Browsing by Author "MacKenzie, David M.A."

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Enhanced thermally aided memory performance using few-layer ReS 2 transistors
(2020-02-03) Goyal, Natasha; MacKenzie, David M.A.; Panchal, Vishal; Jawa, Himani; Kazakova, Olga; Petersen, Dirch Hjorth; Lodha, Saurabh
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Thermally varying hysteretic gate operation in few-layer ReS 2 and MoS 2 back gate field effect transistors (FETs) is studied and compared for memory applications. Clockwise hysteresis at room temperature and anti-clockwise hysteresis at higher temperature (373 K for ReS 2 and 400 K for MoS 2) are accompanied by step-like jumps in transfer curves for both forward and reverse voltage sweeps. Hence, a step-like conductance (STC) crossover hysteresis between the transfer curves for the two sweeps is observed at high temperature. Furthermore, memory parameters such as the RESET-to-WRITE window and READ window are defined and compared for clockwise hysteresis at low temperature and STC-type hysteresis at high temperature, showing better memory performance for ReS 2 FETs as compared to MoS 2 FETs. Smaller operating temperature and voltage along with larger READ and RESET-to-WRITE windows make ReS 2 FETs a better choice for thermally aided memory applications. Finally, temperature dependent Kelvin probe force microscopy measurements show decreasing (constant) surface potential with increasing temperature for ReS 2 (MoS 2). This indicates less effective intrinsic trapping at high temperature in ReS 2, leading to earlier occurrence of STC-type hysteresis in ReS 2 FETs as compared to MoS 2 FETs with increasing temperature.
Fermi velocity renormalization in graphene probed by terahertz time-domain spectroscopy
(2020-07) Whelan, Patrick R.; Shen, Qian; Zhou, Binbin; Serrano, I. G.; Kamalakar, M. Venkata; MacKenzie, David M.A.; Ji, Jie; Huang, Deping; Shi, Haofei; Luo, Da; Wang, Meihui; Ruoff, Rodney S.; Jauho, Antti Pekka; Jepsen, Peter U.; Bøggild, Peter; Caridad, José M.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
We demonstrate terahertz time-domain spectroscopy (THz-TDS) to be an accurate, rapid and scalable method to probe the interaction-induced Fermi velocity renormalization ν∗F of charge carriers in graphene. This allows the quantitative extraction of all electrical parameters (DC conductivity σ DC, carrier density n, and carrier mobility µ) of large-scale graphene films placed on arbitrary substrates via THz-TDS. Particularly relevant are substrates with low relative permittivity (< 5) such as polymeric films, where notable renormalization effects are observed even at relatively large carrier densities (>1012 cm-2, Fermi level > 0.1 eV). From an application point of view, the ability to rapidly and non-destructively quantify and map the electrical (σ DC, n, µ) and electronic (ν∗F) properties of large-scale graphene on generic substrates is key to utilize this material in applications such as metrology, flexible electronics as well as to monitor graphene transfers using polymers as handling layers.