Direct realizing the growth direction of epitaxial nanowires by electron microscopy

Abstract

The growth direction of nanowires is critically important for precisely controlling their physical and chemical properties and the performance of related nanowire-based electronic devices. Realizing the true orientations of nanowires is an important issue regarding designing and growth of nanowires with desired orientations and the subsequent applications. In this study, we demonstrated three electron microscopic techniques to determine the growth directions of epitaxial nanowires: mainly, correlating selected area electron diffraction pattern and brightfield imaging in transmission electron microscopes, tilting the nanowires until their growth directions parallel to the incident electron beams in scanning electron microscopes, and correlating the nature of cleavage planes of the nanowire substrates and nanowire projections in the side-view scanning electron microscopic investigations.

What Can Electron Microscopy Tell Us Beyond Crystal Structures?

“…When a nanorod with the growth direction along the [001] axis is examined in TEM, the growth direction can be determined by SAED or HRTEM imaging, subject to a correct position of the specimen. [25] Unfortunately in many studies, the growth direction of individual nanorods or nanowires is based on a single electron diffraction pattern or HRTEM image, leaving some degree of uncertainty. If the nanorod lies down on specimen grid with its long axis perpendicular to the electron beam, the diffraction spots along the growth direction in the SAED pattern and the corresponding lattice fringes on the HRTEM image would show the [001] orientation (Figure 2, c).…”

“…Zou and co-workers also discussed this problem recently. [25] Rotation of the nanorod around the axis perpendicular to both the electron beam and the long axis of the nanorod allows us to find the position with the longest projected dimension of the nanorod image, at which the observed crystal orientation along the long axis and the real growth orientation are parallel to each other. A correct determination of the growth orientation is an important step prior to the design and growth of nanomaterials with desired orientations and properties.…”

Design and tailoring of patterned ZnO nanostructures for energy conversion applications

“…Regarding the ZnO NAs, a wide range of fabrication techniques, such as metal-organic chemical vapor deposition, chemical vapor deposition, pulsed laser deposition, electrochemical deposition, and hydrothermal methods, have been developed [60][61][62]. However, the ZnO NAs synthesized by traditional vapor-phase and solution-phase growth methods have several drawbacks, such as poor orientation, different space and length of nanorods, and less morphology homogeneity.…”

Understanding of InAs nanostructure growth by molecular beam epitaxy

“…97,98 Since in III-V nanostructure growth, grown nanostructures can have an epitaxial relationship with the substrates, their growth direction can be determined via tilting the samples in the SEM. 99,100 For wurtzite structure III-V nanostructures, the nanowires usually grow along <0001> direction with {1100} or {1120} sidewall facets. 102 In the last decades, other growth directions, such as <11 ̅ 00>…”

“…103 Due to the fact that, the growth direction of low-dimensional nanostructures can have an influence on their crystal quality and properties, 98,105 controlling the growth direction of nanostructures has been investigated. 86,99 For instance, 1-D <001 ̅ > nanostructures, due to an activation barrier resulting from the Frank partial dislocation, 106 can easily obtain high crystalline quality zinc-blende structure. 98,[107][108][109][110] Thus, controlling the growth of high-quality <001 ̅ > nanostructures is critical.…”