Showing papers in "Journal of Optoelectronics and Advanced Materials in 2006"

Photodynamic therapy in oncology

Abstract: One of the greatest problems of the medical world is cancer, the second most important cause of death on Earth. During the last decade an increase of malignant tumors was seen in Romania, cancer being, after the cardiovascular diseases, the most frequent cause of mortality. The powerful impact of cancer on human life is obvious not only in the death rate but in the number of new cases and living diseased. Therefore, early diagnosis and treatment of cancer has become one of the priorities of the medical world. Current ways of treating cancer (surgery, radiotherapy, chemotherapy) are sometimes only palliatives, that’s why research for new methods to cure cancer is a continuous struggle around the world. Such research have lead to new ways of dealing with this disease based on the induced photochemical effect of light radiation on tumors, known as photochemotherapy or photodynamic therapy. Photodynamic therapy is a method of local treatment of the tumor by administrating a photosensitizing substance which is selectively absorbed by the tumor cells and which, during the irradiation with optical radiations, ends in destroying the tumoral tissue. Although in experimental phase, the obtained results of phototherapy in the latest period are remarkable and have lead to growing interest to this method. The application of photodynamic therapy in current practice raises some problems: the type of potosensitizer (the way of administration, how to prepare it, therapeutic concentration), the radiation source (type, irradiation parameters: wavelength, energy, exposure time, pulse duration, pulse frequency, etc), methods of determining the biologic response, etc. Until now, there are numerous studies on each of these matters. A synthesis of these studies is the subject of this article.

Nonlinear properties of chalcogenide glass fibers

Abstract: Chalcogenide glasses have demonstrated high third-order Kerr (Χ (3) ) nonlinearities up to 1000x higher than silica glass which make them attractive for applications such as nonlinear switching, optical regeneration, Raman amplification, parametric amplification, and supercontinuum generation. Poling of chalcogenide glasses to induce an effective second order (Χ (2) ) nonlinearity has also been demonstrated and opens the possibility for the use of poled glass waveguides for applications such as frequency conversion or electro-optic modulation. Stimulated Brillouin scattering (SBS) has also been investigated in As 2 S 3 and As 2 Se 3 single-mode fibers. The threshold intensity for the stimulated Brillouin scattering process was measured and used to estimate the Brillouin gain coefficient. Preliminary results indicate record high values for the figure of merit and theoretical gain, compared to silica, which bodes well for slow-light based applications in chalcogenide fibers.

Structural and optical properties of zinc oxide thin films prepared by spray pyrolysis method

Abstract: Polycrystalline ZnO thin films were deposited on a glass substrate by a spray pyrolysis technique using solution of zinc acetate and air as the carrier gas at 400 °C temperature. Optical constants such as refractive index n and extinction coefficient k, were determined from transmittance spectrum in the ultraviolet-visible-near infrared (UV-VIS-NIR) regions using envelope methods. The films were found to exhibit high transmittance (>90 %), low absorbance and low reflectance in the visible regions. Absorption coefficient a, and the thickness of the film t were calculated from interference of transmittance spectra. The energy band gap, and the thickness of the films were evaluated as 3.27 eV and 0.31-0.52 pm respectively. The crystallographic structure of these films was analyzed with x-ray diffractometer. The films were polycrystalline in nature with preferred (002) orientation perpendicular to substrate surface and the grain size estimated to be 40 nm. The extended x-ray absorption fine structure (EXAFS) calculations above the K-edge of Zn in the ZnO thin film have been performed by using real-space multiple scattering of photoelectrons. For ZnO thin films, the values of the correlated mean square relative displacements of nearest-neighbor atoms derived from EXAFS spectra show good agreement with those measured from the x-ray diffraction experiments.

