In situ high-resolution transmission electron microscopy has been used to witness quasicrystals i... more In situ high-resolution transmission electron microscopy has been used to witness quasicrystals in the act of growing.
ECS Journal of Solid State Science and Technology, 2016
View the article online for updates and enhancements. You may also like Simulation of a multi-flo... more View the article online for updates and enhancements. You may also like Simulation of a multi-floor evacuation with the extended social force model in a multicorridor environment Hu Jun, Zhang Qi, Fan Ling et al.-Scale selection and feedback loops for patterns in drift wave-zonal flow turbulence Weixin Guo, Patrick H Diamond, David W Hughes et al.-Experimental study on pedestrians' uniand bi-directional movement on staircases under emergency conditions Jin Gao, Jinghai Gong, Jun He et al.
A solid-on-solid model of a layered crystal, which has five layers per repeat period in the direc... more A solid-on-solid model of a layered crystal, which has five layers per repeat period in the direction normal to the surface and with only nearest-neighbor interactions, is studied using Monte Carlo simulation to investigate the relationship between crystal structure and the corresponding surface phases. Equilibrium properties, such as the surface specific heat, interface width, and autocorrelation times, are studied as a function of temperature and system size. Results indicate three distinct surface phases exist in this model: a lowtemperature flat phase, an intermediate-temperature disordered but flat phase, and a high-temperature rough phase. We suggest the possibility of introducing several intermediate phases, as well as a rough phase, in a single system by appropriate modulation of the periodicity of the crystal structure normal to the surface. At the same time, growth simulations show an interesting growth-induced smoothing in the intermediate phase where, at low supersaturations, the growing intermediate phase has a smaller interface width than it does in equilibrium.
Carbon isotope exchange between calcite and graphite is a useful and reliable geothermometer for ... more Carbon isotope exchange between calcite and graphite is a useful and reliable geothermometer for medium-to high-grade marbles. Carbon isotope thermometry is based on the temperature dependent carbon isotope exchange between carbonate minerals and biogenic material/graphite during metamorphism. Since the
In this work we study electron transport modeling of a semiconducting quantum dot interacting wit... more In this work we study electron transport modeling of a semiconducting quantum dot interacting with metal electrodes. The modeling utilizes a physics-based kinetic Monte Carlo algorithm to balance accuracy with improved calculation speed, applied to the transport characteristic of a reported experimental Single Electron Transistor (SET) device with semiconducting silicon islands. We introduce an efficient numerical integration method to accurately calculate the electron tunneling rates for all allowable transitions, then apply kinetic Monte Carlo methods to simulate the electronic transport properties of the device. The method accounts for non-constant density of states and transition probabilities, and parasitic field-effect device coupling. A series of test cases have been introduced to demonstrate the relevance of the model. Three test cases explore the physical properties of the SET to confirm the proper modeling of gate, drain, source capacitances, charging energies, and junction widths. A study is designed to explore the temperature sensitivity of a SET with a semiconducting island, where the results show an interesting possibility to control the temperature sensitivity of the system through the applied biases. This behavior is not possible in metallic SET systems. A final study shows that the methodology models a representative experimental three terminal silicon single electron device with a coupled parasitic field effect transistor at low to moderate source-drain biases. The study demonstrates that the complex and aperiodic behavior of the Coulomb oscillations in the experimental device over temperature and bias cannot be fully characterized by the modeled physics of the SET or the nanoscaled MOSFET.
