國際科技信息

歐委會(huì)推出一項(xiàng)新的綠色創(chuàng)新行動(dòng)計(jì)劃

歐盟2020戰(zhàn)略確定三大戰(zhàn)略目標(biāo)：經(jīng)濟(jì)智能性、可持續(xù)及包容性增長。為具體落實(shí)上述目標(biāo)、占領(lǐng)綠色技術(shù)制高點(diǎn)、保持綠色創(chuàng)新（Eco-Innovation）世界領(lǐng)先水平、以及提升綠色工業(yè)世界競爭力，積極應(yīng)對全球面臨的環(huán)境壓力、資源枯竭和氣候變化，

歐委會(huì)于2011年12月15日通過決定，推出了一項(xiàng)新的綠色創(chuàng)新行動(dòng)計(jì)劃（EcoAP）。

EcoAP在原有環(huán)境技術(shù)行動(dòng)計(jì)劃（ETAP，Environment Technologies Action Plan）的基礎(chǔ)上，圍繞五大主題著手促進(jìn)綠色創(chuàng)新的健康快速發(fā)展。一是改善政策法律環(huán)境；二是清除綠色創(chuàng)新障礙；三是擴(kuò)大綠色創(chuàng)新需求；四是增加綠色創(chuàng)新投入；五是強(qiáng)化技術(shù)、創(chuàng)新、工業(yè)及市場銜接。

EcoAP的七項(xiàng)主要關(guān)鍵行動(dòng)分別是：1）充分利用環(huán)境法規(guī)政策，促進(jìn)綠色創(chuàng)新環(huán)境建設(shè)。2）積極支持綠色創(chuàng)新技術(shù)的商業(yè)化應(yīng)用和公私合作伙伴項(xiàng)目，解決綠色創(chuàng)新體系薄弱環(huán)節(jié)障礙。3）適時(shí)創(chuàng)立和修正新標(biāo)準(zhǔn)，擴(kuò)大綠色創(chuàng)新市場需求。4）重新整合投融資機(jī)制、增加公共資金投入，分擔(dān)研發(fā)創(chuàng)新風(fēng)險(xiǎn)，支持綠色創(chuàng)新型中小企業(yè)的健康發(fā)展。5）加強(qiáng)拓展國際協(xié)調(diào)與合作，積極應(yīng)對環(huán)境、資源、氣候變化挑戰(zhàn)。6）努力完善職業(yè)培訓(xùn)、新興就業(yè)、能力建設(shè)體系，滿足勞動(dòng)市場的新興需求。7）繼續(xù)強(qiáng)化歐洲創(chuàng)新伙伴關(guān)系，有利于綠色創(chuàng)新知識(shí)的轉(zhuǎn)移及轉(zhuǎn)化。

歐洲綠色工業(yè)（Eco-Industries）已形成巨大產(chǎn)業(yè)，盡管中小企業(yè)眾多，但2008年產(chǎn)值已達(dá)3190億歐元（最新數(shù)據(jù)），平均每年仍然以接近8%的速度增長。歐委會(huì)對綠色創(chuàng)新的定義是，通過降低對環(huán)境的影響、或緩解環(huán)境的壓力、或自然資源有效合理的利用，對經(jīng)濟(jì)社會(huì)可持續(xù)發(fā)展具有可證實(shí)、顯著改進(jìn)的所有創(chuàng)新形式。

Eco-innovation Action Plan (EcoAP) Launched

The EC has launched the Eco-Innovation Action Plan (EcoAP)as part of the Innovation Union Flagship Initiative of the Europe 2020 strategy for smart, sustainable and inclusive growth. It aims to bridge the gap between innovation and the market and boost innovation that reduces pressure on the environment.

The Action Plan will accelerate eco-innovation across all sectors of the economy with well targeted actions to help create stronger and more stable market demand for eco-innovation, it will take measures in the areas of regulatory incentives, private and public procurement and standards and it will mobilise support for SMEs to improve investment readiness and networking opportunities. The plan outlines a number of action points,including:

· Using environmental policy and legislation to promote ecoinnovation;

· Mobilising financial instruments and support services for SMEs;

· Promoting international co-operation and supporting demonstration projects and partnering;

· Developing new standards to boost eco-innovation;

· Supporting the development of emerging skills and jobs and related training programmes to match labour market needs.

