Metastable Tetragonal Cu₂Se Hyperbranched Structures: Large‐Scale Preparation and Tunable Electrical and Optical Response Regulated by Phase Conversion

Abstract

Despite the promising applications of copper selenide nanoparticles, an in-depth elucidation of the inherent properties of tetragonal Cu(2)Se (β-Cu(2)Se) has not been performed because of the lack of a facile synthesis on the nanoscale and an energy-intensive strategy is usually employed. In this work, a facile wet-chemical strategy, employing HCOOH as reducing agent, has been developed to access single-crystalline metastable β-Cu(2)Se hyperbranched architectures for the first time. The process avoids hazardous chemistry and high temperatures, and thus opens up a facile approach to the large-scale low-cost preparation of metastable β-Cu(2)Se hyperbranched architectures. A possible growth mechanism to explain the formation of the β-Cu(2)Se dendritic morphology has been proposed based on time-dependent shape evolution. Further investigations revealed that the metastable β-Cu(2)Se can convert into the thermodynamically more stable cubic α-Cu(2-x)Se maintaining the dendritic morphology. An increase in electrical conductivity and a tunable optical response were observed under ambient conditions. This behavior can be explained by the oxidation of the surface of the β-Cu(2)Se hyperbranched structures, ultimately leading to solid-state phase conversion from β-Cu(2)Se into superionic conductor α-Cu(1.8)Se, which has potential applications in energy-related devices and sensors.

Aqueous preparation of surfactant-free copper selenide nanowires

“…An example is the cuprous selenide (Cu 2 Se) nanoparticles, which are easily oxidized into non-stoichiometric Cu 1.8 Se, and become into surprisingly good p-type semiconductor with over 3000 times of enhancements in electrical conductivity. [2] In order to tune the properties of nano-scale copper selenides, a number of techniques and strategies, such as hydro-or solvo-thermal approach, [2,15,16] sonochemistry, [17] electrochemical-deposition, [18] microwave-assistant route, [19] ball milling technique, [6] and chemical welding method, [5] have been developed to prepare nanocrystals, [20] nanotubes/wires, [15,[21][22][23] nanocages, [24] dendrimers, [16,25] and nanosheets [26] with well-defined size, morphology, crystal structure, and composition.…”

Facile Microwave-Assisted Synthesis of Klockmannite CuSe Nanosheets and Their Exceptional Electrical Properties

“…All these phases are identified as p-type semiconductors due to the existence of copper vacancies within crystal lattice, and widely used in solar cells45, gas sensors6, and photo-detectors7. Instead of crystal phases, efforts have also been devoted to preparing copper selenides with controlled morphologies such as nanoparticles891011, nanocubes1213, nanotubes14, nanowires1516 and hierarchical nanostructures1718.…”

Monoclinic Copper(I) Selenide Nanocrystals and Copper(I) Selenide/Palladium Heterostructures: Synthesis, Characterization, and Surface‐Enhanced Raman Scattering Performance

“…[16] Additionally, Cu 2 Se is prone to oxidation into more thermodynamically stable nonstoichiometric copper chalcogenide phases. In the present case, we used TOP as an extraction agent, reducing agent, and stabilizing agent and it can cause hexagonal CuSe and cubic Cu 2-x Se to readily convert to monoclinic Cu 2 Se at 220°C.…”

“…Copper selenides exhibit particular optical, superionic, thermoelectric, and photoelectric properties and considerable progress has been made on their applications in electronic and optoelectronic devices. [16] However, no studies of the SERS performance of copper selenide based materials have been reported.…”

“…Recent studies have shown that metastable monoclinic Cu 2 Se exhibits superior field-effect transistor and electrical performances and has promising applications. [16] Owing to the flexibility of the Cu 2 Se family of compounds and the relatively difficult wet chemical synthesis of monoclinic Cu 2 Se, reports on monoclinic Cu 2 Se are rare. [14,15] Thus, the exploration of new and simple phase-controlled synthetic strategies for the formation of Cu 2 Se is desirable and could greatly extend the technological potential of Cu 2 Se-based materials.…”