Tunneling field effect transistors (TFETs) have been proposed to overcome the fundamental issues ... more Tunneling field effect transistors (TFETs) have been proposed to overcome the fundamental issues of Si based transistors, such as short channel effect, finite leakage current, and high contact resistance. Unfortunately, most if not all TFETs are operational only at cryogenic temperatures. Here we report that iron (Fe) quantum dots functionalized boron nitride nanotubes (QDs-BNNTs) can be used as the flexible tunneling channels of TFETs at room temperatures. The electrical insulating BNNTs are used as the onedimensional (1D) substrates to confine the uniform formation of Fe QDs on their surface as the flexible tunneling channel. Consistent semiconductor-like transport behaviors under various bending conditions are detected by scanning tunneling spectroscopy in a transmission electron microscopy system (insitu STM-TEM). As suggested by computer simulation, the uniform distribution of Fe QDs enable an averaging effect on the possible electron tunneling pathways, which is responsible for the consistent transport properties that are not sensitive to bending. Carbon nanotubes (CNTs) 1 and graphene 2,3 have attracted tremendous research interest for applications in electronic devices. The highly flexible mechanical nature of CNTs and graphene has also enabled their applications in wearable devices 4-7. Unfortunately, digital switches based on CNTs are limited by the uncontrollable chirality of as-grown single walled CNTs. Likewise the use of graphene in digital switches is prohibited by its zero band gap nature. On the other hand, the structurally analogous boron nitride nanotubes (BNNTs) 5-11 and boron nitride nanosheets (BNNSs) 9,10,12 have drawn increasing attention due to their extraordinary mechanical properties 13-15 , and highly flexible nanotubular structures 16-19. However, pure BNNTs and BNNSs have a wide band gap (insulating materials) 20,21 , and thus are not applicable as the conduction channels of electronic devices. Significant efforts have been proposed to tune the electronic properties of boron nitride nanostructures, for example BNNTs, including doping with carbon 22 or fluorine 23 , or applying giant Stark effect 24 , etc. However, all these attempts have not lead to any electronic devices. Recently, we have shown that BNNTs functionalized with a one-dimensional (1D) array of gold (Au) quantum dots on their outer surfaces (QDs-BNNTs) could be used as the tunneling channels for tunneling field effect transistors (TFETs) at room temperature 25,26. Results indicate that these TFETs are functional without involving any semiconducting properties as BNNTs are insulators and the QDs are metallic. In this case, BNNTs serve as the one-dimensional (1D) substrates to confine the gold QDs into a linear tunneling channel that conduct current only if sufficient bias voltages are applied. Because of the uniform insulating nature of BNNTs, QDs-BNNTs can be used in digital switches without the need of chirality sorting (as is needed for CNT devices). Band gap creation as required for graphene is also not needed for QDs-BNNTs. This means that switches based on QDs-BNNTs represent a novel class of electronics without the use of semiconducting materials. Thus these TFETs could avoid many of the fundamental scaling issues of Si FETs, including short channel effects, undesired heating due to finite current leakage, and high contact resistance with the metallic electrodes. These features make QDs-BNNTs a promising novel class of materials for future electronics with minimal issues of leakage current, overheating, and contact resistance. As supported by our computer simulations, these TFETs are operated according to the principles of single electron transistors (SETs).