The determination of the thickness and optical constants of the ZnO crystalline thin film by using envelope method

Abstract: ZnO crystalline thin film has been deposited onto glass substrates by the spray pyrolysis method. The crystallographic structure of the film and the size of the crystallites in the film were studied by X-ray diffraction. XRD measurement shows that the film is crystallized in the wurtzite phase and presents a preferential orientation along the c-axis. Only one peak, corresponding to the ( ) 2 0 0 phase (2θ=34.760 o ), appears on the diffractograms. An envelope method, based on the optical reflection spectrum taken at normal incidence, has been successfully applied to the geometrical–optical characterization of thin films having significant surface roughness. Such a method allows the determination of the average thickness and the refractive index of the films with accuracies better than 1%, as well as the average amplitude of the surface roughness with an accuracy of about 2%. Optical constants such as refractive index n and extinction coefficient k, were determined from transmittance spectrum in the ultraviolet-visible-near infrared (UV-VIS-NIR) regions using envelope methods. Absorption coefficient α, and the thickness of the film t were calculated from interference of transmittance spectra. The energy band gap, and the thickness of the films were evaluated as 3.283 eV and 635 nm, respectively.

New polypyrrole-multiwall carbon nanotubes hybrid materials

Abstract: We report the synthesis and characterization of new hybrid materials based on conducting polypyrrole (PPY) and multi wall carbon nanotubes (MWCNTs). MWCNTs were prepared by spray-pyrolysis of liquid hydrocarbon-ferrocene solution in an Ar atmosphere. The composites (PPY-CNT) were obtained by in-situ chemical oxidative polymerization of pyrrole in aqueous solution containing MWCNTs. The addition of a water based Fe 3 O 4 nanofluid to the polymerization solution results in the formation of a new hybrid nanostructure of MWCNTs coated with PPY containing magnetic nanoparticles. The properties of PPY composites were investigated by TEM, SEM, FTIR spectroscopy and X-ray diffraction (XRD) measurements. MWCNTs covered with PPY have a rough surface, containing some globular forms typical for the polymer. Significant differences between IR spectra for PPY and PPY-CNT nanocomposites appear for the bands ascribed to pyrrole ring vibrations, suggesting that an interaction between the polymer and CNT occurs and this could change the polymer conformation. XRD analysis shows that the crystalline structure of MWCNTs doesn't change significantly by the association with conducting PPY.

Soft magnetic nanocrystalline powders produced by mechanical alloying routes

Abstract: This paper presents an overview on the soft magnetic nanocrystalline powders obtained by mechanical alloying routes. First, the different mechanical routes (mechanical alloying, combined mechanical alloying and annealing and mechano-chemical techniques) used for the elaboration of nanocrystalline magnetic powders are discussed. The structural and magnetic properties as a function of experimental conditions are reviewed on the base of following categories of soft magnetic nanocrystalline/nanosized powders: ferrites, Ni-Fe alloys and other iron-based systems. Finally, design of new magnetic materials using nanocrystalline powders produced by mechanical alloying routes is also considered.

Structural, optical and electrical properties of Sb2O3 thin films with different thickness

Abstract: Thin films of Sb 2 O 3 with different thickness (d=0.20-1.10 μm) were deposited onto glass substrates by thermal evaporation technique. The structural, optical and electrical properties were investigated and the effect of films thickness on films properties was discussed. The transmission electron microscopy (TEM) analysis revealed that the Sb 2 O 3 thin films are polycrystalline and have a cubic structure. The small values of the roughness obtained from atomic force microscopy (AFM) measurements, ranging from 4.7 to 17.6 nm, show relatively smooth surfaces. The spectral absorption coefficient and optical band gap energy of the Sb 2 O 3 thin films at the fundamental absorption region were determined using the spectral data of transmittance measurements in the wavelength range 250-1400 nm. Temperature dependence of the electrical conductivity was studied in a wide range, 289-445 K. It is observed that the electrical conductivity of Sb 2 O 3 thin films tend to increase with increasing of the film thickness. Also, it is observed that the surface defects in thinner films cold play a more important role in the effect on optical and electrical properties. For thicker films the grain boundary could play a more important role in the effect on films properties.

Giant photo-expansion in chalcogenide glass

Abstract: Glass exhibits many kinds of photoinduced phenomena, among which the giant photo-expansion appearing in chalcogenide glasses such as As 2 S 3 may be the most dramatic and promising. Its feature, mechanism, and application including micro-lenses are described.

