Deposited Al Films Research Articles

From Aluminum Dissolution in Supercapacitors to Electroplating: A New Way for Al Thin Film Deposition?

AbstractThe present work addresses a new finding observed while performing aluminum dissolution experiments for supercapacitors (SCs) stability investigation. Supercapacitor (SC) electrodes based on carbon‐coated aluminum foils are electrochemically cycled in harsh conditions into bis‐trifluoromethylsulfonyl imide (TFSI)‐based electrolyte and using Acetonitrile (ACN) as solvent. Dissolution of aluminum is observed with subsequent plating on the carbonaceous surface of counter electrodes. Moreover, the same process can be reproduced also on standard SC activated carbon electrodes. This mechanism can open the way to an effective strategy to achieve Al film deposition by electroplating becoming competitive with the most common copper counterpart.

Synthesis of Al Thin Films with High Optical Transmittance by DC Magnetron Sputtering Process Parameter Optimization

Nanostructured Al thin film with higher optical transmittance and electrical conductivity has intensive applications in solar cells and optical and microelectronic devices. This experimental-based research study has optimized the DC magnetron sputtering deposition parameters (sputtering power, sputtering current, voltage, and working gas pressure) for Al thin film deposition to obtain the highest optical transmittance and lower sheet resistance. Optical transmittance, surface roughness, film thickness, sheet resistance, grain size, and surface morphology were characterized using UV-vis-NIR spectroscopy, surface profiler, spectroscopic ellipsometry, four-point probe, and FE-SEM, respectively to determine the effects of sputtering process parameters on Al films’ different properties. Experimental investigations reveal that electrical conductivity, surface roughness, grain size, and deposition rate increase with increasing of sputtering power at certain working gas pressure. At the optimized condition (sputtering power 80 W, working gas pressure 5 mTorr, deposition time 5 min and ambient temperature), the relatively higher optical transmittance in visible region 96%, moderate sheet resistance 0.196 ohm/square and lowest average surface roughness 2.86 nm were obtained for Al thin film. After all, this research study will help to understand the best Al film deposition parameters in terms of optical transmittance and electrical conductivity for future research and industrial applications.

Evolution of the Microstructure, Hybridization, and Internal Stress of Al-Doped Diamond-Like Carbon Coatings: A Molecular Dynamics Simulation.

This work modified some parameters related to the bond order in REBO-II of the C-C interaction and simulated the ta-C:Al film deposition using the large-scale atomic/molecular massively parallel simulator especially focused on the effect of the Al-doping content on the microstructural and mechanical properties of tetrahedral amorphous carbon films. According to the Al existence state, the Al content in the films can be divided into three ranges: range I─under 5 at % Al, a single Al atom or a small cluster with 2-3 Al atoms disperses separately in the matrix; range II─at 5-20 at. % Al, the number and incorporating Al atoms of the clusters increase with the Al content; range III─above 20 at. % Al, only a solid network of aluminum atoms forms, which becomes thickened and densified with Al content increment. The existence states of Al atoms play an essential role in determining mechanical and structural properties. With Al content increasing in the films, the isolated small cluster of atoms evolved into a whole network of aluminum inter-crossing with the C-network. With the evolution of Al existence states, the sp3C fraction decreases monotonically, while the sp2C fraction increases. In range III, the network of aluminum promotes the growth of sp1C sites. The residual compressive stress in the film decreased rapidly with the Al content increasing in range I and II, but it reached a low-level constant value in range III.

Influence of Plasma Surface Treatment of Polyimide on the Microstructure of Aluminum Thin Films

The effects of plasma treatment of polyimide substrates on the texture and grain size distribution of aluminum thin films were studied. Oxygen-argon plasma treatment increased the average grain size and enhanced the (111) film texture. For short oxygen-argon plasma treatment times, the deposited Al films showed a (111) texture with a bimodal grain structure and even a {111}<112¯> type in-plane texture. The preferential nucleation and grain growth of (111) grains are discussed in terms of the interface energy anisotropy.