The recent discoveries of large facets in Al-Li-Cu and other icosahedral quasicrystals, as well a... more The recent discoveries of large facets in Al-Li-Cu and other icosahedral quasicrystals, as well as the observation of spatial disorder in these systems, show that disordered systems with long-range bond-orientational order can have growth facets. A fundamental question which naturally arises is whether such systems have equilibrium facets. In this paper, we study the conditions under which a perfect bond-oriented system can facet at T =0. The T =0 equilibrium shapes of bond-oriented systems with icosahedral and decagonal bond-orientational order are discussed. An explicit example is presented to show that disordered systems can have equilibrium facets at T=0. We also give detailed derivation of the surface energy of quasicrystals. I. INTRODUCTION A. Facets and disorder in icosahedral quasicrystals The recent discoveries of quasicrystal phases in Al-Li-Cu, ' Al-Fe-Cu, and Ga-Mg-Zn alloys are important developments in quasicrystal physics. These quasicrystals have grain sizes much larger than those discovered in other alloys (-micrometer). The grain size of Al-Li-Cu ranges from 0.1 to 1.0 mm. In Al-Fe-Cu, grains up to 2.0 cm in size are found. Unlike all previously found quasicrystals, these big quasicrystals are obtained in slow cooling processes. The cooling rates used are 10 times slower than those in rapid quenching processes. This suggests that these quasicrystals may in fact be thermodynamically stable states. All these large quasicrystals have large facets similar to those of crystals. The grain shape of the Al-Li-Cu quasicrystal is a rhombic triacontahedron, ' whereas those of Al-Fe-Cu and Al-Mg-Zn quasicrystals are of the form of a pentagonal dodecahedron. ' X-ray measurements have been performed on Al-Li-Cu but not yet on Al-Mg-Zn and Al-Fe-Cu. It is found that the diffraction peaks of Al-Li-Cu have "intrinsic" widths similar to those observed in rapidly cooled quasicrystals. The correlation length for posi'tional order implied by these width is about 200-1000 A. The phenomenon that all quasicrystals have similar correlation lengths independent of their chemical composition and sample preparation is now referred to as "universal disorder" of quasicrystals. ' While universal disorder is an interesting phenomenon in itself, together with the observation of facets it raises an intriguing conceptual question. Generally, facets are thought to be properties special to crystals, consequences of long-range positional order (LRPO) (see also Sec. II A) below). (By LRPO, we mean that the density Fourier transform or the x-ray diffraction pattern of the system is a set of 5 functions.) As we have mentioned before, the x-ray measurements show that the positional order of the Al-Li-Cu quasicrystal is short range. The size of its facets, however, is 3 orders of magnitude larger than the correlation length. This is very surprising since one does not expect facets to exist over length scales where positional order is destroyed. From x-ray measurements, one concludes that even though LRPO is sufhcient, it is not necessary for faceting.
2018 IEEE 13th Nanotechnology Materials and Devices Conference (NMDC), 2018
Electron transport through a single-electron transistor (SET) device with two semiconducting isla... more Electron transport through a single-electron transistor (SET) device with two semiconducting islands, two semiconducting electrodes (source and drain), and a metallic gate is investigated using a semi-classical model for electron tunneling and Kinetic Monte Carlo simulation. Experimental studies have demonstrated that there are advantages to utilizing SET devices with semiconducting (silicon) materials, as compared to metallic SETs, such as thermal filtering and improved gate control, which are of a great importance in practical applications. The model of the semiconductors includes an energy band gap and a modified-parabolic density of states in the valence and conduction bands. Although this leads to more complex calculations to predict electron tunneling between semiconducting materials as compared to devices with metallic islands and electrodes, the semiconductors also give more parameters by which to control the device characteristics.
2017 IEEE 17th International Conference on Nanotechnology (IEEE-NANO), 2017
In this work we study electron transport modeling of a semiconducting quantum dot interacting wit... more In this work we study electron transport modeling of a semiconducting quantum dot interacting with metal electrodes. The modeling utilizes a physics-based kinetic Monte Carlo algorithm to balance accuracy with improved calculation speed, applied to the transport characteristic of a reported experimental Single Electron Transistor (SET) device with semiconducting silicon islands. We introduce an efficient numerical integration method to accurately calculate the electron tunneling rates for all allowable transitions, then apply kinetic Monte Carlo methods to simulate the electronic transport properties of the device. The method accounts for non-constant density of states and transition probabilities, and parasitic field-effect device coupling. A series of test cases have been introduced to demonstrate the relevance of the model. Three test cases explore the physical properties of the SET to confirm the proper modeling of gate, drain, source capacitances, charging energies, and junctio...
Diamond is associated with ideals of purity, love, nobility, and wealth and with curses, corrupti... more Diamond is associated with ideals of purity, love, nobility, and wealth and with curses, corruption, and poverty. Its unique properties are studied by physicists and geologists, while its value, brilliance, and cultural importance make it a target of historians, investors, lovers, and thieves. Simple, iconic, and beautiful, diamond is the ultimate gemstone
In situ high-resolution transmission electron microscopy has been used to witness quasicrystals i... more In situ high-resolution transmission electron microscopy has been used to witness quasicrystals in the act of growing.
