Surface Pinholes Research Articles

Electrical and Optical Characterization of R.F.-Sputtered CdTe Thin Films

Four sets of R.F.-sputtered CdS/CdTe thin-film solar cells are activated through comparable treatment procedures. Two samples were rinsed into deionized water for an hour before $\hbox{CdCl}_{2}$ treatment and then activated in Ar or air ambient. The two others are normally treated and activated in Ar and air, respectively. The influence of water rinsing and annealing ambient on the electrical and optical properties of the films is investigated by current–voltage, field-emission scanning electron microscope, X-ray diffraction, and optical transmission spectroscopy. We examined water rinsing as a cheap and simple pretreatment step to modify the semiconductor surface and to obtain quality device. In this way, the fill factor of the cells that were rinsed into water before $\hbox{CdCl}_{2}$ activation was comparable with the one prepared without rinsing. There is a challenge between the effect of water and Ar on the electrical parameters of the cells. Water-rinsed cells annealed in Ar showed better properties than those that received no water rinsing. It seems that water reduces the negative effect of Ar annealing or parasitic diffusion of Cu into the semiconductor. The higher shunt resistance of the rinsed samples represents that water rinsing could passivate the surface defects and pinholes. The grain size, phase, and band gap of the thin films are extracted, analyzed, and compared with the as-deposited devices.

Impact of the coating process on the molecular structure of starch‐based barrier coatings

ABSTRACTMolecular analysis of starch structure can be used to explain and predict changes in physical properties, such as water vapor and oxygen barrier properties in packaging materials. Solution casting is a widely used technique to create films from starch formulations. This study compared the molecular properties of these standard films with those of experimental coatings applied to paper in laboratory‐scale and pilot‐scale trials, with all three techniques using the same starch formulation. The results revealed large differences in molecular structure, i.e., cross‐linking and hydrolysis, between films and coatings. The main differences were due to the shorter drying time allowed to laboratory‐scale coatings and the accelerated drying process in pilot trials owing to the high energy output of infrared dryers. Furthermore, surface morphology was highly affected by the coating technique used, with a rougher surface and many pinholes occurring in pilot‐scale coatings, giving lower water vapor permeability than laboratory‐scale coatings. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41190.

Control of Surface Graphite Degeneration in Ductile Iron for Windmill Applications

The objective of this paper is to review the factors influencing the formation of degenerated graphite layers on the surfaces of ductile iron castings for chemical resin-acid moulding and coremaking systems and how to reduce this defect. In the resin mould technique the sulphur in the P-toluol sulphonic acid (PTSA), usually used as a hardener, has been identified as one factor causing graphite degeneration at the metal mould interface. Less than 0.15% S in the mould (or even less than 0.07% S) can reduce the surface layer depth. Oxygen may also have an effect, especially for sulphur containing systems with turbulent flows in the mould, water-bearing no-bake binder systems, Mg-Silica reactions, or dross formation conditions. Despite the lower level of nitrogen in the iron melt after magnesium treatment (less than 90 ppm), nitrogen bearing resins have a profound effect on the frequency and severity of surface pinholes, but a limited influence on surface graphite degeneration. The specific characteristics and optimum conditions for the manufacture of heavy sectioned ductile iron windmill castings were reviewed. The paper concludes on the optimum iron chemistry, melting procedure, Mg-alloys and specific inoculants systems, as well as the practical solutions to limit graphite degeneration to ensure castings with the highest integrity.

팔라듐 합금 수소 분리막의 전처리에 관한 연구

A Pd-based hydrogen membranes for hydrogen purification and separation need high hydrogen perm-selectivity. The surface roughness of the support is important to coat the pinholes free and thin-film membrane over it. Also, The pinholes drastically decreased the hydrogen perm-selectivity of the Pd-based composite membrane. In order to remove the pinholes, we introduced various surface pre-treatment such as alumina powder packing, nickel electro-plating and micro-polishing pre-treatment. Especially, the micro-polishing pretreatment was very effective in roughness leveling off the surface of the porous nickel support, and it almost completely plugged the pores. Fine Ni particles filled surface pinholes with could form open structure at the interface of Pd alloy coating and Ni support by their diffusion to the membrane and resintering. In this study, a surface pore-free Pd-Cu-Ni ternary alloy membrane on a porous nickel substrate was successfully prepared by micro-polishing, high temperature sputtering and Cu-reflow process. And permeation and leak tests showed that the Pd-Cu-Ni ternary alloy hydrogen membrane achieved both high permeability of permation flux and infinite selectivity.

