Absorption spectrum of monomeric pseudoisocyanine: A new perspective and its implications for formation and spectral response of J-aggregates in solution and in thin films

We argued against the current spectral assignment for absorption spectrum of monomeric PIC which is widely accepted since the pioneering works of Scheibe and Jelley [G. Scheibe, Angew. Chem. 49 (1936) 563; E.E. Jelly, Nature 138 (1936) 1009]. A new spectrum is presented along with its conceptual basis. The hypothesized spectrum attributes the previous 0–0 (≈525 nm) and 0–1 (≈490 nm) assignments, respectively, to intermediates acting as the precursor of J-aggregates and to the 0–0 transition of monomeric PIC and brings the spectrum in accord with the seemingly universal spectral fingerprint of cyanines. The hypothesis is used to analyze and interpret the temperature dependence of the UV–vis absorption of PIC aggregates in saline aqueous solution by incorporating the J-band simulations within frenkel exciton formalism. Its implications for aggregate formation kinetics are given on the basis of current spectroscopic evidence. The hypothesis readily answers several long-standing questions: Why compared to many other cyanines at least an order of magnitude higher dye concentration is needed to form J-aggregates of PIC? Why are there no precursors, since aggregation is expected to be a consecutive process? A large number of observations on steady-state and time-resolved spectral properties, and aggregation kinetics in solution/thin films are likely to find reasonable explanations within this hypothesis.     

Synthesis, characterization and photoelectrochemical properties of n-CdS thin films

Cadmium sulfide thin films have been deposited on glass substrates by simple and cost effective chemical bath deposition technique. Triethanolamine was used as a complexing agent. The preparative parameters like ion concentration, temperature, pH, speed of substrate rotation and deposition time have been optimized for good quality thin films. The ‘as-grown’ films are characterized for structural, electrical, optical and photoelectrochemical (PEC) properties. The X-ray diffraction (XRD) studies reveal that the films are polycrystalline in nature. Energy-dispersive analysis by X-ray (EDAX) shows that films are cadmium rich. Uniform deposition of CdS thin films on glass substrate is observed from scanning electron microscopy (SEM) and atomic force microscopy (AFM) micrographs. Optical studies reveal a high absorption coefficient (10⁴ cm⁻¹) with a direct type of transition. The band gap is estimated to be 2.47 eV. The film shows n-type conduction mechanism. The photoelectrochemical (PEC) cell with CdS thin film as a photoanode and sulfide/polysulfide (1 M) solution as an electrolyte have been constructed and investigated for various cell parameters. The solar to electrical conversion efficiency (η) and fill factor (ff) are found to be 0.049% and 0.36, respectively.     

Structural properties of thermal evaporated SnTe thin films

Summary The morphological structure of SnTe very thin films is here studied by X-ray photoemission spectroscopy, by transmission electron spectroscopy and by X-ray diffraction. The analisys of experimental data evidences the superficial confinement of Sn, with different oxidation states, and the Te excess in the inner layers. The energy shift of the valence band peaks is attributed to modifications induced by the nonstoichiometry of the compound. Preliminary Hall and resistivity measurements seem to confirm the structural obtained results.     

Controlling the thermal stability of thin films by interfacial engineering

The quantized electronic structure in Pb films on Si(111) varies substantially as the film thickness increases. The changes in electronic energy cause the thermal stability of the films to oscillate with an approximate bilayer period. The phase of the oscillations can be controlled by interfacial engineering. Comparison of Pb films prepared on Si(111) terminated by In, Au, and Pb as interfactants reveals a phase reversal. For , films made of odd numbers of atomic layers (5, 7, and 9) are more stable than the even ones. This trend is reversed for the other two cases.     

SiNx薄膜热物性参数实验测量与分析研究

采用一种新的实验测量方案,将金属加热单元与温度探测单元合二为一,间接获得了在半导体和微电子学MEMS领域内有重要用途的SiNx薄膜的导热系数、发射率、比热容和热扩散系数,并对实验结果进行了不确定度分析,为微电子电路设计和掩模成型工艺等提供了可靠的热物性数据. 实验结果表明,薄膜的导热系数、发射率、热扩散系数远比相应体材质低,而且还与温度、厚度有关,尺寸效应显著,而比热容则与体材质相差不大.     

