We report the cell performance of Cu 2 ZnSnS 4 (CZTS) thin film solar cell that showed efficiency... more We report the cell performance of Cu 2 ZnSnS 4 (CZTS) thin film solar cell that showed efficiency in the range of 6 to 7 %. The absorber layer was grown by magnetron sputtering followed by annealing in a H 2 S/N 2 environment. Initially, the CZTS film was co-sputtered with three different targets; copper (Cu), tin sulphide (SnS) and zinc sulphide (ZnS). The Cu target was subjected to DC power and RF power was used for the SnS and ZnS targets. The as-grown CZTS film was sulphurized in H 2 S environment at around 510°C, which re-crystalized the film with larger grains. The quantum efficiency measurement showed internal quantum efficiency as high as 80% around 600 nm wavelength. A typical cell showed 610 mV open circuit voltage, 16 mA/cm 2 short-circuit current, and 6.2% efficiency.
Cu2ZnSnS4 (CZTS) thin film solar cells have attracted scientific and economic interest in the las... more Cu2ZnSnS4 (CZTS) thin film solar cells have attracted scientific and economic interest in the last decade. In this study, accelerated thermal cycling and damp heat tests are used to examine the stability of CZTS thin film solar cells, which are coated with two TCO materials. From the results, the CZTS solar cells with ZnO and ITO perform better durability than the one with ZnO and AZO under the accelerated thermal cycling test. The result also indicates that the ZnO and AZO deposited by using atomic layer deposition (ALD) technique does not improve the stability for CZTS solar cells comparing to the sputtering technique. In the damp heat experiment, the results show that the bare ITO thin films and AZO thin films deposited by the ALD technique have a good durability with regard to the moisture ingress. The AZO thin films deposited by RF sputtering without annealing have a worse performance with regard to electrical properties after the damp heat test. However, the cells with an ITO layer do not sustain a good performance after the damp heat test, which could be attributed smaller thickness of the ITO thin films. Although the AZO thin films using the ALD technique have better durability than the ones using the RF sputtering, the cells coated with the ZnO and AZO by the ALD technique are not much better than the cells coated with the ZnO and AZO by the RF sputtering.
Proceedings of the International Astronomical Union, 2007
We present very deep HST/ACS images of five QSO host galaxies, classified as undisturbed elliptic... more We present very deep HST/ACS images of five QSO host galaxies, classified as undisturbed ellipticals in earlier studies. For four of the five objects, our images reveal strong signs of interaction such as tidal tails, shells, and other fine structure, suggesting that a large fraction of QSO host galaxies may have experienced a relatively recent merger event. Our preliminary results for a control sample of inactive elliptical galaxies do not reveal comparable fine structure.
2012 IEEE Long Island Systems, Applications and Technology Conference (LISAT), 2012
Aluminum-doped zinc oxide (AZO) film is a promising candidate for low cost transparent conductive... more Aluminum-doped zinc oxide (AZO) film is a promising candidate for low cost transparent conductive oxide (TCO) applications. It is a viable alternative to indium tin oxide (ITO), the dominant material used in TCO. Although AZO has good electrical and optical properties, its mechanical properties must be thoroughly considered in the design and manufacturing of flexible devices. During the manufacture and use, thin films' are subjected to bending fatigue (cyclic bending) which leads to degradation and ultimately failure of the films. This work was designed to investigate the effects of the bending frequency, bending diameter, ways of bending, and number of bending cycles on the percentage change in electrical resistance (PCER) and transmittance of 575 nm thick AZO films, which were deposited on 127 μm Kapton substrate using RF-magnetron sputtering technique. Both the film and the substrate were subjected to cyclic bending test under controlled study parameters. The design of experiments technique (DOE) was used to investigate the significant factors on the PCER as well as to provide an average estimate of the effect of each factor and two-factor interaction through the main effects plot and the two-factor interaction plot, respectively. Moreover, the transmittance spectra were studied at different number of bending cycles. The primary result shows that the PCER is very sensitive to all study parameters. However, it increases rapidly in the first 400 bending cycles and then increases linearly until 1000 bending cycles. The result also points out that the PCER is large while the small bending diameter and low bending frequency are applied. Also the two ways bending experiment leads to the larger PCER compared with the one way bending test. The fresh films average transmittance (from 660 to 950 nm wavelength) is 59.6%, which decreased to about 3.4% after 1000 cycles of bending.