The EcoAP builds on the 2004 Environmental Technologies Action Plan (ETAP), and expands the focus from green technologies to the broader field of ecoinnovation. It includes actions both on the demand and supply side,on research and industry and on policy and financial instruments.The Plan recognizes the key role of environmental regulation as a driver of eco-innovation, and stresses the importance of research and innovation to produce more innovative technologies and bring them to the market.

Environment Commissioner Janez Poto?nik described the plan:"The innovation challenge for this Century will be making our resources go further - doing more with less – and reducing the impact of our activities. Europe must be in the lead in meeting that challenge if we want to be competitive in a world of increasing resource constraints. Worldwide demand for environmental technologies,products and services is growing rapidly even in these difficult times,and it's an area where Europe has much to offer. This is a plan for green jobs and green growth."

新合成分子可治療自身免疫類疾病

最近，以色列魏茲曼科學(xué)研究所改變以往的治療策略，用人工合成分子誘導(dǎo)免疫系統(tǒng)產(chǎn)生出特殊的抗體，可封鎖在引發(fā)自身免疫疾病中起重要作用的一種酶MMP9，并在動(dòng)物實(shí)驗(yàn)中取得成功。新合成分子在治療克羅恩氏病等免疫系統(tǒng)疾病方面具有很大潛力，為尋找免疫類疾病療法開辟了新方向。相關(guān)論文發(fā)表在《自然·醫(yī)學(xué)》雜志網(wǎng)站上。

MMP是一種基質(zhì)金屬蛋白酶家族，在細(xì)胞動(dòng)員、分裂、傷口愈合等方面起著關(guān)鍵作用。如果它們中的某些成員，尤其是MMP9失控的話，就會(huì)引發(fā)自身免疫疾病和癌癥轉(zhuǎn)移，封鎖這些蛋白質(zhì)有望找到治療自身免疫類疾病的方法。開始時(shí)，研究人員設(shè)計(jì)出一種直接瞄準(zhǔn)所有MMP成員的人造藥物分子，但太過粗糙而且有很大副作用。

研究所生物調(diào)控分部教授艾麗特 薩基解釋說，正常情況下，機(jī)體也能產(chǎn)生自己的MMP抑制劑，叫做TIMP，作為一種緊縮程序來控制MMP酶。這些自然產(chǎn)生的TIMP具有高度選擇性，由三個(gè)組氨酸多肽圍繞一個(gè)金屬鋅離子構(gòu)成，每個(gè)手臂都極其精確，恰好能到達(dá)MMP酶的活性位點(diǎn)凹槽，像個(gè)軟木塞那樣堵住凹槽，使MMP失去活性。“要想復(fù)制這種精確性是非常困難的。”

研究人員轉(zhuǎn)而尋找另外的替代方法，不是設(shè)計(jì)一種分子，而是直接攻擊MMP。就像死亡病毒引發(fā)免疫系統(tǒng)生成抗體，攻擊活病毒那樣，他們想出了一種方法，通過MMP免疫反應(yīng)“誘騙”機(jī)體生成瞄準(zhǔn)MMP9的天然抗體，鎖住其活性位點(diǎn)。

他們在MMP9的核心活性位點(diǎn)人工合成出一種金屬鋅-組氨酸復(fù)合物，然后把這些小分子注射到小鼠體內(nèi)，并檢查小鼠血液中抵抗MMP酶的免疫反應(yīng)信號。研究人員對所產(chǎn)生抗體的原子結(jié)構(gòu)進(jìn)行了詳細(xì)分析，發(fā)現(xiàn)它和TIMP有所不同，但作用極其相似，同樣能到達(dá)酶的凹槽并封鎖活性位點(diǎn)?？贵w能選擇性地僅針對MMP家族中的兩個(gè)成員MMP2和MMP9，并與它們緊密結(jié)合。

New synthetic molecules treat autoimmune disease in mice

A team of Weizmann Institute scientists has turned the tables on an autoimmune disease. In such diseases, including Crohn's and rheumatoid arthritis, the immune system mistakenly attacks the body's tissues. But the scientists managed to trick the immune systems of mice into targeting one of the body's players in autoimmune processes, an enzyme known as MMP9. The results of their research appear today in Nature Medicine.

