Study on electrical transport and photoconductivity in iodine-doped cellulose fibers

The electrical transport and photoconductivity of pure and iodine-doped cellulose fibers have been studied. The studies were conducted in the temperature range 293–363 K, while the electric field was varied over the range 1–100 V cm⁻¹. The conductivity of the iodine-doped cellulose fibers shows significant enhancement by more than four orders of magnitude as compared to undoped samples. The analysis reveals that the electrical conduction follows Ohm’s law for iodine-doped samples, while for the undoped samples the bulk-limited Pool–Frenkel conduction mechanism is likely to dominate for the steady state current. Especially, the clear photoconduction response at UV and visible region indicates that photoconduction is essential due to band-to-band electron–hole pair’s generation and that doped CF is a good conductor of photogenerated carriers.     

Effect of UV radiation on the relaxation characteristics of ferroelectric thin-film capacitors

The effect of UV radiation with a wavelength near the fundamental absorption edge on the relaxation characteristics of ferroelectric capacitors based on thin (Ba,Sr)TiO₃ (BSTO) films has been studied. The absorption spectra of BSTO films with thicknesses up to 1 μm obtained by RF magnetron sputtering on sapphire substrates have been measured in a 300–600 nm wavelength range, the UV radiation penetration depth in this material was determined, and the optical bandgap width was evaluated. It is established that UV irradiation leads to a significant decrease in the relaxation time of the residual capacitance of BSTO-film-based structures. A minimum relaxation time is achieved upon the irradiation in a 350–360 nm wavelength interval.     

紫外光对芳香族聚噁二唑纤维结构和力学性能的影响

采用一步三阶段式控制法制备了一系列结构及环化率不同的芳香族聚噁二唑纤维,并研究了紫外光老化前后纤维结构和力学性能的变化,初步探讨了其光老化机理。结果表明,光老化24h,纤维强度保持30%,特性黏度保留60%;X射线衍射谱图显示老化后纤维晶粒尺寸发生变化;红外图谱表明老化后1710cm-1附近产生新的羰基吸收峰,可能生成羰基化合物;从扫描电镜观察到老化后试样表面变得粗糙,出现沟槽等现象。     

聚多巴胺修饰聚对苯撑苯并双噁唑纤维增强其抗老化性与功能性

高性能纤维聚对苯撑苯并双噁唑(PBO)容易受紫外光照射而导致其性能显著下降。为了提高PBO材料的抗老化性能,文中通过简易方法在纤维表面直接修饰富含酚羟基的纳米厚度的聚多巴胺薄层,并比较研究了初始纤维与多巴胺修饰纤维在紫外光照射前后的力学性能、热稳定性能、结晶取向等性能的变化。结果表明,未经修饰的PBO纤维的力学等性能在紫外光照射后显著下降,如拉伸强度下降了67%;而表面经过修饰的PBO纤维在经过紫外光照射后,其性能变化显著减小,如拉伸强度仅下降了33%。并且,聚多巴胺修饰的PBO纤维对污染物罗丹明B染料等具有一定的吸附性能,吸附24 h的吸附容量达0.25 mg/g。因此,在材料表面修饰聚多巴胺层可有效改善PBO纤维的抗紫外光老化性能,提高了材料的功能性。     

Fabrication of micro-patterned TiO2 thin films incorporating Ag nanoparticles

A photosensitive TiO₂ thin film embedded with Ag nanoparticles has been prepared from a Ti(OBu)₄–acetylacetone solution, containing dispersed Ag nanoparticles, by the sol–gel method. UV–visible absorption spectra showed that the thin film obtained has two absorption bands, characteristic of the acetylacetone chelate rings and plasmon resonance from Ag nanoparticles. After the irradiation of UV light, the absorption band from the chelate rings almost disappeared, ascribed to structural changes associated with dissociation of the chelate rings. The thin film after the UV irradiation exhibited a broad absorption band in the IR spectrum, indicating that a Ti–O–Ti network was formed in the thin film. HRTEM and EDX spectra revealed that Ag nanoparticles were present and dispersed in the TiO₂ thin film. Micro-patterns of 50 μm dots have been fabricated by UV irradiation through a corresponding photomask, followed by leaching.     

