Zaoli Zhang - Academia.edu (original) (raw)
Papers by Zaoli Zhang
Ultramicroscopy, Aug 31, 2007
The energy loss near edge structure (ELNES) of the O-K and Co-L edges of both Co 3 O 4 and CoO pa... more The energy loss near edge structure (ELNES) of the O-K and Co-L edges of both Co 3 O 4 and CoO particles were studied. Significant changes between the edge and nearby thicker regions are found for the O-K edge, the Co-L edge, the O/Co atomic ratio, the separation between the prepeaks in the O-K edge, as well as the L 3 /L 2 intensity ratios in the Co-L edge. These reflect the changes in the average oxidation state of the specimen from the edge to nearby thicker regions. These variations originate from a surface layer which dominates the results near the edge of the particles. These variations allow us to infer the surface structure, which indicates that both particles are encapsulated by different non-stoichiometric oxides. r
Ultramicroscopy, 2007
The energy loss near edge structure (ELNES) of the O-K and Co-L edges of both Co 3 O 4 and CoO pa... more The energy loss near edge structure (ELNES) of the O-K and Co-L edges of both Co 3 O 4 and CoO particles were studied. Significant changes between the edge and nearby thicker regions are found for the O-K edge, the Co-L edge, the O/Co atomic ratio, the separation between the prepeaks in the O-K edge, as well as the L 3 /L 2 intensity ratios in the Co-L edge. These reflect the changes in the average oxidation state of the specimen from the edge to nearby thicker regions. These variations originate from a surface layer which dominates the results near the edge of the particles. These variations allow us to infer the surface structure, which indicates that both particles are encapsulated by different non-stoichiometric oxides. r
Materials Science and Engineering: A, 2000
Segregation of phosphorus and sulfur to grain boundaries in ultra low carbon steel (IF-steel) was... more Segregation of phosphorus and sulfur to grain boundaries in ultra low carbon steel (IF-steel) was investigated by Auger electron spectroscopy (AES) and scanning electron microscopy (SEM). The segregation kinetics of phosphorus and sulfur while holding at 600°C have ...
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2000
Journal of Materials Research, 2002
Antimony oxide nanorods were synthesized by the microemulsion method. The nanorods had diameter i... more Antimony oxide nanorods were synthesized by the microemulsion method. The nanorods had diameter in the range of 50175 nm and a length of up to several micrometers. The microstructure of the nanorods was examined by analytical transmission electron microscopy and high-...
Journal of Materials Research, 2003
Uniformly distributed nanoparticles created by heating carbon nanotubes synthesized by arc-discha... more Uniformly distributed nanoparticles created by heating carbon nanotubes synthesized by arc-discharge were studied by electron diffraction, high-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), and x-ray energy dispersive ...
Journal of Materials Research, 2001
Ultramicroscopy, May 31, 2009
The stability of Ni, Cu, Mo and Au TEM grids coated with ultra-thin amorphous carbon or silicon m... more The stability of Ni, Cu, Mo and Au TEM grids coated with ultra-thin amorphous carbon or silicon monoxide film is examined by in-situ heating up to a temperature in the range 500~850°C in a transmission electron microscope. It is demonstrated that some grids can generate nano-particles either due to the surface diffusion of metal atoms on amorphous film or due to metal evaporation/redeposition. The emergence of nano-particles can complicate experimental observations, particularly in in-situ heating studies of dynamic behaviours of nanomaterials in TEM. The most widely used Cu grid covered with amorphous carbon is unstable, and numerous Cu nano-particles start to form once heating temperature reaches 600°C. In the case of Ni grid covered with α-C film, a large number of Ni nano-crystals occur immediately when the temperature approaches to 600 °C, accompanied by the graphitization of amorphous carbon. In contrast, both Mo and Au grids covered with α-C film exhibit good stability at elevated temperature, for instance, up to 680°C and 850°C for Mo and Au, respectively, and no any metal nano-particles are detected. Cu grid covered Si monoxide thin film is stable up to 550 °C, but Si nano-crystals appear under intensive electron beam. The generated nano-particles are well characterized by spectroscopic techniques (EDXS/EELS) and high-resolution TEM. The mechanism of nano-particle formation is addressed based on the interactions between the metal grid and the amorphous carbon film and on the sublimation of metal.
