Vacuum Deposition Method Research Articles

Metal-vapor integration/transportation based on metal-atom desorption from polymer surfaces with a low glass-transition temperature

Vacuum evaporation, which is widely used to obtain a metal-film coating on substrates and/or targets, results in a large loss of evaporation materials. The authors discovered a selective metal-vapor deposition phenomenon in which metal-vapor atoms can be deposited selectively without a shadow mask. The core phenomenon of selective deposition is the desorption of metal-vapor atoms from organic surfaces with a low-glass transition temperature (low-Tg). The authors investigated metal-atom desorption from low-Tg polymer [polydimethylsiloxane (PDMS)] surfaces during vacuum deposition and found that greater than 2-μm-thick PDMS film enables high desorption efficiency. The authors proposed two vacuum deposition methods: metal-vapor transportation and metal-vapor integration. The former method attained reduced substrate surface temperatures during vacuum evaporation and the latter enabled extremely high deposition efficiency and three-dimensional deposition in a one-batch process. These new methods can greatly widen applications of vacuum deposition.

Mechanism of rubrene thin film growth using α-quaterthiophene inducing layer at low temperature

Growth of rubrene thin films at room temperature on bare SiO2 substrates and on top of a α-quaterthiophene (α-4T) inducing layer on SiO2 substrates was investigated. The rubrene thin films and α-4T inducing layers were prepared by vacuum deposition method and were characterized by atomic force microscopy and X-ray diffraction. Rubrene thin films directly deposited on SiO2 substrates had a number of holes on their surface, while the ones grown on top of a α-4T inducing layer on SiO2 substrates exhibited highly ordered morphology and structure. It was found that large-area and ordered rubrene thin films could properly match with the α-4T inducing layers in the prepared heterostructures. Two different rubrene film growth mechanisms were observed from results obtained for films with different thicknesses. We conclude that rubrene thin films prepared at low temperature using α-4T inducing layer on SiO2 substrates hold a great promise of application in large-area and flexible displays.

Tuning the Surface Chirality of Adsorbed Gly-Pro Dipeptide/Cu(110) by Changing Its Chemical Form via Electrospray Deposition.

By changing the ultrahigh vacuum (UHV) deposition method, classical sublimation versus electrospray ionization, one can tune the chemistry of a chiral dipeptide molecule (Gly-Pro, GP), when adsorbed on a Cu(110) surface, from anionic to zwitterionic. This chemical shift will influence the adsorption mode of the dipeptide, either in a three-point fashion in the case of anionic GP molecules with a strong interaction among the copper surface, both O atoms of the carboxylate moiety, and the nitrogen atoms, or in the case of zwitterions GP, the adsorption mode relies on the sole interaction of one carboxylate oxygen atom. These different anchoring modes strongly modify the expression of surface 2D chirality and the supramolecular assemblies with two very distinct unit cells.

Influence of annealing on microstructure and optical properties of hot wall deposited PbxSn(1 − x)S thin films

PbxSn(1−x)S (0.05<x<0.20) thin films with the thickness of 2μm were deposited on glass substrates using hot wall vacuum deposition method at the vacuum pressure of 5×10−4Pa, wall temperature of 600°С, substrate temperature of 300°С and subsequently annealed at 450°C in vacuum at 5×10−4Pa. The microstructure and optical properties of the as-deposited and annealed films were examined in relation to the film composition. The explanations of lattice parameter deviations from the bulk crystals for both as-deposited and annealed PbxSn(1−x)S thin films are discussed. The PbxSn(1−x)S thin films exhibit a preferred orientation around the [111] direction. The annealing decreases the film microstrain values and increases the grain size and the degree of preferred orientation. Thermal probe measurements showed the sulfur-deficient films to be p-type and the sulfur-rich films to be n-type. The PbxSn(1−x)S films exhibit direct allowed transitions with energy band gap Eg(d) increasing with the increase of Pb mole fraction. The Eg(d) values for as-deposited films range from 0.95 to 0.98eV and for annealed films they variy from 0.90 to 0.94eV.