Rapid erasing of wettability patterns based on TiO2-PDMS composite films

TiO₂-polydimethylsiloxane (TiO₂-PDMS) composite films are prepared using the sol–gel method from a Ti(OBu)₄–benzoylacetone solution containing PDMS. The prepared films are cured by irradiation with ultraviolet (UV) light. Structural changes in the films after UV irradiation are confirmed by UV–vis absorption experiments, which show that an absorption band characteristic of the benzoylacetonate chelate rings disappears. This finding is ascribed to structural changes associated with the dissociation of the chelate rings. The IR spectra of the thin films exhibit a broad absorption band after UV irradiation, indicating that a Ti–O–Ti network forms in the thin film. Contact angles are measured for the TiO₂-PDMS thin films, showing wettability conversion from hydrophobic to superhydrophilic states by irradiation with oxygen plasma for 1 s. This phenomenon is explained by XPS experiments which reveal that the number of carbon atoms decreases, whereas the number of oxygen atoms increases on the surface of the TiO₂-PDMS composite films. Finally, hydrophobic–superhydrophilic patterns are fabricated based on a patterned TiO₂-PDMS composite film. The film displays a rapid change to superhydrophilicity over the whole film surface upon plasma irradiation for 1 s, which means that the wettability patterns are rapidly erasable.     

Nanoarchitectonics of SnSe with the impacts of ultrasonic powers and ultraviolet radiations on physical and optoelectronic properties

In this study, SnSe nanostructures prepared by the precipitation method were exposed to the irradiation of ultrasound waves at different powers and ultraviolet (UV) rays. The results of structural analyses revealed the formation of SnSe nanostructure phases and the presence of Sn and Se, respectively. The structural properties, including stress and strain, were calculated for all main peaks obtained from the XRD analysis conformed to the orthorhombic phase. The FESEM images demonstrated that they were narrow-size nanorods alongside agglomeration particles dispersed in all samples. PL results illustrated changes in the ultrasonic power, UV, and simultaneous irradiation of these waves led to the shift of emission bands and intensities. The absorption spectra were measured in the range of 200–1100 nm, indicating that they were shifted into higher wavelengths. Additionally, energy band gap (E_g) changes showed that their E_g was in the range of ～ 1.30 eV. I-V characteristics results demonstrated that increase of ultrasonic power, UV, and ultrasound irradiation resulted in the enhancement of responsivity and sensitivity. Furthermore, they had detectivity in the range of 12–122 × 10⁷ (Jones). Moreover, the irradiation of ultrasound and UV rays had a considerable impact on mobility and carrier concentration.     

Structural changes of polyacrylonitrile precursor fiber induced by γ-ray irradiation

The structural changes of polyacrylonitrile precursor fibers under γ-ray irradiation were studied. The Fourier transform infrared spectroscopy (FTIR) results indicated that chemical reactions occurred in the irradiated fibers. The thermal and thermal mechanical behaviors of the fibers, which were characterized by differential scanning calorimetry (DSC), thermal gravimetry (TG) and thermal mechanical analysis (TMA), changed under irradiation, since ladder structure had formed in the fibers under irradiation prior to the heating process. The crystallinity and crystallite size were found to decrease with the increase of irradiation time, as the chemical reactions induced by γ-ray irradiation affected the crystal structure of the fibers. γ-ray irradiation may be useful in accelerating the thermal stabilization of PAN precursor fibers.     

Preparation of porous ultra-fine poly(vinyl cinnamate) fibers

In this study, a new method of preparing porous ultra-fine fibers via photo-crosslinking was developed. Ultra-fine poly(vinyl cinnamate)/poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PVCi/PHBV) blend fibers were electrospun and then the PVCi was photo-crosslinked by UV irradiation. PVCi and PHBV were immiscible and the phase separation proceeded during the electrospinning process. After the photo-crosslinking of PVCi, PHBV was extracted from the blend fibers with chloroform. The average pore sizes in the remaining ultra-fine PVCi fibers were increased with increasing the content of PHBV in the ultra-fine PVCi/PHBV fibers.     

Preparation and characterization of organic layers for UV protection of polycarbonate

In many applications, polycarbonate surfaces need to be coated as a protection against abrasion and decomposition caused by weathering. In particular, UV radiation during exposure to sunlight degrades polycarbonate, which causes delamination of the protective layer. To avoid coating delamination, the layer itself needs an absorption edge near 400 nm. One option is to use UV-absorbing organic molecules. The aim of the present study was to develop UV-protective layer stacks containing suitable organic molecules deposited in a vacuum process, with a focus on the stability of UV-absorbing organic layers during UV irradiation and their optical properties. The commercial UV absorber Tinuvin™ 360 and the organic compound N,N′-di(naphth-1-yl)-N,N′-diphenyl-benzidine were used. Thin layers of the organic materials were evaporated thermally. The optical properties and UV stability were investigated using UV-VIS and infrared spectroscopy.     