ABSTRACT Cu2ZnSnS4 (CZTS) thin film solar cells were successfully fabricated on Corning® Willow® ... more ABSTRACT Cu2ZnSnS4 (CZTS) thin film solar cells were successfully fabricated on Corning® Willow® Glass substrates coated with a Molybdenum (Mo) back contact. The CZTS thin films were deposited by using magnetron sputtering followed by annealing in sulfur vapor for 30 minutes. The best conversion efficiency achieved of the flexible CZTS solar cell was 3.08%, with an active area of 0.45cm2. The conversion efficiency was reduced by 20% when the cell was bent to a 50mm radius. The degradation is caused by higher series resistance, which can be due to the degradation of the TCO layer and the damage in the CZTS/Mo interface.
GRAVITATIONALLY LENSED QUASAR HOST GALAXIES Chris Impey Steward Observatory, University of Arizon... more GRAVITATIONALLY LENSED QUASAR HOST GALAXIES Chris Impey Steward Observatory, University of Arizona, Tucson, AZ 85721, USA cimpeyCas. arizona. edu Hans-Walter Rix Max-Planck-Institut fur Astronomic, Konigstuhl 17, D-69117 Heidelberg, Germany ...
Cu 2 ZnSnS 4 (CZTS) thin film solar cells were fabricated on 100 μm thick flexible glass (FG) sub... more Cu 2 ZnSnS 4 (CZTS) thin film solar cells were fabricated on 100 μm thick flexible glass (FG) substrates coated with Molybdenum (Mo) anodes. The CZTS thin films were deposited by using magnetron sputtering followed by annealing in sulfur vapor. The fabricated cell structure was FG/Mo/CZTS/CdS/ZnO/ITO/Ag, where cadmium sulfide (CdS), zinc oxide (ZnO), tin-doped indium oxide (ITO) and silver (Ag) were used as an n-type window layer, resistive layer, transparent conductor and finger electrode, respectively. The best conversion efficiency achieved of the flexible CZTS solar cell was 3.08%, with an active area of 0.45 cm 2 . The conversion efficiency was reduced by 20% when the cell was bent to a 50 mm radius.
We present deep HST /ACS images and Keck spectroscopy of MC2 1635+119, a QSO hosted by a galaxy p... more We present deep HST /ACS images and Keck spectroscopy of MC2 1635+119, a QSO hosted by a galaxy previously classified as an undisturbed elliptical. Our new images reveal dramatic shell structure indicative of a merger event in the relatively recent past. The brightest shells in the central regions of the host are distributed alternately in radius, with at least two distinct shells on one side of the nucleus and three on the other, out to a distance of ∼13 kpc. The light within the five shells comprises ∼6% of the total galaxy light. Lower surface brightness ripples or tails and other debris extend out to a distance of ∼65 kpc. A simple N-body model for a merger reproduces the inner shell structure and gives an estimate for the age of the merger between ∼30 Myr and ∼1.7 Gyr, depending on a range of reasonable assumptions. While the inner shell structure is suggestive of a minor merger, the total light contribution from the shells and extended structures are more indicative of a major merger. The spectrum of the host galaxy is dominated by a population of intermediate age (∼1.4 Gyr), indicating a strong starburst episode that may have occurred at the time of the merger event. We speculate that the current QSO activity may have been triggered in the recent past by either a minor merger, or by debris from an older (∼Gyr) major merger that is currently "raining" back into the central regions of the merger remnant.
We have obtained and modeled NICMOS images of the Einstein ring lens system MG J1131]0456, which ... more We have obtained and modeled NICMOS images of the Einstein ring lens system MG J1131]0456, which show that its lens galaxy is an H \ 18.6 mag, transparent, early-type galaxy at a redshift of it has a major axis e †ective radius projected axis ratio b/a \ 0.6^0.1, and z l^0 .84 ; R e \ 0A .7^0A .1, major axis P.A. \ 55¡^9¡. The lens is the brightest member of a group of at least seven galaxies with similar R[I and I[H colors, and the two closest group members produce sufficient tidal perturbations to explain the shape of the ring. The host galaxy of the MG J1131]0456 source is a extremely z s Z 2 red object (ERO) that is lensed into optical and infrared rings of dramatically di †erent morphologies. These di †erences imply a strongly wavelength-dependent source morphology that could be explained by embedding the host in a larger, dusty disk. At 1.6 km (H), the ring is spectacularly luminous, with a total observed Ñux of H \ 17.4 mag and a demagniÐed Ñux of 19.3 mag, corresponding to a 1È2 galaxy at L * the probable source redshift of Thus, it is primarily the stellar emission of the radio source host z s Z 2. galaxy that produces the overall colors of two of the reddest radio lenses, MG J1131]0456 and JVAS B1938]666, aided by the suppression of optical active galactic nucleus emission by dust in the source galaxy. The dusty lens hypothesis È that many massive early-type galaxies with have large, 0 [ z l [ 1 uniform dust opacities È is ruled out.
