Some thermally and optically induced changes of optical properties of amorphous As38S62 films

The exposure (in air) of As₃₈S₆₂ amorphous film was found to be accompanied (i) by significant structural changes in the film matrix (an increase of As-S bond density as indicated by IR spectroscopy), and (ii) by darkening of the film. No indications of photo-oxidation have been found. Exposure and subsequent annealing of the well-annealed film are accompanied by reversible changes of the As-S bond density, as indicated by the results of differential infrared spectroscopy. The dispersion of the refractive index of the virgin, annealed and exposed films can be described using the Wemple-DiDomenico (W-D) single-oscillator formula. Annealing- and exposure-induced changes of the parameters of the W-D formula follow the changes of both the optical gap and the As-S bond density.     

Photo-induced changes in the optical properties of amorphous As-Ge-S thin films

Changes in the transmission, absorption edge and refractive coefficient in the UV-VIS and the transmission in the IR spectrum of thin As-Ge-S films after irradiation with an argon laser with =488 nm were studied. X-ray microanalysis showed that the composition of the films (with small variations) corresponded to that of the initial substances. Films with a defined concentration of the elements could also be deposited by evaporation of As₂S₃ and GeS₂ from two sources. The optical properties of thin films prepared by thermal evaporation, flash evaporation and coevaporation from two crucibles have been compared. It was found that depending on the component content, both photodarkening and photobleaching coatings in a wide region of can be obtained in thin As-Ge-S films. The results have been explained from the viewpoint of the photostructural changes in chalcogenide layers.     

Electrical and optical properties of amorphous (In, Sn)-Ga-Zn-O thin film

Films of amorphous In(1-x)Sn(x)GaZnO(delta) (a-ISGZO) (x = 0.0-1.0) were pulsed laser deposited at a temperature range of room temperature to 300 degrees C, and in order to systematically investigate the effect of replacing In with Sn on the properties of amorphous In-Ga-Zn-O (a-IGZO), the electrical and optical properties were measured. The amount of Sn in the deposited film, which was determined by X-ray photoelectron spectroscopy, was very close to the composition of the targets used. Hall mobility and carrier concentration decreased, and resistivity increased as the amount of Sn in the film increased. It was observed that the increase of Sn concentration in films was accompanied by the decrease of oxygen vacancy concentration, which led to the decrease of carrier concentration. The electrical mobility was decreased as the amount of Sn increased, which can be attributed to the increased number of subgap states, which was determined by the UV/VNIS spectrophotometer. Optical transparencies of all samples were larger than 80% in the visible light range. Band gap values were also found to increase as the amount of Sn increased.     

Gamma-ray irradiation induced structural and optical constants changes of thermally evaporated neutral red thin films

Neutral red (NR) is polycrystalline in powder form, it transforms to nanocrystallite phase upon thermal deposition. Gamma-ray irradiation with doses 1.25–6 KGy induced partial transformation of nanocrystallite phase to amorphous structure. The changes of optical constants with γ-ray doses were calculated using spectrophotometer measurements of transmittance and reflectance at normal incidence of light over spectral range 200–2500 nm. The complex refractive index of NR film is highly influenced by exposure to γ-ray irradiation, the onset and optical energy gaps decrease with increasing γ-ray doses, and Urbach tail increases linearly with increasing irradiation dose. The type of electronic transition, oscillator, and electric dipole strengths and dispersion parameters were determined before and after irradiation. The spectral behavior of dielectric constant with γ-ray doses was also estimated.     

Thermally and optically induced irreversible changes in some Ge–As–S amorphous thin films

Thermally and optically induced irreversible changes in the optical gap and refractive index were studied for sulphur rich, nearly stoichiometric and sulphur poor Ge–As–S amorphous films prepared by thermal evaporation. For films studied the optical gap in the virgin state decreases from 2.55₉ (Ge_0.121As_0.172S_0.707) to 1.63₂ eV (Ge_0.254As_0.294S_0.452) and simultaneously the refractive index increases from 2.21 to 2.87, respectively. The most sensitive composition to illumination seems to be nearly stoichiometric film (Ge_0.153As_0.201S_0.646), where the blue shift of the gap is observed close to 150 meV. Sulphur poor film (Ge_0.254As_0.294S_0.452) was found insensitive to illumination. Highest thermally induced blue shift of the gap, close to 250 meV, we observed just for Ge_0.254As_0.294S_0.452 film and for this film it was observed also nearly “giant” decrease in refractive index from 2.85 to 2.42. The behaviour of Ge_0.254As_0.294S_0.452 film is qualitatively discussed using the concept of network rigidity (insensitivity to illumination) and assuming thermally induced changes in bonding arrangement (refractive index changes).     

