Eduardo Heredia - Academia.edu (original) (raw)
Papers by Eduardo Heredia
International Journal of Advanced Applied Physics Research, 2015
Crystalline defects were studied in single crystalline ZnSe grown by chemical transport using I2 ... more Crystalline defects were studied in single crystalline ZnSe grown by chemical transport using I2 as gaseous carrier. Transmission electronic microscopy determined an excellent structural order in the micrometric and nanometric range. Larger material areas were studied by chemical etching using different reagents to determine average dislocations density and average adjacent subgrains misorientation. Comparable micrographic results of different reagents are shown. Characterization values of ZnSe commercial substrate grown by High Pressure Bridgman (HPB) have been compared to those that correspond to our grown material wafers. Characterization proved that the semiconductor crystalline quality in our wafers is appropriate for optical devices.
Journal of Physics: Conference Series, 2009
Tubular furnaces were designed and built to obtain single crystalline ZnTe and ZnSe ingots using ... more Tubular furnaces were designed and built to obtain single crystalline ZnTe and ZnSe ingots using respectively physical and chemical transport methods. Different temperature profiles and growth rates were analyzed in order to optimize the necessary crystalline quality for device development. Optical and scanning electron micrographs of the corrosion figures produced by chemical etching were used to obtain the dislocation density and the misorientation between adjacent subgrains in ZnTe and ZnSe wafers. Structural quality of the single crystalline material was determined by transmission electronic microscopy. Optical transmittance was measured by infrared transmission spectrometry and the resulting values were compared to commercial samples.
Brazilian Journal of Development
ZnO nanostructures are used in device systems such as photodetectors, gas sensors,photoemission d... more ZnO nanostructures are used in device systems such as photodetectors, gas sensors,photoemission devices, UV-photosensors and many others in Optoelectronics.In the present work we studied nanocrystalline ZnO:Ga thin films prepared by the sol–gel dip-coating technique. Samples were characterized by Grazing Incidence X-ray Diffraction(GIXD), X-ray Reflectivity (XR) and Grazing Incidence Small-Angle X-ray Scattering(GISAXS) methods and Field Effect Scanning Electronic Microscopy (FESEM). Characterization of the samples shows that the obtained films were uniform, continuous, with a crystallite size around 12 nm, an average pores size of around 3.5nm, and a volume fraction of nanoporosity between 0.18 and 0.3. Comparison of densities between doped and undoped films is discussed.
Se estudia la calidad cristalina de una oblea comercial monocristalina de ZnSe (Cradley Crystals)... more Se estudia la calidad cristalina de una oblea comercial monocristalina de ZnSe (Cradley Crystals) combinando diferentes técnicas. Se utiliza microscopía óptica para la observación de defectos macroscópicos y figuras de corrosión obtenidas por revelado químico de la misma y microscopía electrónica de transmisión para determinar su calidad estructural, también se evalúa su transmitancia óptica por su aplicación en ventanas infrarrojas. Una presencia pequeña de defectos macroscópicos, un orden estructural notable entre dislocaciones y la baja densidad de dislocaciones y desorientación angular halladas entre subgranos adyacentes confirman una adecuada calidad cristalina para el empleo de este material en dispositivos optoelectrónicos.This project involves the study of the crystalline quality of a single crystalline commercial wafer of ZnSe (Cradley Crystals) combining different techniques. We use optical microscopy for the observation of macroscopic defects and etching figures which wer...
ZnO and ZnO:Al thin films obtained by spin-coating on amorphous SiO2 substrata, were studied by X... more ZnO and ZnO:Al thin films obtained by spin-coating on amorphous SiO2 substrata, were studied by XRR and Gisaxs. Pure ZnO samples showed higher densities and thickness than Al doped one. The thickness of pure ZnO layer films grown linearly with the number of deposits but could not be determined by XRR because of the lack of oscilation in the XRR diagrams being obtained by FESEM. For doped samples the thickness variation with the number of deposit was not significative. The preliminar results about nanopore size, obtained by Gisaxs, were similar.Fil: Bojorge, Claudia Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Canepa, Horacio Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Casanova, Jorge Ramón. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: A.F. Craievich. Universidade de Sao Paulo; BrasilFil: Heredia, Eduardo Armando. Consejo Nacional de Investigaciones Científicas y Técnicas; Argent...
