Morphogenesis of One‐Dimensional ZnO Nano‐ and Microcrystals

Abstract

over timescales of hundreds of seconds (0.00 lm 2 s ±1 ). It is interesting that in the neutral MEA experiment, in which some of the surface amine groups are protonated, the diffusion coefficient was slightly lower than in the other cases.A surprising result was obtained when measuring the diffusion coefficients of the three sizes of MESA particles on the neutral surface derivatized with hexadecanethiol (C 16 H 33 SH).Comparing D values to those found on the MESA surface, we found near agreement for all but the small-diameter particles (6 lm 90 nm), which reproducibly stuck to the substrate immediately on contact. For larger particles, the long-range electrostatic force (presumably between the negatively charged sulfonate groups and an image charge in the substrate) is expected to dominate, [22] but for smaller ones the short-range van der Waals force is more important. Apparently, the two are closely balanced for the C 16 H 33 SH functionalized surface with rods of the size investigated here.While the scaling of these interactions is not completely understood at present, these initial studies provide some guidance as to the conditions that are desirable for nanorod assembly experiments. The observation of pH-dependent diffusion may, for example, be useful for affixing particles to specific areas or in specific conformations on basic surfaces. More importantly, the particle tracking method described here provides a simple and convenient method for quantifying the surface diffusion of non-spherical particles under arbitrary conditions. ExperimentalWhatman Al 2 O 3 filter membranes that contain 300±350 nm diameter internal pores were used as a template material. For 90 nm internal pore diameter, Al 2 O 3 membranes were prepared in-house by the electrochemical anodization of an Al plate [23]. In both cases, one face of the membranes was coated with approximately 150 nm of thermally evaporated Ag. More Ag was electrodeposited (Silver 1024, Technic, Inc.) directly onto the evaporated Ag in order to close any open pores. This Ag layer was then used as the back contact in the electrochemical cell, and more Ag was deposited, further filling-in the pores. The membrane and cell were rinsed with deionized H 2 O, and Au solution was added (Orotemp, Technic, Inc.). Plating was stopped with the desired rod length was reached. The Ag backing was removed by dissolving in 2 mL of 50 % HNO 3 , and the Al 2 O 3 template was dissolved in 2 mL of 5 M NaOH. The rods were sedimented using a laboratory centrifuge. The supernatant was removed and water was added. The rods were resuspended by physical agitation and brief immersion in an ultrasonic water bath. This rinsing process was repeated a total of five times in order to prepare the rods for addition of self-assembled monolayers (SAMs). Rods were derivatized with 2-mercaptoethanesulfonic acid, sodium salt (MESA, Aldrich) by suspending them in 1 mL of 1 mM MESA(aq) for 1 h. The MESA rods were then rinsed as described above, suspended in a total volume of 1 mL, and diluted 1000-fold f...

Colloidal nanocrystal synthesis and the organic–inorganic interface

“…1d). Branched crystals of zinc oxide were originally discovered in smokes from zinc smelting plants and have been prepared and studied in CVD systems for several decades 47 . In colloidal systems, it is now possible to prepare ensembles of centrally branched tetrapod nanocrystals with a high degree of control over the branch length and diameter 48,49 .…”

ZnO Nanorod Arrays as Electron Injection Layers for Efficient Organic Light Emitting Diodes

“…The development and investigation of ZnO nanostructures for optoelectronic applications is extensive and well-documented, showcasing a variety of morphologies achievable across a wide range of deposition techniques [1][2][3][4][5][6][7][8][9] . Of particular interest for device applications is the growth of ZnO nanorod arrays (NRAs) from low temperature, aqueous deposition techniques [10] which, over the past decade, has seen morphological improvements in alignment and uniformity through the introduction of precursor ZnO seed layers [11] , pH control of the growth environment [12,13] , additive incorporation [14] , as well as manipulation of growth variables including duration and temperature [15][16][17][18] .…”

Growth mechanism and characterization of zinc oxide microcages

“…A number of nanometer and micrometer ZnO materials of varied geometries have been produced, e.g. nanowires, nanosprings, nanoneedles, nanowalls, coaxial cables, tubes, tetrapods and sheets [4][5][6][7][8][9][10][11][12][13][14][15][16].…”