Metalizadora Construída em Laboratório: Deposição de Filme de Alumínio sobre Substrato de Vidro e Posterior Anodização para Obtenção de Óxido de Alumínio

In this work, the assembly of a low-cost metallizer is presented, based on physical vapor deposition, to obtain metallic aluminum film deposited over a glass substrate. Later, the Al film is anodized and converted into a porous nanostructured oxide film. The metallic film thickness was measured by profilometry, and the sample position inside the chamber was evaluated. Samples positioned at the center of the sample holder showed considerable thickness and best homogeneity compared to those samples positioned at the edges of the sample holder. A thick metallic film of Al (6 to 7 µm) was deposited over the glass substrate for subsequent anodizing treatment. Mild anodization allowed the total conversion of metallic Al after 7000 s, producing a transparent anodic aluminum oxide (AAO) film adhered to the glass substrate. The AAO morphology was investigated by SEM. Some factors have been listed to describe the low regularity and homogeneity of nanopores in the outer layer of AAO, such as internal defects, compaction of deposited Al film layers and the glass substrate roughness.

Tailoring material properties of electrochemically deposited Al film from chloroaluminate ionic liquid for microsystem technology using pulsed deposition

To practically utilize an electrochemically deposited Al film in microsystems, its material properties have to be elucidated, along with the influence of different deposition conditions. In this study, microstructure, electrical, mechanical and thermal properties of electrochemically deposited Al film from a chloroaluminate ionic liquid electrolyte are comprehensively investigated. The nanoindentation hardness and elastic modulus of the film varied between 486–908 MPa and 41–102 GPa, respectively, depending on the deposition condition. The electrical resistivity and the coefficient of thermal expansion varied between 51–160 nΩ m and 2–20 ppm/K, respectively. The results are compared to those of Al thin films deposited using other techniques. The characterized properties were found to be associated to the microstuctures of the deposits, which can be tailored by the deposition conditions. The microstructures of the deposits were comprehensively characterized by cross-sectional scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) spectroscopy. These results are useful as a design guide for the future applications of the film.

Far- and deep-ultraviolet surface plasmon resonance using Al film for efficient sensing of organic thin overlayer

Recently, a focus has been placed on plasmonics utilizing ultraviolet light because of its higher energy and shorter wavelength, compared to visible light. Al is a suitable metal for plasmonics in the ultraviolet region. However, Al is easily oxidized, and accurate control for Al film deposition is difficult. In this study, organic thin films were formed on the Al films, and their surface plasmon resonance (SPR) wavelengths were measured by our original attenuated total reflectance spectroscopic system. With an increase in the organic film thickness, the SPR wavelength shifted to longer wavelengths. The minimum detection thickness of the organic overlayer reached 2 nm for three Al films under different conditions (i.e., different Al thickness and oxidation effects), and the spectra were reproduced by simulations based on the Fresnel equations. These results showed the practical advantage of the Al-based SPR sensor without accurate control of the chemical state of the Al film.

Nanoelectrode Arrays for in-Situ Identification and Quantification of Halogen Ions

