Browsing by Author "Chattopadhyay, S"

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Growth of single-crystalline wurtzite aluminum nitride nanotips with a self-selective apex angle
(2005-05-01)
Shi, SC
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Chen, CF
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Chattopadhyay, S
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Lan, ZH
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Chen, KH
Single-crystal line, hexagonal aluminum nitride nanotips are fabricated using a vapor-transport and condensation process (VTCP) on silicon substrates with or without a catalyst layer. The resultant tips have very sharp nanoscale apexes (&SIM; 1 nm), while their bases and lengths are up to hundreds of nanometers wide and several micrometers long, respectively. It has been demonstrated that the thickness of the gold-catalyst layer plays a critical role in controlling the size of the tip; in addition, a catalyst-free growth mode has been observed, which results in lesser control over the nanotip morphology. Nevertheless, a remarkably narrow distribution of the apex angle of the nanotips, regardless of whether or not a catalyst was used in the VTCP, has been obtained. Compared with the commonly observed ridge and pyramid structures, the nanotips produced by VTCP have higher angles (&SIM; 81&DEG;) between the tilted (221) and the basal (001) planes that encase it. A mechanism for this self-selective apex angle in aluminum nitride nanotip growth is proposed.
Molecular sensing with ultrafine silver crystals on hexagonal aluminum nitride nanorod templates
(2005-03-09)
Chattopadhyay, S
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Shi, SC
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Lan, ZH
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Chen, CF
;
Chen, KH
Morphology control of silicon nanotips fabricated by electron cyclotron resonance plasma etching
(2006-01-01)
Hsu, CH
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Huang, YF
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Chen, LC
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Chattopadhyay, S
;
Chen, KH
Formation of well-aligned silicon nanotips etched monolithically from a silicon substrate has been demonstrated. The effect of the process temperature on the physicochemical etching of silicon and subsequent fabrication of these nanotips has been investigated. 2.2-mu m-long nanotips were formed at the process temperature of 250 degrees C and then decreased in length with increasing process temperature. Above 800 degrees C, the formation of the silicon nanotips was inhibited. Spectroscopic evidence attributes this fact to the efficient formation of silicon carbide thin film at higher process temperatures, instead of discontinuous nanomasks at lower process temperatures that prevent etching of the substrate. Another reason for this inhibited formation of nanotips is the reduced etching rate of the silicon by agents such as atomic H at higher process temperatures. (c) 2006 American Vacuum Society.
Reduced temperature-quenching of photoluminescence from indium nitride nanotips grown by metalorganic chemical vapor deposition
(2005-11-14)
Shi, SC
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Chen, CF
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Hsu, GM
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Hwang, JS
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Chattopadhyay, S
We report metalorganic chemical vapor deposition of indium nitride (InN) nanotips with apex angles of 10 degrees and length and base diameter of around 1 mu m and 200 nm, respectively. The structure of the hexagonal InN nanotips growing along [002] was studied by electron microscopy and x-ray diffraction, and the optical properties were studied using temperature-dependent photoluminescence (PL) measurements. A narrow emission peak with a 18 meV full width at half maximum positioned at 0.77 eV was obtained with no visible emission. A PL quenching of only 14% was observed with a temperature scan of 15-320 K. (C) 2005 American Institute of Physics.
Structural evolution of AlN nano-structures: Nanotips and nanorods
(2006-01-25)
Shi, SC
;
Chattopadhyay, S
;
Chen, CF
;
Chen, KH
;
Chen, LC
Aluminum nitride (AIN) nanostructures were prepared using thermal chemical vapour deposition process. At growth temperatures of 950 degrees C, AIN nanotips with apex diameters of 10 nm, base diameters of similar to 100 nm, and length of similar to 2000 nm were obtained. Whereas when the growth temperature was 1200 degrees C, we obtained shorter and ihicker AIN nanorods. Compelling microscopic evidences were obtained to show that stacked AIN platelets of diminishing size formed the building blocks for the nanotips. A reducing Ehrlich-Schwoebel barrier introduced into a diffusion mediated growth model explains the formation of AIN nanorods at increasing growth temperatures. (c) 2005 Elsevier B.V. All rights reserved.