7 research outputs found
Cutting Edge Nanotechnology
The main purpose of this book is to describe important issues in various types of devices ranging from conventional transistors (opening chapters of the book) to molecular electronic devices whose fabrication and operation is discussed in the last few chapters of the book. As such, this book can serve as a guide for identifications of important areas of research in micro, nano and molecular electronics. We deeply acknowledge valuable contributions that each of the authors made in writing these excellent chapters
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Designing Novel Semiconductor Nanowire Structures: Synthesis and Fabrication for Localized Photodetection and Sensing
Semiconductor nanowires display a wide range of structural and functional diversity, and as such provide a platform for nanomaterials research. At present, a number of nanowire structural motifs have been discovered and configured into devices with unique electrical and optical functionalities. For example, a kinked nanowire with a localized axial dopant modulation can record intracellular action potentials when incorporated into a three dimensional device. A radially modulated p-i-n nanowire can function as a nanoscale photovoltaic device to power logic gates and sensors. This thesis focuses on novel electrical and optical device functionalities based on rational design, synthesis and characterization of semiconductor nanowire structures for applications in the physical, chemical and biological sciences.
First, I will present the design, synthesis and fabrication of two nanodevices for intracellular sensing that are based on core/shell and branched nanowire structural motifs. In both types of devices, a nanotube bridge templated by nanowires conducts the intracellular electrical and chemical potentials to the gating regions and the change in potential is recorded as the change of the device conductance. Both nanowire-based devices can sense extra- and intracellular action potentials with high spatial resolution. Furthermore, they can be easily multiplexed and scaled up to record intracellular action potentials at multiple sites from either a single cell or cellular network.
Second, I will discuss the synthesis of tapered nanowire structures and their electrical and optical characterization. By finely tuning growth temperature, precursor partial pressure, and catalyst size, detailed control of the nanowire tapering angle can be achieved. Moreover, tapered core/shell nanowires can be configured into devices with highly-localized electrical and optical functionalities. I show that control of the tapering angle plays an important role in determining the electrical and optical properties of nanowires.
Finally, I will demonstrate a novel nanowire structural motif, termed tip-modulated nanowire, in which the modulation of material and dopant is localized at the nanowire tip so that a tip-localized device is encoded. I describe rational bottom-up synthesis of tip-localized p-n junctions, which are connected to the p-type nanowire core and isolated n-type nanowire shell. The electrical and optical properties of the tip-modulated nanowires are investigated by configuring them as devices with electrically independent core and shell contacts. Spatially-resolved electrical and optical characterizations show that a potentiometric sensor as well as a highly sensitive p-n diode photodetector can be localized at the nanowire tip. In addition, a top-down strategy for wafer-scale synthesis and fabrication of vertical tip-modulated nanowires and nanowire device arrays is presented. Finally, by combining the tip-modulated nanowire structure with other structural motifs, we can rationally design self-sustained multi-functional nanodevices. The new tip-modulated nanowire structural motif opens up novel applications in the physical, chemical and biological sciences.Chemistry and Chemical Biolog
ํจํฐ๋๋ ์๊ธฐ ์์ฉ๋์ด ํํ์ ๊ฐ์์ฑ ๊ตฌ์กฐ ๊ฐ์ ๋์ ์ํธ ์์ฉ
ํ์๋
ผ๋ฌธ (๋ฐ์ฌ)-- ์์ธ๋ํ๊ต ๋ํ์ : ์ฌ๋ฃ๊ณตํ๋ถ, 2012. 8. ๊น์๊ตญ.์๊ธฐ ์์ฉ๋์ด๋ ๋ง์ดํฌ๋ก๋ฏธํฐ ์ดํ์ ํจํฐ๋๋ ๊ฐ์์ฑ ๊ตฌ์กฐ์ฒด์์ ์์ ํ ์ํ ๊ตฌ์กฐ๋ก ๋ฐ๋ง ๋ฉด์ ํํํ๋ฉฐ ์์ฉ๋์ด์ ๊ฐ์ ํํ๋ก ๋ฐฐ์ด๋ ์ํ ์ํ ์ฑ๋ถ๊ณผ ๊ตฌ์กฐ์ฒด ์ค์ฌ๋ถ์ ๋ฐ๋ง ๋ฉด์ ์์งํ ๋ฐฉํฅ์ ์ํ ์ฑ๋ถ(์์ฉ๋์ด ํต)์ผ๋ก ์ด๋ฃจ์ด์ ธ ์๋ค. ๋
๋ฆฝ๋ ์ํํ ๋ฐ๋ง์์, ์ธ๋ถ์ ํ์ด ์ธ๊ฐ๋๋ฉด ์์ฉ๋์ด ํต์ด ํํ์ํ์ ์์น๋ฅผ ์ค์ฌ์ผ๋ก ํน์ ์ฃผํ์๋ก ํ์ ํ๋ ์๊ธฐ ์์ฉ๋์ด์ ์์ง์์ด ์ฌ๊ธฐ ๋๋ค.
