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HighlightsA compilation of papers published within the last year

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According to the Oxford dictionary, the word ‘materials’ means the things that are used for making or doing something. Our journal, Science and Technology of Advanced Materials (STAM), places a lot of weight on this concept. This is a very different approach from other journals in the fields of pure physics and chemistry that deal with ‘material’ or ‘matter’. The second special feature of STAM is that it aims to establish links between three different groups – the readers, the contributors and the publishers. Because of this, we believe that STAM is standing on the side of readers compared with other scientific journals.

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Welcome

From the Publisher

Cover image: Detail of the wing of a butterfly from iStockphoto, inspired by ‘Material design and structural color inspired by biomimetic approach’ Akira Saito 2011 Science and Technology of Advanced Materials 12 064709.

http://iopscience.org/stam/highlights-2012

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4 iopscience.org/stam/highlights-2012

ContentsBest Paper Prize 2012 6

TOPICAL REVIEWS

Negative thermal expansion materials: technological key for control of thermal expansion 7Koshi Takenaka

Recent progress in mesoporous titania materials: adjusting morphology for innovative applications 7Juan L Vivero-Escoto, Ya-Dong Chiang, Kevin C-W Wu and Yusuke Yamauchi

Progress in thermomechanical control of steel plates and their commercialization 8Kiyoshi Nishioka and Kazutoshi Ichikawa

Programmed self-assembly of large π-conjugated molecules into electroactive one-dimensional 8 nanostructuresYohei Yamamoto

Progress of key strategies in development of electrospun scaffolds: bone tissue 9Sumit Pramanik, Belinda Pingguan-Murphy and Noor Azuan Abu Osman

Photonic metamaterials: a new class of materials for manipulating light waves 9Masanobu Iwanaga

Revisiting some chalcogenides for thermoelectricity 10Antoine Maignan, Emmanuel Guilmeau, Franck Gascoin, Yohann Bréard and Vincent Hardy

Paradigm shift from self-assembly to commanded assembly of functional materials: recent examples in 11 porphyrin/fullerene supramolecular systemsMao Li, Shinsuke Ishihara, Qingmin Ji, Misaho Akada, Jonathan P Hill and Katsuhiko Ariga

Cell membrane-inspired phospholipid polymers for developing medical devices with 11 excellent biointerfaces Yasuhiko Iwasaki and Kazuhiko Ishihara




PAPERS

Synthesis, characterization and antibacterial activity of superparamagnetic nanoparticles modified 12 with glycol chitosan Baskaran Stephen Inbaraj, Tsung-Yu Tsai and Bing-Huei Chen

Turning refuse plastic into multi-walled carbon nanotube forest 12Eugene Oh, Jaegeun Lee, Seung-Ho Jung, Seungho Cho, Hye-Jin Kim, Sung-Hyun Lee, Kun-Hong Lee, Kyong-Hwa Song,

Chi-Hoon Choi and Do Suck Han

Electrospinning of aligned fibers with adjustable orientation using auxiliary electrodes 13Matthias M L Arras, Christian Grasl, Helga Bergmeister and Heinrich Schima

Microwave sintering and in vitro study of defect-free stable porous multilayered HAp–ZrO2 artificial 13 bone scaffold Dong-Woo Jang, Thi-Hiep Nguyen, Swapan Kumar Sarkar and Byong-Taek Lee

Synthesis of biocompatible multicolor luminescent carbon dots for bioimaging applications 14Nagaprasad Puvvada, B N Prashanth Kumar, Suraj Konar, Himani Kalita, Mahitosh Mandal and Amita Pathak

Electrical isolation of dislocations in Ge layers on Si(001) substrates through CMOS-compatible 14 suspended structures Vishal Ajit Shah, Maksym Myronov, Chalermwat Wongwanitwatana, Lewis Bawden, Martin J Prest, James S Richardson-Bullock,

Stephen Rhead, Evan H C Parker, Terrance E Whall and David R Leadley

A smart hydrogel-based time bomb triggers drug release mediated by pH-jump reaction 15Prapatsorn Techawanitchai, Naokazu Idota, Koichiro Uto, Mitsuhiro Ebara and Takao Aoyagi

In the news 16

Focus issues 2012 19

Editorial board 21




Prototype displays using AOS TFTs.

