文章来源:未知 文章作者:meng 发布时间:2010-09-24 02:43 字体: [ ]  进入论坛

Computers, light bulbs, and even people generate heat—energy that ends up being wasted. With a thermoelectric device, which converts heat to electricity and vice1 versa(反之亦然) , you can harness that otherwise wasted energy. Thermoelectric devices are touted2 for use in new and efficient refrigerators, and other cooling or heating machines. But present-day designs are not efficient enough for widespread commercial use or are made from rare materials that are expensive and harmful to the environment. Researchers at the California Institute of Technology (Caltech) have developed a new type of material—made out of silicon3, the second most abundant element in Earth's crust—that could lead to more efficient thermoelectric devices. The material—a type of nanomesh—is composed of a thin film with a grid5-like arrangement of tiny holes. This unique design makes it difficult for heat to travel through the material, lowering its thermal6 conductivity to near silicon's theoretical limit. At the same time, the design allows electricity to flow as well as it does in unmodified silicon.

"In terms of controlling thermal conductivity, these are pretty sophisticated devices," says James Heath, the Elizabeth W. Gilloon Professor and professor of chemistry at Caltech, who led the work. A paper about the research will be published in the October issue of the journal Nature Nanotechnology.

A major strategy for making thermoelectric materials energy efficient is to lower the thermal conductivity without affecting the electrical conductivity, which is how well electricity can travel through the substance. Heath and his colleagues had previously8 accomplished9 this using silicon nanowires—wires of silicon that are 10 to 100 times narrower than those currently used in computer microchips. The nanowires work by impeding10(阻碍,妨碍) heat while allowing electrons to flow freely.

In any material, heat travels via phonons(声子) —quantized packets of vibration11 that are akin7 to(近似的) photons, which are themselves quantized packets of light waves. As phonons zip along the material, they deliver heat from one point to another. Nanowires, because of their tiny sizes, have a lot of surface area relative to their volume. And since phonons scatter12 off surfaces and interfaces13, it is harder for them to make it through a nanowire without bouncing astray(迷路的) . As a result, a nanowire resists heat flow but remains14 electrically conductive.

But creating narrower and narrower nanowires is effective only up to a point. If the nanowire is too small, it will have so much relative surface area that even electrons will scatter, causing the electrical conductivity to plummet15(大幅下降) and negating16 the thermoelectric benefits of phonon scattering17.

To get around this problem, the Caltech team built a nanomesh material from a 22-nanometer-thick sheet of silicon. (One nanometer is a billionth of a meter.) The silicon sheet is converted into a mesh4—similar to a tiny window screen—with a highly regular array of 11- or 16-nanometer-wide holes that are spaced just 34 nanometers apart.

Instead of scattering the phonons traveling through it, the nanomesh changes the way those phonons behave, essentially18 slowing them down. The properties of a particular material determine how fast phonons can go, and it turns out that—in silicon at least—the mesh structure lowers this speed limit. As far as the phonons are concerned, the nanomesh is no longer silicon at all. "The nanomesh no longer behaves in ways typical of silicon," says Slobodan Mitrovic, a postdoctoral scholar in chemistry at Caltech. Mitrovic and Caltech graduate student Jen-Kan Yu are the first authors on the Nature Nanotechnology paper.

When the researchers compared the nanomesh to the nanowires, they found that—despite having a much higher surface-area-to-volume ratio—the nanowires were still twice as thermally19 conductive as the nanomesh. The researchers suggest that the decrease in thermal conductivity seen in the nanomesh is indeed caused by the slowing down of phonons, and not by phonons scattering off the mesh's surface. The team also compared the nanomesh to a thin film and to a grid-like sheet of silicon with features roughly 100 times larger than the nanomesh; both the film and the grid had thermal conductivities about 10 times higher than that of the nanomesh.

Although the electrical conductivity of the nanomesh remained comparable to regular, bulk silicon, its thermal conductivity was reduced to near the theoretical lower limit for silicon. And the researchers say they can lower it even further. "Now that we've showed that we can slow the phonons down," Heath says, "who's to say we can't slow them down a lot more?"

The researchers are now experimenting with different materials and arrangements of holes in order to optimize20 their design. "One day, we might be able to engineer a material where you not only can slow the phonons down, but you can exclude(排除) the phonons that carry heat altogether," Mitrovic says. "That would be the ultimate goal."