A poly(styrene-co-methyl methacrylate)/room-temperature sputtered hafnium oxide bi-layer dielectrics as gate insulator for a low voltage organic thin-film transistors

In this study, we present a low voltage pentacene organic thin film transistor (OTFT) with poly(styrene-co-methyl methacrylate) grafted hafnium oxide (PS-r-PMMA/HfO x ) as gate dielectrics. The HfO x was sputtered at room temperature to approach low temperature and meet low cost requirements of organic electronics. The thickness of the PS-r-PMMA can be controlled to be extremely thin (<10 nm). Consequently, the gate overdriving voltage as low as 3 V was achieved for an OTFT. Furthermore, by applying PS-r-PMMA on top of the HfO x surface, the traps on the HfO x surface and possible pinholes of the HfO x can be passivated. Therefore, the gate dielectric properties in terms of interface states and leakage current were improved. The leakage current reduced to approximately two orders of magnitude and the interface states reduced to nearly one order of magnitude. The reduction of the interface state density was observed by capacitance–voltage measurement. As a result, the subthreshold swing and on/off current ratio were improved significantly from 1.01 V/dec. and 10 3 to 0.41 V/dec. and 10 5, respectively.

Biodegradable Microcapsules: Optimization of Formulation Using Factorial Design

Biodegradable microcapsules of zidovudine (AZT) were prepared using a solvent evaporation technique. The experimental protocol was based on a 4 times 3 factorial design. The effect of volatile organic solvent was examined at four levels: 100/0, 90/10, 80/20, and 70/30 mixtures of dichloromethane with methanol. Poly(lactide/glycolide) copolymer (PLGA 50:50) was used at three levels: 50, 100, and 200 mg mL−1 The efficiency of encapsulation significantly increased with increasing polymer concentration. The four levels of the organic solvent showed no significant effect on the encapsulation. A comparison of the SEM photographs of the twelve batches of the microcapsules showed that the formation of surface pinholes could be avoided by increasing the concentration of the polymer. Higher methanol concentrations (>10%) in the dichloromethane/methanol mixture also significantly changed the surface morphology. No significant rank order correlation was observed between the median particle sizes of the different batches of the microcapsules and the organic solvent or the amount of PLGA. The median particle sizes were between 33 and 193 μm. Particle size ranges were between 0.5 and 600 μm. The initial drug release was between 15 and 50% during the first day with a sustained release observed up to 60 days.

Study of the leakage current mechanism in Schottky contacts to Al0.25Ga0.75N/GaN heterostructures with AlN interlayers

The leakage current mechanism in Schottky contacts (SCs) to Al0.25Ga0.75N/GaN heterostructures incorporated by a thin high-temperature (HT) AlN interlayer has been investigated using current–voltage measurements, atomic force microscopy and deep level transient spectroscopy. It is found that the HT AlN interlayer thickness has a significant effect on the leakage current in SCs. The leakage current density decreases to 1.1 × 10−4 A cm−2 when the growth time of the AlN interlayer increases from 0 to 10 s, and then changes to increase with increasing growth time. Correspondingly, the heterostructure with the AlN growth time of 10 s has the least number of surface pinholes. The thickness of the HT AlN also influences the density of electron traps with the activation energy of 0.762 eV in an Al0.25Ga0.75N barrier. It is suggested that the HT AlN interlayer adjusts the microstructure and the defect state density in the Al1−xGaxN barrier, and the leakage via these defect states makes the main contribution to the leakage current in SCs to Al1−xGaxN/GaN heterostructures.

Surface Graphite Degeneration in Ductile Iron Castings for Resin Molds

The objective of this paper is to review the factors influencing the formation of degenerated graphite layers on the surfaces of ductile iron castings for chemical resins-acid molding and core-making systems and how to reduce this defect. In the resin mold technique the sulphur in the P-toluol sulphonic acid (PTSA), usually used as the hardener, has been identified as one factor causing graphite degeneration at the metal-mold interface. Less than 0.15% S in the mold (or even less than 0.07% S) can reduce the surface layer depth. Oxygen may also have an effect, especially for sulphur containing systems with turbulent flows in the mold, water-bearing no-bake binder systems, Mg-Silica reactions, or dross formation conditions. Despite the lower level of nitrogen in the iron melt after magnesium treatment (less than 90 ppm), nitrogen bearing resins have a profound effect on the frequency and severity of surface pinholes, but a limited influence on surface graphite degeneration.

