Elasto-plastic properties of gold thin films deposited onto polymeric substrates

This work examines mechanical properties of 50–300 nm gold thin films deposited onto micrometer-thick flexible polymer substrates by means of tensile testing of the film–substrate system and modeling. The film properties are extracted from mechanical testing of the film–substrate system and modeling of the bimaterial. Unlike materials in bulk geometry, the film elastic modulus and yield strength present an important dependence with film thickness, with modulus and yield strength of about 520 and 30 GPa, respectively, for the thinner films and decreasing toward the bulk value as the film thickness increases. The relation between grain size, film thickness, and yield strength is examined. Finite element analysis provides further insight into the stress distribution in the film–substrate system. L. Llanes—MS student at ITM, Merida, Mexico.     

Skeletal tissues as nanomaterials

Collagen is the most abundant protein in the body and, though the fibre-forming collagens have a ‘common’ structure, it is adapted to perform a large range of functions—from the differing mechanical needs of tendon versus bone to forming a transparent support structure in the cornea. This perfidy also suggests that collagen could form a generic basis for a range of scaffold needs for tissue engineering or medical device coating applications. We at the London Centre for Nanotechnology—a joint venture between University College London and Imperial College—are taking a bottom-up approach having decided that many of the ‘accepted dogmas’ of collagen biology may not be quite as soundly based as currently held. We are using several of the tools of ‘hard’ nanotechnology—such as atomic force microscopy—to re-examine collagen structure with the longer term aim of using such information to design materials with appropriate physical attributes. Examples of our current research on mineralised and soft tissue collagens are presented.     

Thermal Diffusivity of Metallic Thin Films: Au, Sn, Mo, and Al/Ti Alloy

The thermal diffusivity of Au, Sn, Mo, and Al_0.97Ti_0.03 alloy thin films, which are commonly used in microelectromechanical (MEMs) system applications, is measured by two independent methods — the ac calorimetric and photothermal mirage methods. Both methods yield similar results of the thin-film thermal conductivity, but the uncertainty of the mirage technique is found to be relatively large because of the large temperature increase during the measurement. The measured thermal diffusivities of the thin films are generally lower than those of the same bulk material. Especially, the Al_0.97Ti_0.03 thin film shows a pronounced thermal conductivity drop compared with bulk Al, which is believed to be mainly due to impurity scattering. Comparison of the thermal conductivity with the electrical conductivity measured by the standard four-probe technique indicates that the relation of thermal and electrical conductivities follows the Wiedemann–Franz law for the case of Au and Sn thin films. However, the Lorentz number is significantly larger than the theoretical prediction for the case of Al_0.97Ti_0.03 and Mo thin films.     

Laser transfer processing for the integration of thin and thick film ferroelectrics

Laser transfer processing (LTP) offers the potential to overcome the problems of integrating ferroelectric thin and thick film materials with polymers and other technologically useful substrate materials that cannot sustain the high process temperatures, 600–1,000 °C, required for normal film deposition. The LTP technique involves the fabrication of a ceramic film on a high-temperature substrate material such as sapphire, and subsequent release by application of pulsed ultra-violet laser radiation. Here, the LTP technique is reviewed in the context of ferroelectric thin and thick films, and current developments are presented. Micro- and nanostructural features of the films before and after transfer to a second substrate are revealed using scanning and transmission electron microscopy. The consequences of laser-generated structural changes on ferroelectric properties are illustrated, and measures to mitigate the effects of an amorphous damage-layer are discussed.     

Steps Toward Application of Photoinduced Phenomena in Superconducting Devices

The interaction of electromagnetic radiation with thin film devices consisting of superconducting, normal conducting, semiconducting, insulating, and magnetic materials can be used for variety of different applications. Some examples will be discussed, including laser modification for patterning and adjustment of thin film high-T_c superconducting devices, ultrafast response, and the photoinduced superconductivity in high-T_c materials which offers interesting possibilities for optoelectronical conversation and controllable weak links in superconducting electronics.     

