Self-organization Of Nanowires Research Articles

Self-organization and tunable characteristic lengths of two-dimensional hexagonal superlattices of nanowires directly grown on substrates

The organization of nano-objects on macroscopic surfaces is a key challenge for the technological improvement and implementation of nanotechnologies. For achieving operational functions, it is required to assemble nano-objects as controllable building blocks in highly ordered superstructures. Herein, we demonstrate the growth and self-organization of metallic nanowires on surfaces into hexagonal superlattices with tunable characteristic lengths depending of the stabilizing surfactants employed. Starting from a reacting mixture containing a Pt(111) substrate, a Co organometallic precursor, an amine, and an acid dissolved in a solvent, we quantify the structural evolution of superlattices of vertical single-crystalline Co nanowires on Pt, using a combined analysis of small angle neutron scattering, transmission, and scanning electron microscopies. We show the concerted steps of a spontaneous growth and self-organization of the nanowires into two-dimensional (2D) hexagonal lattice on Pt, at intervals starting from a few hours of reaction to a highly ordered superlattice at longer times. Furthermore, it is shown that apart from long-chain acid and long-chain aliphatic amine pairs used as stabilizers, the combination of a long-chain aliphatic and a short-chain aromatic ligand in the synthesis can also be employed for the nanowire superlattices development. Interestingly, the possibility to employ different pairs allows quantitative modulation of the nanowire arrays, such as the interwire distance and the packing fraction.

A Way to New Smart Materials – Hierarchical 3D Structures Produced Via Self-Organization of Nanowires

Galina Strukova, Gennady Strukov The beauty of these pictures is intriguing and fascinating by its asymmetric, exquisite and intricate pattern. What is it? Is it a product of a novel computer program or photographs of fine creations of nature? Neither statement is true. In fact, these are not pictures, but images of metal samples made with an electron microscope. Only some color is added to the images to emphasize their resemblance to natural objects of our macroworld: seashells, jelly-fish, leaves of exotic plants. The size of the samples is varied in micron scale. They are produced via self-organization of nano-sized (millionth of a millimeter) wires growing on porous membranes under the action of electric current pulses. This is how such volumetric (3D) sculptures are described in scientific journals [1- 3] along with the experimental conditions for their reproduction, i.e., the conditions of the process (electrolyte composition, porous membrane, pulsed current mode) are specified, when growing nanowires organize themselves in an inexplicable fashion into “sculptures” that show perfect resemblance to natural creations. The authors have managed to isolate and photograph them with a modern electron microscope. Besides, they have proved that the internal structure of this metallic “seashells” is a volumetric multilayer network woven by nano-sized wires. Such antenna-like samples are expected to find application in nanotechnology as new materials for different applications. Now we produce such “sculptures” from various metals “by order”, examine their magnetic properties, study their interaction with plasma and focused electron beam, look for a field of their application and admire their elegant forms. However, it is still a riddle. Why do they so closely resemble shells and leaves? Does this mysterious self-organization have anything in common with formation of plant leaves and seashells? [1] J of Bionic Engineering 10 (2013) 368–376 [2] Materials Today 16 (2013) 98–99 , [3] Materials Letters, 128 (2014) 212-215. Figure 1

A Way to New Smart Materials – Hierarchical 3D Structures Produced Via Self-Organization of Nanowires

The beauty of these pictures is intriguing and fascinating by its asymmetric, exquisite and intricate pattern. What is it? Is it a product of a novel computer program or photographs of fine creations of nature? Neither statement is true. In fact, these are not pictures, but images of metal samples made with an electron microscope. Only some color is added to the images to emphasize their resemblance to natural objects of our macroworld: seashells, jelly-fish, leaves of exotic plants. The size of the samples is varied in micron scale. They are produced via self-organization of nano-sized (millionth of a millimeter) wires growing on porous membranes under the action of electric current pulses. This is how such volumetric (3D) sculptures are described in scientific journals [1- 3] along with the experimental conditions for their reproduction, i.e., the conditions of the process (electrolyte composition, porous membrane, pulsed current mode) are specified, when growing nanowires organize themselves in an inexplicable fashion into “sculptures” that show perfect resemblance to natural creations. The authors have managed to isolate and photograph them with a modern electron microscope. Besides, they have proved that the internal structure of this metallic “seashells” is a volumetric multilayer network woven by nano-sized wires. Such antenna-like samples are expected to find application in nanotechnology as new materials for different applications. Now we produce such “sculptures” from various metals “by order”, examine their magnetic properties, study their interaction with plasma and focused electron beam, look for a field of their application and admire their elegant forms. However, it is still a riddle. Why do they so closely resemble shells and leaves? Does this mysterious self-organization have anything in common with formation of plant leaves and seashells? [1] J of Bionic Engineering 10 (2013) 368–376 [2] Materials Today 16 (2013) 98–99 , [3] Materials Letters, 128 (2014) 212-215. Figure 1

