Composite Thin Film Structures Research Articles

Investigation of Multi‐Phase Structure and Optoelectronic Performance of Bi‐Doped (Cu−Zn) Oxide Composite Thin Films

AbstractIn this research, thin film composite structures were used to prepare optoelectronic devices from bare and Bi‐substituted p‐CuO/n‐ZnO systems. The p‐CuO/n‐ZnO composite thin film structures were prepared by the SILAR technique, and the influences of two different Bi contents on the structure and main physical performances of the samples were investigated. The X‐ray diffraction (XRD) technique showed that the composited thin film materials were multiphased in rutile hexagonal (wurtzite) phase (ZnO) and monoclinic tenorite phase (CuO) type crystal structure. The obtained surface morphological results presented that the structure exhibits an almost homogeneous, plate‐like surface distribution, and depending on the increase of Bi concentration, the plate‐like sheet area widens from ~2.5 μm to 10 μm and the layer boundaries decrease. FT‐IR and Raman spectroscopy were used to investigate the various vibration and Raman active phonon modes of Bi:p‐CuO/n‐ZnO nanostructured heterostructures. For a comprehensive analysis of the optical bandgap of the fabricated composite samples, the estimated values were obtained from the Tauc plot. Produced samples exhibited an Ohmic behavior and dc resistivity values of films can be determined via Ohm′s Law. The adjusted sheet resistance value of 11.51 MΩ/sq when the content of Bi 3.0 % in the growth bath.

Electrochemically co-deposited WO3-V2O5 composites for electrochromic energy storage applications

In this study, a W-V mixed metal oxide composite thin-film structure comprising tungsten oxide (WO3) and vanadium oxide (V2O5) is prepared using a one-step electrochemical co-deposition method. The electrochromic and electrochemical energy storage applications of the prepared thin films comprising different compositions of WO3 and V2O5 are systematically investigated. The films of the W-V mixed composite, comprising WO3 and V2O5 in the ratio of 1:1, exhibits remarkable electrochromic properties, such as an optimum optical contrast of 60%, a fast coloration response of 4.9 s, and the highest coloration efficiency of 61.5 cm2/C. Furthermore, for the electrochemical energy storage application, a maximum areal capacitance of 38.75 mF/cm2 at an applied current of 0.5 mA/cm2 is obtained. Furthermore, it displays a capacitive retention of 78.5%, even after 5000 charge/discharge cycles. The ameliorated characteristics of both electrochromic and electrochemical energy storage applications are attributed to the (a) unique morphology containing more active sites introduced by both WO3 and V2O5, (b) fast charge transfer kinetics, and (c) redox behavior of both metal ions present in the synthesized W-V mixed metal composite.

Structural and optical properties of PEO/CMC polymer blend modified with gold nanoparticles synthesized by laser ablation in water

Eco-friendly and cost-effective route using water were employed for the synthesis of gold nanoparticles (AuNP's) via laser ablation technique. Formation of AuNP's were observed through the appearance of surface plasmon resonance (SPR) peak originally located at 520 nm within the UV/Visible spectrum of synthesized sample and approved with Transmission electron microscope (TEM). X-ray diffraction analysis and TEM micrograph shows the formation of fcc crystal structure of nano-sized gold with a diameter ranging between 10 and 25 nm. Virgin samples of polyethylene oxide (PEO) and carboxymethyl cellulose (CMC) in combination with their 50/50wt% blend films were synthesized via traditional solution casting techniques. Besides other samples of blend films containing a variable amount of gold nanoparticles (AuNPs) within the doping level. Different characterization techniques were employed to study the composite thin film structure. X-ray diffraction pattern reveals a barely noticed increase of the amorphous nature with increasing gold content. FTIR suggests the formation of hydrogen bonding within the composite matrix with an appearance of the characteristic vibrational groups of the constituting matrices regardless of the content of dopant AuNP's. UV/Visible electronic spectra reveal a notable change within the optical energy gap in comparison with the pristine samples attributed to the introduced dopant.

