McGill researchers squeeze light out of quantum dots

April 03, 2009

McGill University researchers have successfully amplified light with so-called "colloidal quantum dots," a technology that had been written off by many as a dead-end.

Over the last 15 years, repeated quantum dot research efforts failed to deliver on expected improvements in amplification, and many researchers started to believe that an unknown but insurmountable law of physics was blocking their path. Essentially, they said, quantum dots would simply never work well for one of their primary applications.

However, after extensive research, Professor Patanjali (Pat) Kambhampati and colleagues at McGill University's Department of Chemistry determined that colloidal quantum dots do indeed amplify light as promised. The earlier disappointments were due to accidental roadblocks, not by any fundamental law of physics, the researchers said. Their results were published in the March 2009 issue of Physical Review Letters.

Colloidal quantum dots can actually be painted directly on to surfaces, and this breakthrough has enormous potential significance for the future of laser technology, and by extension, for telecommunications, next-generation optical computing and an innumerable array of other applications.

Lasers - beams of high-powered coherent light - have applications in dozens of fields, most notably in telecommunications, where they are used to transmit voice and data over fibre-optic cables. Like sound, radio waves or electricity, laser signals gradually lose power over distance and must be passed through an amplifier to maintain signal strength. Until now, the best available amplification technology was the quantum well, a thin sheet made of semi-conductor material which confines electrons to a one-dimensional plane, and consequently amplifies light. Colloidal quantum dots perform a similar function, but in a three-dimensional box-like structure instead of a flat sheet.

"Everyone expected this little box to be significantly better than a thin sheet," Kambhampati said. "You'd require less electrical power, and you wouldn't need to use arrays of expensive cooling racks. The idea was to make the lasing process as cheap as possible. But the expected results were not really there. So people said 'let's forget about the quantum dot' and they tried rods or onion shapes. It became a game of making a whole soup of different shapes and hoping one of them would work.

"In our view," he continued, "no one had figured out how the simple, prototypical quantum dot actually worked. And if you don't know that, how are you going to rationally construct a device out of it?"

In the end, Kambhampati and his colleagues discovered that the major problem lay in the way researchers had been powering their quantum dot amplifiers.

"We discovered that there was nothing fundamentally wrong with the dots. If you weren't careful in your measurements, when powering the quantum dot, you would accidentally create a parasitic effect that would kill the amplification." he said. "Once we understood this, we were able to take a quantum dot that no one believed could amplify anything, and turned it into the most efficient amplifier ever measured, as far as I know."