High efficiency organic light-emitting diodes with in situ synthesized Cu(I) complex emitter: How to do chemical reaction in a vacuum chamber?

Cu(I) complexes are considered as idea emitters in organic light-emitting diodes (OLEDs) due to their low cost and theoretical high internal quantum efficiency, which are two important issues have to be concerned for OLEDs commercialization. However, most Cu(I) complexes are unstable toward sublimation and hence not amenable to the vacuum deposition method typically used to fabricate OLEDs. To solve this problem, a codeposition route that involves codeposition of CuI and pyridine derivative has been proposed to synthesis Cu(I) complex emitter in situ. Since chemical reactions were conducted in a vacuum chamber, we systematically studied the effect of reactant chemical structure, reaction ratio, and deposition rate on the in situ synthesized Cu(I) complex and its application as an emitter in OLEDs. With an optimal chemical reaction condition, the device showed a high external quantum efficiency (EQE) up to 14.2% at a brightness of 100 cd/m2, corresponding to a current and power efficiency of 45.2 cd/A and 33.3 lm/W, respectively. The performance is comparable to those efficient OLEDs with iridium complex emitter, while using a CuI dopant that having only one ten-thousandth of price to bis(2-phenylpyridine) (acetylacetonate)iridium.

Methodologies for high efficiency perovskite solar cells.

Since the report on long-term durable solid-state perovskite solar cell in 2012, perovskite solar cells based on lead halide perovskites having organic cations such as methylammonium CH3NH3PbI3 or formamidinium HC(NH2)2PbI3 have received great attention because of superb photovoltaic performance with power conversion efficiency exceeding 22 %. In this review, emergence of perovskite solar cell is briefly introduced. Since understanding fundamentals of light absorbers is directly related to their photovoltaic performance, opto-electronic properties of organo lead halide perovskites are investigated in order to provide insight into design of higher efficiency perovskite solar cells. Since the conversion efficiency of perovskite solar cell is found to depend significantly on perovskite film quality, methodologies for fabricating high quality perovskite films are particularly emphasized, including various solution-processes and vacuum deposition method.

Fabrication and characterization of silver mirror planar microcavity with dye J–aggregates

Silver mirror planar microcavity containing dye J–aggregates is fabricated by a vacuum deposition method. Characterization of the microcavity with the dye J–aggregates of lower concentration (7.70×10−4M) in comparison with the previous studies is performed. Optical strong coupling between excitons and confined photons within the microcavity is demonstrated from the anticrossing of exciton and photon modes. Angle-resolved transmission measurements give a Rabi-splitting energy of ~190meV for the upper and lower polariton splitting. The fabrication of such a simple metal–mirror–based microcavity (Q–factor ~13) leads to a progress of polaritonic characterization of organic media.

Highly stabilized perovskite solar cell prepared using vacuum deposition

With proper optimization, high efficiency solar cells are fabricated with the perovskite layers prepared using a one-step solution process and vacuum deposition methods and the devices prepared by vacuum deposition show significantly better ambient and thermal stability.

Optical and Electrical Properties of TTF-MPcs (M = Cu, Zn) Interfaces for Optoelectronic Applications.

Sandwich structures were fabricated by a vacuum deposition method using MPc (M = Cu, Zn), with a Tetrathiafulvalene (TTF) derivative, and Indium Tin Oxide (ITO) and aluminum electrodes. The structure and morphology of the deposited films were studied by IR spectroscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The absorption spectra of TTF derivative-MPc (M = Cu, Zn) thin films deposited at room temperature were recorded in the spectral range 200–1000 nm. The optical band gap of the thin films was determined from the (αhν)1/2 vs. hν plot. The direct-current (DC) electrical properties of the glass/ITO/TTFderiv-MPc (M = Cu, Zn)/Al structures were also investigated. Changes in conductivity of the derivative-TTF-enriched Pc compounds suggest the formation of alternative paths for carrier conduction. At low voltages, forward current density obeys an ohmic I-V relationship; at higher voltages, conduction is mostly due to a space-charge-limited conduction (SCLC) mechanism.

