Vacuum Deposition Techniques Research Articles

Electrical characterization of inorganic-organic hybrid photovoltaic devices based on silicon-poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)

Hybrid organic-inorganic photovoltaic devices based on nanostructured silicon and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hybrid devices present excellent light harvesting capabilities as well as a simple fabrication process. Unlike the metal/Si junction, PEDOT:PSS solution can be solution-casted onto the silicon surface structure to build up hybrid photovoltaic devices without using vacuum deposition techniques. Detailed electronic characterization at PEDOT:PSS/Si heterojunctions is indispensable for achieving a high-performance device. In this paper, the electronic properties of current-voltage, capacitance-voltage, and internal quantum efficiency are characterized in order to explore the organic-inorganic heterojunctions properties. The interfacial defect state density (Dit) of hybrid organic-inorganic photovoltaic devices as well as majority carrier charge transfer velocity (vn) has been extracted from the electrical measurement results. It has been found that less Dit and lower vn can lead to improved electric output characteristics of the organic-inorganic heterojunctions photovoltaic devices, which is ascribed to suppressed charge recombination at the organic-inorganic interface.

Transmission/absorption measurements for in situ monitoring of transparent conducting Ga:ZnO films grown via aqueous methods

In this work, we devised a simple optical technique that allowed the nucleation and growth of Ga:ZnO films grown via aqueous synthesis at 90 °C to be studied in situ. Our two fold objective was to study the nucleation processes and to acquire real-time information of the film thickness. In doing so, the growth parameters (e.g. temperature, precursor concentration, and time) could be optimized to give the maximum yield, coupled with the ability to control the film thickness with a greater measure of precision and accuracy. We further demonstrated that such a degree of control could be used to fabricate transparent conducting electrodes of low sheet resistance (<10 Ω sq−1) that meet the demands of photovoltaic applications. The electrical properties of the synthesized Ga:ZnO films and commercial Al:ZnO substrates showed comparable performance in dye-sensitized solar cells. This opened the possibility of a controlled low-cost aqueous route to fabricating high quality transparent conductor films that may well replace existing vacuum deposition techniques.

Development of a new qualification method for photocatalytically active surfaces based on a solid state luminescent dye

Abstract The authors present a new method for the qualification of photocatalytically “active” surfaces (e.g. TiO 2 coated glasses) comprising a solid-state luminescent dye, which is thoroughly characterized and investigated regarding its behavior on different manufactured photocatalytically active substrates versus inactive reference materials. The dye is an europium(III) complex showing the typical intense 5 D 0 → 7 F 2 transition with an emission wavelength maximum of 615 nm upon excitation at 350 nm. The dye is deposited as a thin-film reaching from 10 nm to 100 nm onto the substrates using an ultra-high vacuum (UHV) deposition technique. This system is excited with 20 W/m 2 at 365 nm with a LED and the luminescence is time-dependently monitored with a spectrofluorimeter. The dye's luminescence shows only a slight decrease on inactive substrates such as glass or silicon wafers, while showing a significant decay on photocatalytically active TiO 2 substrates. A possible mechanism for the luminescence decay is proposed. This direct method of luminescence degradation is highly sensitive and reproducible. It represents a promising option to be considered in standardization efforts in the field of photocatalysis.

Evolution of the structure and properties of solution-based Ge23Sb7S70 thin films during heat treatment

Optical devices such as waveguides and resonators have typically been produced through standard vacuum deposition and photolithography techniques. Solution-derived chalcogenide films are presented as an alternative for devices not easily fabricated through these standard techniques; however, many details of the chemical processes involved in film deposition are still unknown. We present a detailed analysis of the formation of Ge23Sb7S70 films from solution: solvent removal was studied using in situ FTIR and UV–visible absorption spectroscopies during heat treatments at various temperatures, and the glass structure and glass–solvent interactions were studied through analysis of the far- and mid-IR regions, respectively. Correlations have been established between atomic-level structural aspects and macroscopic physical properties such as refractive index, band gap energies, and surface roughness.

Growth and characterization of thin Cu-phthalocyanine films on MgO(001) layer for organic light-emitting diodes.

