ZnS Branched Architectures as Optoelectronic Devices and Field Emitters

Abstract

Branched assemblies of nanostructures (nanocrystals, nanowires, nanobelts and nanotubes) as building blocks for functional materials and devices are the key to tailoring properties for specific applications in micro-/nanoelectromechanical systems, optoelectronics, field emitters, and light-emitting diodes. [1][2][3][4][5] Direct fabrication of complex nanostructures with controlled structural characteristics (including morphology, dimensionality, surface architectures, and crystal structures) represents a significant challenge in the field of nanometer-scale science and technology. Intensive efforts have been devoted to achieving desired morphology or shape (such as cones, spheres, tubes, wires, belts, cables, and branched heterostructures) and crystallinity of various inorganic crystals-from micrometer to nanometer size. Such structural parameters represent key elements that determine their electrical, optical, and field-emission (FE) properties. High-quality field emitters are very desirable for applications in a wide range of FE-based devices such as flat-panel displays, parallel-electron-beam microscopes, vacuum microwave amplifiers, and X-ray sources. To date, various FE cold cathode 1D nanostructural materials, such as carbon nanotubes, ZnO, ZnS, Si, SiC, CdS, and AlN nanostructures, have been demonstrated as candidates for achieving a high FE-current density at low electric fields because of their high aspect ratios.[6] Especially, branched nanostructures with a high packing density and highly crystalline nanotips can significantly enhance their FE properties and thus show great promising for practical applications. Recently, special architectures, such as AlN nanoarchitectures, [2] comblike ZnO nanostructures, [7] ZnO nanoarchitectures, [8] cactus-like Ga 2 O 3 Nanostructures, [9] CdTe architectures, [10] and branched ZnS-In heterostructures, [11] have been observed and have shown improved FE properties.ZnS, a wide bandgap semiconductor with a gap energy of 3.7 eV at 300 K, is one of the first discovered compound semiconductors and probably one of the most important materials in electronic/optoelectronic industries with prominent applications in flat-panel displays, sensors, lasers, and photocatalysis. [12,13] Interest in FE from ZnS has been increasing because of its charming performance. Many studies have been reported on manipulating the size, morphology, and crystal structure of ZnS materials for optimizing their FE properties, and various ZnS nanostructures, such as rods, [14] wires, [15] belts, [16][17][18] cables, [19,20] tubes, [21] tetrapods, [22] helices, [23] and conelike structures, [24][25][26] are synthesized. However, understanding of self-assembled single-phased ZnS branched architectures and their associated FE properties is limited, [11] although such information is vital for their potential applications.In this Communication, we report a novel single-phased ZnS branched architecture, self-assembled through a facile thermal evaporation process. This novel architecture consists of a singl...

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