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Science Technology

UV Nanolasers From ZnO Nanowires 53

The Evil Dwarf from Hell writes: "This weeks Science has an article on ZnO nanowire base UV lasers, abstract ( paid subscritption required for article). The 70 to 100 nm diameter wires lase at 386nm, line width .3 nm. The growth takes place on a thin Au film on a sapphire surface, and the wires reach lengths of 2 to 10 m. What makes this lasing unusual is it occurs without the use of mirrors. Apparently ZnO forms a natural lasing cavity. (The lasing is optically pumped from a Nd:YAG laser)." The link above is registration-required, but there's another article which describes the whole process.
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UV Nanolasers From ZnO Nanowires

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  • by Anonymous Coward
    UV laser ionizes atmosphere,high voltage generator discharges along ionized path, ZZZZZAP!

    I'll take 2!
  • by Anonymous Coward
    Nitrogen, Cu vapor, and other lasers can lase without a resonate cavity. It's not that unusual.
  • by Anonymous Coward on Friday June 08, 2001 @08:34AM (#165838)
    What is this all about? This is an article with some substance to it. I mean really. We can't have this kind of thing going on.

    I want Microsoft bashing. I want software release notices. I want anti-big-industry rants. I want free software cheerleading.

    How am I supposed to follow the party line if real News for Nerds and Stuff that matters shows up here?

  • Your link to the other article seems to be dead, but I imagine it was the one about TB/cm^3 storage using femto-second lasers and spectral hole burning. Someone commented then that fs lasers are huge power hungry monsters. A day ro so after reading that I passed a poster display from some of our physics grad students, who now have a suitcase sized, battery powered, fully portable femto-second laser.

    I doubt the ZnO lasers will get down to femto-second pulse lengths very soon though, it is rather a specialized trick that they use to get pulses that short.
  • "Without Zinc Oxide, you wouldn't have that bar of soap. <*ding*>

    "The dish towels you use every day. <*ding*>

    "Your toaster. <*ding*>

    "That brassiere you're wearing. <*ding*>

    "Your kitchen sink. <*ding*>

    "Metal hooks. <*ding*>

    "The heat control on your stove." <*ding*>

    (etc., etc., etc., from The Kentucky Fried Movie.)


  • What makes this lasing unusual is it occurs without the use of mirrors.

    But I thought it was all done with smoke and mirrors

  • There are no free forums. Forums cost money to buy, build, and maintain. You can either subtract the cost of the forum from the research funding (ie, do less research) or you can pay the forum cost afterwards and use all the money for research.

    In an ideal world, the NSF or whatever governmental agency does the funding would do a web site and just stipulate that to whatever extent possible the results of the study be made to them electronically for posting on their web site.

  • Note to slashdot editors: if you value your readers' time, please expand all but the most common acronyms or abbreviations the first time you use them, even if you are quoting an email that you received. For example, the article that does not require registration does not mention an "Nd:YAG laser" and very cursory search on google did not turn up a definition (although it did find references to the term).
  • Electronics in the 20's are NOT what they are today.

    I'm not saying some exorbitant journal prices are justified, only that the peer review process IS important, though it has it's faults.

    I'd rather see every insititution, especially any using public money have to publish all articles, for free, to everyone, on the net. Other 'journals' or peer review boards can link in articles they see as relevant to the state of the art. This also allows many researchers to benefit from each other's work.
  • by mindstrm ( 20013 ) on Friday June 08, 2001 @08:49AM (#165845)
    The peer review costs money.
  • Didn't you read A Wrinkle in Time?

    Once we figure out how to remove/shrink the space between the subatomic particles "small" will take on a whole new meaning.

    What was that line in HG2G? Do to a gross miscalculation in scale, the entire armada was swallowed by a terrier. -something like that

  • by edremy ( 36408 ) on Friday June 08, 2001 @10:00AM (#165847) Journal

    The peer review costs money.

    Not as much as you might think. We reviewers aren't paid for the reviews: it's regarded as part of our professional responsibility. (The same happens with grant reviews: the vast majority is done by other scientists.)

