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Under ultrahigh vacuum conditions, extremely small Ge nanodots embedded in SiO2, i.e., Ge–SiO2 quantum dot composites, have been formed by ion implantation of 74Ge+ isotope into (0001) Z-cut quartz at a low kinetic energy of 9 keV using varying implantation temperatures. Transmission electron microscopy (TEM) images and micro-Raman scattering show that amorphous Ge nanodots are formed at all temperatures. The formation of amorphous Ge nanodots is different from reported crystalline Ge nanodot formation by high energy ion implantation followed by a necessary high temperature annealing process. At room temperature, a confined spatial distribution of the amorphous Ge nanodots can be obtained. Ge inward diffusion was found to be significantly enhanced by a synergetic effect of high implantation temperature and preferential sputtering of surface oxygen, which induced a much wider and deeper Ge nanodot distribution at elevated implantation temperature. The bimodal size distribution that is often observed in high energy implantation was not observed in the present study. Cross-sectional TEM observation and the depth profile of Ge atoms in SiO2 obtained from x-ray photoelectron spectra revealed a critical Ge concentration for observable amorphous nanodot formation. The mechanism of formation of amorphous Ge nanodots and the change in spatial distribution with implantation temperature are discussed. [ABSTRACT FROM AUTHOR]

Organized extremely small Ti–Sn alloy nanodots have been formed in the subsurface of SiO2 by dynamic coimplantation of isotopic 48Ti+ and 120Sn+ at a low kinetic energy of 9 keV into (0001) Z-cut quartz at different substrate temperatures. Transmission electron microscopy images show that the Ti–Sn alloy nanodots are single crystal and have been formed uniformly at room temperature. They are distributed in a two-dimensional array with similar size of ∼4 nm and constant interdot spacing between each dot. The regions beyond and below the two-dimensional array are depleted of detectable nanodots. At high temperature, the distribution and crystallinity were destroyed with much smaller amorphous nanodots in a slightly deeper region. The implantation was carried out by dynamic coimplantation, rather than the commonly used sequential implantation. These results indicate that dynamic low energy coimplantation is capable of forming well-ordered two-dimensional array of alloy nanodots. [ABSTRACT FROM AUTHOR]

Self-organized extremely small Ti nanodots have been formed in the subsurface of SiO2 by implantation of isotopic 48Ti+ at a kinetic energy of 9 keV into (0001) Z-cut quartz, followed by a vacuum annealing process. Transmission electron microscopy (TEM) images show that the Ti nanodots have a two-dimensional distribution, i.e., a uniform size as small as 3.8 nm and relatively uniform positions with nearly constant inter-particle spacing of ~ 1.5 nm. A mechanism for the two-dimensional spatial distribution and the inhibition of chemical reactions between Ti and SiO2 is discussed. [ABSTRACT FROM AUTHOR]

Self-organized extremely small Ti nanodots have been formed in the subsurface of SiO2 by implantation of isotopic 48Ti+ at a kinetic energy of 9 keV into (0001) Z-cut quartz, followed by a vacuum annealing process. Transmission electron microscopy (TEM) images show that the Ti nanodots have a two-dimensional distribution, i.e., a uniform size as small as 3.8 nm and relatively uniform positions with nearly constant inter-particle spacing of ~ 1.5 nm. A mechanism for the two-dimensional spatial distribution and the inhibition of chemical reactions between Ti and SiO2 is discussed. [ABSTRACT FROM AUTHOR]

Extremely small Sn nanodots embedded in the subsurface of SiO2, i.e., Sn–SiO2 quantum dot composites, have been formed by ion implantation of the 120Sn+ isotope into (0001) Z-cut quartz at a low kinetic energy of 9 keV at room temperature. Transmission electron microscopy images show that the Sn nanodots have an average size of about 3 nm, and both single-crystal and amorphous nanodots have been observed at room temperature. The nanodots are randomly distributed in the lateral direction but confined in a narrow layer in the depth direction. The bimodal size distribution that is often observed in high energy implantation was not observed in the present study. The spatial morphology and crystallinity of the Sn nanodots can be modified by thermal annealing, and the extent of the modification is dependent on the annealing temperature. The distribution and crystallinity of the Sn nanodots in single-crystal bulk SiO2 are different from those of Sn nanocrystals in thin SiO2 films on silicon substrates. The mechanisms that could account for these phenomena are discussed. [ABSTRACT FROM AUTHOR]