Total Film Thickness Research Articles

Dual-bath electrodeposition of n-type Bi–Te/Bi–Se multilayer thin films

N-type Bi–Te/Bi–Se multilayer thin films were prepared by dual-bath electrodeposition. We varied the number of layers from 2 to 10 while the total film thickness was maintained at approximately 1 μm. All the multilayer films displayed the X-ray diffraction peaks normally observed from individual Bi2Te3 and Bi2Se3 crystal structures, indicating that both phases coexist in the multilayer. The cross-section of the 10-layer Bi–Te/Bi–Se film was composed of stacked layers with nano-sized grains but the boundaries between the layers were not planar. The Seebeck coefficient was almost constant throughout the entire range of our experiment, but the electrical conductivity of the multilayer thin films increased significantly as the number of layers was increased. This may be because the electron mobility increases as the thickness of each layer is decreased. As a result of the increased electrical conductivity, the power factor also increased with the number of layers. The maximum power factor was 1.44 μW/(cm K2) for the 10-layer Bi–Te/Bi–Se film, this was approximately 3 times higher than that of the 2-layer sample.

(Invited) Tuning of Heat Transport across Thin Films of Polycristalline AlN via Multiscale Structural Defects

Thermal conductivity of the elemental components of device-like structures is of fundamental importance for enhancing the thermoelectrical efficiency. However, the accurate description and control of their thermal properties remain a difficult task due to multiscale defects, and the anisotropic and heterogeneous structures usually present in thin films fabricated by vapor deposition techniques. Experimental thermal characterization, accurate theoretical description and controlled modulation of the thermal properties of these materials are therefore desirable. To accurately asset the thermal role of structural features which are present in mono- and nanocrystalline thin films, we are studying the size-dependent reduction of their effective thermal conductivity by optical and electrothermal techniques. We propose a physical and quantitative description of the reduction of the effective thermal conductivity with film thickness based on an electron microscope study, thickness-dependent 3ω measurements and a theoretical model. The latter takes into account the distribution of the grain geometry and considers the films as a serial assembly of three layers, composed of parallelepiped grains. These structural zones are namely: the near-interface, transition, and columnar region. We show that the resistances due to the interface with the substrate and to the near-interface and transition regions dominate the thermal conduction as the film thickness is scaled down; while for thick films, the effects of the increased mean free paths and intrinsic resistance resulting from the columnar region predominate. These transitions in the thermal transport mechanisms appear due to the relative size of each domain with respect to the total film thickness. In addition, optical techniques have been used to perform thermal measurements on epitaxially grown films. The main objective of these optical measurements is to identify differences in heat transport mechanisms between mono- and nanocrystalline systems, which are related to multiscale defects, such as dislocations and grain boundaries. Furthermore, recent studies of the thermal conductivity using Raman thermometry of III-V/Si structures will be reported, where the relative dimensions of opening in Si prior to the growth of the III-V layers has a marked impact in the value of the thermal conductivity, being larger for larger opening.

A study on total thickness dependency: microstructural, magnetoresistance and magnetic properties of electrochemically deposited permalloy based multilayers

Electrochemically deposited permalloy based NiFe/Cu multilayers, relating their magnetic and magnetoresistance properties with crystal structure and the corresponding film composition were studied as a function of the total film thickness. The permalloy based multilayers were grown on strong (110) textured copper sheets with electrodeposition under potentiostatic control. The total multilayer film thickness was changed from 0.3 to 5 µm while ferromagnetic nickel–iron and nonmagnetic copper layer thickness was kept constant at 3 and 1 nm, respectively. Energy dispersive X-ray analysis revealed that the nickel and iron content of the multilayers decreased and copper content increased as the total film thickness increased. All multilayers exhibited face-centred cubic structure with (110) preferred orientation. The highest peak intensity changed from (220) to (111) when the total thickness was higher than 2 µm. The multilayers exhibited giant magnetoresistance (GMR). The maximum GMR magnitude of ~4 % was obtained for the films with total thickness less than 1 µm and the GMR decreased down to ~1 % with increasing film thickness to 5 µm. The saturation magnetisation and coercivity decreased from 78 to 11 emu/cm3 and from 24 to 12 Oe as the total thickness of the multilayers increased from 0.3 to 5 µm, respectively. The variations in magnetic and magnetoresistive properties related to the microstructure were attributed to the variation of the film contents caused by total film thickness.