Effect of gamma irradiation on the optical properties of amorphous GeSe films

We have studied the influence of gamma irradiation in a ⁶⁰Co source (1.25 MeV, gamma doses from 10² to 10⁶ Gy) and subsequent storage for a year on the structure, fundamental absorption edge, and refractive index of a-GeSe films prepared by flash evaporation in vacuum on silica substrates (T _s = 293 K). The high-energy irradiation has been shown to stimulate structural transformations and to produce changes in the electron-defect subsystem of the films.     

Influence of ultraviolet irradiation on the optical properties of amorphous Sb10Se90 thin films

Amorphous Sb₁₀Se₉₀ thin films were prepared by thermal evaporation of the bulk glass. The changes in the optical properties (transmittance, optical gap, absorption coefficient, refractive index and extinction coefficient) have been measured in the wavelength range 500-900 nm of virgin and ultraviolet (UV) illuminated films. Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. It is found that the optical energy gap decreases (photo-darkening) and the refractive index increases with the increase of UV exposure time. The dispersion of the refractive index (n) has been discussed in terms of Wemple-Didomenico single oscillator model. The oscillator energy E₀ and the dispersion energy E_d have been determined and discussed in terms of UV exposure time. The photo-darkening was discussed in terms of some of the current literature models.     

UV photooxidation induced structural and photoluminescence behaviors in vapor-etching based porous silicon

In this paper, we investigate the effect of UV irradiation on Vapor-Etching (VE) based Porous Silicon (PS) structure and luminescence under controlled atmosphere (N₂, air, O₂). The oxidation evolution is monitored by Fourier transform infrared (FTIR) spectroscopy. FTIR measurements show that the SiH_x bond, initially present in the freshly prepared PS layers, decreased progressively with UV irradiation time until they completely disappear. We found that this treatment accelerates the oxidation process. SiO_x structures appear and gradually become dominant as regard to the SiH_x species, while UV irradiation is in progress. Generally, the photoluminescence (PL) intensity of the PS layer decreases instantaneously at the starting by the UV excitation and stabilizes after a period depending on the ambient gas and the specific surface area of the porous structure. Further UV exposure leads to a linear decrease of the PL intensity due to change of surface passivation from SiH_x to O_ySiH_x. After less than 100 min of UV irradiation, the PL intensity exhibits an exponential decay. UV exposure in air and O₂ leads approximately to the same PL behavior, although faster PL intensity decrease was observed under O₂-rich ambient. This was explained as being due to intense hydrogen desorption in presence of oxygen. Correlations of PL results with FTIR measurements show that surface passivation determine the electronic states of silicon nano-crystallites and influence the photoluminescence efficiency.     

Structural and optical properties of thermally evaporated zinc phthalocyanine thin films

Thermally evaporated zinc phthalocyanine (ZnPc) films in the as deposited condition were identified to be as-amorphous. It undergoes structural transformation upon annealing up to 613 K. The optical properties and spectral behavior of as deposited and annealed thin films of ZnPc were studied using spectrophotometric measurements of the transmissivity and reflectivity at normal incidence of light in the wavelength range 200–2500 nm. The refractive index, n, and absorption index, k, were calculated and it was found that they are independent of film thickness in the thickness range 205–530 nm. Annealing at 613 K increases absorbance of films by 5–6 times in comparison with absorbance of as deposited ones and shifts peak positions of all bands towards low energy side of spectra except the peak position of N-band is shifted towards high energy side of spectra. The absorption spectra in the UV–VIS. region has been analyzed in terms of both molecular orbital and band theories. Indirect allowed transitions near the onset and fundamental absorption edges were observed. The energy at the onset was obtained and equals to 1.45 and 1.51 eV for as deposited and annealed films, respectively. The fundamental energy gap was obtained and equals to 2.94 and 2.88 eV for as deposited and annealed films, respectively. The absorption spectra shows four absorption bands. The oscillator strength, f, the electric dipole strength, q², the molar extinction coefficient, ζ_molar, were calculated for as deposited and annealed ZnPc thin films.     

Graphitization of polyacrylonitrile carbon fibers and graphite irradiated by γ rays

To investigate the effect of γ-ray radiation on the microstructure of carbon fibers (CF) and graphite, the carbon fibers and graphite were irradiated by ⁶⁰Co source at room temperature. X-ray diffraction results indicate that the interlayer spacing d₀₀₂ of CF and graphite decreased after irradiation. The intensity of (002) peak in CF decreased while the peak of the (002) plane in graphite becomes sharper after irradiation. Scanning electron microscopy combined with energy dispersive X-ray spectroscopy determines that γ-ray irradiation slightly improves the carbon content of CF surface layer. Compton scattering effect and heating caused by γ-ray are proposed to be responsible for the graphitization of CF and graphite.     

