Molecular weight effect on void closure and packing at different annealing temperatures during film formation from hard latex particles

Latex particles with high and low molecular weight (HM and LM) poly(methyl methacrylate) (PMMA) were used to prepare two sets of films with various latex contents separately. These films were annealed above the glass transition temperature. A UV-Visible (UVV) technique was used to measure the transmitted photon intensity, I _tr during film formation from latex particles. Transmitted photon intensity from HM and LM films increased as the annealing temperature increased. A void closure equation was derived for I _tr by using the Vogel-Fulcher viscosity equation. It is observed that as the latex film thickness, d, increased void closure constant, B, and viscosity increased in both HM and LM films. For a given thickness, d, the lower viscosity of particles in HM films results in better packing than in LM films.     

Percolation approach to film formation from surfactant-free polystyrene particles

In this study, a film formation process from surfactant-free polystyrene (PS) latex particles is reported. Steady state fluorescence (SSF) and photon transmission (UVV) techniques were used to study the evolution of film formation. The latex films were prepared from pyrene (P)-labeled PS particles at room temperature and annealed at time intervals of 2.5?min above the glass transition temperature (T _g) of PS. During the annealing processes, the transparency of the film changed considerably. Fluorescence intensity (I _0P) from P was measured after each annealing step to monitor the stages of film formation. Evolution of transparency of latex films were monitored by using photon transmission intensity, I _tr. A drastic increase in I _tr and I _0P above the critical annealing times, t _r and t _c were attributed, respectively to percolation behavior of PS material from one side to the other side of the latex film. Critical exponents, β of percolation clusters were measured and found to be around 0.35 and 0.25 for I _tr and I _0P measurements, respectively.     

Film formation from TiO2-polystyrene latex composite: a fluorescence study

This work reports the use of the steady state fluorescence (SSF) technique for studying film formation from TiO₂ covered polystyrene (PS) latex particles. The composite films were prepared from pyrene (P)-labeled PS particles by covering them with TiO₂ at room temperature and then annealed at elevated temperatures in 10 min time interval above glass transition (T _g) temperature of polystyrene. Five different composite films were studied in various TiO₂ layer contents. Fluorescence intensities I _P from P were measured after each annealing step to monitor the stages of film formation. Films showed considerable increase in I _P above the certain onset temperature called minimum film forming temperature, T ₀. Void closure and interdiffusion stages were modeled and related activation energies were determined and found to be 23.12 and 92.80 kJ mol^?1, respectively.     

Thermal Phase Transitions of Agarose in Various Compositions: A Fluorescence Study

The effect of agarose content on thermal phase transitions of the agarose gels was investigated by using Steady State Fluorescence (SSF) method. Scattered light, I _sc and fluorescence intensity, I _fl were monitored against temperature during heating and cooling processes to investigate phase transitions. Two regions were observed during the heating and cooling processes. At the high temperature region, double helix to coil (h-c) transition took place. However, during the cooling process coil to double helix (c-h) transitions occurred at low temperature region. Transition energies were determined using the Arrhenius treatment, and found to be strongly correlated with the agarose content in the gel system. Transition temperatures were determined from the derivative of the sigmoidal transition paths and found to be increased by increasing agarose content in both cases.     

Latex film formation induced by solvent vapor: A photon transmission study

A photon transmission method was used to study latex film formation induced by organic solvent vapor. Various films with the same latex content were prepared separately from the poly(methyl methacrylate) (PMMA) particles and exposed to vapor of chloroform-heptane mixture in various percentage volumes of chloroform. Transmitted photon intensities, I _tr, from these films increased in time under vapor exposure. The increase in I _tr is attributed to the increase in 'crossing density' at the junction surface. The Prager-Tirrell model was employed to obtained back-and-forth frequency, ν of the reptating polymer chain during film formation induced by solvent vapor. ν values were obtained and found to be strongly correlated with the percent of chloroform in the solvent mixture. At high and low chloroform contents, polymer chains diffuse according to t ^1/2 and t ^1/4 laws respectively.     

