ZnO thin films electrodeposited in propylene carbonate under a magnetic field

Electrochemical processing of ZnO films on fluorine-doped indium tin oxide (FTO/ITO) substrate was investigated in organic propylene carbonate electrolyte solutions containing Zn(NO₃)₂·6H₂O. Much finer and more uniform morphologies of the ZnO films were obtained in comparison with those in aqueous electrolyte solutions. The effects of superimposing a magnetic field to the ZnO films were further examined. Superimposing a magnetic field considerably influenced the transient current density in the initial stage, especially in the mass transfer controlled region at −1.5 V vs Zn wire reference electrode. It also introduced substantially no drastic influence on the microstructure in spite of the appearance of considerably significant morphological variations. Contribution to special issue on Magnetic field effects in Electrochemistry.     

Effect of the cadmium ion source on the structural and optical properties of chemical bath deposited CdS thin films

The chemical bath deposition (CBD) technique has been successfully used to deposit cadmium sulphide from cadmium chloride and cadmium acetate as the cadmium ion source and thiourea as the sulphur source on both glass microscope slide and indium tin oxide coated glass substrates. Various properties of the films such as surface morphology, crystallinity, optical properties and resistivitiy have been investigated. XRD patterns reveal that the CdS films deposited from cadmium chloride have an hexagonal structure. Their preferential orientation changes from (002) to (100) with the thermal annealing. Films deposited from cadmium acetate are amorphous but improve their crystallinity with annealing. SEM analysis shows that the grains of the as deposited films are randomly shaped and appear to be bigger in the case of the CdS prepared from cadmium chloride. The optical transmission of the layers are in the 70–80 % range for wavelength above the band gap absorption which makes them more appropriate as window material in heterojunction solar cells.     

Fabrication of CdS films with superhydrophobicity by the microwave assisted chemical bath deposition

A simple method of microwave assisted chemical bath deposition (MA-CBD) was adopted to fabricate cadmium sulfide (CdS) thin films. The superhydrophobic surface with a water contact angle (CA) of 151 degrees was obtained. Via a scanning electron microscopy (SEM) observation, the film was proved having a porous micro/nano-binary structure which can change the property of the surface and highly enhance the hydrophobicity of the film. A possible mechanism was suggested to describe the growth of the porous structure, in which the microwave heating takes an important role in the formation of two distinct characteristic dimensions of CdS precipitates, the growth of CdS sheets in micro-scale and sphere particles in nano-scale. The superhydrophobic films may provide novel platforms for photovoltaic, sensor, microfluidic and other device applications.     

Radiative properties of an electrically-vaporized thin film plasma in an external magnetic field

An external magnetic field of a few kilogauss is used to alter significantly the radiative properties of the plasmas generated by the capacitive discharge vaporization ofthin Ag films. The magnetic field is generated by the plasma current in a large inductor surrounding the plasma. The magnetic field is oriented normal to the electric field in the plasma. This generates a drift motion of the plasma normal to the plane established by the electric and magnetic field vectors. The drift motion can direct the plasma toward the plastic substrate on which the Ag film and a powder or solution residue sample were originally located. This increases the plasma-sample interaction. Time integrated, spatially resolved photographic spectra and spatially resolved photoelectric radiation profiles show that with the magnetic field, the continuum background radiation is confined to a relatively small region near the substrate surface. This results in significantly larger analyte line-to-background intensity ratios in the region 1–2 cm above the substrate surface.     

An improved method for chemical bath deposition of ZnS thin films

ZnS thin films were prepared by an improved chemical bath deposition method, which the substrates were preheated before being mounted in the reaction solution. X-ray diffraction (XRD) and energy dispersive spectrometer (EDS) reveals that thin film ZnS has a cubic structure and the typical composition ratio of Zn/S is 52:48. Scanning electron microscopy (SEM) characterization shows that the surface of the sample is compact and uniform. The transmission spectrum indicates a good transmission characteristic with an average transmittance of 82.2% in the spectra range from 350 nm to 800 nm and the optical band gap is about 3.76 eV.     

