Materials

323 KiB

Open AccessReview

Rare-Earth Activated Nitride Phosphors: Synthesis, Luminescence and Applications

by Rong-Jun Xie, Naoto Hirosaki, Yuanqiang Li and Takashi Takeda

Materials 2010, 3(6), 3777-3793; https://doi.org/10.3390/ma3063777 - 21 Jun 2010

Cited by 268 | Viewed by 19171

Nitridosilicates are structurally built up on three-dimensional SiN4 tetrahedral networks, forming a very interesting class of materials with high thermomechanical properties, hardness, and wide band gap. Traditionally, nitridosilicates are often used as structural materials such as abrasive particles, cutting tools, turbine blade, etc. [...] Read more.

Nitridosilicates are structurally built up on three-dimensional SiN4 tetrahedral networks, forming a very interesting class of materials with high thermomechanical properties, hardness, and wide band gap. Traditionally, nitridosilicates are often used as structural materials such as abrasive particles, cutting tools, turbine blade, etc. Recently, the luminescence of rare earth doped nitridosilicates has been extensively studied, and a novel family of luminescent materials has been developed. This paper reviews the synthesis, luminescence and applications of nitridosilicate phosphors, with emphasis on rare earth nitrides in the system of M-Si-Al-O-N (M = Li, Ca, Sr, Ba, La) and their applications in white LEDs. These phosphors exhibit interesting luminescent properties, such as red-shifted excitation and emission, small Stokes shift, small thermal quenching, and high conversion efficiency, enabling them to use as down-conversion luminescent materials in white LEDs with tunable color temperature and high color rendering index. Full article

(This article belongs to the Special Issue Luminescent Materials)

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1728 KiB

Open AccessReview

Carrier States in Ferromagnetic Semiconductors and Diluted Magnetic Semiconductors—Coherent Potential Approach—

by Masao Takahashi

Materials 2010, 3(6), 3740-3776; https://doi.org/10.3390/ma3063740 - 21 Jun 2010

Cited by 8 | Viewed by 9088

Abstract

The theoretical study of magnetic semiconductors using the dynamical coherent potential approximation (dynamical CPA) is briefly reviewed. First, we give the results for ferromagnetic semiconductors (FMSs) such as EuO and EuS by applying the dynamical CPA to the s-f model. Next, applying [...] Read more.

The theoretical study of magnetic semiconductors using the dynamical coherent potential approximation (dynamical CPA) is briefly reviewed. First, we give the results for ferromagnetic semiconductors (FMSs) such as EuO and EuS by applying the dynamical CPA to the s-f model. Next, applying the dynamical CPA to a simple model for A_1−xMn_xB-type diluted magnetic semiconductors (DMSs), we show the results for three typical cases to clarify the nature and properties of the carrier states in DMSs. On the basis of this model, we discuss the difference in the optical band edges between II-V DMSs and III-V-based DMSs, and show that two types of ferromagnetism can occur in DMSs when carriers are introduced. The carrier-induced ferromagnetism of Ga_1−xMn_xAs is ascribed to a double-exchange (DE)-like mechanism realized in the magnetic impurity band/or in the band tail. Full article

(This article belongs to the Special Issue Ferromagnetic Semiconductors)

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981 KiB

Open AccessArticle

Electrochemical Light-Emitting Gel

by Nobuyuki Itoh

Materials 2010, 3(6), 3729-3739; https://doi.org/10.3390/ma3063729 - 19 Jun 2010

Cited by 39 | Viewed by 10378

Abstract

Light-emitting gel, a gel state electroluminescence material, is reported. It is composed of a ruthenium complex as the emitter, an ionic liquid as the electrolyte, and oxide nanoparticles as the gelation filler. Emitted light was produced via electrogenerated chemiluminescence. The light-emitting gel operated [...] Read more.