Dissolution of Al2O3-polystyrene latex composites: a fluorescence study

This work reports the use of the steady state fluorescence (SSF) technique to study dissolution of a composite film formed from a mixture of Al₂O₃ and polystyrene (PS) latex particles. The composite films were cast from dispersion of pyrene (P)-labeled PS particles in Al₂O₃ solution at room temperature and annealed at 280°C temperature for 10 min. Eight different composite films were studied in various latex contents. Toluene was used as dissolution agent. Fluorescence intensities I _P from P were monitored during dissolution. Fickian diffusion was employed to model the dissolution processes. Dissolution coefficients, D _d, were measured and found to be increased at high PS content in the composite films.     

The incommensurate - commensurate phase transition in Rb2ZnCl4: confrontation of permittivity and birefringence data

Permittivity ϵ and birefringence Δn of the c-plates of Rb₂ZnCl₄ crystals have been measured simultaneously in the vicinity of the incommensurate (IC) - commensurate phase transition. Samples used are characterized by the maximum value ϵ = 150 occuring at a temperature T_m. Since ϵ in the IC phase is determined by the phase of the order parameter while Δn is sensitive to its modulus, confrontation of these data provides some insight into the transition process. The data show that i) the transition is essentially 1st order; ii) T_m marks the beginning of the transition process on cooling and its end on heating. Below T_m, both phases coexist within an interval ΔT_tr = 1.5K on cooling and 0.6K on heating. iii) There is no indication of any significant phase coexistence above T_m. An indirect conclusion is drawn that within ΔT_tr, the anomalous dielectric tail is due both to surviving solitons and to true domain wall contribution; below T_m−ΔT_tr domain walls take over.     

The Effects of Thermal Treatments on Microstructure Phosphorus-Doped ZnO Layers Grown by Thermal Evaporation

The ZnO films doped with 3 wt% phosphorus (P) were produced by activating phosphorus doped ZnO (ZnO:P) thin films in oxygen (O₂) ambient at 600°C for 30, 60, 90 and 120 min, respectively. As-deposited films doped with phosphorus are highly conductive and n type. All the films showed p-type conduction after annealing, in an O₂ ambient atmosphere. The activation energies of the phosphorus dopant in the p-type ZnO under O₂ ambient gases indicate that phosphorus substitution on the O site yielded a deep level in the gap. With a further increase of the annealed durations, the crystalline quality of the ZnO:P sample is degraded. The best p-type ZnO:P film deposited at 600°C for 30 min shows a resistivity of 1.85 Ω cm and a relatively high hole concentration of 5.1 × 10¹⁷cm^–3 at room temperature. The films exhibit a polycrystalline hexagonal wurtzite structure without preferred orientation. The mean grain sizes are calculated to be about 60, 72, 78, 85 and 90 nm for the p-type ZnO films prepared at 600°C for 30, 60, 90 and 120 min, respectively. Room temperature photoluminescence (PL) spectra of the ZnO film exhibit two emission bands — paramount excitonic ultraviolet (UV) emission and weak deep level visible emission. The excellent emission from the film annealed at 600°C for 30 min is attributed to the good crystalline quality of the p-type ZnO film and the low rate of formation of intrinsic defects at such short duration. The visible emission consists of two components in the green range.     

Void formation in Nickel during high temperature proton irradiation

Pure Ni foils, doped with He from 0 to 28 appm, were irradiated with protons at temperatures in the range 0.3–0.6 T_m (T_m = melting point in °K) and void formation was studied. The influence of He doping, irradiation temperature and alloying were investigated. For constant He content and proton fluence, void number density and swelling are maximum at about 400°C, while the void size increases with temperature. Most voids are octahedral in shape with no sign of truncation. Helium is required to nucleate voids, and lowering the stacking fault energy by alloying suppresses void formation completely. Present results suggest that void nucleation is inhomogeneous. Some implications of these findings are discussed.     