Best Paper Prize 2012

Present status of amorphous In–Ga–Zn–O thin-film transistors

Toshio Kamiya, Kenji Nomura and Hideo Hosono

2010 Sci. Technol. Adv. Mater. 11 044305

The present status and recent research results on amorphous oxide semiconductors (AOSs) and their thin-film transistors (TFTs) are reviewed. AOSs represented by amorphous In–Ga–Zn–O (a-IGZO) are expected to be the channel material of TFTs in next-generation flat-panel displays because a-IGZO TFTs satisfy almost all the requirements for organic light-emitting-diode displays, large and fast liquid crystal and three-dimensional (3D) displays, which cannot be satisfied using conventional silicon and organic TFTs. The major insights of this review are summarized as follows. (i) Most device issues, such as uniformity, long-term stability against bias stress and TFT performance, are solved for a-IGZO TFTs. (ii) A sixth-generation (6G) process is demonstrated for 3200 and 3700 displays. (iii) An 8G sputtering apparatus and a sputtering target have been developed. (iv) The important effect of deep subgap states on illumination instability is revealed. (v) Illumination instability under negative bias has been intensively studied, and some mechanisms are proposed. (vi) Degradation mechanisms are classified into back-channel effects, the creation of traps at an interface and in the gate insulator, and the creation of donor states in annealed a-IGZO TFTs by the Joule heating; the creation of bulk defects should also be considered in the case of unannealed a-IGZO TFTs. (vii) Dense passivation layers improve the stability and photoresponse and are necessary for practical applications. (viii) Sufficient knowledge of electronic structures and electron transport in a-IGZO has been accumulated to construct device simulation models.

Congratulations go to the authors of the following paper, which won our Best Paper Prize in 2012. They review the status and recent research results on amorphous oxide semiconductors (ASOSs) and their thin-film transistors (TFTs).


http://iopscience.iop.org/1468-6996/11/4/044305?fromSearchPage=true



Recent progress in mesoporous titania materials: adjusting morphology for innovative applications

Juan L Vivero-Escoto, Ya-Dong Chiang, Kevin C-W Wu and Yusuke Yamauchi


This review article summarizes recent developments in mesoporous titania materials, particularly in the fields of morphology control and applications. We first briefly introduce the history of mesoporous titania materials and then review several synthesis approaches. Currently, mesoporous titania nanoparticles (MTNs) have attracted much attention in various fields, such as medicine, catalysis, separation and optics. Compared with bulk mesoporous titania materials, which are above a micrometer in size, nanometer-sized MTNs have additional properties, such as fast mass transport, strong adhesion to substrates and good dispersion in solution. However, it has generally been known that the successful synthesis of MTNs is very difficult owing to the rapid hydrolysis of titanium-containing precursors and the crystallization of titania upon thermal treatment. Finally, we review four emerging fields including photocatalysis, photovoltaic devices, sensing and biomedical applications of mesoporous titania materials. Because of its high surface area, controlled porous structure, suitable morphology and semiconducting behavior, mesoporous titania is expected to be used in innovative applications.

Topical reviews

Koshi TakenakaNagoya University, Japan

Negative thermal expansion materials: technological key for control of thermal expansion

Koshi Takenaka


Most materials expand upon heating. However, although rare, some materials contract upon heating. Such negative thermal expansion (NTE) materials have enormous industrial merit because they can control the thermal expansion of materials. Recent progress in materials research enables us to obtain materials exhibiting negative coefficients of linear thermal expansion over −30 ppm K−1. Such giant NTE is opening a new phase of control of thermal expansion in composites. Specifically examining practical aspects, this review briefly summarizes materials and mechanisms of NTE as well as composites containing NTE materials, based mainly on activities of the last decade.