Light-emitting gel, a gel state electroluminescence material, is reported. It is composed of a ruthenium complex as the emitter, an ionic liquid as the electrolyte, and oxide nanoparticles as the gelation filler. Emitted light was produced via electrogenerated chemiluminescence. The light-emitting gel operated at low voltage when an alternating current was passed through it, regardless of its structure, which is quite thick. The luminescence property of the gel is strongly affected by nanoparticle materials. TiO₂ nanoparticles were a better gelation filler than silica or ZnO was, with respect to luminescence stability, thus indicating a catalytic effect. It is demonstrated that the light-emitting gel device, with quite a simple fabrication process, flashes with the application of voltage. Full article

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462 KiB

Open AccessArticle

Electrospun Biocomposite Polycaprolactone/Collagen Tubes as Scaffolds for Neural Stem Cell Differentiation

by Joanne M. Hackett, ThucNhi T. Dang, Eve C. Tsai and Xudong Cao

Materials 2010, 3(6), 3714-3728; https://doi.org/10.3390/ma3063714 - 19 Jun 2010

Cited by 45 | Viewed by 12651

Abstract

Studies using cellular therapies, scaffolds, and tubular structured implants have been carried out with the goal to restore functional recovery after spinal cord injury (SCI). None of these therapeutic strategies, by themselves, have been shown to be sufficient to achieve complete restoration of [...] Read more.

Studies using cellular therapies, scaffolds, and tubular structured implants have been carried out with the goal to restore functional recovery after spinal cord injury (SCI). None of these therapeutic strategies, by themselves, have been shown to be sufficient to achieve complete restoration of function. To reverse the devastating effects of SCI, an interdisciplinary approach that combines materials science and engineering, stem cell biology, and neurosurgery is being carried out. We are currently investigating a scaffold that has the ability to deliver growth factors for the proliferation and differentiation of endogenous stem cells. Neural stem cells (NSCs) derived from mice are being used to assess the efficacy of the release of growth factors from the scaffold in vitro. The fabrication of the tubular implant allows a porous scaffold to be formed, which aids in the release of growth factors added to the scaffold. Full article

(This article belongs to the Special Issue Advances in Biomaterials)

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572 KiB

Open AccessArticle

Properties and Clinical Application of Three Types of Dental Glass-Ceramics and Ceramics for CAD-CAM Technologies

by Christian Ritzberger, Elke Apel, Wolfram Höland, Arnd Peschke and Volker M. Rheinberger

Materials 2010, 3(6), 3700-3713; https://doi.org/10.3390/ma3063700 - 19 Jun 2010

Cited by 85 | Viewed by 20087

Abstract

The main properties (mechanical, thermal and chemical) and clinical application for dental restoration are demonstrated for three types of glass-ceramics and sintered polycrystalline ceramic produced by Ivoclar Vivadent AG. Two types of glass-ceramics are derived from the leucite-type and the lithium disilicate-type. The [...] Read more.

The main properties (mechanical, thermal and chemical) and clinical application for dental restoration are demonstrated for three types of glass-ceramics and sintered polycrystalline ceramic produced by Ivoclar Vivadent AG. Two types of glass-ceramics are derived from the leucite-type and the lithium disilicate-type. The third type of dental materials represents a ZrO₂ ceramic. CAD/CAM technology is a procedure to manufacture dental ceramic restoration. Leucite-type glass-ceramics demonstrate high translucency, preferable optical/mechanical properties and an application as dental inlays, onlays and crowns. Based on an improvement of the mechanical parameters, specially the strength and toughness, the lithium disilicate glass-ceramics are used as crowns; applying a procedure to machine an intermediate product and producing the final glass-ceramic by an additional heat treatment. Small dental bridges of lithium disilicate glass-ceramic were fabricated using a molding technology. ZrO₂ ceramics show high toughness and strength and were veneered with fluoroapatite glass-ceramic. Machining is possible with a porous intermediate product. Full article

(This article belongs to the Special Issue Ceramics for Healthcare)

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176 KiB

Open AccessArticle

Digital Computer Matching of Tooth Color

by Won-suk Oh, John Pogoncheff and William J. O’Brien

Materials 2010, 3(6), 3694-3699; https://doi.org/10.3390/ma3063694 - 18 Jun 2010

Cited by 9 | Viewed by 12937

Abstract

This study aimed to determine the validity of the digital photocolorimetric (PCM) method in matching the color of human teeth. First, two Vitapan Classical shade guides, each containing 16 shade guide teeth, were visually shade matched, and digital photographs of each three pair [...] Read more.