Redox equilibrium of samarium ions doped in Al2O3-SiO2 glasses

Redox reaction of samarium ions doped in Al₂O₃-SiO₂ glasses, prepared by a rapid cooling technique of the melts, was examined by the measurement of the optical absorption and fluorescence properties. It was found that the doped samarium ions are easily reduced and oxidized by heating in H₂ and O₂ gases, respectively. The redox kinetics of samarium in the H₂ and O₂ atmospheres obey good first-order kinetics. The activation energy for the Sm³⁺ reduction in the 10Al₂O₃90SiO₂ glass was estimated to be ∼70 kJ/mol, which decreased with the increasing Al₂O₃ content. On the other hand, the activation energies for the oxidation were ∼90 kJ/mol, which only slightly depends on the glass composition. In these glasses, the samarium ions are preferentially surrounded by the Al-O polyhedra, where the oxygen ions are easily removed to form defect centers. It was concluded that the movement of the oxygen ions in the Al-O polyhedra determine the redox equilibrium of the samarium ions.     

有序结构氟聚合物压电驻极体的制备和压电性研究

描述了一种有序微孔结构压电聚合物功能膜的制备方法,利用模板的高度有序实现薄膜微孔结构的精确控制.将此制备方法用于氟聚合物压电驻极体薄膜的制备,通过扫描电子显微镜(SEM)对其微观结构的观察表明薄膜具有理想的有序结构.对氟聚合物压电驻极体压电性的研究则是利用正压电效应测量准静态压电系数d₃₃,通过等温衰减和压强依赖性的测量考察其压电性能.结果表明:有序结构氟聚合物压电驻极体的准静态压电系数d₃₃可高达300 pC/N;与无序结构氟聚合物     

Electrical properties of TiO<Subscript>2</Subscript>: equilibrium vs dynamic electrical conductivity

The present work reports semiconducting properties of high purity TiO₂ determined in the gas/solid equilibrium, as well as during controlled heating and cooling in the range 300–1,273 K. The activation energy of the electrical conductivity is considered in terms of the activation enthalpy of the formation of ionic defects and the activation enthalpy of the mobility of electronic defects. These data, determined from the dynamic electrical conductivity experiments, are compared to the electrical conductivity data determined in equilibrium. It is shown that only the equilibrium electrical conductivity data for high-purity TiO₂ are well defined. It is shown that the activation energy of the electrical conductivity determined in equilibrium differs substantially from that for the dynamic electrical conductivity data during cooling and heating. It is concluded that the formation enthalpy term determined from the dynamic conductivity data is determined by the heating/cooling rate rather than materials’ properties.     

Growth morphology of nanoscale sputter-deposited Au films on amorphous soft polymeric substrates

The growth of a room-temperature sputter-deposited thin Au film on two soft polymeric substrates, polystyrene (PS) and poly(methyl methacrylate) (PMMA), from nucleation to formation of a continuous film is investigated by means of atomic force microscopy. In particular, we studied the surface morphology evolution of the film as a function of the deposition time observing an initial Au three-dimensional island-type growth. Then the Au film morphology evolves, with increasing deposition time, from hemispherical islands to partially coalesced worm-like island structures, to percolation, and finally to a continuous and rough film. The overall Au morphology evolution is discussed in the framework of the interrupted coalescence model, allowing us to evaluate the island critical radius for the partial coalescence R _c=8.7±0.9 nm for Au on PS and R _c=7.6±0.8 nm for Au on PMMA. Furthermore, the application of the kinetic freezing model allows us to evaluate the room-temperature surface diffusion coefficient D _s≈1.8×10⁻¹⁸ m²/s for Au on PS and D _s≈1.1×10⁻¹⁸ m²/s for Au on PMMA. The application of the Vincent model allows us, also, to evaluate the critical coverage (at which the percolation occurs) P _c=61% for Au on PS and P _c=56% for Au on PMMA. Finally, the dynamic scaling theory of a growing interface was applied to characterize the kinetic roughening of the Au film on both PMMA and PS. Such analyses allow us to evaluate the dynamic scaling, growth, and roughness exponents z=3.8±0.4, β=0.28±0.03, α=1.06±0.05 for the growth of Au on PS and z=4.3±0.3, β=0.23±0.03, α=1.03±0.05 for the growth of Au on PMMA, in agreement with a non-equilibrium but conservative and linear growth process in which the surface diffusion phenomenon plays a key role.     

