Nanotechnology Now

Our NanoNews Digest Sponsors

Heifer International

Wikipedia Affiliate Button

Home > Press > Probing dopant distribution: Finding by Berkeley Lab Researchers at the Molecular Foundry Opens the Door to Better Doping of Semiconductor Nanocrystals

Schematic representation of plasmonic nanocrystals with (a) uniform and (b) surface-segregated dopant distributions. In (a), most of the electron cloud is scattered from ionized impurities (green); in (b), most of the electron cloud is oscillating away from the impurities.
Schematic representation of plasmonic nanocrystals with (a) uniform and (b) surface-segregated dopant distributions. In (a), most of the electron cloud is scattered from ionized impurities (green); in (b), most of the electron cloud is oscillating away from the impurities.

Abstract:
The icing on the cake for semiconductor nanocrystals that provide a non-damped optoelectronic effect may exist as a layer of tin that segregates near the surface.

Probing dopant distribution: Finding by Berkeley Lab Researchers at the Molecular Foundry Opens the Door to Better Doping of Semiconductor Nanocrystals

Berkeley, CA | Posted on May 7th, 2014

One method of altering the electrical properties of a semiconductor is by introducing impurities called dopants. A team led by Delia Milliron, a chemist at Berkeley Lab's Molecular Foundry, a U.S Department of Energy (DOE) national nanoscience center, has demonstrated that equally important as the amount of dopant is how the dopant is distributed on the surface and throughout the material. This opens the door for engineering the distribution of the dopant in order to control what wavelength the material will absorb and more generally how light interacts with the nanocrystals.

"Doping in semiconductor nanocrystals is still an evolving art," says Milliron. "Only in the last few years have people begun to observe interesting optical properties as a result of introducing dopants to these materials, but how the dopants are distributed within the nanocrystals remains largely unknown. What sites they occupy and where they are situated throughout the material greatly influences optical properties."

Milliron's most recent claim to fame, a "smart window" technology that not only blocks natural infrared (IR) radiation while allowing the passage of visible light through transparent coated glass, but also allows for independent control over both kinds of radiation, relies on a doped semiconductor called indium tin oxide (ITO).

ITO, in which tin (the dopant) has replaced some of the indium ions in indium oxide (the semiconductor), has become the prototypical doped semiconductor nanocrystal material. It is used in all kinds of electronic devices, including touchscreens displays, smart windows and solar cells.

"The exciting thing about this class of materials is that the dopants are able to introduce free electrons that form at high density within the material, which makes them conducting and thus useful as transparent conductors," says Milliron

But the same electrons cause the materials to be plasmonic in the IR part of the spectrum. This means that light of IR wavelength can be resonant with free electrons in the material: the oscillating electric fields in the light resonate and can cause absorption.

"[These materials] can absorb IR light in a way that's tunable by adjusting the doping, while still being transparent to natural visible light. A tunable amount of absorption of IR light allows you to control heating. For us, that's the driving application," explains Milliron.

Until now, adjustments have been made by changing the amount of dopant in the semiconductor. Puzzled by studies in which optical properties did not behave as expected, Milliron and University of California (UC) Berkeley PhD candidate Sebastien Lounis looked to x-ray photoelectron spectroscopy to probe electrons near the surface of the ITO samples and investigate the distribution of elements within the samples at the Stanford Synchrotron Radiation Lightsource (SSRL).

The SSRL uses a tuneable beam of photons to excite electrons inside the material. If the electrons are close enough to the surface, they can sometimes be emitted and collected by a detector. These electrons provide information about the properties of the material, including the ratio of the amounts of different elements like indium and tin in ITO. Increasing the energy of the x-ray beam shows how the composition of tin and indium changes as one moves deeper into the sample. Ultimately, the spectroscopy technique allowed Milliron and her team to probe the doping distribution as a function of distance from the nanocrystals' surface.

Studies of two sets of samples allowed them to correlated tin distribution with optical properties, and showed that the shape and wavelength of plasmon absorption depended on tin distribution. The tin segregated on the surface showed reduced activation of dopants and symmetric plasmon resonances, with no damping caused by the dopants.

"When the tin sits near the surface, it interacts only weakly with the majority of the free electrons," explains Lounis. "This gives us the benefits of doping without some of drawbacks."

"Now that we know how to probe, we can go after targeted design features for particular applications," concludes Milliron. Deliberate placement of dopants by design provides a new tool for "dialing in plasmonic materials to do exactly what we want in terms of interaction with light."

A paper on this research has been accepted for publication in the Journal of the American Chemical Society (JACS) in April 2014. The paper is titled "The influence of dopant distribution on the plasmonic properties of indium tin oxide nanocrystals" with Lounis as the lead author and Milliron as the corresponding author. Other authors are Evan Runnerstorm, Amy Bergerud, and Dennis Nordlund.

This research was primarily supported by the DOE Office of Science.

####

About DOE/Lawrence Berkeley National Laboratory
Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit www.lbl.gov.