Surface morphology and thermal stability of Cu-phthalocyanine (CuPc) films grown on an epitaxially grown MgO(001) layer were investigated by using atomic force microscope and X-ray diffractometer. The (002) textured β phase of CuPc films were prepared at room temperature beyond the epitaxial MgO/Fe/MgO(001) buffer layer by the vacuum deposition technique. The CuPc structure remained stable even after post-annealing at 350°C for 1 h under vacuum, which is an important advantage of device fabrication. In order to improve the device performance, we investigated also current-voltage-luminescence characteristics for the new top-emitting organic light-emitting diodes with different thicknesses of CuPc layer.

Synthesis of lithium nitride for neutron production target of BNCT by in situ lithium deposition and ion implantation

To achieve high performance of BNCT (Boron Neutron Capture Therapy) device, Li3N/Li/Pd/Cu four layered Li target was designed and the structures of the synthesized four layered target were characterized by X-ray photoelectron spectroscopy. For the purpose of avoiding the radiation blistering and lithium evaporation, in situ vacuum deposition and nitridation techniques were established for in situ production and repairing maintenance of the lithium target.Following conclusions were derived:(1)Uniform lithium layer of a few hundreds nanometer was formed on Pd/Cu multilayer surface by in situ vacuum deposition technique using metallic lithium as a source material.(2)Lithium nitrides were formed by in situ nitridation reaction by the implantation of low-energy nitrogen ions on the deposited lithium layer surface. The chemical states of the nitridated zone were close to the stoichiometric lithium nitride, Li3N.(3)This nitridated zone formed on surface of four layered lithium target is stable for a long time in air condition. The in situ nitridation is effective to protect lithium target from degradation by unfavorable reactions.

Structural, optical and electrical characterization of Ag doped lead chalcogenide (PbSe) thin films

Research and development efforts are currently underway to fabricate a variety of solid state devices. A good deal of information regarding the synthesis, structural, optical and electrical properties of Ag doped lead chalcogenides have been revealed. The bulk polycrystalline (PbSe)100−xAgx ternary chalcogenides are prepared by diffusion technique. The XRD patterns recorded for the (PbSe)100−xAgx thin films prepared by vacuum deposition technique, show that these films are polycrystalline in nature. The optical measurements reveal that the (PbSe)100−xAgx thin films possess direct band gap and the band gap energy decreases with an increase of Ag concentration. The extinction coefficient (k) and refractive index (n) are found to be changing by increasing Ag concentration in PbSe. These results are interpreted in terms of the change in concentration of localized states due to the shift in Fermi level. The dc conductivities of (PbSe)100−xAgx thin films are measured in temperature range 303–403K. It is observed that the dc conductivity increases at all the temperatures with an increase of Ag content in PbSe system. The experimental data suggests that the conduction is due to thermally assisted tunneling of the charge carriers in the localized states near the band edges. The activation energy and optical band gap are found to decrease with increasing Ag concentration in lead chalcogenide and there are good agreements between these two values.

Non-linear optical properties of composite naphthalocyanine thin films with nanocrystalline morphology

Composite thin films of vanadyl naphthalocyanine and tin naphthalocyanine were prepared by the novel mixed and stacked vacuum deposition techniques. Crystalline peaks corresponding to both vanadyl naphthalocyanine and tin naphthalocyanine were detected and nanocrystals of sizes ranging from 2 to 5nm were observed in the film structure. The stacked deposited thin film showed a broad Q band absorption in the near infrared region (700–950nm) compared to the mixed deposited film. Open aperture Z-scan measurements revealed a saturable absorption behavior for both films and the saturation intensity, Isat, was calculated for each sample.

In-situ vacuum deposition technique of lithium on neutron production target for BNCT

For the purpose of avoiding the radiation blistering of the lithium target for neutron production in BNCT (Boron Neutron Capture Therapy) device, trilaminar Li target, of which palladium thin layer was inserted between cupper substrate and Li layer, was newly designed. In-situ vacuum deposition and electrolytic coating techniques were applied to validate the method of fabrication of the Li/Pd/Cu target, and the layered structures of the synthesized target were characterized. In-situ vacuum re-deposition technique was also established for repairing and maintenance for lithium target damaged. Following conclusions were derived;(1) Uniform lithium layers with the thickness from 1.6nm to a few hundreds nanometer were formed on Pd/Cu multilayer surface by in situ vacuum deposition technique using metallic lithium as a source material.(2) Re-deposition of lithium layer on Li surface can be achieved by in situ vacuum deposition technique.(3) Small amount of water and carbonate was observed on the top surface of Li. But the thickness of the adsorbed layer was less than monolayer, which will not affect the quality of the Li target.(4) The formation of Pd-Li alloy layer was observed at the Pd and Li interface. The alloy layer would contribute to the stability of the Li layer.