๋ณธ ํ์ ๋
ผ๋ฌธ์์๋ ์๊ธฐ ์์ฉ๋์ด ์ํ์ ๊ฐ์์ฑ ๊ตฌ์กฐ์ฒด ๊ฐ์ ๋์ ์ํธ์์ฉ์ ๋ฏธ์์๊ธฐ ์ ์ฐ๋ชจ์ฌ, ์ด๋ก ๊ณ์ฐ, ์คํ์ ํตํด ์ดํผ์๋ค. ๋ฌผ๋ฆฌ์ ์ผ๋ก ๋ถ๋ฆฌ๋ ์ํํ ๋ฐ๋ง ์ฌ์ด์์ ์๊ธฐ ์์ฉ๋์ด ์ค์ฌ์ ๊ฒฐํฉ ๊ฑฐ๋์ ์๊ณต๊ฐ ๋ถํด ์๊ธฐ ํฌ๊ณผ ์ฐ X-์ ํ๋ฏธ๊ฒฝ์ ์ด์ฉํด ๊ด์ฐฐํ์๋ค. ํ๋์ ์ํ์์์ ์๊ธฐ์์ฉ๋์ด ํ์ ์ด๋์ ์ํด ํ์ ํ์ ์๊ณ๊ฐ ํ์ฑ๋์ด ๋ค๋ฅธ ์ํ์ ์ํฅ์ ๋ผ์นจ์ ๋ฐํ๋๋ค.
๋๋ถ์ด ๊ทธ์ ๊ฐ์ ์ํธ ์์ฉ์ ๋ฐํ์ผ๋ก ์๋์ง/์ ํธ ์ ๋ฌ ๋ฐฉ๋ฒ์ ์ ์ํ์๊ณ ๋์ ์ํธ์์ฉ์ ๋ฌผ๋ฆฌ์ ์์ธ์ ํ์ฌํ์๋ค. ์ด ๋ฉ์ปค๋์ฆ์ ๋น ๋ฅด๊ณ ์กฐ์ ๊ฐ๋ฅํ ์๋์ง ์ ๋ฌ์ ๊ฐ๋ฅํ๊ฒ ํ๋ค. ์ํ๊ฐ์ ๊ฑฐ๋ฆฌ ๋ฐ ์ํธ์์ฉ ์ธ๊ธฐ์ ๋ฐ๋ผ ์๋์ง ์ ๋ฌ ์๋์ ์กฐ์ ์ด ๊ฐ๋ฅํ๋ฉฐ ๋ฎ์ ์๊ธฐ ๊ฐ์ ์์๋ฅผ ๊ฐ๋ ๋ฌผ์ง์ ์ฌ์ฉํจ์ผ๋ก์จ ์ ํธ ์ ๋ฌ ์์ ์๋์ง ์์ค์ ์ค์ผ ์ ์๋ค.
๋ํ ๋์ ์ํธ์์ฉ์ ๋ํ ๊ทผ๋ณธ์ ์ดํด๋ฅผ ๋ฐํ์ผ๋ก ์๊ธฐ ์์ฉ๋์ด ํ์ ์ด๋์ ์ด์ฉํ ๋
ผ๋ฆฌ ์ฐ์ฐ์ ์ ์, ๊ตฌํํ์๋ค. ์ธ์ ํ ์ํ ๊ฐ์ ์๊ธฐ ์์ฉ๋์ด์ ํ์ ์ด๋์ ์ํ ์ ๋ณด๋ ์ ๋๋
ธ์ด ์ดํ์ ๋น ๋ฅธ ์๊ฐ์ ์ ๋ฌ๋๋ค.
๋ณธ ํ์ ๋
ผ๋ฌธ์ ์๊ธฐ ์์ฉ๋์ด ๊ฐ์ ๋์ ์ํธ ์์ฉ์ ๋ํ ๊ธฐ์ด์ ์ธ ์ดํด์ ์ํํ ์์ฑ ๋ฐ๋ง ๊ฐ์ ํต์ ๊ฐ๋ฅํ ์ ๋ณด ์ ๋ฌ ๋ฐ ์ฒ๋ฆฌ ๋ฐฉ๋ฒ์ ์ ๊ณตํ๋คIn a sub-micrometer-size patterned ferromagnetic structure, the magnetic vortex is in a strongly stable ground state characterized by an in-plane curling magnetization around and an out-of-plane magnetization in the central region. In isolated disks, applied external forces induce vortex excitations, among which a translational mode exists in which the vortex core rotates around its equilibrium position at a characteristic eigenfrequency.
This work focused on dynamic interaction between vortex-state ferromagnetic structures, utilizing micromagnetic simulations, analytical calculations, and experiments. Coupled vortex-core gyration in separated disks was observed by employing time and space resolved full-field magnetic transmission soft x-ray microscopy. We found that the vortex gyration of one disk affects that of the other through their respective dynamically rotating stray fields.
