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Acosta González, Geovannie; Rivera Torres, Cinthia; Cersosimo, Juan C.; Muller, Rafael. Department of Physics and Electronics, UPR-Humacao.
Multi-band inspection of NGC 2237
Our research is focused in the study of NGC 2237, also known as the Rosette nebulae. To study this area we use pictures of the area that we get from two principal sources: the Skyview online database to get optical photos of the area, the NVSS to get contour maps of the same area. Our interest is to study the correlation between the continuum sources and the images of the cometary globules that are shown at the maps of the Palomar Sky Survey. Our main interest is to find potential sites of stellar formation. Results are combined with the emissions of hydrogen radio recombination lines observed from Arecibo.
Biaggi-Labiosa, Azlin M; Vallejo, P.; Fonseca, L. F.; Resto, O. Nanophase Semiconductors Research Laboratory, Department of Physics, University of Puerto Rico, Rio Piedras - Morell, G., Diamond Research Laboratory, Department of Physics, University of Puerto Rico, Rio Piedras - Weisz, S. Z., Nanophase Semiconductors Research Laboratory, Department of Physics, University of Puerto Rico, Rio Piedras.
Cathodoluminescence studies of nanocrystalline silicon films for field emission displays
We study nanocrystalline silicon (nc-Si) systems for applications in displays technology. In particular we evaluate the applicability of porous silicon and nc-Si/SiO2 composite thin films in field emission displays (FED). We developed an experimental setup to measure in situ: photoluminescence (PL), cathodoluminescence (CL) and surface properties of the samples. This setup also allows us to modify surface passivation conditions of the nanoparticles before each analysis so we can understand the role of the surface states on the PL and the CL properties of the materials. In this presentation we will give details about our experimental setup, the preparation of the materials, and the preliminary results already obtained. In particular, we have performed PL, CL, field emission (FE) studies, and Raman Spectroscopy to various PSi films. The films were synthesized using n- and p-type Si wafers of different resistivities by electrochemical anodization with 1:1:2 hydrofluoric acid (HF), water, and ethanol solution. The PL peaks depended on the resistivity of the sample, the current density, and anodization time and range from 674 nm to 768 nm. The CL peak was centered at about 750 nm. We have observed the expected Raman shifts in the PSi spectra when compared with crystalline Si (c-Si) whose peak is at 521 cm-1. The FE studies showed that a high electric field (~35 V/mm) was necessary in order to obtain significant emission from the samples. We also performed secondary ion mass spectroscopy (SIMS) to analyze the surface of the samples and to detect if there were any impurities.
Calderin, Cynthia; Perez, Miguel; Furlan, Rogerio. Physics and Electronics Department, UPR-Humacao
Sealing of microfluidic devices implemented with thick photoresist
In this project we are exploring the sealing of microfluidic devices (microoscillators) fabricated using thick photoresist (SU-8). Microfluidic oscillators are devices formed with microchannels, with one input (supply) and two outputs. Part of the output flow (gas or liquid) is injected to control inputs (using feedback channels) what causes the movement (oscillation) of the main flow inside the device. These devices can be used as sensors and actuators. We are investigating the sealing using acrylic and thermally activated adhesive. Different conditions of temperature and pressure to achieve the bonding with the polymeric device surface are being investigated. Effective sealing has been demonstrated using liquid flow inside the microfluidic device. Set ups for analysis of operation of the microfluidic oscillators with gases and liquids are also being implemented, and for this purpose the attachment of plastic tubes to the microfluidic devices, for input/output interconnections, is being investigated. This work has been supported by NSF-DMR-9872689.
Carrión Morant, Pedro; Cotto Figueroa, Desireé; Rodríguez, Richard; Rosado De Jesús, Iliana; Cersosimo, Juan; Muller, Rafael. Physics and Electronics, UPR-Humacao.
Measurement of neglected-double stars
Binary stars are gravitationally bound multiple star systems. The behavior of those systems is very important for astronomical purposes. We measure the position angle and separation of catalogued binary stars using a simple method. Many of those binaries have not been observed for many years. Our data is obtained at the National Undergraduate Research Observatory (NURO) 31-inch Telescope located in Flagstaff, Arizona. Once the images are captured, and after calibration and other processes, they are printed in order to measure the separation of the stars in units of pixels (equivalents to arc seconds). Further, by using the Pythagoras Theorem we obtain a number, which multiplied by the plate scale of the NURO telescope, gives us the separation of the stars. The angle is obtained using the traditional method. The results that we obtained are compared with the Washington Double Star Catalogue (WDSC). We present the results of 25 neglected binary systems.