Yusuke YamauchiNational Institute for Materials Science, Japan


http://iopscience.iop.org/1468-6996/13/1/013003




Programmed self-assembly of large π-conjugated molecules into electroactive one-dimensional nanostructures

Yohei Yamamoto


Electroactive one-dimensional (1D) nano-objects possess inherent unidirectional charge and energy transport capabilities along with anisotropic absorption and emission of light, which are of great advantage for the development of nanometer-scale electronics and optoelectronics. In particular, molecular nanowires formed by self-assembly of π-conjugated molecules attract increasing attention for application in supramolecular electronics. This review introduces recent topics related to electroactive molecular nanowires. The nanowires are classified into four categories with respect to the electronic states of the constituent molecules: electron donors, acceptors, donor–acceptor pairs and miscellaneous molecules that display interesting electronic properties. Although many challenges still remain for practical use, state-of-the-art 1D supramolecular nanomaterials have already brought significant advances to both fundamental chemical sciences and technological applications.

TOPICAL REVIEWS

Progress in thermomechanical control of steel plates and their commercialization

Kiyoshi Nishioka and Kazutoshi Ichikawa


The water-cooled thermomechanical control process (TMCP) is a technology for improving the strength and toughness of water-cooled steel plates, while allowing control of the microstructure, phase transformation and rolling. This review describes metallurgical aspects of the microalloying of steel, such as niobium addition, and discusses advantages of TMCP, for example, in terms of weldability, which is reduced upon alloying. Other covered topics include the development of equipment, distortions in steel plates, peripheral technologies such as steel making and casting, and theoretical modeling, as well as the history of property control in steel plate production and some early TMCP technologies. We provide some of the latest examples of applications of TMCP steel in various industries such as shipbuilding, offshore structures, building construction, bridges, pipelines, penstocks and cryogenic tanks. This review also introduces high heat-affected-zone toughness technologies, wherein the microstructure of steel is improved by the addition of fine particles of magnesium-containing sulfides and magnesium- or calcium-containing oxides. We demonstrate that thanks to ongoing developments TMCP has the potential to meet the ever-increasing demands of steel plates.

Kiyoshi NishiokaUniversity of Tokyo, Japan

Yohei YamamotoUniversity of Tsukuba, Japan






Progress of key strategies in development of electrospun scaffolds: bone tissue

Sumit Pramanik, Belinda Pingguan-Murphy and Noor Azuan Abu Osman


There has been unprecedented development in tissue engineering (TE) over the last few years owing to its potential applications, particularly in bone reconstruction or regeneration. In this article, we illustrate several advantages and disadvantages of different approaches to the design of electrospun TE scaffolds. We also review the major benefits of electrospun fibers for three-dimensional scaffolds in hard connective TE applications and identify the key strategies that can improve the mechanical properties of scaffolds for bone TE applications. A few interesting results of recent investigations have been explained for future trends in TE scaffold research.

TOPICAL REVIEWS

Photonic metamaterials: a new class of materials for manipulating light waves

Masanobu Iwanaga


A decade of research on metamaterials (MMs) has yielded great progress in artificial electromagnetic materials in a wide frequency range from microwave to optical frequencies. This review outlines the achievements in photonic MMs that can efficiently manipulate light waves from near-ultraviolet to near-infrared in subwavelength dimensions. One of the key concepts of MMs is effective refractive index, realizing values that have not been obtained in ordinary solid materials. In addition to the high and low refractive indices, negative refractive indices have been reported in some photonic MMs. In anisotropic photonic MMs of high-contrast refractive indices, the polarization and phase of plane light waves were efficiently transformed in a well-designed manner, enabling remarkable miniaturization of linear optical devices such as polarizers, wave plates and circular dichroic devices. Another feature of photonic MMs is the possibility of unusual light propagation, paving the way for a new subfield of transfer optics. MM lenses having super-resolution and cloaking effects were introduced by exploiting novel light-propagating modes. Here, we present a new approach to describing photonic MMs definitely by resolving the electromagnetic eigenmodes. Two representative photonic MMs are addressed: the so-called fishnet MM slabs, which are known to have effective negative refractive index, and a three-dimensional MM based on a multilayer of a metal and an insulator. In these photonic MMs, we elucidate the underlying eigenmodes that induce unusual light propagations. Based on the progress of photonic MMs, the future potential and direction are discussed.

