Complementary cathodoluminescence lifetime imaging configurations in a scanning electron microscope
Complementary cathodoluminescence lifetime imaging configurations in a scanning electron microscope
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DOI：
10.1016/j.ultramic.2018.11.006
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发表时间：
2019-02-01
期刊：
影响因子：
2.2
通讯作者：
Polman, A.
中科院分区：
文献类型：
--
作者：
Meuret, S.;Garcia, M. Sola;Polman, A.
阴极射线发光（CL）光谱提供了一种强有力的方法来表征材料的光学性质与深亚波长的空间分辨率。虽然CL成像以获得光谱是一种成熟的技术，但仅在少数研究中探索了具有纳米级分辨率的CL寿命成像。在本文中，我们比较了三种不同的时间分辨CL技术，并比较他们的特点。两种配置是基于使用脉冲电子束的CL衰减轨迹的采集，所述脉冲电子束是用放置在电子柱中的超快束消隐器产生的，或者是由来自激光驱动的电子阴极的光发射产生的。第三种配置使用连续或脉冲电子束测量CL信号的自相关函数g（2）。这三种技术进行了比较，在复杂的实施，空间和时间分辨率，测量精度作为电子剂量的函数。InGaN/GaN量子威尔斯的一个单一的样品进行了研究，使寿命测量特性的三种技术的直接比较。基于g（（2））的方法提供了最佳空间分辨率的衰变测量，因为它不影响电子柱构型。脉冲束方法提供了更好的细节的时间激发和衰减动力学。超快消隐器配置在5 keV下提供短至30 ps的电子脉冲，在30 keV下提供短至250 ps的电子脉冲。重复率可以任意选择高达80 MHz，并需要在电子柱中的共轭平面几何形状，这降低了我们的显微镜的空间分辨率。的光电发射配置，泵浦250 fs 257 nm的脉冲在重复率从10 kHz到25 MHz，允许创建电子脉冲下降到几ps，在空间分辨率的一些损失。
Cathodoluminescence (CL) spectroscopy provides a powerful way to characterize optical properties of materials with deep-subwavelength spatial resolution. While CL imaging to obtain optical spectra is a well-developed technology, imaging CL lifetimes with nanoscale resolution has only been explored in a few studies. In this paper we compare three different time-resolved CL techniques and compare their characteristics. Two configurations are based on the acquisition of CL decay traces using a pulsed electron beam that is generated either with an ultra-fast beam blanker, which is placed in the electron column, or by photoemission from a laser-driven electron cathode. The third configuration uses measurements of the autocorrelation function g(2) of the CL signal using either a continuous or a pulsed electron beam. The three techniques are compared in terms of complexity of implementation, spatial and temporal resolution, and measurement accuracy as a function of electron dose. A single sample of InGaN/GaN quantum wells is investigated to enable a direct comparison of lifetime measurement characteristics of the three techniques. The g((2))-based method provides decay measurements at the best spatial resolution, as it leaves the electron column configuration unaffected. The pulsed-beam methods provide better detail on the temporal excitation and decay dynamics. The ultra-fast blanker configuration delivers electron pulses as short as 30 ps at 5 keV and 250 ps at 30 keV. The repetition rate can be chosen arbitrarily up to 80 MHz and requires a conjugate plane geometry in the electron column that reduces the spatial resolution in our microscope. The photoemission configuration, pumped with 250 fs 257 nm pulses at a repetition rate from 10 kHz to 25 MHz, allows creation of electron pulses down to a few ps, with some loss in spatial resolution.