At low redshift, there are fundamental correlations between the mass of supermassive black holes ... more At low redshift, there are fundamental correlations between the mass of supermassive black holes (M BH ) and the mass (M bulge ) and luminosity of the host galaxy bulge. We investigate the same relation at z k 1. Using virial mass estimates for 11 quasars at z k 2 to measure their black hole mass, we find that black holes at high z fall nearly on the same M BH versus R-band magnitude (M R ) relation (to $0.3 mag) as low-redshift active and inactive galaxies, without making any correction for luminosity evolution. Using a set of conservative assumptions about the host galaxy stellar population, we show that at z k 2 (10 Gyr ago), the ratio of M BH /M bulge was 3-6 times larger than today. Barring unknown systematic errors on the measurement of M BH , we also rule out scenarios in which moderately luminous quasar hosts at z k 2 were fully formed bulges that passively faded to the present epoch. On the other hand, five quasar hosts at z % 1 are consistent with the current-day M BH -M R relationship after taking into account evolution that is appropriate for E/S0 galaxies. Therefore, z % 1 host galaxies appear to fit the hypothesis that they are fully formed early-type galaxies. We also find that most quasar hosts with absolute magnitudes brighter than M R ¼ À23 cannot fade below L Ã galaxies today, regardless of their stellar population makeup, because their black hole masses are too high and they must arrive at the local M BH -M R relationship by z ¼ 0.
We present 1210 Johnson/Cousins B,V,R, and I photometric observations of 22 recent type Most of t... more We present 1210 Johnson/Cousins B,V,R, and I photometric observations of 22 recent type Most of the photometry was obtained at the Fred Lawrence Whipple Observatory (FLWO) of the Harvard-Smithsonian Center for Astrophysics in a cooperative observing plan aimed at improving the data base for SN Ia. The redshifts of the sample range from cz=1200 to 37000 km s −1 with a mean of cz=7000 km s −1 . effort to collect Johnson/Cousins BV RI photometry of type Ia supernovae. Many of these SNe Ia were discovered serendipitously by amateurs or by professionals scanning images collected for another purpose.
We present optical photometry for the type Ia SN 1994D in NGC 4526 from 1994 March 7 to June 4 st... more We present optical photometry for the type Ia SN 1994D in NGC 4526 from 1994 March 7 to June 4 starting 13 days before B-band maximum. The light curves of this SN resemble closely those of the "normal" type Ia events SNe 1989B and 1980N, differing only in a slightly faster decline after maximum in VRI. The optical absolute magnitudes of SN 1994D, however, are significantly brighter than those of its near twins, and brighter than those predicted by Phillips' [ApJ, 413, L105 (1993)] relationship between decline rate and luminosity. Our small amount of IR photometry of SN 1994D is not inconsistent with that of other type IA SNe.
We report the performance of Cu 2 ZnSnS 4 (CZTS) thin film solar cell that showed efficiency in t... more We report the performance of Cu 2 ZnSnS 4 (CZTS) thin film solar cell that showed efficiency in the range of 6.2% without an antireflection coating. Initially, the CZTS precursor film was co-sputtered using three different targets; copper (Cu), tin sulfide (SnS) and zinc sulfide (ZnS). The Cu target was subjected to DC power, and RF power was used for the SnS and ZnS targets. The as-grown CZTS film was sulfurized in a H 2 S/N 2 environment at 525°C, which re-crystalized the film with grain sizes in the range of 1 lm. Cadmium sulfide (CdS) was used as the n-type layer. Current-voltage (I-V), quantum efficiency (QE) and capacitance-voltage (C-V) measurements were used to characterize the cell device. The modeling and analysis of QE and CV data showed that a significant portion of the CZTS layer did not contribute to the photo-generation. Optimizing CZTS phase purity, improving QE in the broader wavelength region, and increasing minority carrier lifetime are necessary steps to further improve CZTS device performance.