We study the use of nanoelectrode arrays (NEAs), consisting of billions/cm2 of ~ 75 nm diameter electrodes, for the electrochemical analysis of ionic halogen species in water. Such NEA sensors were previously demonstrated to detect part-per-billion (ppb) levels of Pb-ions in aqueous solutions without supporting electrolytes. Briefly, the individual electrodes in the NEA can be tailored with sufficient separation coupled with pore-depth control so that each experiences non-overlapping hemispherical diffusion zones within which the ionic flux of an analyte is independent of time. This geometry is well-suited for trace-level detection, as fast voltage sweeps result in a large and steady-state current density. With optimized design, the additive response from the plethora of nanoelectrodes leads to an orders-of-magnitude analytical advantage for electrochemical detection compared to conventional (mm) sized disc electrodes using sweep or pulse voltammetric techniques. NEAs are fabricated by anodizing RF-sputter deposited Al films on a substrate-of-choice, resulting in billions/cm2 tailored with controllable pore diameters. Each nanopore is partially filled via electrochemical plating with an appropriate working electrode material, such as Au, Pt or Ni. A thin W film is beneath the nanopore template for both processing assistance and to provide a backside electrical contact in parallel to every nanoelectrode. In the case that the NEA is recessed within the porous alumina, a thin conducting film can be added to the topside to function as a counter/pseudo-reference electrode. In some situations, the counter electrode can also serve as an ion collector, preconcentrating ionic species near the pore openings prior to beginning an electrochemical measurement. Using such NEA sensors, we will demonstrate trace detection levels for both Cl and I ionic species in water, and compare the limits-of-detection with conventional electrodes. In addition, we explore the possibility of using NEA sensors to detect halogens in the gas phase. By manipulating the NEA structure, the monitoring capability may be extended to gas phase detection of Cl2 or I2. Such gas-phase detection is possible by utilizing the natural humidity in air condensing on the nanopore walls above the recessed working electrodes. Indirect sensing of such gases occurs after they dissolve in the pore water to form electrochemically detectable halogen species. Notably, the electrochemical measurement is achieved with simple, condensed humidity as the sole ionically conducting phase, without the need for a supporting electrolyte. This is because the high resistivity of water† is mitigated by the short ionic path length: the net solution resistance is small because of the sub-micron distance separating the NEA electrodes from the counter/pseudo-reference electrode sputtered upon the surface of the opposite (open) end of the pore. †The conductivity of humidity levels we consider in this study range from 10-6 S/m (humidity from DI water) to 10-3-10-4 S/m (conductivity range of natural humidity across the USA as monitored by the National Atmospheric Deposition Program’s National Trend Network). This work is supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Evaluation of Key Factors for Preparing High Brightness Surfaces of Aluminum Films Electrodeposited from AlCl3-1-Ethyl-3-Methylimidazolium Chloride-Organic Additive Baths

The effects of additives, such as 4-pyridinecarboxylic acid hydrazide (4-PCAH) and its analogs, and organic solvents, such as toluene, benzene and xylene, on the brightness of aluminum (Al) prepared using constant-current deposition from an ionic liquid of ethyl-3-methylimidazolium chloride (EMIC)-aluminum chloride (AlCl3) were investigated by light spectroscopy, scanning electron microscopy (SEM), reflectivity tests, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy. In order for the deposited Al films to exhibit high brightness, a combined use of 4-PCAH and toluene is effective. Moreover, the relationship between the brightness (i.e., reflectance) of the prepared Al films and the molecular structure of a variety of additives was clarified. Both a pyridine ring and an acetyl hydrazine group are necessary for constituting an effective additive. The structural isomers of a given additive bring about different surface brightness, e.g., for PCAHs the reflectance at 450 nm is in the order of para-isomer > meta-isomer > ortho-isomer. It was considered that in 4-PCAH electron-withdrawing acetyl hydrazine group is bounded to the pyridine ring, and consequently the electron density around the nitrogen atom in the pyridine ring is decreased, which is conducive to the adsorption of 4-PCAH on the cathode of deposited Al films. In addition, the reflectance was found to increase with decreasing the crystalline domain size of Al deposits and with increasing the reaction resistance for Al electrodeposition. The reaction mechanism of Al electrodeposition from the present ionic liquid media containing various additives is also discussed briefly.