![Research paper thumbnail of Interfacial microstructure and defect analysis in Cu(In,Ga)Se([sub]2)-based multilayered film by analytical transmission electron microscopy and focused ion beam](https://attachments.academia-assets.com/44658595/thumbnails/1.jpg)
](Thin Solid Films, 2009
Interfacial microstructures of Cu(In,Ga)Se 2 (CIGS)-based multilayered film are closely character... more Interfacial microstructures of Cu(In,Ga)Se 2 (CIGS)-based multilayered film are closely characterized by TEM (transmission electron microscopy), SEM (scanning electron microscopy) and FIB (focused ion beam). A cross-sectional TEM, energy dispersive X-ray spectroscopy and energy-filtered TEM reveal that a pronounced Cu diffusion occurs across the interface of the CdS/CIGS, which leads to a large amount of Cu rich in the CdS layer and a Cu-deficient sub-surface in the CIGS layer as well as a rough interfacial structure. TEM studies further reveal that the interface microstructures in the multilayered film are dissimilar, both ZnO/CdS and CdS/CIGS interfaces are strongly bonded whereas the CIGS/Mo interface is weakly bonded and interface separation occasionally occurs. Mo back contact layer shows a well adhesion to glass substrate. Detailed observation on defects in the CIGS-based multilayered film is carried out by 3D (3-dimensional) FIB and SEM techniques. Sequential 2D (2-demensional) cross-sectioning shows that dominant growth-defects in the CIGS and top SiO 2 layers are micro-scale crack, appearing as diversified morphologies. The micro-scale crack in the CIGS layer is possibly released by propagating into the adjacent layer while the crack in the SiO 2 layer is relieved usually by forming a small particle behind. It is noted that in the multilayered film the interface frequently acts as crack initiation sites due to distinct thermal expansion coefficients.
Ultramicroscopy, 2009
The stability of Ni, Cu, Mo and Au TEM grids coated with ultra-thin amorphous carbon or silicon m... more The stability of Ni, Cu, Mo and Au TEM grids coated with ultra-thin amorphous carbon or silicon monoxide film is examined by in-situ heating up to a temperature in the range 500~850°C in a transmission electron microscope. It is demonstrated that some grids can generate nano-particles either due to the surface diffusion of metal atoms on amorphous film or due to metal evaporation/redeposition. The emergence of nano-particles can complicate experimental observations, particularly in in-situ heating studies of dynamic behaviours of nanomaterials in TEM. The most widely used Cu grid covered with amorphous carbon is unstable, and numerous Cu nano-particles start to form once heating temperature reaches 600°C. In the case of Ni grid covered with α-C film, a large number of Ni nano-crystals occur immediately when the temperature approaches to 600 °C, accompanied by the graphitization of amorphous carbon. In contrast, both Mo and Au grids covered with α-C film exhibit good stability at elevated temperature, for instance, up to 680°C and 850°C for Mo and Au, respectively, and no any metal nano-particles are detected. Cu grid covered Si monoxide thin film is stable up to 550 °C, but Si nano-crystals appear under intensive electron beam. The generated nano-particles are well characterized by spectroscopic techniques (EDXS/EELS) and high-resolution TEM. The mechanism of nano-particle formation is addressed based on the interactions between the metal grid and the amorphous carbon film and on the sublimation of metal.