The comparative study of the photoelectric properties of crystalline and glassy SnGeS3

Comparative investigations of the steady-state characteristics of the photoconductivity for crystalline and glassy tin thiogermanate (SnGeS₃) in the temperature range of 100–500 K were performed. It was determined that the loss of the long-range order in SnGeS₃ at the crystal-glass transition results in the shift of the fundamental absorption edge to the long-wave region of the spectrum, disappearance of the absorption edge anisotropy and photoconductivity (PC) spectra, and reduction of the electrical conductivity. The presence of the same impurity peaks in PC spectra and the peaks on thermally stimulated current (TSC) curves and the identical character of temperature dependences of photoconductivity and lux-ampere characteristics (LAC) indicate the same type of defects, which generate the localized electronic states in the gap, controlling the processes of trapping and recombination in crystalline and glassy phases of SnGeS₃.     

Photoinduced hydrophobic surface of graphene oxide thin films

Graphene oxide (GO) thin films were deposited on transparent conducting oxide substrates and glass slides by spin coating method at room temperature. The wettability of GO thin films before and after ultraviolet (UV) irradiation was characterized with water contact angles, which increased from 27.3° to 57.6° after 3 h of irradiation, indicating a photo-induced hydrophobic surface. The UV-vis absorption spectra, Raman spectroscopy, X-ray photoelectron spectroscopy, and conductivity measurements of GO films before and after UV irradiation were taken to study the mechanism of photoinduced hydrophobic surface of GO thin films. It is demonstrated that the photoinduced hydrophobic surface is ascribed to the elimination of oxygen-containing functional groups on GO molecules. This work provides a simple strategy to control the wettability properties of GO thin films by UV irradiation.     

Enhanced luminescence of UV irradiated Zn(1−x)NixS nanoparticles

PVP-capped Zn_(1−x)Ni_xS (x = 0.001, 0.005, 0.01, 0.03, 0.05 and 0.1) nanoparticles have been synthesized using chemical precipitation route, in aqueous media, at room temperature. The synthesized nanoparticles have been irradiated by UV light for 24 h so as to study the effect on their structural and optical properties. The nanoparticles have been characterized through XRD and HRTEM to study the crystal structure and size. Characterization was also carried out through FTIR spectroscopy to reveal the presence of PVP and the effect of UV irradiation on the surface chemistry of the synthesized nanoparticles. The optical properties have been studied through UV–vis absorption spectroscopy and room temperature photoluminescence. There has been an enhancement in the intensity of the green emission centered at 547 nm, with increase in Ni concentration up to 0.5 at.% and a decrease in the intensity, observed for higher concentrations of Ni. However, the I(green)/I(blue) intensity ratio increases continuously with the increase in Ni concentration and also on prolonged UV irradiation of the samples.     

Gamma rays interactions with Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-doped Na<Subscript>2</Subscript>O–CdO–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses assessed by collective optical and FT infrared absorption spectroscopy

Undoped and Bi₂O₃-doped glasses from the system Na₂O–CdO–P₂O₅ were prepared and studied through investigating their optical and FTIR spectra before and after gamma irradiation beside measuring their thermal expansion properties. Optical spectra reveal distinct UV absorption with additional peaks upon introducing Bi₂O₃ added with different concentrations from 1 to 7.5%. The UV absorption of the undoped sample is related to trace iron impurities while the extended UV absorption peaks are correlated with absorption of Bi³⁺ ions. FTIR spectra show condensed phosphate groups (Q², Q³ units) beside the sharing of bismuth ions in their vibrational sites. Gamma irradiation causes limited changes in the UV spectra but involves the generation of an induced visible band in the undoped glass. These changes are assumed to be due to some suggested photochemical reactions on the trace iron impurities and the formation of an induced visible (POHC) band on the phosphate network. Careful inspection of the selected deconvoluted spectra for the undoped glass and doped (7.5 wt%) supports the introduced assumptions. The thermal expansion parameters are correlated with the type of bonding of bismuth ions within the network structure.     

On the optical properties of bismuth oxide thin films prepared by pulsed laser deposition

The optical properties of bismuth oxide films prepared by pulsed laser deposition (PLD), absorption in the photon energy range 2.50-4.30 eV and optical functions (n, k, ?₁, and ?₂) in the domain 3.20-6.50 eV, have been investigated. As-prepared films (d=0.05-1.50 μm) are characterized by a mixture of polycrystalline and amorphous phases. The fundamental absorption edge is described by direct optical band-to-band transitions with energies 2.90 and 3.83 eV. The dispersion of the optical functions provided values of 4.40-6.25 eV for electron energies of respective direct transitions. In the spectral range 400-1000 nm, bismuth oxide films show a normal dispersion, which can be interpreted in the frame of a single oscillator model.