The Relationship Between Brightness of Aluminum Films Fabricated Using an AlCl3-1-Ethyl-3-Methylimidazolium Chloride-Toluene Bath and Molecular Structure of Additives

In our previous study, we showed that the addition of 4-pyridinecarboxylic acid hydrazide (4-PCAH) to an EMIC/AlCl3/toluene mixture improved the brightness of the deposited Al film [1]. The prepared Al films clearly reflect the characters on the surface so that the characters can be read. The reflectivity of the Al surface prepared with EMIC/AlCl3/toluene/4-PCAH was 84% at 450 nm; to the best of our knowledge, this is the highest value achieved. In this study, to elucidate why the addition of 4-PCAH to the EMIC/AlCl3/toluene bath effectively improves the brightness of the electrodeposited Al surfaces, a systematic series of molecules as additives were studied, and the results obtained for each molecule were compared carefully to determine the relationship between the brightness of the prepared Al surface and the molecular structure of the additive. The effect of additives, such as 4-PCAH and its analogs, on the surface brightness, electrodeposition efficiency and chemical composition of prepared Al films was examined using SEM, visible light reflectance measurements and XPS. The decrease in the surface roughness of the Al films causes the high surface brightness. The strong relationship (Fig. 1) between the high brightness and molecular structure of the additives included in the bath was elucidated via a systematic study of various additives. 4-PCAH achieved the highest surface brightness of the electrodeposited Al films prepared with various additives used in this study. [1] X. Fang, K. Uehara, S. Kaneko, S. Sato, T. Tanabe, T. Gunji, F. Matsumoto, Electrochemistry 84 (2016) 17-24. Figure 1. (A)Micrographs of the Al film surfaces obtained by the electrodeposition of Al from EMIC/AlCl3/toluene/4-PCAH baths, (B) Summary of the relationship between the reflectance of the prepared Al films at a wavelength of 450 nm and the molecular structure of the additive. Preparation conditions of the Al film: deposition time 2 h, constant current density 8 mAcm-2; bath composition: EMIC:AlCl3= 33.3 : 66.7 (mol%), toluene concentration: 9.25 M, additive concentration: 1.8 mM. Figure 1

Evaluation of Key Factors for Preparing High Brightness Surfaces of Aluminum Films Electrodeposited from AlCl3-1-Ethyl-3-Methylimidazolium Chloride-Organic Additive Baths

The effects of additives, such as 4-pyridinecarboxylic acid hydrazide (4-PCAH) and its analogs, and organic solvents, such as toluene, benzene and xylene, on the brightness of aluminum (Al) prepared using constant-current deposition from an ionic liquid of ethyl-3-methylimidazolium chloride (EMIC)-aluminum chloride (AlCl3) were investigated by light spectroscopy, scanning electron microscopy (SEM), reflectivity tests, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy. In order for the deposited Al films to exhibit high brightness, a combined use of 4-PCAH and toluene is effective. Moreover, the relationship between the brightness (i.e., reflectance) of the prepared Al films and the molecular structure of a variety of additives was clarified. Both a pyridine ring and an acetyl hydrazine group are necessary for constituting an effective additive. The structural isomers of a given additive bring about different surface brightness, e.g., for PCAHs the reflectance at 450nm is in the order of para-isomer>meta-isomer>ortho-isomer. It was considered that in 4-PCAH electron-withdrawing acetyl hydrazine group is bounded to the pyridine ring, and consequently the electron density around the nitrogen atom in the pyridine ring is decreased, which is conducive to the adsorption of 4-PCAH on the cathode of deposited Al films. In addition, the reflectance was found to increase with decreasing the crystalline domain size of Al deposits and with increasing the reaction resistance for Al electrodeposition. The reaction mechanism of Al electrodeposition from the present ionic liquid media containing various additives is also discussed briefly.

