Titania Embedded with Nanostructured Sodium Titanate: Reduced Thermal Conductivity for Thermoelectric Application

Titania embedded with layer-cracking nanostructures (sodium titanate) was synthesized by a hydrothermal method and a subsequent sintering process. The structure and morphology were determined by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N₂ adsorption–desorption experiments. In thermoelectric investigations, this nanocomposite has reduced thermal conductivity, where the minimum reaches about 2.4 W/m K at 700°C. This value is relatively low among the transition-metal oxides. Strong boundary scattering at the interfaces of the layered nanostructures and point defect scattering resulting from volatilization of Na⁺ ions seem to be main reasons for the suppression of phonon heat transfer. On the other hand, the power factor shows no apparent deterioration. Our results suggest that introduction of proper layer-cracking nanostructures into thermoelectric hosts might be effective to enhance their performance.     

Nanostructured Surfaces

Many approaches to the structuring of surfaces in the micrometer and nanometer range have been undertaken in the last few decades. Most of these technologies, however, are limited to the fabrication of small areas. In this article two methods for the creation of larger areas of structured surfaces are discussed. The first approach is based on the self‐assembly of ligand‐protected Au₅₅ clusters at the phase boundary between water and dichloromethane, with subsequent transfer to a solid substrate. The other strategy employs nanoporous alumina membranes as masks for the imprinting of metal and polymer surfaces. The self‐assembly generates surfaces with building blocks of about 2 nm (see Figure) whereas the imprinting method leads to structural units of 10–200 nm.     

Aerobijels: Ultralight Carbon Monoliths from Cocontinuous Emulsions

Bijels are used to develop a new class of ultralight hierarchically porous aerogels exhibiting multimodal porosity across multiple length scales. Through in situ functionalization of a particle‐laden liquid interface wherein binary liquid pairs are kinetically trapped out of equilibrium through interfacial jamming, monolithic and freestanding carbon electrodes are produced with prescribed bulk densities down to ≈2 mg cm^?3. Exemplary electrokinetic experiments indicate that the bicontinuity of the pore structure is essential for enhancing transport to and from the active electrode surfaces, demonstrating that these materials possess a superior ability to accumulate and transport charge when compared to analogous systems with restricted pore connectivity and fluid throughput. This approach offers a new synthetic route to bicontinuous and hierarchical aerogel materials with nested multimodal porosities. The flexibility of this scheme can address critical issues related to transport‐limited behaviors that arise in many technological fields, ranging from energy and catalysis research to remediation and sensing applications.     

Hybrid Monoliths for Magnetically‐Driven Protein Separations

Monoliths represent powerful platforms for isolation of large molecules with high added value. This work presents a hybrid approach for antibody (Ab) capture and release. Using mostly natural polymers and clean processes, it is possible to create macroporous monoliths with well‐defined porous networks, tuneable mechanical properties, and easy functionalization with a biomimetic ligand specific for Ab. Magnetic nanoparticles (MNPs) are embedded on the monolith network to confer a controlled magnetic response that facilitates and accelerates Ab recovery in the elution step. The hybrid monolithic systems prepared with agarose or chitosan/poly(vinyl alcohol) (PVA) blends exhibit promising binding capacities of Abs directly from cell‐culture extracts (120 ± 10 mg Ab g^?1 support) and controlled Ab magnetically‐assisted elution yielding 95 ± 2% recovery. Moreover, a selective capture of mAbs directly from cell culture extracts is achieved yielding a final mAb preparation with 96% of purity.     

Nanostructured thermoelectric materials

High values of thermoelectric figures of merit ZT, ranging from ZT=1.6 at 300 K to ZT=3 at 550 K, are reported for Bi-doped n-type PbSeTe/PbTe quantum-dot superlattice (QDSL) samples grown by molecular beam epitaxy (MBE). These ZT values were determined by directly measuring Seebeck coefficients and electrical conductivities and using the low lattice thermal conductivity value (∼3.3 mW/cm-K) determined experimentally from measurements of a one-legged thermoelectric cooler. Initial experiments have also shown that high values of ZT (∼1.1 at 300 K) are achievable for complementary Na-doped p-type PbSeTe/PbTe QDSL samples, in which the conduction and valence bands mirror those in the Bi-doped Pb chalcogenides.     

