Dislocation-free vertical GaN pillars in nanoscale were grown on Si (111) surface through self-assembly by molecular-beam epitaxy. No extra catalytic or nanostructural assistance has been employed. These nanorods have a lateral dimension from ≲10 nm to ∼800 nm and a height of ≲50 nm to ≳3 μm protruding above the film, depending on the growth parameters. The top view of the nanorods has a hexagonal shape from scanning electron microscopy. Transmission electron microscopy shows that the nanorods are hexagonal, single crystal GaN along the c-axis. An extra peak at 363 nm originated from nanorods was observed in photoluminescence spectra at 66 K, which is ascribed to the surface states according to the results of surface passivation. Micro-Raman spectroscopy on a single nanorod reveals E1 and E2 modes at 559.0 and 567.4 cm−1, respectively. Large strain was observed in both the transmission electron micrograph and the Raman shift. A possible growth mechanism is discussed.

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The nonvolatile memory characteristics of metal-oxide-semiconductor structures containing Pt nanocrystals in SiO 2 gate oxide were studied. The Pt nanocrystals of 2 -3 nm in diameter were self-assembled from reduction of an ultrathin PtO x layer embedded in the SiO 2 by vacuum annealing at 425°C. A large hysteresis loop was found in the capacitance-voltage ͑C -V͒ relation indicating this significant memory effect. However, two different charge storage mechanisms were found for the Pt nanocrystals in devices with different tunnel oxide thickness. A counterclockwise C -V hysteresis was induced from substrate injection for the devices made with a thin tunnel oxide layer 2.5-5.0 nm thick. Contrast, a clockwise behavior attributed to the electron transfer from charged defects in the gate oxide was found for the devices having a tunnel oxide layer 7.5 nm thick. The relatively stable memory characteristics of Pt nanocrystals resulted from substrate injection were also demonstrated.Memory-cell structures employing semiconductor or metal nanocrystals as storage elements in metal-oxidesemiconductor (MOS) field effect transistors have attracted much attention due to their properties as nonvolatile memory devices. [1][2][3][4] Most research has focused on the fabrication of Si or Ge nanocrystals in MOS structure, 1-7 but the metalnanocrystal memories are considered to be more beneficial in many aspects. [8][9][10][11][12] The metal nanocrystals have usually been fabricated by annealing an ultrathin metal film deposited on the thin gate oxide of SiO 2 . 8-12 However, the thermal and mechanical incompatibility between metal films and SiO 2 makes the fabrication of discrete and uniformly sized metal nanocrystals in gate oxide quite difficult. It is known that the oxidized phase of noble metals, such as PtO x , is chemically unstable, and can be easily reduced back to metallic state. 13 Accordingly, a self-assembly process of Pt nanocrystal formation from the reduction of an ultrathin PtO x layer embedded in SiO 2 is reported, and its memory characteristics are studied in this work.A trilayer structure containing a thin tunnel oxide layer of SiO 2 , an ultrathin PtO x layer, and a control oxide layer of SiO 2 was prepared. The tunnel oxide layer 2.5-7.5 nm thick was grown at 800°C in pure oxygen on ͑100͒ p-type ͑1-10 ⍀ cm͒ Si. The PtO x layer ϳ4 nm thick and the control oxide layer 24 or 36 nm thick, were deposited subsequently at room temperature by rf-magnetron sputtering with a low rf power giving a deposition rate of 2 nm/ min. All the MOS devices were then annealed at 425°C for 25 min in vacuum, which resulted in a reduction of the ultrathin PtO x layers into discrete Pt nanocrystals embedded in SiO 2 matrix. Figure 1(a) shows the cross-sectional image of transmission electron microscopy (TEM) of the Pt nanocrystals self-assembled in the SiO 2 matrix. Note that the Pt nanocrystals were mostly spherical with a narrow size distribution in the range of 2 -3 nm, as depicted in Fig. 1(b). The chemical state of Pt in the vacuum-a...

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