Materials, 2021
Cd1−xZnxTe (0 ≤ x ≤ 0.1) ingots were obtained by Bridgman’s method using two different speeds in ... more Cd1−xZnxTe (0 ≤ x ≤ 0.1) ingots were obtained by Bridgman’s method using two different speeds in order to find the optimal conditions for single-crystalline growth. Crystalline quality was studied by chemical etching, the elemental composition by wavelength dispersive spectroscopy (WDS), tellurium (Te) precipitates/inclusions concentration by differential scanning calorimetry (DSC), optical transmission by Fourier transformed infrared spectrometry (FTIR), and band gap energy (Egap) by photoluminescence (PL). It was observed that the ingots grown at a lower speed were those of the best crystalline quality, having at most three grains of different crystallographic orientation. The average dislocations density in all of them were similar and correspond to materials of good quality. EPMA results indicated that the homogeneity in the composition was excellent in the ingots central part. The concentration of Te precipitates/inclusions in all ingots was below the instrument (DSC) detection...
Matéria (Rio de Janeiro), 2018
RESUMEN El Cd1-xZnxTe (0 ≤ x ≤ 1) y el ZnTe son semiconductores de la familia II-VI, que se usan ... more RESUMEN El Cd1-xZnxTe (0 ≤ x ≤ 1) y el ZnTe son semiconductores de la familia II-VI, que se usan en forma monocristalina porque así poseen mejores propiedades estructurales y eléctricas. El CZT y el ZnTe deben poseer alta calidad cristalina y eléctrica para ser usados, el primero en detectores de rayos X y γ, y como sustratos ordenadores de películas epitaxiales aptas para la detección de la radiación IR y el segundo para la fabricación de diodos láser y emisores de luz de alta intensidad, ambos casos en el verde. En este trabajo el CZT se sintetizó por el método de Bridgman, bajo un gradiente de temperatura de 10ºC/cm a velocidades de 1,66 mm/h y 3,22 mm/h para diferentes concentraciones de Zn. Por otro lado, el ZnTe se sintetizó por transporte físico en fase vapor bajo un gradiente de temperatura de 6ºC/cm a una velocidad de 6mm/día. Por medio de revelado químico y microscopía electrónica de transmisión convencional TEM y de alta resolución (HRTEM) se estudió la calidad cristalina...
Se estudió la presencia de dislocaciones en ZnSe monocristalino obtenido por transporte químico u... more Se estudió la presencia de dislocaciones en ZnSe monocristalino obtenido por transporte químico utilizando I 2 como portador gaseoso. Para ello se utilizó microscopía electrónica de transmisión que evidenció, en el rango micrométrico y nanométrico, ausencia de defectos, por lo que fue necesario estudiar áreas mayores del material mediante revelado químico. La densidad de dislocaciones y la desorientación entre subgranos contiguos en obleas de ZnSe fueron determinadas mediante el uso de distintos reactivos que permiten la obtención de figuras de corrosión. Se presentan y comparan los resultados micrográficos obtenidos con las diferentes soluciones, determinándose las ventajas relativas. Se midió la transmitancia del ZnSe con un espectrómetro infrarrojo de transmisión resultando comparable a la obtenida para sustratos comerciales utilizados como ventanas. La caracterización realizada permite afirmar que la calidad cristalina del material obtenido es la adecuada para su aplicación en ventanas ópticas. Palabras claves: ZnSe monocristalino; Semiconductores II-VI; Transporte Químico (I 2); Revelado químico; Microscopía electrónica de barrido y transmisión; Espectrometría infrarroja de transmisión The presence of dislocations was studied in single crystalline ZnSe grown by chemical transport using I 2 as gaseous carrier. The presence of defects was not determined in the micrometric and nanometric range employing transmission electronic microscopy in order to study larger material areas was used chemical etching. Dislocation density and adjacent subgrain misorientation were obtained by chemical etching using different reagents. Micrographic results were shown and compared to determine reagents relative advantages. The transmittance of ZnSe was measured using a Fourier transform infrared spectrometer. Commercial substrates used as windows have comparable results to our grown material wafers. This characterization proves that the semiconductor crystalline quality is appropriate for optical windows.