1 vice NU0zQ     
  • He guarded himself against vice.他避免染上坏习惯。
  • They are sunk in the depth of vice.他们堕入了罪恶的深渊。
2 touted 00151f908b31d984fd20d8b48dba34f3     
v.兜售( tout的过去式和过去分词 );招揽;侦查;探听赛马情报
  • She's being touted as the next leader of the party. 她被吹捧为该党的下一任领导人。
  • People said that he touted for his mother and sister. 据说,他给母亲和姐姐拉生意。 来自辞典例句
3 silicon dykwJ     
  • This company pioneered the use of silicon chip.这家公司开创了使用硅片的方法。
  • A chip is a piece of silicon about the size of a postage stamp.芯片就是一枚邮票大小的硅片。
4 mesh cC1xJ     
n.网孔,网丝,陷阱;vt.以网捕捉,啮合,匹配;vi.适合; [计算机]网络
  • Their characters just don't mesh.他们的性格就是合不来。
  • This is the net having half inch mesh.这是有半英寸网眼的网。
5 grid 5rPzpK     
  • In this application,the carrier is used to encapsulate the grid.在这种情况下,要用载体把格栅密封起来。
  • Modern gauges consist of metal foil in the form of a grid.现代应变仪则由网格形式的金属片组成。
6 thermal 8Guyc     
  • They will build another thermal power station.他们要另外建一座热能发电站。
  • Volcanic activity has created thermal springs and boiling mud pools.火山活动产生了温泉和沸腾的泥浆池。
7 akin uxbz2     
  • She painted flowers and birds pictures akin to those of earlier feminine painters.她画一些同早期女画家类似的花鸟画。
  • Listening to his life story is akin to reading a good adventure novel.听他的人生故事犹如阅读一本精彩的冒险小说。
8 previously bkzzzC     
  • The bicycle tyre blew out at a previously damaged point.自行车胎在以前损坏过的地方又爆开了。
  • Let me digress for a moment and explain what had happened previously.让我岔开一会儿,解释原先发生了什么。
9 accomplished UzwztZ     
  • Thanks to your help,we accomplished the task ahead of schedule.亏得你们帮忙,我们才提前完成了任务。
  • Removal of excess heat is accomplished by means of a radiator.通过散热器完成多余热量的排出。
10 impeding 8qtzd2     
  • Fallen rock is impeding the progress of rescue workers. 坠落的石头阻滞了救援人员的救援进程。
  • Is there sufficient room for the kiosk and kiosk traffic without impeding other user traffic? 该环境下是否有足够的空间来摆放信息亭?信息亭是否会妨碍交通或者行走? 来自About Face 3交互设计精髓
11 vibration nLDza     
  • There is so much vibration on a ship that one cannot write.船上的震动大得使人无法书写。
  • The vibration of the window woke me up.窗子的震动把我惊醒了。
12 scatter uDwzt     
  • You pile everything up and scatter things around.你把东西乱堆乱放。
  • Small villages scatter at the foot of the mountain.村庄零零落落地散布在山脚下。
13 interfaces ad63a35ea2ac8a42233e5ac6cb325d34     
界面( interface的名词复数 ); 接口(连接两装置的电路,可使数据从一种代码转换成另一种代码); 交界; 联系
  • If the class needs to be reprogrammed, new interfaces are created. 如果class需要重新程序设计,新的interfaces创建。
  • Interfaces solve this problem of evolving code. Interfaces解决了代码升级的问题。
14 remains 1kMzTy     
  • He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
  • The remains of the meal were fed to the dog.残羹剩饭喂狗了。
15 plummet s2izN     
  • Mengniu and Yili have seen their shares plummet since the incident broke.自事件发生以来,蒙牛和伊利的股票大幅下跌。
  • Even if rice prices were to plummet,other brakes on poverty alleviation remain.就算大米价格下跌,其它阻止导致贫困的因素仍然存在。
16 negating 92a43cdd62e27f9ac780272552c6907e     
v.取消( negate的现在分词 );使无效;否定;否认
  • The decline of community life is negating the work of welfare services. 社区生活的下降否定了福利机构的工作。 来自《简明英汉词典》
  • Post-modernity transcends modernity by the means of negating and clearing up selfhood. 后现代超越现代性是通过否定和消解主体来实现的。 来自互联网
17 scattering 91b52389e84f945a976e96cd577a4e0c     
  • The child felle into a rage and began scattering its toys about. 这孩子突发狂怒,把玩具扔得满地都是。 来自《简明英汉词典》
  • The farmers are scattering seed. 农夫们在播种。 来自《简明英汉词典》
18 essentially nntxw     
  • Really great men are essentially modest.真正的伟人大都很谦虚。
  • She is an essentially selfish person.她本质上是个自私自利的人。
19 thermally 4503c689965bc42ad92334e583f5d8c3     
  • The magnetizing field is then removed while the body is thermally isolated. 在该物体热绝缘时把磁场撤去。
  • They could thermally desorb these ions by heating the foil to red heat. 他们通过加热金属箔至红热以解吸这些离子。
20 optimize WIoxY     
v.使优化 [=optimise]
  • We should optimize the composition of the Standing Committees.优化人大常委会组成人员的结构。
  • We should optimize our import mix and focus on bringing in advanced technology and key equipment.优化进口结构,着重引进先进技术和关键设备。