Non-toxic, inexpensive, and durable are words which, in combination, seem downright magical and all are mentioned in a July 31, 2013 news item on Azonano,
Researchers in the University of Minnesota’s College of Science and Engineering and the National Renewable Energy Laboratory in Golden, Colo., have overcome technical hurdles in the quest for inexpensive, durable electronics and solar cells made with non-toxic chemicals. …
“Imagine a world where every child in a developing country could learn reading and math from a touch pad that costs less than $10 or home solar cells that finally cost less than fossil fuels,” said Uwe Kortshagen, a University of Minnesota mechanical engineering professor and one of the co-authors of the paper.
The July 30, 2013 University of Minnesota news release, which originated the news item, explains the discovery and the issues the researchers are addressing and it mentions, as many do these days, a patent,
The research team discovered a novel technology to produce a specialized type of ink from non-toxic nanometer-sized crystals of silicon, often called “electronic ink.” This “electronic ink” could produce inexpensive electronic devices with techniques that essentially print it onto inexpensive sheets of plastic.
“This process for producing electronics is almost like screen printing a number on a softball jersey,” said Lance Wheeler, a University of Minnesota mechanical engineering Ph.D. student and lead author of the research.
But it’s not quite that easy. Wheeler, Kortshagen and the rest of the research team developed a method to solve fundamental problems of silicon electronic inks.
First, there is the ubiquitous need of organic “soap-like” molecules, called ligands, that are needed to produce inks with a good shelf life, but these molecules cause detrimental residues in the films after printing. This leads to films with electrical properties too poor for electronic devices. Second, nanoparticles are often deliberately implanted with impurities, a process called “doping,” to enhance their electrical properties.
In this new paper, researchers explain a new method to use an ionized gas, called nonthermal plasma, to not only produce silicon nanocrystals, but also to cover their surfaces with a layer of chlorine atoms. This surface layer of chlorine induces an interaction with many widely used solvents that allows production of stable silicon inks with excellent shelf life without the need for organic ligand molecules. In addition, the researchers discovered that these solvents lead to doping of films printed from their silicon inks, which gave them an electrical conductivity 1,000 times larger than un-doped silicon nanoparticle films. The researchers have a provisional patent on their findings.
Here’s a link to and a citation for the published paper,
Hypervalent surface interactions for colloidal stability and doping of silicon nanocrystals by Lance M. Wheeler, Nathan R. Neale, Ting Chen, & Uwe R. Kortshagen. Nature Communications 4, Article number: 2197 doi:10.1038/ncomms3197 Published 29 July 2013
The paper is open access. The researchers also offer a brief video describing the process of making the nanocrystals,
Here’s the video description provided by the researchers (from http://www.youtube.com/watch?v=5Un_HnOl6lQ&feature=youtu.be),
This video shows how silicon nanocrystals are synthesized in a plasma reactor. Inert argon gas flows from the top of the reactor through a glass tube. Fifteen watts of radio frequency power is applied to the copper ring electrodes to ionize the argon gas and produce what is called a plasma. A gas containing silicon (silane) is injected into the reactive plasma environment to produce silicon nanocrystals. Though the plasma is energetic enough to produce these tiny crystals, the glass tube remains cool enough to touch. The plasma is a reactive environment used to produce silicon nanocrystals that can be applied to inexpensive, next-generation electronics.