UC Riverside

Electronic devices utilize the foremost advances in technology. In order to make progress we must understand not only the properties of novel materials but also how best to synthesize these materials in an appropriate way so that they can be used in an industrial setting.

Transition metal dichalcogenides, specifically molybdenum ditelluride (MoTe2) is a class of 2D material that has been well studied for their semiconducting nature in the 2H phase yet they also have 2 other phases with vastly different properties: 1T’ and 1T. The 1T’ phase has metallic properties. There is a 3rd phase, however, that prior to my work has been largely left unstudied, the 1T phase. This phase is calculated to be semi metallic from its calculated band structure but is also highly unfavorable at room temperature. With this in mind we set out to synthesis this elusive phase via a chemical vapor deposition process by selectively using process gases and varying cooling rates to stabilize the 1T phase at ambient temperatures. Measurements confirm the 1T phase of MoTe2 is in fact semi-metallic. In addition, mixed phase 2H/1T films were synthesized and electronically tested to yield a semiconducting film with significantly improved conductivity that could still be gated for on/off current switching.

As copper interconnects decrease in cross-section to below 100 nm in size the resistivity of this, typically, highly conductive metal starts to increase exponentially do to surface and grain boundary scattering of electrons. Quasi-1D Transition metal trichalcogenides, like tantalum triselenide (TaSe3), can have metallic properties. The main issue that is being addressed is that of copper interconnects as they reach their scaling limits. The concentration is 2-fold, 1) develop a growth method/process that could synthesis TaSe3 at temperatures at or lower than 400°C and 2) measure the materials resistivity as a function of decreasing cross-sectional area to see if these highly crystalline transition metal trichalcogenide maintains its bulk resistivity unlike that of copper. Given this momentous task we again set out to develop a chemical vapor deposition process to synthesis TaSe3 using volatilized reagents to help aid in the formation of the crystals at low temperatures. The resistivity of the nanowires grown using this method were tested down to 7nm in cross-sectional area and found no scaling effect present with regards to resistivity. In addition, it was also found to have an electromigration activation energy, the main failing point of interconnects, to be double that of copper and able to withstand current densities of 108 A/cm2, orders of magnitude higher than copper. The results give credence to this class of materials potential for future downscaled devices.