Use of the liquid-liquid interface for generating ultrathin nanocrystalline films of metals, chalcogenides, and oxides

The air-water interface has traditionally been employed to prepare particle assemblies and films of metals and semiconductors. The interface between water and an organic liquid, however, has not been investigated sufficiently for possible use in preparing nanocrystals and thin films of materials. In this article, we demonstrate the use of the liquid-liquid interface as a medium for preparing ultrathin films of metals, chalcogenides and oxides. The method involves the reaction at the interface between a metal-organic compound in the organic layer and an appropriate reagent for reduction, sulfidation, etc. in the aqueous layer. Some of the materials discussed are nanocrystalline films of gold, CuS, CuSe, CuO, and Cu(OH)(2) formed at the liquid-liquid interface. The results reported in this article should demonstrate the versatility and potential of the liquid-liquid interface for preparing nanomaterials and ultrathin films and encourage further research in this area. (c) 2005 Elsevier Inc. All rights reserved.

Structural and photoelectrical characterization of hot wall deposited CuInSe2 thin films and the fabrication of CuInSe2 based solar cells

Films of CuInSe2 were deposited onto glass substrates by a hot wall deposition method using bulk CuInSe2 as a source material. All the deposited CuInSe2 films were found to be polycrystalline in nature exhibiting the chalcopyrite structure with the crystallite orientation along (101),(112),(103),(211),(220),(312) and (400) directions. The photocurrent was found to increase with increase in film thickness and also with increase of light intensity. Photocurrent spectra show a peak related to the band-to-band transition. The spectral response of CuInSe2 thin films was studied by allowing the radiation to pass through a series of interference filters in the wavelength range 700-1200 rim. Films of higher thickness exhibited higher photosensitivity while low thickness films exhibited moderate photosensitivity. CuInSe2-based Solar cells with different types of buffer layers such as US, Cdse, CuInSe2 and CdSe0.7Te0.3 were fabricated. The current and voltage were measured using an optical power meter and an electrometer respectively. The fabricated solar cells were illuminated using 100 mW/cm(2) white light under AM1 conditions. (C) 2006 Elsevier Inc. All rights reserved.

Use of the liquid-liquid interface for generating ultrathin nanocrystalline films of metals,chalcogenides,and oxides

The air-water interface has traditionally been employed to prepare particle assemblies and films of metals and semiconductors. The interface between water and an organic liquid, however, has not been investigated sufficiently for possible use in preparing nanocrystals and thin films of materials. In this article, we demonstrate the use of the liquid-liquid interface as a medium for preparing ultrathin films of metals, chalcogenides and oxides. The method involves the reaction at the interface between a metal-organic compound in the organic layer and an appropriate reagent for reduction, sulfidation, etc. in the aqueous layer. Some of the materials discussed are nanocrystalline films of gold, CuS, CuSe, CuO, and Cu(OH)(2) formed at the liquid-liquid interface. The results reported in this article should demonstrate the versatility and potential of the liquid-liquid interface for preparing nanomaterials and ultrathin films and encourage further research in this area.

Optical, Field-Emission, and Antimicrobial Properties of ZnO Nanostructured Films Deposited at Room Temperature by Activated Reactive Evaporation

ZnO nanostructures were deposited on flexible polymer sheet and cotton fabrics at room temperature by activated reactive evaporation. Room-temperature photoluminescence spectrum of ZnO nanostructured film exhibited a week intrinsic UV emission and a strong broad yellow-orange visible emission. TEM and HRTEM studies show that the grown nanostructures are crystalline in nature and their growth direction was indentified to be along [002]. ZnO nanostructures grown on the copper-coated flexible polymer sheets exhibited stable field-emissio characteristics with a threshold voltage of 2.74 V/mu m (250 mu A) and a very large field enhancement factor (beta) of 23,213. Cotton fabric coated with ZnO nanostructures show an excellent antimicrobial activity against Staphylococcus aureus bacteria (Gram positive), and similar to 73% reduction in the bacterial population is achieved compared to uncoated fabrics after 4 h in viability. Using a shadow mask technique, we also selectively deposited the nanostructures at room temperature on polymer substrates.