Prof. Irit Sagi of the Biological Regulation Department and her research group have spent years looking for ways to home in on and block members of the matrix metalloproteinase (MMP)enzyme family. These proteins cut through such support materials in our bodies as collagen, which makes them crucial for cellular mobilization, proliferation and wound healing, among other things. But when some members of the family, especially MMP9,get out of control, they can aid and abet autoimmune disease and cancer metastasis. Blocking these proteins might lead to effective treatments for a number of diseases.

Originally, Sagi and others had designed synthetic drug molecules to directly target MMPs. But these drugs proved to be fairly crude tools that had extremely severe side effects. The body normally produces its own MMP inhibitors,known as TIMPs, as part of the tight regulation program that keeps these enzymes in line. As opposed to the synthetic drugs, these work in a highly selective manner. An arm on each TIMP is precisely constructed to reach into a cleft in the enzyme that shelters the active bit – a metal zinc ion surrounded by three histidine peptides –closing it off like a snug cork.'Unfortunately,' says Sagi, 'it is quite difficult to reproduce this precision synthetically.'

Dr. Netta Sela-Passwell began working on an alternative approach as an M.Sc. student in Sagi's lab, and continued on through her Ph.D. research. She and Sagi decided that, rather than attempting to design a synthetic molecule to directly attack MMPs, they would try trick the immune system to create natural antibodies that target MMP-9 through immunization. Just as immunization with a killed virus induces the immune system to create antibodies that then attack live viruses, an MMP immunization would trick the body into creating antibodies that block the enzyme at its active site.

Together with Prof. Abraham Shanzer of the Organic Chemistry Department, they created an artificial version of the metal zinchistidine complex at the heart of the MMP9 active site. They then injected these small, synthetic molecules into mice and afterward checked the mice's blood for signs of immune activity against the MMPs. The antibodies they found,which they dubbed 'metallobodies,'were similar but not identical to TIMPS, and a detailed analysis of their atomic structure suggested they work in a similar way –reaching into the enzyme's cleft and blocking the active site. The metallobodies were selective for just two members of the MMP family – MMP2 and 9 – and they bound tightly to both the mouse versions of these enzymes and the human ones.

As they hoped, when they had induced an inflammatory condition that mimics Crohn's disease in mice, the symptoms were prevented when mice were treated with metallobodies. 'We are excited not only by the potential of this method to treat Crohn's,'says Sagi, but by the potential of using this approach to explore novel treatments for many other diseases.' Yeda, the technology transfer arm of the Weizmann Institute has applied for a patent for the synthetic immunization molecules as well as the generated metallobodies.

美研制出負(fù)折射率等離子納米天線

美國科學(xué)家表示，他們的實(shí)驗(yàn)證明，纖細(xì)的等離子體納米天線陣列能采用新奇的方式對光進(jìn)行精確地操控，改變光的相位，創(chuàng)造出負(fù)折射現(xiàn)象，最新研究有望使科學(xué)家們研制出功能更強(qiáng)大的光子計(jì)算機(jī)等新式光學(xué)設(shè)備。相關(guān)研究發(fā)表在12月22日出版的《科學(xué)》雜志上。

該研究的領(lǐng)導(dǎo)者、普渡大學(xué)布瑞克納米技術(shù)研究中心納米光子學(xué)部門主管、電子和計(jì)算機(jī)工程教授弗拉基米爾·薩里切夫表示：“通過大大改變光的相位，我們能顯著改變光的傳播方式，因此，為很多潛在的應(yīng)用打開了大門?！惫獾南辔皇侵腹獠ㄔ谇斑M(jìn)時(shí)，光子振動(dòng)所呈現(xiàn)的交替波形變化。同一種光波通過折射率不同的物質(zhì)時(shí)，相位就會(huì)發(fā)生變化。

