The effect of cesium metal clusters on the optical properties of cesium iodide thin films

Kumar, Kapil; Arun, P.; Kant, Chhaya Ravi; Mehra, N. C.; Mathew, Vincent

doi:10.1007/s00339-009-5532-4

Cited by 23 publications

(15 citation statements)

References 13 publications

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“…The details of calculation of the extinction coefficient ext within Gans' model have been given by Link et al [21] In the present work, we report the results of theoretical calculations made for the extinction coefficients of cesium metal nanorods in CsCl, CsBr, and CsI matrix using Gans' model. These calculations were then compare with the experimental results reported earlier in [12][13][14]. The factors known to influence the SPR peak position are the size of a metal nanoparticle, its dielectric constant (i), par-ticle shape, and (ii) the surrounding media via its dielectric constant.…”

Section: Introductionmentioning

confidence: 88%

“…The recent report on the natural ageing process has again brought the spotlight on AH [11]. It was observed that -centers/ 2 centers or defects are formed due to the halide atoms moving out of their lattice positions under the heat treatment [12][13][14], which leads to the clustering of Cs atoms. This causes the strong absorption in the UV-visible spectral region.…”

Section: Introductionmentioning

confidence: 99%

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SPR in Cesium Halide Thin Films Due to Embedded Elliptic Cesium Metal Nano-Particles

Kumar

Arun

2018

Ukr. J. Phys.

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Cesium nanorods embedded in cesium halides (CsCl, CsBr, and CsI) show surface plasmon resonance (SPR) absorption peaks. The size and shape of these cesium nanorods in the cesium halide matrix evolve with time, which gives some uncontrollable data for comparing with the theory. The theory used here was developed by R. Gans. It leads to the good match between experiment and theory for Cs–Cs halide nanocomposites.

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Section: Introductionmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 99%

SPR in Cesium Halide Thin Films Due to Embedded Elliptic Cesium Metal Nano-Particles

Kumar

Arun

2018

Ukr. J. Phys.

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“…As the film thickness is further increased, we may believe that this strain is communicated through the whole film and as a result, presence of compressive stress continue to increase with the film thickness. In a recent work of K. Kumar et al [31], they have observed tensile stress for "as-deposited" CsI films with thicknesses 580 nm -730 nm. However they also observed a compressive stress below 580 nm CsI films which is in agreement with our findings.…”

Section: Structural Properties Of Csi Thin Filmsmentioning

confidence: 98%

Structural and optical properties of CsI thin films: Influence of film thickness and humidity

Jammal

Rai

Pandit

et al. 2018

Physica B: Condensed Matter

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Structural and optical studies have been performed on the thermally-evaporated "as-deposited" and "humid air aged" CsI thin films. The structural analysis for both "as-deposited" and "humid air aged" films shows a well-oriented peaks position of (110) and (220) lattice planes with a compressive stress in the films. The crystal quality has been investigated through the structural parameters. The increase in peak intensity as well as sharpness with film thickness implies the improvement of crystallinity. The optical absorbance of CsI films has been analyzed in the wavelength range of 190 nm -900 nm in order to estimate the band gap energy of the films. Slater's model has also been used to explain the degradation of band gap energy with the increase in crystallite size. been tested successfully under liquid xenon atmosphere for its use in dark matter search experiment [21]. The detectors used for these experiments generally work in two modes; reflective (opaque) and semitransparent mode. The Quantum Yield (QY) of reflective films has been observed to be higher in comparison with the semitransparent films. This is because the semitransparent films have a small escape length (L≤ 10 nm) [16]. Also, it has been revealed that the reflective films have more chemical stability against the moisture compared to the semitransparent films [17].Keeping these facts in mind, the main issue related to CsI photocathode is the aging which causes a degradation in the photoemission properties and thus limits their life. In order to develop and optimize large area photocathodes based detector, the study of the optical and structural properties of the "as-deposited" and "aged" CsI photocathodes is ultimately required. In literature, there are several studies on CsI ageing, but its mechanism does not have a clear understanding yet. A. S. Tremsin et al. [23] have used TEM technique to study the structural properties of polycrystalline CsI thin film of 100 nm thickness under the impact of humid air and UV irradiation. M. A. Nitti et al. [24] have examined the bulk structure and the surface of freshly and humid air exposed 100 nm CsI film by XRD and XPS measurements. Recently, Triloki et al. [25] have studied the structural properties of thermally-evaporated CsI thin films of different thicknesses by using XRD and TEM techniques. C. Lu and K.T. McDonald [16] have previously reported the optical properties of freshly CsI thin films up to 31 nm thickness. This work is an extension of the previous works, where we have systematically studied the structural and optical properties of semitransparent and reflective CsI thin films grown under similar vacuum-environment in case of "as-deposited" and "humid air aged". Experimental Details Deposition of CsI thin filmsThe deposition of reflective (500 nm and 300 nm) and semitransparent (50 nm and 30 nm) CsI thin films was done in a stainless steel 18" diameter spherical vacuum chamber. Prior to the deposition process, the substrates were cleaned by treating with distilled water, acetone, and alcohol to...