Breakthrough advances in low loss, tunable dielectric materials

 Low loss, tunable dielectric materials are important for phased array antenna and other device applications. Various composites of barium strontium titanium oxide (BSTO) combined with other nonelectrically active oxide ceramics have been formulated for such uses. The dielectric constant and the loss tangents of these composites have been reduced to enhance the overall impedance matching and thereby lowering the overall insertion loss of the device. The material has been fabricated in bulk ceramic, thick film, and thin film form to address a broad range of frequency applications. The material fabrication methods and the electronic properties of these composites will be discussed in this article. Received: 21 July 1998 / Reviewed and accepted: 22 October 1998     

Microstructured Magnetic Calorimeter with Meander-Shaped Pickup Coil

In the last years metallic magnetic calorimeters (MMC) showed an energy resolution of a few eV for x-rays up to 10 keV. This makes MMCs a promising and powerful tool for many applications where photons or energetic massive particles have to be detected—like absolute activity measurements of radioactive isotopes, high resolution x-ray spectroscopy and x-ray fluorescence material analysis. However, in order to fulfill all requirements of these applications and to allow to reach the maximum resolving power a consequent micro-fabrication of the MMC detectors is needed. The micro-fabrication of metallic magnetic calorimeters requires reliable deposition and patterning processes for niobium structures with high critical currents and for paramagnetic sensors. As one result of our advances in microstructuring a fully microfabricated MMC which consists of a meander shaped niobium thin film pickup coil and a 3 μm thick sputter deposited paramagnetic Au:Er temperature sensor will be presented. Deposition of energy in the paramagnetic sensor causes a rise in temperature and results in a change of magnetization, which is measured by a low noise high bandwidth dc-SQUID. The sputter deposited Au:Er films we report on are working well and show thermodynamic properties close to the ones known from bulk material down to temperatures of 45 mK.      

Superconducting materials and applications

The field of superconductivity has witnessed tremendous excitement in recent years, starting with the discovery of what has come to be known as ‘high temperature superconductors’. This has led to extensive activity on many aspects concerning the mechanism of superconductivity, new materials and systems and their technological applications. Further impetus to research in this area has been provided by the discovery of superconductivity in doped fullerenes. The first identification of superconductivity in a quarternary borocarbide system Y-Ni-B-C which must be regarded as the foremost fundamental Indian contribution in recent times, has further stimulated interest in this field. Notwithstanding the new excitements, the conventional superconductors continue to be the workhorses for technological applications. This review selectively presents some of the aspects of the developments in the entire gamut of the known superconducting systems from the stand point of materials and their applications. An update of the article “Current trends in the development and applications of superconducting materials”, Sundaram and Radhakrishnan (1989)     

High-Temperature Superconductivity in Sulfur-Doped Amorphous Carbon Systems

Magnetization measurements performed on amorphous carbon (aC) powder that contained a small amount of sulfur revealed traces of inhomogeneous superconductivity (SC) at T _c=65 K. Thin films of granular aC-W composite obtained by Electron Beam Induced Deposition showed no sign of SC. However, SC at T _c≈40 K was induced upon treating this film with sulfur at 250 ^∘C for 24 hours. Although the superconducting volume fraction in both cases is very low, our results prove the necessity of sulfur for inducing SC in aC, and open new pathways to achieve high-temperature SC in the unique system of aC-based materials.     

Thermal Conductivity Measurements of Thin Insulating Layers Deposited on High-Conducting Sheets

The thermal conductivity of thin insulating layers and coatings deposited on high-conducting sheets has been measured using the hot disk technique. The need for this type of measurements stems mainly from the electronics industry. In many situations, the materials supporting the thin layers or films are in the shape of thin sheets—often highly conducting ceramics, metals or anisotropic composites with a high-conducting component in the plane of the sheet. The present measurement setup has some interesting advantages with possibilities to design and optimize a system for performing convenient measurements on textiles. Although apparent properties are studied in the present investigation, the need to address thermal contact problems in general engineering constructions, including interfacial layers and thermal contact resistances, is discussed here. Experiences in this field indicate that, in order to perform correct thermal analysis and design, it is necessary to treat bulk material, thermal contact resistances, and interfaces separately. This is demonstrated by the fact that there is often a difference in interface conditions when performing a measurement as compared with the situation in which a manufactured component is being used.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China.     

