液晶光阀用ZnSSe薄膜的光电特性研究

用分子束外延法(MBE),在铟锡氧化物(ITO)导电玻璃衬底上生长了ZnSSe薄膜,详细研究了薄膜的光电特性.通过控制反应时的生长参数,制备出了符合紫外液晶光阀设计要求的光导层薄膜.室温下,该薄膜光谱响应截止边的响应度为0.01A/W,紫外/可见光响应对比度大于103.薄膜的暗电阻率随薄膜晶粒增大而减小,在衬底温度为2900C时,所获得的ZnSSe薄膜具有4.3×1011Ω@cm的暗电阻率.频率从40Hz到4000Hz的交流特性测试,也证实该薄膜符合器件紫外成像的工作要求.     

Holographic patterning of luminescent photopolymer nanocomposites

Volume phase gratings in the photopolymerisable composites, containing luminescent nanoparticles have been fabricated for the first time. Nanoparticles of LaPO₄, doped by Ce³⁺ and Tb³⁺ ions (the trade name is REN-X-green) with high luminescence quantum yield were used as a luminescent inorganic additive. The holographic gratings in such materials are formed as a result of the diffusion distribution of the nanoparticles during exposure of photopolymerisable composites to interference pattern. The influence of the pre-polymer formulation and the holographic patterning parameters on the grating formation is comprehensively investigated. The use of the optimised pre-polymer syrup containing two monomers with sufficiently different polymerisation rates allows fabrication of gratings with diffraction efficiency up to 80% at low optical losses (< 5%) (20 μm film thickness). To obtain maximum diffraction efficiency the intensity and the period of the interference pattern were optimised for each formulation. In addition maximum diffraction efficiency was achieved with the nanocomposites containing 30–32 wt.% of nanoparticles. On the other hand the highest possible modulation of the nanoparticles' concentration was obtained for the concentration of about 20 wt.%. In this case maximum ordering of the nanoparticles in the polymer matrix is achieved. The photoluminescence of the nanoparticles within the homogeneous polymer film and within the grating has been measured. The example application of the photopolymerisable composite containing luminescence inorganic nanoparticles in holographic security technology has been demonstrated.     

Photonic crystal fiber for dispersion compensation

The dispersion and mode characteristics in a dual-concentric-core photonic crystal fiber, based on pure silica, are simulated by the multipole method. The fiber exhibits very large negative dispersion due to anticrossing of two individual inner core and outer core modes. Near the wavelength of 1.55 microm, we could obtain narrowband dispersion-compensating fiber with dispersion values of -23,000 ps/km/nm, broadband dispersion-compensating fiber with dispersion values from -1000 ps/km/nm to -2500 ps/km/nm over a 200 nm range, and kappa values near 300 nm, which matched well with standard single mode fiber. It shows that even if there are some changes in the structure parameters during fabrication, these fibers can still maintain a fine dispersion-compensating property.     

Photonic crystal surface waves for optical biosensors

We present a new optical biosensor technique based on registration of dual optical s-polarized modes on a photonic crystal surface. The simultaneous registration of two optical surface waves with different evanescent depths from the same surface spot permits the segregation of the volume and the surface contributions from an analyte, while the absence of metal damping permits an increase in the propagation length of the optical surface waves and the sensitivity of the biosensor. Our technique was tested with the binding of biotin molecules to a streptavidin monolayer that has been detected with signal/noise ratio of approximately 15 at 1-s signal accumulation time. The detection limit is approximately 20 fg of the analyte on the probed spot of the surface.     

Photonic crystal-assisted light extraction from a colloidal quantum dot/GaN hybrid structure

We present a study of the light extraction from CdSe/ZnS core/shell colloidal quantum dot thin films deposited on quantum well InGaN/GaN photonic crystal structures. The two-dimensional photonic crystal defined by nanoimprint lithography is used to efficiently extract the guided light modes originating from both the quantum dot thin films and the InGaN quantum wells. Far-field photoluminescence spectra are used to measure the extraction enhancement factor of the quantum dot emission (x1.4). Microphotoluminescence measurements show that the guided mode effective extraction lengths range between 70 and 180 microm, depending on the wavelength of light.     

Enhanced light extraction efficiency for glass scintillator coupled with two-dimensional photonic crystal structure

In order to improve the light extraction efficiency for Tb³⁺-doped glass scintillator, we propose an effective approach by incorporating a two-dimensional photonic crystal structure: a periodic array of hexagonally close-packed polystyrene nanosphere monolayer onto glass surface. The in-plane vector for the light suffering total internal reflection is changed into light cone resulting light emission out of glass. The optimized diameter of polystyrene nanosphere is 500 nm and the maximum enhancement of extraction efficiency reaches 25%. The enhancement shows angular dependence from the far-filed distribution pattern.     

