Cong Han - Academia.edu (original) (raw)
Papers by Cong Han
Inorganic Chemistry, 2001
There has been tremendous interest in the synthesis and crystal structure of open-framework mater... more There has been tremendous interest in the synthesis and crystal structure of open-framework materials due to their potential applications in catalysis, separations, and ion exchange processes. 1 A variety of organic molecules, including bi-, tri-, and tetradentate (diamondoid) ligands, 2 have been used in the construction of many fascinating structures. 1,4-Benzenedicarboxylic acid (H 2 bdc), a rodlike bifunctional ligand, has afforded a number of extended structures by virtue of an exodentate coordination mode. 3 An interesting lanthanide-bdc system has been reported recently that consists of a microporous structure generated upon removal of water from a condensed phase. This system is potentially important as a fluorescent probe. Our previous studies on dicarboxylic acids have shown that they are highly reactive toward metals under hydrothermal conditions. 5 In this work, 1,4-benzenedicarboxylic acid has been selected as a ligand and a water/ethanol solution as a solvent. Hydrated Er(NO 3 ) 3 (0.075 g), H 2 bdc (0.036 g), H 2 O (10 mL), and EtOH (1 mL) in the mole ratio of 1:1:2645:83 were placed in a 23 mL acid digestion bomb and heated at 160°C for 3 days. The pH of the final solution was 4.5. The pink crystals of Er 4 -(bdc) 6 ‚6H 2 O (1) (0.074 g, 74.2%) were collected after washing by water (3 × 10 mL) and by acetone (3 × 10 mL), respectively. 6a A microcrystalline sample of Er 4 (bdc) 6 (2) resulted after 1 (23 mg) was heated to 300°C under nitrogen gas. 6b A thermogravimetric (TG) curve indicated clearly the weight loss of six water molecules. Er 2 (bdc) 3 ‚4H 2 O (3) was obtained by allowing 2 to be exposed to saturated water vapor for 2 h. 6c This structural transformation was confirmed by PXRD, IR, and elemental microanalysis. 3 is isostructural to Tb 2 (bdc) 3 ‚4H 2 O 4 and can also be prepared using the same method described in ref 4. 6d The crystal structure of 1 is a condensed three-dimensional network. 7 There are four crystallographically independent erbium ions in this structure. The local coordination geometry around 10.
Nano Letters, 2004
We demonstrate detection of NO 2 down to ppb levels using transistors based on both single and mu... more We demonstrate detection of NO 2 down to ppb levels using transistors based on both single and multiple In 2 O 3 nanowires operating at room temperature. This represents orders-of-magnitude improvement over previously reported metal oxide film or nanowire/nanobelt sensors. A ...
Journal of Physical Chemistry B, 2003
ABSTRACT Devices based on single-crystalline In2O3 nanowires were used to detect ammonia gas via ... more ABSTRACT Devices based on single-crystalline In2O3 nanowires were used to detect ammonia gas via electrical measurements at room temperature. Interesting phenomena have been observed, as the direction of the conductance modulation upon NH3 exposure depends on both the initial state of the nanowire surface and the nanowire doping concentration. For nanowires with surfaces cleaned via UV illumination in a vacuum, the conductance has been found to increase for lightly doped nanowires and decrease for heavily doped nanowires upon exposure. In contrast, for nanowires residing in ambient atmosphere, i.e., under practical conditions, the conductance has been consistently observed to increase upon NH3 exposure, regardless of the doping concentration. This is explained by considering electron transfer between In2O3 nanowires and NH3. Our work clearly demonstrates the potential of using In2O3 nanowires as NH3 sensors under practical conditions.
Chemical Physics Letters, 2004
Photoconduction studies have been carried out with single crystal GaN nanowires. The nanowire tra... more Photoconduction studies have been carried out with single crystal GaN nanowires. The nanowire transistors exhibited a substantial increase in conductance upon UV light exposure. Besides the selectivity to different light wavelengths, extremely short response and recovery time ...
Applied Physics Letters, 2003
We present an approach to use individual In2O3 nanowire transistors as chemical sensors working a... more We present an approach to use individual In2O3 nanowire transistors as chemical sensors working at room temperature. Upon exposure to a small amount of NO2 or NH3 , the nanowire transistors showed a decrease in conductance up to six or five orders of magnitude and also ...
Journal of The American Chemical Society, 2005
We descried a method to synthesize single crystalline Fe3O4 nanotubes by wet-etching the MgO inne... more We descried a method to synthesize single crystalline Fe3O4 nanotubes by wet-etching the MgO inner cores of MgO/Fe3O4 core-shell nanowires. Homogeneous Fe3O4 nanotubes with controllable length, diameter, and wall thickness have been obtained. Resistivity of the Fe3O4 nanotubes was estimated to be approximately 4 x 10-2 Omega cm at room temperature. Magnetoresistance of approximately 1% was observed at T = 77 K when a magnetic field of B = 0.7 T was applied. The synthetic strategy presented here may be extended to a variety of materials such as YBCO, PZT, and LCMO which should provide ideal candidates for fundamental studies of superconductivity, piezoelectricity, and ferromagnetism in nanoscale structures.