Crystal Research and Technology, 2010
II-VI, physical transport method, single crystals, chemical etching, transmission electron micros... more II-VI, physical transport method, single crystals, chemical etching, transmission electron microscopy, optical transmission. ZnTe ingots were obtained by the physical transport method, using an in-house designed and built tubular furnace. The growth of ZnTe subsequently to the growth of a seed of this material allowed obtaining an ingot formed by only one large and single crystalline grain. TEM was used for the characterization of the as-grown ZnTe single crystal ingots and commercial single-crystalline wafers of the same material but grown by a higher temperature and more expensive technique, the Bridgman method. Both materials show very good crystalline microstructure, although some stacking faults were found in the commercial one. The infrared transmittance spectra of both materials were measured by FTIR and some differences, most likely due to differences in raw materials and growth methods, were found. The effectiveness and convenience of several chemical etchants to obtain the dislocation density and the minimal misorientation between adjacent subgrains in the as-grown ZnTe wafers were checked. It has been found as the most advantageous the chemical solution that does not produce over-etching.
Journal of Physics: Conference Series, 2009
Cd1-xZnxTe (0 ≤ x ≤ 1) and ZnTe are II-VI semiconductors, which are used in single crystalline st... more Cd1-xZnxTe (0 ≤ x ≤ 1) and ZnTe are II-VI semiconductors, which are used in single crystalline structure to improve their crystalline and electrical properties. The CZT and ZnTe must possess high crystalline and electrical quality to be used, the first in x or γ-ray detectors, and as substrates for suitable epitaxial films for detecting IR radiation and the second for the manufacture of laser diodes and high intensity light emitters, both cases in the green wavelengths. In this work CZT was synthesized by the Bridgman method employing a temperature gradient of 10ºC/cm at speeds of 1.66 mm/h and 3.22 mm/h for different Zn concentrations. Meanwhile ZnTe was synthesized by physical vapor transport employing a temperature gradient of 6ºC/cm at a speed of 6 mm/day. Chemical etching and low and high transmission electron microscopy (LRTEM and HRTEM) were employed to determine the crystalline quality of all materials. It was observed that CZT ingots had an average dislocations density simi...
Matéria (Rio de Janeiro)
CdSe is II-VI semiconductor with compact hexagonal structure. It has a band gap of 1.82 eV and a ... more CdSe is II-VI semiconductor with compact hexagonal structure. It has a band gap of 1.82 eV and a high stopping power for nuclear radiation. Single crystalline CdSe ingots were grown by Physical Vapor Transport (PVT) employing a horizontal reactor. As devices critically depend on material properties its single crystalline quality was determined by chemical etching and transmission electron microscopy. Results were compared to those corresponding to Bridgman High Pressure (HPB) grown material and also to PVT material grown in a vertical reactor.
Cadmium selenide is a II-VI semiconductor compound with 1.67 eV energy gap (300 K) and high stopp... more Cadmium selenide is a II-VI semiconductor compound with 1.67 eV energy gap (300 K) and high stopping power for nuclear radiation. Its crystalline structure is hexagonal (wurtzite) and it is used in solar cells, transistors, light emitting diodes, electroluminescent devices, nuclear radiation detectors at room temperature and nonlinear optical devices [Shan et al. (1994), Young et al. (1994), Van Calster et al. (1988), Chopra (1969), Bhargava (1997)]. It is also employed as substrate for epitaxial growth of HgCdSe [Korostelin et al. (1996)]. Qualities of devices are critically dependent on their material properties. Crystalline characterization of a CdSe commercial wafer was our main goal. The crystalline quality was evaluated by different techniques. Since it is used as an optical window in the IR spectrum, its optical transmittance was measured by FTIR (Perkin-Elmer System 2000). The etch pits distribution was determined by chemical etching. Dislocation density was obtained by counting on optical micrographs (Union Versamet 5279) meanwhile misorientation between adjacent subgrains by means of Shockley-Read approximation. The reliability of the techniques used in determining the crystalline quality was evaluated. The etching solution was sensitive in linear defects detection and crystalline quality was adequate for devices manufacture of this material. Transmission electron microscopy employment confirmed these result.