ECS Journal of Solid State Science and Technology, 2016
View the article online for updates and enhancements. You may also like Simulation of a multi-flo... more View the article online for updates and enhancements. You may also like Simulation of a multi-floor evacuation with the extended social force model in a multicorridor environment Hu Jun, Zhang Qi, Fan Ling et al.-Scale selection and feedback loops for patterns in drift wave-zonal flow turbulence Weixin Guo, Patrick H Diamond, David W Hughes et al.-Experimental study on pedestrians' uniand bi-directional movement on staircases under emergency conditions Jin Gao, Jinghai Gong, Jun He et al.
A solid-on-solid model of a layered crystal, which has five layers per repeat period in the direc... more A solid-on-solid model of a layered crystal, which has five layers per repeat period in the direction normal to the surface and with only nearest-neighbor interactions, is studied using Monte Carlo simulation to investigate the relationship between crystal structure and the corresponding surface phases. Equilibrium properties, such as the surface specific heat, interface width, and autocorrelation times, are studied as a function of temperature and system size. Results indicate three distinct surface phases exist in this model: a lowtemperature flat phase, an intermediate-temperature disordered but flat phase, and a high-temperature rough phase. We suggest the possibility of introducing several intermediate phases, as well as a rough phase, in a single system by appropriate modulation of the periodicity of the crystal structure normal to the surface. At the same time, growth simulations show an interesting growth-induced smoothing in the intermediate phase where, at low supersaturations, the growing intermediate phase has a smaller interface width than it does in equilibrium.
Carbon isotope exchange between calcite and graphite is a useful and reliable geothermometer for ... more Carbon isotope exchange between calcite and graphite is a useful and reliable geothermometer for medium-to high-grade marbles. Carbon isotope thermometry is based on the temperature dependent carbon isotope exchange between carbonate minerals and biogenic material/graphite during metamorphism. Since the
In this work we study electron transport modeling of a semiconducting quantum dot interacting wit... more In this work we study electron transport modeling of a semiconducting quantum dot interacting with metal electrodes. The modeling utilizes a physics-based kinetic Monte Carlo algorithm to balance accuracy with improved calculation speed, applied to the transport characteristic of a reported experimental Single Electron Transistor (SET) device with semiconducting silicon islands. We introduce an efficient numerical integration method to accurately calculate the electron tunneling rates for all allowable transitions, then apply kinetic Monte Carlo methods to simulate the electronic transport properties of the device. The method accounts for non-constant density of states and transition probabilities, and parasitic field-effect device coupling. A series of test cases have been introduced to demonstrate the relevance of the model. Three test cases explore the physical properties of the SET to confirm the proper modeling of gate, drain, source capacitances, charging energies, and junction widths. A study is designed to explore the temperature sensitivity of a SET with a semiconducting island, where the results show an interesting possibility to control the temperature sensitivity of the system through the applied biases. This behavior is not possible in metallic SET systems. A final study shows that the methodology models a representative experimental three terminal silicon single electron device with a coupled parasitic field effect transistor at low to moderate source-drain biases. The study demonstrates that the complex and aperiodic behavior of the Coulomb oscillations in the experimental device over temperature and bias cannot be fully characterized by the modeled physics of the SET or the nanoscaled MOSFET.
