Surface roughness and electrical conductivity of the SnO2 ultra‐thin layers investigated by X‐ray reflectivity

Spray pyrolysis technique was applied to deposit two sets of ultra‐thin layers of tin dioxide (SnO₂). For the first and second sets, 0.01 and 0.05 molar precursor solutions were prepared, respectively. In both sets, utilizing the X‐ray reflectivity (XRR) technique, the effect of precursor concentration (PC) and precursor volume (PV) on the layer structure are investigated. The layer thickness of the samples, in each set, is a PV‐dependent parameter. For the same PV, samples with higher PC have a larger thickness and higher density. The electron density profiles deduced from XRR data analyses establish a link between measured values of sheet resistance and electron densities. The samples with higher PV and PC show less sheet resistance. The quantum size effect was utilized to show that the surface roughness for layers of more than almost 200 Å of samples in set two plays no role in the layer conductivity. Meanwhile, the same effect explains, adequately, the role of the surface roughness in the resistivity of the ultra‐thin layers in Set 1.     

SnOx thin films with tunable conductivity for fabrication of p–n homo‐junction

Tin oxide (SnO_x) has been widely used for the fabrication of transparent and flexible devices because of its excellent optical and electronic properties. In this work, we established a methodology for the synthesis of SnO_x thin films with p‐type and n‐type tunable conductivity by direct currecnt (DC) magnetron sputtering. The SnO_x thin films changed from p‐type to n‐type by increasing the relative oxygen partial pressure (ppO₂) from 4.8% to 18.5% and by varying the working pressure between 1.8 and 2.5 mTorr. The SnO_x thin films were annealed at 160°C, 180°C, and 200°C for 30 min to promote the formation of the desired crystalline structures. At the annealing temperature of 180°C in air ambient, the SnO_x thin films showed a tetragonal structure with Sn traces. Having found the optimal conditions, we deposited both types of SnO_x thin films with the same tetragonal structure and similar chemical stoichiometry. Also, the conditions to obtain thin films with the highest mobility values for p‐type (1.10 cm²/Vs) and n‐type (22.20 cm²/Vs) were used for fabricating the device. Finally, the implementation of a SnO_x‐based p–n diode was demonstrated using transparent SnO_x thin films developed in this work, illustrating their potential use in transparent electronics.     

Ion‐beam‐induced morphology on the surface of thin polymer films at low current density and high ion fluence

The effect of Xe⁺ bombardment on the surface morphology of four different polymers, polystyrene (PS), poly(phenylene oxide), polyisobutylene, and polydimethylsiloxane, was investigated in ion energy and fluence ranges of interest for secondary ion mass spectrometry depth‐profiling analysis. Atomic force microscopy (AFM) was applied to analyze the surface topography of pristine and irradiated polymers. AFM analyses of nonirradiated polymer films showed a feature‐free surface with different smoothness. We studied the influence of different Xe⁺ beam parameters, including the incidence angle, ion energy (660–4000 eV), current density (0.5 × 10² to 8.7 × 10² nA/cm²), and ion fluence (4 × 10¹⁴ to 2 × 10¹⁷ ion/cm²). Xe⁺ bombardment of PS with 3–4 keV at a high current density did not induce any change in the surface morphology. Similarly, for ion irradiation with lower energy, no surface morphology change was found with a current density higher than 2.6 × 10² nA/cm² and an ion fluence up to 4 × 10¹⁶ ion/cm². However, Xe⁺ irradiation with a lower current density and a higher ion fluence led to topography development for all of the polymers. The roughness of the polymer surface increased, and well‐defined patterns appeared. The surface roughness increased with ion irradiation fluence and with the decrease of the current density. A pattern orientation along the beam direction was visible for inclined incidence between 15° and 45° with respect to the surface normal. Orientation was not seen at normal incidence. The surface topography development could be explained on the basis of the balance between surface damage and sputtering induced by the primary ion beam and redeposition–adsorption from the gas phase. Time‐of‐flight secondary ion mass spectrometry analyses of irradiated PS showed strong surface modifications of the molecular structure and the presence of new material. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 314–325, 2001     

