Digenite (Cu₉S₅): Layered p-Type Semiconductor Grown by Reactive Annealing of Copper

Abstract

Most of the recently discovered layered materials such as MoS 2 or MoSe 2 are n-type, while few materials, such as phosphorene, which suffers from rapid oxidation, are p-type. To form devices such as p−n junctions and heterojunctions, new p-type mono-/few-layers are needed. Here, we report a one-step synthesis of layered, crystalline, ptype copper sulfide by thermal annealing of a standard copper foil in an inert environment using chemical vapor deposition (CVD). Optical spectroscopies (photoluminescence and absorption) show definite correlating features around 2.5 eV. Surface photovoltage spectroscopy shows a photovoltage reduction around the same energy range, which would be expected from a bandgap of a p-type material, and p-type conductivity was also observed using a thermoelectric probe. TEM, XRD, and AFM showed that the synthesized material is layered and has a unique stoichiometry of Cu 9 S 5 . Using sonication and dropcasting, we succeeded to isolate few-layers and monolayers. We observed good bulk electrical conductivity and characterized the electrical conductivity of few-layer copper sulfide flakes using peak force tunneling atomic force microscopy (PF-TUNA). We observed an increase in conductivity for increasing number of layers. Given its conductivity and layered morphology, we tested the synthesized Cu 9 S 5 as an electrode for a Li-ion battery. The proposed bottom-up synthesis, which is simple and scalable, allows synthesizing bulk quantities of the p-type layered Cu 9 S 5 which can then be exfoliated (top-down) to deposit monolayer flakes on substrates. Combined with the progress achieved in the preparation of n-type layered materials, this p-type Cu 9 S 5 opens the door to the fabrication of 2D p−n heterojunctions.

Salt‐Assisted Growth of P‐type Cu9S5 Nanoflakes for P‐N Heterojunction Photodetectors with High Responsivity

“…X‐ray diffraction (XRD) was used to identify the crystal phase of the as‐synthesized Cu 9 S 5 nanoflakes. As shown in Figure d, the XRD peaks match well with rhombohedral phase (PDF #26‐0476) …”

“…It is well known that the current density is proportional to carrier mobility multiplies carrier concentration. Because higher temperature reduces carrier mobility due to phonon scattering, the increase of thermo activated carrier density in Cu 9 S 5 , given the preliminary estimation of hole density as high as 10 20 cm −3 in intrinsic bulk Cu 9 S 5 , still exerts higher influence on the conductivity. Furthermore, as shown in Figure d, the calculated conductivity σ versus 1000/ T is plotted and the curve exhibits a typical Arrhenius feature, which also confirm that the conduction is dominated by thermal activation.…”

“…The performance of individual Cu 9 S 5 nanoflake was also tested under 532 nm laser illumination, see Figure S4b in the Supporting Information. Because of the high density of holes in Cu 9 S 5 , its dark current is large, rendering the photoresponse neglectable, though the Cu 9 S 5 has been predicted to be a direct semiconductor …”

Three-Dimensional Graphene-Decorated Copper-Phosphide (Cu3P@3DG) Heterostructure as an Effective Electrode for a Supercapacitor

“…The synthesis of Cu 3 P experiments is performed by using the "fast-heat" technique in which the samples are initially positioned outside the heated zone of the furnace with a fan blowing on the exposed quartz tube surface to keep the sample at room temperature (Itzhak et al, 2018;Kumar et al, 2018). Once the set temperatures of furnaces have reached a stable value, then the quartz tube is shifted to position the sample in the growth zone to start the phosphorization process.…”

“…Also, 3DG effectively minimizes the unwanted agglomeration of metal nanoparticles, thereby enhancing the chemical stability of the electroactive materials. In compliance to develop a novel approach for the synthesis of new hybrid materials (Kumar et al, 2017;Itzhak et al, 2018) herein, we report a facile, industrially scalable and easy method to produce a high yield of hexagonal Cu 3 P by solid-state reaction at low temperature followed by the formation of nano-hybrid with 3DG matrix on graphite substrate. This nano-hybrid has demonstrated significantly high electrochemical performance at an optimized Cu 3 P:3DG ratio with a tremendous C sp of 1,095.85 F/g at a scan rate of 10 mV/s.…”