Low Vacuum Deposition of Aluminum Nitride Thin Films by Sputtering

Conventionally, sputtering deposition of thin films requires a low base pressure (high vacuum) to minimize influences of residual gases. Here, a high base pressure (low vacuum) was used, which can reduce significantly the overall processing time. Aluminum nitride ( AlN ) was selected as a model system of dielectric nitrides. All the analyses revealed that the obtained films under a low vacuum environment within specific processing windows exhibited characteristics similar to those of high‐vacuum made AlN films. Such a low vacuum deposition technique takes advantages of kinetically favorable formation of the nitride films and hence, has great potentials in many more technological applications.

Tunneling Effect in Polythiophene

AbstractPolythiophene has been chemically synthesized using 2,5– dibromothiophene by debromination with magnesium, catalyzed by nickel chloride. The synthesized polymer was undoped using liquid ammonia and then doped again using 5% (wt/volume) aqueous FeCl3 for 2.5, 5 and 10 hour duration. Characterization of undoped as well as doped samples using elemental analysis and FTIR has been carried out. Elemental analysis shows that concentration of Fe+ atoms increases as the duration of doping increases. The FTIR spectrum reveals the complex formation between FeCl3 and polythiophene. All samples were pressed into pellets of about 1cm in diameter. The pellets were coated with gold (Au) on one side and with aluminum (Al) on other side using vacuum deposition technique. I–V measurements of undoped and FeCl3 doped samples, after coating have been carried out using two probe method. I–V measurements, at room temperature, were carried out by applying d. c. voltage with +ve potential to the side of the pellet coated with Au and –ve potential to Al from 0 V to 1 V in step of 0.01 V and then from 1V to 15 V in step of 0.5 V. The measurements were again carried out after interchanging the polarity of the applied voltage. These characteristics are just similar to the characteristics of conventional tunnel diode in forward bias condition and like Schottky diode in reverse bias condition. Various parameters of tunnel diode such as figure of merit, voltage spread, noise figure etc are calculated using the measurements carried out. Noise figure value of undoped polythiophene is very close to ideal value. The performance of all FeCl3 doped sample reduces, however value of the current ratio Ip/Iv (figure of merit) value for 5 hr. FeCl3 doped polythiophene sample matches with that of silicon (Si) tunnel diode.

Fabrication and characterization of thin film ZnO Schottky contacts based UV photodetectors: A comparative study

The authors report on characterization of Pd/ZnO thin film Schottky contacts based UV photodetector fabricated by two methods. The ZnO film was grown on p-type Si ⟨100⟩ substrate by using vacuum thermal evaporation and sol-gel methods. With applied voltage in the range from −2 to +2 V we estimated the photocurrent, contrast ratio, responsivity, and quantum efficiency of the photodetectors for an incident optical power of 0.1 mW at 365 nm ultraviolet wavelength. The current–voltage characteristics were studied and the parameters such as ideality factor, leakage current, and barrier height of the Schottky contacts were extracted from the measured data. The surface morphology and the structural properties of the thin film were studied by atomic force microscope and scanning electron microscope. The bandgap of ZnO is evaluated from the absorbance spectra of ZnO thin film obtained by using double beam spectrophotometer. For the investigation of the surface chemical bonding, x-ray photoelectron spectroscopy measurements were also performed. The study revealed that sol-gel derived devices exhibit better photoresponse as compared to those using thin film deposited by vacuum deposition technique.