Detailed microstructure analysis of as-deposited and etched porous ZnO films

ZnO nanostructured materials in thin film forms are of particular interest for photovoltaic or photocatalysis processes but they suffer from a lack of simple methods for optimizing their microstructure. We have demonstrated that microporous ZnO thin films with optimized inter grain accessibility can be produce by radio frequency magnetron sputtering process and chemical etching with 2.75mM HCl solution for different duration. The as-deposited ZnO thin films were first characterized in terms of structure, grain size, inter grain space, open cavity depth and total thickness of the film by XRD, AFM, SEM, profilometry and optical measurements. A specific attention was dedicated to the determination of the surface enhancement factor (SEF) by using basic geometrical considerations and images treatments. In addition, the porous fraction and its distribution in the thickness have been estimated thanks to the optical simulation of the experimental UV–Visible–IR spectrums using the Bruggeman dielectric model and cross section SEM images analysis respectively. This study showed that the microstructure of the as-deposited films consists of a dense layer covered by a porous upper layer developing a SEF of 12–13m2m−2. This two layers architecture is not modified by the etching process. The etching process only affects the upper porous layer in which the overall porosity and the inter-grain space increase with the etching duration. Column diameter and total film thickness decrease at the same time when the films are soaked in the HCl bath. The microporous structure obtained after the etching process could generate a great interest for the interfaces electronic exchanges for solar cells, photocatalysis and gas sensors applications.

Fracture toughness of esthetic dental coating systems by nanoindentation and FIB sectional analysis

Improving the esthetics of Ti-based dental implants is the last challenge remaining in the optimization process. The optical issues were recently solved by the application of highly and selectively reflective coatings on Ti implants. This work focuses on the mechanical durability of these esthetic ceramic based coating systems (with and without adhesion layers).The coating systems (Ti–ZrO2, Ti–Al–ZrO2, Ti–Ti–Al–ZrO2, Ti–Ag–ZrO2, Ti–Ti–Ag–ZrO2, Ti–Bragg and Ti–TiO2–Bragg) were subjected to nanoindentation experiments and examined using scanning electron microscopy and focused ion beam cross sectional analysis. Three coating systems contained adhesion layers (10nm of Ti or 60nm of TiO2 layers). The fracture toughness of selected samples was assessed applying two different models from literature, a classical for bulk materials and an energy-based model, which was further developed and adjusted.The ZrO2 based coating systems (total film thickness<200nm) followed a circumferential cracking behavior in contrast to Bragg coated samples (total film thickness around 1.5μm), which showed radial cracking emanating from the indent corners. For Ti–ZrO2 samples, a fracture toughness between 2.70 and 3.70MPam1/2 was calculated using an energy-based model. The classical model was applied to Bragg coated samples and their fracture toughness ranged between 0.70 and 0.80MPam1/2. Furthermore, coating systems containing an additional layer (Ti–Ti–Al–ZrO2, Ti–Ti–Ag–ZrO2 and Ti–TiO2-Bragg) showed an improved adhesion between the substrate and the coating.The addition of a Ti or TiO2 layer improved the adhesion between substrate and coating. The validity of the models for the assessment of the fracture toughness depended on the layer structure and fracture profile of the samples investigated here (classical model for thick coatings and energy-based model for thin coatings).

Magnetostriction and complex permeability of [Fe62Co19Ga19/Py]5/glass multilayered films

[Fe62Co19Ga19(x)/Py(40–x)]5/glass multilayered films, where x=0, 5, 10, 15, 20nm, y=x(nm)/40(nm), and 0≤y≤1, were made by the magnetron sputtering method at room temperature. The total number of combined [Fe–Co–Ga/Py] unit-layers was five. The total film thickness (tf) was fixed at 200nm. We have performed two kinds of experiments on these films: (i) the saturation magnetostriction (λS) measurement, and (ii) the complex permeability (μ=μR–jμI) experiment to find the resonance frequency (fR) as a function of external magnetic field (HE). By definition, the microwave power absorption Pabs at ferromagnetic resonance (FMR) for a metallic conductor is written as Pabs=[(μR2+μI2)1/2+μI]1/2. We define the half-width of the absorption peak Δf as Δf ≣ ΔfS+ΔfA, where ΔfS and ΔfA are the symmetric and asymmetric parts in Δf. The degree of asymmetry, ΔfA/Δf, of each absorption peak is associated with the structural and/or magnetic inhomogeneity in the film. The main findings from this study are summarized as follows: (A) maximum λS occurs in the y=1 film, and as y increases, λS increases; (B) biasing field for magnetostriction decreases greatly by adding Py layers; (C) the magnetostriction sensitivity remains almost constant in the range 0.4<y ≦ 1; (D) μR increases, as y decreases. Thus, from this study we conclude that among all the [Fe62Co19Ga19/Py]5/glass films, the [Fe62Co19Ga19(30)/Py(10)]5/glass film should be the most suitable for applications in nano-magnetic switching devices.

