Fabrication of Nanometer-Scale Sensors on Scanning-Probe Microscope Tips

新型扫描传感器和探头的最小特征尺寸约为10纳米，将在扫描探头显微镜的尖端使用新的模板技术制造，这种技术允许将纳米结构直接沉积到非平面表面上。这些传感器将用于成像电子设备和材料的纳米级功能特性，与现有技术相比，分辨率和灵敏度都有很大提高。他们还应该允许几种新的扫描显微镜形式，提供目前无法获取的数量的图像。新的探头将供应给几位追求扫描探头显微镜的领先年轻研究人员，并与他们合作进行优化。将调查的传感器类型和研究主题的例子包括：(1)磁场传感器。单个铁磁性纳米颗粒将沉积在原子力显微镜探针的尖端，用于磁力显微镜(MFM)。与传统的MFM探头相比，在磁性和超导设备的本地研究中，它们将提供更高的空间分辨率和对样品的更少的磁扰动。由铁磁/非磁/铁磁三层膜组成的巨磁电阻传感器也将制成10纳米特征尺寸，用于成像磁场的空间分布。(2)用于近场光学显微镜的蝶形天线。蝴蝶结结构的金属垫将沉积在光纤的顶端，作为光学光子的天线，从而制造用于耳场扫描光学显微镜的纳米级光源。据预测，这将大大提高光学传输效率(与镀铝锥形光纤光源的10-3相比，S的效率为10‘%)，从而允许改进光谱和时间分辨测量。同时，这些天线应提供更高的空间分辨率，约为10纳米，而不是传统光源的约50纳米。(3)扫描式单电子晶体管静电计。将直径约10 nm的金属颗粒沉积在扫描针尖的尖端，与两个电极进行隧道接触，制成单电子隧道器件，用作灵敏的静电计。这将被用来探测半导体和金属器件在运行时的电场配置，金属表面的杂质对功函数产生局部变化的影响，以及单电子隧道器件中偏移电荷和电荷噪声的微观来源。(4)门控扫描隧道显微镜针尖。两个电分离的金属电极将被紧密地沉积在同一绝缘尖端上。一种将用于传统的扫描隧道显微镜，而独立的电压可以施加到第二个电极上，使其充当栅极，移动被研究样品的局部静电势。这将提供一种新的能力来表征参与电子隧穿的量子力学能级，在量子点和单分子器件中。其他可以在10纳米尺度上制造的新型传感器或探测器包括可扫描温度计、加热器和冰箱、微波辐射源和探测器，以及用于自旋分辨扫描隧道显微镜的电子自旋过滤器。

New classes of scanning sensors and probes, with minimum feature sizes of approximately 10 nm, will be made on the tips of scanning-probe microscopes using a new stencil technique, which allows the direct deposition of nanostructures onto non-planar surfaces. These sensors will be used to image the nm-scale functional properties of electronic devices and materials with greatly improved resolution and sensitivity, as compared with existing techniques. They should also allow several new forms of scanning microscopy, providing images of quantities not currently accessible. The new probes will be supplied to and optimized in cooperation with several of the leading young researchers pursuing scanned-probe microscopy. Examples of the types of sensors and the research subjects that will be investigated include: (1) magnetic field sensors. Single ferromagnetic nanoparticles will be deposited on the tips of atomic-force-microscope probes, for use in magnetic force microscopy (MFM). Compared to conventional MFM probes, they will provide improved spatial resolution and less magnetic perturbation on the sample, in local studies of magnetic and superconducting devices. Giant-magnetoresistance sensors composed of a ferromagnetic / non-magnetic / ferromagnetic trilayer will also be made with 10-nm feature sizes for imaging the spatial distributions of magnetic fields. (2) bow-tie antennas for near-field optical microscopy. Metallic pads in a bow-tie configuration will be deposited at the tips of optical fibers, to serve as an antenna for optical photons, and thereby make a nm-scale optical source for use in ear-field scanning optical microscopy. This is predicted to allow greatly improved optical transmission efficiency (10's of % efficiency, as compared to 10 -3 for aluminum-coated tapered-optical-fiber sources), thus permitting improved spectroscopy and time-resolved measurements. At the same time, these antennas should provide improved spatial resolution, on the order of 10 nm rather than approximately 50 nm for conventional sources. (3) scanning single-electron-transistor electrometers. A metal particle approximately 10 nm in diameter will be deposited on the tip of a scanning tip, in tunneling contact with 2 electrodes, to make a single-electron tunneling device that will serve as a sensitive electrometer. These will be employed to probe electric-field configurations of semiconductor and metal devices while they are in operation, the effects that impurities on metal surfaces have in producing local changes in the work function, and the microscopic origin of offset charges and charge noise in single-electron tunneling devices. (4) gated scanning-tunneling-microscope tips. Two electrically separate metal electrodes will be deposited in close proximity on the same insulating tip. One will be used for conventional scanning tunneling microscopy, while an independent voltage can be applied to the second electrode so that it acts as a gate to shift the local electrostatic potential of the sample under study. This will provide a new capability for characterizing the quantum-mechanical levels participating in electron tunneling, within quantum dots and single-molecule devices. Other new types of sensors or probes that may be fabricated on the 10 nm scale include scannable thermometers, heaters, and refrigerators, sources and detectors of microwave radiation, and electronic spin-filters for use in spin-resolved scanning tunneling microscopy.