100 keV H+ ion irradiation of as‐deposited Al‐doped ZnO thin films: An interest in tailoring surface morphology for sensor applications

We report the influence of 100 keV H⁺ ion beam irradiation on the surface morphology, crystalline structure, and transport properties of as‐deposited Al‐doped ZnO (Al:ZnO) thin films. The films were deposited on silicon (Si) substrate by using DC sputtering technique. The ion irradiation was carried out at various fluences ranging from 1.0 × 10¹² to 3.0 × 10¹⁴ ions/cm². The virgin and ion‐irradiated films were characterized by X‐ray diffraction, Raman spectroscopy, atomic force microscopy, and Hall probe measurements. Using X‐ray diffraction spectra, 5 points Williamson‐Hall plots were drawn to deduce the crystallite site and strain in Al:ZnO films. The analysis of the measurements shows that the films are almost radiation resistant in the structural deformation under chosen irradiation conditions. With beam irradiation, the transport properties of the films are also preserved (do not vary orders of magnitude). However, the surface roughness and the crystallite size, which are crucial parameters of the ZnO film as a gas sensor, are at variation with the ion fluence. As ion fluence increases, the root‐mean‐square surface roughness oscillates and the surface undergoes for smoothening with irradiation at chosen highest fluence. The crystallite size decreases initially, increases for intermediate fluences, and drops almost to the value of the pristine film at highest fluence. In the paper, these interesting experimental results are discussed in correlations with ion‐matter interactions especially energy losses by the ion beam in the material.     

Scanning force microscopy study of the morphology of spin‐cast molecular‐imprinted nylon thin films

The morphology of thin, selectively imprinted films of Nylon‐6 was investigated by scanning force microscopy. Four amino acids were used as template molecules in the spin‐cast films. Film thickness ranged from 2 µm to 500 nm, depending on the nylon and template concentration in the casting solution. The thin‐film properties, including the presence of nanometer‐ to micrometer‐sized pores, are clearly associated with the imprinting process. The larger features observed by scanning force microscopy are attributed to amino acid clustering during the casting process. Copyright © 2004 John Wiley & Sons, Ltd.     

Nanostructure formation in polymer thin films influenced by humidity

The influence of relative humidity (RH) during the film preparation on the surface morphology and on the material distribution of the resulting technical polymer blend films consisting of poly (methyl methacrylate) (PMMA) and poly (vinyl butyral) (PVB) is investigated by atomic force microscopy. Both pure polymers and polymer blends with different compositions of PVB/PMMA dissolved in tetrahydrofuran (THF) were used. Polymer films prepared under dry conditions (RH < 20%) are compared with those that have the same polymer composition but were prepared under increased humidity conditions (RH > 80%). The films consisting of the pure polymers showed a nonporous surface morphology for low‐humidity preparation conditions, whereas high‐humidity preparation conditions lead to porous PVB and PMMA films, respectively. These pores are explained as the result of a breath figure formation. In the case of the polymer blend films containing both polymers, porous or phase‐separated surface structures were observed even at low‐humidity conditions. A superposition of the effects of phase separation and breath figure formation is observed in the case of polymer blend films prepared under high‐humidity conditions. Atomic force microscopy (AFM) images taken before and after the treatment with ethanol as a selective solvent for PVB indicate that PMMA is deposited on top of a PVB layer in the case of the low‐humidity preparation process whereas for high‐humidity conditions the silicon substrate is covered with a PMMA film. Copyright © 2006 John Wiley & Sons, Ltd.     