Sumit PramanikUniversity of Malaya, Malaysia

Masanobu IwanagaNational Institute for Materials Science, Japan






Revisiting some chalcogenides for thermoelectricity

Antoine Maignan, Emmanuel Guilmeau, Franck Gascoin, Yohann Bréard and Vincent Hardy


Thermoelectric materials that are efficient well above ambient temperature are needed to convert waste-heat into electricity. Many thermoelectric oxides were investigated for this purpose, but their power factor (PF) values were too small (~10−4 W m−1 K−2) to yield a satisfactory figure of merit zT. Changing the anions from O2− to S2− and then to Se2− is a way to increase the covalency. In this review, some examples of sulfides (binary Cr–S or derived from layered TiS

2) and an example of selenides, AgCrSe2, have been selected to illustrate the characteristic features of their physical properties. The comparison of the only two semiconducting binary chromium sulfides and of a layered AgCrSe

2 selenide shows that the PF values are also in the same order of magnitude as those of transition metal oxides. In contrast, the PF values of the layered sulfides TiS

2 and Cu0.1TiS2 are higher, reaching ~10−3 W m−1 K−2. Apparently the magnetism related to the Cr–S network is detrimental for the PF when compared to the d0 character of the Ti4+ based sulfides. Finally, the very low PF in AgCrSe

2 (PF = 2.25 × 10−4 W m1 K−2 at 700 K) is compensated by a very low thermal conductivity (κ = 0.2 W m−1 K−1 from the measured Cp) leading to the highest zT value among the reviewed compounds (zT700K = 0.8). The existence of a glassy-like state for the Ag+ cations above 475 K is believed to be responsible for this result. This result demonstrates that the phonon engineering in open frameworks is a very interesting way to generate efficient thermoelectric materials.

TOPICAL REVIEWS

Antoine MaignanLaboratoire CRISMAT, France

Did you know?Papers published in STAM are downloaded on average 600 times

Did you know?Once accepted, articles submitted to STAM are published online within 27 days





TOPICAL REVIEWS

Cell membrane-inspired phospholipid polymers for developing medical devices with excellent biointerfaces

Yasuhiko Iwasaki and Kazuhiko Ishihara


This review article describes fundamental aspects of cell membrane-inspired phospholipid polymers and their usefulness in the development of medical devices. Since the early 1990s, polymers composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) units have been considered in the preparation of biomaterials. MPC polymers can provide an artificial cell membrane structure at the surface and serve as excellent biointerfaces between artificial and biological systems. They have also been applied in the surface modification of some medical devices including long-term implantable artificial organs. An MPC polymer biointerface can suppress unfavorable biological reactions such as protein adsorption and cell adhesion—in other words, specific biomolecules immobilized on an MPC polymer surface retain their original functions. MPC polymers are also being increasingly used for creating biointerfaces with artificial cell membrane structures.

Paradigm shift from self-assembly to commanded assembly of functional materials: recent examples in porphyrin/fullerene supramolecular systems

Mao Li, Shinsuke Ishihara, Qingmin Ji, Misaho Akada, Jonathan P Hill and Katsuhiko Ariga


Current nanotechnology based on top-down nanofabrication may encounter a variety of drawbacks in the near future so that development of alternative methods, including the so-called bottom-up approach, has attracted considerable attention. However, the bottom-up strategy, which often relies on spontaneous self-assembly, might be inefficient in the development of the requisite functional materials and systems. Therefore, assembly processes controlled by external stimuli might be a plausible strategy for the development of bottom-up nanotechnology. In this review, we demonstrate a paradigm shift from self-assembly to commanded assembly by describing several examples of assemblies of typical functional molecules, i.e. porphyrins and fullerenes. In the first section, we describe recent progress in the design and study of self-assembled and co-assembled supramolecular architectures of porphyrins and fullerenes. Then, we show examples of assembly induced by external stimuli. We emphasize the paradigm shift from self-assembly to commanded assembly by describing the recently developed electrochemical-coupling layer-by-layer (ECC-LbL) methodology.