Low-temperature processable Sn-doped ZnO films as electron transporting layers for perovskite solar cells

Charge-transporting processable layers at a low temperature is a challenge for fabricating novel, highly stable and flexible optoelectronic devices. In fact, the crystallization of metal oxide usually needs to be processed under a high-temperature to obtain excellent semiconducting properties. In this work, Sn-doped ZnO (TZO) thin films, as electron transporting layers (ETLs) in perovskite solar cells, were prepared via sol–gel method at a temperature of less than 180 °C. The effects of annealing temperature on the properties of TZO thin films were investigated. It was found that the electrical properties of the TZO films were improved with increasing annealing temperature. In addition, an elemental composition analysis revealed that a temperature of only 140 °C sufficed for converting the precursor gel film into TZO film. The perovskite solar cell, which utilized a low-temperature TZO thin film, yielded a better power conversion efficiency than one with high-temperature ETLs (180 °C). These results imply that discovering low-temperature ETL processing for sol–gel enables good-quality metal oxide ETL, which can also be used in flexible solar cell applications.

     

The effects of temperature on the molecular orientation of zinc phthalocyanine films

Phthalocyanine compounds have been widely investigated as candidate materials for technological applications, which is mainly due to their thermal stability and possibility of processing in the form of thin films. In most applications, the controlled growth of thin films with high crystalline quality is essential. In this study, zinc phthalocyanine (ZnPc) thin films were prepared by evaporation on glass and Au-coated glass substrates with subsequent annealing at different temperatures in ambient atmosphere. The morphological and structural features of 80 nm thick zinc phthalocyanine films were investigated, evidencing an α → β phase transformation after annealing the films at 200 °C, as indicated by UV–Vis spectroscopy and FTIR analyses. A better uniformity of the annealed films was also evidenced via AFM analysis, which may be of importance for applications where film homogeneity and excellent optical quality are required.     

High temperature (Tc) superconductors and their possible applications

The background of the recent discovery of high temperature oxide superconductors is given. The new class of materials poses many challenges to researchers and raises many exciting possibilities in technological and industrial applications. To physicists and chemists there are the questions of why this particular structure and type of compounds and what is the mechanism for superconductivity; to material scientists and electronic engineers there remain many questions concerning the preparation and the stability of the materials in forms suitable for thin film as well as heavy current uses.     

Preparation, characterization, and electrocatalytic performance of graphene-methylene blue thin films

We report a general method to graft aromatic molecules onto graphene thin film electrodes through a simple immersion process. Large-area electroactive graphene thin films grafted with methylene blue (MB) have been developed as electrocatalytic electrodes for the oxidation of β-nicotinamide adenine dinucleotide (NADH). The oxidation of NADH starts from −0.08 V (vs. Ag/AgCl) at the graphene-MB thin film electrodes, showing a decrease of 530 mV in overpotential compared to a Ti metal electrode. The graphene-MB thin films have promising applications in biosensors and biofuel cells due to their ability to promote NADH electron transfer reaction.     

On Elastic Compliances of Interfacial Cracks

Results for elastic compliances of interfacial cracks — quantities that determine change in the overall elastic compliances of a material due to interfacial cracks — are obtained. Such cracks may develop in composite materials as a result of debonding at inclusion/matrix interfaces or at boundaries between layers in layered materials, for example, at film/substrate interfaces. Our method is based on the thermodynamic formalism developed by Rice (1975) and utilization of the available results for the stress intensity factors (SIFs). Compliance contribution tensors of the rectilinear, circular and penny-shaped interfacial cracks are derived in closed form.     

Probing material properties with sharp indenters: a retrospective

A retrospective on the use of sharp, fixed-profile indenters as materials probes is presented. Indentation is proposed as a simple but powerful methodology for evaluating basic mechanical properties—elastic modulus, hardness, toughness—in all classes of materials. Indentation also provides unique insight into fundamental deformation and fracture processes. Of particular interest is the existence of intrinsic size effects as characteristic contact dimensions pass from macro- to micro- to nano-scale dimensions. The utility of indentations as ‘controlled flaws’ in the context of strength of materials is outlined. The roles of two other important material factors—rate effects and microstructure—are considered. Examples of technological and biological applications are presented as illustrations of the widespread power of the technique. Strengths and limitations of the methodology as a routine testing protocol are discussed.     