Control of self‐organized low‐dimensional morphology in poly(styrene‐b‐4vinylpyridine)/polystyrene blend thin films

The surface morphologies of poly(styrene‐b‐4vinylpyridine) (PS‐b‐P4VP) diblock copolymer and homopolystyrene (hPS) binary blend thin films were investigated by atomic force microscopy as a function of total volume fraction of PS (?_PS) in the mixture. It was found that when hPS was added into symmetric PS‐b‐P4VP diblock copolymers, the surface morphology of this diblock copolymer was changed to a certain degree. With ?_PS increasing at first, hPS was solubilized into the corresponding domains of block copolymer and formed cylinders. Moreover, the more solubilized the hPS, the more cylinders exist. However, when the limit was reached, excessive hPS tended to separate from the domains independently instead of solubilizing into the corresponding domains any longer, that is, a macrophase separation occurred. A model describing transitions of these morphologies with an increase in ?_PS is proposed. The effect of composition on the phase morphology of blend films when graphite is used as a substrate is also investigated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3496–3504, 2004     

Effects of gold‐induced crystallization process on the structural and electrical properties of germanium thin films

Gold‐induced (Au‐) crystallization of amorphous germanium (α‐Ge) thin films was investigated by depositing Ge on aluminum‐doped zinc oxide and glass substrates through electron beam evaporation at room temperature. The influence of the postannealing temperatures on the structural properties of the Ge thin films was investigated by employing Raman spectra, X‐ray diffraction, and scanning electron microscopy. The Raman and X‐ray diffraction results indicated that the Au‐induced crystallization of the Ge films yielded crystallization at temperature as low as 300°C for 1 hour. The amount of crystallization fraction and the film quality were improved with increasing the postannealing temperatures. The scanning electron microscopy images show that Au clusters are found on the front surface of the Ge films after the films were annealed at 500°C for 1 hour. This suggests that Au atoms move toward the surface of Ge film during annealing. The effects of annealing temperatures on the electrical conductivity of Ge films were investigated through current‐voltage measurements. The room temperature conductivity was estimated as 0.54 and 0.73 Scm⁻¹ for annealed samples grown on aluminum‐doped zinc oxide and glass substrates, respectively. These findings could be very useful to realize inexpensive Ge‐based electronic and photovoltaic applications.     

Medium energy,heavy and inert ion irradiation of metallic thin films: studies of surface nano‐structuring and metal burrowing

In context to the ion induced surface nanostructuring of metals and their burrowing in the substrates, we report the influence of Xe and Kr ion‐irradiation on Pt:Si and Ag:Si thin films of ~5‐nm thickness. For the irradiation of thin films, several ion energies (275 and 350 keV of Kr; 450 and 700 keV of Xe) were chosen to maintain a constant ratio of the nuclear energy loss to the electronic energy loss (S_n/S_e) in Pt and Ag films (five in present studies). The ion‐fluence was varied from 1.0 × 10¹⁵ to 1.0 × 10¹⁷ ions/cm². The irradiated films were characterized using Rutherford backscattering spectroscopy (RBS), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The AFM and SEM images show ion beam induced systematic surface nano‐structuring of thin films. The surface nano‐structures evolve with the ion fluence. The RBS spectra show fluence dependent burrowing of Pt and Ag in Si upon the irradiation of both ion beams. At highest fluence, the depth of metal burrowing in Si for all irradiation conditions remains almost constant confirming the synergistic effect of energy losses by the ion beams. The RBS analysis also shows quite large sputtering of thin films bombarded with ion beams. The sputtering yield varied from 54% to 62% by irradiating the thin films with Xe and Kr ions of chosen energies at highest ion fluence. In the paper, we present the experimental results and discuss the ion induced surface nano‐structuring of Pt and Ag and their burrowing in Si. Copyright © 2016 John Wiley & Sons, Ltd.     