Indentation behaviour of 'soft film on hard substrate' composite system type

This investigation has been carried out in order to analyse and compare the hardness response of different composite systems of the same type, named 'soft film on hard substrate' composite system. Composite systems of mono- and multilayered electrodeposited Ni and Cu thin films on (100) and (111)-oriented monocrystalline Si wafers and 100 µm-thick electrodeposited Ni film as the substrates were fabricated. The indentation behaviour of these composite structures was characterized using Berkovich nanohardness and Vickers microhardness testing. The measured hardness is so-called 'composite hardness', because the substrate participates in the plastic deformation during the indentation process. The contribution of the substrate to the measured hardness starts at indentation depths of the order of 0.07- 0.2 times the film thickness. Dependence of nanohardness and microhardness values on electrodeposition process conditions, substrate and film microstructure, total film thickness, layer thickness and Ni/Cu layer thickness ratio for different composite systems ratio was investigated. Composite hardness model of Chicot-Lesage (C-L) was chosen and applied to experimental data in order to determine absolute film hardness.

Multi-layer film flow down an inclined plane: experimental investigation

We report the results from an experimental study of the flow of a film down an inclined plane where the film itself is comprised of up to three layers of different liquids. By measuring the total film thickness for a broad range of parameters including flow rates and liquid physical properties, we provide a thorough and systematic test of the single-layer approximation for multi-layer films for Reynolds numbers \(Re = \rho Q/\mu \approx 0.03 - 60\). In addition, we also measure the change in film thickness of individual layers as a function of flow rates for a variety of experimental configurations. With the aid of high-speed particle tracking, we derive the velocity fields and free-surface velocities to compare to the single-layer approximation. Furthermore, we provide experimental evidence of small capillary ridge formations close to the point where two layers merge and compare our experimental parameter range for the occurrence of this phenomenon to those previously reported.

Platinum–zirconium composite thin film electrodes for high-temperature micro-chemical sensor applications

Stable metal interconnect thin films are critical in the development of various micro-machined devices that may operate continuously at elevated temperatures. The main objective of this work was to investigate the microstructural and electrical stability of a functionally gradient platinum (Pt)–zirconium (Zr) composite thin film electrode designed for resistive-type chemical sensors. Thin film electrodes were fabricated using a DC magnetron sputtering process. Zirconium was used as both the conventional adhesion promoter and the Pt grain modifier within the bulk electrode microstructure. The thin film deposition was completed on highly polished alumina substrates at 200°C. The various composite Pt thin films were further annealed at 1200°C after deposition for 1–24h for rapid evaluation of the microstructure stability. This temperature was chosen since the electrodes are expected to operate beyond 1000°C for high-temperature MEMS applications. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were conducted to characterize the alterations in chemistry, microstructure and distribution of the constituent elements through the film thickness. The electrical resistivity of the as-deposited and thermally processed Pt thin films was measured by utilizing a van der Pauw's four-point probe technique. The work identified a Zr/Zr+Pt/Pt composite thin film with the 525nm total film thickness that demonstrated resistivity <5.08×10−7Ωm after being processed to 1200°C for 15h. A lift-off technique was finally used to produce a micro-electrode patterns with the optimized film structure for high-temperature applications.

