Vy Yam

Kinetics of Ge growth at low temperature on Si(001) by ultrahigh vacuum chemical vapor deposition

The growth of germanium at low temperature by ultrahigh vacuum chemical vapor deposition on Si(001) is investigated in real time by reflection high-energy electron diffraction. These observations are complementarily checked by atomic force microscopy, Rutherford backscattering spectrometry, transmission electron microscopy, and x-ray diffraction experiments. It can be seen that the currently observed Stranski–Krastanov-related two-dimensional (2D) to three-dimensional transition is avoided at 330°C and that the major part of the relaxation process occurs during the deposition of the first two monolayers. Then, the measured in-plane lattice parameter evolves slowly and approaches that of bulk Ge after deposition of 50 monolayers. The corresponding relaxation equals 83%. The resulting surface is flat, with a rms roughness of 0.55nm. The relaxation is found to be mainly due to misfits dislocations located at the Ge∕Si interface. Regrowth experiments at 600°C show that the low-temperature films are not stable...

Gold anchoring on Si sawtooth faceted nanowires

This paper reports on the sawtooth faceting and the related gold coverage of silicon nanowires (NWs). 111-oriented Si NWs were grown on Si(111) substrates by ultra high vacuum chemical vapor deposition using the vapor-liquid-solid mechanism with a gold catalyst. We observed that gold nanoclusters are unequally distributed on the NW surface. They are mainly distributed on only three non-consecutive sidewalls corresponding to the (), () and () planes among the six available crystallographic {112} surfaces. In addition they are anchored on upward {111} facets. This original observation brings enhanced knowledge on the faceting mechanisms. The threefold symmetry of the facet formation and gold anchoring is supported by criteria of minimal Au/Si interfacial energy. Moreover results evidence that the selective presence of gold on the NW sidewalls affects the overall morphology due to an increased radial growth on the covered sidewalls.

Composition and local strain mapping in Au-catalyzed axial Si/Ge nanowires

For most applications, heterostructures in nanowires (NWs) with lattice mismatched materials are required and promise certain advantages thanks to lateral strain relaxation. The formation of Si/Ge axial heterojunctions is a challenging task to obtain straight, defect free and extended NWs. And the control of the interface will determine the future device properties. This paper reports the growth and analysis of NWs consisting of an axial Si/Ge heterostructure grown by a vapor-liquid-solid process. The composition gradient and the strain distribution at the heterointerface were measured by advanced quantitative electron microscopy methods with a resolution at the nanometer scale. The transition from pure Ge to pure Si shows an exponential slope with a transition width of 21 nm for a NW diameter of 31 nm. Although diffuse, the heterointerface makes possible strain engineering along the axis of the NW. The interface is dislocation-free and a tensile out-of-plane strain is noticeable in the Ge section of the NW, indicating a lattice accommodation. Experimental results were compared to finite element calculations.

Integrated plasmonic nanotweezers: Toward the manipulation of nanoobjects

In this paper, we present the numerical conception of a surface plasmon-based nanotweezers obtained by coupling a short nanoparticle chain to a traditional SOI waveguide. In particular, we detail on simplified calculation scheme, based on the estimation of the gradient force, able to ease the analysis when the refractive index of the tweezed particles is similar to that of the background. Results suggest the possibility of controlling the position where the trapping occurs along the chain as a function of the wavelength. This may be crucial for achieving the possibility of manipulating objects in the nanoscale by means of integrated devices.

Integrated plasmonic tweezer for linear repositioning of nanometric objects

Plasmonic nanoparticles chains coupled to traditional SOI waveguides allow for nanoobjects trapping and jumpless linear repositioning. This innovative feature is here numerically detailed. This may be extremely captivating for the conception of integrated optomechanical nanoactuators.

Integrated magnetoplasmonic nanostructures for non-reciprocal optical devices

We have numerically shown that when a magneto-optical bismuth iron garnet waveguide is coupled to a gold grating on its top, surface plasmon polaritons can strongly enhance transverse magneto-optical Kerr effect, and thus non-reciprocal transmission.

Bloch mode spatial harmonic decomposition in integrated localized surface plasmon chain

We consider a gold nanoparticle chain integrated on a dielectric waveguide. With appropriate geometrical parameters, such a chain behaves as a waveguide. We show that the spatial harmonics generated in the sub-wavelength periodic structure can be locally separated or extracted. This is done by playing with the phase matching condition of the coupling with the dielectric waveguide: only the fundamental component is locally cancelled in the periodic structure, resulting in a non-monotone phase evolution along the structure. Additionnally we show that the analysis of spatial harmonics allows extracting more information on the localized surface plasmon mode generation.

Evolution and ripening of Ge crystals grown by nanoscale induced lateral epitaxy on localized oxide

We have previously demonstrated that a high quality Ge on SiO2 layer can be grown by nanoscale seed induced lateral epitaxy, using a method based on the standard local oxidation of silicon technique for creating nanoscale silicon seeds. The growth of Ge from germane is initiated in two silicon seed lines and evolves toward a complete wetting of the SiO2 stripe after coalescence. For isolated crystals, the wetting mechanism of SiO2 by Ge is strongly dependent upon the seed orientation and closely related to the development of {111} facets. We show here that the energetic balance between different surface and interface energies governs the wetting configuration of SiO2 by Ge, and therefore defines the angle of contact between Ge and SiO2, that can only be satisfied by the development of a (11-1) facet in the case studied. We derive from Young’s equation an interfacial energy between Ge and SiO2 equal to 5.67 eV/nm2. We show that the coalescence of Ge crystals is mainly driven by surface diffusion, which includes two main aspects. Diffusion driven by the chemical potential gradient due to the variation of seed curvatures leads to preferential nucleation at concave corners of patterns. At the same time, a ripening phenomenon is observed when the two crystals come in contact with each other.

Localisation of silicon nanowires grown by UHV-CVD in (111)-oriented apertures opened in Si (001)

In this paper, we have investigated an alternative method to obtain well-organized silicon nanowires grown by vapor-liquid-solid process. We have studied the influence of the droplet size on the growth direction of nanowires on plain wafers. By using self-organized Au droplets grown by molecular beam epitaxy on vicinal Si(111) surface with a 2° miscut towards the [11-2] crystallographic direction, we have obtained well organized gold droplets along the steps with small size dispersion. The growth of Si nanowires from these droplets allows defining a critical diameter for changing the Si nanowires growth direction. When the gold droplet diameter is larger than 100 nm, Si nanowires exhibit a orientation and remain free of structural defects. The localisation of Si nanowires was performed in nanoscale silicon seeds formed by modified local oxidation of silicon process. This approach, based on a simple and reliable method, enable the organisation of Si nanowires with orientation on Si(001) substrates.