Tetracene thin films grown by organic molecular beam deposition under a static magnetic field

The diamagnetic response of tetracene is exploited to increase the in-plane orientation of thin films grown by organic molecular beam deposition, while applying a magnetic field of 0.2 T parallel to the surface of the silica and potassium hydrogen phthalate substrates. The combined spectroscopic analysis of the films in the UV/visible region and morphological investigation of their surface performed by atomic force microscopy demonstrate a substantial increment of the film order when the magnetic field is applied along the c axis of potassium hydrogen phthalate, in agreement with the anisotropic magnetic susceptibility of tetracene.     

CdS和CdSe薄膜的制备及其光电化学性质

本文采用简易的化学水浴沉积法和自牺牲模板法制备CdS、CdSe薄膜,对两种薄膜进行了XRD表征,比较了两种薄膜的紫外吸收光谱并研究了CdS、CdSe薄膜作为太阳能电池中的光阳极时所产生的光电流和光电压,对两种薄膜的电化学性能进行了比较.     

Superfluorescent transitions in an external magnetic field

Polarisation properties of the superfluorescence in the near-infrared regime have been investigated between high-lying levels of Sr and Ba under the influence of a static homogeneous external magnetic field. In some transitions the time-resolved measurements show a change of the polarisation of the superfluorescence depending on the magnetic field strength. In suitable experimental conditions intensity modulations were observed. These were assigned as Zeeman quantum beats or indirectly observed Zeeman superfluorescent beats. The experimental findings of superfluorescence in two-level, three-level, or multi-level configurations in dependence on the magnetic field strength can be explained well in a semiclassical model of multi-level superfluorescence.     

Desorption of hydrogen from the electrode surface under influence of an external magnetic field

The effect of a uniform magnetic field in perpendicular-to-electrode configuration, on the hydrogen evolution reaction was investigated during the deposition of Fe and CoFe alloys. It was found that the desorption of hydrogen is supported in a magnetic field. This effect is discussed in details with respect to the micro-magnetohydrodynamic convection, which arises due to the fluctuation of the current distribution close to the H₂ bubble.     

Effect of the chemical environment on the light-induced degradation of a photochromic dye in ormosil thin films

The naphthopyran (NP) derivative (3-(2,4-dimethoxyphenyl)-3-(4-methoxyphenyl)-3H-naphtho[2,1-b]pyran) exhibits photochromism in solution or embedded in solid matrices. The molecule suffers a progressive photodegradation upon prolonged irradiation with UV-light, which depends strongly on the solvent or the embedding matrix. The photodegradation of the dye molecules in THF or benzene solutions is much faster than that of the molecules embedded in solid matrices (polymer or ormosil).The organic functional groups incorporated in the network of the ormosil matrix play an important role in the photostability of the dye, as they determine the chemical environment of the dye molecules in the matrix. In this way, the dye embedded in matrices whose inner pore surface is functionalized with phenyl groups exhibits a photostability nine times higher than in unmodified matrices, being their degradation half-life (t_1/2(deg)) 181 h and 21 h, respectively. The photostability of the photochromic dye in the ormosil matrices was also measured as a function of the dye loading, showing higher stability as the amount of dye is increased. The photostability of the dye in photochromic materials is an important issue in sight of the possible applications of these materials, as the performance of the devices involves repeated exposure to UV radiation.     

Anomalous relaxation of a twisted cell under an external magnetic field: The nearly homogeneous relaxation

We report experimental and theoretical investigations of the dynamic behaviour of a π/2 twisted NLC layer in a magnetic field. When a magnetic field H is applied in the layer plane at a suitable angle β with respect to the easy axis on the first surface, the relaxation towards the equilibrium texture occurs through a slow decay of unstable textures. Depending on the values of H and β, the relaxation of the system can be nearly homogeneous or strongly inhomogeneous. In this paper we restrict our attention to the case where the relaxation occurs in a nearly homogeneous way. The theoretical relaxation time τw of the unstable textures is found to depend strongly on the angle β and on the amplitude of the magnetic field. The experimental dependence of τw on H and β is found to be in good agreement with the theoretical predictions. The relaxation process is extremely sensitive to small dishomogeneities of the director easy alignment on the surfaces. From the measured relaxation we are able to estimate a spread of 0.3° on the surface easy axes at a planar anchored SiO surface.     