In addition, energy/signal transfer based on the transfer mechanism having been provided, the details including the fundamentals of the dynamic interaction between magnetic vortices were investigated. This robust mechanism for energy transfer offers the advantages of a fast and tunable transfer rate, which is a function of disk interdistance and interaction strength. The energy loss during gyration-mediated signal transfer is reduced by using magnetic material that has a low damping constant.
Based on a fundamental understanding of that dynamic interaction, a logic operation using vortex gyration was demonstrated. Remarkably, the excitation of vortex gyrations and signal transfer between neighboring disks were as fast as a few ns.
This work provides a fruitful fundamental understanding of dynamic interaction between magnetic vortices and a robust means of information-signal transport between physically separated magnetic disks.Contents
Abstract i
List of Tables viii
List of Figures ix
1. Introduction 1
2. Research Background 8
2.1 Micromagnetics 8
2.2 Translational mode of magnetic vortex 13
2.3 Interaction between mangnetic vortices 15
3. Sample Design and Fabrication 19
3.1 Thin film deposition 20
3.2 Lithography 25
3.3 Magnetic field strength and distribution 28
4. Magnetic Imaging using Transmission Soft X-ray Microscopy 30
4.1 Magnetic imaging techniques 31
4.2 X-ray magnetic circular dichroism 35
4.3 Full-field magnetic transmission soft x-ray microscopy (MTXM) 38
4.4 Time resolved imaging using pump and probe technique 41
5. Coupled Vortex Cores Oscillation 43
5.1 Sample preparation and experimental setup 45
5.2 Imaging of vortex core oscillation 48
5.3 Dipolar induced vortex core oscillation 53
6. Energy Transfer through Vortex Core Gyration 56
6.1 Coupled oscillator 57
6.2 Experimental observation of dipolar induced vortex gyrations 61
6.3 Energy transfer between two dipolar-coupled vortex oscillators 68
6.4 Normal modes representation of coupled vortex oscillations 74
6.5 Micromagnetic simulation procedure and results 79
6.6 Frequency splitting and energy transfer rate 82
6.7 Dependence on interdistance 83
6.8 Dependence on relative vortex polarization 86
6.9 Energy attenuation 89
6.10 Propagation of gyration in longer chain 92
7. Logic Operation using Vortex State Structures 96
7.1 Design of archetypal XOR logic by simulations 98
7.2 Experimental verification using soft X-ray microscopy 105
7.3 Differential XMCD images of individual disks vortex gyrations 109
7.4 Programmable logic operations 114
7.5 Limitation 118
8. Summary 122
Bibliography
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Presentations in ConferencesDocto
A study of electron scattering through noise spectroscopy
Charge counting statistics (C.S.) of traversing electron in quantum devices like atomic-molecular junctions is sensitive to the local perturbation in the charge field at the contact and in the quantum channels. The first cumulant of C.S. i.e. current-voltage characteristic of such devices has been tool for such investigation since long time. Here we have used the second cumulant i.e. shot noise to study the electron-electron and electron-phonon interaction in the atomic contacts. The shot noise measurement on the Au atomic chain reveals the inelastic scattering in the noise. These signatures can provide vital information on the feedback of the local phonon population on electron transport. The current-voltage characteristic of the ferromagnetic atomic contacts unexpectedly shows zero bias anomalies. This observation is attributed to the interaction of traversing electron with localized magnetic moments within same host species. The observed connection between the Fano factor and the weight of the zero bias anomalies supports the view that the zero bias anomaly originates from spin scattering by localized magnetic moments. However, whether this is true Kondo scattering as suggested by Calvo et al. cannot be stated conclusively from our data. At the end of thesis we have presented a low noise high frequency broadband noise measurement setup suitable for break junction setup.FOMUBL - phd migration 201
Implementation of multi-CLB designs using quantum-dot cellular automata
CMOS scaling is currently facing a technological barrier. Novel technologies are being proposed to keep up with the need for computation power and speed. One of the proposed ideas is the quantum-dot cellular automata (QCA) technology. QCA uses quantum mechanical effects in the device at the molecular scale. QCA systems have the potential for low power, high density, and regularity. This thesis studies QCA devices and uses those devices to build a simple field programmable gate array (FPGA). The FPGA is a combination of multiple configure logical blocks (CLBs) tiled together. Most previous work on this area has focused on fixed logic and programmable interconnect. In contrast, the work at the Rochester Institute of Technology (RIT) has designed and simulated a configurable logic block (CLB) based on look-up tables (LUTs). This thesis presents a simple FPGA that consists of multiple copies of the CLB created by the RIT group. The FPGA is configured to emulate a ripple-carry adder and a bit-serial multiplier. The latency and throughput of both functions are analyzed. We employ a multilevel approach to design specification and simulation. QCADesigner software is used for layout and simulation of an individual CLB. For the FPGA, the high-level HDLQ Verilog library is used. This hybrid approach provides a high degree of confidence in reasonable simulation time