Structural nanocrystalline materials: an overview

This paper presents a brief overview of the field of structural nanocrystalline materials. These are materials in either bulk, coating, or thin film form whose function is for structural applications. The major processing methods for production of bulk nanocrystalline materials are reviewed. These methods include inert gas condensation, chemical reaction methods, electrodeposition, mechanical attrition, and severe plastic deformation. The stability of the nanocrystalline microstructure is discussed in terms of strategies for retardation of grain growth. Selected mechanical properties of nanocrystalline materials are described; specifically strength and ductility. Corrosion resistance is briefly addressed. Examples of present or potential applications for structural nanocrystalline materials are given.     

Probing the bulk ionic conductivity by thin film hetero-epitaxial engineering

Highly textured thin films with small grain boundary regions can be used as model systems to directly measure the bulk conductivity of oxygen ion conducting oxides. Ionic conducting thin films and epitaxial heterostructures are also widely used to probe the effect of strain on the oxygen ion migration in oxide materials. For the purpose of these investigations a good lattice matching between the film and the substrate is required to promote the ordered film growth. Moreover, the substrate should be a good electrical insulator at high temperature to allow a reliable electrical characterization of the deposited film. Here we report the fabrication of an epitaxial heterostructure made with a double buffer layer of BaZrO₃ and SrTiO₃ grown on MgO substrates that fulfills both requirements. Based on such template platform, highly ordered (001) epitaxially oriented thin films of 15% Sm-doped CeO₂ and 8 mol% Y₂O₃ stabilized ZrO₂ are grown. Bulk conductivities as well as activation energies are measured for both materials, confirming the success of the approach. The reported insulating template platform promises potential application also for the electrical characterization of other novel electrolyte materials that still need a thorough understanding of their ionic conductivity.     

Peritectic melting of thin films,superheating and applications in growth of REBCO superconductors

Superheating of solids, an unconventional phenomenon in nature, can be achieved by suppressing the heterogeneous nucleation of melt at defect sites, such as free surfaces and internal grain boundaries. In recent years, experimental evidences have clearly proved that the YBCO (Y123) thin film with a free surface possesses a superheating capacity, which is mainly attributed to the film/substrate structures, distinctively consisting with low-energy surface and semi-coherent interface. Like most functional oxides, YBCO (denoted as α phase) is characterized by a peritectic melting: α → β + liq. Its superheating behavior certainly relates to this peritectic reaction. Furthermore, REBCO (RE123, RE: rare earth elements) thin films with high thermal stability have been successfully employed as seed materials in inducing the growth of REBCO materials, such as thick film, single crystal and single domain bulk. Therefore, this superheating property of thin films is of great importance in both scientific study and practical application. In this paper, the up-to-date researches covering on the superheating phenomenon of the α phase film, its mechanism and applications in growth of REBCO superconductors are reviewed, which is supposed to be valid for more thin films of functional oxides that have the same nature as the YBCO film/substrate.     

Probing the bulk ionic conductivity by thin film hetero-epitaxial engineering

Abstract

Highly textured thin films with small grain boundary regions can be used as model systems to directly measure the bulk conductivity of oxygen ion conducting oxides. Ionic conducting thin films and epitaxial heterostructures are also widely used to probe the effect of strain on the oxygen ion migration in oxide materials. For the purpose of these investigations a good lattice matching between the film and the substrate is required to promote the ordered film growth. Moreover, the substrate should be a good electrical insulator at high temperature to allow a reliable electrical characterization of the deposited film. Here we report the fabrication of an epitaxial heterostructure made with a double buffer layer of BaZrO₃ and SrTiO₃ grown on MgO substrates that fulfills both requirements. Based on such template platform, highly ordered (001) epitaxially oriented thin films of 15% Sm-doped CeO₂ and 8 mol% Y₂O₃ stabilized ZrO₂ are grown. Bulk conductivities as well as activation energies are measured for both materials, confirming the success of the approach. The reported insulating template platform promises potential application also for the electrical characterization of other novel electrolyte materials that still need a thorough understanding of their ionic conductivity.