Photo-CuAAC Induced Wrinkle Formation in a Thiol–Acrylate Elastomer via Sequential Click Reactions

Two sequential click reactions are implemented in a facile methodology used to generate well-defined spatiotemporally controlled and persistent wrinkles on the surface of an elastomer. The click thiol-Michael addition reaction was utilized to form a cross-linked polymer with residual, reactive alkyne sites that remained tethered throughout the network. The latent, unreacted alkyne sites are subsequently reacted with diazide monomers via a photoinduced Cu(I)-catalyzed alkyne–azide cycloaddition (CuAAC) reaction to increase the cross-link density. Increased cross-linking raised the modulus and glass transition temperature from 1.6 MPa and 2 °C after the thiol–acrylate reaction to 4.4 MPa and 22 °C after the CuAAC reaction. However, the second-stage photopolymerization of the CuAAC reaction is significantly spatially restricted via limited Cu(II) ion diffusion into the thiol–acrylate elastomer, thereby creating the desired cross-linking gradient throughout the depth of the initial network and leading to the formation of a highly cross-linked skin layer. This approach leads to the formation of well-defined, persistent, reproducible wrinkles on the surface of the material with wavelength and amplitude of 8.50 ± 1.60 and 1.41 μm, respectively, for a polymer with a 1280 μm total film thickness. Control over the wavelength and amplitude of these wrinkles using the resin film thickness is further demonstrated by studying the surface profiles using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Additionally, this novel technique allows the spatial selectivity of wrinkle formation with a wrinkled area that is only 8 μm wider than the photomasked area. This strategy represents a unique approach to generate photodirected wrinkling on the entire surface of the elastomer in one single step.

열처리가 Al-Mg 코팅 강판의 내식성에 미치는 영향

Double layer films which consisted of aluminum(Al) and magnesium(Mg) have been prepared by e-beam deposition. The structure, alloy phase, and corrosion resistance of the prepared films were investigated before and after heat treatment. The first (bottom) layer fixed with Al, and the thickness ratio between Al and Mg layers has been changed from 1 : 1 to 5 : 1, respectively. Total thickness of Al-Mg film was fixed at <TEX>$3{\mu}m$</TEX>. The cold-rolled steel sheet was used as a substrate. Heat treatment was fulfilled in an nitrogen atmosphere at the temperature of <TEX>$400^{\circ}C$</TEX> for 2, 3 and 10 min. Surface morphology of as-deposited Al-Mg film having Mg top layer showed plate-like structure. The morphology was not changed even after heat treatment. However, cross-sectional morphology of Al-Mg films was drastically changed after heat treatment, especially for the samples heat treated for 10 min. The morphology of as-deposited films showed columnar structure, while featureless structure of the films appeared after heat treatment. The x-ray diffraction data for as-deposited Al-Mg films showed only pure Al and Mg peaks. However, Al-Mg alloy peaks such as <TEX>$Al_3Mg_2$</TEX> and <TEX>$Al_{12}Mg_{17}$</TEX> appeared after heat treatment of the films. It is believed that the formation of Al-Mg alloy phase affected the structure change of Al-Mg film. It was found that the corrosion resistance of Al-Mg film was increased after heat treatment.

X‐Ray Photoelectron Spectroscopy Investigations of the Surface Reaction Layer and its Effects on the Transformation Properties of Nanoscale Ti51Ni38Cu11 Shape Memory Thin Films

The depth‐dependent chemical constitution of Ti51Ni38Cu11 thin films of different total film thickness from 400 to 50 nm was characterized using X‐ray photoelectron spectroscopy (XPS). It was analyzed how reaction layers, which form on the surface of the film significantly change the chemical composition of the transforming phase, which leads in turn to altered phase transformation properties. For thinner films, the deviation from the nominal chemical composition increases. For a film thickness of 50 nm, a Ti loss of ≈9 at% is observed. The Ni content is increased by ≈5 at%, whereas the Cu content stays relatively constant for films of different thickness. The results are summarized in a layer model, which supports designing nanoscale shape memory thin films.

Nanostructured ZnO thin films prepared by sol–gel spin-coating

ZnO thin films deposited on silica flat plates were prepared by spin-coating and studied by applying several techniques for structural characterization. The films were prepared by depositing different numbers of layers, each deposition being followed by a thermal treatment at 200°C to dry and consolidate the successive layers. After depositing all layers, a final thermal treatment at 450°C during 3h was also applied in order to eliminate organic components and to promote the crystallization of the thin films. The total thickness of the multilayered films – ranging from 40nm up to 150nm – was determined by AFM and FESEM. The analysis by GIXD showed that the thin films are composed of ZnO crystallites with an average diameter of 25nm circa. XR results demonstrated that the thin films also exhibit a large volume fraction of nanoporosity, typically 30–40vol.% in thin films having thicknesses larger than ∼70nm. GISAXS measurements showed that the experimental scattering intensity is well described by a structural model composed of nanopores with shape of oblate spheroids, height/diameter aspect ratio within the 0.8–0.9 range and average diameter along the sample surface plane in the 5–7nm range.