Ascent of open-circuit voltage on diamond-like carbon photovoltaic cell by infrared heating-assisted pulsed-laser deposition

Phosphorus-doped diamond-like carbon (DLC) films were deposited on quartz and p-type silicon (p-Si) substrates by pulsed-laser deposition. Open-circuit voltage (V _oc) and short-circuit density (I _sc/cm²) from a heating process converted from one type of electrode to another and the two types of electrode pattern are shown by the V–I characteristics. The first heating process was by a ceramic heater, and the other was by an infrared heater. We adopted two electrode patterns, from a bipectinate electrode and a plot pattern electrode, to measure electric photovoltaic characteristics. We were able to upgrade V _oc and I _sc/cm² to 35∼45 mV, and 0.24 μA/cm², respectively, under infrared heating. V _oc by the plot pattern electrode was over 2 V under infrared heating and ceramic heating did not match this on deposition by the PLD method.     

Preparation and Characterization of Nano‐TiO2 Doped Polystyrene Materials by Melt Blending for Inertial Confinement Fusion

Abstract

Nano‐TiO₂ doped polystyrene (PS) materials (TiO₂‐d‐PS) used for inertial confinement fusion (ICF) targets were prepared by means of melt blending. The effect of the pretreatment process, including coupling agents and ultrasonic dispersion on nano‐TiO₂, was studied. Tensile tests were conducted to evaluate the mechanical properties of the TiO₂‐d‐PS materials. Scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS) was used to characterize the degree of dispersion of nano‐TiO₂ in the PS matrix. Transmission electron microscopy (TEM) and dynamic contact angle (DCA) measurements were introduced to demonstrate the surface state of untreated and pretreated nano‐TiO₂. The results showed that coupling agents improved the interfacial adhesion between the PS matrix and dopants; ultrasonic dispersion contributed to the increase in the tensile properties of the TiO₂‐d‐PS materials. The dispersion stability of nano‐TiO₂ powder and the stability of the TiO₂‐d‐PS materials were significantly enhanced through pretreatment, which was supported by the increase in the DCA when the nano‐TiO₂ was pretreated by the coupling agent. The results of SEM and EDS indicated that the nano‐TiO₂ dispersed homogeneously in the PS matrix. The pretreatment process is an effective way to break the aggregation of nano‐TiO₂, which was confirmed by TEM results. Melt blending is a feasible method to prepare PS doped high Z element ICF target materials.     

Rotational and Translational Mobility of Nitroxide Spin Probes in Ionic Liquids and Molecular Solvents

Rotational and translational movements of 1-oxyl-2,2,6,6-tetramethyl-4-oxypiperidine (TEMPOL) spin probe in the room temperature ionic liquid (RTIL) 1-octyl-3-methylimidazolium tetrafluoroborate (omimBF₄) and in two molecular solvents, 1-propanol and isopropyl benzene (cumene), have been studied by X-band electron paramagnetic resonance (EPR) spectroscopy. Rotational correlation times τ _c of spin probes and the intermolecular spin exchange rate constants k _e were measured from EPR spectra at different temperatures and TEMPOL concentrations, and compared with the published data. The τ _c values were calculated both by known equations and from the EPR spectra simulation. Rotation movements of TEMPOL in omimBF₄ cannot be described by the model of the isotropic Brownian diffusion, which is valid for conventional solvents. The correct modeling of EPR spectra in RTIL can be achieved with the assumption of different rotational mobility of the spin probe around different molecular axes. The rotational, D _rot, and translational, D _tr, diffusion coefficients were calculated from τ _c and k _e values. The Debye–Stokes–Einstein law is valid in all three solvents while the dependence of D _tr on T/η is not linear in Stokes–Einstein coordinates. The effective activation energy E _rot^a of the rotational movements in omimBF₄ is noticeably higher than the corresponding values for conventional solvents, while the effective activation energies E _tr^a of the translational movements are comparable in all solvents studied.     