McGill University

---

---

	Quantum Wells, Wires and Dots: Theoretical and Computational Physics of Semiconductor Nanostructures by Paul Harrison (Author) Quantum Wells, Wires and Dots, 3rd Edition is aimed at providing all the essential information, both theoretical and computational, in order that the reader can, starting from essentially nothing, understand how the electronic, optical and transport properties of semiconductor heterostructures are calculated. Completely revised and updated, this text is designed to lead the reader through a series of simple theoretical and computational implementations, and slowly build from solid foundations, to a level where the reader can begin to initiate theoretical investigations or explanations of their own.
	Quantum Dots: Applications in Biology (Methods in Molecular Biology) by Charles Z. Hotz (Editor), Marcel Bruchez (Editor) Quantum Dots captures many diverse applications enabling utility in biological detection. Organized into five parts, the first two parts cover the use of QDs in imaging fixed and living cells (and tissues). Protocols are included for using QDs in routine as well as enabling applications. Part 3 shows early efforts aimed at using QDs in live animals. The final two parts demonstrate the versatility of QD technology in existing assay technology.
	The Quantum Dot: A Journey into the Future of Microelectronics by Richard Turton (Author) Since first developed in the early sixties, silicon chip technology has made vast leaps forward. From a rudimentary circuit with a mere handful of transistors, the chip has evolved into a technological miracle, packing millions of bits of information on a surface no larger than a human thumbnail. And most experts predict that in the near future, we will see chips with over a billion bits. At the same time, this revolution in microelectronics has sparked a dramatic change in the way we live. An integral part of the computer industry, the microchip is found in everything from lasers, fax machines, and satellites to greeting cards and children's toys. And yet few people have any idea how chips work, or how so much information can be captured in such a miniscule space. Now, in The...
	Nanocrystal Quantum Dots, Second Edition (Laser and Optical Science and Technology) by Victor I. Klimov (Editor) A review of recent advancements in colloidal nanocrystals and quantum-confined nanostructures, Nanocrystal Quantum Dots is the second edition of Semiconductor and Metal Nanocrystals: Synthesis and Electronic and Optical Properties, originally published in 2003. This new title reflects the book’s altered focus on semiconductor nanocrystals. Gathering contributions from leading researchers, this book contains new chapters on carrier multiplication (generation of multiexcitons by single photons), doping of semiconductor nanocrystals, and applications of nanocrystals in biology. Other updates include: New insights regarding the underlying mechanisms supporting colloidal nanocrystal growth A revised general overview of multiexciton phenomena, including spectral and dynamical signatures...
	Quantum Dots (NanoScience and Technology) by Lucjan Jacak (Author), Pawel Hawrylak (Author), Arkadiusz Wojs (Author) This book covers many topics concerned with the man-made electronic systems called quantum dots, in particular: methods of creation, internal properties (electronic structure), directly observed properties (response to the experimental probes, e.g. light or electrodes), experimental methods and results, physical effects occuring in dots, theoretical models, computational methods, and future applications. The review part requires only basic knowledge on quantum mechanics and solid state physics.
	Handbook of Nanophysics: Nanoparticles and Quantum Dots by Klaus D. Sattler (Editor) In the 1990s, nanoparticles and quantum dots began to be used in optical, electronic, and biological applications. Now they are being studied for use in solid-state quantum computation, tumor imaging, and photovoltaics. Handbook of Nanophysics: Nanoparticles and Quantum Dots focuses on the fundamental physics of these nanoscale materials and structures. Each peer-reviewed chapter contains a broad-based introduction and enhances understanding of the state-of-the-art scientific content through fundamental equations and illustrations, some in color. This volume provides an overview of the major categories of nanoparticles, including amorphous, magnetic, ferroelectric, and zinc oxide nanoparticles; helium nanodroplets; and silicon, tetrapod-shaped semiconductor, magnetic ion-doped...
	Quantum Dot Heterostructures by Dieter Bimberg (Author), Marius Grundmann (Author), Nikolai N. Ledentsov (Author) Quantum Dot Heterostructures Dieter Bimberg, Marius Grundmann and Nikolai N. Ledentsov Institute of Solid State Physics, Technische Universit?t Berlin, Germany Quantum dots are nanometer-size semiconductor structures, and represent one of the most rapidly developing areas of current semiconductor research as increases in the speed and decreases in the size of semiconductor devices become more important. They present the utmost challenge to semiconductor technology, making possible fascinating novel devices. This important new reference book focuses on the key phenomena and principles. Chapter 1 provides a brief account of the history of quantum dots, whilst the second chapter surveys the various fabrication techniques used in the past two decades, and introduces the concept of...
	Microbial detection in microfluidic devices through dual staining of quantum dots-labeled immunoassay and RNA hybridization [An article from: Analytica Chimica Acta] by Q. Zhang (Author), L. Zhu (Author), H. Feng (Author), S. Ang (Author), F.S. Chau (Author), Liu (Author) This digital document is a journal article from Analytica Chimica Acta, published by Elsevier in 2006. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser. Description: This paper reported the development of a microfludic device for the rapid detection of viable and nonviable microbial cells through dual labeling by fluorescent in situ hybridization (FISH) and quantum dots (QDs)-labeled immunofluorescent assay (IFA). The coin sized device consists of a microchannel and filtering pillars (gap=1-2@mm) and was demonstrated to effectively trap and concentrate microbial cells (i.e. Giardia lamblia). After sample injection, FISH probe solution and QDs-labeled antibody solution were...
	Quantum Dots: Applications, Synthesis and Characterization by Orion Ciftja (Editor)
	Proceedings of the 2nd International Conference on Semiconductor Quantum Dots (QD2002): physica status solidi (c) - conferences and critical reviews, ... Solidi: Conferences & Critical Reviews) by Yasuhiko Arakawa (Editor), Seigo Tarucha (Editor) physica status solidi (c) conferences and critical reviews publishes conference proceedings, ranging from large international meetings to specialized topical workshops as well as collections of topical reviews on various areas of current solid state physics research. The International Conference on Semiconductor Quantum Dots (QD2002) was held at Komaba Campus of University of Tokyo, Japan, from Monday 30 September through Thursday 3 October 2002. The purpose of the QD2002 was to bring together scientists from different fields of physics and chemistry to discuss topics of common interest and significance in such growing areas including semiconductur quantum dots, nanocrystals, and clusters. The conference was focused on the optical and electronic...