Form Quantum Wires and Quantum Dots on Surfaces 4/27/2017 Form Quantum Wires and Quantum Dots on Surfaces with Vapor Deposition Techniques David Ji Feb. 7th, 06

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

2. solid–liquid–solid mechanism (is not Vapor deposition) SiNW as an example alloy heating Gas cooling Ni supersaturated Amorphous nanowire! Inert gas flow plays important role in the formation of the nanowire Ref: Chem. Phys. Lett. 323 (2000) 224.

3. Standing in Hard Template prepare well-aligned NWs arrays by CVD without catalyst. Templates: Mesoporous template Nano porous alumina template Advantages: a. The size and shape of SiNWs can be controlled and vary over a wide range b. Well template-isolated nanowires arrays c. Sharp tips and perfect lattices can be obtained Ref: Chemical Physics Letters 374 (2003) 542–547

B. Suspended NW Lying on Substrate Suspended Carbon Nanotube Quantum Wires with Two Gates 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. Ref: small 2005, 1, No. 1

In order to be capable of being incorporated into devices, C. Challenges in Synthesizing NW: In order to be capable of being incorporated into devices, Controlled orientation and size of the grown nanostructure required.

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 This is why people like Zero dimensionality Ref: Appl. Phys. Lett., vol. 40, pp. 939–941, 1982.

Organometal chemical vapor deposition (OMCVD) 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 – 1184 Appl. Phys. Lett., Vol. 82, No. 6, 10 February 2003