Effects of high-pressure heat treatment on the solid-state phase transformation and microstructures of Cu61.13Zn33.94Al4.93 alloys

The phase transformation activation energy of the Cu61.13Zn33.94Al4.93 alloys, which were treated at 4 GPa and 700℃ for 15 minutes, was calculated by means of differential scanning calorimetry curves obtained at various heating and cooling rates. Then, the effects of high-pressure heat treatments on the solid-state phase transformation and the microstructures of Cu61.13Zn33.94Al4.93 alloys were investigated. The results show that high-pressure heat treatments can refine the grains and can change the preferred orientation from (111) to (200) of α phase. Compared with the as-cast alloy, the sample with high-pressure heat treatment has finer grains, lower β′→β and β→β' transformation temperature and activation energy. Furthermore, we found that high cooling rate favours the formation of fine needle-like α phase in the range of 5-20℃/min.     

Transition processes occurring under continuous and stepwise heating of GaAs surface-barrier structures

Evolution of the capacitance-voltage (C-U) and current-voltage (I _f-U and I _r-U) characteristics of solid metal-semiconductor structures (Ni/GaAs) in the process of their continuous and stepwise heating are studied. Properties of the initial structures obey the theory of thermionic emission. It has been shown that as a result of continuous heating, the rectifying structures become ohmic at a temperature of T _Ohm=720 K, which is substantially lower than the melting points of the metal or the metal-semiconductor eutectic. For comparison, properties of the structures annealed at different temperatures T _ann are measured after cooling to room temperature (stepwise heating). In this case, I-U characteristics are closer to the initial ones for annealing temperatures T _ann<T ₀=553 K; for T _ann>T ₀, the characteristics display excess currents; and, finally, for T _ann exceeding T ₀ by 200–300 K, the characteristics become purely ohmic. It is suggested that these effects are due to a chemical interaction between Ni and GaAs, which changes the properties of the semiconductor surface.     

Effect of atomic hydrogen on the properties of metal-GaAs Schottky barrier contacts

The effect of treatment with atomic hydrogen on the properties of GaAs and the characteristics of Au−GaAs Schottky barrier contacts has been studied in terms of the ideality coefficient n of the I-V characteristics, the barrier height ϕ _b , and the reverse breakdown voltage V_r at 10 μA. The source of the atomic hydrogen was a generator based on an arc reflected Penning discharge with a self-heating element. It has been shown that there is an optimal treatment regime (temperature (T_tr) 200–250°C; duration (t_tr) 5 min) for which n and V_r reach a corresponding minimum and maximum. It is proposed that with lower T_tr and t_tr there is nonuniform etching of the surface oxides and with higher it is possible to have nonuniform etching of the GaAs itself. The barrier height depends on the treatment regime in a more complicated way but on the whole decreases. The effect of passive impurities (decrease in the charge carrier concentration) is already pronounced at T_tr=100°C and changes relatively little with further growth of the temperature. Annealing (reactivation of impuritics) is observed for T≥250°C with sufficiently slow cooling of the sample after treatment. State Scientific-Manufacturing Enterprise for NII Semiconductor Devices. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 115–121, August, 1997.     

用简并四波混频对聚[3’-甲基-4’-二(N,N-氧亚乙基)胺基-4-硝基偶氮苯癸二酰]薄膜三阶非线性光学性质、光信息储存及光致异构过程的研究

通过简并四波混频法(DFWM)对“聚[3’-甲基-4’一二(N,N-氧亚乙基)胺基-4-硝基偶氮苯癸二酰]”薄膜的三阶非线性光学性质进行了研究,测得其三阶非线性系数X⁽³⁾达到6.6×10^-5esu.通过EFWM,测得样品有很强的光信息储存,另外通过对材料的光致异构过程的研究,测得在上升和下降过程中相位共轭光I^pc与时间t均满足确定的关系式,并与文中所推的理论相符.