada pelo nível socioeconômico. Nos segmentos de intermediária e baixa escolaridade e renda familiar, as donas de casa apresentaram pior QVRS que as trabalhadoras remuneradas, mas não houve diferença entre os dois segmentos nos estratos de alta escolaridade e renda. A pior QVRS das donas de casa enfatiza a importância de políticas públicas que visem a ampliar as oportunidades de inserção da mulher no mercado de trabalho e de acesso à educação.
Estrutura dimensional da versão brasileira do instrumento s-EMBU para aferição de práticas educativas parentais em adolescentes
Authors: Reichenheim Michael Eduardo , Sampaio Paula Florence , Moraes Claudia Leite
Published: August 2016

Resumo: O objetivo deste estudo foi avaliar a estrutura dimensional do instrumento s-EMBU, utilizado para a mensuração de práticas educativas parentais, quando aplicado a adolescentes. A amostra contou com 487 estudantes da Região Metropolitana do Rio de Janeiro, Brasil, no ano de 2013. A média de idade foi 14 anos, sendo 47% meninas. A estrutura dimensional original foi avaliada por análise fatorial do tipo confirmatória (AFC). Também foram implementados modelos de equação estrutural exploratórios (MEEE). O ajuste da AFC foi insatisfatório. À luz dos MEEE, a solução mais parcimoniosa concerniu o modelo de três fatores (RMSEA = 0,03; CFI = 0,97; e TLI = 0,96), porém vários itens da dimensão superproteção apresentaram cargas fatoriais maiores na dimensão Rejeição. Os itens das dimensões rejeição e calor emocional se mostraram mais apropriados. No Brasil, o s-EMBU capta parcialmente as dimensões propostas para aferição das práticas educativas parentais em adolescentes. A dimensão calor emocional teve sua estrutura dimensional confirmada, no entanto, a de rejeição e especialmente a de superproteção requerem aprimoramento.
O Procedimento Selective Reminding na Avaliação da Memória e Aprendizagem: Um Levantamento de Estudos Brasileiros
Authors: Bordignon Suelen , Zibetti Murilo Ricardo , Trentini Clarissa Marceli
Published: August 2016

RESUMO Os pesquisadores têm à sua disposição uma variedade de métodos que auxiliam a compreensão dos processos de memória e aprendizagem. O presente artigo tem como objetivo revisitar o procedimento de recordação seletiva, apresentando suas características e variações, e realizar um levantamento de estudos brasileiros que fizeram uso do mesmo. São apresentadas as diferenças entre a recordação seletiva e o procedimento padrão em tarefas de aprendizagem por recordação livre. Constatou-se que, no Brasil, além de diferentes tarefas, são utilizadas formas de aplicações distintas do procedimento. A utilização da recordação seletiva apresenta relevância no estudo da memória e da aprendizagem, em especial na busca pela diferenciação entre as dificuldades normais de memórias e os déficits patológicos dessa função cognitiva.
Contribuições das Neurociências para o Estudo do Comportamento Discriminativo1
Authors: Fonseca Júnior Amilcar Rodrigues , Hunziker Maria Helena Leite
Published: August 2016

RESUMO Este artigo buscou examinar algumas das contribuições das neurociências para o estudo da discriminação de estímulos. Foram discutidos experimentos relacionados a processos discriminativos envolvendo (a) estimulação cerebral como estímulo antecedente e consequente, (b) atividade neural como resposta, (c) lesão cerebral, (d) drogas e (e) mudanças no cérebro em função do treino discriminativo. Argumenta-se que a integração entre dados comportamentais e (neuro) fisiológicos tem se mostrado uma estratégia promissora para um entendimento mais completo sobre o comportamento dos organismos.
Avaliação do Conhecimento sobre Trauma Craniano Violento por Pais Brasileiros
Authors: Lopes Nahara Rodrigues Laterza , Williams Lúcia Cavalcanti de Albuquerque
Published: August 2016

RESUMO A ocorrência do trauma craniano violento (TCV) pode estar associada à falta de conhecimento de pais e cuidadores sobre o desenvolvimento infantil. Neste sentido, o presente estudo pretendeu investigar o conhecimento de pais sobre o choro do bebê, as estratégias para lidar com o choro e as consequências de sacudi-lo. Participaram da pesquisa 83 mães e 7 pais de recém-nascidos, que responderam ao instrumento Questionário sobre o Choro do Bebê. Os resultados do estudo sugerem um desconhecimento por parte dos pais sobre o TCV, principalmente no que se refere à sua gravidade. Além disso, 34,4% dos participantes relataram que sacudiriam seus bebês para fazê-los parar de chorar. Tais resultados parecem indicar a necessidade de desenvolver intervenções de educação parental sobre o TCV, especialmente durante o pré-natal, de modo a contribuir para o aumento do conhecimento dos pais, prevenindo assim tal forma de maus-tratos.
Projeções de Vazão Afluente à Lagoa Mangueira com Base em Cenários de Mudanças Climáticas
Authors: Tejadas Bruno Espinosa , Bravo Juan Martin , Sanagiotto Daniela Guzzon , Tassi Rutinéia , Marques David Manuel Lelinho da Motta
Published: August 2016

Resumo Neste trabalho é apresentada a avaliação dos impactos das mudanças climáticas sobre a vazão de contribuição à lagoa Magueira, localizada no sul do Brasil, com base em projeções de precipitação de vinte Modelos Climáticos Globais (MCGs) que alimentam o modelo hidrológico IPH II. As projeções foram baseadas em dois cenários de mudanças climáticas definidos pelo IPCC que estabelecem as forçantes para que os MCGs estimem o clima futuro: A2, caracterizado pelas altas emissões e B2, caracterizado pelas baixas emissões. O MAGICC/ScenGen foi utilizado para obter as projeções de anomalias mensais de precipitação nos cenários A2/B2 em períodos futuros centrados em 2030 e 2070. As séries temporais de precipitação projetadas foram estimadas usando o método delta change. Os resultados em termos de vazão média anual mostraram que o valor médio das anomalias no horizonte próximo é parecido em ambos cenários, sendo igual a +2,86%(A2) e +2,48%(B2). Este valor aumentou no horizonte longo, com valor médio das anomalias de +16,94%(A2) e +11,83%(B2). A dispersão entre os resultados dos MCGs mostrou anomalias que podem atingir [+10%,−7%] no horizonte próximo e [+30%,−20%] no horizonte longo. Assim, embora existisse uma maior concordância nos MCGs ao aumento das vazões, é importante ressaltar a dispersão dos resultados.