In Situ Magnetic Field-Assisted Low Temperature Atmospheric Growth of GaN Nanowires via the Vapor–Liquid–Solid Mechanism

Abstract

We report the growth of GaN nanowires at a low temperature of 750 °C and at atmospheric pressure in a conventional chemical vapor deposition (CVD) setup via the vapor-liquid-solid mechanism with remarkable control of directionality and growth behavior by using an in situ magnetic field. Under typical growth conditions, without any magnetic field, the nanowires are severely twisted and kinked, and exhibit a high density of planar stacking defects. With increasing in situ magnetic field strength, the microstructural defects are found to decrease progressively, and quasi-aligned nanowires are produced. At an applied magnetic field strength of 0.80 T, near-vertical aligned straight and several micrometers long nanowires of average diameter of ~40 nm with defect-free microstructure are routinely produced. Photoluminescence measurements show that the relative intensity of the defect-related peaks in the visible region with respect to the near-band-edge emission continuously decrease with increase in the applied in situ magnetic field strength, ascribable to the magnetic field-assisted significant structural improvement of the wires. It is found out that the degree of agglomerative Ni droplet on Si is critically influenced by the surface tension driven by the magnetic force, which in turn determines the eventual properties of the nanowires.

Large Local‐Compressive Stress‐Induced Improvements in Piezoelectric Characteristics of Lead Zirconate Titanate Thin Films on a Ni Nanodots Array

“…Initially, a Ni thin‐film layer with different film thickness is deposited by direct current (DC) sputtering. An AlNiCo magnet was then placed on top of the Ni‐deposited substrate to produce a uniform array of nanodots by annealing the Ni thin layer at 750 °C under the influence of magnet . During the annealing, a Ga gaseous source is provided to facilitate the consolidation process into liquid droplets at the temperature of 750 °C.…”

“…The final film/electrode structure corresponds to Pt/Nb‐doped PZT/Ir/TiW/Ni nanodots/SiO 2 /Si. The role of magnet used here provides uniform external magnetic field strength to facilitate consolidation of the Ni nanodots at high temperature, as reported by our group . The existence of Ni nanodots incurs extra compressive stress in the initial stage of film growth due to an enormous difference of ≈94% in thermal expansion coefficient (TEC) between the PZT film and Ni.…”

“…As published previously for the preparation of Ni catalysts, a 10 or 30 nm thick Ni layer was first deposited on the SiO 2 (300 nm)/Si (100) substrate by DC magnetron sputtering as a source layer for Ni nanodot arrays. The deposition of Ni was conducted at a working pressure of 15 mTorr and a DC power of 100 W with the flowing Ar gas at a rate of 30 SCCM.…”

“…[5,6] Because the properties of PZT depend strongly on both intrinsic (stoichiometry and orientation) and processing-related (phase purity and defect density) parameters, a lot of noticeable studies have been recently introduced to chase the requirements for coming competitive piezoelectric devices based on PZT. [19] The existence of Ni nanodots incurs extra compressive stress in the initial stage of film growth due to an enormous difference of ≈94% in thermal expansion coefficient (TEC) between the PZT film and Ni. The role of magnet used here provides uniform external magnetic field strength to facilitate consolidation of the Ni nanodots at high temperature, as reported by our group.…”

Nanostructure Formation by controlled dewetting on patterned substrates: A combined theoretical, modeling and experimental study

“…The SSD technique has typically been used to fabricate nanodot arrays with diameter from tens to hundreds nanometers, which are important elements in a variety of nanodots-based applications, including high-density magnetic recording media12, solar cells34, catalysts for nanowire growth56, and many plasmonic devices, such as plasmon-resonance wave guides78, plasmon-enhanced photovoltaic devices910, plasmonic LEDs1112, and biosensors13. Our recent work14 showed that SSD can also be used to fabricate nano-aperture arrays with high yield and at low costs.…”