Influence of External Light Waves on the Thermoelectric Power Under Strong Magnetic Field in Ultrathin Films, Quantum Wires and Quantum Dots of Optoelectronic Materials

In this paper, an attempt is made to study the influence of external light waves on the thermoelectric power under strong magnetic field (TPSM) in ultrathin films (UFs), quantum wires (QWs) and quantum dots (QDs) of optoelectronic materials whose unperturbed dispersion relation of the conduction electrons are defined by three and two band models of Kane together with parabolic energy bands on the basis of newly formulated electron dispersion laws in each case. We have plotted the TPSM as functions of film thickness, electron concentration, light intensity and wavelength for UFs, QWs and ODs of InSb, GaAs, Hg1-xCdxTe and In1-xGaxAsyP1-y respectively. It appears from the figures that for UFs, the TPSM increases with increasing thickness in quantum steps, decreases with increasing electron degeneracy exhibiting entirely different types of oscillations and changes with both light intensity and wavelength and these two latter types of plots are the direct signature of light waves on opto-TPSM. For QWs, the opto-TPSM exhibits rectangular oscillations with increasing thickness and shows enhanced spiky oscillations with electron concentration per unit length. For QDs, the opto-TPSM increases with increasing film thickness exhibiting trapezoidal variations which occurs during quantum jumps and the length and breadth of the trapezoids are totally dependent on energy band constants. Under the condition of non-degeneracy, the results of opto-TPSM gets simplified into the well-known form of classical TPSM equation which the function of three constants only and being invariant of the signature of band structure.

The Path to a Porous Semiconductor Multilayer

Thin films are the basis of much of recent technological advance, ranging from coatings with mechanical or optical benefits to platforms for nanoscale electronics. In the latter, semiconductors have been the norm ever since silicon became the main construction material for a multitude of electronical components. The array of characteristics of silicon-based systems can be widened by manipulating the structure of the thin films at the nanoscale - for instance, by making them porous. The different characteristics of different films can then to some extent be combined by simple superposition. Thin films can be manufactured using many different methods. One emerging field is cluster beam deposition, where aggregates of hundreds or thousands of atoms are deposited one by one to form a layer, the characteristics of which depend on the parameters of deposition. One critical parameter is deposition energy, which dictates how porous, if at all, the layer becomes. Other parameters, such as sputtering rate and aggregation conditions, have an effect on the size and consistency of the individual clusters. Understanding nanoscale processes, which cannot be observed experimentally, is fundamental to optimizing experimental techniques and inventing new possibilities for advances at this scale. Atomistic computer simulations offer a window to the world of nanometers and nanoseconds in a way unparalleled by the most accurate of microscopes. Transmission electron microscope image simulations can then bridge this gap by providing a tangible link between the simulated and the experimental. In this thesis, the entire process of cluster beam deposition is explored using molecular dynamics and image simulations. The process begins with the formation of the clusters, which is investigated for Si/Ge in an Ar atmosphere. The structure of the clusters is optimized to bring it as close to the experimental ideal as possible. Then, clusters are deposited, one by one, onto a substrate, until a sufficiently thick layer has been produced. Finally, the concept is expanded by further deposition with different parameters, resulting in multiple superimposed layers of different porosities. This work demonstrates how the aggregation of clusters is not entirely understood within the scope of the approximations used in the simulations; yet, it is also shown how the continued deposition of clusters with a varying deposition energy can lead to a novel kind of nanostructured thin film: a multielemental porous multilayer. According to theory, these new structures have characteristics that can be tailored for a variety of applications, with precision heretofore unseen in conventional multilayer manufacture.

Growth, self-assembly and dynamics of nano-scale films at fluid interfaces

Ultrathin films at fluid interfaces are important not only from a fundamental point of view as 2D complex fluids but have also become increasingly relevant in the development of novel functional materials. There has been an explosion in the synthesis work in this area over the last decade, giving rise to many exotic nanostructures at fluid interfaces. However, the factors controlling particle nucleation, growth and self-assembly at interfaces are poorly understood on a quantitative level. We will outline some of the recent attempts in this direction. Some of the selected investigations examining the macroscopic mechanical properties of molecular and particulate films at fluid interfaces will be reviewed. We conclude with a discussion of the electronic properties of these films that have potential technological and biological applications.

Influence of finite size effect on magnetic and magnetotransport properties of La0.5Sr0.5CoO3 thin films

We present a comprehensive study of the thickness dependent structural, magnetic and magnetotransport properties of oriented La0.5Sr0.5CoO3 thin films grown on LaAlO3 by Pulsed Laser Deposition. We observe that these films undergo a reduction in Curie temperature (T-c) with a decrease in film thickness, and it is found to be primarily caused by the finite size effect since the finite scaling law [T-c(infinity) T-c(t)/T-c(infinity) = (c/t)lambda holds good over the studied thickness range. We rule out the contribution from the strain induced suppression of Curie temperature with decreasing film thickness since all the films exhibit a constant out of plane tensile strain (0.5%) irrespective of their varying thickness. However, we observe that the coercivity of the films is an order of magnitude higher than that of the bulk due to the tensile strain. In addition, we also observe an increase in the magneto resistance peak and a decrease in coercivity and electrical resistivity with an increase in film thickness. (C) 2010 Elsevier Ltd. All rights reserved.

