Microwave plasma chemical vapor deposition of nano-composite C/Pt thin-films

Marek Marcinek, Xiangyun Song, Robert Kostecki, Electrochemistry Communications 9 (2007) 1739–1743

Purpose: To present a new, one step method of synthesizing nano-composite C/Pt thin films using MPCVD.  The new method is boasted to be inexpensive, quick and easy.   The films are also said to be able to uniformly distribute the Pt nano-particles in the carbon substrate.

Methods: Pt precursor was placed on one end of a slide and HOPG was placed 5mm away from the Pt precursor on the same glass slide.  This slide was located in a chamber which was then purged with Ar, which was in turn positioned close to a magnetron.  The magnetron generated Ar plasma such that the hot edge of the plasma was near the Pt precursor and the cold edge near the HOPG (substrate).  The microwave radiation caused the Ar plasma to suddenly discharge which evaporated the Pt precursor.  This lead to the deposition of the Pt in the HOPG substrate, creating a nano-composite film.

Key Findings:

Found to be reproducable using the same precursor and deposition times.

The broad peaks in the Raman spectrum result from the sp2 hybridized carbons.

The thickness of the films is uniform for similar conditions: ~2 micrometers.

Definitions:

MPCVD: microwave plasma chemical vapor deposition

HOPG: highly-oriented, pyrolitic graphite

Ordered Arrays of ZnO Nanorods Grown on Perodically Polarity-Inverted Surfaces

November 4, 2008

Sang Hyun Lee, Tsutomu Minegishi, Jin Sub Park, Seung Hwan Park, Jun-Seok Ha, Hyo-Jong Lee, Hyun-Jae Lee, Sungmo Ahn, Jaehoon Kim, Heonsu Jeon, and Takafumi Yao

Nano Letters  2008, 8, 2419-2422

Purpose

The authors present a method to create periodically polarity inverted (PPI) ZnO templates using molecular beam epitaxy (MBE), which can lead to the synthesis of ZnO nanorods. The goal is to study and understand how to control the size and shape of these 1-D nanostructures for use in electronic devices.  

Methods

Polar surfaces were produced by utilizing ionic crystals that consist of alternating layers of oppositely charged ions stacked perpendicular to the polar surfaces. In short, a Zn-polar ZnO film was produced on a sapphire substrate with a MgO buffer layer using MBE. After using lithography and etching with piranha, MBE is used again to create Zn-polar and O-polar regions. After deposition of an Au film, ZnO nanorods are grown on the Zn-polar surface.

 

Key Findings

·The controlled polar surfaces allow for the fabrication of highly ordered ZnO nanorods with submicron spacing

·The polarity of the template determines the position, density, and diameter of the ZnO nanorods

·Each of the nanorods have a unique piezoelectric response to an applied voltage

 

Definitions

MBE – Molecular beam epitaxy

 

Nonthermal plasma synthesis of size-controled, monodisperse, freestanding germanium nanocrystals

Appl. Phys. Lett. 91, 093119 (2007)

Authors: Ryan Gresback, Zachary Holman, and Uwe Koortshagen, Department of Machanical Engineering, University of Minnesota

The purpose of this study was to synthesize monodisperse freestanding germanium nanoparticles the same way that they has previously synthesized silicon nanocrystals. Germanium nanocrystals were chosen as they have a smaller band gap, and exhibit stronger quantum confinement then silicon.

These particles were synthesized by flowing gases through a flow through, nonthermal plasma reactor with a pathlength of five centimeters through the plasma. To create the reaction mixture argon was bubbled through GeCl₄ at 200kPa. Additional argon and hydrogen gas were added to the mixture as it entered the reactor. The argon was added to adjust the flow rate and the hydrogen gas to react with the chlorine from the GeCl₄. The ratio of flow was held at 220:20:1 for Ar:H₂:GeCl₄. The size of the nanocrystals was dependant on how long they remained in the reactor. TEM was used on some of the particles coming out of the reactor to determine the size and shape of the nanocrystals. Crystalinity was also determined by using XRD.

One key finding was that the nanocrystals created by this process had smaller size and shape distribution than most processes reported in literature. Also the nanocrystals did not tend to agglomerate due to the plasma environment that they were created in. Another key finding was that the crystalinity of the nanocrystals could be changed by the amount of power imputed into the plasma. 60 W gave an amorphous product and 90 W gave crystalline nanocrystals according to the x-ray diffraction patterns. Finally, they reported their yield to be in the 10s of milligrams per hour.

Nanoimprint lithography patterns with a vertically aligned nanoscale tubular carbon structure

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Youn-Su Kim, Kyeongmi Lee, Jae Suk Lee, Gun Young Jung,

Won Bae Kim. Nanotechnology 2008, 19, 365305.

Purpose:

The authors present a new method using a carbon array as a mold for nanoimprint lithography (NIL) .

Methods:

The carbon array was grown inside a template layer of anodic aluminum oxide (AAO). The AAO exhibits a regularly and vertically alligned pore structure. 1-D carbon structures are then deposited on the surface by thermal chemical vapor deposition. The surface layer is then removed via iron milling, and then the AAO was etched with phosphoric acid.

Key Points:

The method shown enables the fabrication of highly regular, vertically alligned tubular nanostructures for use as molds in nanoimprint lithography. The method is also inexpensive compareed to e-beam and other similar processes. It also could be potentially used in the manufacture of photonic crystals.