The authors report the use of in situ optical reflectometry to determine the incubation time for the onset of growth, mean growth rate, and average length of Si nanowires during chemical vapor deposition vapor-liquid-solid synthesis. Results for the constructive and destructive interferences of 635nm linearly polarized laser light scattering from growing nanowire layers are compared to simulations. This real time optical reflectance approach is shown to quantitatively determine nanowire growth rates as well as reveal a pressure dependence for the time to nucleate nanowire growth.
Pure, nanoscale Ge dots were deposited on Si3N4 substrates by decomposing digermane (Ge2H6) using a focused electron beam. Deposited feature diameters are larger than that of the electron beam used for deposition by an amount comparable to the secondary electron escape depth. This result suggests that axial secondary electron emission through the surface of a growing feature limits the minimum attainable feature size. In situ, electron energy-loss spectroscopy shows that the dots are pure Ge with C contents below the carbon detection limit of less than 18%. Analyzing the bright field image in the thin film, single scattering approximation yields the height of the Ge dots allowing the average Ge deposition efficiency to be estimated.
Epitaxial germanium quantum dots (QDs) embedded in boron-doped silicon have been studied using off-axis electron holography to estimate the number of holes associated with a single QD. Holes were confined near the base of the pyramidal, 25-nm-wide Ge QDs. The resulting estimate of charge density was 0.03 holes/nm3 which corresponded to about 30 holes localized to the investigated dot. For comparison, the average number of holes confined to each Ge dot was found to be about 40, using a capacitance-voltage measurement. The difference emphasizes the value of measuring charges confined to individual nm-scale regions of a heterogeneous sample.
Nanoscale Au rich dots were deposited on SiO2 and Si3N4 substrates by decomposing an adsorbed organometallic precursor using a focused electron beam. The precursor, dimethyl acetylacetonate gold ((CH3)2(C5H7O2)Au), does not react with either substrate without electron irradiation. Deposited feature diameters are larger than that of the electron beam used for deposition by an amount comparable to the secondary electron escape depth. This result suggests that axial secondary electron emission through the surface of a growing feature limits the minimum attainable feature size. Real-time composition analysis during growth using electron energy-loss spectroscopy indicates that mature features entrain significant carbon.
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