    Many journals charge money to print articles, others charge literally thousands of dollars/year for a subscription. This is a huge bone of contention on many campuses: Professor A and B want the Journal of Obscure Latvian Chemistry at $2000/year, but C and D would rather have Acta Trivia at $2500/year. Academic budgets aren't much- what do you do?

    Science and Nature are special cases: there's significant editorial comment in each, and so the costs of printing them are much higher. (The first 3rd of each is quite understandable by any interested layman.)

    So why not go electronic? Simple: electronic reserves have a miserable record of longevity. I can and have looked up articles from 1920, and that's hardly the limit. We can't read electronic Pioneer data from the 1960s.

    Keeping old journal articles in a format that's always readable is going to cost, and cost big. You'll need multiple servers so that a single crash doesn't kill you, and sysadmins to care for the machines, bandwidth costs, plus format conversion.

    And of course, you'll still need to pay for the staff to handle sending articles around for peer review.

    Stanford has a program that's looking into solving some of these problems with a distributed system, but it's going to be a long, long time before we abandon paper.


  • by British ( 51765 ) <british1500@gmail.com> on Friday June 08, 2001 @09:40AM (#165848) Homepage Journal
    Who wrote this? Michael or Geordi LaForge?
  • Simple. In the interest of academic freedom, scientific journals (as opposed to magazines like science news) do not print advertisments, thus the entire cost of publication is borne by the authors and/or subscribers.

    Many articles in physics appear on xxx.lanl.gov before they a published. However, these are pre-print drafts that haven't been peer reviewed or selected in any other way. Many, many of the articles published there are Just Plain Wrong. When you pay for a peer reviewed journal, you are paying for a lower (though not zero) probability of something being totally wrong.

    That isn't to say that publication costs are not a major source of contention. Obviously, scientists want as wide of a distribution as possible, and university library budgets, especially at smaller schools is limited. Some journals Nature are real assholes about this sort of thing, others are not so bad, but in the end, someone needs to pay the bills.

    Many researchers post some or all of their published papers in PDF format on their webpages, but journals differer on if, how, and when you are allowed to do so.
  • http://slashdot.org/article.pl?sid=01/06/07/222022 3
  • There's no such thing as watching too much Star Trek.
  • by billstewart ( 78916 ) on Friday June 08, 2001 @12:56PM (#165852) Journal
    Wait a minute here! Zinc Oxide is the stuff you use to keep damaging UltraViolet sunlight off your face. Now they're using it to turn it into UV Lasers? I can feel my nose burning already. Ouch!
  • Will any of this cause the price of corrective laser eye surgery to drop?
  • Oh! Wait I want to guess!
    Neodymium doped with Yttrium silver?

    Woot! Woot! I would like to thank my high school chemistry teacher!

    okay, I had to look it up on the periodic table.
  • Okay, I suck.

    Evidently, I wasn't paying that much attention in chemistry.
  • by egomaniac ( 105476 ) on Friday June 08, 2001 @08:47AM (#165856) Homepage
    Not quite. The physical size of the lasing device is irrelevant; all that matters (WRT putting data on a surface) is the light coming out of it.

    Any decent laser can be used to produce an incredibly thin beam, such that the limiting factor becomes the wavelength of the light. This is the reason for all the brouhaha over blue lasers - nothing to do with the physical size of the laser, but the fact that using a smaller wavelength allows you to pack more data on the surface.

    Now, physical dimensions aside, these *are* UV, so clearly they're short-wavelength lasers, but IIRC the blue lasers are around 460nm (is that right?) so a 386nm UV would allow for roughly 42% more data to be packed on a given surface.

    Of course, use of UV lasers in home electronics devices could be *really* dangerous, because if you somehow looked into the laser you wouldn't even realize it until you noticed the irreparable damage to your retina.
  • to be able to carry a little clear crystal in my pocket with several terabytes of information on it and I just set it in a device with these nice lasers that can read/write the information from it. I just think that would be kinda cool and a whole lot cooler than cdrw/dvdrw/floppy/tape/zip/dat etc.