Anales des la Asociacion Quimica Argentina
A thin film sensor for soils to detect ammonia in aqueous media, operating at room temperature, i... more A thin film sensor for soils to detect ammonia in aqueous media, operating at room temperature, is reported. The sensor was built by depositing pure tellurium by thermal evaporation in conventional vacuum (10-6 Hg mm) on electronic purity alumina substrates fitted with gold electrodes. The resistance of tellurium films was measured when the sensor was exposed to ammonia in humid air. Films were characterized by using the following techniques: Scanning Electron Microscopy (SEM) to observe films morphology, X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) to look for possible surface tellurium oxides. In every case, specimens were observed or analyzed in its initial state and after being aged in different atmospheres: humidity, air and (ammonia + humidity). The appearance of surface TeO 2 in Te specimens aged in air, enabled to infer a probable sensing mechanism of NH 3 in humid media. Resumen Se informa sobre un sensor de película delgada para detectar amoníaco en medio húmedo en suelos, operable a temperatura ambiente. El sensor fue construido depositando telurio puro por evaporación térmica en vacío convencional (10-6 mm Hg) sobre sustratos de alúmina de pureza electrónica provistos con electrodos de oro. La variación de la resistencia de las películas de telurio se midió cuando el sensor era expuesto a amoniaco en aire húmedo. La superficie de las películas se caracterizó empleando las siguientes técnicas: Microscopía Electrónica de Barrido (SEM) para observar la morfología de las películas, Difracción de Rayos X (XRD) y Espectroscopía de Fotoelectrones (XPS) para buscar posibles óxidos de telurio superficiales. En cada caso, las muestras fueron observadas o analizadas en su estado inicial o después de habérselas envejecido por exposición a diferentes atmósferas: humedad, aire y (amoníaco + agua). La presencia de TeO 2 superficial en muestras de Te envejecidas en aire permitió inferir un mecanismo probable de sensado de NH 3 en medio húmedo.
ABSTRACT http://www.aqa.org.ar/iyq.htm
Procedia Materials Science, 2015
A solution growth approach for zinc oxide (ZnO) nanowires is highly appealing because of the low ... more A solution growth approach for zinc oxide (ZnO) nanowires is highly appealing because of the low growth temperature and possibility for large area synthesis. In our work, ZnO nanowires were obtained from thin films prepared on silica glass, Si (100) and Si (111) from a single and five layers spin-coating deposition of a sol-gel prepared with dehydrate zinc acetate, monoethanolamine and isopropanol. Crystallization annealing was performed at 450 °C. These films were used as seed layer to prepare ZnO nanowires/nanorods from a zinc nitrate and hexamethylenetetramine solution. X-ray diffraction analysis showed that nanowires/nanorods grown on Si (111) were preferentially orientated along the [002] direction.
Procedia Materials Science, 2015
Procedia Materials Science, 2015
Titanium dioxide thin films have been deposited on silicon (100) and 316L stainless steel substra... more Titanium dioxide thin films have been deposited on silicon (100) and 316L stainless steel substrates by cathodic arc deposition in oxygen atmosphere with a titanium cathode. The process was run at room temperature and at 300 ºC, biasing the substrate with pulsed voltage (up to-10 kV) and DC voltage (up to-120 V). The crystalline structure was studied by Raman spectroscopy and X-ray diffraction. At room temperature, the films were obtained with an amorphous base with small isolated crystals of rutile and anatase. At 300 ºC, with DC bias, samples grew crystalline with the presence of both anatase and rutile.