Gravitational lensing assists in the detection of quasar hosts by amplifying and distorting the h... more Gravitational lensing assists in the detection of quasar hosts by amplifying and distorting the host light away from the unresolved quasar core images. We present the results of HST observations of 30 quasar hosts at redshifts 1 < z < 4.5. The hosts are small in size (r e 6 kpc), and span a range of morphologies consistent with early-types (though smaller in mass) to disky/late-type. The ratio of the black hole mass (M BH , from the virial technique) to the bulge mass (M bulge , from the stellar luminosity) at 1 z 1.7 is broadly consistent with the local value; while M BH /M bulge at z 1.7 is a factor of 3-6 higher than the local value. But, depending on the stellar content the ratio may decline at z 4 (if E/S0-like), flatten off to 6-10 times the local value (if Sbc-like), or continue to rise (if Im-like). We infer that galaxy bulge masses must have grown by a factor of 3-6 over the redshift range 3 z 1, and then changed little since z ∼ 1. This suggests that the peak epoch of galaxy formation for massive galaxies is above z ∼ 1. We also estimate the duty cycle of luminous AGNs at z 1 to be ∼ 1%, or 10 7 yrs, with sizable scatter.
IEEE Transactions on Device and Materials Reliability, 2000
Aluminum-doped zinc oxide (AZO) thin film is a promising candidate for low-cost transparent condu... more Aluminum-doped zinc oxide (AZO) thin film is a promising candidate for low-cost transparent conductive oxide applications. AZO thin films have good electrical and optical properties; however, their reliability must be carefully considered in manufacturing and usage of flexible devices such as flexible solar cells. Cyclic bending leads to both electrical and optical degradation of AZO thin films. Therefore, this paper was designed to investigate the effects of the bending frequency, bending diameter, number of bending cycles, and film thickness on the electrical and optical degradation of AZO films, which were deposited on polyimide (PI) substrates using a radio frequency-magnetron sputtering technique. The cycling was conducted on identical specimens under controlled study parameters. The design of experiments technique was used to determine the significant factors on the percentage change in electrical resistance (PCER) and the degradation of average transmittance (DAT), considering a wavelength range from 660 to 950 nm. The result shows that the PCER is very sensitive to number of bending cycles, particularly in the first 300 cycles. After 1000 cycles, the mean PCER of 425-and 600-nm AZO films are about 300% and 600%, respectively. The DAT is sensitive to number of bending cycles, bending diameter, and bending frequency. The mean DAT is about 2.8% after 1000 bending cycles.
Consider a production system where products are produced continuously and screened for conformanc... more Consider a production system where products are produced continuously and screened for conformance with their specification limits. When product performance falls below a lower specification limit or above an upper limit, a decision is made to rework or scrap the product. The majority of the process target models in the literature deal with a single-stage production system. In the real-world industrial settings, however, products are often processed through multi-stage production systems. If the probabilities associated with its recurrent, transient and absorbing states are known, we can better understand the nature of a production system and thus better capture the optimum target for a process. This paper first discusses the roles of a Markovian approach and then develops the general form of a Markovian model for optimum process target levels within the framework of a multi-stage serial production system. Numerical examples and sensitivity analysis are performed.
Most gravitational lens galaxies are early-type galaxies in relatively low density environments. ... more Most gravitational lens galaxies are early-type galaxies in relatively low density environments. We show that they lie on the same fundamental plane as early-type galaxies in both local and distant rich clusters. Their surface brightness evolution requires a typical star formation epoch of z f ≃ 2-3, almost indistinguishable from that of rich cluster galaxies at comparable redshifts. The restricted galaxy type range of the lenses means that photometric redshifts work well even with only 1-3 filter photometry. We make preliminary measurements of the mass and luminosity functions of the lens galaxies, and find they are consistent with the standard model used for deriving cosmological limits using lens statistics. As expected for a mass-weighted sample, they are more massive and more luminous than the overall early-type galaxy population.