    Hmmm, Maybe I've just been watching too much star trek.
  • Well, What I'd do is use a rotating angled mirror to skew the beam slightly off center. The head assembly gives you a coarse adjustment, and the angled mirror gives a fine adjustment. This combination wouldn't be too hard to engineer, would it?


  • Nd:YAG means Neodymnium, Yttrium Aluminum Gem.

    Essentially a Nd:YAG laser has a rod of material made of a structure of the above elements. This rod is pumped with energy [typically via an arc-lamp], and lases typically in the 1080nm range [somewhere infrared, I'm not certain on the exact wavelength, so don't jump me]. Nd:YAG's were used quite commonly for medical procedures before solid state ones became more common [ie: cheaper].

    Now, before someone screams: "I HAVE A GREEN YAG!" The commerically available YAG's are[were] typically run through a KTP [Potassium-Titanium-Phosphate] crystal. This crystal had the effect of doubling the wavelength [two 1080 photons -> one 540 photon].
  • I need to proof read more carefully. KTP doubles the *frequency*, not the wavelength [the illustration is correct though]

  • Once configured to work with electron pumping, the nanolaser could be put to any number of uses, Yang said. "Lab-on-a-chip" devices could contain small laser analysis kits -- nanodetectors -- capable of such things as Raman spectroscopy, a laser technique that can be used to identify chemicals.

    A short-wavelength ultraviolet laser also could increase the amount of data that can be stored on a high-density compact disk, just as the advent of blue-light gallium nitride lasers boosted data density.

    And in the field of photonics and optical computing, cheap bright lasers are ssential.
    I think a really cool application of this would be in combination with wearable computing technology. Can anyone picture a suit of clothes with these on the inside to give you a tan as you go about your day? No more time wasted in the tanning booths. Tune them to precisely the wavelength needed to get your perfect tan.
  • by joto ( 134244 )
    I think it'd be cool...

    to be able to carry a little clear crystal in my pocket with several terabytes of information on it and I just set it in a device with these nice lasers that can read/write the information from it.

    Nah, it would just be usual stuff by the time it happens...

    Technology is only cool untill it's available. Then it becomes daily life and nobody cares unless it stops working.

    Do you daily think about how incredibly cool it is to have a computer thousand times more powerful than computers 50 years ago in your pocket? Having a cell-phone? Running a multi-user OS on your PC? Crossing the atlantic ocean in less than 8 hours? Using satellites for mass communication? Being able to cure almost any decease that used to kill people before they reached 40 just a few hundred years ago? Manipulating the genetic code in plants and animals? Paying with plastic cards? Controlling nuclear energy? Drilling for oil hundreds of meters below the seabed? Surfing and communicating worldwide on the Internet? Driving your own car? Having automated appliances in your house doing your laundry and dishes? We live in an incredibly advanced world, it's just that because things become commonplace we stop seeing the wonders technology already performs for us.

  • would I be correct in guessing that the optical discs resulting from this new technology would store 100 times more data (or maybe 10000 times, if it works in two dimesions)?

    No, it's not the size of the laser that matters for data density, it's the wavelength.

    However, if they are 100 times smaller (and cheaper) you could put a hundred of them into your device of choice to improve data throughput and access time (even if they can't be controlled independently, there would still be much less head-movement).

  • Yang said. "Lab-on-a-chip" devices could contain small laser analysis kits -- nanodetectors -- capable of such things as Raman spectroscopy, a laser technique that can be used to identify chemicals.

    Wow, tricorder, here I come!

  • There is others problems... Can you imagine for example a motor precise enough so the laser is within .3 nm of where it should be, so the data can be read back?
  • I'm not holding my breath. Sure, it's easy and cheap to make the lasing cavities themselves but the article really downplays the difficulty of coming up with a non-optical pumping mechanism. Why should we think this is even possible, and even if it is, do we have any reason to hope that it will be easy and economical to interface this tiny wire with an electronic pumping unit?

