Talk:Quantum dot

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Quantum dot was a good article nominee, but did not meet the good article criteria at the time. There are suggestions below for improving the article. Once these are addressed, the article can be renominated. Editors may also seek a reassessment of the decision if they believe there was a mistake.

Reviewed version: April 12, 2006
  • Re: "Compare to quantum wires (confined in 2D) and quantum wells (confined in 1D)."... Is that right?? I'd think that wires correspond to 1D, and wells to 0D (a point)... --Cheese Sandwich 20:40, 19 August 2005 (UTC)
  • You've misread/misunderstood the sentence. A wire is confined in two of its dimensions - thus it is a one dimensional structure. A well is confined in one dimension, and it is thus a two dimensional structure. A dot is effectively comfined in all three spatial dimensions, it is a zero dimensional structure. Daz - 9/11/06
  • Also: This sentence portion could use some editing: "...as the larger and more red-shifted the Quantum Dots is, the less the quantum properties are." --Cheese Sandwich 20:43, 19 August 2005 (UTC)

Is there somewhere in the public domain one of those beautiful (and prevalent) pictures of solutions of quantum dots emitting at different wavelengths? If someone could find one, I think it would add to the appeal of this article. If not, perhaps some group would release their copyright for the exposure... To give an idea of what I'm talking about, here's a link http://www.research.philips.com/newscenter/pictures/downloads/ldm-nanotech_04-0_h.jpg to an awful enlargement of one of these displays. Jonnyapple 06:28, 2 February 2006 (UTC)

I think most of the problems have been addressed. --Walkman16 (talk) 15:21, 24 February 2008 (UTC)

Contents

[edit] Company by this name

There is a company, Quantum Dot, that could be treated with an article; "Quantum Dot" currently redirects to "Quantum dot". The website is located at http://www.qdots.com . The company would fall into the Category:Research support companies. Courtland 23:38, 26 November 2005 (UTC)

The first company to offer commerical quantum dots was Evident Technologies in 2001. The company is currently located in Troy, New York; website: www.evidenttech.com. Commercial quantum dots include CdSe, PbS, and InGaP quantum dots for life science applications, LEDs, solar cells etc.

[edit] Images

This article needs some illustrations.--24.241.230.126 17:29, 31 March 2006 (UTC)

Added a link to some YouTube videos for colloidal QDs. --Walkman16 (talk) 04:24, 19 February 2008 (UTC)

Added a photograph --Walkman16 (talk) 06:09, 24 February 2008 (UTC)

[edit] Good article nomination

Sadly, this article failed it's nomination. This is for two main reasons:

  1. Past the lead (which while too short is understandable), it is unitelligible to a non-specialist (like myself).
  2. It has no inline citations whatsoever.

Regards, --Celestianpower háblame 23:41, 12 April 2006 (UTC)

[edit] Move/redirect

I think this article should be moved to its more precise scientific name: semiconductor nanocrystal. --Sunpower 14:37, 26 April 2006 (UTC)

[edit] Big mistake!

I am pretty sure this sentence is wrong: "Quantum dots have quickly found their way into homes in many electronics. The new PlayStation 3 and high-definition DVD players (notably Blu-ray and HD-DVD) to come out all use a blue laser for data reading. The blue laser up until only a few years ago was beginning to be seen as something of an impossibility, until the synthesis of a blue quantum dot laser."

Blu-ray and HD-DVD use gallium nitride (and other nitrogen-base compounds) as materials for quantum wells structures, not quantum dots! Quantum dot lasers are just now trying to find their way into the market, but absolutely not in the short wavelength region (green-blue-violet)! Quantum dots have nothing to do with blue lasers!

    • I have removed the paragraph regarding the Playstation 3/Blue-ray/HD DVD and blue lasers. It's spurious.

I would recommend to correct such a sentence, or (better) to completely erase it off.