Structural investigation of CuO-Bi 2 O 3 -B 2 O 3 glasses by FT-IR, Raman and UV-VIS spectroscopies

Abstract: Glasses from xCuO·(100-x)[2Bi 2 O 3 ·B 2 O 3 ] system were studied by means of FT-IR, Raman and UV-VIS spectroscopies in order to obtain informations about the changes that appear in the structure of 2Bi 2 O 3 ·B 2 O 3 glass matrix with the doping of copper ions. FT-IR measurements indicate that the network structure of the studied glasses is based on the BiO 3 pyramidal and BiO 6 octahedral units and also on BO 3 and BO 4 units. The Raman spectra evidenced the presence of the structural units established by IR absorption and also of some other characteristic structural units. The FT-IR and Raman spectra do not present any absorption bands characteristic to CuO, but the absorption of Bi 2 O 3 and B 2 O 3 structural units depends of its presence in to a glass matrix. The UV-VIS absorption spectra for all glasses have a single asymmetric band, which corresponds to a 2 B 1g → 2 B 2g transition of the Cu 2+ ions in octahedral symmetry with an elongated tetragonal distortion. These measurements indicate the presence of Cu 2+ ions in the glasses.

Structural study of the Fe2O3-B2O3-BaO glass system by FTIR spectroscopy

Abstract: Glasses belonging to the xFe 2 O 3 ·(100-x)[3B 2 O 3 ·BaO] system, with 0 ≤ x ≤ 50 mol% were prepared and characterized by IR spectroscopy. It was establised the mode in wich Fe 2 O 3 influence the local structure of the 3B 2 O 3 ·BaO glass matrix. The IR absorption data indicate that the BO 4 / BO 3 ratio in the studied glasses is dependent on the iron ions content.

The morphology control of polyaniline as conducting polymer in fuel cell technology

Abstract: Electrically conducting polymers described as a new class of 'synthetic metals' reached a high interest in the last years, confirmed by the 2000 Nobel Prize in chemistry for the discovery and development of conductive polymers (Alan J. Heeger, Alan G. MacDiarmid and Hideki Shirakawa). The most commonly studied classes of conducting polymer were: polyacetylene, polytiophene, polypyrole, polyaniline and derivates, being investigated as conducting matrices for electrocatalytic applications. Among them, polyaniline (PANI) is one of the most studied materials because of its high conductivity upon doping with acids (10 -10 2 S/cm), well behaved electrochemistry, and easy preparation under reproducible conditions by both electro - polymerization and chemically oxidation of aniline, chemical and electrical stability and good environmental stability. The purpose of our research is to obtain a conductive and stable polymer, with a high surface area, by variation of different preparation techniques and parameters, in sense of polymer morphology control. The research interest is to implement the conducting polymers in fuel cell technology, as Membrane Electrode Assembly (MEA) components or conducting supports for noble metal deposition.

Crystallite size effect in PbS thin films grown on glass substrates by chemical bath deposition

Abstract: Nanocrystalline PbS thin films were grown on glass substrates using Chemical Bath Deposition (CBD) method. The presence of nanocrystals was revealed by optical absorption and photocurrent measurements. We have compared the absorption threshold between large size and nanocrystalline PbS. Our study was performed in order to demonstrate that the size of the PbS thin films crystallites affects the photoelectric properties of the material. Using the Scanning Electron Microscopy (SEM) we have determined that the grains inside large size PbS crystallites are 300 nm. From the optical absorption measurements we have determined that the size of PbS nanocrystals is between 5-50 nm. The photoconduction measurements show that large size PbS has a maximum in infrared situated at 2.4 μm, and in PbS nanocrystalline thin film this maximum is shifted toward smaller wavelengths towards visible and near infrared.

Synthesis and magnetic studies of Ni-Zn ferrite nanoparticles

Abstract: Ni-Zn ferrite nanoparticles of the system, Ni 0.65 Zn 0.35 Fe 2 O 4 , were synthesized by a soft chemical approach of coprecipitation method. These nanoparticles were separated into four batches and they were annealed at different temperatures from 200 to 800°C for improved crystallization. All the samples were then characterized by X-ray diffraction, vibrating sample magnetometer and ferromagnetic resonance spectrometer techniques. The XRD patterns confirm spinel structures while the particle sizes, ranging from 9.9 to 15.7 nm, increase with the increase in heat treating temperature. The magnetization values are extremely small even at 10 kOe fields with vanished hysteresis at lower heat treating temperatures; thus leading close to the superparamagnetic nature. The resonance parameters deduced from the FMR spectra are in support of the magnetisation data.