The Effect of Brighteners on the Fabrication of Electroplated Bright Aluminum Films Using an AlCl3-Emic-Toluene Bath (2)

In this study, we will report that the effectiveness of 4-pyridinecarboxylic acid hydrazide (4-PCAH) to smooth the deposited Al surfaces were compared with 3-pyridinecarboxylic acid hydrazide (3-PCAH), 2-pyridinecarboxylic acid hydrazide (2-PCAH) and PH in the view point of brightness, surface roughness and the film thickness. The Al films prepared with ionic liquid containing 4-PCAH showed brighter surfaces in the film thickness from 20 to 100 micrometer although generally the increase in the thickness of the deposited films causes the increase in the surface roughness. Figure 1 shows photographs of Al film obtained by electrodeposition of Al from (A) EMIC/AlCl3/toluene/4-PCAH, (B) EMIC/AlCl3/toluene/3-PCAH, (C) EMIC/AlCl3/toluene/2-PCAH and (D) EMIC/AlCl3/toluene/PH baths. In the baths, a constant current of 8 mAcm-2 (A-D) was used for electrodeposition of Al. In order to recognize the difference in brightness of Al surfaces, the characters of “KU UNIV” were reflected in the Al film surface. Whether the characters that were reflected in the Al surfaces can be seen or not is an index of surface brightness, in other words, surface smoothness. The Al films obtained with the EMIC/AlCl3/toluene/4-PCAH bath exhibits the highest brightness among four brighteners used in this study although the brightness became degrade as the deposition time became longer (Fig. 1). On the other hand, the Al films obtained with EMIC/AlCl3/toluene/PH bath and the deposition times of 2 h barely reflect the characters on its surface. In the deposition time which is longer 2 h, dull characters can be barely seen in the partial area. PH has been reported as a representative brightener for Al electrodeposition as long as we know in several papers. 4-PCAH which was applied to Al deposition for the first time as brightener by us exhibits remarkable effect for improvement of brightness of Al surface when compared with that obtained with EMIC/AlCl3/toluene/3-PCAH, EMIC/AlCl3/toluene/2-PCAH and EMIC/AlCl3/toluene/PH bath. The electrodeposition of Al from EMIC/AlCl3/toluene/4-PCAH bath for 2 h with 4 and 12 mAcm-2, and from EMIC/AlCl3/toluene/PH bath with 4 mAcm-2 showed degradation of the brightness. Employment of current of 12 mAcm-2 in the EMIC/AlCl3/toluene/PH bath naturally leaded to the same brightness as the deposited Al films prepared with 8 mAcm-2 from the EMIC/AlCl3/toluene/PH bath (these results are not shown here).Figure 2 shows reflectance spectra of Al films deposition from AlCl3-EMIC-toluene-4-PCAH (b), AlCl3-EMIC-toluene-3-PCAH (c), AlCl3-EMIC-toluene-2-PCAH (d) and AlCl3-EMIC-toluene-PH (e). The spectrum (a) was obtained with a commercial Al foil (A1N80H-H18, Mitsubishi Aluminum, Japan). Preparation conditions of Al films are deposition time of 2 h and constant current of 8 mAcm-2. The Al film obtained with AlCl3-EMIC-toluene-4-PCAH (b) exhibits the reflectivity similar to one observed with the Al foil, followed by the Al film obtained with AlCl3-EMIC-toluene-PH (e) in the view point of the reflectivity. Although the brighteners of 4-PCAH, 3-PCAH and 2-PCAH are positional isomer, the difference in the reflectivity of the Al films obtained with 4-PCAH, 3-PCAH and 2-PCAH are interesting result, indicating the importance of adsorption of brightener to Al surfaces. Fig. 1 Micrographs of the Al film surfaces obtained on a Cu substrate by coulometeric electrodeposition from (a) AlCl3-EMIC-toluene-4-PCAH, (b) AlCl3-EMIC-toluene-4-PCAH, (c) AlCl3-EMIC-toluene-2-PCAH and (d) AlCl3-EMIC-toluene-PH baths. Deposition time: 2 h; constant current: 8 mAcm-2. Fig. 2 Reflectance spectra of Al films deposition from AlCl3-EMIC-toluene-4-PCAH (b), AlCl3-EMIC-toluene-3-PCAH (c), AlCl3-EMIC-toluene-2-PCAH (d) and AlCl3-EMIC-toluene-PH (e). The spectrum (a) was obtained with a commercial Al foil. Figure 1