Journal of The American Chemical Society, 2005
We report high-throughput growth of highly aligned single-walled carbon nanotube arrays on a-plan... more We report high-throughput growth of highly aligned single-walled carbon nanotube arrays on a-plane and r-plane sapphire substrates. This is achieved using chemical vapor deposition with ferritin as the catalyst. The nanotubes are aligned normal to the [0001] direction for growth on the a-plane sapphire. They are typically tens of micrometers long, with a narrow diameter distribution of 1.34 +/- 0.30 nm. In contrast, no orientation was achieved for growth on the c-plane and m-plane sapphire, or when Fe films, instead of ferritin, were used as the catalyst. Such orientation control is likely related to the interaction between carbon nanotubes and the sapphire substrate, which is supported by the observation that when a second layer of nanotubes was grown, they followed the gas flow direction. These aligned nanotube arrays may enable the construction of integrable and scalable nanotube devices and systems.
Superquadric is an implicit model which was recently introduced and successfully applied in compu... more Superquadric is an implicit model which was recently introduced and successfully applied in computer vision research. The authors introduce its generalization, the use of the hyperquadric models, for computer vision applications, and focus on its utilization for shape recovery from range data. The hyperquadric model can be composed of any number of terms. Its geometric bound is an arbitrary convex polyhedron, and thus it can describe more complex shapes than the superquadric. A fitting method is proposed that starts with a rough fit with only two terms in the 2-D case or three terms in the 3-D case, and then adds additional terms to improve the fit. The experiments indicate that the use of hyperquadrics is a promising paradigm for shape representation and recovery in computer vision.>
IEEE Transactions on Pattern Analysis and Machine Intelligence, 1995
Abstract This paper discusses the applications of hyperquadric models in computer vision and foc... more Abstract This paper discusses the applications of hyperquadric models in computer vision and focuses on their recovery from range data. Hyperquadrics are volumetric shape models that include superquadrics as a special case. A hyperquadric model can be composed of ...
Economic Journal, 2001
Some of the important implications of the parental investment model of intergenerational mobility... more Some of the important implications of the parental investment model of intergenerational mobility have been derived under the assumption that parental income is the main source of heterogeneity. We explicitly model the variability and inheritability of "innate" earnings ability and the variability of tastes, showing how they affect observed degrees of intergenerational consumption and earnings mobility. Heterogeneity increases the difficulty of detecting the existence of borrowing constrained families. Conversely, the presence of heterogeneity means that economic and linear statistical models of inheritance generate similar intergenerational data on consumption and earnings.
Inorganic Chemistry, 2001
There has been tremendous interest in the synthesis and crystal structure of open-framework mater... more There has been tremendous interest in the synthesis and crystal structure of open-framework materials due to their potential applications in catalysis, separations, and ion exchange processes. 1 A variety of organic molecules, including bi-, tri-, and tetradentate (diamondoid) ligands, 2 have been used in the construction of many fascinating structures. 1,4-Benzenedicarboxylic acid (H 2 bdc), a rodlike bifunctional ligand, has afforded a number of extended structures by virtue of an exodentate coordination mode. 3 An interesting lanthanide-bdc system has been reported recently that consists of a microporous structure generated upon removal of water from a condensed phase. This system is potentially important as a fluorescent probe. Our previous studies on dicarboxylic acids have shown that they are highly reactive toward metals under hydrothermal conditions. 5 In this work, 1,4-benzenedicarboxylic acid has been selected as a ligand and a water/ethanol solution as a solvent. Hydrated Er(NO 3 ) 3 (0.075 g), H 2 bdc (0.036 g), H 2 O (10 mL), and EtOH (1 mL) in the mole ratio of 1:1:2645:83 were placed in a 23 mL acid digestion bomb and heated at 160°C for 3 days. The pH of the final solution was 4.5. The pink crystals of Er 4 -(bdc) 6 ‚6H 2 O (1) (0.074 g, 74.2%) were collected after washing by water (3 × 10 mL) and by acetone (3 × 10 mL), respectively. 6a A microcrystalline sample of Er 4 (bdc) 6 (2) resulted after 1 (23 mg) was heated to 300°C under nitrogen gas. 6b A thermogravimetric (TG) curve indicated clearly the weight loss of six water molecules. Er 2 (bdc) 3 ‚4H 2 O (3) was obtained by allowing 2 to be exposed to saturated water vapor for 2 h. 6c This structural transformation was confirmed by PXRD, IR, and elemental microanalysis. 3 is isostructural to Tb 2 (bdc) 3 ‚4H 2 O 4 and can also be prepared using the same method described in ref 4. 6d The crystal structure of 1 is a condensed three-dimensional network. 7 There are four crystallographically independent erbium ions in this structure. The local coordination geometry around 10.
Nano Letters, 2004
We demonstrate detection of NO 2 down to ppb levels using transistors based on both single and mu... more We demonstrate detection of NO 2 down to ppb levels using transistors based on both single and multiple In 2 O 3 nanowires operating at room temperature. This represents orders-of-magnitude improvement over previously reported metal oxide film or nanowire/nanobelt sensors. A ...