Black Titania with Nanoscale Helicity

The fabrication of mesoporous black titanium dioxide (TiO_2?x ) with a chiral nematic organization of core–shell nanorods is reported. Chiral templating of TiO₂ nanoparticles onto gelatin‐functionalized cellulose nanocrystals (CNCs) followed by calcination yields carbonized TiO₂/CNC helical materials that recover white TiO₂ replicas after carbon removal. The hydrothermal surface reduction of the traditional white TiO₂ by ascorbic acid affords freestanding chiral nematic black TiO_2?x. The black TiO_2?x is a visible light active semiconducting mesoporous structure constructed by chiral nematic crystalline–amorphous TiO₂ core–shell nanorods. The chiral black TiO_2?x nanoparticles supported on mesoporous nanocarbon networks are evaluated as lithium‐ion battery anode electrodes. Beyond the current efforts, these black TiO_2?x materials and their composites may be useful in the fields of energy storage and catalysis.     

Nanostructured Interfaces for Thermoelectrics

Temperature drops at the interfaces between thermoelectric materials and the heat source and sink reduce the overall efficiency of thermoelectric systems. Nanostructured interfaces based on vertically aligned carbon nanotubes (CNTs) promise the combination of mechanical compliance and high thermal conductance required for thermoelectric modules, which are subjected to severe thermomechanical stresses. This work discusses the property require- ments for thermoelectric interface materials, reviews relevant data available in the literature for CNT films, and characterizes the thermal properties of vertically aligned multiwalled CNTs grown on a candidate thermoelectric material. Nanosecond thermoreflectance thermometry provides thermal property data for 1.5-μm-thick CNT films on SiGe. The thermal interface resistances between the CNT film and surrounding materials are the dominant barriers to thermal transport, ranging from 1.4 m² K MW⁻¹ to 4.3 m² K MW⁻¹. The volumetric heat capacity of the CNT film is estimated to be 87 kJ m⁻³ K⁻¹, which corresponds to a volumetric fill fraction of 9%. The effect of 100 thermal cycles from 30°C to 200°C is also studied. These data provide the groundwork for future studies of thermoelectric materials in contact with CNT films serving as both a thermal and electrical interface.     

Nanostructured Biomaterials for Regeneration

Biomaterials play a pivotal role in regenerative medicine, which aims to regenerate and replace lost/dysfunctional tissues or organs. Biomaterials (scaffolds) serve as temporary 3D substrates to guide neo tissue formation and organization. It is often beneficial for a scaffolding material to mimic the characteristics of extracellular matrix (ECM) at the nanometer scale and to induce certain natural developmental or/and wound healing processes for tissue regeneration applications. This article reviews the fabrication and modification technologies for nanofibrous, nanocomposite, and nanostructured drug‐delivering scaffolds. ECM‐mimicking nanostructured biomaterials have been shown to actively regulate cellular responses including attachment, proliferation, differentiation, and matrix deposition. Nanoscaled drug delivery systems can be successfully incorporated into a porous 3D scaffold to enhance the tissue regeneration capacity. In conclusion, nanostructured biomateials are a very exciting and rapidly expanding research area, and are providing new enabling technologies for regenerative medicine.     

Combined Surface and Volume Templating of Highly Porous Nanocast Carbon Monoliths

Nanocast carbon monoliths exhibiting a three‐ or four‐modal porosity have been prepared by one‐step impregnation, using silica monoliths containing a bimodal porosity as the scaffold. Combined volume and surface templating, together with the controlled synthesis of the starting silica monoliths used as the scaffold, enables a flexible means of pore‐size control on several length scales simultaneously. The monoliths were characterized by nitrogen sorption, scanning electron microscopy, transmission electron microscopy, and mercury porosimetry. It is shown that the carbon monoliths represent a positive replica of the starting silica monoliths on the micrometer length scale, whereas the volume‐templated mesopores are a negative replica of the silica scaffold. In addition to the meso‐ and macropores, the carbon monoliths also exhibit microporosity. The different modes of porosity are arranged in a hierarchical structure‐within‐structure fashion, which is thought to be optimal for applications requiring a high surface area in combination with a low pressure drop over the material.     