Current Understanding on Starch Granule Structures

Starch is synthesized in semi-crystalline granular structures. Starches of different botanical origins possess different granular sizes, morphology, polymorphism and enzyme digestibility. These characteristics are related to the chemical structures of the amylopectin and amylose and how they are arranged in the starch granule. In this paper, structures and locations of amylose and amylopectin molecules in the granule are reviewed. The branch structures of amylopectin molecules and their relationship with the polymorphism, structures, and morphology of the starch granules are discussed. Internal structures of starch granules revealed by confocal laser-scattering microscopy and by using a surface-gelatinization method are compared and their effects on surface pinholes and serpentine channels of the starch granules are discussed.

Mould pressure control in rotational moulding

The technology of the rotational moulding of plastics has improved dramatically in recent years due to the recognition that measuring the temperature inside the mould is fundamental to process control. The next major advance will be made when the benefits of controlling the pressure inside the mould are fully utilized. A drawback of the rotational moulding process has always been the surface pinholes and internal bubbles that occur in the moulded part. These occur because, as the powder particles melt and coalesce, they trap pockets of air and it takes a considerable time for these to disappear. It is known that factors such as the viscosity of the polymer melt, the shape of the powder particles, the particle size and size distribution, the mould release agent and the metal used for the mould all affect the pinholing problem. However, the major factor that influences pinhole removal is mould pressure. If pressure is applied at a strategic point in the heating cycle, it can force trapped air out of the melted plastic. Indeed the use of mould pressurization can offer additional benefits such as cycle time reduction and significant improvements in the mechanical properties of the moulded part. However, few moulders make any attempt to monitor or control the mould pressure, mainly because its effect is not understood. This paper explains why mould pressure control throughout the moulding cycle is crucial to the rotational moulding industry in terms of, firstly, achieving good part quality and, secondly, reducing cycle times. It is also suggested that a fundamental change from passive venting to active venting of the mould is an important development that must occur in this industry.

Breakaway bubble growth during the annealing of helium bubbles in metals

Recent experimental studies on the annealing of helium implanted copper showed unusual surface pinholes which could not be explained using conventional bubble migration and coalescence theory. However, computer simulation results indicated that at some threshold, breakaway bubble swelling was taking place, thus giving a plausible picture of the experimental results. In the present study the computer simulations have been repeated for an initially uniform helium level in bulk material, allowing the threshold effects to be examined without any surface effects and any loss of helium. Assuming equilibrium bubble conditions, the results showed that when bubble coarsening reached an average of 20% swelling, breakaway swelling occurred. This phenomenon has been examined as a function of helium content and results extrapolated (with some assumptions) to other temperatures and metals. The implications for fusion reactor materials is briefly discussed.

A correlation study between the conformation of the 1,4-dithiane SAM on gold and its performance to assess the heterogeneous electron-transfer reactions

A gold electrode spontaneously modified by 1,4-dithiane (1,4-dt) organosulfur species has been characterized by cyclic voltammetry of [Fe(CN) 6] 3−/4− and cytochrome c (cyt c) probe molecules, SERS (surface-enhanced Raman scattering), and EIS (electrochemical impedance spectroscopy), using [Fe(CN) 6] 3−/4− as the redox-active molecule in solution. The cyclic voltammograms showed a decrease in the faradaic current response with an increase of the immersion time of the gold substrate into the 1,4-dt modifier solution, suggesting that the heterogeneous electron-transfer (hET) process of the [Fe(CN) 6] 3−/4− probe molecule occurs through the surface pinholes. This observation is an indication that the 1,4-dt chemisorption mechanism must involve a slow step that is responsible for the final configuration of the modifier molecules on the surface. The SERS spectra acquired for the surface as a function of immersion time of the gold electrode in the modifier solution presented an intensity enhancement of the bands assigned to the trans and gauche conformation of the 1,4-dt on the surface. The apparent rate constant, k app, estimated by the EIS results, decreases with increase of the immersion time indicating that the pinholes on the surface act as a microarray. This result is consistent with those observed by cyclic voltammetry of the probe molecules, i.e., the pinhole density decreases with increase of the immersion time of the gold electrode in the 1,4-dt modifier solution, and a strong attenuation of the probe molecules interfacial electron-transfer response is observed.