    Since Nd:YAG lasers fire in the infrared range and you probably don't need much intensity to pump one of these wire lasers, I bet you that electronic pumping will be done using using a cheap IR laser and not with electrons directly. This would kill any hopes of making these lasers efficient.

    Well, here's to hoping I'm wrong. According to a guesstimate, a cd-sized disk burned with deep UV should hold several Terabytes of data (based on an extrapolation from the capacity of DVDs which use red lasers).

  • The paper only reports optically driven lasing, which requires a Nd:YAG laser to drive the UV laser. Without electrically driven lasing at high integration densities, ZnO couldn't be used for optical storage and probably not in an optical computer. This will take some time to develop, if it is at all possible, depending on the ease of making electrical contacts, and the current density required to reach threshold. The use as a coherent imaging system is possible almost immediately though.
  • If the wavelength is 100th of currently used systems, then the area of pits on a cd type system can be 10,000th of the size, so that data densities could be 10,000 tims as great. Near UV light is actually about 1/3rd the wavelength of green light. However, UV photons also have 3 times as much energy, so the disc used would heat up more, and have to be stable against this, which would quite difficult for Write operations (assuming everything keeps the same as CD-RW).

    The real power of these lasers for data storage may be in holographic systems, as there may be a way to store phase information at UV frequencies that can't be used for visible lasers. Holographic techniques would also allow data densities to scale as wavelength^-3, so that going from green to UV would give 27 times the data density (which is already estimated at 10Tb for 1 cubic inch in visible light systems)
  • And in the field of photonics and optical computing, cheap bright lasers are essential.

    Yang said that at this preliminary stage of development, the nanolaser is comparable to or better than the gallium nitride blue laser in terms of ease of manufacture, brightness and much smaller dimensions.

    "It basically has high enough intensity to think about making a practical device," he said. Plus it operates at room temperature.

    Congratulations /., you've finally found a story that can be used for something practical. Now my only question is, how long until 10 TB drives ship?

  • I'd rather see every insititution, especially any using public money have to publish all articles, for free, to everyone, on the net

    That was exactly the idea behind my original post. I consider science, nature, acm, journalXXX and journalYYY important. But government-funded articles should be made available for free, or perhaps for a small fee representing handling costs only, or transmition costs.

  • by rnbc ( 174939 ) on Friday June 08, 2001 @08:39AM (#165871) Homepage
    I wonder why most "hard" science is still published only in pay-per-read magazines.

    Shoudn't this kind of research, mostly funded by with government money, be published in free foruns?

    I understand paper and ink costs money, and atm-links also cost, but this kind of public-funded research should be made freely available to the interested public, besides perhaps being published in "reference magazines".

  • Yes, piezo drives. This one [physikinstrumente.com] has a resolution of better than 0.01 nm. They are used e.g. for scanning tunnel microscopy.
  • I wonder when someone will submit a story about the attosecond laser (Science 292, p. 1689) - far more ground braking than just another UV laser.
  • Neodym doped Yttrium-Aluminium-Garnet crystals are the lasing medium for this kind of lasers, properties of Nd:YAG see here [kharkov.com], basically it's a high power (several Watt) infrared laser often used to pump other lasers. Also, it's not really small.
  • Did you read the article ? I promise you will hear from it in the newspapers soon (in case you didn't already).
  • Room-Temperature Ultraviolet Nanowire Nanolasers Michael H. Huang,1 Samuel Mao,2 Henning Feick,3 Haoquan Yan,1 Yiying Wu,1 Hannes Kind,1 Eicke Weber,3 Richard Russo,2 Peidong Yang1,3*

    Room-temperature ultraviolet lasing in semiconductor nanowire arrays has been demonstrated. The self-organized, oriented zinc oxide nanowires grown on sapphire substrates were synthesized with a simple vapor transport and condensation process. These wide band-gap semiconductor nanowires form natural laser cavities with diameters varying from 20 to 150 nanometers and lengths up to 10 micrometers. Under optical excitation, surface-emitting lasing action was observed at 385 nanometers, with an emission linewidth less than 0.3 nanometer. The chemical flexibility and the one-dimensionality of the nanowires make them ideal miniaturized laser light sources. These short-wavelength nanolasers could have myriad applications, including optical computing, information storage, and microanalysis.