Yasuhiko IwasakiKansai University, Japan

Kazuhiko IshiharaUniversity of Tokyo, Japan

Katsuhiko ArigaNational Institute for Materials Science, Japan






Synthesis, characterization and antibacterial activity of superparamagnetic nanoparticles modified with glycol chitosan

Baskaran Stephen Inbaraj, Tsung-Yu Tsai and Bing-Huei Chen


Iron oxide nanoparticles (IONPs) were synthesized by coprecipitation of iron salts in alkali media followed by coating with glycol chitosan (GC-coated IONPs). Both bare and GC-coated IONPs were subsequently characterized and evaluated for their antibacterial activity. Comparison of Fourier transform infrared spectra and thermogravimetric data of bare and GC-coated IONPs confirmed the presence of GC coating on IONPs. Magnetization curves showed that both bare and GC-coated IONPs are superparamagnetic and have saturation magnetizations of 70.3 and 59.8 emu g−1, respectively. The IONP size was measured as

~8–9 nm by transmission electron microscopy, and their crystal structure was assigned to magnetite from x-ray diffraction patterns. Both bare and GC-coated IONPs inhibited the growths of Escherichia coli ATCC 8739 and Salmonella enteritidis SE 01 bacteria better than the antibiotics linezolid and cefaclor, as evaluated by the agar dilution assay. GC-coated IONPs showed higher potency against E. coli O157:H7 and Staphylococcus aureus ATCC 10832 than bare IONPs. Given their biocompatibility and antibacterial properties, GC-coated IONPs are a potential nanomaterial for in vivo applications.

Turning refuse plastic into multi-walled carbon nanotube forest

Eugene Oh, Jaegeun Lee, Seung-Ho Jung, Seungho Cho, Hye-Jin Kim, Sung-Hyun Lee, Kun-Hong Lee, Kyong-Hwa Song, Chi-Hoon Choi and Do Suck Han


A novel and effective method was devised for synthesizing a vertically aligned carbon nanotube (CNT) forest on a substrate using waste plastic obtained from commercially available water bottles. The advantages of the proposed method are the speed of processing and the use of waste as a raw material. A mechanism for the CNT growth was also proposed. The growth rate of the CNT forest was ~2.5 μm min−1. Transmission electron microscopy images indicated that the outer diameters of the CNTs were 20–30 nm on average. The intensity ratio of the G and D Raman bands was 1.27 for the vertically aligned CNT forest. The Raman spectrum showed that the wall graphitization of the CNTs, synthesized via the proposed method was slightly higher than that of commercially available multi-walled carbon nanotubes (MWCNTs). We expect that the proposed method can be easily adapted to the disposal of other refuse materials and applied to MWCNT production industries.

Papers

Bing-Huei ChenFu Jen University, Japan

Kun-Hong LeePohang University of Science and Technology, Korea






PAPERS

Electrospinning of aligned fibers with adjustable orientation using auxiliary electrodes

Matthias M L Arras, Christian Grasl, Helga Bergmeister and Heinrich Schima


A conventional electrospinning setup was upgraded by two turnable plate-like auxiliary high-voltage electrodes that allowed aligned fiber deposition in adjustable directions. Fiber morphology was analyzed by scanning electron microscopy and attenuated total reflection Fourier transform infrared spectroscopy (FTIR-ATR). The auxiliary electric field constrained the jet bending instability and the fiber deposition became controllable. At target speeds of 0.9 m s−1 90% of the fibers had aligned within 2°, whereas the angular spread was 70° without the use of auxiliary electrodes. It was even possible to orient fibers perpendicular to the rotational direction of the target. The fiber diameter became smaller and its distribution narrower, while according to the FTIR-ATR measurement the molecular orientation of the polymer was unaltered. This study comprehensively documents the feasibility of directed fiber deposition and offers an easy upgrade to existing electrospinning setups.

Microwave sintering and in vitro study of defect-free stable porous multilayered HAp–ZrO2 artificial bone scaffold

Dong-Woo Jang, Thi-Hiep Nguyen, Swapan Kumar Sarkar and Byong-Taek Lee


Continuously porous hydroxyapatite (HAp)/t-ZrO2 composites containing concentric laminated frames and microchanneled bodies were fabricated by an extrusion process. To investigate the mechanical properties of HAp/t-ZrO

2 composites, the porous composites were sintered at different temperatures using a microwave furnace. The microstructure was designed to imitate that of natural bone, particularly small bone, with both cortical and spongy bone sections. Each microchannel was separated by alternating lamina of HAp, HAp–(t-ZrO