Fabrication and photoresponse characteristics of high rectification photodetector based on methyl violet nanoparticles-PVA/p-si heterojunction for optoelectronic applications

In this perspective research, methyl violet 6B, a nanocrystalline dye, is exploited as an impregnating material for improving the absorption and photoconductivity characteristics of polyvinyl alcohol, PVA. The PVA-MV composite thin film's structure and morphology revealed a uniform smooth surface with 9.7 nm root mean square roughness. The optical absorption of PVA thin film is enhanced after the dye incorporation and exhibited an energy gap modification from 4.36 to 1.75 eV. Moreover, we fabricated an Ag/PVA-MV/p-Si/Al MIS Schottky diode and investigated its electrical characteristics in dark. The heterojunction's microelectronic parameters such as ideality factor, reverse saturation current, barrier height, rectification ratio are estimated and found to be 2.5, 6.4 nA, 0.78 eV, and 8795.2 at 3 V, respectively. A significant quasi-saturated reverse photocurrent with obvious sensitivity for light intensity variations is detected. The fabricated photodetector exhibited responsivity, specific detectivity, and signal-to-noise ratio ~ 2.622 mA/W, 6.46 × 109 Jones, and 407.9, respectively.

Modeling the constraint effects of compliant electrodes in dielectric elastomers under uniaxial loading

Dielectric elastomers are composite thin film structures composed of a dielectric polymer between compliant electrodes. Previous hyperelastic models have not modeled the constraint effects of compliant electrodes on the lateral contraction of the dielectric material as it stretches, and are therefore unable to fully describe the electromechanical behavior of the dielectric elastomer or provide a means to understand the constraint effects. An empirical boundary coefficient is introduced to model these constraint effects on the lateral boundaries of the material under uniaxial tension. Employing an averaged stretch ratio concept, it is shown that this coefficient can be obtained from experimentally measurable geometric variables. Values for the boundary coefficients of sample dielectric elastomer films were obtained from experiments performed on a uniaxial test stand. Incorporating the boundary coefficient into the model formulation, a specific hyperelastic stress–strain relation is derived to describe the electromechanical behavior of dielectric elastomers under combined uniaxial tension and electrical loading. Comparison of the experimental and predicted values of the induced force in the axial direction due to the Maxwell stress based on the uniaxial model shows favorable agreement.

Optical and structural properties of fullerene films doped with cadmium telluride

Composite thin-film structures based on C60/CdTe were prepared by discrete vacuum evaporation in a quasi-closed volume and by vacuum evaporation from a Knudsen cell. The synthesized fullerene samples contained cadmium telluride with a content ranging from 1 to 50 wt %. The morphology and composition of the films were controlled using scanning electron microscopy and energy-dispersive X-ray analysis. The optimum geometry, the total energy, and the spectrum of excited states of the fullerene-cadmium telluride molecular complex were calculated by quantum-chemical methods. The spectral dependences of the photo-luminescence, Raman scattering, extinction coefficient, and refractive index were measured for different compositions. It was found that, in contrast to the spectra of pure fullerene, the luminescence and absorption spectra of the fullerene doped with cadmium telluride exhibit an additional peak in the wavelength range of 600–620 nm. These data were interpreted as the existence of dipole-allowed transitions in the spectrum of excited singlet states of the fullerene due to the interaction with cadmium telluride. The composite films had an increased resistance to degradation under the action of oxygen and water vapor.