Synthesis and characterization of ZnO thin films by thermal evaporation

ZnO thin films have been successfully synthesized by thermal evaporation of pure zinc at 900 °C under the flow of different percentages of argon and oxygen gases. The films were characterized by X-ray diffraction (XRD), variable pressure scanning electron microscopy (VPSEM), energy dispersive X-ray spectroscopy (EDS) and UV–vis spectroscopy. The aim of this paper is to study the influence of the oxygen percentage on the structural and morphological properties of the ZnO films. VPSEM results show that very thick needle structures were produced at high oxygen percentages. EDS results revealed that only Zn and O are present in the sample, indicating a composition of pure ZnO. XRD results showed that the ZnO synthesized under different quantities of oxygen were crystalline with the hexagonal wurtzite structure. UV–vis spectroscopy results indicated that the optical band gap energies from the transmission spectrum are between 3.62 and 3.69 eV for ZnO thin films.     

Morphology and spectral properties of thin films of benzoxazole derivatives of biphenyl

We have studied the spectral properties and morphology of thin films (TVD films) formed by thermal vacuum deposition of 4,4′-bis[(E)-1-(1,3-benzoxazol-2-yl)-2-ethenyl]-1,1′-biphenyl and its substituted derivatives. We have shown that introducing bulky 2,2′-oxyhexyl substituents into the biphenyl units leads to a shift of the fluorescence maximum for the TVD films toward shorter wavelengths, a decrease in their photostability, and aggregation of the films during storage. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 300–303, May–June, 2007.     

Magnetic properties and phase stability in Co-Ni base alloy thin films

Co-Ni base thin films were deposited by reactive radio frequency magnetron sputtering in N₂+Ar atmosphere at different partial pressure ratios. Only the nitrogen content in the films changes when changing . Amorphous magnetic films can be obtained for compositions around N/Co=1–1.5, whereas higher N₂ contents lead to non-magnetic nitride phases. Significant changes in structural and magnetic properties are observed upon heating thin films in a TG(M) apparatus. Only the sample having a N/Co=1.5, when heat treated, appears to be made of a stable ferromagnetic phase. The N content is appropriate to keep Cr, Al and N, which exert an adverse effect on the magnetization of Co-Ni base alloys, out of the ferromagnetic phase in the form of separated nitride phases. PACS 68.55.-a; 68.60.Dv; 68.18.Jk; 75.70.Ak; 75.75.+a; 85.70.-w     

Synthesis and thermoelectric properties of Bi-doped SnSe thin films

Bi doped n-type SnSe thin films were prepared by chemical vapor deposition (CVD) and their structure and thermoelectric properties were studied. The x-ray diffraction patterns, x-ray photoelectron spectroscopy, and microscopic images show that the prepared SnSe thin films were composed of pure SnSe crystals. The Seebeck coefficients of the Bi-doped SnSe were greatly improved compared to that of undoped SnSe thin films. Specifically, Sn_0.99Bi_0.01Se thin film exhibited a Seebeck coefficient of -905.8μV·K^-1 at 600 K, much higher than 285.5 μV·K^-1 of undoped SnSe thin film. Further first-principles calculations reveal that the enhancement of the thermoelectric properties can be explained mainly by the Fermi level lifting and the carrier pockets increasing near the Fermi level due to Bi doping in the SnSe samples. Our results suggest the potentials of the Bi-doped SnSe thin films in thermoelectric applications.     