Preparation and characterization of nanometer‐thin freestanding polymer foils for laser‐ion acceleration

We report on the production and characterization of polymer‐based ultra‐thin (sub 10 nm) foils suited for experiments on laser‐ion acceleration in the regime of radiation pressure acceleration. Beside the remarkable mechanical stability compared with commonly used diamond‐like‐carbon foils, a very homogeneous layer thickness and a small surface roughness have been achieved. We describe the technical issues of the production process as well as detailed studies of the mechanical stability and surface roughness tests. The capability of producing uniform targets of large area is essential for advanced laser‐ion acceleration projects which are dealing with high repetition rate and extended measurement series, but might also be useful for other applications which require ultra‐thin and freestanding substrates of high quality. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1355–1360     

Direct current conductivity and ion motions in poly(vinyl chloride)‐poly‐1,4‐cis butadiene blends by electrical relaxation method

Ionic conduction in poly(vinyl chloride) (PVC)‐poly‐1,4‐cis butadiene blends has been studied using the electrical relaxation method. Temperature dependence of direct current (dc) conductivity does not change at the glass transition of PVC but does change at higher temperatures. The shape of the frequency dispersion curve of the electric modulus in a frequency range from 0.01 to 100 Hz depends on temperature. At low temperatures, the shape of the dispersion curve is reproduced by calculation assuming the Debye decay function, whereas this is not reproduced at high temperatures. Two kinds of analysis of the dispersion curve are discussed for this complicated change in the shape of the dispersion. One is that the dispersion curve is regarded as a single process expressed by the Kohlrausch decay function, and the other is that the curve is regarded as two processes expressed by the Debye and the Kohlrausch decay functions. The observed dispersion of the electric modulus is not expressed by the single process but by the two processes. One of the two processes is characterized by the Debye decay function, and the other is characterized by the Kohlrausch decay function. The parameter of the Kohlrausch decay function for one of these processes has a value of 0.82, and this value does not depend on temperature. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 226–235, 2002     

Scanning thermal microscopy techniques for polymeric thin films using temperature contrast mode to measure thermal diffusivity and a novel approach in conductivity contrast mode to the mapping of thermally conductive particles

Advances in production are leading to increasing use of polymeric thin films in applications such as automotive bearings. Two approaches have been developed to study the thermophysical properties of these thin films: The first technique based on Flash theory uses a scanning thermal microscopy (SThM) tip in temperature contrast mode to measure thermal diffusivity over a nano-scale area. The SThM tip is in contact with the upper surface of the film to detect a heat pulse delivered by a microelectromechanical heater platform from the lower surface. The second technique is a conductivity contrast mode SThM based approach for measuring the size and distribution of thermally conducting particles in thin film polymeric coatings. Topographical and thermal conductivity data are combined to produce a “correlation analysis value” 3D particle map of the coating. Good practice and a case study are highlighted.     

Interpreting the conductive atomic force microscopy measured inhomogeneous nanoscale surface electrical properties of Al‐doped ZnO films

In this work, conductive atomic force microscopy is used to study the inhomogeneous surface electrical conductivity of Al‐doped ZnO thin films at a nanoscale dimension. To this end, Al‐doped ZnO films were deposited onto the soda lime glass substrates at substrate temperature (T_s) varying from 303 to 673 K in radio frequency magnetron sputtering. The obtained local surface electrical conductivity values are found to be influenced by their bulk electrical resistivity, surface topography and tip geometry. Further, the average (local) surface conductivity from the film surface is found to increase with increasing T_s from 303 to 623 K, beyond which they decrease until 673 K. Copyright © 2016 John Wiley & Sons, Ltd.     

Cross‐sectional high‐resolution microscopy of thin pretreatment layers on hot dip galvanized steel

Hexavalent chromium containing pretreatments and primers for coil coating are soon to be entirely prohibited, which sets new demands for Cr‐free alternatives. Most of the presently used Cr‐free pretreatment layers operate predominantly via barrier formation and adhesion promotion mechanisms and lack the self‐healing effect typical for Cr⁶⁺‐pretreatments. This sets new demands also for the formation and monitoring of these layers. The barrier thickness and chemical composition of Cr‐free pretreatment layers on hot dip galvanized steel were studied using cross sections from broad ion beam (BIB) sample preparation and ultramicrotome cutting. BIB milling provided finely polished cross sections of pretreated samples. Film thicknesses of 20–50 nm were accurately determined for Cr‐free pretreatments containing 4–10 mg Ti/m² using BIB milling and scanning electron microscopy imaging. Scanning transmission electron microscopy, integrated with aberration correctors and X‐ray energy dispersive spectrometry, of an ultramicrotome cut pretreated and painted samples provided detailed chemical information. Metal complexes were detected close to the pretreatment/zinc interface, while the polymeric part of the pretreatment layer prevailed closer to paint. Copyright © 2014 John Wiley & Sons, Ltd.     