In situ growth of CuS thin films on functionalized self-assembled monolayers using chemical bath deposition

Nano-structured CuS thin films were deposited on the functionalized -NH(2)-terminated self-assembled monolayers (SAMs) surface by chemical bath deposition (CBD). The deposition mechanism of CuS on the -NH(2)-terminated group was systematically investigated using field emission scanning electron microscope (FESEM), X-ray photoelectron spectroscope (XPS), UV-vis absorption. The optical, electrical and photoelectrochemical performance of CuS thin films incorporating with the X-ray diffraction (XRD) analysis confirmed the nanocrystalline nature of CuS with hexagonal crystal structure and also revealed that CuS thin film is a p-type semiconductor with high electrical conductivity (12.3Ω/□). The functionalized SAMs terminal group plays a key role in the deposition of CuS thin films. The growth of CuS on the varying SAMs surface shows different deposition mechanisms. On -NH(2)-terminated surfaces, a combination of ion-by-ion growth and cluster-by-cluster deposition can interpret the observed behavior. On -OH- and -CH(3)-terminated surfaces, the dominant growth mechanism on the surface is cluster-by-cluster deposition in the solution. According to this principle, the patterned CuS microarrays with different feature sizes were successfully deposited on -NH(2)-terminated SAMs regions of -NH(2)/-CH(3) patterned SAMs surface.     

Optimization of the synthesis and characterizations of chemical bath deposited Cu2S thin films

Semiconducting copper sulphide (Cu₂S) thin films have been deposited on various substrates (SnO₂:F/glass, glass) by the simple and economical chemical bath deposition technique. The depositions were carried out during a deposition time of about 32.5 min in the pH range of 9.4 to 11. The synthesized Cu₂S thin films were characterized using various techniques without any annealing treatment. X-ray diffraction study shows that Cu₂S films exhibit the best crystallinity for pH = 10.2. For this pH value, Auger electron spectroscopy investigations show that Cu₂S thin films grown on an SnO₂/glass substrate exhibit stochiometric composition with [Cu]/[S] concentrations ratio equal to 2.02. Using the Kelvin method, the work function difference (Ф_material– Ф_probe) for the Cu₂S films deposited on SnO₂/glass substrates at the optimum pH value was found to be equal to 145 meV. Hall measurements confirm the p-type electrical conductivity of the obtained films. The electrical resistivity was of the order of 3.85 × 10⁻⁴ Ω-cm. The transmission and reflection coefficients vary in the range of [35–60] % and [5–15] % respectively, in the visible range, and the band gap energy is about 2.37 eV.     

Reactivity dynamics of a confined molecule in presence of an external magnetic field

Reactivity dynamics and stability of a confined hydrogen molecule in presence of an external magnetic field has been studied using quantum fluid density functional theory. Dynamic profiles of various reactivity parameters such as hardness, electrophilicity, magnetizability, phase volume, entropy, etc. have been studied within a confined environment. Responses in the reactivity parameters as well as the associated electronic structure principles validate the stability of the confined H₂ molecule in ground and excited states in presence of an external magnetic field. Confinement to the system has been imposed by the Dirichlet type boundary condition. Confinement and excitation act in opposite directions. Ground state type dynamics is obtained on simultaneous electronic excitation and confinement. © 2014 Wiley Periodicals, Inc.     

