Towards molecular bits: molecules that can represent binary information

1974年，当第一个商业上成功的微处理器问世时，它在一个硅芯片上包含了大约6000个晶体管，每个晶体管代表一位二进制信息。32年后，奔腾4在一块芯片上集成了4200万个晶体管，这让我们对小型化在这段时间内的进展有了一个了解。然而，由于两个问题，晶体管不会变得非常小。首先，随着晶体管尺寸的减小，使其通断变得更加困难(晶体管只是使用通断状态来表示0和1的开关)。其次，晶体管产生热量，晶体管密度变得如此之高，以至于消除热量并阻止芯片熔化是一个真正的挑战。这项拟议的研究的目的是合成一些化合物，可以用来取代电子设备中的晶体管，使用一种新的表示和操作二进制信息的方法，称为量子点细胞自动机(QCA)范例。QCA电池由四个排列成正方形的金属点组成，每个点能够容纳一个电荷。对电池两个相对角落的点进行电充电可以用来对0进行编码，而对另外两个点充电表示1。如果存在一个以上的QCA电池，一个电池内带电点的排列会影响相邻电池中的排列。由于相同的电荷相互排斥，相邻的点往往具有相反的电荷，这意味着当两个电池并排时，第二个电池将具有与第一个电池相同的值(0或1)。相反，共享一个角的两个单元格将采用相反的值。这种第二种布置，其中输入单元的值1被转换为输出单元的值0，等同于传统电子学中的非门。其他类型的逻辑门可以被其他类型的单元布置来模仿，因此正确的单元布置可以像计算机一样工作。已经证明，在开尔文温度下，在角落具有大约50 nm大小的金属纳米颗粒的QCA单元可以作为逻辑门工作，虽然这对于一般用途的计算来说太冷了，但据预测，如果金属部件可以缩小到大约2 nm，那么它们将在室温下工作。两个纳米与单个分子的大小差不多，所以如果我们能构建一个包含四个中心的阵列的分子，每个中心都可以如上所述地打开或关闭，那么我们就可以在计算中使用它们。在化学术语中，打开或关闭每个点只是一个氧化还原过程-添加或移除一个电子-所以每个角落都需要由在不止一个氧化状态下稳定的物质组成。建议将四个这样的实体与一些化学支架结合在一起，形成分子QCA细胞，然后研究它们的行为，看看它们是否会像预期的那样工作。

When the first commercially successful microprocessor was launched in 1974 it contained roughly 6000 transistors on one silicon chip, each transistor representing one bit of binary information. Thirty-two years later, the Pentium 4 has 42 million transistors on a chip, giving an idea of how miniaturisation has progressed in that time. However, transistors are not going to become very much smaller because of two problems. Firstly, as the size of a transistor decreases, it becomes more difficult to make it turn on and off cleanly (a transistor is just a switch that uses on and off states to represent 0 and 1). Secondly, transistors generate heat, and transistor densities are becoming so high that removing that heat and stopping the chips from melting is a real challenge.The aim of this proposed research is to synthesise some chemical compounds that could be used to replace transistors in electronic devices, using a new way of representing and manipulating binary information called the Quantum-dot Cellular Automata (QCA) paradigm. A QCA cell consists of four metallic dots arranged in a square, each dot being able to accommodate an electrical charge. Electrically charging the dots at two of the opposite corners of a cell can be used to encode 0, while charging the other two dots represents 1. Where more than one QCA cell is present, the arrangement of the charged dots within one cell affects that in neighbouring cells. Because like charges repel each other, dots that are next to each other tend to have opposite charges, which means that where two cells are side-by-side the second will have the same value (0 or 1) as the first. Conversely, two cells sharing a corner will adopt opposite values. This second kind of arrangement, where a value of the input cell of 1 is converted to an output cell value of 0, is equivalent to a NOT gate in conventional electronics. Other kinds of logic gate can be mimicked by other arrangements of cells, and so the correct arrangement of cells could function as a computer.It has been shown that an arrangement of QCA cells with metallic nanoparticles about 50 nm in size at the corners can work as a logic gate at milliKelvin temperatures, and whilst this is too cold for general purpose computing it is predicted that if the metallic components can be shrunk to about 2 nm then they will work at room temperature. Two nanometres is about the same size as a single molecule, so if we can build a molecule that contains an array of four centres, each of which can be switched 'on' or 'off' as described above, then we might be able to use them in computing.In chemical terms, switching each 'dot' on or off is simply a redox process - adding or removing an electron - so each corner needs to be made from something that is stable in more than one oxidation state. What is proposed is to join four such entities together with some chemical scaffolding to form molecular QCA cells, and then investigate their behaviour to see whether they would work as desired.