Mechanical stability of sol-gel films

The relationship between film cracking and film thickness has been studied experimentally for films of ceria gel deposited by spinning on to stainless steel substrates from an aqueous ceria sol. A critical film thickness below which films were crack-free was observed at about 0.6 m. For films thicker than the critical thickness the crack spacing was approximately ten times the film thickness. Existing models for the mechanical stability of the films were examined to explain the observations, encompassing different forms of relaxation of the stress in the vicinity of a crack through the film. The model in best accord with the experimental observations is one in which stable delamination cracks are formed at the film-substrate interface on both sides of a crack through the film. However, for the model to be applicable some rather restrictive conditions must be assumed to be satisfied.     

Enhancement of light extraction efficiency of ultraviolet light emitting diodes by patterning of SiO2 nanosphere arrays

Here we introduce a simple and robust method to improve the light extraction efficiency of ultraviolet light emitting diodes (UV LEDs). Although many previous efforts have focused on etching the GaN surfaces, we employed a simple solution process to texture the GaN surface. Arrays of SiO₂ nanosphere monolayers were spun cast onto a polymer layer, consisting of benzocyclobutene (BCB) resins; subsequently, the bottom half of the SiO₂ nanospheres sunk into the BCB layer. The resulting array formed in a hexagonal-like pattern of ‘nano-lenses’ and the photoluminescence measurement exhibited that these patterns enhanced the light extracting efficiency of UV LEDs by 23%.     

Direct patterning of polymer-based photo luminescent structures with a mask

We report a simple method to directly pattern polymer-based photo luminescent material, i.e. a prepatterned mask is placed a close distance above it. The final structure is a positive replica of the lateral structures in the mask with submicrometer resolution. The comparison of luminescence efficiency before and after patterning indicates almost no degradation in optical property of the material during the experiments. The mechanism of pattern formation is also discussed.     

Influence of crystal structure on the light scatter of zirconium oxide films

The relationship of light scatter by a thin film to thin-film morphology is examined. Light scatter by reactively evaporated ZrO(2) thin films is analyzed by using in situ total internal reflection microscopy and angle-resolved scatterometry. Film crystal structure is analyzed by transmission electron microscopy and x-ray diffraction. Relations between film crystal structure and film scatter are established by using this information. Surface topography is analyzed by the use of scanning force microscopy. Results of a spectrophotometric determination of the film refractive index are reported. The film scatter is found to be sensitive to the crystal phase of the film, which is a function of substrate deposition temperature. A simple method of separating bulk from surface scatter is described.     

Lithographic patterning of superconducting YBCO films

Microbridges of YBa₂Cu₃O₇ thin films have been fabricated by conventional photolithography and wet chemical etching using EDTA, and by the lift-off lithography technique. The variation of etch rate with etch time, etchant temperature, and post-deposition sintering temperature has been studied. It has been shown that both techniques are useful for film patterning. However, an additional sintering step is necessary for the chemically etched sample to regain the original film properties. An order of increase in critical current density is observed for the patterned film.     

Crystallinity and luminescent properties of citrate sol-gel derived BAM phosphor

By adopting a facile citrate sol-gel process, pure well-crystallized BaMgAl₁₀O₁₇:Eu²⁺(BAM) blue phosphors were successfully prepared. The crystallinity, particle size, morphology, chemical composition and luminescent properties were characterized by XRD, FE-SEM, EDS and spectrofluorometer respectively. The results indicated the precursor was amorphous below 800 °C, and begun to crystallize at 1100 °C. The synthesis temperature decreased by about 300 °C compared to solid-state method to prepare BAM. FE-SEM images showed a well-crystallized, platelet morphology with a particle size of 1-3 μm. The obtained BAM phosphors were fine powders and had higher luminescent intensity compared to solid-state derived BAM phosphors due to high purity and perfect crystalline morphology.     

金属光子晶体薄膜可见光和微波波段传输性能

一维金属光子晶体薄膜是由金属-介质多层结构组成的等效均匀的各向异性超构材料。相比单层金属膜层,该结构在色散调控方面具有更多的自由度。在该结构中由于表面等离子体激元(SPP)的存在,可实现倏逝波的定向传输。在本文中,等效介质理论、时域有限元差分法(FDTD)的计算结果和实验结果都表明,传输倏逝波的波长、频宽和强度可通过金属光子晶体结构调整实现主动设计。金属膜厚比例越小,传输波长的中心和截止波长越长,频带越宽。当金属膜层厚度小于SPP穿透深度时,可获得宽频段的倏逝波的传输。同时,对金属光子晶体在微波波段的传输性能也进行了研究,发现其在微波波段等效介电常数为负,具有良好的反射性能。该结构的屏蔽效能远大于厚度相近的ITO薄膜的电磁屏蔽效能。在厚度只有几百纳米时,该结构即可实现良好的电磁屏蔽效能。通过金属光子晶体薄膜可实现电磁屏蔽材料的薄膜化、轻质化和可视化。     