今年10月份，哈佛大學(xué)電子工程學(xué)教授費(fèi)德里科·卡帕索領(lǐng)導(dǎo)的科研團(tuán)隊(duì)在《科學(xué)》雜志上撰文指出，他們利用一種新技術(shù)誘導(dǎo)光線路徑，使得沿用了多年的斯涅耳定律受到挑戰(zhàn)。斯涅耳定律指出，當(dāng)光從一種介質(zhì)進(jìn)入另一種介質(zhì)時(shí)，在這兩種介質(zhì)的交界處，相位不會(huì)突然發(fā)生變化。而哈佛大學(xué)的實(shí)驗(yàn)表明，通過使用一種新型結(jié)構(gòu)的“超材料”，光的相位和傳播方向都會(huì)發(fā)生巨大變化。這一研究發(fā)現(xiàn)使在預(yù)測光線由一種介質(zhì)進(jìn)入另一種介質(zhì)時(shí)，其有別于經(jīng)典的折射和反射定律，可以創(chuàng)建負(fù)折射現(xiàn)象，光的偏振也可以得到控制。

普渡大學(xué)的科研團(tuán)隊(duì)則更近一步，制造出了納米天線陣列并大大改變了光波波長介于1微米（百萬分之一米）到1.9微米之間的近紅外線附近光波的相位和傳播方向。薩里切夫表示：“我們將哈佛大學(xué)的研究拓展到近紅外線區(qū)域，近紅外線，尤其是波長為1.5微米的光線對通訊來說至關(guān)重要，通過光纖傳送的信息使用的就是這個(gè)波長，最新研究在通訊領(lǐng)域?qū)⒎浅?shí)用。我們也證明，這并非單頻效應(yīng)，適用于很多波段，因此，可廣泛應(yīng)用于很多技術(shù)領(lǐng)域?！?/p>

這種納米天線是蝕刻在一層硅上方的金做成的V型結(jié)構(gòu)，它們是一種“超材料”（一般都是所謂的等離子體結(jié)構(gòu)），寬40納米?？茖W(xué)家們也已證明，他們能讓光通過一個(gè)寬度僅為光波波長五十分之一的超薄“等離子體納米天線層”。

科學(xué)家們解釋道，每種材料都有自己的折射率，可描述光在其中的彎曲程度。包括玻璃、水、空氣等在內(nèi)的所有天然材料的折射率都為正數(shù)，而新的超薄等離子體納米天線層能導(dǎo)致光線大大改變其傳播方向，甚至產(chǎn)生負(fù)折射現(xiàn)象，使用傳統(tǒng)材料則無法做到這一點(diǎn)。這一創(chuàng)新有望讓人們引導(dǎo)激光并改變激光的形狀，應(yīng)用于軍事和通訊領(lǐng)域；有助于科學(xué)家們研制出使用光處理信息的光子計(jì)算機(jī)中的納米電路以及功能強(qiáng)大的新型透鏡等。

'Plasmonic nanoantennas' show promise in optical innovations

Researchers have shown how arrays of tiny "plasmonic nanoantennas" are able to precisely manipulate light in new ways that could make possible a range of optical innovations such as more powerful microscopes, telecommunications and computers.

The researchers at Purdue University used the nanoantennas to abruptly change a property of light called its phase. Light is transmitted as waves analogous to waves of water, which have high and low points. The phase defines these high and low points of light.

"By abruptly changing the phase we can dramatically modify how light propagates, and that opens up the possibility of many potential applications," said Vladimir Shalaev, scientific director of nanophotonics at Purdue's Birck Nanotechnology Center and a distinguished professor of electrical and computer engineering.

Findings are described in a paper to be published online Thursday (Dec. 22) in the journal Science.