Thermal Design of a Thermoelectric Micro-Generator

In this study, we fabricated micro thermoelectric power generator using freestanding film substrate, and we evaluated the performance of the generator from the standpoint of thermoelectric performance and thermal design. We fabricated a SiNx free-standing film substrate about 5 μm thick on Si wafer, using MEMS processes. Then, we prepared for both p and n type of bismuth telluride thermoelectric thin films by using a coaxial type vacuum arc evaporation method, and annealed for one hour at 573 K. As an electrode, Cu was deposited using a vacuum deposition method. We fabricated the thermoelectric power generator of 5 mm × 5 mm using a shadow mask for the patterning. The fabricated generator can create temperature difference of 22.3 K due to its high thermal resistance of the structure when the heat source temperature is 373 K. The exergy of the thermoelectric device is up to 7%. Therefore, the generator can convert about 0.4% of thermal energy into electric energy, even though the material performance is low with ZT = 0.28. The conversion efficiency is much higher than that of the conventional Π type thermoelectric module. It was possible to get higher performance by the thermal design, which is a more simple way than an improvement of ZT.

Photovoltaic devices employing vacuum-deposited perovskite layers

Abstract

Mechanism of the dissolution of As–S chalcogenide glass in n-butylamine and its influence on the structure of spin coated layers

Chalcogenide glass thin layers are useful to many practical applications especially for the fabrication of infrared (IR) optical elements. In comparison to the conventional vacuum deposition methods of their preparation, recently chemical methods such as spin coating are gaining attention. They involve dissolution of the source bulk glass in appropriate solvent and then depositing its thin layer. Chemical processes occurring during the glass dissolution and thin layer deposition determine the physico-chemical properties of deposited thin layers. The structure of chalcogenide bulk glasses (AsxS100−x, where 30≤×≤40) and their solutions in n-butylamine have been studied in this work by Raman spectroscopy. From the composition and time dependence of Raman spectra of solutions the mechanism of arsenic–sulfur glass dissolution involving the reaction of aliphatic amine solvent with homopolar SS bonds is proposed and the presence of alkyl ammonium arsenic sulfide salts in thin layers is established.

A new method for fabricating ultrathin metal films as scratch-resistant flexible transparent electrodes

Metals are favorable candidates for flexible transparent electrodes because they have high electrical conductivity and good ductility. Theoretically, ultrathin metal films can present low sheet resistance and high transmittance simultaneously. However, due to Ostwald ripening many metal films (e.g., Ag) tend to form in island growth mode, leading to isolated metal islands and non-conducting feature until the films become relatively opaque. Here we present a new vacuum deposition method that can effectively suppress the Ostwald ripening in metal films, which become conducting at a thickness much smaller than the percolation threshold. The conducting and transparent metal films are smooth and scratch-resistant, and are stretchable by forming distributed ruptures upon stretching. This work presents a new and versatile strategy to fabricate scratch-resistant flexible transparent electrodes.

Properties of double-layer Al2O3/TiO2 antireflection coatings by liquid phase deposition

In this investigation, Al2O3/TiO2 double-layer antireflection coatings were deposited on polished silicon substrate by using liquid phase deposition. The deposition solution of ammonium hexafluoro-titanate and boric acid was used for TiO2 deposition. Aluminum sulfate and sodium bicarbonate were used for Al2O3 deposition. The concentration of the sodium bicarbonate and boric acid in the deposition solution controls the rate of deposition of Al2O3 and TiO2 films. Under optimal conditions, the average refractive index of liquid phase deposited Al2O3 and liquid phase deposited TiO2 films was 1.58 and 1.76, respectively. The average reflectance was 3.3% at wavelengths from 400 to 800nm for liquid phase deposited Al2O3 and liquid phase deposited TiO2 film thicknesses of 99 and 89nm, respectively. This antireflective property was comparable to other vacuum deposition methods, such as plasma-enhanced chemical vapor deposition and sputtering; thus, the liquid phase deposition of antireflection coatings was highly favorable for silicon-based solar cells.