International Journal of Advanced Applied Physics Research, 2015
Crystalline defects were studied in single crystalline ZnSe grown by chemical transport using I2 ... more Crystalline defects were studied in single crystalline ZnSe grown by chemical transport using I2 as gaseous carrier. Transmission electronic microscopy determined an excellent structural order in the micrometric and nanometric range. Larger material areas were studied by chemical etching using different reagents to determine average dislocations density and average adjacent subgrains misorientation. Comparable micrographic results of different reagents are shown. Characterization values of ZnSe commercial substrate grown by High Pressure Bridgman (HPB) have been compared to those that correspond to our grown material wafers. Characterization proved that the semiconductor crystalline quality in our wafers is appropriate for optical devices.
Journal of Physics: Conference Series, 2009
Tubular furnaces were designed and built to obtain single crystalline ZnTe and ZnSe ingots using ... more Tubular furnaces were designed and built to obtain single crystalline ZnTe and ZnSe ingots using respectively physical and chemical transport methods. Different temperature profiles and growth rates were analyzed in order to optimize the necessary crystalline quality for device development. Optical and scanning electron micrographs of the corrosion figures produced by chemical etching were used to obtain the dislocation density and the misorientation between adjacent subgrains in ZnTe and ZnSe wafers. Structural quality of the single crystalline material was determined by transmission electronic microscopy. Optical transmittance was measured by infrared transmission spectrometry and the resulting values were compared to commercial samples.
Brazilian Journal of Development
ZnO nanostructures are used in device systems such as photodetectors, gas sensors,photoemission d... more ZnO nanostructures are used in device systems such as photodetectors, gas sensors,photoemission devices, UV-photosensors and many others in Optoelectronics.In the present work we studied nanocrystalline ZnO:Ga thin films prepared by the sol–gel dip-coating technique. Samples were characterized by Grazing Incidence X-ray Diffraction(GIXD), X-ray Reflectivity (XR) and Grazing Incidence Small-Angle X-ray Scattering(GISAXS) methods and Field Effect Scanning Electronic Microscopy (FESEM). Characterization of the samples shows that the obtained films were uniform, continuous, with a crystallite size around 12 nm, an average pores size of around 3.5nm, and a volume fraction of nanoporosity between 0.18 and 0.3. Comparison of densities between doped and undoped films is discussed.
Se estudia la calidad cristalina de una oblea comercial monocristalina de ZnSe (Cradley Crystals)... more Se estudia la calidad cristalina de una oblea comercial monocristalina de ZnSe (Cradley Crystals) combinando diferentes técnicas. Se utiliza microscopía óptica para la observación de defectos macroscópicos y figuras de corrosión obtenidas por revelado químico de la misma y microscopía electrónica de transmisión para determinar su calidad estructural, también se evalúa su transmitancia óptica por su aplicación en ventanas infrarrojas. Una presencia pequeña de defectos macroscópicos, un orden estructural notable entre dislocaciones y la baja densidad de dislocaciones y desorientación angular halladas entre subgranos adyacentes confirman una adecuada calidad cristalina para el empleo de este material en dispositivos optoelectrónicos.This project involves the study of the crystalline quality of a single crystalline commercial wafer of ZnSe (Cradley Crystals) combining different techniques. We use optical microscopy for the observation of macroscopic defects and etching figures which wer...
ZnO and ZnO:Al thin films obtained by spin-coating on amorphous SiO2 substrata, were studied by X... more ZnO and ZnO:Al thin films obtained by spin-coating on amorphous SiO2 substrata, were studied by XRR and Gisaxs. Pure ZnO samples showed higher densities and thickness than Al doped one. The thickness of pure ZnO layer films grown linearly with the number of deposits but could not be determined by XRR because of the lack of oscilation in the XRR diagrams being obtained by FESEM. For doped samples the thickness variation with the number of deposit was not significative. The preliminar results about nanopore size, obtained by Gisaxs, were similar.Fil: Bojorge, Claudia Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Canepa, Horacio Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Casanova, Jorge Ramón. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: A.F. Craievich. Universidade de Sao Paulo; BrasilFil: Heredia, Eduardo Armando. Consejo Nacional de Investigaciones Científicas y Técnicas; Argent...
