Well‐Aligned Nanocylinder Formation in Phase‐Separated Metal‐Silicide–Silicon and Metal‐Germanide–Germanium Systems

Abstract

In recent years, there has been great interest in self-organized pattern systems, such as patterned structures of wellaligned rods embedded in a matrix. These systems have been important in many research fields since Turing [1] mathematically demonstrated that such pattern formation in reactiondiffusion systems could account for morphogenesis. Some examples are: the fish-skin textures seen in mathematical biology, [2] concentration patterns like the Belousov-Zhabotinsky reaction in chemical systems, [3] and the phase separation seen during the directional solidification of some inorganic alloy substances.[4] These patterns are created in nonlinear open systems with a diffusion factor, where substance injection and ejection are allowed. Well-aligned structures of phase-separated inorganic materials are particularly attractive for use in new devices and processes. Such materials can be classified into two systems: 1) one-directional solidification into bulk and 2) film growth in vacuum. These are nonlinear open systems as they accompany injection caused by melting or depositing substances, and accompany ejection caused by freezing substances in a plane of solidification. Various well-aligned structures with a micrometer scale like the NiAl-Mo, [5] NaCl-LiF, [6] MgO-CaF 2 , [7] and EuB 6 -ZrB 2 [8] systems have been created by using a one-directional solidification method. However, it is difficult to obtain nanometerscale structures in bulk systems by using this method. Film-growth methods have provided a successful means for synthesizing well-aligned nanometer-scale structures, which are sometimes smaller than that achievable by using lithography techniques. Fe-LaSrFeO 4 , [9] BaTiO 3 -CoFe 2 O 4 , [10] AlSi, [11,12] and Al-Ge [13] systems have already been examined by using conventional physical vapor-deposition (PVD) methods. These deposited films also consist of two phases. One phase forms well-aligned rods normal to the substrate and another phase forms a matrix. Because of the interaction of these two phases, new effects are expected in these nanometer-scale phase-separated materials. In addition, several silicides have been investigated as material candidates for next-generation semiconductor devices. [14] These silicides can create Schottky-barrier and p-n junctions with silicon or other silicides. [14,15,16] It has been reported that iron disilicide, in particular, has an absorption coefficient almost 100 times higher than silicon in the near-infrared region. [17] This indicates that these are promising materials for near-infrared detector devices. Our concept is to fuse the physical properties in each phase of the nanometer-scale phase-separated structures to create new detector devices and to display quantum effects from the interaction of each phase. If a narrow distribution of diameters and spacing of rods in these phase-separated films could be achieved, their physical properties would also be well-defined with low dispersion. In this Communication, we report the well-aligned structure formation in var...

Shape control of nickel nanostructures incorporated in amorphous carbon films: From globular nanoparticles toward aligned nanowires

“…55 The structure corresponding to Zone II has been reported in literature for nanocomposite material based on various systems such as Co/C, 25,28 metal/ silicon, [65][66][67] and metal/germanium. 67 Several theoretical studies were devoted to understand the growth mechanisms leading to the formation of such a structure with a cylindrical geometry in multiphase systems.…”

“…55 The structure corresponding to Zone II has been reported in literature for nanocomposite material based on various systems such as Co/C, 25,28 metal/ silicon, [65][66][67] and metal/germanium. 67 Several theoretical studies were devoted to understand the growth mechanisms leading to the formation of such a structure with a cylindrical geometry in multiphase systems. [68][69][70][71] An analogy between Ni/C and these multiphase systems can be established in order to construct a scenario explaining the driving forces leading to the formation of such cylindrical structures in our study.…”

Nanoscale precipitation patterns in carbon–nickel nanocomposite thin films: Period and tilt control via ion energy and deposition angle

“…25,33 Any considerable surface diffusion destroys the periodic precipitation pattern 33 and results in the formation of columnar structures. 19,20,22,23,33,43 During film growth, short-range ballistic displacement of atoms takes place in a near-surface region ͑ϳ1 -2 nm thick͒ due to hyperthermal ion impacts. 28,29 Thermodynamic forces lead to a precipitation of metal carbide or pure metal phase in the carbon matrix.…”

“…3,14,[16][17][18] Bulk diffusion during growth of physical-vapor and chemical-vapor deposited inorganic thin films is usually too small to initiate a Liesegang mechanism. Therefore, in this case structure evolution can occur only by an interplay of surface ad-atom mobility, surface reactions, and the coverage rate, [19][20][21][22][23] resulting usually in dispersed nanoprecipitates or columnar nanoparticles.…”

Compositionally modulated ripples during composite film growth: Three-dimensional pattern formation at the nanoscale

“…1(a)]. This distance is related to the magnitude of the surface diffusivity [54,55]. If phase separation was the driving mechanism for the pattern formation [28], the characteristic length of such a pattern would scale with the Ni diffusivity and would be of the order of L x or of the NP-NP distance in the columnar growth mode (∼4 nm).…”