Self‐Organized Nanoporous Anodic Titania Films and Ordered Titania Nanodots/Nanorods on Glass

We report a new method to fabricate self‐organized nanoporous titania films (pore diameter ≈ 30 nm; ≈ 1100 nm thick) and ordered titania nanorod arrays (rod diameter ≈ 30–60 nm; 70–260 nm high) by combined anodizing of superimposed Al/Ti layers sputter‐deposited on glass substrates. The titania nanostructures mimic the ordered nanoporous anodic alumina films via a through‐mask anodization. We propose a new anodizing electrolyte, i.e., a diluted nitric acid solution, for fabricating uniform, self‐organized, ordered nanoporous titania films with parallel cylindrical pores and without any thickness limit. More significantly, the nanoporous titania films contain a small amount of titanium nitride and dissociated nitrogen, and exhibit a moderate transparency and an enhanced absorption throughout the UV and visible light regions of the electromagnetic spectrum. After heating at 600 °C for 2 h, the nanoporous titania films develop a small absorption red‐shift and exhibit high photocatalytic activity under UV illumination.     

二氧化钛压敏电阻势垒高度的测定

按配方TiO2+0.3%(SrCO3+Bi2O3+SiO2)+0.075%Ta2O5,以典型的陶瓷工艺制备样品。通过I-T和I-V测量,将压敏电阻视为双向导通的二极管,应用半导体理论对低压下的I-V数据进行处理,测定了TiO2-SrCO3-Bi2O3-SiO2-Ta2O5压敏陶瓷的势垒高度?b为0.43eV。     

Luminescence of copper-aluminum diselenide

The results of a multifaceted investigation of the luminescence properties of single crystals of copper-aluminum diselenide CuAlSe₂ are presented. The luminescence spectrum of undoped single crystals of this compound with homogeneous composition was found to have a complex structure. The luminescence properties were modified by annealing the compound in various atmospheres. The nature of the radiative transitions in this semiconductor was analyzed. Fiz. Tekh. Poluprovodn. 31, 377–380 (March 1997)     

硅发光研究进展

硅是间接带隙半导体, 不能有效地发光.量子理论、超晶格理论和纳米技术的发展,给硅基发光研究提供了理论的和技术的支撑.研究者通过不同的途径去实现硅的有效发光:多孔硅、纳米硅、Si/SiO2超晶格、计算化设计与硅晶格匹配的直接带隙半导体.文章报道了这些方面的最新研究进展.     

Mossbauer-Spectroscopy Characterization of Nanostructured Magnetic Materials

Two mechanisms are examined underlying the formation of the magnetic hyperfine structure in the Mossbauer spectra of magnetic materials containing nanoparticles. The absorption spectra of ⁵⁷Fe nuclei in Fe-Cu-Nb-B nanostructured magnetic alloys are evaluated within the generalized two-level relaxation model, which includes interparticle interaction. All the unconventional features of the spectra are thus explained in qualitative terms. Furthermore, the precession of the magnetic moments of nanoparticles in a magnetic anisotropy field is investigated. It is shown that in a precessing hyperfine field the nuclear g factors should be subject to renormalization. As a result, the hyperfine spectra should undergo a radical transformation. It is concluded that the conventional techniques of Mossbauer-spectra evaluation in the context of nanostructured magnetic materials should be modified to include the transformation.     