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“…由于光子吸收以及二次电子传输等性质与 CsI 薄膜厚度直接相关, 对光阴极厚度的理论设计与实验研究受到了人们广泛关注。对于透射式 CsI 光阴极而言, QE 对厚度变化敏感。 Valentini 等 [26] 的计算结果表明, 对于波长为 170 nm 的光子, 10 nm 厚度的 CsI 薄膜具有最大的 QE, 当厚度为 60 nm 时 QE 已经非常低。Lu [27] 和 Boutboul [28] 等认为用于 160~190 nm 波段 CsI 光阴极的最优厚度为 10~20 nm, 但在实验中发现 20 nm 厚的 CsI 薄膜暴露在空气中仅几分钟就发生了破裂。我们课题组建立了软 X 光能区(0.1~10 keV)CsI 二次电子产出与膜厚及入射角的关系, 并采用同步辐射光源测试了透射式光阴极谱响应灵敏度, 结果表明最优厚度约为 60 nm [29][30][31] 。对于反射式 CsI 薄膜光阴极, QE 在膜厚为几十 nm 时达到最大值 [32][33] , 并且在一定范围内, 厚度增加对 QE 的影响不大, 大于 500 nm 的膜厚会使电场作用减弱导致 QE 下降 [17] 。Braem 等 [32] [7] 、色心 [34] 、位错 [23] 、颗粒内部和边界中的水分子以及颗粒界面 [35] 等都可能使电子在传输中损失能量; 薄膜表面的吸附水 [13] 、O 2 [36] 、C 元素及化合物 [6,9,11,37] 以及 Cs、I 元素比例的变化和相应化合物的生成 [14] 都可能造成电子亲和势增大, 阻碍电子向真空发射。目前, 人们对 CsI 薄膜中缺陷及表面污染产生的原因及影响 QE 的原理还存在不同的看法。薄膜在生长过程中可能会受到镀膜系统中残余水分子、碳氢化合物以及挥发 I 元素的污染 [12,23,38] , 并可能产生色心及 Cs 析出 [38][39] 。受潮和辐照引起的缺陷等将在第 2 节中具体讨论。…”

Section: 膜厚unclassified

“…Xie 等 [6] 认为这可能是 QE 下降的原因之一。图 3 (a)刚制备、(b)在空气中暴露后、(c)在极端潮湿环境中暴露后 CsI 薄膜的 SEM 照片 [49] ; (d)NIF 采用的 X 射线条纹相机上 200 nm 厚的 CsI 透射式光阴极信号下降与空气暴露时间的关系 [47] Fig. 3 SEM images of as-deposited (a), aged in ambient air (b) and extreme moisture exposed CsI films (c) [49] ; Percent degradation in the yield signal of streak camera used at NIF from a 200 nm thick CsI cathode as a function of air exposure time [47] Kumar 等 [39,51] 的实验结果表明 Cs 的含量仅在部分微区域偏高, 他们认为 Cs 含量在真空热蒸发一开始就出现增加, 原因为 I 的升华和色心聚集与析出。一些研究者认为受潮导致的薄膜形貌及颗粒尺寸的变化对 QE 也有影响 [2,11,18,35] , 其中 Nitti 等 [18] 认为这是 QE 下降的重要原因。几乎所有对 CsI 薄膜光阴极受潮的研究都发现薄膜中颗粒尺寸变大, 但对颗粒生长的动力学过程有不同的描述: Xie 等 [6] 认为, 薄膜中较小颗粒在颗粒顶端岛状水溶液重力、静电引力及表面张力作用下发生合并形成大颗粒; Triloki [50] 和 Boutboul [28] 等认为颗粒长大源于薄膜表面溶液相中水分挥发所引起的再结晶;…”

Section: 老化研究unclassified

Recent Progress in Research on CsI Thin Film Photocathodes

Fan¹,

Li²,

Chen³

et al. 2015

Journal of Inorganic Materials

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Caesium iodide (CsI) thin films have attracted much attention due to good electron transport and emission properties in the soft X-ray and extreme ultraviolet range. With the rapid development of nuclear physics, high energy physics and astrophysics, the requirements for CsI film photocathodes become increasingly severe, and it is therefore of considerable interest to develop CsI photocathodes with high quantum efficiency (QE) and stable performance. However, the internal mechanisms of QE variation and photocathode aging are not entirely clear or certain up to date. In this paper, the recent progress on CsI film photocathodes is reviewed and some controversial issues are introduced. Several perspectives are also proposed in the end.

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The effect of cesium metal clusters on the optical properties of cesium iodide thin films

Cited by 23 publications

References 13 publications

SPR in Cesium Halide Thin Films Due to Embedded Elliptic Cesium Metal Nano-Particles

SPR in Cesium Halide Thin Films Due to Embedded Elliptic Cesium Metal Nano-Particles

Structural and optical properties of CsI thin films: Influence of film thickness and humidity

Recent Progress in Research on CsI Thin Film Photocathodes

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