Sol-Gel Synthesis, characterization and optical properties of Tio2 thin films deposited on ITO/Glass substrates

TiO2 thin films have been deposited on glass and indium tin oxide (ITO) coated glass substrates by sol-gel technique. the influence of annealing temperature on the structural , morphological and optical properties has been examined. X-ray diffraction (XRD) results reveal the amorphous nature of the as-deposited film whereas the annealed films are found to be in the crystalline anatase phase. The surface morphology of the films at different annealing temperatures has been examined by atomic force microscopy (AFM). The in situ surface morphology of the as-deposited and annealed TiO2 films has also been examined by optical polaromicrograph (OPM). TiO2 films infatuated different structural and surface features with variation of annealing temperature. The optical studies on these films suggest their possible usage in sun-shielding applications.

On photooxidation of Ge in obliquely deposited Ge and Ge25X75(X = S, Se, Te) thin films

It has been established by photoemission studies that Ge in obliquely deposited pure Ge and Ge-chalcogenide thin films undergoes predominant photooxidation when irradiated with band gap photons. The role of Ge appears to be that of providing a highly porous low density microstructure and photooxidation seems to be a direct consequence of such large scale porosity in these films. The formation of low vapour pressure oxide fractions of Ge and Te and volatile high vapour pressure oxide fractions of S and Se is responsible for anomalous photoinduced transformations in these films.

Deposition of ZnO Films by Combustion Flame Pyrolysis of Solution Precursors

The structural features,including preferred orientation and surface morphology of zinc oxide (ZnO) films deposited by combustion flame pyrolysis were investigated as a function of process parameters, which include precursor solution concentration, substrate-nozzle (S-N) distance, gas flow rate, and duration of deposition. In this technique, the precursor droplets react within the flame and form a coating on an amorphous silica substrate held in or near the flame. Depending on the process parameters, the state of decomposition at which the precursor arrives on the substrate varies substantially and this in turn dictates the orientation and microstructure of the films.

Hexagonally ordered arrays of metallic nanodots from thin films of functional block copolymers

We demonstrate a new and simple route to fabricate highly dense arrays of hexagonally close packed inorganic nanodots using functional diblock copolymer (PS-b-P4VP) thin films. The deposition of pre-synthesized inorganic nanoparticles selectively into the P4VP domains of PS-b-P4VP thin films, followed by removal of the polymer, led to highly ordered metallic patterns identical to the order of the starting thin film. Examples of Au, Pt and Pd nanodot arrays are presented. The affinity of the different metal nanoparticles towards P4VP chains is also understood by extending this approach to PS-b-P4VP micellar thin films. The procedure used here is simple, eco-friendly, and compatible with the existing silicon-based technology. Also the method could be applied to various other block copolymer morphologies for generating 1-dimensional (1D) and 2-dimensional (2D) structures. (c) 2010 Elsevier Ltd. All rights reserved.

Laser processing of high-Tc superconducting thin films

High-Tc superconducting thin films can be deposited and processed by pulsed and CW lasers, and a respectable materials technology for the Y-Ba-Cu-O superconductor is rapidly emerging. The pulsed laser deposition technique is simple because it produces films with compositions nearly identical to those of the target pellets. A larger variety of substrates can be used, compared to other deposition technologies, because of the relatively low temperature requirements. The laser deposition mechanism has been investigated. As-deposited superconducting films, epitaxial films with smooth surfaces, and multilayer structures with abrupt interfaces have been produced. The electrical transport properties can be changed locally using a focused argon-ion laser by modifying the oxygen stoichiometry. This laser writing can be erased by room-temperature exposure to an oxygen plasma. Other laser patterning methods such as material removal, melt-quench, and direct pattern transfer are being developed.

Characterization of strain in Si1-xGex films using multiple angle of incidence ellipsometry

In this letter we characterize strain in Si1-xGex based heterojunction bipolar transistors and modulation doped field effect transistors grown by rapid thermal chemical vapor deposition exploiting the phenomenon of strain-induced birefringence. The technique used is multiple angle of incidence ellipsometry at a wavelength of 670 nm to measure the ordinary and extraordinary refractive indices of the Si1-xGex films. We report measurements on thin fully strained films (with thicknesses less than the critical thickness) with Ge concentration varying from 9% to 40% with an accuracy of the order of 1 part in 10(4) and propose an empirical relation between the difference in the ordinary and extraordinary refractive indices (deltan) and the Ge concentration (x) given by deltan(x)=0.18x-0.12x(2). (C) 2000 American Institute of Physics. [S0003-6951(00)03948-6].