    1 Department of Chemistry, University of California,

    2 Environmental Energy Technology Division,

    3 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.

    To whom correspondence should be addressed. E-mail: pyang@cchem.berkeley.edu

    The interest in developing short-wavelength semiconductor lasers has culminated in the realization of room-temperature green-blue diode laser structures with ZnSe and InxGa1-xN as the active layers (1-3). ZnO is a wide band-gap (3.37 eV) compound semiconductor that is suitable for blue optoelectronic applications, with ultraviolet lasing action being reported (4-6) in disordered particles and thin films. For wide band-gap semiconductor materials, a high carrier concentration is usually required in order to reach an optical gain that is high enough for lasing action in an electron-hole plasma (EHP) process (7). Such an EHP mechanism, which is common for conventional laser diode operation, typically requires high lasing thresholds. As an alternative to an EHP process, excitonic recombination in semiconductors is a more efficient radiative process and can facilitate low-threshold stimulated emission (8, 9). To achieve efficient excitonic laser action at room temperature, the binding energy of the exciton must be much greater than the thermal energy at room temperature (26 meV). In this regard, ZnO is a good candidate because its exciton binding energy is ~60 meV, substantially larger than that of ZnSe (22 meV) and GaN (25 meV). To further lower the threshold, low-dimensional compound semiconductor nanostructures have been fabricated, in which quantum size effects yield a substantial density of states at the band edges and enhance radiative recombination due to carrier confinement. The use of semiconductor quantum well structures as low-threshold optical gain media represents a sizable advancement in semiconductor laser technology (10). Light emission from semiconductor nanowhiskers has been previously reported in GaAs and GaP systems (11, 12). Stimulated emission and optical gain have also been demonstrated recently in Si and CdSe nanoclusters and their ensembles (13, 14). Here, we demonstrate excitonic lasing action in ZnO nanowires with a threshold of 40 kW/cm2 under optical excitation.

    ZnO nanowires were synthesized with a vapor phase transport process via catalyzed epitaxial crystal growth (15). Using Au thin film as the catalysts for nanowire growth, we epitaxially grew the nanowires, which are highly oriented, on the substrate. Selective nanowire growth can be readily achieved by patterning the Au thin film before growth. Typical scanning electron microscopy (SEM) images of nanowire arrays grown on sapphire (110) substrates with patterned Au thin film (Fig. 1) confirm that the ZnO nanowires grow only in the Au-coated areas. The diameters of these wires range from 20 to 150 nm, whereas more than 95% of them have diameters of 70 to 100 nm. The diameter dispersity is due to the inhomogeneous sizes of the Au nanocluster catalysts when the substrate is annealed during the growth process. The lengths of these nanowires can be varied between 2 and 10 m by adjusting the growth time. The capability of patterned nanowire growth allows us to fabricate nanoscale light emitters on the substrate in a controllable fashion.

    Fig. 1. (A through E) SEM images of ZnO nanowire arrays grown on sapphire substrates. A top view of the well-faceted hexagonal nanowire tips is shown in (E). (F) High-resolution TEM image of an individual ZnO nanowire showing its growth direction. For the nanowire growth, clean (110) sapphire substrates were coated with a 10 to 35 Å thick layer of Au, with or without using TEM grids as shadow masks (micro contact printing of thiols on Au followed by selective etching has also been used to create the Au pattern). An equal amount of ZnO powder and graphite powder were ground and transferred to an alumina boat. The Au-coated sapphire substrates were typically placed 0.5 to 2.5 cm from the center of the boat. The starting materials and the substrates were then heated up to 880 to 905C in an Ar flow. Zn vapor is generated by carbothermal reduction of ZnO and transported to the substrates where ZnO nanowires grow. The growth generally took place within 2 to 10 min (15). [View Larger Version of this Image (109K GIF file)]

