Nanotechnology Now

Our NanoNews Digest Sponsors





Heifer International

Wikipedia Affiliate Button


android tablet pc

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

Organometallics welcomes new editor-in-chief: Paul Chirik, Ph.D. July 22nd, 2014

The Hiden EQP Plasma Diagnostic with on-board MCA July 22nd, 2014

Iran to Hold 3rd Int'l Forum on Nanotechnology Economy July 22nd, 2014

Nanometrics Announces Upcoming Investor Events July 22nd, 2014

Laboratories

NIST shows ultrasonically propelled nanorods spin dizzyingly fast July 22nd, 2014

Sono-Tek Corporation Announces New Clean Room Rated Laboratory Facility in China July 18th, 2014

Fundamental Chemistry Findings Could Help Extend Moore’s Law: A Berkeley Lab-Intel collaboration outlines the chemistry of photoresist, enabling smaller features for future generations of microprocessors July 15th, 2014

Chemistry

Oregon chemists eye improved thin films with metal substitution: Solution-based inorganic process could drive more efficient electronics and solar devices July 21st, 2014

Fundamental Chemistry Findings Could Help Extend Moore’s Law: A Berkeley Lab-Intel collaboration outlines the chemistry of photoresist, enabling smaller features for future generations of microprocessors July 15th, 2014

Physics

Physicists Use Computer Models to Reveal Quantum Effects in Biological Oxygen Transport: The team solved a long-standing question by explaining why oxygen – and not deadly carbon monoxide – preferably binds to the proteins that transport it around the body. July 17th, 2014

Flashes of light on the superconductor: Using light to modulate the properties of a copper-based superconductor July 15th, 2014

Govt.-Legislation/Regulation/Funding/Policy

NIST shows ultrasonically propelled nanorods spin dizzyingly fast July 22nd, 2014

Penn Study: Understanding Graphene’s Electrical Properties on an Atomic Level July 22nd, 2014

Oregon chemists eye improved thin films with metal substitution: Solution-based inorganic process could drive more efficient electronics and solar devices July 21st, 2014

More than glitter: Scientists explain how gold nanoparticles easily penetrate cells, making them useful for delivering drugs July 21st, 2014

Chip Technology

Nanometrics Announces Upcoming Investor Events July 22nd, 2014

Penn Study: Understanding Graphene’s Electrical Properties on an Atomic Level July 22nd, 2014

NUS scientists use low cost technique to improve properties and functions of nanomaterials: By 'drawing' micropatterns on nanomaterials using a focused laser beam, scientists could modify properties of nanomaterials for effective applications in photonic and optoelectric applicat July 22nd, 2014

Dongbu HiTek Unveils Low-Voltage BCDMOS Process for Efficient Power Management in Smart Phones and Tablet Computers July 21st, 2014

Discoveries

Researchers create vaccine for dust-mite allergies Main Page Content: Vaccine reduced lung inflammation to allergens in lab and animal tests July 22nd, 2014

NIST shows ultrasonically propelled nanorods spin dizzyingly fast July 22nd, 2014

Penn Study: Understanding Graphene’s Electrical Properties on an Atomic Level July 22nd, 2014

NUS scientists use low cost technique to improve properties and functions of nanomaterials: By 'drawing' micropatterns on nanomaterials using a focused laser beam, scientists could modify properties of nanomaterials for effective applications in photonic and optoelectric applicat July 22nd, 2014

Materials/Metamaterials

Penn Study: Understanding Graphene’s Electrical Properties on an Atomic Level July 22nd, 2014

NUS scientists use low cost technique to improve properties and functions of nanomaterials: By 'drawing' micropatterns on nanomaterials using a focused laser beam, scientists could modify properties of nanomaterials for effective applications in photonic and optoelectric applicat July 22nd, 2014

Steam from the sun: New spongelike structure converts solar energy into steam July 21st, 2014

Carbyne morphs when stretched: Rice University calculations show carbon-atom chain would go metal to semiconductor July 21st, 2014

Announcements

Nanometrics Announces Upcoming Investor Events July 22nd, 2014

Bruker Awarded Fourth PeakForce Tapping Patent: AFM Mode Uniquely Combines Highest Resolution Imaging and Material Property Mapping July 22nd, 2014

NIST shows ultrasonically propelled nanorods spin dizzyingly fast July 22nd, 2014

Penn Study: Understanding Graphene’s Electrical Properties on an Atomic Level July 22nd, 2014

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

Researchers create vaccine for dust-mite allergies Main Page Content: Vaccine reduced lung inflammation to allergens in lab and animal tests July 22nd, 2014

Organometallics welcomes new editor-in-chief: Paul Chirik, Ph.D. July 22nd, 2014

NIST shows ultrasonically propelled nanorods spin dizzyingly fast July 22nd, 2014

Penn Study: Understanding Graphene’s Electrical Properties on an Atomic Level July 22nd, 2014

Energy

Oregon chemists eye improved thin films with metal substitution: Solution-based inorganic process could drive more efficient electronics and solar devices July 21st, 2014

Steam from the sun: New spongelike structure converts solar energy into steam July 21st, 2014

3-D nanostructure could benefit nanoelectronics, gas storage: Rice U. researchers predict functional advantages of 3-D boron nitride July 15th, 2014

Nanotechnology that will impact the Security & Defense sectors to be discussed at NanoSD2014 conference July 8th, 2014

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







© Copyright 1999-2014 7th Wave, Inc. All Rights Reserved PRIVACY POLICY :: CONTACT US :: STATS :: SITE MAP :: ADVERTISE