We present 15 Einstein Rings and arcs in the CfA--Arizona--Space Telescope Gravitational Lensing ... more We present 15 Einstein Rings and arcs in the CfA--Arizona--Space Telescope Gravitational Lensing survey (CASTLES), the majority of which are candidate quasar host galaxies. All of the objects are at z&amp;amp;gt;=1.3, thus lensing provides one of the largest quasar hosts samples beyond z&amp;amp;gt;1. Gravitational lensing stretches out quasar hosts into Einstein rings and arcs, enhancing host detections and enabling measurements
We report the cell performance of Cu 2 ZnSnS 4 (CZTS) thin film solar cell that showed efficiency... more We report the cell performance of Cu 2 ZnSnS 4 (CZTS) thin film solar cell that showed efficiency in the range of 6 to 7 %. The absorber layer was grown by magnetron sputtering followed by annealing in a H 2 S/N 2 environment. Initially, the CZTS film was co-sputtered with three different targets; copper (Cu), tin sulphide (SnS) and zinc sulphide (ZnS). The Cu target was subjected to DC power and RF power was used for the SnS and ZnS targets. The as-grown CZTS film was sulphurized in H 2 S environment at around 510°C, which re-crystalized the film with larger grains. The quantum efficiency measurement showed internal quantum efficiency as high as 80% around 600 nm wavelength. A typical cell showed 610 mV open circuit voltage, 16 mA/cm 2 short-circuit current, and 6.2% efficiency.
Cu2ZnSnS4 (CZTS) thin film solar cells have attracted scientific and economic interest in the las... more Cu2ZnSnS4 (CZTS) thin film solar cells have attracted scientific and economic interest in the last decade. In this study, accelerated thermal cycling and damp heat tests are used to examine the stability of CZTS thin film solar cells, which are coated with two TCO materials. From the results, the CZTS solar cells with ZnO and ITO perform better durability than the one with ZnO and AZO under the accelerated thermal cycling test. The result also indicates that the ZnO and AZO deposited by using atomic layer deposition (ALD) technique does not improve the stability for CZTS solar cells comparing to the sputtering technique. In the damp heat experiment, the results show that the bare ITO thin films and AZO thin films deposited by the ALD technique have a good durability with regard to the moisture ingress. The AZO thin films deposited by RF sputtering without annealing have a worse performance with regard to electrical properties after the damp heat test. However, the cells with an ITO layer do not sustain a good performance after the damp heat test, which could be attributed smaller thickness of the ITO thin films. Although the AZO thin films using the ALD technique have better durability than the ones using the RF sputtering, the cells coated with the ZnO and AZO by the ALD technique are not much better than the cells coated with the ZnO and AZO by the RF sputtering.
Proceedings of the International Astronomical Union, 2007
We present very deep HST/ACS images of five QSO host galaxies, classified as undisturbed elliptic... more We present very deep HST/ACS images of five QSO host galaxies, classified as undisturbed ellipticals in earlier studies. For four of the five objects, our images reveal strong signs of interaction such as tidal tails, shells, and other fine structure, suggesting that a large fraction of QSO host galaxies may have experienced a relatively recent merger event. Our preliminary results for a control sample of inactive elliptical galaxies do not reveal comparable fine structure.
2012 IEEE Long Island Systems, Applications and Technology Conference (LISAT), 2012
Aluminum-doped zinc oxide (AZO) film is a promising candidate for low cost transparent conductive... more Aluminum-doped zinc oxide (AZO) film is a promising candidate for low cost transparent conductive oxide (TCO) applications. It is a viable alternative to indium tin oxide (ITO), the dominant material used in TCO. Although AZO has good electrical and optical properties, its mechanical properties must be thoroughly considered in the design and manufacturing of flexible devices. During the manufacture and use, thin films' are subjected to bending fatigue (cyclic bending) which leads to degradation and ultimately failure of the films. This work was designed to investigate the effects of the bending frequency, bending diameter, ways of bending, and number of bending cycles on the percentage change in electrical resistance (PCER) and transmittance of 575 nm thick AZO films, which were deposited on 127 μm Kapton substrate using RF-magnetron sputtering technique. Both the film and the substrate were subjected to cyclic bending test under controlled study parameters. The design of experiments technique (DOE) was used to investigate the significant factors on the PCER as well as to provide an average estimate of the effect of each factor and two-factor interaction through the main effects plot and the two-factor interaction plot, respectively. Moreover, the transmittance spectra were studied at different number of bending cycles. The primary result shows that the PCER is very sensitive to all study parameters. However, it increases rapidly in the first 400 bending cycles and then increases linearly until 1000 bending cycles. The result also points out that the PCER is large while the small bending diameter and low bending frequency are applied. Also the two ways bending experiment leads to the larger PCER compared with the one way bending test. The fresh films average transmittance (from 660 to 950 nm wavelength) is 59.6%, which decreased to about 3.4% after 1000 cycles of bending.