Effect of substrate patterning on hydroxyapatite sol-gel thin film growth

The effect of substrate patterning on hydroxyapatite (HA) sol-gel thin film growth is investigated. Sol-gel derived HA was spun onto wet and dry etched micro-patterned titanium substrates to obtain thin films of thickness ~ 400 nm. The amorphous films were made crystalline by firing at temperatures ranging from 650 to 850 °C for 5 min. Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD), and atomic force microscopy (AFM) were used to characterize the films. Crystal sizes calculated from XRD data show that films on patterned substrates contained larger grains than those on un-patterned substrates. The films on wet etched substrates contained larger grains than the films on dry etched substrates. AFM results confirm XRD results. A marked difference between the films on patterned and unpatterned substrates was observed, with those on the patterned substrates being much rougher than those on the unpatterned substrates. The films inside the channels contained larger grains than those outside of channels, on the polished, unetched portion of the substrate.     

Enhanced light extraction from GaN-based LEDs with a bottom-up assembled photonic crystal

Photonic crystal (PhC) structure is an efficient tool for light extraction from light-emitting diodes (LEDs). The fabrication of a large area PhC structure on the light output surface of LEDs often involves sophisticated equipments such as nanoimprint lithography machine. In this study a monolayer of polystyrene (PS) microspheres was employed as a template to fabricate a noninvasive photonic crystal of indium tin oxide (ITO) on the surface of GaN-based LED. PS spheres can help to form periodic arrangement of bowl-like holes, a photonic crystal with gradually changed fill factors. Importantly, the electroluminescence intensity of LED with a photonic crystal was significantly enhanced by 1.5 times compared to that of the conventional one under various forward injection currents.     

Optical and luminescent properties of ion-implanted films

It has been shown that band parameters for unimplanted films differ from those for bulk materials. Mechanical stresses and increased concentrations of defects seem to be responsible for this difference. The neighbourhood of the surface and the existence of drain paths for bulk defects determine the activity of the surface as a collector for mobile defects and hence their accumulation and their subsequent combination and annihilation reactions. From this point of view ion-implanted films with radiation-induced defects exhibit specific types of behaviour. For example, low energy ion bombardment (together with the removal of a very thin surface layer by etching) leads to an extensive movement of defects towards the surface and to a purification of the corresponding layer. In a number of cases even structural phase transformations take place within the surface layer, which lead in particular to the creation of surface excitons.High energy ion bombardment does not alter the band parameters of the films at the depth d of ion penetration but distorts the structure at the surface owing to a drain of defects into this layer. At the same time centres of scattering and radiative recombination are effectively induced at the depth d.     

Microstructure characterization of sol-gel derived PZT films

The crystallization of sol-gel derived amorphous PZT films deposited on a MgO single-crystal substrate and a SiO₂ glass substrate was examined. The pyrochlore crystallites, 5 nm in size, were homogeneously nucleated in the amorphous films at 350 °C. The nucleation temperature of pyrochlore did not depend on the type of substrate. Fine pyrochlore grains were stable even during annealing at high temperatures up to 600 °C. The perovskite formation temperature was dependent on the substrate, and was about 550 °C on the MgO single-crystal substrate and about 750 °C on the SiO₂ glass substrate. The perovskite was heterogeneously nucleated preferentially at the substrate-film interface. Perovskite nucleation was more difficult at the SiO₂ glass-film interface than at the MgO single crystal-film interface. The ease of nucleation reflected the perovskite formation temperature. Perovskite crystals grew fairly rapidly, once they were nucleated in the films. In the multiple-coated films, the interface between successive layers of PZT films was a favourable nucleation site of perovskite, and the columnar perovskite grains passing through the interface were often developed.     

Preparation and characterization of ultra-thin sol-gel films

The formation and characterization of nanometer thick sol-gel films are reported. The films were prepared by spin-coating of a diluted solution of a silane precursor on a number of different substrates. The effect of dilution, rotation speed and nature of substrate on the thickness and homogeneity of the films was examined. Characterization of the films was carried out by profilometry, reflectance spectroscopy, atomic force microscopy, adhesion test and electrochemistry. We find that the dilution factor has a pronounced effect on the film thickness. Moreover, the time of dilution, namely, whether dilution was carried out before or after a period of hydrolysis, has a noticeable effect on the thickness as well as on the permeability of embedded species.