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A look into the future
With a little imagination, it is not difficult to conjure up visions of future developments in high technology, in whatever direction one cares to look. The following two examples illustrate how advances may take place both by novel applications and refinements of old technologies and by development of new ones.
(1) Molecular electronics
Lithography and thin-film technology are the key technologies that have made possible the continuing and relentless reduction in the size of integrated circuits, to increase both packing density and operational speed. Miniaturization has been achieved by engineering downwards from the macro to the micro scale. By simple extrapolation it will take approximately two decades for electronic switches to be reduced to molecular dimensions. The impact of molecular biology and genetic engineering has thus provided a stimulus to attempt to engineer upwards, starting with the concept that single molecules, each acting as an electronic device in their own right, might be assembled using biotechnology, to form molecular electronic devices or even biochip computers.
Advances in molecular electronics by downward engineering from the macro to the micro scale are taking place over a wide front. One fruitful approach is by way of the Langmure-Biodgett(LB) film using a method first described by Blodgett(1935). A multi-layer LB structure consists of a sequence of organic monolayers made by repeatedly dipping a substrate into a trough containing the monolayer floating on a liquid (usually water), one layer being added at a time. The classical film forming materials were the fatty acids such as stearic acid and their salts. The late 1950s saw the first widespread and commercially important application of LB films in the field of X-ray spectroscopy (e.g,Henke 1964,1965). The important properties of the films that were exploited in this application were the uniform thickness of each film, i.e. one molecule thick, and the range of thickness, say from 5to 15nm, which were available by changing the composition of the film material. Stacks of fifty or more films were formed on plane of curved substrates to form two-dimensional diffraction gratings for measuring the characteristic X-ray wavelengths of the elements of low atomic number for analytical purposes in instruments such as the electron probe of X-ray micro-analyzer.
(2) Scanning tunneling engineering
It was stated that observational techniques such as microscopy do mot, at least for the purposes of this article, fall within the domain of nanotechnology. However,it is now becoming apparent that scanning tunneling microscopy(STM) may provide the basis of a new technology, which we shall call scanning tunneling engineering.
In the STM, a sharp stylus is positioned within a nanometre of the surface of the sample under investigation. A small voltage applied between the sample and the stylus will cause a current to foow through the thin intervening insulating medium(e.g.air,vacum, oxide layer). This is the tunneling electron current which is exponentially dependent on the sample-tip gap. If the sample is scanned in a planr parallel to ies surface and if the tunneling current is kept cnstant by adjusting the height of the stylus to maintain a constant gap, then the displacement of the stylus provides an accurate representation of the surface topographyu of the sample. It is relevant to the applications that will be discussed that individual atoms are easily resolved by the STM,that the stylus tip may be as small as a single atom and that the tip can be positioned with sub-atomic dimensional accuracy with the aid of a piezoelectric transducer.
The STM tip has demonstrated its ability to draw fine lines, which exhibit nanometre-sized struture, and hence may provide a new tool for nanometre lithography.The mode of action was not properly understood,but it was suspected that under the influence of the tip a conducting carbon line had been drawn as the result of polymerizing a hydrocarbon film, the process being assisted by the catalytic activity of the tungsten tip. By extrapolating their results the authors believed that it would be possible to deposit fine conducting lines on an insulating film. The tip would operate in a gaseous environment that contained the metal atoms in such a form that they could either be pre-adsorbed on the film and then be liberated from their ligands or they would form free radicals at the location of the tip and be transferred to the film by appropriate adjustment of the tip voltage.
Feynman proposed that machine tools be used to make smaller machine tools which in turn would make still smaller ones, and so on all the way down to the atomic level. These machine tools would then operate via computer control in the nanometre domain, using high resolution electron microscopy for observation and control. STM technology has short-cricuired this rather cumbrous concept,but the potential applications and benefits remain.