Multilayer Structures with Giant Magnetoresistance

The phenomenological description of the giant magnetoresistance effect as well as the discussion of the requirements which must be fulfilled in giant magnetoresistance thin film structures are given in the first part of our review. In the second part the magnetization reversal and giant magnetoresistance effect of antiferromagnetically coupled multilayers, spin valve and pseudo-spin valve thin film structures are explained. For these structures we also discuss the influence of the structure defects such as surface roughness and pinholes on the giant magnetoresistance effect.

Inhomogeneous incorporation of In and Al in molecular beam epitaxial AlInGaN films

Plasma-induced molecular beam epitaxial AlInGaN heterostructures have been characterized by spatial resolved cathodoluminescence and x-ray energy dispersive microanalysis. Competitive incorporation of Al and In has been observed, with the formation of In-rich regions, showing enhanced luminescence around surface pinholes. These island-like In-rich regions are favored by growth at lower temperature due to the higher incorporation of indium into the alloy. The elastic strain relaxation associated to pinhole formation induces preferential local indium incorporation. The diffusion of carriers to these areas with reduced band gap enhances the luminescence emission of the quaternary film. The width and intensity of the luminescence appear to be sensitive to the mismatch between the quaternary film and the GaN layer below.

Optimisation of bubble size in qc rotationally moulded parts

Rotational moulding is one of the most important methods of manufacture of hollow plastic products. However, there are several unsolved problems that confound the overall success of this technique, including surface pin holes and internal bubbles of moulded parts, caused by inappropriate mould design and processing conditions. In this report, an L′18 experimental matrix design based on the Taguchi method was conducted to optimise the bubble size of rotationally moulded parts. Experiments were carried out on a laboratory scale biaxial rotation moulding unit. The polymeric material used to mould the parts was linear low density polyethylene. After moulding, the size of the bubbles on the surface of moulded parts was characterised by an image analysis system. For the factors selected in the main experiments, the cooling conditions and the particle size of the material were found to be the principal factors affecting the bubble size of rotationally moulded thermoplastics. In addition, mould pressurisation helped decrease the size of the bubbles. The bubble size of moulded parts was not affected by the water content of the polymeric powder, but increased with the viscosity of the materials.

Local nucleation and lateral crystallization of silicide cobalt phases at interaction of cobalt film with silicon surface

The phenomena of local nucleation and lateral crystal growth of cobalt silicide phases have been investigated with emphasis on a possible reason of the surface roughness and pinholes of the silicide layer. Local nucleation of the CoSi 2 grains on the structural defects of the silicon surface is found for the silicide films formed by vacuum annealing the Co/Si(100),(111) structures. Self-sustaining crystallization of CoSi 2 phase around a crystal defect is observed. Lateral growth of the silicide crystallites from the Si crystal defects, on the Co-patterned step edge and SiO 2 island steps, indicate that the lateral growth mode is preferable for the silicide phases at Co/Si interface. The silicide film surface and CoSi 2/Si interface are much smoother if an additional zircon (Zr) layer is deposited onto the Co film before subsequent annealing. The CoSi 2 films were used as a buffer layer for the YBCO/CoSi 2/Si and YBCO/CeO 2/YSZ/CoSi 2/Si/Al 2O 3 heterostructures in this work. The superconducting transition temperatures of the YBCO films were obtained to be up to 86 K.

Triple-chain phospholipid monolayers: a scanning force microscopy and grazing incidence X-ray diffraction study