Microscopy and Microanalysis, 2012
Inorganic Chemistry, 2007
Single-phase titania nanomaterials were prepared by autoclaving titanium tetrachloride in acetone... more Single-phase titania nanomaterials were prepared by autoclaving titanium tetrachloride in acetone at 80−140°C. Depending on the molar ratio of TiCl 4 to acetone (TiCl 4 /Ac), TiO 2 materials with different phases and morphologies were obtained. When the TiCl 4 concentration was no higher than TiCl 4 /Ac ) 1/15, single-phase anatase TiO 2 nanocrystals in sizes ranging from 4 to 10 nm were prepared by tuning TiCl 4 /Ac ratios from 1/90 to 1/15. However, when the TiCl 4 concentration was high enough (e.g., TiCl 4 /Ac g 1/10), single-phase rutile TiO 2 nanofibers were obtained selectively. The materials were characterized comprehensively using X-ray diffraction, transmission electron microscopy, Raman spectroscopy, thermogravimetric analysis, and nitrogen adsorption measurements. With the aid of GC/MS analysis of organic products in the liquid phase, it is shown that the controlled hydrolysis of TiCl 4 with water, which was in situ generated from the TiCl 4 -catalyzed aldol condensation reactions of acetones, played an important role in the formation of the titania nanomaterials. Some of the organic condensates may function to stabilize the phase and morphology of the materials. This mechanism was also supported by our success in using other ketones as alternatives to acetone in the synthesis.
Acta Materialia, 2003
The electrical properties of 3 mol% Y 2 O 3 doped ZrO 2 were measured by impedance spectroscopy a... more The electrical properties of 3 mol% Y 2 O 3 doped ZrO 2 were measured by impedance spectroscopy as a function of grain size, and the microstructure studied by SEM and HREM. In spite of the very clean grain boundaries, the grain boundary conductivity was still found to be ෂ2 orders of magnitude lower than the bulk conductivity, while it increased with decreasing grain size. The low grain boundary conductivity, according to the Schottky barrier model, is due to the depletion of oxygen vacancies in the grain boundary space charge layers. Within this framework, the grain boundary space charge potential and the concentration of oxygen vacancies in the space charge layers were calculated; it was found that the space charge potential decreased, but the oxygen vacancy concentration increased with decreasing grain size. Analyses of literature results for 8.2 mol% Y 2 O 3 and 15 mol% CaO doped ZrO 2 , respectively, revealed similar phenomena.
Advanced Materials Research, 2010
ABSTRACT
Advanced Materials, 2014
Epitaxially grown functional perovskites on silicon (001) and the ferroelectricity of a 3.2 nm th... more Epitaxially grown functional perovskites on silicon (001) and the ferroelectricity of a 3.2 nm thick BaTiO3 barrier layer are demonstrated. The polarization-switching-induced change in tunneling resistance is measured to be two orders of magnitude. The obtained results suggest the possibility of integrating ferroelectric tunnel junctions as binary data storage media in non-volatile memory cells on a silicon platform.
Physical Review Letters, 2000
Experimental evidence has been found for the existence of small single wall carbon nanotubes with... more Experimental evidence has been found for the existence of small single wall carbon nanotubes with diameters of 0.5 and 0.33 nm by high resolution transmission electron microscopy, and their mechanical stability was investigated using tight-binding molecular dynamics simulations. It is shown that, while the carbon tubes with diameters smaller than 0.4 nm are energetically less favorable than a graphene sheet, some of them are indeed mechanically stable at temperatures as high as 1100 ± C. The 0.33 nm carbon tube observed is likely a (4, 0) tube and is indeed part of a compound nanotube system that forms perhaps the smallest metal-semiconductor-metal tubular junction yet synthesized.
Acta Materialia, 2012
In this study the influence of interrupted quenching (IQ) in the temperature range 150-250°C for ... more In this study the influence of interrupted quenching (IQ) in the temperature range 150-250°C for periods of 15-1080 s on artificial aging after long-term natural pre-aging was studied for the Al-Mg-Si alloy AA6061 by atom probe tomography, transmission electron microscopy, electrical resistivity and hardness measurements, and differential scanning calorimetry. Compared with a standard quenching procedure, the results showed that hardening kinetics and the age hardening response were enhanced for IQ at low temperatures but reduced at high temperatures. Quenched-in vacancies were shown to be of particular importance for the nucleation of precipitates occurring during IQ at the lower end of the temperature range, finally leading to the formation of a dense distribution of b 00 during artificial aging. For standard water quenching and subsequent natural aging, nucleation is hindered by a low concentration of quenched-in vacancies in the matrix. IQ at high temperatures affects subsequent artificial aging via the formation of precipitates which do not contribute to hardening but consume a significant amount of solute.