    Because of the good epitaxial interface between the (0001) plane of the ZnO nanowire and the (110) plane of the substrate (16), nearly all of the nanowires grow vertically from the substrates (Fig. 1, A through D). The a plane (110) of sapphire is twofold symmetric, whereas the ZnO c plane is sixfold symmetric. They are essentially incommensurate, with the exception that the a axis of ZnO and the c axis of sapphire are related almost exactly by a factor of 4, with a mismatch of less than 0.08% at room temperature. Such a coincidental matchup along the sapphire [0001] direction, along with a strong tendency of ZnO to grow in the c orientation and the incoherence of interfaces in directions other than sapphire [0001], leads to the unique vertical epitaxial growth configuration. The anisotropy of the sapphire's a plane is critical for growing high-quality c-oriented ZnO nanowire arrays.

    Hexagon end planes of the nanowires can be clearly identified in the SEM image of the nanowire array (Fig. 1E), providing strong evidence that these nanowires grow along the direction and are indeed well-faceted at both the end and side surfaces. The well-faceted nature of these nanowires will have important implications when they are used as effective laser media. Additional structural characterization of the ZnO nanowires was carried out with transmission electron microscopy (TEM). The high-resolution TEM image of a single-crystalline ZnO nanowire (Fig. 1F) shows that spacing of 2.56 ± 0.05 Å between adjacent lattice planes corresponds to the distance between two (0002) crystal planes, further proving to be the preferred growth direction for the ZnO nanowires. This preferential nanowire growth on the sapphire substrate is also reflected in the x-ray diffraction pattern (Fig. 2). Only (000l) peaks are observed, indicating excellent overall c-axis alignment of these nanowire arrays over a large substrate area.

    Fig. 2. X-ray diffraction pattern of ZnO nanowires on a sapphire substrate. Only (000l) peaks are observed, owing to their well-oriented growth configuration. The diffraction pattern is taken on a Siemens Z5000 x-ray diffractometer. a.u., arbitrary units. [View Larger Version of this Image (12K GIF file)]

    Photoluminescence spectra of nanowires were measured with a He-Cd laser (325 nm) as an excitation source. Strong near-band-gap edge emission at ~377 nm has been observed (15). In order to explore the possible stimulated emission from these oriented nanowires, the power-dependent emission has been examined. The samples were optically pumped by the fourth harmonic of Nd:yttrium-aluminum-garnet laser (266 nm, 3-ns pulse width) at room temperature. The pump beam was focused on nanowires at an incidence angle 10 to the symmetric axis of the nanowire. Light emission was collected in the direction normal to the end surface plane (along the symmetric axis) of the nanowires. In the absence of any fabricated mirrors, we observed lasing action in these ZnO nanowires during the evolution of the emission spectra with increasing pump power (Fig. 3, A and B). At low excitation intensity, the spectrum consists of a single broad spontaneous emission peak (Fig. 3A) with a full width at half maximum of ~17 nm. This spontaneous emission is 140 meV below the band gap (3.37 eV) and is generally ascribed to the recombination of excitons through an exciton-exciton collision process, where one of the excitons radiatively recombines to generate a photon (4-6). As the pump power increases, the emission peak narrows because of the preferential amplification of frequencies close to the maximum of the gain spectrum. When the excitation intensity exceeds a threshold (~40 kW/cm2), sharp peaks emerge in the emission spectra. The linewidths of these peaks are 50 times smaller than the linewidth of the spontaneous emission peak below the threshold. Above the threshold, the integrated emission intensity increases rapidly with the pump power (Fig. 3B). The narrow linewidth and the rapid increase of emission intensity indicate that stimulated emission takes place in these nanowires. The observed single or multiple sharp peaks represent different lasing modes at wavelengths between 370 and 400 nm. The lasing threshold is quite low in comparison with previously reported values for random lasing (~300 kW/cm2) in disordered particles or thin films (4). These short-wavelength nanowire nanolasers operate at room temperature, and the areal density of these nanolasers readily reaches 1.1 × 1010 cm2.