Materials, 2021
Cd1−xZnxTe (0 ≤ x ≤ 0.1) ingots were obtained by Bridgman’s method using two different speeds in ... more Cd1−xZnxTe (0 ≤ x ≤ 0.1) ingots were obtained by Bridgman’s method using two different speeds in order to find the optimal conditions for single-crystalline growth. Crystalline quality was studied by chemical etching, the elemental composition by wavelength dispersive spectroscopy (WDS), tellurium (Te) precipitates/inclusions concentration by differential scanning calorimetry (DSC), optical transmission by Fourier transformed infrared spectrometry (FTIR), and band gap energy (Egap) by photoluminescence (PL). It was observed that the ingots grown at a lower speed were those of the best crystalline quality, having at most three grains of different crystallographic orientation. The average dislocations density in all of them were similar and correspond to materials of good quality. EPMA results indicated that the homogeneity in the composition was excellent in the ingots central part. The concentration of Te precipitates/inclusions in all ingots was below the instrument (DSC) detection...
Matéria (Rio de Janeiro), 2018
RESUMEN El Cd1-xZnxTe (0 ≤ x ≤ 1) y el ZnTe son semiconductores de la familia II-VI, que se usan ... more RESUMEN El Cd1-xZnxTe (0 ≤ x ≤ 1) y el ZnTe son semiconductores de la familia II-VI, que se usan en forma monocristalina porque así poseen mejores propiedades estructurales y eléctricas. El CZT y el ZnTe deben poseer alta calidad cristalina y eléctrica para ser usados, el primero en detectores de rayos X y γ, y como sustratos ordenadores de películas epitaxiales aptas para la detección de la radiación IR y el segundo para la fabricación de diodos láser y emisores de luz de alta intensidad, ambos casos en el verde. En este trabajo el CZT se sintetizó por el método de Bridgman, bajo un gradiente de temperatura de 10ºC/cm a velocidades de 1,66 mm/h y 3,22 mm/h para diferentes concentraciones de Zn. Por otro lado, el ZnTe se sintetizó por transporte físico en fase vapor bajo un gradiente de temperatura de 6ºC/cm a una velocidad de 6mm/día. Por medio de revelado químico y microscopía electrónica de transmisión convencional TEM y de alta resolución (HRTEM) se estudió la calidad cristalina...
Se estudió la presencia de dislocaciones en ZnSe monocristalino obtenido por transporte químico u... more Se estudió la presencia de dislocaciones en ZnSe monocristalino obtenido por transporte químico utilizando I 2 como portador gaseoso. Para ello se utilizó microscopía electrónica de transmisión que evidenció, en el rango micrométrico y nanométrico, ausencia de defectos, por lo que fue necesario estudiar áreas mayores del material mediante revelado químico. La densidad de dislocaciones y la desorientación entre subgranos contiguos en obleas de ZnSe fueron determinadas mediante el uso de distintos reactivos que permiten la obtención de figuras de corrosión. Se presentan y comparan los resultados micrográficos obtenidos con las diferentes soluciones, determinándose las ventajas relativas. Se midió la transmitancia del ZnSe con un espectrómetro infrarrojo de transmisión resultando comparable a la obtenida para sustratos comerciales utilizados como ventanas. La caracterización realizada permite afirmar que la calidad cristalina del material obtenido es la adecuada para su aplicación en ventanas ópticas. Palabras claves: ZnSe monocristalino; Semiconductores II-VI; Transporte Químico (I 2); Revelado químico; Microscopía electrónica de barrido y transmisión; Espectrometría infrarroja de transmisión The presence of dislocations was studied in single crystalline ZnSe grown by chemical transport using I 2 as gaseous carrier. The presence of defects was not determined in the micrometric and nanometric range employing transmission electronic microscopy in order to study larger material areas was used chemical etching. Dislocation density and adjacent subgrain misorientation were obtained by chemical etching using different reagents. Micrographic results were shown and compared to determine reagents relative advantages. The transmittance of ZnSe was measured using a Fourier transform infrared spectrometer. Commercial substrates used as windows have comparable results to our grown material wafers. This characterization proves that the semiconductor crystalline quality is appropriate for optical windows.