Castillo, Roberto; Rogerio, Furlan. Departamento de Física y Electrónica, UPR-Humacao.
Microfluidic devices fabricated in low temperature co-fired ceramic substrates (LTCC) using micromolding technology
Microfluidic devices (microoscillators) were fabricated in Co-Fired Ceramic (LTCC) substrates, in the context of Micro-Electro-Mechanical Systems (MEMS). The devices were stamped in the ceramic substrate by using micromolds fabricated using photolithography of SU-8 photoresist, followed by nickel electroformation. We determined that the microchannel depth is a function of the number of layers and that to obtain higher depths, comparable to the value of the thickness of the master, 3 or more LTCC layers have to be used. Our results show that there is a good correspondence between the profile obtained in the ceramics and the reverse one of the mold. Also, we analyzed the characteristics of the LTCC substrate as a function of the sintering temperature. A best condition in terms of sample manipulation and surface roughness was determined, which is associated to a sintering at 700 C. At this condition the sample presents sufficient rigidity to be manipulated and presents a maximum roughness lower than 1 µm, which is tolerable in terms microfluidic applications. This work has been supported by NASA Space Grant Scholarship/Fellowship and NSF-DMR-9872689.
Cotto Figueroa, Desireé; Muller, R.J.; Cersosimo, J.C.; Carrión, P. L.; Rosado, I.; Rodríguez; R. Physics and Electronics Department, UPR-Humacao.
Binary stars: measurement of separation/angle
A precise, simple and straightforward method for measuring separation and angle of binary stars when using a CCD camera coupled to a telescope is presented. The data used for this research was obtained at the National Undergraduate Research Observatory (NURO) Telescope located in Flagstaff, Arizona. The 31-inch is equipped with a Tektronix 512 X 512 CCD camera with cryogenic cooling to -110º C. Once the data is obtained, it is processed using some computer software and analyzed by mathematical methods. We compare our results of the standard binaries with the Washington Double Star Catalog to test that our method is effective. Then we proceed to analyze the binary star systems neglected by others. This method seems to be accurate and promising.
De Jesus, Joel. Fisica, UPR-Rio Piedras - Gonzalez, Juan. Fisica Electronica, UPR-Humacao - Weiner, Brad. Quimica, UPR-Rio Piedras - Morell, Gerardo. Ciencias Fisicas, UPR-Rio Piedras.
Parallel bias effects on sulfur-doped diamond
The transformations induced by the application of a continuous bias voltage parallel to the growing surface during the sulfur-assisted hot-filament chemical vapor deposition (HFCVD) of microcrystalline diamond (m-D) and nanocrystalline diamond (n-D) films were investigated by Raman spectroscopy (RS), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and X‑ray photoelectron spectroscopy (XPS). The films were deposited on molybdenum substrates using CH4, H2 and H2S. Bias voltages in the range of 0 - 1000 VDC were applied parallel to the substrate surface continuously during deposition. The study revealed a significant improvement in the films’ density and a lowering in the defect density of the diamond structure for parallel bias (PB) voltages above 400V. These high PB conditions cause the preferential removal of electrons from the gaseous environment, thus leading to the net accumulation of positive species in the volume above the growing film. For low methane (below 1 vol%) concentrations, PB results in the accumulation of precursor species promoting high-quality film growth. For high methane concentrations (above 1 vol%), PB results in continuous secondary nucleation, promoting the self-assembly of carbon nano-clusters with diameters in the range of tens of nanometers, which contain diamond (sp3-bonded C) in their cores and graphitic (sp2-bonded C) enclosures. Hence, the observed improvement in film density and in atomic arrangement appears to be connected to the enhanced presence of positively charged ionic species, consistent with models which propose that positively charged carbon species are the crucial precursors for CVD diamond film growth.
Diaz, Melissa; Rivas Morales, Guillermo; Furlan, Rogerio; Nicholas J. Pinto. Physics and Electronics Department, UPR-Humacao - Jorge J. Santiago-Aviles, Electrical Engineering Department, University of Pennsylvania.