Perovskite solar cells prepared by flash evaporation.

A simple vacuum deposition method for the preparation of high quality hybrid organic-inorganic methylammonium lead iodide perovskite thin films is reported. When sandwiched in between organic charge transporting layers, such films lead to solar cells with a power conversion efficiency of 12.2%.

Physical and Mechanical Research for Synthesis of Carbon Emocompatibly Coatings for Artificial Heart

To create an implant of the circulatory system using materials of different origin. The main requirements for such materials: rapid adaptation to the body and a long service life. Important characteristics are the hydrophobicity and surface roughness. Surface modification of materials by coating is the most common way to increase the functional properties. The study consisted in finding the perfect combination of the coating material and the technology of its application to the polyurethane product to increase its service life. In this study, we were applied two different methods of carbon coatings, which do not require heating of the polyurethane substrate: the method of laser deposition in a vacuum magnetron vacuum deposition method, and the pulverization of fine colloidal solution. Pulverization method applied to colloids with different powder: carbon nanotubes (CNT) and highly oriented pyrolytic graphite (HOPG), titanium oxide. Visualization of the surface produced on the optical, scanning electron and atomic force microscopy. Out of the samples, the most hydrophobic properties of the coated, fine colloidal solution HOPG caused by pulverization.

Plume propagation and Pt film growth during shadow-masked pulsed laser deposition in a buffer Ar gas

Shadow-masked pulsed laser deposition (SMPLD) enables the preparation of films that contain none of the droplets that are normally formed in laser irradiation of the target. The platinum (Pt) film produced by SMPLD was studied using scanning electron microscopy (SEM), atomic force microscopy (AFM), and Rutherford backscattering spectroscopy (RBS) of helium ions. The film thickness distribution across the substrate surface took the shape of a simple crater, and the film thickness on the crated “bottom” (center of the shadow area) was approximately 5 times less than that on the “mound” (edge of the shadow area). Monte Carlo collision (MCC) modeling of the laser plume movement during SMPLD was performed to clarify the role of the mask in the formation of the Pt films. The dynamics of the Pt atoms in the laser plume was studied using the vacuum deposition method through a narrow slit onto a rapidly displaced substrate, augmented by RBS measurements of the deposited film thickness along the substrate movement direction. The ionic flux was specifically measured using an ion probe. MСС simulation allowed the changes in the basic parameters of the deposited atom stream to be evaluated with the use of a mask. Comparison of the experimental and calculated distribution of the Pt film indicated that the best correlation was observed using the interpenetration model of the plume and buffer gas (argon, Ar) accompanied by elastic collisions of Pt atoms with the Ar atoms using the variable hard sphere model. Atomic flux models were utilized to imitate the growth of individual Pt crystals using the kinetic Monte Carlo method. In the SMPLD case, the root mean square roughness of the model crystal surface increased by ∼10% and the concentration of vacancies increased by ∼4% compared with the model crystal obtained by pulsed laser deposition (PLD). The surface topography of the experimental Pt films was defined by the nanocrystal nature of their structure. The use of a mask promoted the growth of relatively large nanocrystals and, thus, an increase in the surface roughness in AFM scans on the submicron scale.

Planar heterojunction perovskite solar cells with superior reproducibility.

Perovskite solar cells (PeSCs) have been considered one of the competitive next generation power sources. To date, light-to-electric conversion efficiencies have rapidly increased to over 10%, and further improvements are expected. However, the poor device reproducibility of PeSCs ascribed to their inhomogeneously covered film morphology has hindered their practical application. Here, we demonstrate high-performance PeSCs with superior reproducibility by introducing small amounts of N-cyclohexyl-2-pyrrolidone (CHP) as a morphology controller into N,N-dimethylformamide (DMF). As a result, highly homogeneous film morphology, similar to that achieved by vacuum-deposition methods, as well as a high PCE of 10% and an extremely small performance deviation within 0.14% were achieved. This study represents a method for realizing efficient and reproducible planar heterojunction (PHJ) PeSCs through morphology control, taking a major step forward in the low-cost and rapid production of PeSCs by solving one of the biggest problems of PHJ perovskite photovoltaic technology through a facile method.