Please see blue laser and the reference in Appl. Phys. Lett. 86, 073102 (2005).
While the wikipedia entry says today: "Use of indium gallium nitride as a semiconductor material suitable for formation of quantum heterostructures is proposed. Recently, CdS/ZnS quantum dots have been used as the gain material in spherical Whispering Gallery Mode lasers; see Applied Physics Letters, 2005, 86:073102.", the reference does not mention the term quantum dots. Someone can give an opinion here? (Please sign your comments).
Miguel Andrade 18:29, 14 July 2006 (UTC)
  • A quick note on the use of "quantum dot" vs "nanocrystal." In common usage the two terms are more or less interchangable. However, over the past several years, the nanoscience community has started to make a distinction between what each term refers to. Generally, "quantum dot" refers to small semiconductor islands grown onto a substrate using molecular beam epitaxy, chemical vapor deposition or other methods, and hence are fixed in place. In contrast, "nanocrystal" usually refers to colloidal particles grown in solution, which can then be processed using different methods. The APL article mentioned above uses colloidal CdS/ZnS particles which are then deposited onto substrates to make devices (rather than being grown there directly), hence use of the term "nanocrystal" rather than "quantum dot." --Aaron 15:31, 7 August 2006 (UTC)

Well I think there is certainly a physical difference between quantum dots and nanocrystal which comes from the basic definition of crystal. You can have a lot of quantum dots which are not talking to each other and therefore the physical properties (energy, wavefunction etc) are not changed due to the absence of this interaction. A crystal on the other hand would be an ensemble of dots which are so near in space (or otherwise) that each of the energies are some sort of summation of individual energies (similarly for the wavefunction). I think a crystal structure is so that each contributing atom had energy band structure and wavefunction are some summation of this ensemble. —Preceding unsigned comment added by Pranobmisra (talk • contribs) 16:50, 26 October 2007 (UTC)

This must be wrong: "etching on two-dimensional electron gases" you don't etch gases and they are hardly 2d, would it be gates?

[edit] Discretization of charge?

I have a problem with the following sentence: "This confinement leads to (...) and to the quantization of charge in units of the elementary electric charge e" I agree that the confinement leads to discrete levels and that the charge on the dot is a multiple of the electron charge. To me this sentence sounds however as if charge quantization was a special feature of the quantum dot, which it is not. Bamse 01:38, 8 August 2006 (UTC)

[edit] One of the "stated" applications

"Another paper, published in the October 18, 2005 issue of the Journal of the American Chemical Society, reports that Michael Bowers II at Vanderbilt University discovered that certain size crystals of cadmium and selenium emit white light when excited by an ultraviolet laser. This emission appears to be coming from the surface of the crystal, rather than the center. The crystals contain either 33 or 34 pairs of atoms. While they are being pyrolytically synthesized, they preferentially form into just this size; so Bowers can make a batch of such crystals in about an hour. Another student then mixed these quantum dots into ordinary varnish, applied it to a blue LED, and observed that the emission is yellowish-white, like a light bulb. The researchers believe that it will be possible to achieve this emission of white light via electrical stimulation as well as photonic, and hope to demonstrate it soon."

The quality of writing in this paragraph is a bit lacking, since it reads like someone's laboratory book; is it really relevant which students are involved, or how long it takes to make a batch of crystals? The ideas are ordered haphazardly and some of the sentences are plainly speculative. I suggest this paragraph be rewritten, or just removed.

146.232.75.208 15:34, 10 August 2006 (UTC)


Seems as though this section was written by the author of the article itself. This article is far from a seminal paper in the field. It should be removed.

[edit] Red-shift meaning unclear

The current last two paragraphs in "Description" discuss the "red-shifting" of larger quantum dots. The link is to Redshift, but it's not clear to me if that article actually discusses the phenomenon that occurs in quantum dots. Most of that article talks about Doppler red-shifting, which seems irrelevant. It does mention the effect due to "physical optics or radiative transfer", which is often called "reddening" rather than "red-shifting" to reduce confusion (at least in astrophysics), but I'm too rusty on my physics to see if this forms the basis of the quantum-dot coloration effect. There is also bathochromic shift, also called "red-shifting", but I'm not sure that's relevant here, either. Can someone clarify, preferably with a reliable source? ~ Jeff Q (talk) 00:57, 28 November 2006 (UTC)

The problem is that the two Wikipedia articles on "red-shift" are about two technical definitions of the term: red-shifting due to doppler effects (cosmological, etc.), and red-shifting due to chemical/solvent effects (bathochromic shift). But in the QD article it refers to "red-shift" only in a very loose way... because there is no particular item or particle whose spectrum is shifting towards the red. Instead, the article means that as you increase the size of the particles, the spectrum is shifted more and more to the red. So only conceptually is there a red-shift going on (if you compare a bunch of particles). So really the article shouldn't link to "red-shift" at all. I've edited the page accordingly. Kebes 20:36, 7 December 2006 (UTC)

[edit] Band Gap energy

"Quantitatively speaking, the bandgap energy that determines the energy (and hence color) of the fluoresced light is inversely proportional to the square of the size of the quantum dot." Is size the number of atoms, the diameter, or some other value?


