The promise of plasmonics
The promise of plasmonics
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DOI：
10.1038/scientificamerican0407-56
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发表时间：
2007-04-01
影响因子：
3
通讯作者：
Atwater, Harry A.
中科院分区：
文献类型：
--
作者：
Atwater, Harry A.
光纤现在遍布地球仪，引导光信号，传送大量的语音通信流和大量的数据。这种巨大的能力使一些研究人员预言光子装置-不幸的是，光子器件的尺寸和性能受到衍射极限的限制;由于紧密间隔的光波之间的干涉，携带它们的光纤的宽度必须至少是材料内光波长的一半。对于基于芯片的光信号，最有可能使用约1,500纳米（十亿分之一米）的近红外波长，最小宽度比目前使用的最小电子器件要大得多;例如，硅集成电路中的一些晶体管具有小于100纳米的特征。然而，最近，科学家们一直在研究一种通过微小的纳米结构传输光信号的新技术。20世纪80年代，研究人员通过实验证实，在适当的条件下，将光波引导到金属和电介质（空气或玻璃等非导电材料）之间的界面上，可以在光波和金属表面的移动的电子之间产生共振相互作用。(In由于是导电金属，电子不会牢固地附着在单个原子或分子上。）换句话说，表面电子的振荡与金属外部电磁场的振荡相匹配。其结果是产生表面等离子体激元--电子的密度波，这种波沿着界面传播，就像你把石头扔进水里后，涟漪在池塘表面扩散一样。在过去的十年里，研究人员发现，通过创造性地设计金属-电介质界面，他们可以产生与外部电磁波频率相同但波长短得多的表面等离子体激元。这种现象可以使等离子体激元沿着称为互连的纳米级导线传播，将信息从微处理器的一部分传送到另一部分。等离子体互连对芯片设计者来说将是一个巨大的布恩，他们已经能够开发出更小更快的晶体管，但更难构建可以在芯片上快速移动数据的微小电子电路。2000年，我在加州理工学院的研究小组将这一新兴学科命名为“等离子体激元学”，他们认为这一领域的研究可能会导致一种全新的设备。最终有可能在各种仪器中使用等离子体元件，使用它们来提高显微镜的分辨率，发光二极管（LED）的效率以及化学和生物检测器的灵敏度。科学家们也在考虑医学应用，例如设计可以利用等离子体共振吸收杀死癌组织的微小粒子。一些研究人员甚至提出理论，认为某些等离子体材料可以改变物体周围的电磁场，使其变得不可见。尽管并非所有这些潜在的应用都是可行的，但研究人员正在热切地研究等离子体，因为这个新领域有望真正揭示宇宙的奥秘。
Optical fibers now span the globe, guiding light signals that convey voluminous streams of voice communications and vast amounts of data. This gargantuan capacity has led some researchers to prophesy that photonic devices—which channel and manipulate visible light and other electromagnetic waves—could someday replace electronic circuits in microprocessors and other computer chips. Unfortunately, the size and performance of photonic devices are constrained by the diffraction limit; because of interference between closely spaced light waves, the width of an optical fiber carrying them must be at least half the light’s wavelength inside the material. For chip-based optical signals, which will most likely employ near-infrared wavelengths of about 1,500 nanometers (billionths of a meter), the minimum width is much larger than the smallest electronic devices currently in use; some transistors in silicon integrated circuits, for instance, have features smaller than 100 nanometers. Recently, however, scientists have been working on a new technique for transmitting optical signals through minuscule nanoscale structures. In the 1980s researchers experimentally confirmed that directing light waves at the interface between a metal and a dielectric (a nonconductive material such as air or glass) can, under the right circumstances, induce a resonant interaction between the waves and the mobile electrons at the surface of the metal.(In a conductive metal, the electrons are not strongly attached to individual atoms or molecules.) In other words, the oscillations of electrons at the surface match those of the electromagnetic field outside the metal. The result is the generation of surface plasmons—density waves of electrons that propagate along the interface like the ripples that spread across the surface of a pond after you throw a stone into the water.Over the past decade investigators have found that by creatively designing the metal-dielectric interface they can generate surface plasmons with the same frequency as the outside electromagnetic waves but with a much shorter wavelength. This phenomenon could allow the plasmons to travel along nanoscale wires called interconnects, carrying information from one part of a microprocessor to another. Plasmonic interconnects would be a great boon for chip designers, who have been able to develop ever smaller and faster transistors but have had a harder time building minute electronic circuits that can move data quickly across the chip. In 2000 my group at the California Institute of Technology gave the name “plasmonics” to this emerging discipline, sensing that research in this area could lead to an entirely new class of devices. Ultimately it may be possible to employ plasmonic components in a wide variety of instruments, using them to improve the resolution of microscopes, the efficiency of light-emitting diodes (LEDs) and the sensitivity of chemical and biological detectors. Scientists are also considering medical applications, designing tiny particles that could use plasmon resonance absorption to kill cancerous tissues, for example. And some researchers have even theorized that certain plasmonic materials could alter the electromagnetic field around an object to such an extent that it would become invisible. Although not all these potential applications may prove feasible, investigators are eagerly studying plasmonics because the new field promises to literally shine a light on the mysteries of the nanoworld.