Structural and optical properties of thermally evaporated 1,4,8,11,15,18,22,25-octahexylphthalocyanine thin films

Metal-free 1,4,8,11,15,18,22,25-octahexylphthalocyanine was prepared directly by the cyclotetramerization of 3,6-dihexylphthalonitrile using lithium butoxide in butanol. Thin films of the material were deposited on glass substrates by the thermal evaporation technique. The structure of the films was found to be in the form, and showed a strong peak indicating preferential orientation. The surface morphology of the thin films was investigated by atomic force microscopy and showed that the molecules of 1,4,8,11,15,18,22,25-octahexylphthalocyanine grow in stacks of parallel rows. The spectrophotometric measurements of transmittance and reflectance were carried out in the wavelength range 190–3000 nm. The refractive index, n, and absorption index, k, were found to be independent of annealing at 373 K. The B band absorption occurred at 356 nm, and the Q band showed a doublet at 667 and 739 nm. Other optical parameters, such as absorption coefficient and optical dielectric constant ε, were determined.     

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.     

Pr掺杂ZnTe薄膜的结构及光学特性

利用真空蒸发的方法制备ZnTe多晶薄膜.并采用双源法对薄膜进行了稀土元素Pr的掺杂.用XRD、紫外可见分光光度仪、冷热探针对薄膜的性质进行了表征.结果表明,当原子配比Zn:Te:1:0.7,热处理温度T=500℃时,可制备较理想的ZnTe多晶薄膜.稀土Pr掺杂并未改变样品的物相结构,但使薄膜光吸收增大而光学带隙增大.     

磷酸亚铁锂纳米薄膜的制备及其光学性能

将水热法合成的LiFePO4粉体作为原料,通过浸渍-提拉法制备了LiFePO4纳米薄膜。观察了热处理温度对薄膜折射率和透光率等光学性能的影响。结果表明,在120～450℃范围内,随着热处理温度的升高,薄膜折射率和透射率(在可见光区)增大,并膜厚减小。     

Microstructural transitions and dielectric properties of boron-doped amorphous alumina thin film

Dielectric Al_2?x B _x O_Y thin films were deposited onto Pt (100)/Ti/SiO₂/Si substrates via sol–gel and spin-coating technology. The microstructural transition occurred at ~500 °C due to boron loading was confirmed by DSC and XRD. FTIR, ²⁷Al MAS NMR and XPS measurements were employed to investigate the microstructural transition caused by different boron concentrations. The results revealed that Al–O–B bonds and [AlO₄] tetrahedrons were produced resulting in the reinforcement of structure with relatively low boron concentrations. With the increase of boron concentration, [BO₃] chains and new surfaces crossing over the internal structure gradually produced and disrupted the structural stability. Meanwhile, hydroxyl groups were accumulated in the internal structure owing to the hydrophilic property of boron. According to the reinforced structure with low boron concentrations, the current density decreased and the breakdown strength was enhanced. Typically, the current density was decreased two orders of magnitude at 100 MV m^?1 and the breakdown strength of the 0.5 mol% B-doped alumina thin film was increased by 59% (from 293 to 465 MV m^?1) in comparison with that of the undoped alumina thin film, whereas the dielectric properties gradually become poor due to the weak structure with the increase of boron concentration. Moreover, the dielectric constant increased owing to hydroxyl groups when the boron doping increased. This work may provide a general strategy for enhancing dielectric properties of the alumina thin film.     

Photo- and thermo-induced changes in the properties of thin amorphous As-S films

Changes in transmittance, refractive index, transmissivity in the infrared spectral region, and activation energy of the dissolution process were studied for thin films of the system As _x S_100–x (28.6 x45) as they result from illumination and annealing at temperatures of T _g . It is assumed that the irreversible changes occurring in the layers after treatment are accompanied by an increase in the concentration of As-S bonds. This leads to an increase in dissolution rate, a decrease in the activation energy of the process, and considerable changes in the absorption peaks at 370 and 310 cm^–1 obtained by infrared spectroscopy. It is shown that the photo- and thermoinduced changes in as-deposited chalcogenide films follow identical courses. The results obtained are explained from the viewpoint of the structural changes occurring in chalcogenide films.     

A study of the optical properties of amorphous thin films of germanium and silicon monoxide

Amorphous films of Ge-SiO have been co-evaporated and some of their optical properties are reported. The optical constants have been measured and estimated. At the high absorption end of the absorption edge, an equation due to non-direct transitions inK-space is found to match the optical absorption data. The variation of the optical band gapE _opt with film composition is reported. The infrared spectrum of a mixed layer is presented and a simple conclusion is drawn.     

