The transition from linear to helical growth of amorphous boron carbide nanowires has been examined with high-resolution transmission electron microscopy. Based on the observed changes of the iron catalyst at the transition point from linear to helical growth, a model of helical growth of solid nanowires has been developed based on the work of adhesion of the metallic catalyst to the tip of the nanowire. This model demonstrates that contact angle anisotropy at the catalyst/wire interface drives helical growth. The anisotropy is introduced when the radius of the droplet (R) exceeds the radius of the nanowire (ρ), and the center of mass of the metal droplet is displaced laterally from the central axis of the nanowire.

Amorphous silicon carbide nanosprings, as well as biphase (crystalline core/amorphous sheath) helical nanowires, have been synthesized by plasma enhanced chemical vapor deposition. Both variants grow via the vapor−liquid−solid mechanism. The formation of the amorphous silicon carbide nanosprings is explained in terms of the contact angle anisotropy model initially proposed to explain the formation of amorphous boron carbide nanosprings. A modified contact angle anisotropy model, where the presence of temperature gradients within the catalyst are imposed, has been proposed to explain the formation of the biphase helical nanowires. The basis for this model is that the crystalline core acts to pin the catalyst, thereby prohibiting nanospring formation. The model is supported by the experimental observation of a transition to nanospring growth at the point of extinction of the crystalline core of a linear biphase nanowire at a position where the catalyst is off-center with respect to the axis of the growth direction.

Nanomechanical bending behavior and elastic modulus of silver nanowires (65–140nm∅) suspended across silicon microchannels were investigated using digital pulsed force mode (DPFM) atomic force microscopy through coincident imaging and force profiling. Deflection profiles analyzed off-line demonstrate the role of bending nanowire shape and symmetry in experimentally determining boundary conditions, eliminating the need to rely on isolated midpoint bending measurements and the usual assumptions for supported-end behavior. Elastic moduli for as-prepared silver nanowires ranged from 80.4±5.3to96.4±12.8GPa, which met or exceeded the literature values for bulk silver. The calculated moduli were based on classic modeling, both with one-dimensional analytical solutions and three-dimensional finite element analysis. Modeling results indicate that the classic models are accurate as long as the boundary conditions are not arbitrarily assumed but directly confirmed by data analysis. DPFM also facilitated the experimental determination of sample gauge lengths from images and bending profiles.

Nanosprings are a new form of nanowires that have potential applications in nanoelectronics, nanomechanics, and nanoelectromechanical systems. In this review we will examine the growth mechanism of these novel nanostructures. The synthesis of nanowires by the vapour–liquid–solid growth mechanism, first proposed by Wagner and Ellis, will be explored and then extended to the development of a model to explain the formation of nanosprings.

The electronic structure of strained ultra-thin and thin films of Gd grown on a corrugated Mo(112) surface are described. Gadolinium overlayers order at a coverage of monolayers forming a LEED pattern. At this coverage an interface state of symmetry is formed at a binding energy of at the surface Brillouin zone centre . The effective mass of this interface state was determined to be , in both orthogonal directions along the nearly square reduced Brillouin zone. For thicker Gd films of approximately 3 to 10 ML thickness, the corresponding gadolinium state switches symmetry to the representation (Gd or 6s character) and has a much larger effective mass. The overlayer forms a rectangular surface Brillouin zone resembling the hcp surface. Gadolinium films thicker than approximately 10 ML form strained hexagonal ordered films also with substantial misfit dislocations. The strain of the thin hexagonal ordered Gd films is reflected by a reduced Brillouin zone size along by approximately 4% with respect to the less strained Gd overlayers on W(110) and Gd(0001) single crystals. The induced strain severely alters the band structure of the Gd 5d/6s bulk bands, which disperse in the opposite direction relative to the corresponding bands of the relaxed Gd(0001) structure. The surface of the strained hexagonal fcc (111) or hcp (0001) Gd films forms a localized state of symmetry (Gd or 6s character) at approximately 0.7 eV binding energy. There is little observed strain relief within the Gd films up to approximately 150 Å film thickness.