展望未來
不論在什么方面展望，想象未來高科技發(fā)展是很容易的。以下兩個(gè)例子闡述了通過舊技術(shù)的改進(jìn)和新技術(shù)采用可以使科技取得新的進(jìn)展。
（ 1 ）分子電子學(xué)
光刻和薄膜技術(shù)是關(guān)鍵技術(shù)，有可能持續(xù)和縮小集成電路的規(guī)模， 為了增加包裝密度和運(yùn)行速度。小型化已取得了從宏觀到微觀規(guī)模的向下工程。由簡單外推法，將會(huì)采取將近兩個(gè)幾十年來通過電子轉(zhuǎn)換來減少分子尺寸。分子生物學(xué)和基因工程的影響提供了一個(gè)刺激，從而使工程師向上思考，開始將單分子概念，瓦赫代理作為一個(gè)電子裝置來思考，這樣可能會(huì)使生物技術(shù)形成分子電子器件或甚至生物芯片的電腦。
分子電子學(xué)優(yōu)勢從宏觀到微觀的各個(gè)領(lǐng)域都在體現(xiàn)。一個(gè)卓有成效的方法，是透過該langmure - biodgett （磅）電影使用的一種方法由blodgett所描述的（ 1935年）來實(shí)現(xiàn) 。多層磅的結(jié)構(gòu)組成一個(gè)序列的有機(jī)單分子膜通過多次浸漬，包含漂浮在液體中的單層（通常是水） ， 一層在同一時(shí)間補(bǔ)充。經(jīng)典電影形成的材料都是不飽和脂肪酸，如硬脂酸及其鹽類。 50年代后期看到的第一廣泛和具有重要商業(yè)價(jià)值的應(yīng)用LB膜在該領(lǐng)域的X射線光譜（例如， henke 1964,1965 ） 。薄膜的重要性能被剝削，在這方面應(yīng)用統(tǒng)一的厚度，即一個(gè)分子厚，厚度的范圍從5to 15nm ，其中可通過改變薄膜材料的組成。成堆的五十或以上的薄膜上形成的平面基板彎曲，形成兩個(gè)空間為衍射光柵測量特征，低原子序數(shù)的各項(xiàng)要素的X射線波長為分析目的，如電子探針X射線微型分析器。
（ 2 ）掃描隧道工程
據(jù)指出，觀測技術(shù)，如顯微鏡不能屬于該域的納米技術(shù)，至少為本條的目的。不過，它現(xiàn)在正成為明顯的掃描隧道顯微鏡（ STM ）可提供的基礎(chǔ)上的新技術(shù)，我們應(yīng)響應(yīng)掃描隧道工程。
在掃描隧道顯微鏡，一個(gè)尖銳的筆是定位在正在調(diào)查中的一個(gè)納米的表面樣本。一個(gè)小電壓應(yīng)用之間的樣本及筆會(huì)造成電流通過干預(yù)薄絕緣介質(zhì)（ 例如，空氣 ，真空，氧化層） 。這是隧道電子電流指數(shù)依賴于樣本尖端的差距。如果樣本在一個(gè)平面平行它的表面進(jìn)行掃描，如果隧道電流是通過筆不斷調(diào)整高度以維持恒定的差距，那么，位移筆提供了一個(gè)準(zhǔn)確的該樣本的代表性表面地勢。這是將討論的有關(guān)應(yīng)用個(gè)別原子由掃描隧道顯微鏡很容易解決，手寫筆的秘訣可作為小型單一的原子，并可以隨著壓電換能器的幫助與分原子尺寸精度定位。
該STM針尖已表明，它有能力制定罰款線，展示納米大小的結(jié)構(gòu)，因而可能為納米石版印刷術(shù)提供一個(gè)新的工具.這種模式的運(yùn)行是不正確的理解，但作為聚合烴電影的結(jié)果尖端導(dǎo)電碳線已造成的影響是值得懷疑的，這一進(jìn)程正在協(xié)助催化活性的鎢針尖。通過推測其結(jié)果，作者認(rèn)為進(jìn)行線對絕緣膜將有可能被罰款。在氣體環(huán)境下尖端會(huì)經(jīng)營，載有金屬原子這樣的形式，它們可以預(yù)先吸附于電影，然后從解放他們的或他們會(huì)形成自由基的尖端位置和由提示的電壓適當(dāng)?shù)恼{(diào)整轉(zhuǎn)移向電影。
費(fèi)曼提出機(jī)床被用來制造較小的機(jī)床，這反過來又會(huì)使其仍然較小，所以對所有的方式到原子水平。在納米領(lǐng)域這些機(jī)床會(huì)通過計(jì)算機(jī)控制操作，用高分辨電子顯微學(xué)來觀察和控制。掃描隧道顯微鏡技術(shù)短期電路這個(gè)頗為繁復(fù)的概念，但潛在的應(yīng)用和效益仍然存在。