Formation and Rupture of Schottky Nanocontacts on ZnO Nanocolumns
In this paper, the electrical transport and mechanical properties of Pt/ZnO Schottky nanocontacts have been studied simultaneously during the formation and rupture of the nanocontacts. By combining multidimensional conducting scanning force spectroscopy with appropriated data processing, the physical relevant parameters (the ideality factor, the Schottky barrier height, and the rupture voltage) are obtained. It has been found that the transport curves strongly depend on the loading force. For loading forces higher than a threshold value, the transport characteristics are similar to those of large-area Schottky contact, while below this threshold deviations from strictly thermionic emission …
Nanogoniometry with scanning force microscopy: a model study of CdTe thin films.
In this paper scanning force microscopy is combined with simple but powerful data processing to determine quantitatively, on a sub-micrometer scale, the orientation of surface facets present on crystalline materials. A high-quality scanning force topography image is used to determine an angular histogram of the surface normal at each image point. In addition to the known method for the assignment of Miller indices to the facets appearing on the surface, a quantitative analysis is presented that allows the characterization of the relative population and morphological quality of each of these facets. Two different CdTe thin films are used as model systems to probe the capabilities of this met…
Structural characterization of selective area growth GaN nanowires by non-destructive optical and electrical techniques
The growth selectivity and structural quality of GaN nanowires obtained by plasma-assisted molecular beam epitaxy on pre-patterned GaN(0001) templates are investigated by means of non-destructive techniques. Optimum control over the nanowire arrangement and size requires a pitch between the mask apertures below twice the diffusion length of Ga atoms. Lower pitches, however, seem to slightly diminish the structural quality of the material, as revealed by the increase of the Raman peak linewidths. The photoluminescence spectra of the nanowires show a considerable presence of basal plane stacking faults, whose density increases for decreasing nanowire diameter. The capabilities of Kelvin probe…
Polarity Effects on ZnO Films Grown along the Nonpolar[112¯0]Direction
The surface electrical properties of ZnO thin films grown along the nonpolar $[11\overline{2}0]$ direction have been investigated by Kelvin probe microscopy on a nanometer scale. Two different charge domains, with a 75 meV work function difference, coexist within the ZnO surface, which is covered by rhombohedral pyramids whose sidewalls are shown to be ${10\overline{1}1}$-type planes. The presence and relative orientation of the two kinds of charge domains are explained in terms of the atomic arrangement at the ${10\overline{1}1}$ polar surfaces.
Anisotropic chemical etching of semipolar \{10\bar {1}\bar {1}\}\mbox {/} \{10\bar {1}{+}1\} ZnO crystallographic planes: polarity versus dangling bonds
ZnO thin films grown by metal?organic vapor phase epitaxy along the nonpolar direction and exhibiting semipolar facets have been chemically etched with HCl. In order to get an insight into the influence of the ZnO wurtzite structure in the chemical reactivity of the material, Kelvin probe microscopy and convergent beam electron diffraction have been employed to unambiguously determine the absolute polarity of the facets, showing that facets are unstable upon etching in an HCl solution and transform into planes. In contrast, facets undergo homogeneous chemical etching perpendicular to the initial crystallographic plane. The observed etching behavior has been explained in terms of surface oxy…
Assessment of Polarity in GaN Self-Assembled Nanowires by Electrical Force Microscopy
In this work, we demonstrate the capabilities of atomic force microscopies (AFMs) for the nondestructive determination of the polarity of GaN nanowires (NWs). Three complementary AFMs are analyzed here: Kelvin probe force microscopy (KPFM), light-assisted KPFM, and piezo-force microscopy (PFM). These techniques allow us to assess the polarity of individual NWs over an area of tens of μm(2) and provide statistics on the polarity of the ensemble with an accuracy hardly reachable by other methods. The precise quantitative analysis of the tip-sample interaction by multidimensional spectroscopic measurements, combined with advanced data analysis, has allowed the separate characterization of elec…
The influence of AlN buffer over the polarity and the nucleation of self-organized GaN nanowires
We experimentally investigate the influence of AlN buffer growth on the nucleation and the polarity of a self-organized assembly of GaN nanowires (NWs) grown on Si. Two complementary growth mechanisms for AlN buffer deposited on Si are demonstrated. Both emphasize the aggregation of Si on the AlN surface and the growth of large cubic crystallites, namely, AlN pedestals. Further growths of GaN NWs assembly reveal that the GaN 2D layer found at the bottom of the NW assembly is the result of the coalescence of Ga-polar pyramids, whereas AlN pedestals are observed as preferential but not exclusive NW nucleation sites. NWs are N-polar or exhibit inversion domains with a Ga-polar core/N-polar she…