2) and t-ZrO2. HAp and ZrO2 phases existed on the surface of the microchannel and the core zone to increase the biocompatibility and mechanical properties of the HAp–ZrO

2 artificial bone. The sintering behavior was evaluated and the optimum sintering temperature was found to be 1400 °C, which produced a stable scaffold. The material characteristics, such as the microstructure, crystal structure and compressive strength, were evaluated in detail for different sintering temperatures. A detailed in vitro study was carried out using MTT assay, western blot analysis, gene expression by polymerase chain reaction and laser confocal image analysis of cell proliferation. The results confirmed that HAp–ZrO

2 performs as an artificial bone, showing excellent cell growth, attachment and proliferation behavior using osteoblast-like MG63 cells.

Byong-Taek LeeSoonchunhyang University, Korea






Synthesis of biocompatible multicolor luminescent carbon dots for bioimaging applications

Nagaprasad Puvvada, B N Prashanth Kumar, Suraj Konar, Himani Kalita, Mahitosh Mandal and Amita Pathak


Water-soluble carbon dots (C-dots) were prepared through microwave-assisted pyrolysis of an aqueous solution of dextrin in the presence of sulfuric acid. The C-dots produced showed multicolor luminescence in the entire visible range, without adding any surface-passivating agent. X-ray diffraction and Fourier transform infrared spectroscopy studies revealed the graphitic nature of the carbon and the presence of hydrophilic groups on the surface, respectively. The formation of uniformly distributed C-dots and their luminescent properties were, respectively, revealed from transmission electron microscopy and confocal laser scanning microscopy. The biocompatible nature of C-dots was confirmed by a cytotoxicity assay on MDA-MB-468 cells and their cellular uptake was assessed through a localization study.

PAPERS

Electrical isolation of dislocations in Ge layers on Si(001) substrates through CMOS-compatible suspended structures

Vishal Ajit Shah, Maksym Myronov, Chalermwat Wongwanitwatana, Lewis Bawden, Martin J Prest, James S Richardson-Bullock, Stephen Rhead, Evan H C Parker, Terrance E Whall and David R Leadley


Suspended crystalline Ge semiconductor structures are created on a Si(001) substrate by a combination of epitaxial growth and simple patterning from the front surface using anisotropic underetching. Geometric definition of the surface Ge layer gives access to a range of crystalline planes that have different etch resistance. The structures are aligned to avoid etch-resistive planes in making the suspended regions and to take advantage of these planes to retain the underlying Si to support the structures. The technique is demonstrated by forming suspended microwires, spiderwebs and van der Pauw cross structures. We finally report on the low-temperature electrical isolation of the undoped Ge layers. This novel isolation method increases the Ge resistivity to 280 Ω cm at 10 K, over two orders of magnitude above that of a bulk Ge on Si(001) layer, by removing material containing the underlying misfit dislocation network that otherwise provides the main source of electrical conduction.

Amita PathakIndian Institute of Technology, India

Vishal Ajit ShahWarwick University, UK






PAPERS

Did you know?The 2011 Impact Factor increased to 3.513

Did you know?STAM has a global readership and features top research from institutions throughout the world

A smart hydrogel-based time bomb triggers drug release mediated by pH-jump reaction

Prapatsorn Techawanitchai, Naokazu Idota, Koichiro Uto, Mitsuhiro Ebara and Takao Aoyagi


We demonstrate a timed explosive drug release from smart pH-responsive hydrogels by utilizing a phototriggered spatial pH-jump reaction. A photoinitiated proton-releasing reaction of o-nitrobenzaldehyde (o-NBA) was integrated into poly(N-isopropylacrylamide-co-2-carboxyisopropylacrylamide) (P(NIPAAm-co-CIPAAm)) hydrogels. o-NBA-hydrogels demonstrated the rapid release of protons upon UV irradiation, allowing the pH inside the gel to decrease to below the pKa value of P(NIPAAm-co-CIPAAm). The generated protons diffused gradually toward the non-illuminated area, and the diffusion kinetics could be controlled by adjusting the UV irradiation time and intensity. After irradiation, we observed the enhanced release of entrapped L-3,4-dihydroxyphenylalanine (DOPA) from the gels, which was driven by the dissociation of DOPA from CIPAAm. Local UV irradiation also triggered the release of DOPA from the non-illuminated area in the gel via the diffusion of protons. Conventional systems can activate only the illuminated region, and their response is discontinuous when the light is turned off. The ability of the proposed pH-jump system to permit gradual activation via proton diffusion may be beneficial for the design of predictive and programmable devices for drug delivery.