Influence of total film thickness on high-frequency magnetic properties of the [FeCoSiN/SiNx]n multilayer thin films

[FeCoSiN/SiNx]n multilayer thin films with different number of layers were fabricated by alternating magnetron sputtering at room temperature with no external magnetic field applied on substrates. A well-defined laminated structure consisting of 7nm FeCoSiN magnetic layer and 2nm SiNx insulating layer was observed by transmission electron microscopy (TEM). The static magnetic hysteresis loops of the [FeCoSiN/SiNx]n multilayer thin films measured by vibrating sample magnetometer (VSM) presented an obvious in-plane uniaxial magnetic anisotropy. The dynamic magnetic performance of the [FeCoSiN/SiNx]n multilayer films was studied by vector network analyzer and LLG equation. The results indicated that the total film thickness has slightly impact on the high-frequency magnetic performance of the multilayer thin films. When the total thickness of the [FeCoSiN/SiNx]n multilayer thin films increased to micron level, they could still maintain encouraging high-frequency magnetic properties and electrical property: the ferromagnetic resonance frequency fr=3.74GHz, real permeability µ′=93.73, and electrical resistivity ρ=196µΩcm.

X-ray analysis of strain distribution in two-step grown epitaxial SrTiO3 thin films

Epitaxial SrTiO3 (STO) thin films were grown on (001)-oriented LaAlO3 (LAO) substrates using a two-step growth method by ion beam sputter deposition. An STO buffer layer was initially grown on the LAO substrate at a low temperature of 150 °C prior to growing the STO main layer at 750 °C. The thickness of the STO buffer layer was varied at 3, 6, and 10 nm, while the total film thickness was kept constant at approximately 110 nm. According to x-ray structural analysis, we show that the STO buffer layer plays an essential role in controlling the strain in the STO layer grown subsequently. It is found that the strains in the STO films are more relaxed with an increase in buffer layer thickness. Moreover, the strain distribution in two-step grown STO films becomes more homogeneous across the film thickness when compared to that in directly grown STO film.

Luminescent Properties of Multilayered Eu2O3 and TiO2 Grown by Atomic Layer Deposition**

Atomic layer deposition (ALD) is used to control the interatomic interactions of Eu and Ti in multilayered structures, as measured by characterizing the luminescent properties of the deposited material. Luminescent multilayer structures of Eu2O3 and TiO2 are deposited as thin films by ALD at 300 °C using Eu(thd)3/O3 and TiCl4/H2O (thd = 2,2,6,6‐tetramethyl‐3,5‐heptanedione) as precursor systems. The individual layer thickness of the multilayered structure is produced from first N ALD cycles Eu2O3 and then N ALD cycles TiO2 (N = 1 to 50), while the total film thickness is kept constant. The thinnest distinct layers are detected for N = 10, where each layer is measured to be less than 0.4 nm thick. The as‐deposited films are smooth (root mean square (rms) roughness &lt; 0.4 nm) and amorphous, independent of the layer thickness, N. The refractive index and extinction coefficient are also independent of N, while the luminescence efficiency is constant for N up to 10 cycles, and decreases for thicker superlayers. Annealing deteriorates the layered structures, causing a decrease in luminescence efficiency for thin superlayers, while thick superlayers increase in efficiency upon annealing. The films are characterized by spectroscopic ellipsometry (SE), photoluminescence (PL), X‐ray diffraction (XRD), X‐ray fluorescence (XRF), X‐ray reflectivity (XRR), and atomic force microscopy (AFM).

Preparation of the working electrode of dye-sensitized solar cells: Effects of screen printing parameters

The working electrode films of dye-sensitized solar cells are screen printed using a stainless steel cloth screen or a stencil screen. The as-prepared films and the corresponding cells are characterized and evaluated. The films prepared using the stainless steel cloth screen are thinner than those prepared using the stencil screen under the same screen printing conditions. Thus, while the stainless steel cloth screen is suitable for multi-layer film preparations, the stencil screen is ideal for mono-layer film preparations. Provided that the total working electrode film thickness is about the same, a three-layer working electrode prepared using the stainless steel cloth screen gives a cell with the conversion efficiency of 5.46% and a mono-layer working electrode prepared using the stencil screen gives a cell with the conversion efficiency of 5.30%. When using the stainless steel cloth screen for the working electrode preparation, a low squeegee angle and a low printing speed gives a porous thick film, which is ideal for dye absorption.