For more information, please click here

Contacts:
Rachel Berkowitz
(510) 486-7254

Copyright © DOE/Lawrence Berkeley National Laboratory

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related Links

Download article:

Related News Press

News and information

New nano approach could cut dose of leading HIV treatment in half February 24th, 2017

Atom-scale oxidation mechanism of nanoparticles helps develop anti-corrosion materials February 24th, 2017

Atomic force imaging used to study nematodes: KFU bionanotechnology lab (head - Dr. Rawil Fakhrullin) has obtained 3-D images of nematodes' cuticles February 23rd, 2017

Particle Works creates range of high performance quantum dots February 23rd, 2017

Chemistry

Molecular phenomenon discovered by advanced NMR facility: Cutting edge technology has shown a molecule self-assembling into different forms when passing between solution state to solid state, and back again - a curious phenomenon in science - says research by the University of Wa February 22nd, 2017

In-cell molecular sieve from protein crystal February 14th, 2017

Nano-level lubricant tuning improves material for electronic devices and surface coatings February 11th, 2017

Physics

Breakthrough with a chain of gold atoms: In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport February 20th, 2017

Research reveals novel quantum state in strange insulating materials February 14th, 2017

Laboratories

Francis Alexander Named Deputy Director of Brookhaven Lab's Computational Science Initiative February 16th, 2017

Govt.-Legislation/Regulation/Funding/Policy

Atom-scale oxidation mechanism of nanoparticles helps develop anti-corrosion materials February 24th, 2017

Atomic force imaging used to study nematodes: KFU bionanotechnology lab (head - Dr. Rawil Fakhrullin) has obtained 3-D images of nematodes' cuticles February 23rd, 2017

Molecular phenomenon discovered by advanced NMR facility: Cutting edge technology has shown a molecule self-assembling into different forms when passing between solution state to solid state, and back again - a curious phenomenon in science - says research by the University of Wa February 22nd, 2017

'Lossless' metamaterial could boost efficiency of lasers and other light-based devices February 20th, 2017

Chip Technology

GLOBALFOUNDRIES Announces Availability of 45nm RF SOI to Advance 5G Mobile Communications: Optimized RF features deliver high-performance solutions for mmWave beam forming applications in 5G smartphones and base stations February 22nd, 2017

Strem Chemicals and Dotz Nano Ltd. Sign Distribution Agreement for Graphene Quantum Dots Collaboration February 21st, 2017

Particles from outer space are wreaking low-grade havoc on personal electronics February 19th, 2017

Liquid metal nano printing set to revolutionize electronics: Creating integrated circuits just atoms thick February 18th, 2017

Discoveries

New nano approach could cut dose of leading HIV treatment in half February 24th, 2017

Atom-scale oxidation mechanism of nanoparticles helps develop anti-corrosion materials February 24th, 2017

Atomic force imaging used to study nematodes: KFU bionanotechnology lab (head - Dr. Rawil Fakhrullin) has obtained 3-D images of nematodes' cuticles February 23rd, 2017

Molecular phenomenon discovered by advanced NMR facility: Cutting edge technology has shown a molecule self-assembling into different forms when passing between solution state to solid state, and back again - a curious phenomenon in science - says research by the University of Wa February 22nd, 2017

Materials/Metamaterials

Atom-scale oxidation mechanism of nanoparticles helps develop anti-corrosion materials February 24th, 2017

EmTech Asia breaks new barriers with potential applications of space exploration with NASA and MIT February 22nd, 2017

Molecular phenomenon discovered by advanced NMR facility: Cutting edge technology has shown a molecule self-assembling into different forms when passing between solution state to solid state, and back again - a curious phenomenon in science - says research by the University of Wa February 22nd, 2017

Tiny nanoclusters could solve big problems for lithium-ion batteries February 21st, 2017

Announcements

New nano approach could cut dose of leading HIV treatment in half February 24th, 2017

Atom-scale oxidation mechanism of nanoparticles helps develop anti-corrosion materials February 24th, 2017

Atomic force imaging used to study nematodes: KFU bionanotechnology lab (head - Dr. Rawil Fakhrullin) has obtained 3-D images of nematodes' cuticles February 23rd, 2017

Particle Works creates range of high performance quantum dots February 23rd, 2017

Interviews/Book Reviews/Essays/Reports/Podcasts/Journals/White papers

New nano approach could cut dose of leading HIV treatment in half February 24th, 2017

Atom-scale oxidation mechanism of nanoparticles helps develop anti-corrosion materials February 24th, 2017

Molecular phenomenon discovered by advanced NMR facility: Cutting edge technology has shown a molecule self-assembling into different forms when passing between solution state to solid state, and back again - a curious phenomenon in science - says research by the University of Wa February 22nd, 2017

Tiny nanoclusters could solve big problems for lithium-ion batteries February 21st, 2017

Energy

Strem Chemicals and Dotz Nano Ltd. Sign Distribution Agreement for Graphene Quantum Dots Collaboration February 21st, 2017

'Lossless' metamaterial could boost efficiency of lasers and other light-based devices February 20th, 2017

In-cell molecular sieve from protein crystal February 14th, 2017

NREL research pinpoints promise of polycrystalline perovskites February 8th, 2017

NanoNews-Digest
The latest news from around the world, FREE



  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project