Stable 2D Conductive Ga/Ga(O_xH_y) Multilayers with Controlled Nanoscale Thickness Prepared from Gallium Droplets with Oxide Skin

Abstract

The practical applicability of ultrathin films, which offer interesting and novel functionalities, is often limited by difficulties in achieving large area deposition while maintaining homogenous layer properties. Herein, a new deposition method allowing ultrathin, conductive gallium‐containing layers to be prepared at ambient conditions on wafer‐scaled areas is presented. Multilayers are formed by repetition of the deposition procedure. High‐resolution structural analysis using X‐ray reflectometry shows that the multilayer thickness is proportional to the number of deposition cycles, yielding a highly reproducible single layer thickness of 2.9 ± 0.2 nm. Furthermore, it is shown that single layers consist of a complex heterostructure composed of a nanometer‐thin metallic Ga core, which is surrounded by stabilizing gallium (hydr)oxide skin layers. The macroscopic electric conductivity of these multilayers increases with increasing number of deposited layers, approaching the value of bulk gallium after six deposition cycles, thereby showing that functional properties such as the multilayer's electrical conductivity can be fine‐tuned based on the chosen number of deposition cycles.

Stable Metal/Metal Hydroxide Multilayers with Controlled Nanoscale Thickness Prepared from Liquid Metal Droplets with Oxide Skin

“…Furthermore, increasing the number of uniform repeat units results in narrowing the peak while the peak intensity increases. However, with films made from Ga, 9 we observed an increase in the peak width with peak order. Furthermore, we found a relative increase in the intensity of the second-order peak with increasing layer number.…”

“…In a recent publication, we introduced a cost-efficient and environmentally friendly deposition method for ultrathin heterocomposite metal-and metal (hydr)oxide layers. 9 Gallium with a melting temperature of 29.76 °C was employed. 10 This deposition method called induced breakup after forced wetting leads to laterally homogeneous and vertically heterostructured multilayers with a thickness from 2.9 up to 24 nm depending on the number of deposited layers.…”

“…10 This deposition method called induced breakup after forced wetting leads to laterally homogeneous and vertically heterostructured multilayers with a thickness from 2.9 up to 24 nm depending on the number of deposited layers. 9 This paper aims to extend the method to other metals than pure gallium and alloys. The required properties of the metals or alloys are relatively low melting temperatures and high surface tensions in the liquid state.…”

“…24,25 Measurements with an optical microscope (Olympus BX61WI with a CCIR Camera, Olympus K.K., Shinjuku, Japan) indicated the presence of irregular small (μm-sized) metal-containing droplets on top of the deposited films, which cause diffuse scatter and thus artificially reduce the reflected intensity, especially at low angles. 9 Therefore, measurements below Q z = 0.3 nm −1 were disregarded in the fitting procedure. The primary intensity became a fitting parameter, which was determined for each sample.…”

Identifying surface structural changes in a newly-developed Ga-based alloy with melting temperature below 10 °C

“…When the Ga-based liquid metal is exposed to ambient atmosphere, a thin self-limiting oxide layer can spontaneously and rapidly form on the surface. Consequently, it significantly changes the bulk behavior of liquid metal along with its surface tension and wetting [21][22][23] , allowing the liquid metal to adhere to almost any solid surface and providing a new insight to manipulate the liquid-metal structure for specific applications [22,[24][25][26][27] . For example, Khan et al recently reported an approach to tune the interfacial tension of an EGaIn via electrochemical deposition (or removal) of an oxide layer on its surface using external electrical field [22] .…”