Tunneling field effect transistors (TFETs) have been proposed to overcome the fundamental issues ... more Tunneling field effect transistors (TFETs) have been proposed to overcome the fundamental issues of Si based transistors, such as short channel effect, finite leakage current, and high contact resistance. Unfortunately, most if not all TFETs are operational only at cryogenic temperatures. Here we report that iron (Fe) quantum dots functionalized boron nitride nanotubes (QDs-BNNTs) can be used as the flexible tunneling channels of TFETs at room temperatures. The electrical insulating BNNTs are used as the onedimensional (1D) substrates to confine the uniform formation of Fe QDs on their surface as the flexible tunneling channel. Consistent semiconductor-like transport behaviors under various bending conditions are detected by scanning tunneling spectroscopy in a transmission electron microscopy system (insitu STM-TEM). As suggested by computer simulation, the uniform distribution of Fe QDs enable an averaging effect on the possible electron tunneling pathways, which is responsible for the consistent transport properties that are not sensitive to bending. Carbon nanotubes (CNTs) 1 and graphene 2,3 have attracted tremendous research interest for applications in electronic devices. The highly flexible mechanical nature of CNTs and graphene has also enabled their applications in wearable devices 4-7. Unfortunately, digital switches based on CNTs are limited by the uncontrollable chirality of as-grown single walled CNTs. Likewise the use of graphene in digital switches is prohibited by its zero band gap nature. On the other hand, the structurally analogous boron nitride nanotubes (BNNTs) 5-11 and boron nitride nanosheets (BNNSs) 9,10,12 have drawn increasing attention due to their extraordinary mechanical properties 13-15 , and highly flexible nanotubular structures 16-19. However, pure BNNTs and BNNSs have a wide band gap (insulating materials) 20,21 , and thus are not applicable as the conduction channels of electronic devices. Significant efforts have been proposed to tune the electronic properties of boron nitride nanostructures, for example BNNTs, including doping with carbon 22 or fluorine 23 , or applying giant Stark effect 24 , etc. However, all these attempts have not lead to any electronic devices. Recently, we have shown that BNNTs functionalized with a one-dimensional (1D) array of gold (Au) quantum dots on their outer surfaces (QDs-BNNTs) could be used as the tunneling channels for tunneling field effect transistors (TFETs) at room temperature 25,26. Results indicate that these TFETs are functional without involving any semiconducting properties as BNNTs are insulators and the QDs are metallic. In this case, BNNTs serve as the one-dimensional (1D) substrates to confine the gold QDs into a linear tunneling channel that conduct current only if sufficient bias voltages are applied. Because of the uniform insulating nature of BNNTs, QDs-BNNTs can be used in digital switches without the need of chirality sorting (as is needed for CNT devices). Band gap creation as required for graphene is also not needed for QDs-BNNTs. This means that switches based on QDs-BNNTs represent a novel class of electronics without the use of semiconducting materials. Thus these TFETs could avoid many of the fundamental scaling issues of Si FETs, including short channel effects, undesired heating due to finite current leakage, and high contact resistance with the metallic electrodes. These features make QDs-BNNTs a promising novel class of materials for future electronics with minimal issues of leakage current, overheating, and contact resistance. As supported by our computer simulations, these TFETs are operated according to the principles of single electron transistors (SETs).