Molecular organization in MAPLE‐deposited conjugated polymer thin films and the implications for carrier transport characteristics

The morphological structure of poly(3‐hexylthiophene) (P3HT) thin films deposited by both Matrix Assisted Pulsed Laser Evaporation (MAPLE) and solution spin‐casting methods are investigated. The MAPLE samples possessed a higher degree of disorder, with random orientations of polymer crystallites along the side‐chain stacking, π–π stacking, and conjugated backbone directions. Moreover, the average molecular orientations and relative degrees of crystallinity of MAPLE‐deposited polymer films are insensitive to the chemistries of the substrates onto which they were deposited; this is in stark contrast to the films prepared by the conventional spin‐casting technique. Despite the seemingly unfavorable molecular orientations and the highly disordered morphologies, the in‐plane charge carrier transport characteristics of the MAPLE samples are comparable to those of spin‐cast samples, exhibiting similar transport activation energies (56 vs. 54 meV) to those reported in the literature for high mobility polymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 39–48     

Influence of substrate chemistry and the network homogeneity of ultra‐thin cross‐linked polymer films cured at their surface on the main relaxations temperatures probing by microthermal analysis

Thin 200‐nm epoxy–amine mixtures were cured on silicon wafers with different surface chemistry to quantify the effect of the chemistry on the glass transition temperature evolution in ultra‐thin thermosetting films. Two surface treatments were investigated: the first one only consisted in the activation of the silanols groups at the silicon surface, whereas the second one consisted in the grafting 3‐aminopropyltrimethoxysilane (APTMS) monolayer on the silicon wafers. The epoxy films were deposited on these chemistry modified wafers by spin coating a toluene solution of DGEBA–amine mixture at stoichiometric ratio. The same cure processing was used for both samples. Thin films were analysed not only using microthermal and thermomechanical analysis to determine the relaxation transitions temperatures of these films but also using FTIR in infrared reflection absorption spectroscopy mode to determine the curing rate of these networks. It was found that all these thin films showed two different glass transitions, the first one at 96 °C and was independent of the surface treatments, whereas the second one increasing from 142 °C for the oxidised wafers surface to 167 °C for the aminosilane grafted on the silicon wafer. The substrate chemistry extent on the film network structure, the interfacial bonds and interactions are discussed. This work also illustrates the interest in using microthermal analysis to obtain relevant temperature glass transition of thin film at sub‐micrometre scale, strongly dependant of local structure and chemistry composition. Copyright © 2009 John Wiley & Sons, Ltd.     

Concurrent genesis of color and electrical conductivity in leathers through in‐situ polymerization of aniline for smart product applications

We present a simple method to produce self‐colored and conducting leathers using in‐situ polymerization of aniline with ammonium persulfate as oxidant and hydrochloric acid as dopant. The structural and morphological features of treated leathers were examined using Fourier transformed infra‐red spectroscopy, X‐ray diffraction and scanning electron microscopic analyses. Results suggest the deposition of conducting emeraldine salt form of polyaniline on the leather substrate rather than other poorly conducting states. We also show that the treated leathers are bluish green through reflectance measurements thereby suggesting that the use of toxic and expensive dyes can be avoided for coloration process. Further, we demonstrate that a maximum electrical conductivity of 0.15 S/cm is obtained for the leather treated with optimal experimental conditions, which aids its application to operate touch‐screen devices. Copyright © 2015 John Wiley & Sons, Ltd.     