Fabrication of metallic microtubes using a polymeric fugitive phase
The feasibility of miniaturized fluidic systems relies on the development of simple technology to fabricate micro and nano interconnectors. This scaling of the interconnections facilitates the manipulation of small quantities of fluids and provides reduced dead volumes. In this context, in this work we successfully demonstrated the possibility of formation of metallic microtubes (niquel and gold / niquel) using a process with a fugitive phase (PAN composite microfibers) that can be removed by a thermal treatment at 750  C in air. Using a single fiber, the microtubes result with a diameter of ~ 7 µm and a wall thickness of less than 1 µm. The metal thickness, obtained on the fiber (measured using SEM) can be controlled as a function of deposition time. Using groups of fibers larger tubes with non-circular shapes can also be obtained. The use of a double metallic layer (gold / nickel) allows to obtain smoother walls. These microtubes can find important applications as part of microfluidic systems. This work was supported by NSF-DMR-9872689 and NSF-SBE-0123654.
Diaz, Ramon D.; Furlan, Rogerio; Ramos, Idalia. Physics and Electronics Department, UPR-Humacao.
Electrospinning of nanofibers for electrical interconnection and chemical sensors
We are studying and developing carbon nanofibers using electrostatic deposition (electrospinning) from polymeric solutions followed by annealing in vacuum, for crystallization. In this work, based on our previous results of nanofiber formation, we are exploring different conditions of electrosppining, aiming at to obtain nanofibers with very small diameters (of the order of 100 nm or less) for applications as electronic interconnection and sensors. Fibers are being electrospun using a homemade apparatus, composed of a DC power supply, a syringe (volume of 3 cubic centimeters, needle type 26G5/6) and a collection screen placed at a horizontal distance of 15 cm from the tip. The fibers are being deposited on silicon substrates. The syringe is tilted at approximately 15 from horizontal so that a small drop is maintained at the capillary tip, due to the surface tension of the solution. We are working with a fixed potential difference of 15 kV between the tip and the grounded screen. The polymer solutions are being prepared using different amounts of commercial polyacrylonitrile (PAN) and a fixed amount (10 ml) of solvent (N,N dimethylformamide - DMF). The resulting fibers and their distribution are being analyzed with optical microscopy and Scanning Electron Microscopy (SEM). Our results demonstrates that the diameter of the fiber decrases with the dilution of the solution, as a less viscous solution is obtained. This work has been supported by NSF-DMR-9872689.
Figueroa Freytes, Glendalys; Ramos, Idalia; Furlan, Rogerio. Department of Physics and Electronics, University of Puerto Rico at Humacao - Santiago, Jorge. Department of Electrical Engineering, University of Pennsylvania.
Study of dielectrical properties of sintered Low Temperature Co-Fired Ceramics
LTCC is a glass-ceramic composite material also known as green tape because of its color and flexibility before being fired. The study of the dielectric properties of sintered LTCC (Low Temperature Co-Fired Ceramic) is important for the development of micro and meso electromechanical systems. Two different types of ceramics are being studied: Dupont-951 and Heraeus CT2000. During 2 hours, the samples are fired for temperatures ranging from 350 to 950¢XC. The real permittivity (ƒÕƒnƒvƒç)) and the dielectric loss (tan ƒÔ) are measured using a high frequency impedance analyzer for frequencies in the range of 1MHz to 1.2GHz. A Scanning Electron Microscope (SEM) was used to analyze the LTCC microstructural characteristics (grain size, pore and crystallite characteristics). Correlations between sintering (firing) temperature, dielectric and microstructural properties are established for both types of LTCC. This research was supported by NSF-DMR-9872689 and the Puerto Rico Alliance for Minority Participation.
González, Rosana; Gonzalez, Luis A. Department of Physics and Electronics, UPR-Humacao.
Radio frequency signals at Ka-Band using satellite links
The scope of the work is to analyze and correlate radio frequency (RF) signal attenuation and rain intensity using a satellite link at 20.7 GHz (Ka-band). At this frequency band the attenuation of the RF signal due to rain is of great concern for the development of space communication systems. The data was recorded using a special Ka-band ground station located in Humacao, Puerto Rico. Humacao is a tropical rain zone. This zone is characterized for having many rain events and heavy rainfall during a typical year. The Humacao ground station consist of a 1.2 meters offset reflector antenna, a radiometer that also works at 20.7 GHz and a digital receiver to process the satellite beacon. Additionally a computerized meteorological station that provides wind speed, cumulative rain, outside temperature, outside relative humidity and barometric pressure data is in site. This presentation details the analysis and results of collected data since May 2001 to December 2002 in Humacao, Puerto Rico. The analysis consisted of calculating the probability density function (PDF) and cumulative distribution functions (CDF). These distributions are obtained for each month in the period specified.