The recent discoveries of large facets in Al-Li-Cu and other icosahedral quasicrystals, as well a... more The recent discoveries of large facets in Al-Li-Cu and other icosahedral quasicrystals, as well as the observation of spatial disorder in these systems, show that disordered systems with long-range bond-orientational order can have growth facets. A fundamental question which naturally arises is whether such systems have equilibrium facets. In this paper, we study the conditions under which a perfect bond-oriented system can facet at T =0. The T =0 equilibrium shapes of bond-oriented systems with icosahedral and decagonal bond-orientational order are discussed. An explicit example is presented to show that disordered systems can have equilibrium facets at T=0. We also give detailed derivation of the surface energy of quasicrystals. I. INTRODUCTION A. Facets and disorder in icosahedral quasicrystals The recent discoveries of quasicrystal phases in Al-Li-Cu, ' Al-Fe-Cu, and Ga-Mg-Zn alloys are important developments in quasicrystal physics. These quasicrystals have grain sizes much larger than those discovered in other alloys (-micrometer). The grain size of Al-Li-Cu ranges from 0.1 to 1.0 mm. In Al-Fe-Cu, grains up to 2.0 cm in size are found. Unlike all previously found quasicrystals, these big quasicrystals are obtained in slow cooling processes. The cooling rates used are 10 times slower than those in rapid quenching processes. This suggests that these quasicrystals may in fact be thermodynamically stable states. All these large quasicrystals have large facets similar to those of crystals. The grain shape of the Al-Li-Cu quasicrystal is a rhombic triacontahedron, ' whereas those of Al-Fe-Cu and Al-Mg-Zn quasicrystals are of the form of a pentagonal dodecahedron. ' X-ray measurements have been performed on Al-Li-Cu but not yet on Al-Mg-Zn and Al-Fe-Cu. It is found that the diffraction peaks of Al-Li-Cu have "intrinsic" widths similar to those observed in rapidly cooled quasicrystals. The correlation length for posi'tional order implied by these width is about 200-1000 A. The phenomenon that all quasicrystals have similar correlation lengths independent of their chemical composition and sample preparation is now referred to as "universal disorder" of quasicrystals. ' While universal disorder is an interesting phenomenon in itself, together with the observation of facets it raises an intriguing conceptual question. Generally, facets are thought to be properties special to crystals, consequences of long-range positional order (LRPO) (see also Sec. II A) below). (By LRPO, we mean that the density Fourier transform or the x-ray diffraction pattern of the system is a set of 5 functions.) As we have mentioned before, the x-ray measurements show that the positional order of the Al-Li-Cu quasicrystal is short range. The size of its facets, however, is 3 orders of magnitude larger than the correlation length. This is very surprising since one does not expect facets to exist over length scales where positional order is destroyed. From x-ray measurements, one concludes that even though LRPO is sufhcient, it is not necessary for faceting.
2018 IEEE 13th Nanotechnology Materials and Devices Conference (NMDC), 2018
Electron transport through a single-electron transistor (SET) device with two semiconducting isla... more Electron transport through a single-electron transistor (SET) device with two semiconducting islands, two semiconducting electrodes (source and drain), and a metallic gate is investigated using a semi-classical model for electron tunneling and Kinetic Monte Carlo simulation. Experimental studies have demonstrated that there are advantages to utilizing SET devices with semiconducting (silicon) materials, as compared to metallic SETs, such as thermal filtering and improved gate control, which are of a great importance in practical applications. The model of the semiconductors includes an energy band gap and a modified-parabolic density of states in the valence and conduction bands. Although this leads to more complex calculations to predict electron tunneling between semiconducting materials as compared to devices with metallic islands and electrodes, the semiconductors also give more parameters by which to control the device characteristics.
2017 IEEE 17th International Conference on Nanotechnology (IEEE-NANO), 2017
In this work we study electron transport modeling of a semiconducting quantum dot interacting wit... more In this work we study electron transport modeling of a semiconducting quantum dot interacting with metal electrodes. The modeling utilizes a physics-based kinetic Monte Carlo algorithm to balance accuracy with improved calculation speed, applied to the transport characteristic of a reported experimental Single Electron Transistor (SET) device with semiconducting silicon islands. We introduce an efficient numerical integration method to accurately calculate the electron tunneling rates for all allowable transitions, then apply kinetic Monte Carlo methods to simulate the electronic transport properties of the device. The method accounts for non-constant density of states and transition probabilities, and parasitic field-effect device coupling. A series of test cases have been introduced to demonstrate the relevance of the model. Three test cases explore the physical properties of the SET to confirm the proper modeling of gate, drain, source capacitances, charging energies, and junctio...
Diamond is associated with ideals of purity, love, nobility, and wealth and with curses, corrupti... more Diamond is associated with ideals of purity, love, nobility, and wealth and with curses, corruption, and poverty. Its unique properties are studied by physicists and geologists, while its value, brilliance, and cultural importance make it a target of historians, investors, lovers, and thieves. Simple, iconic, and beautiful, diamond is the ultimate gemstone
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Papers by John Jaszczak