    Fig. 3. (A) Emission spectra from nanowire arrays below (line a) and above (line b and inset) the lasing threshold. The pump power for these spectra are 20, 100, and 150 kW/cm2, respectively. The spectra are offset for easy comparison. (B) Integrated emission intensity from nanowires as a function of optical pumping energy intensity. (C) Schematic illustration of a nanowire as a resonance cavity with two naturally faceted hexagonal end faces acting as reflecting mirrors. Stimulated emission from the nanowires was collected in the direction along the nanowire's end-plane normal (the symmetric axis) with a monochromator (ISA, Edison, New Jersey) combined with a Peltier-cooled charge-coupled device (EG&G, Gaithersburg, Maryland). The 266-nm pump beam was focused to the nanowire array at an angle 10 to the end-plane normal. All experiments were carried out at room temperature. [View Larger Version of this Image (22K GIF file)]

    The observation of lasing action in these nanowire arrays without any fabricated mirror prompts us to consider these single-crystalline, well-faceted nanowires as natural resonance cavities (Fig. 3C). It is possible that the giant oscillator strength effect (8), which can occur in high-quality nanowire crystals with dimensions larger than the exciton Bohr radius but smaller than the optical wavelength, enables the excitonic stimulated emission in these nanowire arrays. For II-VI semiconductors, the cleaved edge of the specimen is usually used as a mirror (1-3, 17). For our nanowires, one end is the epitaxial interface between the sapphire and ZnO, whereas the other end is the sharp (0001) plane of the ZnO nanocrystals. Both can serve as good laser cavity mirrors, considering that the refractive indexes for sapphire, ZnO, and air are

    1.8, 2.45, and 1, respectively (18). This natural cavity or waveguide formation in nanowires suggests a simple chemical approach to forming a nanowire laser cavity without cleavage and etching. In fact, when multiple lasing modes were observed for these nanowires (Fig. 3A, inset), the observed mode spacing is ~5 nm for ~5-m-long wires, which agrees quantitatively well with the calculated spacing between adjacent resonance frequencies vF = c/2nl (17), where vF is emission mode spacing, c is the speed of light, n is the refractive index, and l is the resonance cavity length.

    Furthermore, lifetime measurements (Fig. 4) show that the radiative recombination of the excitons is a superposition of a fast and a slow process with time constants of ~70 and 350 ps, respectively. The luminescence lifetime is mainly determined by the concentration of defects, which trap the electrons and/or holes and eventually cause their nonradiative recombination. Although the exact origin of the luminescence decay remains unclear at this stage, the long lifetime measured for these wires [350 ps, as compared with 200 ps for ZnO thin films (4)] demonstrates the high crystal quality achieved with the nanowire growth process.

    Fig. 4. The decay of the luminescence from the ZnO nanowires was studied with a frequency-tripled mode-locked Ti:sapphire laser for pulsed excitation (200-fs pulse length) and a streak camera with picosecond resolution for detection. A good fit (solid line) to the experimental data (dotted line) recorded at room temperature is obtained with a biexponential decay model assuming a fast and a slow process with time constants of ~70 and 350 ps, respectively. The time-resolved spectrum was recorded at an excitation power of 6.39 mW. [View Larger Version of this Image (15K GIF file)]


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    18. A simple estimation of the possible number of transversal modes that a waveguide can support indicates that our nanowires with diameters between 80 and 120 nm are actually single-mode waveguides for ultraviolet light.

    19. This work was supported by the Camille and Henry Dreyfus Foundation, the 3M Corporation, the NSF through a Career Award (DMR-0092086), the U.S. Department of Energy, and the University of California, Berkeley. P.Y. is an Alfred P. Sloan Research Fellow. Work at the Lawrence Berkeley National Laboratory was supported by the Office of Science, Basic Energy Sciences, Division of Materials Science of the U.S. Department of Energy under contract DE-AC03-76SF00098. H.K. thanks the Swiss National Science Foundation for financial support. We thank the National Center for Electron Microscopy for the use of their facilities.

