Halide based MBE of crystalline metals and oxides

Abstract

AbstractA halide based growth chemistry has been demonstrated which can deliver a range of transition metals using low to moderate effusion cell temperatures (30‐700 °C) even for high melting point metals. Previously, growth with transition metal species required difficult to control electron beam or impurity inducing metal organic sources. Both crystalline oxide and metal films exhibiting excellent crystal quality are grown using this halide‐based growth chemistry. Films are grown using a plasma assisted Molecular Beam Epitaxy (MBE) system with metal‐chloride precursors. Crystalline niobium, cobalt, iron, and nickel were grown using this chemistry but the technology can be generalized to almost any metal for which a chloride precursor is available. Additionally, the oxides LiNbO3 and LiNbO2 were grown with films exhibiting X‐ray diffraction (XRD) rocking curve full‐widths at half maximum of 150 and 190 arcseconds respectively. LiNbO2 films demonstrate a memristive response due to the rapid movement of lithium in the layered crystal structure. The rapid movement of lithium ions in LiNbO2 memristors is characterized using impedance spectroscopy measurements. The impedance spectroscopy measurements suggest an ionic current of.1 mA for a small drive voltage of 5 mV AC or equivalently an ionic current density of ∼87 A/cm2. This high ionic current density coupled with low charge transfer resistance of ∼16.5 Ω and a high relaxation frequency (6.6 MHz) makes this single crystal material appealing for battery applications in addition to memristors. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)