Fabrication of &lt;italic&gt;L&lt;/italic&gt;1&lt;sub&gt;1&lt;/sub&gt; Phase CoPt Film on Glass Substrate With [Co/Pt] Multilayer Structure

L1 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> CoPt hlms were fabricated on glass substrate with Pt underlayer by alternate deposition of Co and Pt hlms. The effect of individual Co and Pt thickness, and the total CoPt hlm thickness on structural and magnetic properties were investigated. In this paper, the experiments were divided into two parts. In the hrst part, [(x)Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> /(x)Pt <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.75</sub> ] <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> hlms with varying Co and Pt hlms were deposited and overall film thickness was kept at 7 nm. In the second part, [(x)Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> /(x)Pt <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.75</sub> ] <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> hlms with different total thickness were deposited. In the first case, the coercivity (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c⊥</sub> ), squareness (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">⊥</sub> ), and perpendicular magnetic anisotropy are found to deteriorate with increasing Co and Pt layer thickness due to longer diffusion length. In the second case, the higher H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c⊥</sub> with value of 110 kA/m is obtained in [(x)Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> /(x)Pt <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.75</sub> ] <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> film, and increasing total thickness of film results in lower H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c⊥</sub> . Therefore, it is demonstrated that the CoPt film sputtered by multilayer type with lower thicknesses of Co and Pt layer promotes the formation of L1 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> structure with excellent perpendicular magnetic properties.

Tailoring the surface morphology of zinc oxide films for high-performance micromorph solar cells

Self-textured zinc oxide polycrystalline films prepared by metalorganic low-pressure chemical vapor deposition combine excellent transparency, conductivity and light-scattering ability when used as electrodes for high-efficiency thin-film silicon solar cells. However, the growth of silicon layers with low defect density, which are necessary for high-performance solar cells, often requires the rough surface morphology of as-deposited zinc oxide films to be smoothened. This is usually achieved by a post-deposition argon plasma-etching treatment. We investigate here an alternative method to modify the surface morphology by changing the zinc oxide growth conditions over only the last hundreds of nanometers of the total film thickness. We discuss two types of zinc oxide cap layers, one grown with the addition of ethanol and the other with an enhanced diethylzinc (DEZ) precursor flow. We show that the presence of either type of cap layer does not alter the layer׳s electrical properties, but does slightly diminish the layer׳s light-scattering ability. The cap layer grown with ethanol leads to a more pronounced leveling of the film texture, while the high-DEZ-grown layer better preserves the sharp features of the underlying ZnO. Finally, zinc oxide films with cap layer are used as front electrodes for tandem amorphous/microcrystalline silicon solar cells, and are compared to rough films treated with an argon plasma. With rising thickness of the capping layers, the efficiency of tandem cells increases reaching values over 12%, and approaches that of cells on Ar plasma treated ZnO films.

Effect of Emitting Current Ion Source on Structural, Optical and Electrical Properties of Nanostructured ITO Thin Films by Ion-Beam Assisted Evaporation

Transparent conductive oxides (TCOs) with indium tin oxide (ITO) thin films were deposited without substrate heating and post-deposition anneal using ion-beam assisted evaporation technique on glass and silicon substrates. The oxygen ion with emitting current produced using End-Hall ion source for bombardment of growing surface to improve ITO films structure. In this study, we investigate the effect of an ion flux to ITO films in terms of structural, optical and electrical properties. The emitting current can be varied from 0.5 to 2.0 A with the oxygen flow rate 7 sccm. The total film thickness and deposition rate are 200 nm and 0.2 nm/s, respectively. The structural properties of thin films were characterized by X-ray diffraction (XRD) to discover the preferred orientation with phase of crystalline and scanning electron microscopy (SEM) to examine the surface morphology in cross-section view. To determine the transmission spectra of the films, UV-visible spectrometer is introduced. Moreover, the films were also measured to investigate resistivity, carrier concentration, mobility and sheet resistance by Hall-effect measurements and four-point probe. It has been found that the ITO films with lowest electrical resistivity for the emitting current of 1 A about 5.57x10-4 Ω.cm and slightly increases with increase of the emitting current. The mobility and carrier concentration rapidly decreases with increase the emitting current from 1.0 A to 2.0 A.