Journal of Physical Chemistry B, 2003
ABSTRACT Devices based on single-crystalline In2O3 nanowires were used to detect ammonia gas via ... more ABSTRACT Devices based on single-crystalline In2O3 nanowires were used to detect ammonia gas via electrical measurements at room temperature. Interesting phenomena have been observed, as the direction of the conductance modulation upon NH3 exposure depends on both the initial state of the nanowire surface and the nanowire doping concentration. For nanowires with surfaces cleaned via UV illumination in a vacuum, the conductance has been found to increase for lightly doped nanowires and decrease for heavily doped nanowires upon exposure. In contrast, for nanowires residing in ambient atmosphere, i.e., under practical conditions, the conductance has been consistently observed to increase upon NH3 exposure, regardless of the doping concentration. This is explained by considering electron transfer between In2O3 nanowires and NH3. Our work clearly demonstrates the potential of using In2O3 nanowires as NH3 sensors under practical conditions.
Chemical Physics Letters, 2004
Photoconduction studies have been carried out with single crystal GaN nanowires. The nanowire tra... more Photoconduction studies have been carried out with single crystal GaN nanowires. The nanowire transistors exhibited a substantial increase in conductance upon UV light exposure. Besides the selectivity to different light wavelengths, extremely short response and recovery time ...
Applied Physics Letters, 2003
We present an approach to use individual In2O3 nanowire transistors as chemical sensors working a... more We present an approach to use individual In2O3 nanowire transistors as chemical sensors working at room temperature. Upon exposure to a small amount of NO2 or NH3 , the nanowire transistors showed a decrease in conductance up to six or five orders of magnitude and also ...
Journal of The American Chemical Society, 2005
We descried a method to synthesize single crystalline Fe3O4 nanotubes by wet-etching the MgO inne... more We descried a method to synthesize single crystalline Fe3O4 nanotubes by wet-etching the MgO inner cores of MgO/Fe3O4 core-shell nanowires. Homogeneous Fe3O4 nanotubes with controllable length, diameter, and wall thickness have been obtained. Resistivity of the Fe3O4 nanotubes was estimated to be approximately 4 x 10-2 Omega cm at room temperature. Magnetoresistance of approximately 1% was observed at T = 77 K when a magnetic field of B = 0.7 T was applied. The synthetic strategy presented here may be extended to a variety of materials such as YBCO, PZT, and LCMO which should provide ideal candidates for fundamental studies of superconductivity, piezoelectricity, and ferromagnetism in nanoscale structures.
Journal of The American Chemical Society, 2005
We report high-throughput growth of highly aligned single-walled carbon nanotube arrays on a-plan... more We report high-throughput growth of highly aligned single-walled carbon nanotube arrays on a-plane and r-plane sapphire substrates. This is achieved using chemical vapor deposition with ferritin as the catalyst. The nanotubes are aligned normal to the [0001] direction for growth on the a-plane sapphire. They are typically tens of micrometers long, with a narrow diameter distribution of 1.34 +/- 0.30 nm. In contrast, no orientation was achieved for growth on the c-plane and m-plane sapphire, or when Fe films, instead of ferritin, were used as the catalyst. Such orientation control is likely related to the interaction between carbon nanotubes and the sapphire substrate, which is supported by the observation that when a second layer of nanotubes was grown, they followed the gas flow direction. These aligned nanotube arrays may enable the construction of integrable and scalable nanotube devices and systems.
Superquadric is an implicit model which was recently introduced and successfully applied in compu... more Superquadric is an implicit model which was recently introduced and successfully applied in computer vision research. The authors introduce its generalization, the use of the hyperquadric models, for computer vision applications, and focus on its utilization for shape recovery from range data. The hyperquadric model can be composed of any number of terms. Its geometric bound is an arbitrary convex polyhedron, and thus it can describe more complex shapes than the superquadric. A fitting method is proposed that starts with a rough fit with only two terms in the 2-D case or three terms in the 3-D case, and then adds additional terms to improve the fit. The experiments indicate that the use of hyperquadrics is a promising paradigm for shape representation and recovery in computer vision.>
IEEE Transactions on Pattern Analysis and Machine Intelligence, 1995
Abstract This paper discusses the applications of hyperquadric models in computer vision and foc... more Abstract This paper discusses the applications of hyperquadric models in computer vision and focuses on their recovery from range data. Hyperquadrics are volumetric shape models that include superquadrics as a special case. A hyperquadric model can be composed of ...
Economic Journal, 2001
Some of the important implications of the parental investment model of intergenerational mobility... more Some of the important implications of the parental investment model of intergenerational mobility have been derived under the assumption that parental income is the main source of heterogeneity. We explicitly model the variability and inheritability of "innate" earnings ability and the variability of tastes, showing how they affect observed degrees of intergenerational consumption and earnings mobility. Heterogeneity increases the difficulty of detecting the existence of borrowing constrained families. Conversely, the presence of heterogeneity means that economic and linear statistical models of inheritance generate similar intergenerational data on consumption and earnings.