Graphene-stabilized copper nanoparticles as an air-stable substitute for silver and gold in low-cost ink-jet printable electronics

Norman A Luechinger, Evagelos K Athanassiou and Wendelin J Stark

Institute for Chemical and Bioengineering, Department of Chemistry and Applied

Biosciences, ETH Zurich, CH-8093 Zurich, Switzerland

NANOTECHNOLOGY   NOV 5 2008

 

The purpose of this study as can be surmised from the title was to find a cost effective alternative to the noble metal nanoparticles used in ink-jet printers that would be just as stable in air.  There are a few interesting concepts behind this.  The first is that most metals now used in bulk, have either an oxide coating or other coating keeping them from reacting.  Similar to this is how nanoparticles are capped to alter their properties, and specifically there has recently been copper and cobalt nanoparticles that have been capped with graphene.

 

Reducing flame synthesis was used to created the graphene passivated copper nanoparticles.  These particles were then characterized by microanalysis, thermogravimetric analysis, and X-ray diffraction.  These particles were then dissolved in water with a dispersion agent that also decreased the surface tension, and then sonicated to ensure that there were no aggregates.  This ink was then used, and the results tested for conductivity.

 

There were a number of findings in this study.  The copper and graphene nanoparticle ink was successfully used in a standard ink-jet printer.  The result produced an ink with a metallic luster, and enough conductivity to operate an LED.  However, there was not nearly as much conductivity as bulk copper.  The TGA analysis confirmed that the nanoparticles were inert to 165C.  This means that elements that normally would be too reactive to be used for nanoparticles, can be used with a graphene coating

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.

Quenching of photoconductivity in Fe doped CdS thin films prepared by spray pyrolysis technique

Badera N, Godbole B, Srivastava SB, et al.

APPLIED SURFACE SCIENCE Vol. 254 Issue: 21 p7042-7048, 2008

Purpose

The purpose of this study was to synthesize a CdS thin film material that is Fe doped prepared using spray pyrolysis technique, and then characterize it with X-ray diffraction, Raman spectroscopy, and AFM comparing the different levels of Fe doping.

Methods Used

The Cd_1−xFe_xS film was created using a spray pyrolysis technique where the amount of iron was altered within the range of {x: 0<x<.21}, and then the ratio was confirmed by energy dispersive X-ray analysis. The characterization was done using Raman spectroscopy, an AFM in contact mode, UV–vis spectroscopy, and conductivity measurements from a specially created apparatus.

Key Findings

The first interesting finding was from the x-ray diffraction. As the concentration of iron increased the cell volume of the crystal structure decreased. This was confirmed by the AFM where the hexagonal cells slowly converted into nanorods as the concentration of iron increased. Second is that the Raman peaks did not change with the iron doping. As the concentration of iron increased, so did the size of the nanorods from nanoneedle size, which the authors attributed to Ostwald ripening. Finally as the concentration of the iron increases the photoconductivity goes to zero. This property could be useful for sensors.

Photovoltaic cells fabricated by electrophoretic deposition of CdSe nanocrystals

Nathanawl J. Smith, Kevin J. Emmert, and Sandra J. Rosenthal. Photovoltaic cells fabricated by electrophoretic deposition of CdSe nanocrystals. Applied Physics Letters. 93. 043504 (2008)

Purpose of Study.

The purpose of this study was to show that electrophoretic deposition of CdSe nanocrystals on TiO₂ would be a viable alternative to previous methods. These previous methods were not as ideal because they took so much more time as in hours to days as compared to at most twenty minutes. This process is of interest because of the potential as a solar cell.

Methods/Procedures Used

The Nanocrystals were grown according to well known methods, isolated, and stored in hexanes. The nanocrystals were then deposed with two electrodes 1.5mm apart using 500 V potential. This layer of nanocrystals was deposited on a previously made substrate of indium tin oxide on glass. The cell was completed when an aluminum contact was evaporated on top of the nanocrystals.

Key Findings and Major Points

The success of the deposition was dependent on a few things. One was the conditions of the synthesis of the nanocrystals, and the other was the thermal charge of the solution. However the current of the deposition did behave in a simple decay regardless of how well the nanocrystals were deposited. One interesting thing that was found was that the film of nanocrystals was fully formed in the first minute of the deposition. The photo cell device resulting from this process did produce a current, but the efficiency was very small. However, this was a proof of concept study, and several things could be changed to increase efficiency.