Putting spin into carbon nanoelectronics

单壁碳纳米管正在证明自己是突破性纳米电子器件的显着候选人。电子可以弹道式地流过它们，这意味着它们不会被纳米管材料中的特征散射。可以用具有电子和空穴导体的单壁纳米管制造晶体管，从而为完整的逻辑电路提供元件。甚至有可能制造出在有源区中只改变一个电子就工作的晶体管。所有这些都对未来的电子应用非常重要，但这仅仅是开始，因为这些设备只使用电子上的电荷。还有另一个秘密武器可以使用，以电子自旋的形式。电子自旋可以被认为是一个微小的磁铁，它可以指向两个方向之一（通常被称为向上和向下）。由此开辟的电子学的新领域已经有了一个名字，自旋电子学，还有它自己的诺贝尔奖获得者。自旋电子学目前最大的应用是在计算机硬盘上的阅读数据的磁头上，彻底改变了这个数十亿美元的产业。磁性随机存取存储器现在正在制造和销售，并承诺更高的访问速度。研究人员正在寻找可用于自旋电子器件的新材料系统，这反过来又可能在新的应用中被利用。新的影响一直在被发现。例如，如果你在金属磁体的两端施加不同的温度，电子自旋的电流就可以流动。我们的愿景是将自旋引入碳纳米电子学。如果我们能做到这一点，我们可能会增加一个全新的能力，已经有可能与纳米管晶体管。为此，我们将使用其他碳材料，甚至比纳米管更小，以称为富勒烯分子（也称为巴基球）的笼的形式。这些分子每个都可以包含一个或多个携带电子自旋的原子。它们可以插入单壁纳米管中，由此产生的结构有时被称为豆荚，因为这是它们在电子显微镜下的样子。豆荚提供了一个理想的方式把自旋到纳米管。在我们的研究计划中，我们将制造豆荚晶体管，并在最小化样品损伤的条件下，通过高分辨率透射电子显微镜观察它们。这样，我们就能以原子分辨率看到装置中起作用的那块材料。当我们改变磁场和温度时，我们将测量通过晶体管的电流，并寻找可能对磁场和温度中的一个或另一个非常敏感的效应。我们将应用微波辐射，当我们通过自旋共振扫描磁场时，检测对电导的影响。最后，我们将进行控制实验，用电测量自旋的方向。虽然这些都是基本的实验，我们希望它们将导致实际应用。对于纳米电子电路和传感器等应用，这些可能是通过集体激发的影响，或者它们可能是通过直接控制自旋态，用于更革命性的设备，如量子逻辑设备，量子存储器，甚至可能最终量子计算。

Single walled carbon nanotubes are proving themselves to be remarkable candidates for disruptive nanoelectronic devices. Electrons can flow through them ballistically, which means that they travel without being scattered by features in the material of the nanotube. It is possible to make transistors with single walled nanotubes with both electron and hole conductors, thus providing components for complete logic circuits. It is even possible to make transistors which work with a change of only a single electron in the active region. All of this could be very significant for future electronics applications, but that would be only the beginning, because these devices use only the charge on the electron. There is another secret weapon which can be used, in the form of the electron spin.The electron spin can be thought of as a tiny magnet, which can point in one of two directions (often referred to as up and down). The new field of electronics which this opens up already has a name, spintronics, and its own Nobel Prize Winners. The biggest current application of spintronics is in the heads for reading data on hard discs in computers, revolutionizing this multibillion dollar industry. Magnetic random access memory is now being made and sold, with the promise of ever higher access speeds. The search is on for new materials systems which can be used for spintronic devices, which may in turn be exploited in new applications. New effects are being discovered all the time. For example, if you apply different temperatures to the two ends of a metallic magnet, a current of electron spins can flow.Our vision is to put spin into carbon nanoelectronics. If we can do this, we may be able to add a whole new capability to what is already possible with nanotube transistors. For this purpose we shall use other carbon materials, even smaller than nanotubes, in the form of cages called fullerene molecules (also known as Bucky balls). These molecules can each contain one or more atoms which carry a resulting electron spin. They can be inserted into single walled nanotubes, and the resulting structures are sometimes called peapods, because that is what they look like in an electron microscope. Peapods provide an ideal way to put spin into nanotubes.In our research programme, we shall fabricate peapod transistors, and look at them by high resolution transmission electron microscopy under conditions which minimise the damage to the samples. In this way we shall be able to see with atomic resolution the very piece of material which is active in the device. We shall measure the current through the transistor while we vary the magnetic field and the temperature, and look for effects which may be very sensitive to one or other of these. We shall apply microwave radiation, and detect the effect on electrical conductance as we sweep the magnetic field through the spin resonance. Finally we shall perform controlled experiments to measure electrically the direction of the spin.Although these are fundamental experiments, our hope is that they will lead to practical applications. These may be through the effects of collective excitations, for applications such as nanoelectronic circuits and sensors, or they may be through direct control of the spin states, for more revolutionary devices such as quantum logic devices, quantum memories and perhaps even eventually quantum computing.