Photonic crystals in biology

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Poster Session, Tuesday, June 15 Theme A1 - B702 Effect of defects on the radiat ion sensitivity o f PECVD Ge doped amorphous SiO x Sedat A 1 , 1 1 2 1 TURKEY 2 Department of Physics, Abstract- In this study, optical properties of Ge nanocrystals in SiOx structures are investigated by using Raman, photoluminescence spectroscopy and electron spin resonans (ESR) techniques. Ge nanocrystal in silicon oxide thin films have been grown with different flow rate of GeH 4 , SiH 4 and N 2 O by plazma enhanced chemical vapor deposition (PECVD) technique. We report experimental investigation by ESR measurements of room temperature -ray irradiation effects in PECVD Ge doped amorphous SiO x . Electronically active defects have a very significant influence on the electronic transport and optical properties, leading to compensation effects or to fast nonradiative recombination. Ge-related defects that are cause of attenuation for the waveguides, thus leading to detrimental losses of part of the transmitted signals [1-2]. The identification of the specific defects, sensitive to radiation, is therefore of crucial importance to make clear the microscopic origin of technologically relevant processes. Various experiments have shown that this defect centre can be produced by either two-photon absorption of excimer laser light (KrF, XeCl or ArF), single-photon absorption of light from a KrCl excimer lamp [3] or by ionizing radiation such as x- or -rays. In the interaction of radiation with Ge-doped silica new defects are induced. These defect centers are usually named Ge-related paramagnetic point defects (GECs). Electron paramagnetic Resonance (EPR), one of the most powerful techniques for determining point defects in semiconducting crystals. The aim of our work is to determine the paramagnetic point defects as well as the defect concentration in the gamma ray irradiation with annealed and as-grown germano-silicate PECVD grown samples which consist of 45, 90 and 120 sscm Ge-doped ratios no EPR activities were found before the -ray irradiation. After -irradiation at 300 K, an electron spin resonans (ESR) signals emerged for all of the samples. The characteristic splittings are observed, there is a ESR line at g = 2.0055 which can be attributed to a typical a-center, identical to Si dangling bonds (DB) in the amorphous silicon/o xide matrix surrounding the crystalline core. In addition, the spectra shown contain overlapping ESR signals of several centers the region near g = 2 and these EPR signals closely resembles the spectra of the least two different Ge-related paramagnetic point defects (GECs) previously reported in the literature. *Corresponding author: sedatagan@kku.edu.tr [1] Origlio G., Girard S., Cannas M., Ouerdane Y., Boscaino R., Boukenter A., Journal of Non-Cristaline Solids , 355, 1050 (2009). [2] Agnello S., Alessi A., Gelardi F.M., Boscaino R., Parlato A., Grandi S. and Magistris A., Eur. Phys. J.,B 61, 25 (2008). [3] Messina F., Cannas M., Boscaino R., Grandi S. and Mustarelli P., Phys. Stat. sol. (c), 4, Number 4, 200673788 (2007). 800 600 400 1100-45-2 1100-90-6 1100-120-0D 200 0 -200 -400 -600 -800 -1000 3425 3450 3475 3500 3525 3550 G Figure 1. The EPR spectrum as recorded in the sample 45, 90 and 120 at 1100 K annealed. 6th Nanoscience and Nanotechnology Conference, zmir, 2010 260
Poster Session, Tuesday, June 15 Theme A1 - B702 Fabrication of D-Shaped Fiber Optic Waveguide Sensors with Nanostructured Surfaces for Biological & Chemical Detections Mustafa M. Aslan, 1* Sergio B. Mendes 2 and Kerim Allakhverdiev 1,3 1 Materials Institute, TUBITAK Marmara Research Center, Gebze- Kocaeli, Turkey 2 Department of Physics, University of Louisville, Louisville, KY 40209, USA 3 Institute of Physics ANAS, Baku, Azerbaijan Abstract— In this study, we present fabrication and characterization of D-shaped fiber optic waveguides (FOWs) that are capable of measuring absorbance and fluorescence of biological and chemical alterations in a thin cover layer. The results are encouraging to expend this study for surface nanostructuring of the FOWs. Also future work for surface nanostructuring with