The new work at Purdue extends findings by researchers led by Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at the Harvard School of Engineering and Applied Sciences. In that work, described in an October Science paper, Harvard researchers modified Snell's law, a long-held formula used to describe how light reflects and refracts, or bends, while passing from one material into another.

"What they pointed out was revolutionary," Shalaev said.

Until now, Snell's law has implied that when light passes from one material to another there are no abrupt phase changes along the interface between the materials. Harvard researchers,however, conducted experiments showing that the phase of light and the propagation direction can be changed dramatically by using new types of structures called metamaterials, which in this case were based on an array of antennas.

The Purdue researchers took the work a step further,creating arrays of nanoantennas and changing the phase and propagation direction of light over a broad range of near-infrared light.The paper was written by doctoral students Xingjie Ni and Naresh K.Emani, principal research scientist Alexander V. Kildishev, assistant professor Alexandra Boltasseva,and Shalaev.

可在p型與n型間轉(zhuǎn)換的新式晶體管問世

最近，德國科學(xué)家研制出一種新式的通用晶體管，其既可當(dāng)p型晶體管又可當(dāng)n型晶體管使用，最新晶體管有望讓電子設(shè)備更緊湊；科學(xué)家們也可用其設(shè)計(jì)出新式電路。相關(guān)研究發(fā)表在最新一期的《納米快報(bào)》雜志上。

目前，大部分電子設(shè)備都包含兩類不同的場效應(yīng)晶體管：使用電子作為載荷子的n型和使用空穴作為載荷子的p型。這兩種晶體管一般不會(huì)相互轉(zhuǎn)化。而德累斯頓工業(yè)大學(xué)和德奇夢達(dá)公司攜手研制的新式晶體管可通過電信號對其編程，讓其自我重新裝配，游走于n型晶體管和p型晶體管之間。

新晶體管由單條金屬—半導(dǎo)體—金屬結(jié)構(gòu)組成的納米線嵌于一個(gè)二氧化硅外殼中構(gòu)成。從納米線一端流出的電子或空穴通過兩個(gè)門到達(dá)納米線的另一端。這兩個(gè)門采用不同方式控制電子或空穴的流動(dòng)：一個(gè)門通過選擇使用電子或空穴來控制晶體管的類型；另一個(gè)門則通過調(diào)諧納米線的導(dǎo)電性來控制電子或空穴。

傳統(tǒng)晶體管通過在制造過程中摻雜不同元素來確定其是p型還是n型，而新式晶體管不需要在制造過程中摻雜任何元素，通過在一個(gè)門上施加外部電壓即可重新配置晶體管的類型。施加的電壓會(huì)使門附近的肖特基結(jié)阻止電子或空穴流過設(shè)備，如果電子被阻止，空穴能流動(dòng)，那么，晶體管就是p型，反之則是n型。

研究人員解釋道，使這種再配置能起作用的關(guān)鍵是調(diào)諧分別通過肖特基結(jié)（每個(gè)門一個(gè)）的電子流動(dòng)情況，模擬顯示，納米線的幾何形狀在這方面起關(guān)鍵作用。

盡管該研究還處于初期階段，但新式晶體管展示出了極佳的電學(xué)特性。比如，與傳統(tǒng)納米線場效應(yīng)晶體管相比，其開/閉比更高，且漏電更少。該研究的領(lǐng)導(dǎo)者沃爾特·韋伯表示：“除采用人造納米線外，采用目前先進(jìn)的硅半導(dǎo)體制造技術(shù)也可以制造出這種晶體管，還可以用到自對準(zhǔn)技術(shù)，大大提高工作頻率和速度?！?/p>

接下來，科學(xué)家們計(jì)劃通過改變材料的組成來改進(jìn)新式晶體管的性能，并制造出由其運(yùn)行的電路。他們表示，最大的挑戰(zhàn)是，在將其與其他晶體管結(jié)合在一起時(shí)，如何將額外的門信號整合進(jìn)來。

Universal transistor serves as a basis to perform any logic function

Most of today’s electronics devices contain two different types of field-effect transistors (FETs):n-type (which use electrons as the charge carrier) and p-type (which use holes). Generally, a transistor can only be one type or the other,but not both. Now in a new study,researchers have designed a transistor that can reconfigure itself as either n-type or p-type when programmed by an electric signal. A set of these “universal transistors”can, in principle, perform any Boolean logic operation, meaning circuits could perform the same number of logic functions with fewer transistors. This advantage could lead to more compact hardware and novel circuit designs.