Electrochemical Scanning Tunneling Microscopic Observations of Pt Nanostructures Prepared by Ultra-High Vacuum Deposition Methods

Background Carbon-supported Pt (Pt/C) is widely used as electrocatalysts for polymer electrolyte fuel cells (PEFC). However, in highly acidic environments under applying electro-potentials, e.g., PEFC operating conditions [1], catalytic activity of Pt/C is gradually degraded due to aggregation and dissolution of Pt nanoparticles as well as corrosion of carbon support. Therefore, electrochemical (EC) structural stability of Pt nanoparticles on carbon support is an important subject for practical application of the Pt/C catalyst. However, in-situ, real-time observation of degradation process of the practical Pt/C catalyst is generally difficult. In this study, we prepared two types of model nanostructures of Pt to investigate dynamic behavior in EC environments. One is Pt nanoparticles on highly-oriented pyrolytic graphite (HOPG) (Pt/HOPG) prepared by arc-plasma deposition (APD) method. Another is molecular beam epitaxially (MBE) grown Pt monolayer on Au(111) (Pt/Au(111)). In-situ observations for both Pt nanostructures by using electrochemical scanning tunnelling microscopy (EC-STM) are conducted under applying electro-potentials. Experimental Sample preparations: All samples were fabricated in ultra-high vacuum (UHV). Mass of Pt was estimated by a quartz microbalance installed in deposition chambers. (1)APD-Pt/HOPG：Pt nanoparticles were deposited by an arc-plasma gun on 773K-HOPG substrate at arc-voltage of 100V.(2)MBE-Pt1ML/Au(111)：1ML thick Pt epitaxial layer was formed on Au(111) at room temperature by MBE [2]. EC-STM observations: EC-STM observations were conducted in 0.1M HClO4. A tip (Pt-Ir) was approached to the sample surfaces at applying potential of Ework=+0.4V (vs. RHE). Then, the potential was increased up to +1.0V and then decreased back to +0.4V. EC-STM images were collected at fixed several voltages during the potential sweep. EC-STM observations were also conducted at +0.4V after applying potential cycles between +0.6V and + 1.2V. Applied potentials are presented with respected to RHE. Results and discussion Fig.1 shows EC-STM images for Pt nanoparticles (0.404μg/cm2) on HOPG recorded at specific voltages. At +0.4V (a), The Pt nanoparticles were highly oriented on HOPG. The Pt nanoparticles diffused on the substrate with increasing applied voltages, and at +1.0V (b), roughness in height increased relative to the image recorded at +0.4V, revealing that EC-oxidation of the Pt nanoparticles by the positive potential sweep. After negative potential swept from +1.0V to +0.4V (c), a mean particle size was slightly increased. The result suggests that reduction of the oxidized Pt nanoparticles formed by the +1.0V potential sweep correlates with aggregation of the Pt nanoparticles. Acknowledgement This work was supported by New Energy and Industrial Technology Development Organization (NEDO) of Japan.

Annealing-temperature effects on the properties of ZnO thin films and Pd/ZnO Schottky contacts grown on n-Si (1 0 0) substrates by vacuum deposition method

The effects of annealing temperature on the properties of ZnO thin films and Pd/ZnO thin film Schottky contacts grown on the n-silicon (n-Si) substrates by vacuum evaporation technique have been reported for the first time in this paper. The as-grown ZnO thin films were annealed in the Argon gas atmosphere for a same duration of 20min at 450°C, 550°C and 650°C temperatures. The surface morphology of the films analyzed by the scanning electron microscopy and X-ray diffraction spectroscopy are observed to be modified with annealing temperature. The photoluminescence and resistivity measurements were carried out to report the effects of annealing temperature on the optical and electrical properties of the vacuum deposited ZnO thin films. The Pd Schottky contacts grown on the annealed ZnO thin films at 550°C annealing temperature is observed to have the superior electrical characteristics over the Schottky contacts on ZnO films annealed at 450°C and 650°C temperatures.