The Effect of Brighteners on the Fabrication of Electroplated High-Bright Aluminum Films Using AlCl3-Emic Ionic Liquids

Aluminum (Al) is the second most abundant metallic element in the Earth's crust after silicon. Al has been widely used as a coating material, because it has the ability to resist corrosion due to passivation and has high visible-light reflectivity. Al has many uses in the transportation, packaging, construction and consumer goods industries. Thin layers of Al are typically deposited onto a flat surface by physical vapor deposition, chemical vapor deposition or a hot-dip coating process. However, electrochemical deposition of Al at ambient temperatures has attracted much interest in corrosion-resistive and decorative coatings, electro-refining processes and Al-ion batteries, because the deposition processes do not need expensive equipment, the size of Al films can be easily scaled-up or scaled-down, and Al films of uniform thickness can be prepared on various surface geometries. However, as understood from the Pourbaix Diagram of Al, at any pH, the reduction of proton preferentially occurs in aqueous solutions and the electrodeposition of Al is not feasible. Aprotic electrolytes, such as inorganic molten salts, organic molten salts (i.e., ionic liquids), and molecular organic solvents, have been applied for the electrodeposition of Al. There are many examples in the literature in which various electrolytes and conditions were used. Among aprotic electrolytes, ionic liquids that are composed solely of ions and have melting points below 100℃ have increasingly been replacing organic solvents in the research field of metals that are unable to be electrodeposited from aqueous solutions. Numerous ionic liquid electrolytic systems have been investigated for the electrodeposition of Al. These studies have focused on the formation of smooth Al films that exhibit high visible-light reflectivity on the Al surface. It was reported that in order to obtain a smooth surface for the Al films, trace amount of brighteners, such as 1,10-phenanthroline (PH) and nicotinic acid were added to the ionic liquid electrolytes. However, the electrodeposition of high bright Al has not been realized even with the presence of additives in the electrolytes. In this study, we found a more effective brightener: isonicotinic acid hydrazine (IAH) for the preparation of high bright Al films and report that the effectiveness of the two additives, IAH and PH, for smoothing the deposited Al surfaces was compared in terms of brightness, surface roughness, and film thickness. The Al films prepared with ionic liquid containing IAHshowed brighter surfaces in the film thickness range of 2 to 250 mm, although generally an increase in the thickness of the deposited films caused an increase in the surface roughness.We found that the addition of IAH to EMIC/AlCl3/toluene improved the brightness of deposited Al films. The Al films clearly and legibly reflected the characters on the Al surface. Although the EMIC/AlCl3/toluene/IAH and EMIC/AlCl3/toluene/PH baths exhibited high current efficiencies close to 100%, as expected from the high brightness of the Al films prepared with the EMIC/AlCl3/toluene/IAH bath, both the grain size and average roughness of the Al films prepared with the EMIC/AlCl3/toluene/IAH bath were smaller than that of the Al films prepared with the EMIC/AlCl3/toluene/PH bath. In addition, the Al films prepared with the EMIC/AlCl3/toluene/IAH bath have the perpendicularly preferred [100] orientation on the Cu plate when compared with the EMIC/AlCl3/toluene/PH bath sample. The strong orientation preference in the [100] plane likely causes flattening of the deposited Al surface in the EMIC/AlCl3/toluene/IAH. The mechanism for flattening the deposited Al surface with IAH will be discussed in our presentation.