ABSTRACT Cu2ZnSnS4 (CZTS) thin film solar cells were successfully fabricated on Corning® Willow® ... more ABSTRACT Cu2ZnSnS4 (CZTS) thin film solar cells were successfully fabricated on Corning® Willow® Glass substrates coated with a Molybdenum (Mo) back contact. The CZTS thin films were deposited by using magnetron sputtering followed by annealing in sulfur vapor for 30 minutes. The best conversion efficiency achieved of the flexible CZTS solar cell was 3.08%, with an active area of 0.45cm2. The conversion efficiency was reduced by 20% when the cell was bent to a 50mm radius. The degradation is caused by higher series resistance, which can be due to the degradation of the TCO layer and the damage in the CZTS/Mo interface.
GRAVITATIONALLY LENSED QUASAR HOST GALAXIES Chris Impey Steward Observatory, University of Arizon... more GRAVITATIONALLY LENSED QUASAR HOST GALAXIES Chris Impey Steward Observatory, University of Arizona, Tucson, AZ 85721, USA cimpeyCas. arizona. edu Hans-Walter Rix Max-Planck-Institut fur Astronomic, Konigstuhl 17, D-69117 Heidelberg, Germany ...
Cu 2 ZnSnS 4 (CZTS) thin film solar cells were fabricated on 100 μm thick flexible glass (FG) sub... more Cu 2 ZnSnS 4 (CZTS) thin film solar cells were fabricated on 100 μm thick flexible glass (FG) substrates coated with Molybdenum (Mo) anodes. The CZTS thin films were deposited by using magnetron sputtering followed by annealing in sulfur vapor. The fabricated cell structure was FG/Mo/CZTS/CdS/ZnO/ITO/Ag, where cadmium sulfide (CdS), zinc oxide (ZnO), tin-doped indium oxide (ITO) and silver (Ag) were used as an n-type window layer, resistive layer, transparent conductor and finger electrode, respectively. The best conversion efficiency achieved of the flexible CZTS solar cell was 3.08%, with an active area of 0.45 cm 2 . The conversion efficiency was reduced by 20% when the cell was bent to a 50 mm radius.
We present deep HST /ACS images and Keck spectroscopy of MC2 1635+119, a QSO hosted by a galaxy p... more We present deep HST /ACS images and Keck spectroscopy of MC2 1635+119, a QSO hosted by a galaxy previously classified as an undisturbed elliptical. Our new images reveal dramatic shell structure indicative of a merger event in the relatively recent past. The brightest shells in the central regions of the host are distributed alternately in radius, with at least two distinct shells on one side of the nucleus and three on the other, out to a distance of ∼13 kpc. The light within the five shells comprises ∼6% of the total galaxy light. Lower surface brightness ripples or tails and other debris extend out to a distance of ∼65 kpc. A simple N-body model for a merger reproduces the inner shell structure and gives an estimate for the age of the merger between ∼30 Myr and ∼1.7 Gyr, depending on a range of reasonable assumptions. While the inner shell structure is suggestive of a minor merger, the total light contribution from the shells and extended structures are more indicative of a major merger. The spectrum of the host galaxy is dominated by a population of intermediate age (∼1.4 Gyr), indicating a strong starburst episode that may have occurred at the time of the merger event. We speculate that the current QSO activity may have been triggered in the recent past by either a minor merger, or by debris from an older (∼Gyr) major merger that is currently "raining" back into the central regions of the merger remnant.
We have obtained and modeled NICMOS images of the Einstein ring lens system MG J1131]0456, which ... more We have obtained and modeled NICMOS images of the Einstein ring lens system MG J1131]0456, which show that its lens galaxy is an H \ 18.6 mag, transparent, early-type galaxy at a redshift of it has a major axis e †ective radius projected axis ratio b/a \ 0.6^0.1, and z l^0 .84 ; R e \ 0A .7^0A .1, major axis P.A. \ 55¡^9¡. The lens is the brightest member of a group of at least seven galaxies with similar R[I and I[H colors, and the two closest group members produce sufficient tidal perturbations to explain the shape of the ring. The host galaxy of the MG J1131]0456 source is a extremely z s Z 2 red object (ERO) that is lensed into optical and infrared rings of dramatically di †erent morphologies. These di †erences imply a strongly wavelength-dependent source morphology that could be explained by embedding the host in a larger, dusty disk. At 1.6 km (H), the ring is spectacularly luminous, with a total observed Ñux of H \ 17.4 mag and a demagniÐed Ñux of 19.3 mag, corresponding to a 1È2 galaxy at L * the probable source redshift of Thus, it is primarily the stellar emission of the radio source host z s Z 2. galaxy that produces the overall colors of two of the reddest radio lenses, MG J1131]0456 and JVAS B1938]666, aided by the suppression of optical active galactic nucleus emission by dust in the source galaxy. The dusty lens hypothesis È that many massive early-type galaxies with have large, 0 [ z l [ 1 uniform dust opacities È is ruled out.