The researchers who designed the transistor, led by Walter M. Weber at Namlab gGmbH in Dresden, Germany, have published the new concept in a recent issue of Nano Letters.

“Synthetic nanowires are used to realize the proof-ofprinciple,” Weber told PhysOrg.com. “However, the concept is fully transferable to state-of-the-art CMOS silicon technology and can make use of self-aligned processes.”

The new transistor’s core consists of a single nanowire made of a metal-semiconductor-metal structure, which is embedded in a silicon dioxide shell. Electrons or holes flow from the source at one end of the nanowire through two gates to the drain at the other end of the nanowire. The two gates control the flow of electrons or holes in different ways. One gate selects the transistor type by choosing to use either electrons or holes, while the other gate controls the electrons or holes by tuning the nanowire’s conductance.

Using a gate to select por n-type configuration is quite different from conventional transistors. In conventional transistors, p- or n-type operation results from doping that occurs during the fabrication process,and cannot be changed once the transistor is made. In contrast, the reconfigurable transistor doesn’t use any doping. Instead, an external voltage applied to one gate can reconfigure the transistor type even during operation. The voltage causes the Schottky junction near the gate to block either electrons or holes from flowing through the device. So if electrons are blocked, holes can flow and the transistor is p-type. By applying a slightly different voltage, the reconfiguration can be switched again, without interfering with the flow.

The scientists explain that the key to making this reconfiguration work is the ability to tune the electronic transport across each of the two junctions (one per gate) separately. Their simulations showed that the current is dominated by tunneling, suggesting that the nanowire geometry plays an important role in the ability for independent junction control.

Because the reconfigurable transistor can perform the logic functions of both p- and n-type FETs, a single transistor could replace both a p- and n-type FET in a circuit, which would significantly reduce the size of the circuit without reducing functionality.Even at this early stage, the reconfigurable transistor shows very good electrical characteristics,including a record on/off ratio and reduced leakage current compared to conventional nanowire FETs. In the future, the researchers plan to further improve the transistor’s performance.

“We are varying the material combinations to further boost device performance,” Weber said. “Further on, first circuits implementing these devices are being built. … The biggest challenge will be to incorporate the extra gate signals in the cell layout allowing flexible interconnection to the other transistors.”

西班牙科學(xué)家首次觀察到磁振子拖曳

西班牙卡特蘭納米技術(shù)研究院研究人員稱，他們在一項(xiàng)最新發(fā)現(xiàn)中首次觀察到了磁振子拖曳。這一發(fā)現(xiàn)結(jié)束了科學(xué)家50年來追尋獨(dú)立熱電效應(yīng)的歷程，對研究能量轉(zhuǎn)化應(yīng)用、開發(fā)自旋信息傳輸新途徑也具有重要意義。相關(guān)論文發(fā)表在12月18日《自然·材料學(xué)》雜志網(wǎng)站上。

熱電效應(yīng)能幫助人們在納米尺度管理熱量，利用熱量流動(dòng)來操控自旋信息。隨著信息技術(shù)的發(fā)展，自旋電子學(xué)中的熱電效應(yīng)越來越受到人們關(guān)注。上世紀(jì)50年代首次發(fā)現(xiàn)熱電效應(yīng)，在固體中，當(dāng)電子經(jīng)過原子，其電荷就會(huì)改變附近的晶格結(jié)構(gòu)，產(chǎn)生波動(dòng)；反過來，晶格波動(dòng)也會(huì)影響電子運(yùn)動(dòng)，就像海浪推動(dòng)一個(gè)沖浪運(yùn)動(dòng)員在滑行。這種相互作用導(dǎo)致的熱電效應(yīng)其實(shí)是一種聲子拖曳效應(yīng)。此后不久，科學(xué)家預(yù)言在磁性材料中也存在類似現(xiàn)象：磁振子拖曳。