coated Au single nanoparticles and colloids is summarized. Optical waveguides(OWs) have been widely used for many biological and chemical sensing applications [1]. They are generally in two distinct forms: pre-shaped waveguides in predetermined geometries such as fibers (fiber optic waveguides-FOWs) and planar waveguides that involve deposition of high refractive index film on a planar surface (planar optical waveguides-POWs). In general, FOWs are preferred for sensing applications to avoid complicated and expensive fabrication process and it is easy to setup. In this study, we present fabrication and characterization of D-shaped FOWs that are capable of measuring absorbance and fluorescence of biological and chemical alterations in a thin cover layer. Also future work for surface nanostructuring of the FOWs is summarized. The FOW is assembled using a stepped-index multimode fiber and silicon V-shaped groove. The silicon wafers are etched along its crystalline plane to form a V-groove. The striped fiber is assembled using an optical grade epoxy into V- groove. Fibers need to be polished near their cores, while the highest possible quality of the polished surface should be maintained, and thereby evanescent fields in fiber cladding can be effectively exploited in order to increase sensitivity for better detection of biological or chemical changes on the surface [2]. Polishing of multi-mode fibers embedded in silicon V-shaped grooves in order to get flat sensor surface and increase sensitivity serves two distinct purposes. The first (rough) polishing step is done with a 1 m aluminum oxide slurry. This step is to remove the excess epoxy from the surface of the device and to approach the core of the fiber. The second step is fine polishing uses a 0.5 m cerium oxide slurry. This polishing step continues to polish nearer into the core increase sensitivity, but also allows for a smooth active surface (RMS = 0.7 nm). As the final step for the fabrication, custom-made patch cables that consist of a section of fiber-optic cable and an FC connectors are epoxed and hand polished. Each patch cable is tested for loss and then can be spliced onto the FOW sensor using a fusion splice machine. A schematic cross-sectional image of the FOW sensor, a side-polished multi-mode fiber with a radius of curvature R, is shown in Fig. 1(a) whereas overall view of the fabricated FOW sensor is shown in Fig. 1(b). D-shaped FOWs are tested and calibrated using blue dextran to take bulk absorption measurements. The results are promising. Measured absorption curve for 20 μM blue dextran with fabricated FOW sensor is shown in Fig. 2. Nanostructuring of the FOWs will be done by coated single and colloid gold (Au) nanoparticles deposited on the sensor’s surface to increase sensitivity and better sensor response can be achieved especially for Raman scattering [3]. Development and control of the sensor’s second output (scattering) will provide significant advantages, allowing the study of the organization of biological and chemical molecules on a surface. Also the FOWs may allow for Surface Enhanced Raman Scattering (SERS) measurements and possible completely integrated Raman Spectroscopy. Utilizing the evanescent fields from the exposed core of a multimode fiber allows for a robust chip that may be used remotely. The structure of the sensor also is conducive to fully integrated measurements. Figure 2. Blue dextran absorbance curve measured with the FOW sensor. *Corresponding email: mustafa.aslan@mam.gov.tr (a) (b) Figure 1. (a) Cross section of the D-shaped FOW and (b) overall view of the fabricated FOW sensor. Some part of this study was done at University of Louisville, KY, USA. Authors would like to thank: Dr. Tark Baykara, Dr. Rodrigo S. Wiederkehr, Courtney L. Byard, Nathan A Webster, and staff of Micro and Nano Fabrication Facility, University of Louisville. [1] R.A. Potyrailo et al., Fresenius J Anal Chem 362, 373 (1998). [2] S.M. Tripathi et al, Journal of Lightwave Tech.26, No 13, 1980- 85 (2008). [3] S.W. James and R.P. Tatam, J. Opt. A: Pure Appl. Opt. 8, S430 (2006). 6th Nanoscience and Nanotechnology Conference, zmir, 2010 261
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