The use of multi-temporal and multispectral satellite data for change detection analysis of the Romanian Black Sea coastal zone

Abstract: The Romanian North Western coastal and shelf zones of the Black Sea and Danube delta are a mosaic of complex, interacting ecosystems, rich natural resources and socio-economic activity. Dramatic changes in the Black Sea's ecosystem and resources are due to natural and anthropogenic causes (increase in the nutrient and pollutant load of rivers input, industrial and municipal wastewater pollution along the coast, and dumping on the open sea). A scientific management system for protection, conservation and restoration must be based on reliable information on bio-geophysical and geomorphologic processes, coastal erosion, sedimentation dynamics, mapping of macrophyte fields, water quality, climatic change effects. Synergetic use of quasi-simultaneously acquired multi-sensor data may therefore allow for a better approach of change detection of coastal area. This paper is an application of multi-temporal and multi-spectral satellite remotely sensed data (Landsat MSS, TM, ETM, SAR ERS, ASTER, MODIS) over a period of time between 1975 and 2003 for North-Westem Black Sea coastal zone change detection assessment. Spectral mixture analysis, supervised and unsupervised classification are used to study chosen test areas. The results can be utilized as a temporal land-use change model for a region to quantify the extent and, nature of change, and aid in future prediction studies, which helps in planning environmental agencies to develop sustainable land-use practices.

Heterojunctions of hydrogenated amorphous silicon and monocrystalline silicon

Abstract: Heterojunctions of hydrogenated amorphous silicon and monocrystalline silicon, a-Si:H/c-Si, are of technological interest in particular for highly efficient solar cells. Here, we report about studies of the most important material and device parameters of such pn- and np- heterojunctions and their performance as solar cells and light emitting diodes. The electronic structure of the heterojunction is characterized by unsymmetrical band offsets at the conduction and valence bands, ΔE c and AEv, of 0.14 eV and 0.45 eV, respectively. It is shown that the performance of the devices is strongly determined by the defect structure of the thin doped amorphous emitter layer and the density of states at the amorphous/crystalline interface. This work led to confirmed solar cell efficiencies of 19.8 % for a textured a-Si:H(p)/c-Si(n)/a-Si:H(n) structure without using undoped a-Si:H(i) buffer layers. Heterojunction solar cells are shown to exhibit electroluminescence of high power efficiency (0.3 %) under forward bias.

Fabrication of fiber grating by phase mask and its sensing application

Abstract: This paper reports an investigation of a fabricated fiber grating device characteristics and its applications, using a phase mask writing technique. The phase mask technique used for writing fiber gratings has the advantages over the traditional holographic method because of its simpler writing setup and more reproducible characteristics. Specifically, the utilization of phase mask relaxes the strict requirement on the coherence of a UV light source. On the other hand, to photo induce an index change in the fiber core, light absorption must somehow occur. Alkins measured the absorption spectrum in a standard germanium doped mono mode telecommunication fiber to the wavelength as short as 200 nm. The results show that a light source in the UV spectral region 228 to 253 nm is most effective in photo inducing refractive index changes in such optical fibers. Therefore, we used a KrF excimer laser with wavelength ∼248 nm as light source, and applied the phase mask technique to writing fiber grating. This method has the significant advantage for its much less relaxed requirement on the spatial coherence of exposure light source. The device (i-e grating) characteristics especially, in sensing application, were investigated. In addition, the possibility of using such device as a temperature and strain sensors is also discussed in detail.

The physical characteristics of Cu2S/CdS thin-film solar cell

Abstract: Cu 2 S/CdS heterojunction has been prepared and characterized by using the vacuum evaporation technique on glass substrate. The Cu 2 S layer was obtained by the dry method, i.e. by evaporation of a CuCI film followed by heat treatment. The photovoltaic properties including I-V characteristics, short-circuit current (I sc ), open-circuit voltage (V oc ), fill factor (ft), efficiency (η) of -Cu 2 S/CdS heterojunction cells have been examined after formation. Heat treatment improved the photovoltaic cells. High resistivity of CdS thin film, high series resistance and the poor design of the grid have lead to low efficiency.