Direct simulation Monte Carlo modeling of metal vapor flows in application to thin film deposition

Thin films of metal for electronics, nano/microelectromechanical systems and optical coatings are often prepared by various vacuum deposition techniques. Modeling such metal vapor flows using methods such as the direct simulation Monte Carlo (DSMC) can aid in the design and analysis of deposition systems and accelerate development of films with desired properties. The determination of suitable variable hard sphere (VHS) molecular model parameters for DSMC simulations using measured growth rate distribution is demonstrated with aluminum vapor as an example. Axisymmetric DSMC simulations using a VHS model corresponding to a reference diameter of 0.8 nm and a viscosity-temperature exponent of 1 are shown to agree well with available experimental data. The model is then used in two-dimensional DSMC simulations to study the interaction of plumes from multiple sources. An expression for substrate mass flux assuming no interaction between sources agrees well with DSMC simulations for a mass flow rate of 0.1 g/min corresponding to a Knudsen number (Kn) of about 0.1. The non-additive interaction of plumes at a higher flow rate of 1 g/min corresponding to a Kn of about 0.01 results in a higher mass flux non-uniformity in the DSMC simulations which is not captured by the simplified analytical expression.

INFRARED SENSOR ON THE BASIS OF LEAD-TIN CHALCOGENIDE MULTICOMPONENT SOLID SOLUTIONS

The linear photovoltaic infrared sensor arrays have been formed on the basis of -layer//(KCl, )/Al(Pb) and Pb/ -layer/ barrier-surface structures, which were obtained by the liquid phase epitaxy and thermal vacuum deposition techniques. At the80 170170 K, peak wavelength 8 12,2 and cutoff wavelength 8,3 12,8 they had the zero bias resistance area product = 0,18 2,72 , peak quantum efficiency =0,28 0,52 and peak detectivity (0,61 4,51) 1010 cm·

Novel nanostructured biomaterials: implications for coronary stent thrombosis

BackgroundNanomedicine has the potential to revolutionize medicine and help clinicians to treat cardiovascular disease through the improvement of stents. Advanced nanomaterials and tools for monitoring cell–material interactions will aid in inhibiting stent thrombosis. Although titanium boron nitride (TiBN), titanium diboride, and carbon nanotube (CNT) thin films are emerging materials in the biomaterial field, the effect of their surface properties on platelet adhesion is relatively unexplored.Objective and methodsIn this study, novel nanomaterials made of amorphous carbon, CNTs, titanium diboride, and TiBN were grown by vacuum deposition techniques to assess their role as potential stent coatings. Platelet response towards the nanostructured surfaces of the samples was analyzed in line with their physicochemical properties. As the stent skeleton is formed mainly of stainless steel, this material was used as reference material. Platelet adhesion studies were carried out by atomic force microscopy and scanning electron microscopy observations. A cell viability study was performed to assess the cytocompatibility of all thin film groups for 24 hours with a standard immortalized cell line.ResultsThe nanotopographic features of material surface, stoichiometry, and wetting properties were found to be significant factors in dictating platelet behavior and cell viability. The TiBN films with higher nitrogen contents were less thrombogenic compared with the biased carbon films and control. The carbon hybridization in carbon films and hydrophilicity, which were strongly dependent on the deposition process and its parameters, affected the thrombogenicity potential. The hydrophobic CNT materials with high nanoroughness exhibited less hemocompatibility in comparison with the other classes of materials. All the thin film groups exhibited good cytocompatibility, with the surface roughness and surface free energy influencing the viability of cells.

Reactivity classification in saline solution of magnetron sputtered or EBPVD pure metallic, nitride and Al-based alloy coatings

In this study, various metallic or nitride coatings elaborated by Electron Beam Physical Vapour Deposition (EBPVD) or magnetron sputtering techniques are characterised in terms of mechanical properties and corrosion behaviour in saline solution. The incorporation of transition metals permits to modify the mechanical or physico-chemical characteristics of aluminium coatings, so several alloying elements are compared. These alloys are also compared with pure metallic coatings and/or coatings synthesized by reactive magnetron sputtering. Evolution of microstructure of the Al based coatings was discussed versus the alloying element content. Different compositions of alloys were examined. This paper presents the synthesis of the main tendency reported during the evaluation of the mechanical and corrosion properties of these alloys.The objective is to build a reactivity classification in saline solution of several Al based coatings synthesized by vacuum deposition techniques. Combined with the classification of mechanical properties, these standards would become relevant guides in the choice of PVD coatings and/or alloys for applications exposed to saline environments. In our study, this guide is helpful in the synthesis of nanometric multilayer architectures, which proves to be a promising way to combine improved mechanical properties with sacrificial character for the future coating configurations.