Takao AoyagiUniversity of Tsukuba, Japan





In the newsArticles from Science and Technology of Advanced Materials are often picked up by other media and benefit from the extra exposure that this generates.

Brighter future for carbon dots

Carbon dots are light-emitting nanoparticles that can be used to track biological processes inside cells. They are less toxic than similar alternatives, making them more suitable for use in live biological systems, but the light-emitting properties of current versions are not ideal.

Most attempts to make carbon dots have required the particles to be coated with other molecules to achieve useful luminescence. In work reported in Science and Technology of Advanced Materials, a team led by Amita Pathak at the Indian Institute of Technology has produced water-soluble carbon dots that selectively emit light across the entire visible range, but do not need any surface coating.

The team produced the carbon dots by using microwaves to break down dextrin, a low-molecular-weight carbohydrate, and found that the resulting nanoparticles emit different colours of light when excited by specific wavelengths. It remains unclear how this multi-coloured luminescence arises, but it allows precise control of the light emission that can be tailored to specific applications.

To ensure that the carbon dots were non-toxic, the team added different concentrations of the nanoparticles to cultured cells. Increasing the concentration of carbon dots made little difference to cell survival, showing that they are safe to use in live tissue.

The properties of these new carbon dots make them ideal for bioimaging applications and medical diagnostics. The researchers have already begun to look at their potential for investigating interactions between drugs and cells.


From Materials science: from research to technology – an IOP Publishing publication




Taking control of self-assembly

Spontaneous self-assembly and other bottom-up fabrication techniques have enabled nanopatterning with feature sizes previously inaccessible by top-down fabrication methods. Nanostructures created with these techniques hold promise for a range of photovoltaic and electronic devices, but so far there have been few practical examples because such spontaneous fabrication processes are difficult to control.

One solution now being investigated is to develop synthesis methods that exploit a system’s responses to external stimuli, mimicking the way that sophisticated programming and external triggers contribute to self-assembly processes in biological systems. In a review article published in Science and Technology of Advanced Materials, researchers at the Research Center for Materials Nanoarchitectonics in Tsukuba, Japan, describe how this paradigm shift from self-assembly to so-called commanded assembly delivers extremely fine nanoscale features with impressive levels of control.

The review focuses on porphyrins and fullerenes, since their morphological and electronic properties make them suitable for device applications. Indeed, a number of self-assembled porphyrin and fullerene nanostructures have already been shown to exhibit device potential, but the researchers say that further technological development has been limited because ‘scientific accomplishments regarding self-assembly lag far behind those that have been evolved in nature’.

To demonstrate the power of commanded assembly, the authors take the example of layer-by-layer fabrication – a simple and inexpensive method that allows different types of material to be incorporated into thin-film structures. Layer-by-layer assembly is normally a spontaneous process, but in this case electrical signals are used to control electrochemical reactions during assembly. The effectiveness of this technique enables area-selective patterning, demonstrated here by using a mask to create the letters M, A and O on a transparent electrode made of indium tin oxide.

Such electrochemically controlled layer-by-layer self-assembly provides a good example of a bottom-up fabrication empowered to achieve more sophisticated structures. The authors also suggest that the versatility of the technique could allow it to be coupled to other top-down techniques. ‘When the paradigm shift from self-assembly to commanded assembly has been successfully completed, molecular/material assembly can be promoted from being only a scientific curiosity to a practically useful technology,’ they conclude.


From Materials science: from research to technology – an IOP Publishing publication

IN THE NEWS




IN THE NEWS

Field guide: technological advances in electrospinning of nanofibres

A better understanding of the electric field profile and its effect on the electrospinning jet together with upgrades in mechanical set-ups are allowing researchers to fabricate ever more elaborate structures based on a stream of nanofibre. Writing in our partner journal Science and Technology of Advanced Materials, Wee-Eong Teo, Ryuji Inai and Seeram Ramakrishna track the developments.

