First-Principles Study of Cu 9 S 5 : A Novel p-Type Conductive Semiconductor

Zuo

Advanced Energy Materials

et al. 2021

As a bridge between nanocrystal catalysts and single‐atom catalysts, single‐unit‐cell catalysts seem at first glance to be unavailable for catalysis due to quantum effects and synthetic difficulties. Here, 24 nm Cu9S5 nanowires are synthesized via the LaMer pathway. Interestingly, when polyoxometalate (POM) clusters are introduced during the nucleation process, the 0.9 nm Cu9S5 nanowires are finally formed via covalent co‐assembly, analog to A–B–A–B‐type block co‐polymerization in the polymer field (“A” and “B” represent Cu9S5 unit cells and POM clusters, respectively). Multiple characterizations show that Cu9S5 exists as single‐unit‐cell structure. Therefore, each unit cell can work as an isolated active site. The single‐unit‐cell structure exhibits higher electrocatalytic activity and Faradaic efficiency (FE) of formic acid (82.0% at −0.8 V vs reversible hydrogen electrode (RHE)) during CO2 electroreduction, while the nanocrystal structure generates HCOO−, methanol, and ethanol with low FEs. This study suggests that the single‐unit‐cell catalyst displays great potential for precise catalysis by the finite size effect.

Section: Resultsmentioning

confidence: 96%

Single‐Unit‐Cell Catalysis of CO₂ Electroreduction over Sub‐1 nm Cu₉S₅ Nanowires

Zuo

Advanced Energy Materials

et al. 2021

“…Cu atoms locate in three different positions: Cu1 (triangular plane), Cu2(tetrahedron units), Cu3 (octahedron units) . This quasi‐layered structure formed by the relatively longer Cu‐S bond of Cu3 is similar to Bi 2 O 2 Se, with both of their layers linked by weak electrostatic forces, which is in significant contrast to typical van der Waals 2D layered structure such as MoS 2 . High quality Cu 9 S 5 nanoflakes were grown by salt‐assisted CVD method.…”

Section: Resultsmentioning

confidence: 99%

“…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 …”

Section: Resultsmentioning

confidence: 99%

“…Because of the high density of holes [26] 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. [14] We also test the photoresponse of the Cu 9 S 5 /MoS 2 photodetector under zero bias voltage (V ds = 0 V). Figure S5 in the Supporting Information shows that the self-driven photocurrent exhibits a high on/off ratio of approximately 10 4 and the rise time (decay time) τ rise (τ decay ) is about 8 ms (2 ms).…”

Section: Optoelectronic Performance Of Cu 9 S 5 /Mos 2 Heterostructurementioning

confidence: 99%

“…The high density of holes in Cu 2− x S can, according to the Anderson heterojunction model,9a,13 helps to build a strong electric field in the depletion layer of p‐n junction diode that may result in improved photoresponsivity. Cu 9 S 5 ( x = 0.2), among Cu 2− x S, is a direct band gap p‐type semiconductor with good stability and high optical absorption coefficient. The high hole mobility of Cu 9 S 5 can also decrease series resistance in lateral channel, which reduces diffusion time of majority carriers and hence increase the responsivity and response rate of p‐n diodes .…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

Liu

Han

et al. 2019

Adv Funct Materials

P‐n junctions based on two dimensional (2D) van der Waals (vdW) heterostructure are one of the most promising alternatives in next‐generation electronics and optoelectronics. By choosing different 2D transition metal dichalcogenides (TMDCs), the p‐n junctions have tailored energy band alignments and exhibit superior performance as photodetectors. The p‐n diodes working at reverse bias commonly have high detectivity due to suppressed dark current but suffer from low responsivity resulting from small quantum efficiency. Greater build‐in electric field in the depletion layer can improve the quantum efficiency by reducing recombination of charge carriers. Herein, Cu9S5, a novel p‐type semiconductor with direct bandgap and high optical absorption coefficient, is synthesized by salt‐assisted chemical vapor deposition (CVD) method. The high density of holes in Cu9S5 endows the constructed p‐n junction, Cu9S5/MoS2, with strong build‐in electric field according to Anderson heterojunction model. Consequently, the Cu9S5/MoS2 p‐n heterojunction has low dark current at reverse bias and high photoresponse under illumination due to the efficient charge separation. The Cu9S5/MoS2 photodetector exhibits good photodetectivity of 1.6 × 1012 Jones and photoresponsivity of 76 A W−1 under illumination. This study demonstrates Cu9S5 as a promising p‐type semiconductor for high‐performance p‐n heterojunction diodes.

High‐Performance Memristors Based on Ultrathin 2D Copper Chalcogenides

et al. 2022

generally prepared by molecular beam epitaxy (MBE) or wet-chemical methods, have started attracting attention. [11][12][13][14][15][16] However, due to the limitation of their small lateral size, the electronic properties and applications of 2D copper chalcogenides have rarely been touched despite dimensionality plays a crucial role in determining their properties. For example, the quantum confinement effect in reduced dimensionalities is considered to be effective on enhancing the power factor of thermoelectric materials, thereby improving the thermoelectric performance. [17] Thus, a novel synthetic strategy to prepare 2D copper chalcogenides with nanometer thickness and regular structures is needed to be developed.In addition, the small migration barrier of Cu ions, originated from their relatively loose bonding in copper chalcogenides, would result in a low defect formation energy and ubiquitous Cu vacancies. [4,8,18] Considering that ions/defects motion is the basis for resistive switching (RS) devices and related information storage technologies, it is natural to expect a memristive behavior with small switching thresholds in copper chalcogenides, which is highly desired in memristor research since most of 2D memristors own a switching voltage larger than 1 V. [19][20][21][22][23][24] Memristor-based electronics are a mainstream effort to realize low-power artificial intelligence through their analog multiply-accumulate operations in non von Neumann architecture, [25][26][27] and also they can be a promising platform for mimicking the actual biological synaptic connectivity maps. [26] Recently, memristive switching behavior was observed in relatively thick copper sulfide films, and was attributed to the reversible migration of Cu vacancies, [28] an intrinsic nature of copper chalcogenides. As a contrast, the reported 2D memristors mostly require either active metal (such as Cu and Ag) electrodes [24,[29][30][31] or precise control of oxidation to produce extrinsic mobilizable ions/defects/grain boundaries, [23,[32][33][34] which obviously restricts their further applications in an open architecture such as fabricating 2D heterostructures.van der Waals (vdW) epitaxy, which is based on relatively weak vdW interactions between the epitaxial layers and growth substrates, has been proven to be effective in synthesizing 2D planar structures from both layered and nonlayered materials. [3,35,36] In this work, we demonstrate the controllable preparation of a series of 2D binary copper chalcogenideCopper chalcogenides represent a class of materials with unique crystal structures, high electrical conductivity, and earth abundance, and are recognized as promising candidates for next-generation green electronics. However, their 2D structures and the corresponding electronic properties have rarely been touched. Herein, a series of ultrathin copper chalcogenide nanosheets with thicknesses down to two unit cells are successfully synthesized, including layered Cu 2 Te, as well as nonlayered CuSe and Cu 9 S 5 , via van der Wa...