Factors Influencing the Interdiffusion of Weak Polycations in Multilayers

One promising aspect of the electrostatic multilayer assembly techniques is the ability to consistently and predictably create controlled heterostructures that may be of interest for active devices, designed biomaterials, membranes, or other composite thin film structures. This promise is mitigated by the challenge of controlling diffusion and exchange processes that can take place in certain layer-by-layer assembled film systems and cause unanticipated or unwanted materials distributions and in extreme cases completely disrupt the assembly. To further understanding toward prediction and control of these processes, we investigate a series of polyamines and their interdiffusion and exchange within preassembled multilayer films to explore the role of polyion degree of ionization, hydrophobicity/hydrophilicity of the backbone, basicity of amine groups, and polyion topology in a polyelectrolyte interdiffusion and exchange process. Interdiffusion of these polyamines will be examined within a polyhexylviologen (PXV)/poly(acrylic acid) multilayer model system in which conditions favor exchange of the polyamine with PXV, a strong polycation containing quarternary ammonium groups along the backbone. Four amine-containing polycations were examined: linear and branched polyethylene imine (LPEI and BPEI), polyamidoamine (PAMAM) dendrimer, and poly(allylamine hydrochloride) (PAH). It was found that fully charged polycations in dilute aqueous solution are unable to diffuse through the multilayer film whereas partially charged polycations have the necessary mobility. Remarkably, despite strong differences in the nature of the polycation, as in the case of PAH, LPEI, and BPEI, for every polyamine there existed the same critical degree of ionization in solution below which interdiffusion was possible, which was seen to be near 70% in these exchange experiments with PXV. Only for the highly branched PAMAM dendrimer was this value different; the critical degree of ionization for PAMAM was observed to be 55%. Kinetics of the interdiffusion were significantly impacted by the polyion degree of ionization and molecular weight.

Charge generation and photovoltaic properties of hybrid solar cells based on ZnO and copper phthalocyanines (CuPc)

Photovoltaic properties and charge transfer process within the blend of p-type organic semi conducting copper phthalocyanine (CuPc) and inorganic n-type semiconductor zinc oxide (ZnO) nanoparticle have been determined. The photo-induced electron transfer mechanism in the composite thin film structure is predicted on the basis of its optical absorption behavior, photo-action spectra and photoluminescence (PL) characteristics, supported by current–voltage characteristics in dark and under illumination. An efficient electron transfer between donor (CuPc) and acceptor (ZnO) nanoparticle is explained by analyzing the photo-action spectra of the device and respective quenching of photoluminescence (PL) in composite thin film structure. The increase in photocurrent in composite blend based device is justified in terms of formation of bulk heterojunction between CuPc and ZnO nanoparticles. Also, the subsequent increase in photovoltaic response is ascribed to the formation of interconnecting network in between CuPc and ZnO nanoparticles. Our experimental results supports that photo-generation of charge carriers is induced by the production of excitons and their subsequent dissociation of into free carriers at ZnO–CuPc interface which is spread over the bulk region sandwiched between Al and ITO. Additionally, the optical and electrical properties of the composite blend based device have been discussed in details. The capacitance–voltage characteristics of the device support the formation of bulk heterojunction between CuPc and ZnO nanoparticles.

Sol-gel strategies for controlled porosity inorganic materials

The porosity (i.e., pore volume, pore size, and surface area) of ceramic materials prepared by sol-gel processing depends on the size and structure of primary particles or polymers formed by condensation reactions, the organization of these structures, often by aggregation, to form a gel, and the collapse of the gel by drying. This paper reviews these ideas in the context of the formation of thin films suitable for inorganic membranes and introduces a number of specific strategies designed to control pore sizes in the range appropriate for gas separation: (1) aggregation of fractals; (2) management of capillary pressure, (3) control of condensation rate, and (4) the use of organic or microporous templates in composite thin film structures. These strategies are contrasted with the more traditional particle packing approach to preparing controlled porosity materials.

Electrical Characteristics of Barium Strontium Titanate-Oxide Composite Films

AbstractIn a previous work. composites of BSTO combined with other nonelectrically active oxide ceramics have been formulated and have demonstrated adjustable electronic properties which can be tailored for use in various electronic devices. One application has been for use in phased array antennas and insertion has been accomplished into several working antenna systems. To further accommodate the frequencies required by these phased array antennas, thin films of the composites have been fabricated using a Krypton Fluoride excimer laser as an ablation source. The electrical properties, including the dielectric constant and the tunability (change in the dielectric constant with applied voltage) have been measured. The results have been compared to those obtained for the bulk, ceramic composites and other BSTO/oxide composite thin film structures.