致密ZnO薄膜的电化学制备及光学性能研究

采用电化学沉积法在ITO导电玻璃上沉积1层致密的ZnO薄膜。用扫描电镜（SEM）对在不同电解液浓度、电压和时间下制备的ZnO薄膜的表面形貌作了表征,并观测了ZnO薄膜的厚度,结果表明当电解液的质量分数为1.2%,电压为1.0V,时间为60s时,制备的ZnO薄膜致密且厚度仅为120nm,利用分光光度计测得ZnO薄膜在可见光波段的透射率高于50%,为ZnO薄膜在多层光学超材料中的应用奠定了基础。     

Comparative analysis of temperature thermally induced instability between Si-In-Zn-O and Ga-In-Zn-O thin film transistors

Thermally induced instability of amorphous Si-In-Zn-O (SIZO) with 1 wt.% silicon (Si) concentration and Ga-In-Zn-O (GIZO) with gallium (Ga) of 30 wt.% thin film transistors (TFTs) has been investigated, by comparing the density of states extracted from multi-frequency method. It was observed that the density of state of SIZO-TFT was lower than that of GIZO-TFT, in spite of low processing temperature of SIZO-TFT and thermally induced instability of SIZO- and GIZO-TFT was strongly related with the total trap density. We report that Si of only 1 wt.% in SIZO can improve thermal stability of threshold voltage of In-Zn-O based TFTs more effectively than Ga of 30 wt.% in GIZO.     

Electrical and optical properties of diketopyrrolopyrrole-based copolymer interfaces in thin film devices

Two donor-acceptor diketopyrrolopyrrole (DPP)-based copolymers (PDPP-BBT and TDPP-BBT) have been synthesized for their application in organic devices such as metal-insulator semiconductor (MIS) diodes and field-effect transistors (FETs). The semiconductor-dielectric interface was characterized by capacitance-voltage and conductance-voltage methods. These measurements yield an interface trap density of 4.2 × 10(12) eV?1 cm?2 in TDPP-BBT and 3.5 × 1012 eV?1 cm?2 in PDPP-BBT at the flat-band voltage. The FETs based on these spincoated DPP copolymers display p-channel behavior with hole mobilities of the order 10?3 cm2/(Vs). Light scattering studies from PDPP-BBT FETs show almost no change in the Raman spectrum after the devices are allowed to operate at a gate voltage, indicating that the FETs suffer minimal damage due to the metal-polymer contact or the application of an electric field. As a comparison Raman intensity profile from the channel-Au contact layer in pentacene FETs are presented, which show a distinct change before and after biasing.     

A comparison of the optical properties of glass and of evaporated amorphous thin films of BaO-TeO2

Two series of glass and thin film specimens of BaO-TeO₂ were prepared. The optical absorption edges and infrared absorption spectra were investigated. It was found that the fundamental absorption edge is a function of BaO content in both kinds of films and that the absorption is due to indirect electronic transitions. The values of optical gap for blown films were greater than those of thin evaporated films, but the widths of the band tails were greater for the evaporated thin films, which were expected to be more disordered than the thin blown glass films.     

Interface specific variations in the steady-state optical properties of polyfluorene thin films

The top and bottom interfaces of spin cast poly(di-n-octylfluorene) (PF8) and poly[bis(2-ethylhex-yl)fluorene] (PF2/6) films are investigated by optical absorption and emission spectroscopy. In this study both the pure polyfluorene homopolymers and random copolymers comprised of linear di-n-octyl (F8) and the branched bis(2-ethylhexyl) (F2/6) units are used. PF2/6 is noted for forming a single conformationally disordered helix whereas PF8 adopts a number of near-planar conformational isomers. PF2/6, PF8 and their copolymers form asymmetric films in which the local structure at or near the top and bottom interfaces are distinctly different. This asymmetry is least apparent in pure PF2/6 films but increases in F8 containing polymers. In polymers containing a large fraction of F2/6 monomers the substrate-polymer side exhibits chains with slightly improved intrachain structural order and also increased green band emission. The effects of thermal and solvent vapor annealing are also reported.     

化学水浴法制备ZnS薄膜及其光学性能

以酒石酸与柠檬酸钠为络合剂,采用化学水浴法(CBD)沉积ZnS薄膜.利用X射线衍射仪(XRD)、X射线能谱仪(EDAX)、扫描电镜(SEM)、紫外-可见分光光度计(UV-Vis)研究ZnS薄膜的结构、组成、形貌及光学性能,利用透射光谱计算ZnS薄膜的光学禁带宽度(Eg).结果表明:ZnS薄膜呈立方相晶体结构,经过300℃熟处理1h的ZnS薄膜原子比为Zn:S=1:0.85,表面均一致密,在可见光区的平均透射率达到80%,光学禁带宽度为3.74ev,适合作为太阳能电池过渡层.     

GaN薄膜大型V形表面坑的形成和光学性质

研究了用MOCVD设备在高温和低Ⅴ/Ⅲ条件下生长的GaN薄膜表面存在的与位错相连的大型Ⅴ形表面坑,并提出了一个有关质量疏运机制的模型以解释其形成机理.由衬底扩散上出来的Al原子对大型坑的形成具有辅助作用,并阻止了深能级杂质或空位缀饰与坑相连的位错.GaN内的位错是非辐射复合中心,但对深能级发光不起作用.