At low redshift, there are fundamental correlations between the mass of supermassive black holes ... more At low redshift, there are fundamental correlations between the mass of supermassive black holes (M BH ) and the mass (M bulge ) and luminosity of the host galaxy bulge. We investigate the same relation at z k 1. Using virial mass estimates for 11 quasars at z k 2 to measure their black hole mass, we find that black holes at high z fall nearly on the same M BH versus R-band magnitude (M R ) relation (to $0.3 mag) as low-redshift active and inactive galaxies, without making any correction for luminosity evolution. Using a set of conservative assumptions about the host galaxy stellar population, we show that at z k 2 (10 Gyr ago), the ratio of M BH /M bulge was 3-6 times larger than today. Barring unknown systematic errors on the measurement of M BH , we also rule out scenarios in which moderately luminous quasar hosts at z k 2 were fully formed bulges that passively faded to the present epoch. On the other hand, five quasar hosts at z % 1 are consistent with the current-day M BH -M R relationship after taking into account evolution that is appropriate for E/S0 galaxies. Therefore, z % 1 host galaxies appear to fit the hypothesis that they are fully formed early-type galaxies. We also find that most quasar hosts with absolute magnitudes brighter than M R ¼ À23 cannot fade below L Ã galaxies today, regardless of their stellar population makeup, because their black hole masses are too high and they must arrive at the local M BH -M R relationship by z ¼ 0.
We present 1210 Johnson/Cousins B,V,R, and I photometric observations of 22 recent type Most of t... more We present 1210 Johnson/Cousins B,V,R, and I photometric observations of 22 recent type Most of the photometry was obtained at the Fred Lawrence Whipple Observatory (FLWO) of the Harvard-Smithsonian Center for Astrophysics in a cooperative observing plan aimed at improving the data base for SN Ia. The redshifts of the sample range from cz=1200 to 37000 km s −1 with a mean of cz=7000 km s −1 . effort to collect Johnson/Cousins BV RI photometry of type Ia supernovae. Many of these SNe Ia were discovered serendipitously by amateurs or by professionals scanning images collected for another purpose.
We present optical photometry for the type Ia SN 1994D in NGC 4526 from 1994 March 7 to June 4 st... more We present optical photometry for the type Ia SN 1994D in NGC 4526 from 1994 March 7 to June 4 starting 13 days before B-band maximum. The light curves of this SN resemble closely those of the "normal" type Ia events SNe 1989B and 1980N, differing only in a slightly faster decline after maximum in VRI. The optical absolute magnitudes of SN 1994D, however, are significantly brighter than those of its near twins, and brighter than those predicted by Phillips' [ApJ, 413, L105 (1993)] relationship between decline rate and luminosity. Our small amount of IR photometry of SN 1994D is not inconsistent with that of other type IA SNe.
We report the performance of Cu 2 ZnSnS 4 (CZTS) thin film solar cell that showed efficiency in t... more We report the performance of Cu 2 ZnSnS 4 (CZTS) thin film solar cell that showed efficiency in the range of 6.2% without an antireflection coating. Initially, the CZTS precursor film was co-sputtered using three different targets; copper (Cu), tin sulfide (SnS) and zinc sulfide (ZnS). The Cu target was subjected to DC power, and RF power was used for the SnS and ZnS targets. The as-grown CZTS film was sulfurized in a H 2 S/N 2 environment at 525°C, which re-crystalized the film with grain sizes in the range of 1 lm. Cadmium sulfide (CdS) was used as the n-type layer. Current-voltage (I-V), quantum efficiency (QE) and capacitance-voltage (C-V) measurements were used to characterize the cell device. The modeling and analysis of QE and CV data showed that a significant portion of the CZTS layer did not contribute to the photo-generation. Optimizing CZTS phase purity, improving QE in the broader wavelength region, and increasing minority carrier lifetime are necessary steps to further improve CZTS device performance.
