Aqueous chemical growth and patterning of ZnO nanopillars on different substrate materials

Abstract

Aqueous chemical growth (ACG) is a low-temperature approach that is only weakly influenced by the substrate and allows for the growth of ZnO nanopillars on various substrates. ACG is an efficient way to generate wafer-scale and densely packed arrays of ZnO nanopillars even on polymer materials. Photoluminescence (PL) characterisation clearly shows a comparatively strong band-edge luminescence even at room temperature that is accompanied with a rather weak visible luminescence in the yellow / orange spectral range. We introduce a rather simple postgrowth lithographic technique. Patterning of ZnO nanopillars even on layered conducting and flexible substrate materials using ACG as a low-temperature growth technique is demonstrated. The economical potential for future applications and devices using ZnO nanopillar arrays is discussed.1 Introduction ZnO materials have received broad attention in the last years due to its wide direct bandgap of 3.37 eV at room temperature, large exciton binding energy (60 meV in bulk ZnO), piezoelectric properties, excellent chemical and thermal stability and pronounced ability to build a variety of nanostructures. Nanosized materials are of special interest due to novel electrical, mechanical, chemical and optical properties that are introduced by surface and quantum confinement effects [1]. Gas-phase approaches that are based on evaporation and condensation steps are frequently used due to their simplicity and high-quality products [2][3][4][5]. However, the economic potential of gas-phase grown structures is restricted because these approaches require rather expensive and / or insulating substrate materials [6]. In recent years aqueous chemical growth (ACG) approaches gain in importance because ACG is a costefficient and low temperature growth technique. Vayssieres et al. developed an ACG process under hydrothermal like conditions [7,8]. A further growth approach is based on a two step process: first generation of a nucleation layer followed by an aqueous chemical growth step [6,9,10]. Up to now only little progress was achieved with respect to generation and position control of well defined geometric arrays of ZnO nanostructures. Recently the report of Hsu et al. shows directed bottom up growth of ZnO nanorods on prestructured Si (001) wafers using a combination of expensive electron beam and microcontact printing techniques [11]. Here we report on further developments and characterisation of the two step ACG technology. Moreover we introduce a rather simple lithographic patterning technique that allows for the generation of well defined geometric arrays on various substrate materials.

Electrical characterization of ZnO nanorods

“…The growth solution contained equimolar amounts of analytic grade hexamethyl- . The growth time was 3 h at a constant temperature of 90 °C [7]. Current-voltage characteristics of the as grown nanorod array were obtained by using an AFM system with conductive tips.…”

Surface effects and nonlinear optical properties of ZnO nanowires

“…Such demands are met by low-temperature chemical synthesis methods such as the aqueous chemical growth (ACG) [65][66][67] and the electrochemical deposition process (ECD) [68][69][70][71]. To exploit the large potential of lowtemperature grown nanowires, we systematically studied their fundamental optical properties and relevant microscopic recombination processes [72,73].…”

“…We studied the second-harmonic generation from arrays of ZnO nanowires fabricated by the wet-chemical ACG synthesis method [67]. This technique typically yields large scale (substrate size typically several cm 2 ) nanowires with diameters of 100 nm and lengths of a couple of microns.…”

Growth of c-axis oriented ZnO nanowires from aqueous solution: The decisive role of a seed layer for controlling the wires’ diameter

“…Tian et al [19] have later introduced a lowtemperature synthetic route for the fabrication of complex and oriented ZnO nanostructures, in which citrate anions were used to control crystal morphology. In the last years, many groups have reported the growth of highly oriented ZnO nanowires and other nanostructures from aqueous solutions [20][21][22][23][24][25][26][27][28]. It is currently believed that a ZnO seed layer is needed to initialize the uniform growth of oriented nanowires from aqueous solutions.…”