Ultrafast Fabrication of Covalently Cross‐linked Multifunctional Graphene Oxide Monoliths

Stable graphene oxide monoliths (GOMs) have been fabricated by exploiting epoxy groups on the surface of graphene oxide (GO) in a ring opening reaction with amine groups of poly(oxypropylene) diamines (D₄₀₀). This method can rapidly form covalently bonded GOM with D₄₀₀ within 60 s. FTIR and XPS analyses confirm the formation of covalent C‐N bonds. Investigation of the GOM formation mechanism reveals that the interaction of GO with a diamine cross‐linker can result in 3 different GO assemblies depending on the ratio of D₄₀₀ to GO, which have been proven both by experiment and molecular dynamics calculations. Moreover, XRD results indicate that the interspacial distance between GO sheets can be tuned by varying the diamine chain length and concentration. We demonstrate that the resulting GOM can be moulded into various shapes and behaves like an elastic hydrogel. The fabricated GOM is non‐cyctotoxic to L929 cell lines indicating a potential for biomedical applications. It could also be readily converted to graphene monolith upon thermal treatment. This new rapid and facile method to prepare covalently cross‐linked GOM may open the door to the synthesis and application of next generation multifunctional 3D graphene structures.     

Luminescence of cathodochromic sodalite

A bright green luminescence at 5250 Å is reported for cathodochromic sodalite powders under ultraviolet excitation. This emission is observed in germanium-doped sodalite samples in which the halogen ion is either Cl, Br, or I and under certain conditions in germanium-free bromine sodalite. These powders constitute a new class of materials which allow the construction of cathodochromic CRT's whose images can be viewed in either high or low ambient light.     

Open Air Plasma Deposition of Superhydrophilic Titania Coatings

A method for the deposition and functionalization of a nanostructured organotitanate thin film, which imparts superhydrophilicity to a surface with a one‐step, open‐air process, is described. Extreme wetting (Θ < 5°) is achieved through synergistic contributions from both nanoscale roughness, visible light absorption caused by nonmetal dopants, and oxygen vacancies and surface activation by reactive plasma species. To test the efficacy of this material as an antifog coating, glass is coated and subjected to aggressive changes in humidity. Under both fogging and defrosting conditions, the superhydrophilic coating achieves a high degree of transparency, showing nearly two orders of magnitude improvement over the bare glass. The measured adhesion of the superhydrophilic coating is 5.9 J m^?2, nearly double that of the solution‐processed control. The reliability of the coating is further validated by demonstrating scratch‐resistance. Additionally, the incorporation of organic matter into the molecular structure of the coating disrupts long‐range crystallinity from developing. This structural and subsequent chemical analysis of the coating reveals that inorganic and organic species are intimately connected at the nanoscale via alkyl and alkoxy bridges. The amorphous organotitanate material is distinct from conventional TiO₂, which requires high temperature crystallization and extensive UV irradiation to display similar superhydrophilic qualities.     

掺硅对二氧化钛压敏电阻性能的影响

采取通用的陶瓷工艺,按配方(摩尔分数)TiO2+0.3%(BaCO3+Bi2O3)+0.075%Ta2O5+x%SiO2,其中x=0.1,0.2,0.3,0.4,0.5,制备试样。经过R-f,C-f和I-V测量,研究了SiO2对(Ba,Bi,Si,Ta)掺杂的TiO2基压敏陶瓷的压敏特性、电容特性及晶粒半导化的影响。结果表明:当x=0.3时,压敏电压最低(E10mA为8V.mm–1),电容量最大(C为30pF,1kHz)及晶粒电阻最小(1.4?)。     

纳米锂电池技术

简介根据美国BusinessCommuncation Co.之调查分析结果,纳米材料在整体产业的应用上,于2005年市场需求值可达9亿美元(图1)。根据诺贝尔奖得主Dr.Smalley认为,未来50年人类面临十大问题中,以能源居首,能源需求量成长了3~4倍。而纳米技术将可带动纳米能源的革命性发展与突破,包括纳米锂电池、太阳能电池、燃料电池、储氢系统、光触媒、光电池等等应用。本文主要探讨纳米材料在纳米锂电池上的应用。纳米锂电池技术的关键点是高容量、高功率、高安全性之纳米级锂电池材料的开发与落实应用,本文将探讨目前工研院材料所在纳米级锂电池材料与纳米…