Http Dx Doi Org 10 1080 09500830310001621623, Jun 4, 2010
ABSTRACT
Ultramicroscopy, Aug 31, 2007
The energy loss near edge structure (ELNES) of the O-K and Co-L edges of both Co 3 O 4 and CoO pa... more The energy loss near edge structure (ELNES) of the O-K and Co-L edges of both Co 3 O 4 and CoO particles were studied. Significant changes between the edge and nearby thicker regions are found for the O-K edge, the Co-L edge, the O/Co atomic ratio, the separation between the prepeaks in the O-K edge, as well as the L 3 /L 2 intensity ratios in the Co-L edge. These reflect the changes in the average oxidation state of the specimen from the edge to nearby thicker regions. These variations originate from a surface layer which dominates the results near the edge of the particles. These variations allow us to infer the surface structure, which indicates that both particles are encapsulated by different non-stoichiometric oxides. r
Ultramicroscopy, 2007
The energy loss near edge structure (ELNES) of the O-K and Co-L edges of both Co 3 O 4 and CoO pa... more The energy loss near edge structure (ELNES) of the O-K and Co-L edges of both Co 3 O 4 and CoO particles were studied. Significant changes between the edge and nearby thicker regions are found for the O-K edge, the Co-L edge, the O/Co atomic ratio, the separation between the prepeaks in the O-K edge, as well as the L 3 /L 2 intensity ratios in the Co-L edge. These reflect the changes in the average oxidation state of the specimen from the edge to nearby thicker regions. These variations originate from a surface layer which dominates the results near the edge of the particles. These variations allow us to infer the surface structure, which indicates that both particles are encapsulated by different non-stoichiometric oxides. r
Materials Science and Engineering: A, 2000
Segregation of phosphorus and sulfur to grain boundaries in ultra low carbon steel (IF-steel) was... more Segregation of phosphorus and sulfur to grain boundaries in ultra low carbon steel (IF-steel) was investigated by Auger electron spectroscopy (AES) and scanning electron microscopy (SEM). The segregation kinetics of phosphorus and sulfur while holding at 600°C have ...
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2000
Journal of Materials Research, 2002
Antimony oxide nanorods were synthesized by the microemulsion method. The nanorods had diameter i... more Antimony oxide nanorods were synthesized by the microemulsion method. The nanorods had diameter in the range of 50175 nm and a length of up to several micrometers. The microstructure of the nanorods was examined by analytical transmission electron microscopy and high-...
Journal of Materials Research, 2003
Uniformly distributed nanoparticles created by heating carbon nanotubes synthesized by arc-discha... more Uniformly distributed nanoparticles created by heating carbon nanotubes synthesized by arc-discharge were studied by electron diffraction, high-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), and x-ray energy dispersive ...
Journal of Materials Research, 2001
Ultramicroscopy, May 31, 2009
The stability of Ni, Cu, Mo and Au TEM grids coated with ultra-thin amorphous carbon or silicon m... more The stability of Ni, Cu, Mo and Au TEM grids coated with ultra-thin amorphous carbon or silicon monoxide film is examined by in-situ heating up to a temperature in the range 500~850°C in a transmission electron microscope. It is demonstrated that some grids can generate nano-particles either due to the surface diffusion of metal atoms on amorphous film or due to metal evaporation/redeposition. The emergence of nano-particles can complicate experimental observations, particularly in in-situ heating studies of dynamic behaviours of nanomaterials in TEM. The most widely used Cu grid covered with amorphous carbon is unstable, and numerous Cu nano-particles start to form once heating temperature reaches 600°C. In the case of Ni grid covered with α-C film, a large number of Ni nano-crystals occur immediately when the temperature approaches to 600 °C, accompanied by the graphitization of amorphous carbon. In contrast, both Mo and Au grids covered with α-C film exhibit good stability at elevated temperature, for instance, up to 680°C and 850°C for Mo and Au, respectively, and no any metal nano-particles are detected. Cu grid covered Si monoxide thin film is stable up to 550 °C, but Si nano-crystals appear under intensive electron beam. The generated nano-particles are well characterized by spectroscopic techniques (EDXS/EELS) and high-resolution TEM. The mechanism of nano-particle formation is addressed based on the interactions between the metal grid and the amorphous carbon film and on the sublimation of metal.