在鐵磁體中，自旋保持著平行的方向。如果發(fā)生了紊亂，就會(huì)產(chǎn)生自旋波影響電子運(yùn)動(dòng)，因此磁振子流（自旋波量子）也會(huì)拖動(dòng)電子。研究人員解釋說，盡管這和聲子拖曳很相似，但要觀察磁振子拖曳卻非常困難。主要原因是聲子拖曳太顯著，把磁振子拖曳和聲子拖曳區(qū)別開非常困難。多年來，科學(xué)家只報(bào)道過一些間接證據(jù)。

為此，研究人員設(shè)計(jì)了一種特殊設(shè)備來分開磁振子拖曳和其他熱電效應(yīng)。這種設(shè)備類似一種溫差電堆，在冷熱源之間以熱并聯(lián)電串連的方式排布大量成對的鐵磁線，通過控制成對鐵磁線中的磁方向，來分離電子和聲子拖曳的熱電效應(yīng)，獨(dú)立研究磁振子拖曳。

論文指出，檢測結(jié)果作為溫度的函數(shù)，顯示出磁振子拖曳效應(yīng)服從磁振子和聲子總體變化。這一信息對理解電子—磁振子相互作用、磁振子動(dòng)力學(xué)和熱自旋傳輸?shù)奈锢頇C(jī)制非常關(guān)鍵。

A 50-year quest to isolate the thermoelectric effect is now over:Magnon drag unveiled

In a paper published in Nature Materials, a group of researchers at the Catalan Institute of Nanotechnology(ICN, Spain) led by Prof. Sergio O. Valenzuela reports the observation of the magnon drag. This work ends a 50-year long effort to isolate this elusive thermoelectric effect.

As electrons move past atoms in a solid, their charge distorts the nearby lattice and can create a wave. Reciprocally, a wave in the lattice affects the electrons motion, in analogy to a wave in the sea that pushes a surfer riding it. This interaction results in a thermoelectric effect that was first observed during the 1950's and has come to be known as phonondrag, because it can be quantified from the flow of lattice-wave quanta (phonons) that occurs over the temperature gradient.

Soon after the discovery of the phonon drag, an analogous phenomenon was predicted to appear in magnetic materials:the so called magnon drag. In a magnetic material the intrinsic magnetic moment or spin of the electrons arrange in an organized fashion. In ferromagnets, the spins maintain a parallel orientation. If a distortion in the preferred spin orientation occurs, a spin wave is created that could affect electron motion. It is therefore reasonable to expect that the flow of magnons(spin-wave quanta) could also drag the electrons.

Despite the similarities with phonon drag, the observation of the magnon drag has been elusive, and only a few indirect indications of its existence have been reported over the years. The main reason being the presence of other thermoelectric effects, most notably the phonon drag, that make it difficult to discriminate its contribution to the thermopower.

Researchers of ICN's Physics and Engineering of Nanodevices Group, Marius V. Costache,Germán Bridoux, Ingmar Neumann and group leader ICREA Prof.Sergio O. Valenzuela used a unique device geometry to discriminate the magnon drag from other thermoelectric effects. The device resembles a thermopile formed by a large number of pairs of ferromagnetic wires placed between a hot and a cold source and connected thermally in parallel and electrically in series. By controlling the relative orientation of the magnetization in pairs of wires, the magnon drag can be studied independently of the electron and phonon drag thermoelectric effects.

The work is very timely as thermoelectric effects in spinelectronics (spintronics) are gathering increasing attention as a means of managing heat in nanoscale structures and of controlling spin information by using heat flow. Measurements as a function of temperature reveal the effect on magnon drag following a variation of magnon and phonon populations. This information is crucial to understand the physics of thermal spin transport. It both provides invaluable opportunities to gather knowledge about electron-magnon interactions and may be beneficial for energy conversion applications and for the search of novel pathways towards transporting spin information.