Variation of optical constants in ge10se60te30 thin film

Abstract: Chalcogenide glasses are good candidates for applications in the infrared (IR) region [1,2]. Chalcogenide glasses are vitreous materials having one or more of the chalcogen elements (Group VI): sulfur (S), selenium (Se), and tellurium (Te). The addition of the network formers (Group IV and V) such as silicon (Si), germanium (Ge), tin (Sn), phosphorus (P), arsenic (As), and antimony (Sb) establishes cross-linking between the tetrahedral and pyramidal units which facilitates stable glass formation [3,4]. Depending on the composition, the chalcogenide glasses are stable against crystallization and are chemically inert. They have excellent thermal stability, and are relatively easy to fabricate. In our present work we have taken the

Gas sensitivity of nanocrystalline nickel ferrite

Abstract: Nanometer-sized materials, which have high surface activity due to their small particle size and enormous surface area, have been widely studied in the field of gas sensors in recent years. The samples were obtained by self-combustion method and were studied using powder X-ray diffraction and scanning electron microscopy. It was investigated the sensitivity of the electrical resistivity to acetone, ethanol, methane (CH 4 ) and liquefied pertroleum gas (LPG). It is observed that the gas sensitivity depends on the temperature and the test gases to be detected.

Synthesis, photophysical and photoelectrical properties of glass-forming phenothiazinyl- and carbazolyl-substituted ethylenes

Abstract: Phenothiazinyl- and carbazolyl-substituted ethylenes have been synthesized and found to constitute electro-active materials with high thermal stability as characterised by thermo-gravimetric analysis. Steady state absorption and luminescence spectra of the synthesized derivatives were examined in detail revealing green-blue emission with efficiency ranging from 13 % to 28 %. Based on the emission spectra of the synthesized compounds Commission Internationale d'Edairage (CIE) chromaticity coordinates have been obtained. Major luminescence decay time component of ∼2.5 ns was determined in dilute solutions of the compounds, whereas significantly shorter one has been estimated in thin films. Electron photoemission spectra of the materials have been recorded and the ionisation potentials of 5.3-5.4 eV have been established. Room temperature hole drift mobilities of the diarylethylenes dispersed in polymeric host approached 10 -5 cm 2 /Vs at high electric fields.

The study of Mg2+ /Ca2+ substitution of β-tricalcium phosphate

Abstract: This study aimed to investigate the formation and properties of magnesium substituted tricalcium phosphate containing various amounts of Mg 2+ and Ca 2+ ions (β-TCMP), isostructural with β- Mg 2+ ions (β-Ca 3 (PO 4 ) 2 . Beta-TCP and β-TCMP were prepared by a solid-state reaction, then calcination at 900°C for 2hr, and finally sintered at 1100°C for 2hr. The incorporation of Mg was reflected in the shift in the x-ray diffraction peaks due to partial Mg-for-Ca substitution in tricalcium phosphate, causing a contraction in the unit cell dimension. Unit cell parameters ao and C o , and molar volume V o decrease linearly for atomic ratios Mg 2+ / Mg 2+ +Ca 2+ varying from 0 to 10 mol%.. The morphology and chemical composition were analyzed semiquantitatively using X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron microscopy (SEM) and infrared spectroscopy (IR). The dissolution behaviour of Mg-substituted samples was tested in distilled water, at pH=6.1. Results demonstrated that Mg 2+ ions can easily substitute for Ca 2+ ions in the TCP lattice. Increasing the Mg content from 0 to 10%m reduces the dissolution rate of Mg-TCP samples.

The correlation of morphology and surface resistance in porous silicon

Abstract: We have studied the dependence of porous silicon morphology on fabrication conditions and the link between morphology, porosity and surface resistance. Porosity of the samples and thickness were determined gravimetrically. Electron microscopy reveals the evolution of porous silicon layer morphology with variation in preparation conditions. Mean size of silicon nano particles decreases with increased silicon porosity as revealed in photoluminescence spectra, I-V characteristics and surface resistance. Results are consistent with the quantum confinement model of porous silicon luminescence.

