Research & Development World

  • R&D World Home
  • Topics
    • Aerospace
    • Automotive
    • Biotech
    • Careers
    • Chemistry
    • Environment
    • Energy
    • Life Science
    • Material Science
    • R&D Management
    • Physics
  • Technology
    • 3D Printing
    • A.I./Robotics
    • Software
    • Battery Technology
    • Controlled Environments
      • Cleanrooms
      • Graphene
      • Lasers
      • Regulations/Standards
      • Sensors
    • Imaging
    • Nanotechnology
    • Scientific Computing
      • Big Data
      • HPC/Supercomputing
      • Informatics
      • Security
    • Semiconductors
  • R&D Market Pulse
  • R&D 100
    • Call for Nominations: The 2025 R&D 100 Awards
    • R&D 100 Awards Event
    • R&D 100 Submissions
    • Winner Archive
    • Explore the 2024 R&D 100 award winners and finalists
  • Resources
    • Research Reports
    • Digital Issues
    • Educational Assets
    • R&D Index
    • Subscribe
    • Video
    • Webinars
  • Global Funding Forecast
  • Top Labs
  • Advertise
  • SUBSCRIBE

How electrons behave inside nano-pyramids

By R&D Editors | September 28, 2012

NanoPyramid1-250

Near-field microscopy using the free electron laser at HZDR: An adjusting laser is employed to align the measuring tip of the microscope that comes from above. Below the movable sample stage is to be seen.

Quantum dots are nanostructures of semiconducting materials that behave a lot like single atoms and are very easy to produce. Given their special properties, researchers see huge potential for quantum dots in technological applications. Before this can happen, however, we need a better understanding of how the electrons “trapped” inside them behave. Dresden physicists have recently observed how electrons in individual quantum dots absorb energy and emit it again as light. Their results were recently published in the journal Nano Letters.

Quantum dots look like miniscule pyramids. Inside each of these nano-pyramids are always only one or two electrons that essentially “feel” the constricting walls around them and are therefore tightly constrained in their mobility. Scientists from Helmholtz-Zentrum Dresden-Rossendorf (HZDR), TU Dresden. TU Dresden and the Leibniz Institute for solid State and Materials Research Dresden (IFW) have now studied the special energy states of the electrons trapped inside individual quantum dots.

Sharp energy levels

The behaviour of electrons in a material essentially determines its properties. Being spatially constrained in all three spatial dimensions, electrons inside a nano-pyramid can only occupy very specific energy levels – which is why quantum dots are also called “artificial atoms”. Where these energy levels lie depends on the chemical composition of the semiconductor material as well as the size of the nano-pyramid.

“These sharply defined energy levels are exploited, for example, in highly energy-efficient lasers based on quantum dots. The light is produced when an electron drops from a higher energy level into a lower one. The energy difference between the two levels determines the colour of the light,” Dr. Stephan Winnerl of HZDR explains.

Seeing electrons inside individual quantum dots

The researchers in Dresden working with Dr. Winnerl were recently the first to succeed in scanning transitions between energy levels in single quantum dots using infrared light. Although, they could only do this after overcoming a certain hurdle: While the pyramids of indium arsenide or indium gallium arsenide form spontaneously during a specific mode of crystal growth, their size varies within a certain range. Studying them with infrared light, for example, one obtains blurred signals because electrons in different sized pyramids respond to different infrared energies. This is why it is so important to obtain a detailed view of the electrons trapped inside a single quantum dot.

NanoPyramid2

The two free electron lasers at HZDR. Image: Sven Claus

The scientists approached this task with the special method of scanning near-field microscopy. Laser light is shone onto a metallic tip less than 100 nm thick, which strongly collimates the light to a hundred times smaller than the wavelength of light, which is the spatial resolution limit for “conventional” optics using lenses and mirrors. By focusing this collimated light precisely onto one pyramid, energy is donated to the electrons, thereby exciting them to a higher energy level. This energy transfer can be measured by watching the infrared light scattered from the tip in this process. While near-field microscopy involves major signal losses, the light beam is still strong enough to excite the electrons inside a nano-pyramid. The method is also so sensitive that it can create a nanoscale image in which the one or two electrons inside a quantum dot stand out in clear contrast. In this fashion, Stephan Winnerl and his colleagues from HZDR, plus physicists from TU and IFW Dresden, studied the behaviour of electrons inside a quantum dot in great detail, thereby contributing towards our understanding of them.  

Infrared light from the free electron laser

The infrared light used in the experiments came from the free electron laser at HZDR. This special laser is an ideal infrared radiation source for such experiments because the energy of its light can be adjusted to precisely match the energy level inside the quantum dots. The laser also delivers such intense radiation that it more than makes up for the unavoidable losses inherent to the method.

“Next, we intend to reveal the behaviour of electrons inside quantum dots at lower temperatures,” Dr. Winnerl says. “From these experiments, we hope to gain even more precise insights into the confined behavior of these electrons. In particular, we want to gain a much better understanding of how the electrons interact with one another as well as with the vibrations of the crystal lattice.”

Thanks to its intense laser flashes in a broad, freely selectable spectral range, the free electron laser offers ideal conditions for the method of near-field microscopy in Dresden, which benefits particularly from the close collaboration with Prof. Lukas Eng of TU Dresden in the scope of DRESDEN-concept.

Intersublevel spectroscopy on single InAs-quantum dots by terahertz near-field microscopy

Helmholtz-Zentrum Dresden-Rossendorf

Related Articles Read More >

Floating solar mats clean polluted water — and generate power
Nanodots enable fine-tuned light emission for sharper displays and faster quantum devices
New photon-avalanching nanoparticles could enable next-generation optical computers
New “nose-computer interface” aims to upgrade Rover’s nose for better drug detection methods
rd newsletter
EXPAND YOUR KNOWLEDGE AND STAY CONNECTED
Get the latest info on technologies, trends, and strategies in Research & Development.
RD 25 Power Index

R&D World Digital Issues

Fall 2024 issue

Browse the most current issue of R&D World and back issues in an easy to use high quality format. Clip, share and download with the leading R&D magazine today.

Research & Development World
  • Subscribe to R&D World Magazine
  • Enews Sign Up
  • Contact Us
  • About Us
  • Drug Discovery & Development
  • Pharmaceutical Processing
  • Global Funding Forecast

Copyright © 2025 WTWH Media LLC. All Rights Reserved. The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media
Privacy Policy | Advertising | About Us

Search R&D World

  • R&D World Home
  • Topics
    • Aerospace
    • Automotive
    • Biotech
    • Careers
    • Chemistry
    • Environment
    • Energy
    • Life Science
    • Material Science
    • R&D Management
    • Physics
  • Technology
    • 3D Printing
    • A.I./Robotics
    • Software
    • Battery Technology
    • Controlled Environments
      • Cleanrooms
      • Graphene
      • Lasers
      • Regulations/Standards
      • Sensors
    • Imaging
    • Nanotechnology
    • Scientific Computing
      • Big Data
      • HPC/Supercomputing
      • Informatics
      • Security
    • Semiconductors
  • R&D Market Pulse
  • R&D 100
    • Call for Nominations: The 2025 R&D 100 Awards
    • R&D 100 Awards Event
    • R&D 100 Submissions
    • Winner Archive
    • Explore the 2024 R&D 100 award winners and finalists
  • Resources
    • Research Reports
    • Digital Issues
    • Educational Assets
    • R&D Index
    • Subscribe
    • Video
    • Webinars
  • Global Funding Forecast
  • Top Labs
  • Advertise
  • SUBSCRIBE