Two triple-chain and one double-chain phospholipid monolayers have been characterised both on water and on different solid substrates by grazing incidence X-ray diffraction and scanning force microscopy. The formation of holes could be observed on water and on a solid support. SFM in contact and tapping mode has revealed surface defects and pinholes in the submicrometer range of all phospholipid films transferred at room temperature on hydrophobic (glass) and hydrophilic (mica) substrates both horizontally and vertically. The double-chain lipids exhibit only a few defects after the transfer, whereas the triple-chain lipids show more and larger holes in the monolayer. SFM contact mode enables the formation of artificial holes in the monolayer on mica in order to estimate the real thickness of the transferred layer. Surprisingly, for all substances investigated the height of the monolayer is too small compared to the length of the molecules. Phospholipids provide suitable model systems for biological membranes. Therefore they have traditionally been used for studying the competitive interaction between polar hydrophilic head groups and hydrophobic chains connected to the glycerol backbone [1–4]. With synchrotron grazing incidence X-ray diffraction (GIXD) measurements one can study the structure of condensed monolayers on the A-scale in considerable detail [5]. In the case of glycerophosphocholines substituted with 2-alkyl branched fatty acids containing long branches, these measurements have shown that the packing of the molecules in monolayers is determined by the space requirements of the chains [6]. However, for glycerophosphoethanolamines (PE) which are able to form a hydrogen bonding network between adjacent head groups there remain many open questions about the influence of lateral disturbances on the phase behaviour in monolayers and multilayers. Therefore, we have investigated double-chain and triple-chain PEs. Over the last few years, it has been shown that scanning force microscopy is a powerful tool for investigating a large variety of materials with high spatial resolution [7–10]. Morphological information, such as topographic features of monolayers and multilayers, height of structures, step sites and also friction and elastic compliance in the local regions have been shown. There have been several SFM and AFM/LFM studies of self-assembled phospholipid layers [11], but until now only very few AFM images on phospholipid monolayers or bilayers have been published [12, 13]. Moreover, it is known that there is a reorganisation of lipid films after the transfer in air [14]. This reorganisation is faster for molecules having short hydrocarbon chains, such as cadmium palmitate, than for longer-chain molecules [15]. The observation and characterisation of microstructures of organic thin films, such as monolayers and multilayers of phospholipids on solid substrates, are of particular importance for further practical application of the organic films as a matrix for functional organics or biomolecules in biosensors and biochemical probes. The aim of the current research is to characterise doubleand triple-chain phospholipids on water and on a solid support using the combination of SFM/LFM and GIXD. 1 Experimental details 1.1 Monolayer preparation The triple-chain phospholipids 1(2-hexadecylstearoyl)-2hexadecyl-glycerophosphoethanolamine 1(2C16-18:0)-2HPE (I) and 1(2-hexadecylstearoyl)-2-hexadecyl-glycerophospho-N-methylethanolamine 1(2C16-18:0)-2H-NMe (II) were synthesised according to [16]. The corresponding chemical structures are presented in Figures 1a and 1b. The lipids were purified by column chromatography. High-performance liquid chromatography (HPLC) and electron mass spectroscopy have been used for analytical characterisation. All lipids were spread from an approximately 1 mM p.a.-grade chloroform (Merck, FRG) solution. The preparation of the Langmuir–Blodgett films was performed using a circular trough with a subphase temperature of 20 ◦C. The subphase was ultrapure water (pH 5.5) with a specific resistance above

Local nucleation and lateral crystallization of the silicide phases in the CoSi 2 buffer layer of YBa 2Cu 3O 7− x/CoSi 2/Si structure

The phenomena of the local nucleation and lateral crystal growth of cobalt silicide phases have been investigated with the emphasis on a possible cause of the surface roughness and pinholes of the silicide layer. Local nucleation of the CoSi 2 grains on the structural defects of the silicon surface is found for the silicide films formed by vacuum annealing the Co/Si(100),(111) structure. Self-sustaining crystallization of the CoSi 2 phase around a crystal defect is observed. Lateral growth of the silicide crystallites from the Si crystal defects indicates that the lateral growth mode is preferable for the silicide phases at the CoSi interface. The silicide film surface and CoSi 2/Si interface are much smoother if an additional zircon (Zr) layer is deposited onto the Co film before subsequent annealing. The CoSi 2 films were used as a buffer layer for the YBCO/CoSi 2/Si and YBCO/CeO 2/YSZ/CoSi 2/Si/Al 2O 3 heterostructures in this work. The superconducting transition temperatures of the YBCO films was found to be 86 K.

Removal of Pinholes and Bubbles from Rotationally Moulded Products

The rotational moulding processing method for plastics is steadily expanding its product range and market areas. However, a drawback of the process has always been the surface pinholes and internal bubbles which occur in the products due to the inherent nature of the process. In an attempt to alleviate this problem, a programme of research has been carried out to investigate the factors that affect the formation of the bubbles and more importantly influence their removal. This paper describes how bubbles in rotationally moulded products can be removed by pressurizing the inner atmosphere of the mould. It has been shown that bubbles were successfully removed from MDPE (medium density polyethylene) by introducing a low pressure (0.5 bar) inside the mould after the polymer had melted. The removal of bubbles using pressure was shown to increase the impact properties (25 per cent) and the tensile properties (5 per cent) of the moulding while also reducing the cycle time. Pressure was successfully used to remove bubbles from other rotational moulding materials, such as polypropylene, Nylon 12, polycarbonate, ethylene vinyl acetate and ethylene butyl acetate.