Amorphous chalcogenide nano-multilayers: Research and development

Abstract: Investigations of photophysical processes in amorphous chalcogenide layers were extended during the last two decades towards the nanostructures. Namely the nano-layered films were in the focus of development of new photosensitive, optical recording media. A short review of the progress made in the development of the technology, selection of the components and in the understanding of the physics of stimulated transformations is presented.

Spectroscopic investigation on some calcium-phosphate glasses

Abstract: Phosphate glasses containing transitional metal ions (TMI) are interesting because of their semiconducting and optical properties and because of their potential applications in solid-state lasers and as optical fibres for communication devices. In order to the following two changes induced by CuO and V 2 O 5 in the phosphate glass network and their modifier or former role, the following two glass systems were prepared and investigated by EPR and Raman spectroscopy: with 0≤x≤40 mol%. EPR results obtained for copper doped glasses show vanadium ions exist in a square In the case of vanadium doped glasses, g 20 mol%) the bands belonging to the vibration of V 2 O 5 groups dominates the spectra while the bands belonging to the phosphate groups are strongly reduced except the specific bands of the short chain phosphate units. From this consideration we can conclude that vanadium prefers to bridge with the oxygen that do not take part in the PO 4 units and in consequence it acts as a network former.

The cavity perturbation method for the measurement of the relative dielectric permittivity in the microwave range

Abstract: The cavity (small) perturbation is a very suitable method for the measurement of the dielectric relative permittivity at microwave frequencies. In this paper we give the most important relations of this method, particular relations for rectangular resonant cavities and some experimental results. Also, an analysis of total relative errors and the second order perturbations method are presented.

Methods of purification and characterization of carbon nanotubes

Abstract: In an attempt to purify MWNT in mild conditions, we have applied two different methods of purification. The first method of purifying the material was a combination of relatively often used methods, such as etching and acid treatment, and the second method was a relatively new one, using an organic polymer PmPV. Sample purity was obtained with SEM and ESR techniques.

Nanostructuring of chalcogenide glasses using electron beam lithography

Abstract: We have investigated nanostructuring capabilities of As-S chalcogenide glasses using electron beam lithography. After exposure to electron beam the thin films of these inorganic glasses can be etched in alkaline amine solvent with high selectivity. Dissolution rate is linearly proportional to the electron dose and Gaussian electron beam intensity profile is well replicated in the shape of individual lines. High resolution smooth, shaped nanostructures have been fabricated in chalcogenide thin films with dimensions well below 100 nm and aspect ratio about 3.

High efficiency In2O3/c-Si heterojunction solar cells produced by rapid thermal oxidation

Abstract: In this paper, Indium oxide (In 2 O 3 )In-Si junction solar cells were prepared by novel rapid thermal oxidation (RTO) technique using halogen lamp at 300 °C/25 sec condition at static air. The fabricated solar cells subjected to post-deposition annealing at 450 °C/30 min and 450 °C/35 min. High conversion efficiencies ranging between 11.5% and 14.5% at AM1 condition for unannealed an annealed cells respectively were obtained without using frontal grid contact. The photovoltaic properties of solar cells before and after annealing are characterized and analyzed. Furthermore, the stability conditions and reliability of these cells have been tested.

Possibilities for poly(aspartic acid) preparation as biodegradable compound

Abstract: The paper presents the preparation of poly(aspartic acid) (PAAs) from maleic anhydride and ammonia through a two steps reaction: first the polysuccinimide (PSI) obtainment followed by the hydrolysis reaction of PSI in order to open the imide group and to prepare the polyaspartate. Poly(aspartic acid) as friendly environmental and biodegradable product can be used in pharmacy, cosmetics, agriculture, etc.

Fiber optic micro-displacement sensor using coupler

Abstract: A simple technique is presented for the fiber optic displacement sensor using coupler, using multimode plastic 50:50 coupler based on intensity-modulated technique. We have measured very accurately the displacement of the order of 10 µm. The source in the IR region of wavelength 783 nm, output power of 3 mW and Laser drive of model-501 (Newport) and detector model-818-SL (Newport) are used for experimental setup. The displacement of 0-1 mm is quite interesting for the sensing. The sensor characteristics are measured at back slope. The working principle of the sensor is presented as well as experimentation results. The designed simplest sensor finds its application in industries as position control and micro displacement measurement in the hazardous region.