Photocathode device using diamondoid and cesium bromide films

Abstract

A photocathode structure is presented that shows promise for use in high brightness electron sources. The structure consists of a metal substrate, a monolayer of a diamondoid derivative, and a thin film of cesium bromide. Diamondoid monolayers reduce the energy spread of electron emitters, while cesium bromide increases the yield and stability of cathodes. We demonstrate that the combined structure retains these properties, producing an emitter with lower energy spread than the corresponding cesium bromide emitter (1.06 eV versus 1.45 eV) and higher yield and stability than un-coated diamondoid emitters. 3 An ideal emitter for these devices would have high intensity, small physical size, good stability under operating conditions, and low energy spread. One method for achieving high yield and small physical size is to use a focused laser beam to create photoelectrons. However, performance of such devices is limited by the quantum yield and the energy spread. In this work, we present a photocathode structure that improves on the quantum yield and reduces the energy spread of laser photoemission devices without sacrificing the other desirable properties. This device consists of a monolayer of diamondoid combined with a thin film of cesium bromide.Diamondoids are hydrocarbon molecules with the same carbon-lattice structure as bulk diamond. They inherit many of the superior properties of diamond 4,5 and possess emergent properties relating to their small size and high surface area ratio. [6][7][8][9][10][11][12] One unique property of these diamondoids is their behavior in photoemission devices. A monolayer of diamondoids on a metal substrate can largely monochromatize the photoemission, with the majority of the electrons emitting in a single peak with a full-width half-max (FWHM) of around 0.3 eV.6,7 This low energy spread is ideal for many cathode applications, but the diamondoid monolayers that have been studied are not stable enough for use in most devices. In order to correct this problem, we have added cesium bromide as a protective over-layer to provide mechanical stability and protection.Cesium bromide provides more than just protection, however. CsBr coatings on photocathodes have been extensively studied [13][14][15][16][17][18] and have desirable properties. They greatly enhance the quantum yield of the emitter by reducing the effective work function and are robust and capable of operation under the demanding conditions of ultra bright FEL sources. 19 Our objective is to combine these attractive properties with the reduced energy spread of diamondoids by creating a device that contains both films using a thiolated diamondoid to create a self-assembled monolayer (SAM).We tested these devices using ultra-violet (UV) laser photoemission, as shown in Figure 1. We measured the quantum yield, the energy spread, and lifetime of devices with and without the diamondoid present with varying thicknesses of CsBr. Through these investigations, we demonstrate that the high quantum yield of the CsBr emitter is preserved ...

Nanotechnology of diamondoids for the fabrication of nanostructured systems

“…Another approach to solving the long-term stability issue of the diamondoid monolayer, as reported by Clay et al [147], is by providing a protective overlayer. In their study, cesium bromide (CsBr), which is an electron transparent compound, was deposited onto the monolayer of TA 121 -6-thiol on Au through vapor deposition.…”

Towards 3-(2-adamantylidene)diamantane derivatives through the McMurry cross coupling reaction

“…Higher diamondoids have a potential as building blocks for nanoelectronic devices. It was shown that tetramantane thiol form well-ordered self-assembled monolayers (SAMs) on gold surface and material [2][3][4][5][6] thus obtained display monochromatic electron emission with low-kinetic energy threshold [3]. Besides, diamondoids and their derivatives serve as a model for hydrogen terminated diamond nanoparticles [7][8][9][10].…”

Synthesis of 10-Methoxydiamantan-3-One

“…In fact, the diamondoid only exists as hexamantanes and pentamantanes (particle size of 0.6-0.75 nm) for the rod-shaped isomer in limited quantities from oil. Therefore, diamondoids with the desired size larger than 1 nm, in order to explore applications in nanoelectronics [1][2][3][4], for which the present of quantum limitation effects are theoretically presaged, remains problematic at the present time. This can be solved by a coupling reaction using lower diamondoids with various spacers.…”