Gonzalez-Berrios, Adolfo. Fisica, UPR-Rio Piedras - Huang, Dachun. Quimica, UPR-Rio Piedras - De Jesus, Joel; Vargas, Iris M. Fisica, UPR-Rio Piedras - Weiner, Brad. Quimica, UPR-Rio Piedras - Morell, Gerardo. Ciencias Fisicas, UPR-Rio Piedras.
Enhancing the field emission properties of nanocomposite carbon films by heavy-ion radiation
The effects of heavy ion radiation over the electron field emission (EFE) properties of sulfur‑doped nanocomposite carbon (n‑C:S) films were investigated. Two identical sets of n-C:S films were prepared in a hot filament chemical vapor deposition (HFCVD) system using CH4, H2 and H2S. Films with various sp3 C and sp2 C fractions were present within each set. Raman spectroscopy revealed the composite nature of the films. One set of films was submitted to a 20 Krad dose of energetic Si and Fe ions (GeV/amu) at Brookhaven National Laboratory's Alternating Gradient Synchrotron (AGS). Films originally having poor EFE properties showed a dramatic emission enhancement as result of irradiation, while those having good EFE properties before irradiation showed a small emission improvement upon irradiation. This improved EFE behavior is explained as due to the formation of conductive trigonal carbon nano-channels within the tetragonally-bonded carbon matrix. The diameter of these trigonal carbon nano-channels is small enough to produce large local field enhancement, and large enough to withstand the relatively large emitted current densities. A mechanism is proposed for the creation of this graphitic carbon nano-wire network within the tetragonal carbon matrix upon energetic irradiation. The results suggests that radiation-hard cold cathodes can be fabricated using nanocomposite carbon materials that would remain stable in their EFE properties while exposed to ionizing radiation.
Hernández, Juan; Furlan, Rogerio; Ramos, Idalia. Physics and Electronics Department, UPR-Humacao.
Study of electrospinning conditions to obtain alignment of carbon nanofibers
Applications of carbon nanofibers such as interconnection lines and sensors require a previous electrical characterization of the fibers using specific devices. We propose the use of four-point probe devices which consist of metallic pads and electrodes defined on an insulating substrate (as quartz plates or oxidized silicon wafers). The deposited nanofiber has to be aligned with the four metallic electrodes that compose the characterization device. Our current approach to obtain the carbon nanofibers consists in the use of electrostatic deposition (electrospinning) using solutions with PAN (polyacrylonitrile) followed by annealing in vacuum, for crystallization. The electrospinning process results in a random distribution of the fibers on the collecting substrate. Thus, in this work, based on our previous results of nanofiber formation, we are exploring different conditions of electrosppining, aiming at to obtain a low density of fibers with good adhesion to the substrate. Deposition parameters as solvent concentration, electrode distances and voltage have been evaluated. The resulting fibers and their distribution and possible alignment with electrodes are being analyzed with optical microscopy and SEM. Preliminary results reveal that the tendency to alignment can be improved by adjusting the deposition parameters, but we will also evaluate the use of polarization of the electrodes present on the substrate to improve this condition. This work has been supported by NSF-DMR-9872689.
Leon, Neliza; Aponte, Milca I.; Ramos, Idalia; Furlan, Rogelio; Pinto, Nicholas. Department of Physics and Electronics, University of Puerto Rico in Humacao - Santiago-Aviles, Jorge J.; Wang, Yu. Department of Electrical Engineering, University of Pennsylvania, Philadelphia.
Characterization of electrospun Tin Oxide fibers
Tin Oxide based films are used as a gas sensors due to their sensitivity in the presence of small amounts of gases such as Carbon Monoxide, Oxygen, Ethanol and Methane. The objective of this research is to develop and characterize Tin Oxide fibers to be used in the development of gas microsensors. The Tin Oxide fibers were developed using the electrospinning process with anydrous SnCl4 as the precursor solution. The fibers were deposited in a Si substrate for analysis. The size and morphology of the fibers were analyzed using Optical Microscopy, Scanning Electronic Microscopy (SEM) and Atomic Force Microscopy (AFM). Fibers of approximately 2ìm of diameter have been obtained using this method. The presence of Tin Oxide on the fibers has been confirmed using X-ray Photoelectron Spectroscopy (XPS) and Raman Spectroscopy. This work was supported by NSF-DMR-9872689, NSF-SBE-0123456 and PRLSAMP.
