UC Riverside

ABSTRACT OF THE DISSERTATION

Electrical and Thermal Characterization of Low Dimensional Materials and Devices

by

Ruben A. Salgado

Doctor of Philosophy, Graduate Program in Materials Science and Engineering

University of California, Riverside, June 2019

Dr. Alexander A. Balandin, Chairperson

Low-dimensional materials such as quasi-one-dimensional carbon nanotubes and quasi-two-dimensional transition metal dichalcogenides reveal interesting properties, which have potential for future device applications. In some cases, the attractive feature of low-dimensional materials is their heat conduction capabilities, in other cases – it is the unusual electronic conduction and switching phenomena. In this dissertation research, I investigate (i) the thermal characteristics of carbon nanotubes incorporated in the battery electrode; and (ii) the electronic characteristics of quasi-two-dimensional 1T-TaS2 material system and devices based on these systems The selected material systems and different properties demonstrate a wide range of possibilities of the device applications for the low-dimensional materials. In the first part of this dissertation work, I describe the effects of the incorporation of carbon nanotubes, known for their high thermal conductivity, into Li-ion battery electrodes. It was demonstrated that the in-plane thermal conductivity of the composite electrodes with incorporated carbon nanotubes is as large as ~206 W/mK. This value exceeds the thermal conductivity of conventional laminated electrodes by about three orders of magnitude. The cross-plane thermal conductivity of the carbon-nanotube-based electrodes is in the same range as thermal conductivity values of conventional laminated electrodes. The electrodes with carbon nanotubes revealed a superior electrochemical performance and stability. The results of this research demonstrated that incorporation of highly thermally conductive low-dimensional materials can substantially improve the thermal properties of the battery electrodes without degrading their electrochemical performance. In the second part of this dissertation research, I report results of the investigation of current-voltage characteristics and low-frequency current fluctuations in vertical 1T-TaS2 charge-density-wave devices. The electron transport, perpendicular to the atomic planes, was studied in the temperature range below T=180 K, which is a known transition temperature to the commensurate charge-density-wave regime. The resistivity of the vertical 1T-TaS2 devices reveal an intriguing abrupt change below 100 K. The low-frequency noise spectra suggest a presence of an additional “hidden” phase transition at this point. The obtained results confirmed the potential use of low-frequency noise spectroscopy for the investigation of electron transport and switching phenomena in low dimensional materials.