Over the last decade, advances in electrospinning have seen nanofibrous arrangements evolve from a non-woven form to yarn, 3D assemblies and patterned structures. The process has emerged as a popular nanotechnology since the late 1990s owing to the ease of fabricating nanofibres from a wide selection of materials and has become an important route to learning more about the properties of materials in nanofibre form.

Future advances in electrospinning are likely to be driven by applications that require specialized nanofibre chemistry and structure, multifunctional hierarchical organizations and their scaling to industrial production.

Tuning the technologyTechniques such as ultraviolet cutting, chemical fragmentation and ion etching have been developed to address the preference for short fibres in non-invasive surgical and solar-energy applications. And owing to the high surface area of nanofibres, interesting properties and improved device performance can be expected.

From a commercial perspective, the application of electrospun nanofibres will be in high-performance or high-value-added products.

Precision patterningThe ability to precisely control fibre deposition to form patterns using electrospinning has the potential to significantly expand the application of this technique and improve device performance. For example, signals from sensors made of nanofibres can be quickly routed to a receiver.

Although conductive nanofibres have been fabricated using electrospinning, the chaotic nature of the deposition process seems incompatible with the high accuracy required for the fabrication of electronic devices. Nevertheless, electrospinning offers several advantages over existing methods. First, it is a relatively fast process and can be used for the rapid prototyping of nanofibrous devices. Second, it is very simple to obtain fibres with diameters smaller than 500 nm. Third, the nanofibre is continuous, which reduces the likelihood of a breakage in the connection compared with ink-jet printing methods.

Technological advances in electrospinning of nanofibers Wee-Eong Teo, Ryuji Inai and Seeram Ramakrishna 2012 Sci. Technol. Adv. Mater. 13 013002

From nanotechweb.org5 August 2011


http://nanotechweb.org



Focus issues 2012Focus on superconducting properties of iron chalcogenides

Guest editor: Yoshihiko Takano

Since the discovery of iron-based superconductors, much attention has been given to the exploration of new superconducting compounds. Numerous superconducting iron compounds have been found and categorized into five groups: LnFeAsO (Ln = lanthanide), BaFe

2As2, KFeAs, FeSe and FeAs with perovskite blocking layers. Among them, FeSe has the simplest crystal structure. Since the crystal structure is composed of only superconducting Fe layers, the FeSe family must be the best material to investigate the mechanism of iron-based superconductivity. FeSe shows very strong pressure effects. The superconducting transition temperature (T

c) of FeSe is approximately 8 K at ambient pressure. However T

c dramatically increases up to 37 K under applied pressure of 4–6 GPa. This is the third highest Tc value among binary superconductors, surpassed only by CsC

60 under pressure (Tc = 38 K) and MgB2 (Tc = 39 K).

On the other hand, despite FeTe having a crystal structure analogous to that of FeSe, FeTe shows antiferromagnetic properties without superconductivity. Doping of small ions, either Se or S, however, can induce superconductivity in FeTe1-xSex or FeTe1-xSx. The superconductivity is very weak for small x values, and annealing under certain conditions is required to obtain strong superconductivity, for instance annealing in oxygen or alcoholic beverages such as red wine.

From biomedical-engineering research to clinical application and industrialization

Guest editors: Tetsushi Taguchi and Takao Aoyagi

The rising costs and aging of the population due to a low birth rate negatively affect the healthcare system in Japan. In 2011, the Council for Science and Technology Policy released the 4th Japan’s Science and Technology Basic Policy Report from 2011 to 2015. This report includes two major innovations, ‘Life Innovation’ and ‘Green Innovation’, to promote economic growth. Biomedical engineering research is part of ‘Life Innovation’ and its outcomes are required to maintain people’s mental and physical health. It has already resulted in numerous biomedical products, and new ones should be developed using nanotechnology-based concepts. The combination of accumulated knowledge and experience, and ‘nanoarchitechtonics’ will result in novel, well-designed functional biomaterials.






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