The role of substrate surface alteration in the fabrication of vertically aligned CdTenanowires

Abstract

Previously we have described the deposition of vertically aligned wurtzite CdTe nanowiresderived from an unusual catalytically driven growth mode. This growth mode could onlyproceed when the surface of the substrate was corrupted with an alcohol layer, althoughthe role of the corruption was not fully understood. Here, we present a studydetailing the remarkable role that this substrate surface alteration plays in thedevelopment of CdTe nanowires; it dramatically improves the size uniformityand largely eliminates lateral growth. These effects are demonstrated to arisefrom the altered surface’s ability to limit Ostwald ripening of the catalytic seedmaterial and by providing a surface unable to promote the epitaxial relationshipneeded to sustain a lateral growth mode. The axial growth of the CdTe nanowiresis found to be exclusively driven through the direct impingement of adatomsonto the catalytic seeds leading to a self-limiting wire height associated with thesublimation of material from the sidewall facets. The work presented furthers thedevelopment of the mechanisms needed to promote high quality substrate-basedvertically aligned CdTe nanowires. With our present understanding of the growthmechanism being a combination of selective area epitaxy and a catalytically drivenvapour–liquid–solid growth mode, these results also raise the intriguing possibility ofemploying this growth mode in other material systems in an effort to produce superiornanowires.