Morales, Miguel A. Arts and Science, University of Puerto Rico-Mayagüez - Kim, Yong-Jihn. Physics, University of Puerto Rico-Mayagüez.
A new approach to the AC Josephson effect
We introduce a new method of calculating the Josephson coupling energy and the Josephson supercurrents in SIS Junctions in the presence of the electric field. This method is based on the coupling of real space Cooper pair wavefunctions in two superconductors divided by an insulating barrier. We calculate the Josephson coupling energy and supercurrents from the one-particle tunneling probability and the corresponding Cooper pair wavefunctions using the Airy functions. We have found that the Cooper pair tunneling matrix elements are decreased significantly due to the electric field, leading to the decrease of the magnitude of oscillating supercurrents compared to that of the DC supercurrents, in agreement with experimental findings. This may be the main reason why the direct observation of the AC supercurrents was very difficult.
Nocua, Jose; De Jesus, Joel; Velazquez, Rafael. Fisica, UPR Rio Piedras - Weiner, Brad. Quimica, UPR Rio Piedras - Morell, Gerardo. Ciencias Fisicas, UPR Rio Piedras.
Synthesis and characterization of boron nitride nanotubes
Boron nitride nanotubes (BNNTs) have an exceptionally high elastic modulus at around 1.2 TPa, which is similar to that of carbon nanotubes (CNTs). However, unlike CNTs, BNNTs are resistant to oxidation at high temperatures in air. We have produced BNNTs by the arc-discharge technique using graphite electrodes. They were characterized using contrast imaging technique of Electron Energy Loss Spectroscopy (EELS) under the Transmission Electron Microscopy (TEM). It was found that BNNTs form in close proximity to CNTs, are very long, and their diameter is always larger than that of CNTs. These results seem to indicate that CNTs serve as templates for BNNTs formation. Moreover, BNNTs show amorphous-like tips or conical caps, in contrast to the rounded hemispherical caps of carbon nanostructures. It has been argued that these morphological features are due to the high energy of boron dangling bonds, which causes instability of the odd-membered rings that may form at the growing tube edge, and results in a metastable open‑tip structure with only even‑membered rings and no dangling bonds, for tubes with armchair helicity. This feature makes BNNTs more stable than CNTs, since there are no B‑B or N‑N bonds within even-numbered rings. In zigzag BNNTs, dangling bonds are imposed, thus leading to an amorphous tip structure.
Ortiz, José; Pérez, Raúl D. Physics and Electronics, UPR Humacao.
An easy method to fabricate closely spaced metal electrodes using electrospinning
We propose a simple method that only takes a few minutes, to fabricate closely spaced metal electrodes. Unlike conventional lithographic techniques that use sophisticated instruments, this method only requires the use of a high voltage source and a thermal evaporator. In this method, fibers are made using the electrospinning technique. In this technique, a polymer solution is placed in a pipette, then a high voltage is applied to a copper wire inserted into the pipette in order to create an electrical field between the polymer solution and a grounded metallic cathode (aluminum foil). As the voltage to the polymer is increased, a jet is produced, and as the solvent evaporates, micron to sub-micron sized fibers of the polymer accumulate on the cathode. These fibers were captured on a degenerately doped Si/SiO2 wafer. A thermal evaporator is used to evaporate metal on the surface of the wafer. When the fiber is removed, we find that the metal on either side of the fiber do not make contact with each other. SEM (scanning electron microscope) and IV current voltage characteristics of the substrate before and after the fiber removal will be presented.
Perez, Raul; Pinto, Nicholas. Physics and Electronics Department, University of Puerto Rico at Humacao.