Crystal Research and Technology, 2010
II-VI, physical transport method, single crystals, chemical etching, transmission electron micros... more II-VI, physical transport method, single crystals, chemical etching, transmission electron microscopy, optical transmission. ZnTe ingots were obtained by the physical transport method, using an in-house designed and built tubular furnace. The growth of ZnTe subsequently to the growth of a seed of this material allowed obtaining an ingot formed by only one large and single crystalline grain. TEM was used for the characterization of the as-grown ZnTe single crystal ingots and commercial single-crystalline wafers of the same material but grown by a higher temperature and more expensive technique, the Bridgman method. Both materials show very good crystalline microstructure, although some stacking faults were found in the commercial one. The infrared transmittance spectra of both materials were measured by FTIR and some differences, most likely due to differences in raw materials and growth methods, were found. The effectiveness and convenience of several chemical etchants to obtain the dislocation density and the minimal misorientation between adjacent subgrains in the as-grown ZnTe wafers were checked. It has been found as the most advantageous the chemical solution that does not produce over-etching.
Journal of Physics: Conference Series, 2009
Cd1-xZnxTe (0 ≤ x ≤ 1) and ZnTe are II-VI semiconductors, which are used in single crystalline st... more Cd1-xZnxTe (0 ≤ x ≤ 1) and ZnTe are II-VI semiconductors, which are used in single crystalline structure to improve their crystalline and electrical properties. The CZT and ZnTe must possess high crystalline and electrical quality to be used, the first in x or γ-ray detectors, and as substrates for suitable epitaxial films for detecting IR radiation and the second for the manufacture of laser diodes and high intensity light emitters, both cases in the green wavelengths. In this work CZT was synthesized by the Bridgman method employing a temperature gradient of 10ºC/cm at speeds of 1.66 mm/h and 3.22 mm/h for different Zn concentrations. Meanwhile ZnTe was synthesized by physical vapor transport employing a temperature gradient of 6ºC/cm at a speed of 6 mm/day. Chemical etching and low and high transmission electron microscopy (LRTEM and HRTEM) were employed to determine the crystalline quality of all materials. It was observed that CZT ingots had an average dislocations density simi...
Matéria (Rio de Janeiro)
CdSe is II-VI semiconductor with compact hexagonal structure. It has a band gap of 1.82 eV and a ... more CdSe is II-VI semiconductor with compact hexagonal structure. It has a band gap of 1.82 eV and a high stopping power for nuclear radiation. Single crystalline CdSe ingots were grown by Physical Vapor Transport (PVT) employing a horizontal reactor. As devices critically depend on material properties its single crystalline quality was determined by chemical etching and transmission electron microscopy. Results were compared to those corresponding to Bridgman High Pressure (HPB) grown material and also to PVT material grown in a vertical reactor.
Cadmium selenide is a II-VI semiconductor compound with 1.67 eV energy gap (300 K) and high stopp... more Cadmium selenide is a II-VI semiconductor compound with 1.67 eV energy gap (300 K) and high stopping power for nuclear radiation. Its crystalline structure is hexagonal (wurtzite) and it is used in solar cells, transistors, light emitting diodes, electroluminescent devices, nuclear radiation detectors at room temperature and nonlinear optical devices [Shan et al. (1994), Young et al. (1994), Van Calster et al. (1988), Chopra (1969), Bhargava (1997)]. It is also employed as substrate for epitaxial growth of HgCdSe [Korostelin et al. (1996)]. Qualities of devices are critically dependent on their material properties. Crystalline characterization of a CdSe commercial wafer was our main goal. The crystalline quality was evaluated by different techniques. Since it is used as an optical window in the IR spectrum, its optical transmittance was measured by FTIR (Perkin-Elmer System 2000). The etch pits distribution was determined by chemical etching. Dislocation density was obtained by counting on optical micrographs (Union Versamet 5279) meanwhile misorientation between adjacent subgrains by means of Shockley-Read approximation. The reliability of the techniques used in determining the crystalline quality was evaluated. The etching solution was sensitive in linear defects detection and crystalline quality was adequate for devices manufacture of this material. Transmission electron microscopy employment confirmed these result.