This study aimed to determine the validity of the digital photocolorimetric (PCM) method in matching the color of human teeth. First, two Vitapan Classical shade guides, each containing 16 shade guide teeth, were visually shade matched, and digital photographs of each three pair of shade guide teeth were taken in a color matching booth. Secondly, visual shade matching of the upper central incisors of 48 subjects was performed by two prosthodontists independently in a chair, using the Vitapan Classical shade guide. The three closest shade guide teeth were visually selected and ranked in order of preference, for which digital photographs were taken under ceiling daylight-corrected fluorescent lighting. All digital images were analyzed on a computer screen using software to calculate the color difference between the reference tooth and other teeth in the same digital image. The percent color matching for the shade guide teeth and human teeth was 88% and 75%, respectively. There was no statistically significant difference in matching the tooth color between the shade guide teeth and human teeth. The digital PCM method is valid for the range of human teeth based on the Vitapan Classical shade guide. This method enhances communication with the laboratory personnel in matching the tooth color. Full article

(This article belongs to the Special Issue Dental Biomaterials)

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567 KiB

Open AccessArticle

Scanning Tunneling Spectroscope Use in Electrocatalysis Testing

by Turid Knutsen

Materials 2010, 3(6), 3675-3693; https://doi.org/10.3390/ma3063675 - 14 Jun 2010

Viewed by 9264

Abstract

The relationship between the electrocatalytic properties of an electrode and its ability to transfer electrons between the electrode and a metallic tip in a scanning tunneling microscope (STM) is investigated. The alkaline oxygen evolution reaction (OER) was used as a test reaction with [...] Read more.

The relationship between the electrocatalytic properties of an electrode and its ability to transfer electrons between the electrode and a metallic tip in a scanning tunneling microscope (STM) is investigated. The alkaline oxygen evolution reaction (OER) was used as a test reaction with four different metallic glasses, Ni₇₈Si₈B₁₄, Ni₇₀Mo₂₀Si₅B₅, Ni₅₈Co20Si₁₀B₁₂, and Ni₂₅Co₅₀Si₁₅B₁₀, as electrodes. The electrocatalytic properties of the electrodes were determined. The electrode surfaces were then investigated with an STM. A clear relationship between the catalytic activity of an electrode toward the OER and its tunneling characteristics was found. The use of a scanning tunneling spectroscope (STS) in electrocatalytic testing may increase the efficiency of the optimization of electrochemical processes. Full article

(This article belongs to the Special Issue SPM in Materials Science)

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1565 KiB

Open AccessReview

Nanocomposites Derived from Polymers and Inorganic Nanoparticles

by In-Yup Jeon and Jong-Beom Baek

Materials 2010, 3(6), 3654-3674; https://doi.org/10.3390/ma3063654 - 14 Jun 2010

Cited by 448 | Viewed by 23273

Abstract

Polymers are considered to be good hosting matrices for composite materials because they can easily be tailored to yield a variety of bulk physical properties. Moreover, organic polymers generally have long-term stability and good processability. Inorganic nanoparticles possess outstanding optical, catalytic, electronic and [...] Read more.

Polymers are considered to be good hosting matrices for composite materials because they can easily be tailored to yield a variety of bulk physical properties. Moreover, organic polymers generally have long-term stability and good processability. Inorganic nanoparticles possess outstanding optical, catalytic, electronic and magnetic properties, which are significantly different their bulk states. By combining the attractive functionalities of both components, nanocomposites derived from organic polymers and inorganic nanoparticles are expected to display synergistically improved properties. The potential applications of the resultant nanocomposites are various, e.g. automotive, aerospace, opto-electronics, etc. Here, we review recent progress in polymer-based inorganic nanoparticle composites. Full article

(This article belongs to the Special Issue Nanocomposites of Polymers and Inorganic Particles)

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276 KiB

Open AccessArticle

Ti-doped ZnO Thin Films Prepared at Different Ambient Conditions: Electronic Structures and Magnetic Properties

by Zhihua Yong, Tao Liu, Tomoya Uruga, Hajime Tanida, Dongchen Qi, Andrivo Rusydi and Andrew T. S. Wee

Materials 2010, 3(6), 3642-3653; https://doi.org/10.3390/ma3063642 - 9 Jun 2010

Cited by 26 | Viewed by 11711

Abstract

We present a comprehensive study on Ti-doped ZnO thin films using X-ray Absorption Fine Structure (XAFS) spectroscopy. Ti K edge XAFS spectra were measured to study the electronic and chemical properties of Ti ions in the thin films grown under different ambient atmospheres. [...] Read more.

