Telling tales with tellurium

Telling tales with tellurium
揭秘碲元素

CAMERA-PHONES, a gimmick and a luxury a few years ago, have become ubiquitous. The International Telecommunications Union estimates that 4.6 billion mobile phones are in use at the moment. Of those, more than a billion are equipped with cameras, according to Tom Hausken, an analyst at Strategies Unlimited, a market research firm based in Mountain View, California. Dr Hausken estimates that some 800m camera-phones will be sold this year.
几年前拍照手机象征着精巧与奢华，而如今它代表着普遍的潮流。国际电信联盟估计目前已有46亿部手机处于使用中。据来自加州山景城市场调研公司
Strategies Unlimited的一名分析家Tom Hausken说，其中多达10亿部的手机装配有照相机。Hausken博士估计今年拍照手机的销售量将达到约80亿部。

Yet most of the photos taken with these phones will be grainy and of low resolution―fine for capturing the essence of a moment to send to friends and family, but not good enough to frame for the wall. The reason is that both camera and lens have to be small, to fit with all the other gubbins on a phone. A typical camera-phone is equipped with a one- or two-megapixel silicon-based camera chip that is about 8mm across. Phone cameras with up to five megapixels are becoming available, but InVisage, a small firm based in Menlo Park, California, hopes to leap from that to a photographically respectable 12 megapixels, without an increase in size or cost, by adding tiny crystals called quantum dots to the process.
然而，这类手机拍摄所得的大部分照片都存在噪点，且分辨率低――捕捉朋友和家人们瞬间的影像较为清晰，但拍摄墙时就很模糊。原因是相机和镜头太小，只有这样才能在手机上安装其它的小元件。一款标准的拍照手机会装有一个用于相机拍摄的1兆或2兆像素且仅厚8毫米的硅芯片。能达到5兆像素的拍照手机即将问世，但是，位于加州门洛帕克的一家小公司InVisage期望能够超越这个数值，在体积或成本不增加的情况下，通过在制作工序中添加所谓量子点的微型晶体，使其达到出人意料的12兆。

In a typical camera-phone, the image is focused by the lens onto a photosensitive silicon chip. Light striking this detector liberates electrons from some of the silicon atoms, producing an electrical signal that is converted by the chip's electronics into a picture. Silicon, however, is not the best material for sensing light. Its physical properties (its narrow bandgap, in physics parlance) mean that it sometimes releases electrons even though no light has fallen on it, resulting in a noisy image. On top of that, the way chips are made requires the incoming light to pass through circuitry that has been deposited on to the silicon, reducing the level of illumination.
对标准的拍照手机而言，图像是由基于感光性硅芯片的镜头聚焦而得。当有入射光时，这种感光传感器就会使一些硅原子释放出电子，从而产生能由芯片的电子设备转化为图像的电信号。然而，硅并不是制作光传感器的最佳材料。其物理特性，即用物理学的说法是有局限的频带间隙，这意味着尽管没有入射光，它有时也会释放电子，导致图像噪点。首要问题是，这种材质的芯片要求入射光线须穿透置于硅芯片之上的电路，这样就会减弱光线的强度。

InVisage's approach is to build the photodetector out of quantum dots on the surface of a chip, above the circuitry. A quantum dot is a semiconducting crystal just a few nanometres (billionths of a metre) across that can be engineered to absorb light of a particular colour by changing its size. The larger the dot, the redder the light it absorbs; the smaller, conversely, the bluer. Placing the quantum dots on top of the electronics means more pixels can be crammed into a given area and less incoming light is lost. Moreover, photodetectors based on quantum dots produce less noisy images, so the picture is sharper even if the number of pixels is not increased.
InVisage的方法是将表面涂有量子点的芯片传感器置于电路之上。量子点是一种半导体晶体，仅有几纳米厚即十亿分之一米，它能通过改变粒子尺寸来吸收一种特定颜色的光。量子点越大，其吸收的光线越偏红；相反其越小，吸收的光线就越偏蓝。将这种量子点涂在电子设备上意味着每一个特定区域都能产生更高的像素，并且入射光线的散失会更少。此外，基于量子点的光传感器产生的图像噪点较少，所以即便不增加像素，图像也会更清晰。

Edward Sargent, InVisage's chief technology officer and a professor of optoelectronics at the University of Toronto, says his firm's quantum dots are made of metal chalcogenides (which are a combination of metals such as zinc, indium, bismuth and lead with selenium, sulphur or tellurium). The dots are synthesised in a paint-like colloidal suspension which is then coated on to silicon wafers before they are cut up into chips.
InVisage首席技术官，多伦多大学的光电子学教授萨金特•爱德华说，他所在的公司用金属硫化物制作量子点，即一种金属化合物，其包括锌、铟、铋，且最重要的是硒、硫磺或碲。这些量子点由一种类似涂料的胶状悬浮液合成，接着将其涂在未被切割成碎片的硅晶片上。

In addition to using them in camera-phones, Dr Sargent is working on employing quantum dots to make solar cells. He thinks cells made this way will be comparable in cost to organic solar cells (themselves much cheaper than traditional silicon ones) while being at least twice as efficient. But commercialisation of quantum-dot solar cells is still a few years away. For the moment, he is concentrating on camera-phones.
除了将量子点应用于拍照手机外，萨金特博士正研制将其用以制造太阳能电池。他认为用这种方法制造电池在成本方面可与有机太阳能电池一较高下，即前者较比传统硅电池而言更加廉价，且功效至少要高出原先的两倍。但是量子粒太阳能电池的商业化仍需待数年之久。而当前，他正全力以赴地研发拍照手机。