It's not as simple as a single-parameter. It depends upon many things (see the lovely papers by Brus in 1984 and 1985, that are considered THE seminal papers in the field), however, to zeroth order you can just think about comparing the physical dimensions of the nanocrystal (diameter, if you like) to the bohr exciton radius of that material in bulk. That is considered one way to estimate the extent of quantum confinement in a quantum dot (at least vis-a-vis optical absorption, etc.).Lesotho 18:25, 22 March 2007 (UTC)

[edit] Intro section

The first paragraph contains no fewer than 5 sets of parantheses, two of which start with 'e.g.'. Would someone be able to copyedit this into something approaching brilliant prose, without all the hedging? I don't know the subject matter at all, or I would do it myself. Stevage 06:11, 29 March 2007 (UTC)


Sure, I'll do it. Some of the associated commentary there is not absolutely relevant (and slightly inaccurate) anyway. Lesotho 14:32, 29 March 2007 (UTC)

http://www.sciencedaily.com/articles/q/quantum_dot.htm Who copied from who? —Preceding unsigned comment added by 129.110.195.33 (talk) 05:28, 28 January 2008 (UTC)

Rewrote intro, w/ citations Walkman16 (talk) 06:50, 19 February 2008 (UTC)

[edit] Biased references?

Mark Reed's papers are hardly the foundational references in this area. I would suggest adding the two papers by Lou Brus that basically established this as a field of inquiry and laid all the groundwork for the theory of how electronic structure is modified in quantum dots.Lesotho 17:40, 4 May 2007 (UTC)

[edit] Better comparison?

"At 10 nm in diameter, nearly 3 million quantum dots could be lined up end to end and fit within the width of a human thumb." It's nice idea to give a real-world comparison for a lay-person. However, most folks don't have a good grasp on just how big 3M of anything really is. How about a comparison to the head of a pin, or a single ground of espresso? Russella (talk) 02:34, 21 November 2007 (UTC)

[edit] Intro cleanup tag (suggestions)

Missing from the intro:

  • What a quantum dot is (should be first sentence of the article)
  • What are its applications

The current content of the intro should be trimmed down and/or made less technical. GregorB (talk) 10:53, 28 December 2007 (UTC)


Agreed, I can't make any sense of the current description, something for the layman would be useful. 82.144.243.247 (talk) 12:38, 28 December 2007 (UTC)


Let me third that. I know beans about the topic, so I'm sure my summary would be wrong in the particulars. But as far as tone goes, I'm thinking something like "A quantum dot is an experimental element of integrated circuit where a nanoscale group of 100 to 100,000 atoms acts electrically like a single atom, exhibiting quantum properties. Although not yet in commercial use, researchers have used quantum dots as transistors, solar cells, and LEDs, and hope to use them as qubits and diode lasers." There are 25 recent Google News hits for "quantum dot", so the intro should accessible to a general audience, even if the rest of the article rapidly becomes too technical for them. William Pietri (talk) 15:32, 28 December 2007 (UTC)

Could the introduction make a clear distinction between quantum dots that are embeded in a semiconductor and quantum dots that are discrete particiles (such as proposed for medical therapies)? —Preceding unsigned comment added by Musical lawnmower (talk • contribs) 10:38, 22 January 2008 (UTC)

[edit] Interesting Paper out

There is an article over at ars technica about possible (fast and persistent) storage devices referencing an apl paper. Could be an interesting application to mention and provide more linkage into scientific publications? --Danieloberhoff (talk) 15:48, 28 December 2007 (UTC)

[edit] Merge

There is a request to merge nanocrystal solar cell into this page. I oppose this because quantum dot is about the theory and the other is a specific application. -- Alan Liefting (talk) - 03:10, 12 June 2008 (UTC)