Low cost CuInSe 2 thin films production by stacked elemental layers process for large area fabrication of solar cell application

Low cost deposition of large area CuInSe 2 (CIS) thin films have been grown on Mo-coated glass substrate by simple and economic stacked elemental layer deposition technique in vacuum. The grown parameters such as concentration of Cu, In and Se elements have been optimized to achieve uniform thin film in vacuum chamber. The as-grown Cu/In/Se stacked layers have been annealed at 200 °C and 350 °C for 1 h in air ambient. The as-grown and annealed films have been further subjected to characterization by X-ray diffraction (XRD), optical absorption, atomic force microscopy (AFM) and I– V measurement techniques. XRD patterns revealed that as-grown Cu/In/Se stacked layers represent amorphous nature while annealed CIS film reproduces nano-polycrystalline nature with chalcopyrite structure. The optical band gap of annealed films increases with respect to air annealing which confirms the reduction of crystallite size. Surface morphology of as-grown Cu/In/Se stacked layers and annealed CIS thin films have been confirmed by AFM images. The electrical measurements show enhancement of conductivity which is useful for solar cell application.

Atomic Layer Deposition of CdS Quantum Dots for Solid‐State Quantum Dot Sensitized Solar Cells

AbstractFunctioning quantum dot (QD) sensitized solar cells have been fabricated using the vacuum deposition technique atomic layer deposition (ALD). Utilizing the incubation period of CdS growth by ALD on TiO2, we are able to grow QDs of adjustable size which act as sensitizers for solid‐state QD‐sensitized solar cells (ssQDSSC). The size of QDs, studied with transmission electron microscopy (TEM), varied with the number of ALD cycles from 1‐10 nm. Photovoltaic devices with the QDs were fabricated and characterized using a ssQDSSC device architecture with 2,2',7,7'‐tetrakis‐(N,N‐di‐p methoxyphenylamine) 9,9'‐spirobifluorene (spiro‐OMeTAD) as the solid‐state hole conductor. The ALD approach described here can be applied to fabrication of quantum‐confined structures for a variety of applications, including solar electricity and solar fuels. Because ALD provides the ability to deposit many materials in very high aspect ratio substrates, this work introduces a strategy by which material and optical properties of QD sensitizers may be adjusted not only by the size of the particles but also in the future by the composition.

A Self-Defined Hollow Needle Formation on Silicon Membranes with the Aids of Carbon Nanotubes

A self-defined method for the formation of hollow needles and micro-cylindrical structures on silicon substrates is reported which uses the combination of high aspect ratio vertical etching of silicon with a small angle vacuum deposition technique. These structures can be used as the media to transfer gas and liquid through their tiny holes. The fabrication is further continued with the growth of carbon nanotubes on the already created silicon-based features to form a cage-like cylindrical structure. In addition, the growth of vertical carbon nanotubes just inside the cup-like structures has been demonstrated without a need for an extra lithography step.

An integrated enzyme‐linked immunosorbent assay system with an organic light‐emitting diode and a charge‐coupled device for fluorescence detection

A fluorescence detection system for a microfluidic device using an organic light-emitting diode (OLED) as the excitation light source and a charge-coupled device (CCD) as the photo detector was developed. The OLED was fabricated on a glass plate by photolithography and a vacuum deposition technique. The OLED produced a green luminescence with a peak emission at 512 nm and a half bandwidth of 55 nm. The maximum external quantum efficiency of the OLED was 7.2%. The emission intensity of the OLED at 10 mA/cm(2) was 13 μW (1.7 mW/cm(2)). The fluorescence detection system consisted of the OLED device, two band-pass filters, a five microchannel poly(dimethylsiloxane) (PDMS) microfluidic device and a linear CCD. The fluorescence detection system was successfully used in a flow-based enzyme-linked immunosorbent assay on a PDMS microfluidic device for the rapid determination of immunoglobulin A (IgA), a marker for human stress. The detection limit (S/N=3) for IgA was 16.5 ng/mL, and the sensitivity was sufficient for evaluating stress. Compared with the conventional 96-well microtiter plate assay, the analysis time and the amounts of reagent and sample solutions could all be reduced.