Fabrication of a Au Nanoporous Film by Self-Organization of Networked Ultrathin Nanowires and Its Application as a Surface-Enhanced Raman Scattering Substrate for Single-Molecule Detection

Due to its demonstrated usefulness in fields such as trace analysis, biodiagnosis, and in vivo study, surface-enhanced Raman scattering (SERS) has received renewed interest in recent years. Development of SERS substrates is of great importance as the SERS intensity and reproducibility depend strongly on the SERS substrates. In this paper we report the fabrication of Au nanoporous film (NPFs) by self-organization of networked ultrathin Au nanowires for use as SERS substrates. The acquired Au NPFs display controllable thickness, low relative density, and considerable specific surface area. Furthermore, this self-organization of nanowires not only provides abundant junctions between nanowires, 5-20 nm nanopores, and three-dimensional nanowells, but also makes nanopores/nanogaps down to 1-2 nm. These nanoscale characteristics result in a high spatial density of hotspots with Raman enhancement factors up to 10(9). Combined with the uniformity and high purity, our Au NPF provides high-quality substrates for SERS sensing.

Why self-catalyzed nanowires are most suitable for large-scale hierarchical integrated designs of nanowire nanoelectronics

Nanowires are grown by a variety of mechanisms, including vapor-liquid-solid, vapor-quasiliquid-solid or vapor-quasisolid-solid, oxide-assisted growth, and self-catalytic growth (SCG) mechanisms. A critical analysis of the suitability of self-catalyzed nanowires, as compared to other nanowires, for next-generation technology development has been carried out. Basic causes of superiority of self-catalyzed (SCG) nanowires over other nanowires have been described. Polytypism in nanowires has been studied, and a model for polytypism has been proposed. The model predicts polytypism in good agreement with available experiments. This model, together with various evidences, demonstrates lower defects, dislocations, and stacking faults in SCG nanowires, as compared to those in other nanowires. Calculations of carrier mobility due to dislocation scattering, ionized impurity scattering, and acoustic phonon scattering explain the impact of defects, dislocations, and stacking faults on carrier transports in SCG and other nanowires. Analyses of growth mechanisms for nanowire growth directions indicate SCG nanowires to exhibit the most controlled growth directions. In-depth investigation uncovers the fundamental physics underlying the control of growth direction by the SCG mechanism. Self-organization of nanowires in large hierarchical arrays is crucial for ultra large-scale integration (ULSI). Unique features and advantages of self-organized SCG nanowires, unlike other nanowires, for this ULSI have been discussed. Investigations of nanowire dimension indicate self-catalyzed nanowires to have better control of dimension, higher stability, and higher probability, even for thinner structures. Theoretical calculations show that self-catalyzed nanowires, unlike catalyst-mediated nanowires, can have higher growth rate and lower growth temperature. Nanowire and nanotube characteristics have been found also to dictate the performance of nanoelectromechanical systems. Defects, such as stacking faults, dislocations, and nanopipes, which are common in catalyst-mediated nanowires and nanotubes, adversely affect the efficiency of nanowire (nanotube) nanoelectro-mechanical devices. The influence of seed-to-seed distance and collection area radius on the self-catalyzed, self-aligned nanowire growths in large arrays of seeds has been examined. A hypothesis has been presented for this. The present results are in good agreement with experiments. These results suggest that the SCG nanowires are perhaps the best vehicles for revolutionary advancement of tomorrow’s nanotechnology.

Self-Organized Pattern Formation in Porous Silicon Using a Lattice Model with Quantum Confinement Effect

A spatial structure of porous silicon formed by anodization was simulated using a lattice model considering the quantum confinement effect. Calculation starting from a random distribution of null cells at the surface yielded the final granular, columnar or flat surface structures depending on the magnitude of the anodizing bias voltage in concordance with previously reported structures. Our calculations suggest that columnar and dendritic structures can be produced in degenerately doped p-type Si wafers by self-organization of nanowires with quantum confinement effects.