We present a comprehensive study on Ti-doped ZnO thin films using X-ray Absorption Fine Structure (XAFS) spectroscopy. Ti K edge XAFS spectra were measured to study the electronic and chemical properties of Ti ions in the thin films grown under different ambient atmospheres. A strong dependence of Ti speciation, composition, and local structures upon the ambient conditions was observed. The XAFS results suggest a major tetrahedral coordination and a 4+ valence state. The sample grown in a mixture of 80% Ar and 20% O₂ shows a portion of precipitates with higher coordination. A large distortion was observed by the Ti substitution in the ZnO lattice. Interestingly, the film prepared in 80% Ar, 20% O₂shows the largest saturation magnetic moment of 0.827 ± 0.013 µB/Ti. Full article

(This article belongs to the Special Issue Ferromagnetic Semiconductors)

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443 KiB

Open AccessArticle

Preparation and Characterization of New Inclusion Compounds Using Stable Nitroxide Radicals and an Organic 1-D Nanochannel as a Template

by Hirokazu Kobayashi, Tetsuo Asaji and Atsushi Tani

Materials 2010, 3(6), 3625-3641; https://doi.org/10.3390/ma3063625 - 9 Jun 2010

Cited by 13 | Viewed by 10818

Abstract

A new inclusion compound (IC) using di-t-buthyl nitroxide (DBNO) radical and tris(o-phenylenedioxy)cyclotriphosphazene (TPP) (1), which has an organic one-dimensional (1-D) nanochannel in the crystal, is reported. According to the characterization using thermogravimetric analysis (TG), ESR measurements, etc., the composition of the inclusion [...] Read more.

A new inclusion compound (IC) using di-t-buthyl nitroxide (DBNO) radical and tris(o-phenylenedioxy)cyclotriphosphazene (TPP) (1), which has an organic one-dimensional (1-D) nanochannel in the crystal, is reported. According to the characterization using thermogravimetric analysis (TG), ESR measurements, etc., the composition of the inclusion compound was assigned as TPP:DBNO = 1:0.62. The narrowing of the isotropic ESR adsorption line of 1 was observed with a temperature increase from 103 K to room temperature. The line shape indicated a type of 1-D spin diffusion as observed in our previous study of the IC using TPP and 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO). Full article

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635 KiB

Open AccessArticle

Effects of Interfacial Charge Depletion in Organic Thin-Film Transistors with Polymeric Dielectrics on Electrical Stability

by Jaehoon Park, Jin-Hyuk Bae, Won-Ho Kim, Min-Hoi Kim, Chang-Min Keum, Sin-Doo Lee and Jong Sun Choi

Materials 2010, 3(6), 3614-3624; https://doi.org/10.3390/ma3063614 - 9 Jun 2010

Cited by 20 | Viewed by 10996

Abstract

We investigated the electrical stabilities of two types of pentacene-based organic thin-film transistors (OTFTs) with two different polymeric dielectrics: polystyrene (PS) and poly(4-vinyl phenol) (PVP), in terms of the interfacial charge depletion. Under a short-term bias stress condition, the OTFT with the PVP [...] Read more.

We investigated the electrical stabilities of two types of pentacene-based organic thin-film transistors (OTFTs) with two different polymeric dielectrics: polystyrene (PS) and poly(4-vinyl phenol) (PVP), in terms of the interfacial charge depletion. Under a short-term bias stress condition, the OTFT with the PVP layer showed a substantial increase in the drain current and a positive shift of the threshold voltage, while the PS layer case exhibited no change. Furthermore, a significant increase in the off-state current was observed in the OTFT with the PVP layer which has a hydroxyl group. In the presence of the interfacial hydroxyl group in PVP, the holes are not fully depleted during repetitive operation of the OTFT with the PVP layer and a large positive gate voltage in the off-state regime is needed to effectively refresh the electrical characteristics. It is suggested that the depletion-limited holes at the interface, i.e., interfacial charge depletion, between the PVP layer and the pentacene layer play a critical role on the electrical stability during operation of the OTFT. Full article

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3073 KiB

Open AccessReview

Element Specific Versus Integral Structural and Magnetic Properties of Co:ZnO and Gd:GaN Probed with Hard X-ray Absorption Spectroscopy

by Andreas Ney

Materials 2010, 3(6), 3565-3613; https://doi.org/10.3390/ma3063565 - 7 Jun 2010

Cited by 20 | Viewed by 12021

Abstract

Dilute magnetic semiconductors (DMS) are envisioned as sources of spin-polarized carriers for future semiconductor devices which simultaneously utilize spin and charge of the carriers. The hope of discovering a DMS with ferromagnetic order up to room temperature still motivates research on suitable DMS [...] Read more.

