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Part One: Quantum Wires A. Growth of Quantum Wires Pinned on Substrate 1.vapor–liquid–solid (VLS) Three Steps: Alloying process Nucleation of precursors Axial growth Why? Growing under the catalyst? Vapors diffuse and condense at the existing solid/liquid interface, due to that less energy will be involved with the crystal step growth as compared with secondary nucleation events in a finite volume. Ref: 3165 J. Am. Chem. Soc. 2001, 123, 3165-3166
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Form Quantum Wires and Quantum Dots on Surfaces
with Vapor Deposition Techniques
David Ji
Feb. 7th, 06
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A. Growth of Quantum Wires Pinned on Substrate
1.vapor–liquid–solid (VLS)
Three Steps:
Alloying process
Nucleation of precursors
Axial growth
Ref: 3165 J. Am. Chem. Soc. 2001, 123, 3165-3166
Why? Growing under the catalyst?
Vapors diffuse and condense at the existing solid/liquid interface, due to that less energy will be involved with the crystal step growth as compared with secondary nucleation events in a finite volume.
Part One: Quantum Wires
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2. solid–liquid–solid mechanism (is not Vapor deposition) SiNW as an example
Ref: Chem. Phys. Lett. 323 (2000) 224.
Inert gas flow plays important role in the formation of the nanowire
alloy
heating
Gas cooling
Ni supersaturated
Amorphous nanowire!
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a. The size and shape of SiNWs can be controlled and vary over a wide range
Ref: Chemical Physics Letters 374 (2003) 542–547
3. Standing in Hard Template
c. Sharp tips and perfect lattices can be obtained
Mesoporous template Nano porous alumina template
prepare well-aligned NWs arrays by CVD without catalyst.
Advantages:
b. Well template-isolated nanowires arrays
Templates:
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Suspended Carbon Nanotube Quantum Wires with Two Gates
Ref: small 2005, 1, No. 1
Electron beam lithography (EBL): define the local-gate pattern, S/D pattern, pattern catalyst islands.
Source (S) and drain (D) metal electrodes, a metal local gate (VGL) at the bottom of the trench and a global Si back gate (VGB).
Show different properties compared with pinned CNT on substrate.
B. Suspended NW Lying on Substrate
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In order to be capable of being incorporated into devices, Controlled orientation and size of the grown nanostructure required.
C. Challenges in Synthesizing NW:
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Part Two: Quantum Dots (QD)
Formation Mechanism:
Stranski–Krastanow (SK) growth mode responsible
Applications: Optical and electronic properties
About quantum laser:
Characteristics would be improved dramatically due to reduction of dimensionality of the electron motions in quantum nanostructures, proposed by Arakawa and Sakaki
Ref: Appl. Phys. Lett., vol. 40, pp. 939–941, 1982.
This is why people like Zero dimensionality
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Hot Research Field:Semiconductors QD. ex. binary & tertiary compound from IIIA and IVA. InAs/GaAs dots extensively investigated.
GaSb/GaAs attracted interest for its potential application in capacitors.
Synthesis Method: Organometal chemical vapor deposition (OMCVD) ex. In forming QD compound containing Ar. ArH3 was replaced by tertiarybutylarsine (TBAs)
Molecular beam epitaxy (MBE) Creating a 'molecular beam' of a material which impinges on to the substrate.
Ref: Physica E 13 (2002) 1181 – 1184Appl. Phys. Lett., Vol. 82, No. 6, 10 February 2003