Electrical properties of polyaniline synthesized using one-phase emulsion polymerization process
Results of the electrical properties of polyaniline synthesized using the one-phase emulsion polymerization process will be reported. In this procedure the following chemicals were all mixed together in a single beaker. Ammonium peroxidisulfate, the dopant [2-Acrylamido-2-methyl-1-propanesulfonicacid (AMPSA) or camphorsulfonic acid(CSA), Triton-X, aniline, and deionized water. The solution was stirred for approximately 20 minutes to give a dark green color in the mixture. The solution was filtered and washed with water and acetone, the polymer was then left to dry at room temperature. A mortar and pestle were used to grind the polymer and leave a free-flowing powder. 100 mg of the powder were placed in a Pellet Press to produce a pellet using a pressure of 15,000 psi. A rectangular piece of the pellet was cut, and four in-line contacts were made. Current versus voltage measurements were performed using an Electrometer/High Resistance Meter. Using the Closed Cycle Helium Refrigerator current versus voltage measurements were also taken at different temperatures (297 K- 16K). The purpose of this experiment was to study the behavior of the conductivity of these polymers at different temperatures.
Rivera-Torres, Cinthia; Acosta Gonzalez, Geovanie; Cersosimo, Juan C.; Muller, Rafael J. Physics and Electronics, UPR Humacao.
IR and continuum emission in Rosette Nebula
The Rosette nebula is an outstanding region of ongoing star formation in the constellation of Monoceros. That nebula has a nearly circular shape around the open stellar cluster NGC2244, in where contain early type stars which ionize gas. The molecular materials located in the Rosette are a distribution of the ionized gas. We are looking for details of the Rosette Nebula. Our interest is the study of the correlation between the continuum sources in the images. In the study of the infrared radiation associated with Rosette Nebula based on the data coverage of the All Sky Survey data obtained by the Infrared Astronomical Satellite, we identified the difference in the infrared maps and the contour maps. With these maps the analysis of the emission is more detailed. We discuss the properties in the region in where the contour maps located ionize gas and low temperatures, of the infrared point sources with the molecular particles in the region. We find an interest point in the Rosette, we found infrared and bulk of the molecular material. This material is situated in the south area of the Rosette Nebula in the H II region at (6 32 2º 40’). This is an important investigation for our studies, and to understand the Rosette Nebula complex.
Rodríguez, Richard; Torres, Luis; Cersosimo, Juan C.; Muller, Rafael. Physics and Electronics, UPR Humacao.
Photometric measurements at wide band
We started a photometric project at the Humacao University observatory in order to measure stellar magnitude by using U, V, B, R, I Filters. We observed the open cluster NGC 2343. The observation was made with the NURO telescope at Flagstaff, Arizona. The data was processed with IRAF, using the operative systems Linux, at the Humacao observatory. For each observation we removed the atmospheric absorption using a method to calculate the coefficient extinction which it’s analytic expression for the correction of the air mass theory was X=sec Z(∆X). We removed all the atmospheric absorption of each star.
Rosado De Jesús, Iliana; Cotto Figueroa, Desireé; Carrión Morant, Pedro; Muller, Rafael; Cersosimo, Juan C. Physics and Electronic, UPR-Humacao.
Measurement of standard double stars
The objective of our research is to measure the angle and the separation of standard binary star system. The data for our research is obtained in the NURO observatory in Flagstaff, Arizona using the 31-one inch telescope. The sample contains about 30 stars. We measured the separation and angle of position by using images of CCD camera. Once we have the images, they are calibrated and analyzed in the Humacao University Observatory. All the data is used for a calibration procedure, in which we obtained a pixelized image. With the pixelized image we obtain the angle and the separation of the stars using the Pythagoras Theorem. One part of our research includes comparing it with The Washington Double Stars Catalogue. In this way we have confirmation that our procedure is very precise. We also calculate the systematic error (offset). This systematic error is created by the way that the CCD camera is set in the NURO telescope. The remaining number it’s added or subtract to neglected stars to obtain the most precise values of angle.
Ruiz, Amaliris; Diaz, Luz; Feliciano, Jennie. Ingenieria Quimica, UPR-RUM - Vasquez, Omar; Huimin, Liu. Fisica, UPR-RUM.