Solution-Processable Low Voltage Organic Transistors of Thieno[3,2-b]thiophene-Based Conducting Polymer

A low-operating voltage and high performance polymeric field effect transistors using octadecylphosphonic acid-treated high-k AlOx and HfO2 hybrid dielectrics were demonstrated. High-k metal oxide hybrid dielectrics were prepared by oxygen plasma treatment of deposited Al film for AlOx and by spin coating of solution-processable HfO2 sol-gel solution for HfO2 in combination with phosphoric acid-based self-assembled monolayer (SAM), resulting in high capacitance (10 nF/cm2 for SiO2, 600 nF/cm2 for AlOx and 580 nF/cm2 for HfO2). With phosphoric acid-based SAM on high-k metal oxide and thermal annealing of thieno[3,2-b]thiophene-based conducting polymer, the device performance was significantly enhanced. The highest mobility of the transistors using ODPA-treated AlOx as a gate dielectric is 2.3 × 10−2 cm2 V−1 s−1 in the saturation region with the source-drain of −2 V. In ODPA-treated HfO2 hybrid dielectric, the saturated mobility is 1.1 × 10−2 cm2 V−1 s−1 and the threshold voltage was measured to be −0.31 V, which is at least one order lower than SiO2 hybrid dielectric (−3 V).

Optical constants of aluminum films prepared by electron beam evaporation

The metal aluminum (Al) is widely used because it has high reflectivity from the ultraviolet to the infrared band. But the new deposited Al films is exposed to the atmosphere, it forms transparent Al2O3 films on its surface at once. In this letter, the Al films is deposited on the quartz substrate by electron beam evaporation. The effect of Al films oxidation on refractive index and extinction coefficient is investigated by spectroscopic ellipsometry (SE). The optical constants of Al films change with the increase of oxidation time. The two parameters become stable when these films are exposed in air more than 2 days.

Determination of Stress-Strain Constitutive Relation of Echelle Grating Al Film by Nanoindentation Test and Simulation

For the research on elastic-plastic deformation characteristics of the echelle grating in the mechanical ruling depth range, a series of nanoindentation tests are completed about the deposited Al film of available echelle grating with a Berkovich indenter on a CSM nanoindentation instrument. Then a finite element analysis of the nanoindentation process is studied with an orthogonal experiment method for a series of given parameters containing the yield stress and strain-hardening exponent. The optimum combinations of yield stress and strain-hardening exponent are 200MPa and 0.1, which are got by the objective of the least absolute value of maximum loads deviation between the indentation test and the finite element analysis. Finally the elastic-plastic stress-strain curve of power function of the Al film is represented with the difference analysis from the orthogonal simulations.

New selective two-step anodization of porous anodic alumina for thin-film encapsulation

In this paper, we propose a new selective two-step method of anodization of porous anodic alumina (PAA) for thin-film encapsulation. It is based on the formation of a selectively anodized porous alumina membrane using only photoresist (PR) which offers lots of vertical nanopores as release holes for sacrificial layer etching. This method allows finer patterning in the selective PAA process and reduces the whole process time and cost. Furthermore, it does not leave isolated aluminum (Al) residue during the anodization process, and the deposited Al film is not conformal over the 3-dimensional structure. The key for this new selective anodization method is the technique to form the locally anodized PAA membrane with the masking material PR by two-step anodization. The nanopores in the PAA membrane allow the penetration of plasma gas or etchant into the cavity to release the sacrificial layer underneath. To seal the packaging, a thin-film is deposited over the selectively anodized PAA membrane in a vacuum ambient atmosphere with no detectable internal deposition of the sealing material. Hermetically sealed thin-film vacuum encapsulation using the proposed selective anodization method is demonstrated, and its hermeticity is also monitored through the measurement of the center deflection of the sealing layer.