Thin Solid Films, 2009
Interfacial microstructures of Cu(In,Ga)Se 2 (CIGS)-based multilayered film are closely character... more Interfacial microstructures of Cu(In,Ga)Se 2 (CIGS)-based multilayered film are closely characterized by TEM (transmission electron microscopy), SEM (scanning electron microscopy) and FIB (focused ion beam). A cross-sectional TEM, energy dispersive X-ray spectroscopy and energy-filtered TEM reveal that a pronounced Cu diffusion occurs across the interface of the CdS/CIGS, which leads to a large amount of Cu rich in the CdS layer and a Cu-deficient sub-surface in the CIGS layer as well as a rough interfacial structure. TEM studies further reveal that the interface microstructures in the multilayered film are dissimilar, both ZnO/CdS and CdS/CIGS interfaces are strongly bonded whereas the CIGS/Mo interface is weakly bonded and interface separation occasionally occurs. Mo back contact layer shows a well adhesion to glass substrate. Detailed observation on defects in the CIGS-based multilayered film is carried out by 3D (3-dimensional) FIB and SEM techniques. Sequential 2D (2-demensional) cross-sectioning shows that dominant growth-defects in the CIGS and top SiO 2 layers are micro-scale crack, appearing as diversified morphologies. The micro-scale crack in the CIGS layer is possibly released by propagating into the adjacent layer while the crack in the SiO 2 layer is relieved usually by forming a small particle behind. It is noted that in the multilayered film the interface frequently acts as crack initiation sites due to distinct thermal expansion coefficients.
Ultramicroscopy, 2009
The stability of Ni, Cu, Mo and Au TEM grids coated with ultra-thin amorphous carbon or silicon m... more The stability of Ni, Cu, Mo and Au TEM grids coated with ultra-thin amorphous carbon or silicon monoxide film is examined by in-situ heating up to a temperature in the range 500~850°C in a transmission electron microscope. It is demonstrated that some grids can generate nano-particles either due to the surface diffusion of metal atoms on amorphous film or due to metal evaporation/redeposition. The emergence of nano-particles can complicate experimental observations, particularly in in-situ heating studies of dynamic behaviours of nanomaterials in TEM. The most widely used Cu grid covered with amorphous carbon is unstable, and numerous Cu nano-particles start to form once heating temperature reaches 600°C. In the case of Ni grid covered with α-C film, a large number of Ni nano-crystals occur immediately when the temperature approaches to 600 °C, accompanied by the graphitization of amorphous carbon. In contrast, both Mo and Au grids covered with α-C film exhibit good stability at elevated temperature, for instance, up to 680°C and 850°C for Mo and Au, respectively, and no any metal nano-particles are detected. Cu grid covered Si monoxide thin film is stable up to 550 °C, but Si nano-crystals appear under intensive electron beam. The generated nano-particles are well characterized by spectroscopic techniques (EDXS/EELS) and high-resolution TEM. The mechanism of nano-particle formation is addressed based on the interactions between the metal grid and the amorphous carbon film and on the sublimation of metal.
Microscopy and Microanalysis, 2012
Inorganic Chemistry, 2007
Single-phase titania nanomaterials were prepared by autoclaving titanium tetrachloride in acetone... more Single-phase titania nanomaterials were prepared by autoclaving titanium tetrachloride in acetone at 80−140°C. Depending on the molar ratio of TiCl 4 to acetone (TiCl 4 /Ac), TiO 2 materials with different phases and morphologies were obtained. When the TiCl 4 concentration was no higher than TiCl 4 /Ac ) 1/15, single-phase anatase TiO 2 nanocrystals in sizes ranging from 4 to 10 nm were prepared by tuning TiCl 4 /Ac ratios from 1/90 to 1/15. However, when the TiCl 4 concentration was high enough (e.g., TiCl 4 /Ac g 1/10), single-phase rutile TiO 2 nanofibers were obtained selectively. The materials were characterized comprehensively using X-ray diffraction, transmission electron microscopy, Raman spectroscopy, thermogravimetric analysis, and nitrogen adsorption measurements. With the aid of GC/MS analysis of organic products in the liquid phase, it is shown that the controlled hydrolysis of TiCl 4 with water, which was in situ generated from the TiCl 4 -catalyzed aldol condensation reactions of acetones, played an important role in the formation of the titania nanomaterials. Some of the organic condensates may function to stabilize the phase and morphology of the materials. This mechanism was also supported by our success in using other ketones as alternatives to acetone in the synthesis.