Anales des la Asociacion Quimica Argentina
A thin film sensor for soils to detect ammonia in aqueous media, operating at room temperature, i... more A thin film sensor for soils to detect ammonia in aqueous media, operating at room temperature, is reported. The sensor was built by depositing pure tellurium by thermal evaporation in conventional vacuum (10-6 Hg mm) on electronic purity alumina substrates fitted with gold electrodes. The resistance of tellurium films was measured when the sensor was exposed to ammonia in humid air. Films were characterized by using the following techniques: Scanning Electron Microscopy (SEM) to observe films morphology, X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) to look for possible surface tellurium oxides. In every case, specimens were observed or analyzed in its initial state and after being aged in different atmospheres: humidity, air and (ammonia + humidity). The appearance of surface TeO 2 in Te specimens aged in air, enabled to infer a probable sensing mechanism of NH 3 in humid media. Resumen Se informa sobre un sensor de película delgada para detectar amoníaco en medio húmedo en suelos, operable a temperatura ambiente. El sensor fue construido depositando telurio puro por evaporación térmica en vacío convencional (10-6 mm Hg) sobre sustratos de alúmina de pureza electrónica provistos con electrodos de oro. La variación de la resistencia de las películas de telurio se midió cuando el sensor era expuesto a amoniaco en aire húmedo. La superficie de las películas se caracterizó empleando las siguientes técnicas: Microscopía Electrónica de Barrido (SEM) para observar la morfología de las películas, Difracción de Rayos X (XRD) y Espectroscopía de Fotoelectrones (XPS) para buscar posibles óxidos de telurio superficiales. En cada caso, las muestras fueron observadas o analizadas en su estado inicial o después de habérselas envejecido por exposición a diferentes atmósferas: humedad, aire y (amoníaco + agua). La presencia de TeO 2 superficial en muestras de Te envejecidas en aire permitió inferir un mecanismo probable de sensado de NH 3 en medio húmedo.
ABSTRACT http://www.aqa.org.ar/iyq.htm
Procedia Materials Science, 2015
A solution growth approach for zinc oxide (ZnO) nanowires is highly appealing because of the low ... more A solution growth approach for zinc oxide (ZnO) nanowires is highly appealing because of the low growth temperature and possibility for large area synthesis. In our work, ZnO nanowires were obtained from thin films prepared on silica glass, Si (100) and Si (111) from a single and five layers spin-coating deposition of a sol-gel prepared with dehydrate zinc acetate, monoethanolamine and isopropanol. Crystallization annealing was performed at 450 °C. These films were used as seed layer to prepare ZnO nanowires/nanorods from a zinc nitrate and hexamethylenetetramine solution. X-ray diffraction analysis showed that nanowires/nanorods grown on Si (111) were preferentially orientated along the [002] direction.
Procedia Materials Science, 2015
Procedia Materials Science, 2015
Titanium dioxide thin films have been deposited on silicon (100) and 316L stainless steel substra... more Titanium dioxide thin films have been deposited on silicon (100) and 316L stainless steel substrates by cathodic arc deposition in oxygen atmosphere with a titanium cathode. The process was run at room temperature and at 300 ºC, biasing the substrate with pulsed voltage (up to-10 kV) and DC voltage (up to-120 V). The crystalline structure was studied by Raman spectroscopy and X-ray diffraction. At room temperature, the films were obtained with an amorphous base with small isolated crystals of rutile and anatase. At 300 ºC, with DC bias, samples grew crystalline with the presence of both anatase and rutile.