Dilute magnetic semiconductors (DMS) are envisioned as sources of spin-polarized carriers for future semiconductor devices which simultaneously utilize spin and charge of the carriers. The hope of discovering a DMS with ferromagnetic order up to room temperature still motivates research on suitable DMS materials. Two candidate wide-band gap DMS are Gd:GaN and Co:ZnO. We have used hard X-ray absorption spectroscopy (XAS) and in particular X-ray linear dichroism (XLD) and X-ray magnetic circular dichroism (XMCD) to study both DMS materials with element specificity and compare these findings with results from integral SQUID magnetometry as well as electron paramagnetic resonance (EPR). Full article

(This article belongs to the Special Issue Ferromagnetic Semiconductors)

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544 KiB

Open AccessReview

Polymeric Microspheres for Medical Applications

by Ketie Saralidze, Leo H. Koole and Menno L.W. Knetsch

Materials 2010, 3(6), 3537-3564; https://doi.org/10.3390/ma3063537 - 7 Jun 2010

Cited by 146 | Viewed by 18973

Abstract

Synthetic polymeric microspheres find application in a wide range of medical applications. Among other applications, microspheres are being used as bulking agents, embolic- or drug-delivery particles. The exact composition of the spheres varies with the application and therefore a large array of materials [...] Read more.

Synthetic polymeric microspheres find application in a wide range of medical applications. Among other applications, microspheres are being used as bulking agents, embolic- or drug-delivery particles. The exact composition of the spheres varies with the application and therefore a large array of materials has been used to produce microspheres. In this review, the relation between microsphere synthesis and application is discussed for a number of microspheres that are used for different treatment strategies. Full article

(This article belongs to the Special Issue Advances in Biomaterials)

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1745 KiB

Open AccessReview

Silicone Resin Applications for Ceramic Precursors and Composites

by Masaki Narisawa

Materials 2010, 3(6), 3518-3536; https://doi.org/10.3390/ma3063518 - 2 Jun 2010

Cited by 93 | Viewed by 17141

Abstract

This article reviews the applications of silicone resins as ceramic precursors. The historical background of silicone synthesis chemistry is introduced to explain the production costs and supply availability of various silicones. Thermal degradation processes of silicones are classified in terms of the main [...] Read more.

This article reviews the applications of silicone resins as ceramic precursors. The historical background of silicone synthesis chemistry is introduced to explain the production costs and supply availability of various silicones. Thermal degradation processes of silicones are classified in terms of the main chain structure and cyclic oligomer expulsion process, which determine the resulting ceramic yield and the chemical composition. The high temperature decomposition of Si-O-C beyond 1,400 °C in an inert atmosphere and formation of a protective silica layer on material surfaces beyond 1,200 °C in an oxidative atmosphere are discussed from the viewpoints of the wide chemical composition of the Si-O-C materials. Applications of the resins for binding agents, as starting materials for porous ceramics, matrix sources with impregnation, fiber spinning and ceramic adhesions are introduced. The recent development of the process of filler or cross-linking agent additions to resin compounds is also introduced. Such resin compounds are useful for obtaining thick coatings, MEMS parts and bulk ceramics, which are difficult to obtain by pyrolysis of simple organometallic precursors without additives. Full article

(This article belongs to the Special Issue Composite Materials)

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2014 KiB

Open AccessReview

Polymer-Nanoparticle Composites: From Synthesis to Modern Applications

by Thomas Hanemann and Dorothée Vinga Szabó

Materials 2010, 3(6), 3468-3517; https://doi.org/10.3390/ma3063468 - 28 May 2010

Cited by 710 | Viewed by 35001

Abstract

The addition of inorganic spherical nanoparticles to polymers allows the modification of the polymers physical properties as well as the implementation of new features in the polymer matrix. This review article covers considerations on special features of inorganic nanoparticles, the most important synthesis [...] Read more.

The addition of inorganic spherical nanoparticles to polymers allows the modification of the polymers physical properties as well as the implementation of new features in the polymer matrix. This review article covers considerations on special features of inorganic nanoparticles, the most important synthesis methods for ceramic nanoparticles and nanocomposites, nanoparticle surface modification, and composite formation, including drawbacks. Classical nanocomposite properties, as thermomechanical, dielectric, conductive, magnetic, as well as optical properties, will be summarized. Finally, typical existing and potential applications will be shown with the focus on new and innovative applications, like in energy storage systems. Full article

(This article belongs to the Special Issue Nanocomposites of Polymers and Inorganic Particles)

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Materials, Volume 3, Issue 6 (June 2010) – 15 articles , Pages 3468-3793

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