Review Article: Rare-earth monosulfides as durable and efficient cold cathodes

Abstract

In their rocksalt structure, rare-earth monosulfides offer a more stable alternative to alkali metals to attain low or negative electron affinity when deposited on various III-V and II-2 VI semiconductor surfaces. In this article, we first describe the successful deposition of Lanthanum Monosulfide (LaS) via pulsed laser deposition on Si and MgO substrates and alumina templates. These thin films have been characterized by X-ray diffraction, atomic force microscopy, high resolution transmission electron microscopy, ellipsometry, Raman spectroscopy, ultraviolet photoelectron spectroscopy and Kelvin probe measurements. For both LaS/Si and LaS/MgO thin films, the effective work function of the submicron thick thin films was determined to be about 1 eV from field emission measurements using the Scanning Anode Field Emission Microscopy technique. The physical reasons for these highly desirable low work function properties were explained using a patchwork field emission model of the emitting surface. In this model, nanocrystals of low work function materials having a <100> orientation perpendicular to the surface and outcropping it are surrounded by a matrix of amorphous materials with higher work function. To date, LaS thin films have been used successfully as cold cathode emitters with measured emitted current densities as high as 50 A/cm 2 . Finally, we describe the successful growth of LaS thin films on InP substrates and, more recently, the production of LaS nanoballs and nanoclusters using Pulsed Laser Ablation.3

Anion Photoelectron Spectroscopy and CASSCF/CASPT2/RASSI Study of Lan– (n = 1, 3–7)

“…For example, the detachment process 3 A → 2 A(1,2) can be associated with emptying the orbital 2π (Tables S3 and S4, compare roots with CSF coefficient 0.632 in triplet and 0.732 in doublet). Similar matching VDEs and participating orbitals (σ/ δ) can be found for the next three lines f−h in the range 1.0− 1.2 eV; they fit within the computational accuracy to the first significant experimental peak around 1.1−1.2 and contributing detachments are 1 A → 2 A(1,2), 5 A → 6 A(1), and 5 A → 6 A(2). The last three theoretical lines i−k belong approximately to the second peak at 1.5−1.6 eV and contributing detachments are 1 A → 2 A(8), 5 A → 6 A(6), and 5 A → 6 A(7).…”

“…Lanthanum sits at the beginning of the lanthanide series, having the electronic configuration [Xe]­5d6s 2 ; it is the only rare earth element which does not fill the 4f shell. This metal has applications in optical fibers, nonlinear optical crystals, ZBLAN fluoride glasses, catalysts, electron cathodes, , scintillators, doping materials for the fuel cells, and in studio lighting and projection. In order to enable the utilization of this metal at the subnanoscale, studies of the molecular clusters of La are desirable.…”

Influence of Changes in Defect States on the Properties of Si–Gd–O Photocathode

“…However, various groups of researchers continue to study them till now -in particular, on Si [3], GaAs [4,5], and diamond [6] in order to improve the physical models of their functioning and due to the necessity to change the activating Cs-O layers, which turned out insufficiently stable at the long-term usage [7]. The search for more stable compounds showed that it can be both oxides [8][9][10] and monosulfides [11][12][13] of rare-earth metal atoms.…”