Laser direct written silicon nanowires for electronic and sensing applications

Silicon nanowires are promising building blocks for high-performance electronics and chemical/biological sensing devices due to their ultra-small body and high surface-to-volume ratios. However, the lack of the ability to assemble and position nanowires in a highly controlled manner still remains an obstacle to fully exploiting the substantial potential of nanowires. Here we demonstrate a one-step method to synthesize intrinsic and doped silicon nanowires for device applications. Sub-diffraction limited nanowires as thin as 60 nm are synthesized using laser direct writing in combination with chemical vapor deposition, which has the advantages of in-situ doping, catalyst-free growth, and precise control of position, orientation, and length. The synthesized nanowires have been fabricated into field effect transistors (FETs) and FET sensors. The FET sensors are employed to detect the proton concentration (pH) of an aqueous solution and highly sensitive pH sensing is demonstrated. Both top- and back-gated silicon nanowire FETs are demonstrated and electrically characterized. In addition, modulation-doped nanowires are synthesized by changing dopant gases during the nanowire growth. The axial p-n junction nanowires are electrically characterized to demonstrate the diode behavior and the transition between dopant levels are measured using Kelvin probe force microscopy

Sub-diffraction Laser Synthesis of Silicon Nanowires

We demonstrate synthesis of silicon nanowires of tens of nanometers via laser induced chemical vapor deposition. These nanowires with diameters as small as 60 nm are produced by the interference between incident laser radiation and surface scattered radiation within a diffraction limited spot, which causes spatially confined, periodic heating needed for high resolution chemical vapor deposition. By controlling the intensity and polarization direction of the incident radiation, multiple parallel nanowires can be simultaneously synthesized. The nanowires are produced on a dielectric substrate with controlled diameter, length, orientation, and the possibility of in-situ doping, and therefore are ready for device fabrication. Our method offers rapid one-step fabrication of nano-materials and devices unobtainable with previous CVD methods

Laser direct writing of silicon field effect transistor sensors

We demonstrate a single step technique to fabricate silicon wires for field effect transistor sensors. Boron-doped silicon wires are fabricated using laser direct writing in combination with chemical vapor deposition, which has the advantages of precise control of position, orientation, and length, and in situ doping. The silicon wires can be fabricated to have very rough surfaces by controlling laser operation parameters, and thus, have large surface areas, enabling high sensitivity for sensing. Highly sensitive pH sensing is demonstrated. We expect our method can be expanded to the fabrication of various sensing devices beyond chemical sensors. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4794147

Yttrium Oxyfluoride Coatings Deposited by Suspension Plasma Spraying Using Coaxial Feeding

The recently discovered yttrium oxyfluoride (YOF) coating has been found to be a highly promising plasma-resistant material which can be coated onto the inner wall of the dry etching chambers used in the manufacturing of the three-dimensional stacking circuits of semiconductors, such as vertical NAND flash memory. Here, the coating behavior of the YOF coating which was deposited by suspension plasma spraying was investigated using a high-output coaxial feeding method. Both the deposition rate and density of YOF coatings increased with the plasma power, which was determined by the gas ratio of Ar/H2/N2 and the arc current. The coating thicknesses were 58 ± 3.4, 25.8 ± 2.1, 5.6 ± 0.6, and 0.93 ± 0.4 µm at plasma powers of 112, 83, 67, and 59 kW, respectively, for 20 scans with a feeding rate of the suspension at 0.045 standard liters per minute (slm). The porosities were 0.15% ± 0.01%, 0.25% ± 0.01%, and 5.50% ± 0.40% at corresponding plasma powers of 112, 83, and 67 kW. High-resolution X-ray diffraction (HRXRD) shows that the major and minor peaks of the coatings which were deposited at 112 kW stem from trigonal YOF and cubic Y2O3, respectively. Increasing the flow rate of the atomizing gas from 15 slm to 30 slm decreased the porosity of the YOF coating from 0.22% ± 0.03% to 0.07% ± 0.03%. The Vickers hardness of the YOF coating containing some Y2O3 deposited at 112 kW was 550 ± 70 HV

Laser direct synthesis of graphene on quartz

We demonstrate a laser-based technique to directly synthesize few layer graphene on quartz substrates without using any metal catalyst. In our approach, a photoresist S-1805 (from Shipley Comp.) film coated on quartz wafers was heated, and then decomposed, by irradiation of a continuous-wave laser. The carbon atoms from the photoresist were dissolved in the molten quartz, and then extracted to form graphene when the temperature of the quartz was decreased. Raman spectroscopy shows the as-produced graphene is two to three layers thick. This laser-based method will provide a new approach and platform for applications of graphene-based devices. (C) 2012 Elsevier Ltd. All rights reserved