Physical properties of vacuum evaporated CdTe thin films with post-deposition thermal annealing

This paper presents the physical properties of vacuum evaporated CdTe thin films with post-deposition thermal annealing. The thin films of thickness 500 nm were grown on glass and indium tin oxide (ITO) coated glass substrates employing thermal vacuum evaporation technique followed by post-deposition thermal annealing at temperature 450 °C. These films were subjected to the X-ray diffraction (XRD),UV-Vis spectrophotometer, source meter and atomic force microscopy (AFM) for structural, optical, electrical and surface morphological analysis respectively. The X-ray diffraction patterns reveal that the films have zinc-blende structure of single cubic phase with preferred orientation (111) and polycrystalline in nature. The crystallographic and optical parameters are calculated and discussed in brief. The optical band gap is found to be 1.62 eV and 1.52 eV for as-grown and annealed films respectively. The I–V characteristics show that the conductivity is decreased for annealed thin films. The AFM studies reveal that the surface roughness is observed to be increased for thermally annealed films.     

Magnetic, dielectric and thermal stability of Ni-Zn ferrite-epoxy composite thin films for electronic applications

The fabrication of flexible epoxy thin film composites was investigated in this study. Neat epoxy with a resin-to-hardener ratio of 100:32 exhibits higher tensile properties and thermal stability than neat epoxy with a resin-to-hardener ratio of 100:45. In addition, the thermal stability of epoxy composites decreased as the NiZn ferrite content in the epoxy was increased. This result could be caused by the catalytic effect of ferrite. Vibration sample magnetometer results revealed the ferrimagnetic behavior of the ferrite-filled epoxy composites. The degree of saturation magnetization of the epoxy composites increased with the addition of NiZn ferrite nanoparticles. Dielectric tests were performed at room temperature and at frequencies ranging from 10⁴ Hz to 10⁶ Hz. These findings indicate that the dielectric constant and the dielectric loss are dependent on the filler concentration and test frequency.     

Synthesis, crystal structure, spectral and thermal properties of 4-dimethylaminopyridinium salicylate monohydrate

4-dimethylaminopyridinium salicylate monohydrate (DMAPSA) was synthesized and its crystal structure was determined using single crystal X-ray diffraction analysis. From the crystal structure analysis it can be inferred that the crystal belongs to monoclinic system with space group of P2₁/n. Investigation has been carried out to assign the vibrational frequencies of the grown crystals by FTIR spectral studies. ¹H and ¹³C FT–NMR has been recorded to elucidate the molecular structure. The molecular mass of DMAPSA has been measured using mass spectroscopic analysis. The thermal stability and thermal decomposition of DMAPSA have been investigated by means of thermogravimetric analysis and differential thermal analysis. The melting point of crystal was observed as 172 °C by melting point apparatus. Fluorescence spectra were taken for the excitation wavelength of 240 nm.     

Synthesis,deposition and characterization of tin selenide thin films by thermal evaporation technique

Tin selenide alloy was synthesized by following simple chemical reaction method, at comparatively lower temperature of 100 °C, from alkaline medium using SnCl₂.2H₂O and selenium as source materials. Powder X-ray diffraction analysis reveals that the particle size of the synthesized product is in nanometer scale. Using the reaction product as source material, the SnSe films were deposited on glass substrates at room temperature, 150 °C, 250 °C, 350 °C and 450 °C. Structural, elemental, optical, surface morphological and electrical properties of the as deposited films were studied by X-ray diffraction, Energy Dispersive X-ray Analysis, UV-Vis-NIR, Scanning Electron Microscopy and Hall effect measurement techniques and the relevant details have been obtained.     

Effect of thermal annealing on spectral properties of electrodeposited carbon films

The effect of thermal annealing on properties of carbon films deposited on nickel electrodes by the electrodeposition method was studied. It has been shown that annealing at a temperature of 300°C results in the formation of nanosize diamond clusters. With an increase in the annealing temperature, the size of diamond clusters diminishes. At an annealing temperature of 900°C, all of the carbon enters into reaction with nickel, thus forming nickel carbide.     

Growth and thermal stability of epitaxial BiFeO3 thin films

We have investigated the oxygen pressure and the temperature dependence on BiFeO₃ thin films deposited on SrTiO₃ substrates by pulsed laser deposition. Reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM) and X-ray diffraction measurements indicate that high-quality epitaxial thin films are obtained for and T=650 °C. Outside of this pressure-temperature window, parasitic peaks attributed to β-Bi₂O₃ appear. We find an increase of the out-of-plane lattice parameter with oxygen pressure that we ascribe to Bi-deficiency due to its high volatility at low pressure. Ex-situ anneals have been performed and results show that as-grown single-phase BiFeO₃ thin films degrade after annealing, whereas as-grown BiFeO₃ containing impurity phases evolve toward a single-phase structure. These experiments demonstrate that parasitic phases can stabilize compounds which are usually unstable in air at elevated temperatures.     