Gravitational lensing assists in the detection of quasar hosts by amplifying and distorting the h... more Gravitational lensing assists in the detection of quasar hosts by amplifying and distorting the host light away from the unresolved quasar core images. We present the results of HST observations of 30 quasar hosts at redshifts 1 < z < 4.5. The hosts are small in size (r e 6 kpc), and span a range of morphologies consistent with early-types (though smaller in mass) to disky/late-type. The ratio of the black hole mass (M BH , from the virial technique) to the bulge mass (M bulge , from the stellar luminosity) at 1 z 1.7 is broadly consistent with the local value; while M BH /M bulge at z 1.7 is a factor of 3-6 higher than the local value. But, depending on the stellar content the ratio may decline at z 4 (if E/S0-like), flatten off to 6-10 times the local value (if Sbc-like), or continue to rise (if Im-like). We infer that galaxy bulge masses must have grown by a factor of 3-6 over the redshift range 3 z 1, and then changed little since z ∼ 1. This suggests that the peak epoch of galaxy formation for massive galaxies is above z ∼ 1. We also estimate the duty cycle of luminous AGNs at z 1 to be ∼ 1%, or 10 7 yrs, with sizable scatter.
IEEE Transactions on Device and Materials Reliability, 2000
Aluminum-doped zinc oxide (AZO) thin film is a promising candidate for low-cost transparent condu... more Aluminum-doped zinc oxide (AZO) thin film is a promising candidate for low-cost transparent conductive oxide applications. AZO thin films have good electrical and optical properties; however, their reliability must be carefully considered in manufacturing and usage of flexible devices such as flexible solar cells. Cyclic bending leads to both electrical and optical degradation of AZO thin films. Therefore, this paper was designed to investigate the effects of the bending frequency, bending diameter, number of bending cycles, and film thickness on the electrical and optical degradation of AZO films, which were deposited on polyimide (PI) substrates using a radio frequency-magnetron sputtering technique. The cycling was conducted on identical specimens under controlled study parameters. The design of experiments technique was used to determine the significant factors on the percentage change in electrical resistance (PCER) and the degradation of average transmittance (DAT), considering a wavelength range from 660 to 950 nm. The result shows that the PCER is very sensitive to number of bending cycles, particularly in the first 300 cycles. After 1000 cycles, the mean PCER of 425-and 600-nm AZO films are about 300% and 600%, respectively. The DAT is sensitive to number of bending cycles, bending diameter, and bending frequency. The mean DAT is about 2.8% after 1000 bending cycles.
Consider a production system where products are produced continuously and screened for conformanc... more Consider a production system where products are produced continuously and screened for conformance with their specification limits. When product performance falls below a lower specification limit or above an upper limit, a decision is made to rework or scrap the product. The majority of the process target models in the literature deal with a single-stage production system. In the real-world industrial settings, however, products are often processed through multi-stage production systems. If the probabilities associated with its recurrent, transient and absorbing states are known, we can better understand the nature of a production system and thus better capture the optimum target for a process. This paper first discusses the roles of a Markovian approach and then develops the general form of a Markovian model for optimum process target levels within the framework of a multi-stage serial production system. Numerical examples and sensitivity analysis are performed.
Most gravitational lens galaxies are early-type galaxies in relatively low density environments. ... more Most gravitational lens galaxies are early-type galaxies in relatively low density environments. We show that they lie on the same fundamental plane as early-type galaxies in both local and distant rich clusters. Their surface brightness evolution requires a typical star formation epoch of z f ≃ 2-3, almost indistinguishable from that of rich cluster galaxies at comparable redshifts. The restricted galaxy type range of the lenses means that photometric redshifts work well even with only 1-3 filter photometry. We make preliminary measurements of the mass and luminosity functions of the lens galaxies, and find they are consistent with the standard model used for deriving cosmological limits using lens statistics. As expected for a mass-weighted sample, they are more massive and more luminous than the overall early-type galaxy population.
We present 15 Einstein Rings and arcs in the CfA--Arizona--Space Telescope Gravitational Lensing ... more We present 15 Einstein Rings and arcs in the CfA--Arizona--Space Telescope Gravitational Lensing survey (CASTLES), the majority of which are candidate quasar host galaxies. All of the objects are at z&amp;amp;gt;=1.3, thus lensing provides one of the largest quasar hosts samples beyond z&amp;amp;gt;1. Gravitational lensing stretches out quasar hosts into Einstein rings and arcs, enhancing host detections and enabling measurements
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Papers by Chien-Yi Peng