Effect of Surface Morphology in ZnO:Al/Ag Back Reflectors for Flexible Silicon Thin Film Solar Cells on Light Scattering Properties

Changes in surface morphology and roughness of dc sputtered ZnO:Al/Ag back reflectors by varying the deposition temperature and their influence on the performance of flexible silicon thin film solar cells were systematically investigated. By increasing the deposition temperature from <TEX>$25^{\circ}C$</TEX> to <TEX>$500^{\circ}C$</TEX>, the grain size of Ag thin films increased from 100 nm to 1000 nm and the grain size distribution became irregular, which resulted in an increment of surface roughness from 6.6 nm to 46.6 nm. Even after the 100 nm thick ZnO:Al film deposition, the surface morphology and roughness of the ZnO:Al/Ag double structured back reflectors were the same as those of the Ag layers, meaning that the ZnO:Al films were deposited conformally on the Ag films without unnecessary changes in the surfacefeatures. The diffused reflectance of the back reflectors improved significantly with the increasing grain size and surface roughness of the Ag films, and in particular, an enhanced diffused reflectance in the long wavelength over 800 nm was observed in the Ag back reflectors deposited at <TEX>$500^{\circ}C$</TEX>, which had an irregular grain size distribution of 200-1000 nm and large surface roughness. The improved light scattering properties on the rough ZnO:Al/Ag back reflector surfaces led to an increase of light trapping in the solar cells, and this resulted in a noticeable improvement in the <TEX>$J_{sc}$</TEX> values from 9.94 mA/<TEX>$cm^2$</TEX> for the flat Ag back reflector at <TEX>$25^{\circ}C$</TEX> to 13.36 mA/<TEX>$cm^2$</TEX> for the rough one at <TEX>$500^{\circ}C$</TEX>. A conversion efficiency of 7.60% (<TEX>$V_{oc}$</TEX> = 0.93, <TEX>$J_{sc}$</TEX> = 13.36 mA/<TEX>$cm^2$</TEX>, FF = 61%) was achieved in the flexible silicon thin film solar cells at this moment.

Al and Zn film deposition using a vacuum arc plasma source with a refractory anode

The radially expanding plasma plume generated in a Hot Refractory Anode Vacuum Arc was used to deposit thin Al and Zn films on glass substrates. The electrode separation was 10mm, arc time varied up to 165s, and current (I) was 100–225A. The cathode was a water-cooled Al or Zn cylinder. A graphite anode with 9 or 30mm height was used with the Al cathode, and 10 or 30mm height Mo anode was used with the Zn cathode. A mechanical shutter controlled the substrate exposure onset and duration (15s) to the anodic plasma. The distance from the arc axis to the substrate (L) was varied between 80 and 165mm. The film thickness was measured with a profilometer, and macroparticle (MP) presence on the coating surface was examined by optical microscopy.It was found that the deposition rate increased as a function of time to a peak, and then decreased to a steady-state value. The peak occurred sooner using the 9mm anode than with the 30mm anode. The peak deposition rate increased and the peak time decreased with I. The steady-state deposition rate was larger for Zn (~2μm/min) than for Al cathodes (~1μm/min) at I=225A and L=110mm. The arc voltage for Al was ~20–22V and for Zn it was 11V. The deposition rate peak appeared due to MPs evaporating from the hot anode, where they had initially condensed during the conventional arc stage when the anode was still cold. This effect was significant with low melting temperature Al and Zn cathodes, and negligible with Cu and Ti cathodes studied previously.

Effects of surface roughness and oxide layer on the thermal boundary conductance at aluminum/silicon interfaces

In nanosystems, the primary scattering mechanisms occur at the interfaces between the material layers. As such, the structure and composition around these interfaces can affect scattering rates and, therefore, thermal resistances. In this work, we measure the room-temperature thermal boundary conductance of aluminum films grown on silicon substrates subjected to various pre-Al-deposition surface treatments with a pump-probe thermoreflectance technique. The Si surfaces are characterized with atomic force microscopy to determine mean surface roughness. The measured thermal boundary conductances decrease as Si surface roughness increases. In addition, stripping of the native oxide layer from the surface of the Si substrate immediately prior to Al film deposition causes the thermal boundary conductance to increase. The measured data are compared to an extension of the diffuse mismatch model that accounts for interfacial mixing and structure around the interface in order to better elucidate the thermal scattering processes affecting thermal boundary conductance at rough interfaces.