Acta Materialia, 2003
The electrical properties of 3 mol% Y 2 O 3 doped ZrO 2 were measured by impedance spectroscopy a... more The electrical properties of 3 mol% Y 2 O 3 doped ZrO 2 were measured by impedance spectroscopy as a function of grain size, and the microstructure studied by SEM and HREM. In spite of the very clean grain boundaries, the grain boundary conductivity was still found to be ෂ2 orders of magnitude lower than the bulk conductivity, while it increased with decreasing grain size. The low grain boundary conductivity, according to the Schottky barrier model, is due to the depletion of oxygen vacancies in the grain boundary space charge layers. Within this framework, the grain boundary space charge potential and the concentration of oxygen vacancies in the space charge layers were calculated; it was found that the space charge potential decreased, but the oxygen vacancy concentration increased with decreasing grain size. Analyses of literature results for 8.2 mol% Y 2 O 3 and 15 mol% CaO doped ZrO 2 , respectively, revealed similar phenomena.
Advanced Materials Research, 2010
ABSTRACT
Advanced Materials, 2014
Epitaxially grown functional perovskites on silicon (001) and the ferroelectricity of a 3.2 nm th... more Epitaxially grown functional perovskites on silicon (001) and the ferroelectricity of a 3.2 nm thick BaTiO3 barrier layer are demonstrated. The polarization-switching-induced change in tunneling resistance is measured to be two orders of magnitude. The obtained results suggest the possibility of integrating ferroelectric tunnel junctions as binary data storage media in non-volatile memory cells on a silicon platform.
Physical Review Letters, 2000
Experimental evidence has been found for the existence of small single wall carbon nanotubes with... more Experimental evidence has been found for the existence of small single wall carbon nanotubes with diameters of 0.5 and 0.33 nm by high resolution transmission electron microscopy, and their mechanical stability was investigated using tight-binding molecular dynamics simulations. It is shown that, while the carbon tubes with diameters smaller than 0.4 nm are energetically less favorable than a graphene sheet, some of them are indeed mechanically stable at temperatures as high as 1100 ± C. The 0.33 nm carbon tube observed is likely a (4, 0) tube and is indeed part of a compound nanotube system that forms perhaps the smallest metal-semiconductor-metal tubular junction yet synthesized.
Acta Materialia, 2012
In this study the influence of interrupted quenching (IQ) in the temperature range 150-250°C for ... more In this study the influence of interrupted quenching (IQ) in the temperature range 150-250°C for periods of 15-1080 s on artificial aging after long-term natural pre-aging was studied for the Al-Mg-Si alloy AA6061 by atom probe tomography, transmission electron microscopy, electrical resistivity and hardness measurements, and differential scanning calorimetry. Compared with a standard quenching procedure, the results showed that hardening kinetics and the age hardening response were enhanced for IQ at low temperatures but reduced at high temperatures. Quenched-in vacancies were shown to be of particular importance for the nucleation of precipitates occurring during IQ at the lower end of the temperature range, finally leading to the formation of a dense distribution of b 00 during artificial aging. For standard water quenching and subsequent natural aging, nucleation is hindered by a low concentration of quenched-in vacancies in the matrix. IQ at high temperatures affects subsequent artificial aging via the formation of precipitates which do not contribute to hardening but consume a significant amount of solute.
Http Dx Doi Org 10 1080 09500830310001621623, Jun 4, 2010
ABSTRACT