Optical properties of heavy metal nanoparticles in glasses
In recent years inorganic glass doped with heavy metal nanoparticles such as Au or Ag, or Cu has attracted much attention due to its potential application for ultrafast nonlinear optical devices. The metals were introduced into the batch of phosphate glasses. During melting process the valence state of those heavy metals was controlled to be M+. Right after casting of melting glasses, the samples were annealed in a specially reducing atmosphere so that these metallic ions M+ changed to M0 and aggregated to form nanoparticles. Optical absorption, fluorescence as well as optical excitation were measured and characterized. All samples obtained are clear, transparent with optical quality. Absorption spectra reveal that silver-doped sample exhibits a relatively narrow absorption band with a peak at around 415 nm after annealing process when the nanoparticles formed. The full width at half maximum (FWHM) is about 1600 cm-1. The fluorescence excited at 290 nm shows a broad emission with a band maximum at ~440 nm, while excited at 320 nm shows the maximum at 480. A possible mechanism is believed to be due to the inter-band transition. It indicates that the particle size in the sample has a wide distribution around 8 ~11 nm. Au-, and Cu- doped glasses also show a broad emission with the band maximum shifted to ~ 470 nm and 500 nm, respectively. A systematic characterization of emission peak versus excitation wavelength was conducted. It is believed that the nanoparticle size is closely related to the absorption and fluorescence peak position as well as the band width.
Sanchez, Pedro J.; Santiago Freddie. Department of Physics, UPR Mayagüez.
Aperture masking tabletop demonstration
The theoretical angular resolution limit of telescopes is determined by the laws of diffraction, but in practice the effects of atmospheric turbulence degrade this significantly. The larger the telescope, the worse this degradation becomes. Aperture synthesis is an interferometric technique that can filter out the effects of the atmosphere, so improving the images seen through a telescope. The primary goal of this study is to construct an aperture synthesis tabletop demonstration that can be used as a powerful teaching technique for optics. This tool will help the students to understand basic concepts in a simple and cheap way. We created the aperture mask tabletop demonstration in the laboratory by locating a three hole mask at the exit pupil of a telescope. This poster will show proof–of–concept results, realized in the laboratory using both a HeNe laser and a white light source. Currently we plan to modify the testbench optical system so that it can be installed on any midsized to large telescope, recording the resulting fringe pattern for later analysis.
Solá, Francisco; Fonseca, Luis. Physics, UPR Rio Piedras.
In situ growth analysis of nanotrees using the Transmission Electron Microscope
Si-derived nanorods are grown inside the TEM vacuum chamber from a nanostructured Silicon substrate by irradiation of the substrate with the TEM electron beam. The step-by step growth process has been monitored using the TEM. Starting from an initial trunk, the branches are observed to grow initially with diameters below ~ 1nm and later they also produce other sub-branches after reaching proper thickness. Eventual nucleation of spherical nanoparticles is also observed with time. Even though one can not completely disregard the presence of catalytic material such as silver, the growth of these structures appears not to be related with possible contamination with metals. Images of the growth process and characteristics of their nanostructured will be shown and explained.
Torres Ramírez, Luis E.; Rodriquez, Richard; Cersosimo, Prof. Juan; Muller, Prof. Rafael. Fisica, UPR-Humacao.
Extinction corrections and transformations coefficients of NGC 2343
We started a photometric project at the Humacao University observatory in order to measure stellar magnitude by using U, V, B, R, I filters. We observed the open cluster NGC 2343. The observation was made with the NURO telescope at Flagstaff, Arizona. The data was processed with IRAF at the Humacao observatory. We made the plot with the filters (V-B, B-V, X, V, R-I). The extinction correction and transformation coefficients for the cluster were obtained. The color-color plots were obtained for the samples to determine the coefficients.
Vargas, Iris Monica; Wu, Javier; Martinez, Antonio. Fisica, UPR, Rio Piedras - Weiner, Brad. Quimica, UPR Rio Piedras - Morell, Gerardo. Ciencias Fisicas, UPR Rio Piedras.
Diamond ultra violet sensors for UV astronomy
We are developing ultraviolet sensors using diamond thin films as the photoelectric material. Diamond is a wide band gap (Eg=5.45 eV) material suited for UV applications such as UV Astronomy. Diamond‑based devices will be especially robust due to its radiation hardness, chemical inertness, high thermal conductivity (1-5 W/cmK for thin films), and small thermal expansion coefficient (1.1 X 10-6 K-1). Prototypical diamond UV detectors have already been fabricated using chemical vapor deposited (CVD) polycrystalline diamond (Jackman et al). These devices are expected to show high levels of discrimination (>106) between UV and visible, and thus have a strong potential for UV astronomy. The optimized diamond UV detectors are expected to show response times in the order of 10 ns have been achieved by controlling the impurity levels and reducing the inter-electrode distance using maskless photolithography. Our ability to produce smoother diamond thin films and to fabricate metal‑semiconductor‑metal (MSM) structures on them with electrode spacing of one mm using electron‑beam lithography will improve response times and sensitivity.