Non‐optical bimorph‐based force sensor for scanning near‐field optical microscopy of biological materials: characteristics,design and applications

A non‐optical force sensor that allows operation both in lateral (shear) and in vertical (tapping) force detection modes has been introduced for dynamic tip–sample distance regulation in scanning near‐field optical microscopy (SNOM) of biological samples. The sensor is based on a rectangular bimorph cantilever consisting of two thin piezoceramic layers bonded to a brass centre shim. One of the piezo layers serves as the probe dither and another as the responder of the sensed forces. The sensor is driven with a home‐made Q‐control electronics so that its sensitivity and bandwidth can be adjusted. The dynamics, characteristics and design considerations of the sensor are theoretically and experimentally discussed. Driving the bimorph cantilever at its eigenfrequency with appropriate force feedback allows one to obtain a quality factor (Q‐factor) up to 10³ in water, suitable for different sample softness and imaging environments. The high sensitivity of the sensor is demonstrated both by shear force and by tapping mode imaging of soft biological samples in their natural state. Near‐field optical resolution of better than 100 nm on red blood cells in water has been obtained. The experimental results suggest that this SNOM sensor would be a promising set‐up for biological applications. Copyright © 2007 John Wiley & Sons, Ltd.     

Layer‐by‐layer assembly of weak‐strong copolymer polyelectrolytes: A route to morphological control of thin films

Multilayer films were assembled from a strong polyelectrolyte (poly(diallyldimethylammonium chloride), PDADMAC) and a copolymer containing both strongly charged styrene sulfonate moieties and weakly charged maleic acid moieties (poly(4‐styrenesulfonic acid‐co‐maleic acid), PSSMA). Growth of PSSMA/PDADMAC multilayers was linear, as characterized by UV‐vis spectroscopy and quartz crystal microgravimetry. The influence of both the pH of the PSSMA adsorption solutions and the ratio of SS:MA in the PSSMA on multilayer properties was investigated. Fourier transform infrared spectroscopy results showed that the ionization of carboxylic acid groups in PSSMA/PDADMAC multilayers did not vary significantly with changes in the PSSMA assembly pH. However, the multilayers showed different thicknesses, surface morphologies, and stability to post‐assembly pH treatment. We also demonstrate that PSSMA/PDADMAC multilayers are significantly more stable than PSSMA/PAH multilayers after post‐assembly pH treatment (i.e. the films remain intact when exposed to pH extremes). In addition, the surface morphology of two films (PSSMA 1:1 assembled at pH 5.8, post‐treated at pH 2 and PSSMA 3:1 assembled at pH 5.8, post‐treated at pH 11) changed significantly when the films were exposed to solutions of different pH and, in the former case, this change in film morphology was reversible. The porous morphology after treatment at pH 2 could be reversed to give a significantly smoother film after subsequent exposure to water for 24 h. Our results demonstrate that by the rational choice of the assembly pH of PSSMA, stable and pH‐responsive films can be obtained via the sequential assembly of PSSMA and PDADMAC. These films have potential in controlled release applications where film stability and pH‐responsive behavior are essential. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4341‐4351, 2007     

Mechanical and electrical properties of the phosphor‐doped nano‐silicon film under an external electric field

The mechanical and electrical properties of the phosphor‐doped nano‐silicon film (nc‐Si:H) prepared by the plasma‐enhanced chemical vapor deposition (PECVD) method under electric field have been studied by Tribolab system, which is equipped with nano‐electrical contact resistance (ECR) tool. During indentation, different voltages and loads were applied. The topography of the sample surface was studied by atomic force microscopy (AFM). The experimental results show that the roughness of the film is 5.69 nm; the electric current was measured through the sample/indenter tip with different loads at a fixed voltage, and it increased nonlinearly during the indentation. The maximum current value depth was shallower than the maximum depth of each indent due to the plasticity of the film. When the loading speed is increased to 250 µN/s, the microcrack occurred on the film; the hardness (H) and elastic modulus (E) changed with the voltage applied both in open circuit and in short circuit case, which resulted in different values of H/E rate from 0.082 to 0.096. Copyright © 2009 John Wiley & Sons, Ltd.