Polymer translocation through a nanopore under an applied external field

We investigate the dynamics of polymer translocation through a nanopore under an externally applied field using the two-dimensional fluctuating bond model with single-segment Monte Carlo moves. We concentrate on the influence of the field strength E, length of the chain N, and length of the pore L on forced translocation. As our main result, we find a crossover scaling for the translocation time tau with the chain length from tau approximately N2nu for relatively short polymers to tau approximately N1+nu for longer chains, where nu is the Flory exponent. We demonstrate that this crossover is due to the change in the dependence of the translocation velocity v on the chain length. For relatively short chains v approximately N-nu, which crosses over to v approximately N(-1) for long polymers. The reason for this is that with increasing N there is a high density of segments near the exit of the pore, which slows down the translocation process due to slow relaxation of the chain. For the case of a long nanopore for which R parallel, the radius of gyration Rg along the pore, is smaller than the pore length, we find no clear scaling of the translocation time with the chain length. For large N, however, the asymptotic scaling tau approximately N1+nu is recovered. In this regime, tau is almost independent of L. We have previously found that for a polymer, which is initially placed in the middle of the pore, there is a minimum in the escape time for R parallel approximately L. We show here that this minimum persists for weak fields E such that EL is less than some critical value, but vanishes for large values of EL.     

Density-functional study of model bidisperse ferrocolloids in an external magnetic field

We present phase diagrams of a model bidisperse ferrocolloid consisting of a binary mixture of dipolar hard spheres (DHSs) under the influence of an external magnetic field. The dipole moments of the particles are chosen proportional to the particle volume to mimic real ferrocolloids, and we focus on dipole-dominated systems where isotropic attractive interactions are absent. Our results are based on density-functional theory in the modified mean-field (MMF) approximation. For one-component DHS fluids in external fields, and for corresponding mixtures dominated by one of the components, MMF theory predicts the tricritical point of the transition between an isotropic gas and a ferromagnetic liquid occurring at zero field to be changed into a critical point separating two magnetically ordered phases of different density. The corresponding critical temperature displays a nonmonotonic dependence on the field strength. Completely different behavior is found for the critical temperature related to the demixing phase transitions appearing in strongly asymmetric mixtures [G. M. Range and S. H. L. Klapp, Phys. Rev. E 70, 061407 (2004)]. For such systems, we find a monotonic decrease of the demixing critical temperature with increasing field. The field strength dependence of the critical temperature can therefore be tuned between nonmonotonic and monotonic behaviors just by changing the composition of the mixture--e.g., by adjusting the chemical potentials. This allows us to efficiently control the influence of external magnetic fields on the phase behavior over a large temperature interval.     

The isotropic-nematic interface of colloidal goethite in an external magnetic field

Polarization microscopy was used to study the behavior around the isotropic-nematic interface of colloidal goethite dispersions in a magnetic field. It has been found before that the nematic phase is favored in an external field. In the case of goethite this was also observed; nematic droplets formed inside the isotropic phase and coalesced with the nematic phase. However, the behavior was found to be much richer because of the particle rotation around a certain critical field strength. The simultaneous occurrence of (parallel)nematic-(perpendicular)nematic phase separation under the influence of a magnetic field also plays a role here.     

Effect of an external periodic field on the rate of chemical reactions

The rates of direct and concert passages of nuclei through a potential barrier in an external periodic field were determined within a generalized Slater model of thermal dissociation of multiatomic molecules. The external field accelerated direct and — to a much greater degree — concert passages. The curves of the efficiency of the concert mechanism of the chemical reaction as a function of the field amplitude were estimated.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 2, pp. 127–132, March–April, 1993.     

Desorption of hydrogen from an electrode surface under influence of an external magnetic field – In-situ microscopic observations

The effect of a magnetic field in the perpendicular-to-electrode configuration on the hydrogen evolution reaction (HER) was investigated during the deposition of Co. An enhanced desorption of hydrogen in the form of numerous small bubbles was found by combining potentiostatic investigations, coupled with an electrochemical quartz crystal microbalance (EQCM), and simultaneous microscopic observations of the electrode surface. The results are consistent with the recently proposed qualitative model [J.A. Koza, M. Uhlemann, A. Gebert, L. Schultz, Electrochem. Commun. 10 (2008) 1330].