SiNx薄膜热物性参数实验测量与分析研究

采用一种新的实验测量方案，将金属加热单元与温度探测单元合二为一，间接获得了在半导体和微电子学MEMS领域内有重要用途的SiN_x薄膜的导热系数、发射率、比热容和热扩散系数，并对实验结果进行了不确定度分析，为微电子电路设计和掩模成型工艺等提供了可靠的热物性数据. 实验结果表明，薄膜的导热系数、发射率、热扩散系数远比相应体材质低，而且还与温度、厚度有关，尺寸效应显著，而比热容则与体材质相差不大. 关键词： 微尺度传热 热物性参数 x薄膜')" href="#">SiN_x薄膜 测量技术     

Evolution of structural and magnetic properties of sputtered nanocrystalline Co thin films with thermal annealing

Ultrafine grain films of cobalt prepared using ion-beam sputtering have been studied using X-ray diffraction (XRD), X-ray reflectivity (XRR), atomic force microscopy (AFM) and magneto-optical Kerr effect (MOKE) measurements. As-prepared films have very smooth surface owing to the ultrafine nature of the grains. Evolution of the structure and morphology of the film with thermal annealing has been studied and the same is correlated with the magnetic properties. Above an annealing temperature of 300 °C, the film gradually transforms from HCP to FCC phase that remains stable at room temperature. A significant contribution of the surface energy, due to small grain size, results in stabilisation of the FCC phase at room temperature. It is found that other processes like stress relaxation, grain texturing and growth also exhibit an enhanced rate above 300 °C, and may be associated with an enhanced mobility of the atoms above this temperature. Films possess a uniaxial anisotropy, which exhibits a non-monotonous behaviour with thermal annealing. The observed variation in the anisotropy and coercivity with annealing can be understood in terms of variations in the internal stresses, surface roughness, and grain structure.     

A contactless method for investigating the thermal properties of thin films

The photothermal deflection technique has been extended as a contactless method to investigate thermal transport in thin films. A theoretical model is developed which quantitatively describes the transport behavior, and is shown to be in excellent agreement with experimental results. This approach yields the thermal diffusivity directly and in a spatially-resolved manner.     

Effect of substituents in benzoxazole derivatives of biphenyl on the optical properties and photostability of their thin films

We have studied the characteristic features of the luminescence of thin films, formed by deposition from solutions and thermal vacuum deposition (TVD), of 4,4′-bis[(E)-1-(1,3-benzoxazol-2-yl)-2-ethenyl]-2-fluorobiphenyl (BPh-1) and 4,4′-bis[(E)-1-(1,3-benzoxazol-2-yl)-2-ethenyl]-2,2′-difluorobiphenyl (BPh-2). We have established that fluorine atoms in the biphenyl moiety of the benzoxasole derivatives significantly improve the stability of the TVD films relative to oxidative aging compared with hexyloxy substituents. Irradiation with UV light stimulates quenching of luminescence and structuring of the TVD film of the difluoro-substituted derivative.     

Self-localization of excitons and nonlinear optical properties of J-aggregates in a periodically modulated thin film

Nonlinear optical properties of dye J-aggregates embedded in a one-dimensional periodic medium are analyzed theoretically and numerically. The effect of strain-induced exciton self-localization in a chain of monomers on nonlinear optical properties of the system is investigated for weakly and highly ordered J-aggregates. It is found that exciton self-localization in a periodic medium enhances light absorption and effective optical susceptibility. Optical bistability thresholds are examined for weakly and strongly excited dye J-aggregate thin films. It is shown that the threshold intensity of incident electromagnetic field is lower by more than an order of magnitude as compared to that for a homogeneous medium.