Synthesis of composite thin films by simultaneous use of pulsed laser and conventional thermal evaporation

The concept of simultaneous use of pulsed laser evaporation and conventional thermal evaporation has been used for the first time to synthesize composite thin-film structures. It is shown that the use of pulsed laser evaporation of α-Fe2O3 concurrently with thermal evaporation of aluminum leads to a composite state defined by the presence of clusters of iron-related material in the aluminum matrix. The microstructural aspects of the physical state of the composite are studied by using conversion electron Mössbauer spectroscopy, glancing angle x-ray diffraction, and scanning electron microscopy.

Formation of p-n Junctions by Laser Processing Sb-Pt Thin Films on Si

ABSTRACTPlanar p-n junctions with Pt silicide contacts have been formed by laser irradiating p-type Si/120Å Sb/400Å Pt composite thin film structures. The samples were prepared in a standard e-beam evaporation system. They were never ion implanted. Laser processing was performed with either a scanning cw Ar laser or a Q-switched Nd:YAG (λ = 0.53 μm) laser which provided 100 nsec long pulses. After the irradiations were performed, a p-type Si/n+Si/Pt-Si structure was present. The n+ region resulted from Sb incorporated in the Si lattice. When the same initial composite was furnace annealed, the Sb diffused to the surface and sublimated, leaving a p-type Si/PtSi near-ohmic contact. Depth profiles of the samples were determined with Auger electron spectroscopy. The structure of the Pt-Si layer was studied using wide film Debye X-ray diffraction. The electrical properties of the junctions were examined by measuring their I-V and C-V characteristics and minority carrier lifetimes. Differences in the structural and electrical properties that resulted from the two types of laser irradiation will be discussed.

Silver Halide‐Chalcogenide Glass Inorganic Resists for X‐Ray Lithography

Silver halide‐chalcogenide glass composite thin film structures are evaluated as inorganic x‐ray resists at Al line. The sensitivity is shown to be a factor of 2 better than the PMMA 2041 for a 300 nm thick resist layer. A comparable contrast is indicated. A high resolution capability is expected because of the amorphous nature of the composite. A possible mechanism of this inorganic resist action is discussed.

Metallurgical and electrical properties of alloyed Ni/AuGe films on n-type GaAs

An experimental study of the alloying characteristics of a composite thin-film structure which is often used as an ohmic contact to GaAs is presented. A AuGe layer of eutectic composition covered by a thin-film of Ni and deposited on n-type epitaxial GaAs is investigated in order to better understand the relationship between the alloying behavior and the electrical properties of the contact. The barrier energy ϕ Bn and the specific contact resistance of the Ni/AuGe/GaAs system is measured for a wide range of alloy temperatures and times. The metallurgical properties of the Ni/AuGe/GaAs system are obtained with Auger electron spectroscopy and scanning electron microscopy. Auger spectroscopy combined with in situ sputter etching is used to determine depth-composition profiles for all constituents of both as-deposited and alloyed Ni/AuGe/GaAs contacts. In samples heat-treated below the AuGe eutectic temperature, Ni is found to move rapidly through the intervening AuGe layer to collect at the GaAs interface, and the effective value of ϕ Bn rises to the value characteristic of Ni/GaAs Schottky diodes. For heat-treatment above the AuGe eutectic temperature, ohmic contact behavior is observed, and uniform alloyed contact surfaces are found to result from the presence of Ni at the GaAs interface. Ga outdiffusion and surface accumulation resulting from GaAs dissociation occurs for all alloy temperatures and times. The Ga outdiffusion appears to be characterized by a very low activation energy.

RADIANT SELF-STABILIZATION OF TEMPERATURE

The change in optical constants of VO2 associated with the semiconductor-to-metal transition at 340°K can be used to stabilize the temperature of a radiating body. Calculations based on a particular composite thin-film structure show that the temperature of a body remains fixed for an eightfold change in radiated power. Optical measurements over a limited range of the infrared confirm the calculations.