Microsystems Technology Laboratories and ‡Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
Nano Lett. 2014 Sep 10;14(9):5035-43. doi: 10.1021/nl501589j. Epub 2014 Aug 7.
Femtosecond ultrabright electron sources with spatially structured emission are an enabling technology for free-electron lasers, compact coherent X-ray sources, electron diffractive imaging, and attosecond science. In this work, we report the design, modeling, fabrication, and experimental characterization of a novel ultrafast optical field emission cathode comprised of a large (>100,000 tips), dense (4.6 million tips·cm(-2)), and highly uniform (<1 nm tip radius deviation) array of nanosharp high-aspect-ratio silicon columns. Such field emitters offer an attractive alternative to UV photocathodes while providing a direct means of structuring the emitted electron beam. Detailed measurements and simulations show pC electron bunches can be generated in the multiphoton and tunneling regime within a single optical cycle, enabling significant advances in electron diffractive imaging and coherent X-ray sources on a subfemtosecond time scale, not possible before. At high charge emission yields, a slow rollover in charge is explained as a combination of the onset of tunneling emission and the formation of a virtual cathode.
具有空间结构发射的飞秒超强电子源是自由电子激光、紧凑型相干 X 射线源、电子衍射成像和阿秒科学的一项使能技术。在这项工作中，我们报告了一种新型超快光场发射阴极的设计、建模、制造和实验特性，该阴极由一个大（>100,000 个尖端）、密集（460 万个尖端·cm(-2)）和高度均匀（<1nm 尖端半径偏差）的纳米级高纵横比硅柱阵列组成。这种场发射器提供了一种有吸引力的替代紫外光阴极的方案，同时提供了一种直接构造发射电子束的方法。详细的测量和模拟表明，在单个光周期内，可以在多光子和隧道发射模式下产生皮库电子束，从而能够在亚飞秒时间尺度上实现电子衍射成像和相干 X 射线源的重大进展，这在以前是不可能的。在高电荷发射产额下，电荷缓慢滚降可解释为隧道发射的开始和虚阴极的形成的综合作用。