    2 March 2001; accepted 26 April 2001 10.1126/science.1060367 Include this information when citing this paper.


  • This is a huge bone of contention on many campuses: Professor A and B want the Journal of Obscure Latvian Chemistry at $2000/year, but C and D would rather have Acta Trivia at $2500/year. Academic budgets aren't much- what do you do?

    To say nothing of inter colegiate competition. I'm at the University of Virginia, my fiancee is at Virginia Tech. Because our schools co-operate Tech's liberal arts departments rely heavily on UVA's archives. UVA's engineering school works closely with VA Tech for scientific journals. While UVA and Tech are rivals in sports and have been for some time this rivalry is extending more and more into academics. As the lines of communication break down between the universities a lot of this data is becoming unavailable to students who need it.

    Ultimately this could and should be fixed by placing all publicly funded research in the public domain (with all appropriate restrictions as to who gets credit for it of course). I just don't see that happening. Shame really.

    This has been another useless post from....
  • About 9 months before the 20 TB drive.

  • me thinkssome one is suffering from linux philosophy overdose.

  • The lasers are obviously very good for optics tech but the atrical mettions nothing about the power avalible to the lasers. If they can be used 4 heat.

    This will allow cos of the size of the laser, mould makeing on a much grander and smoother scale

  • by OxideBoy ( 322403 ) on Friday June 08, 2001 @08:06AM (#165882) Homepage
    ...lots of research just as interesting as this gets published all the time. ZnO is a wide-bandgap material enjoying a renaissance of interest, and might compete with SiC, DLC [aps.org], and GaN, but I'm not sure this is worthy of a full-blown /. article. Now combinatorial MBE to explore the TiO2:Co [siliconstrategies.com] system, that was /. worthy ;-)
  • "Daddy, will galium arsenide and arsenic acid spills stop from that bad-chip-industry?"

    "Yes, kids. It'll stop. Now, put your nose back to your face, and go to school."

    Don't worry, I'm too depressed [to|every]day

  • Why does LASER have to be broken into a verb? Leave my acronyms alone thank you very much. And if you really wan't a verb it would be the LA part anyway. Besides lase sounds so dainty, i'd much prefer beam, or shoot, or even blast
  • Hmmm...

    First a quote:

    *begin quote from the article (UniSci's)*

    Though Yang now must use another optical laser to excite the zinc oxide molecules so that they will emit UV light -- a process called optical pumping -- he hopes eventually to "pump" the zinc oxide with electrons. Electron pumping is necessary for a laser to be integrated into an electronic circuit.

    *end quote*

    Now then, once they're capable of electron-pumping, you'll have an incredibly small laser (which, most likely can be pumped by miniscule--comparatively--voltages). This will probably involve growing the lasers in place on something that later is etched as the circuit to provide the electrons.... So you'll have an incredibly small solid state UV laser.... I don't know what the characteristics of the laser are (especially the firing time), but it'd be entertaining if they could be fired in the short enough pulses to allow the kind of storage [slashdot.org] this other article talked about

    Nietzsche on Diku:
    sn; at god ba g
    :Backstab >KILLS< god.
  • Smallest Laser 1,000 Times Thinner Than A Human Hair
    this research is completely useless! How are we supposed to play lasergames now? How will we ever enjoy lightshows again with lasers this small? A damn waste of resources IM(not-so-)HO!
  • by ausduck ( 454886 ) <mathematics_NO@SPAMhotmail.com> on Friday June 08, 2001 @08:28AM (#165887)
    If these new lasers are 100 times smaller than the old ones, would I be correct in guessing that the optical discs resulting from this new technology would store 100 times more data (or maybe 10000 times, if it works in two dimesions)? How long then, would it be before such discs could replace your old hard disks?

    One day, you know, this miniaturisation will just stop... there has to be a limit to it.
  • I hear that. Jeez cut the mumbo jumbo and make a point already.

Programmers used to batch environments may find it hard to live without giant listings; we would find it hard to use them. -- D.M. Ritchie