Abstract
A method for fabricating monolithic nanoscopic tunnel junctions (MNTJs) for tunneling spectroscopy measurements using atomic layer deposition (ALD) of Cu on Pd seed layers has recently been introduced [Gupta and Willis, Appl. Phys. Lett. 90, 253102 (2007)]. The ALD grown layers are characterized here using planar thin films as models for the nanoelectrode composition and structure. ALD Cu films grown on Pd seed layers using a varying number of deposition cycles were characterized using transmission electron microscopy, Auger electron spectroscopy (AES), and glancing incidence x-ray diffraction (GIXRD) to investigate the chemical composition and structure of the nanoelectrodes. Electron diffraction and GIXRD show that as Cu is deposited, the bulk composition progresses from being Pd rich to becoming predominately Cu. In contrast, AES data show that significant Pd consistently remains on the surface of the growing film. The divergence in surface and bulk behaviors is attributed to Pd surface segregation that is driven by hydrogen adsorption during the ALD process. In contrast to the results for Pd seed layers, it is demonstrated that Pt seed layers can be used to grow pure Cu ALD films. This is because hydrogen adsorption does not induce Pt surface segregation within the ALD temperature window.
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