Speakers

Biography

Professor Paulo César De Morais, PhD, was a full Professor of Physics at the University of Brasilia (UnB) – Brazil up to 2013. Appointed as UnB’s (Brazil) Emeritus Professor (2014); Visiting Professor at the Huazhong University of Science and Technology (HUST) – China (2012-2015); Distinguished Professor at the Anhui University (AHU) – China (2016-2019); Full Professor at the Catholic University of Brasília (CUB) – Brazil (2018); CNPq-1A Research Fellow since 2010; 2007 Master Research Prize from UnB. He held a two-year (1987-1988) post-doc position with Bell Communications Research, New Jersey – USA, and received his Doctoral degree in Solid State Physics (1986) from the Federal University of Minas Gerais (UFMG) – Brazil. With more than 12,000 citations, He has published about 500 papers (Web of Science) and more than 16 patents.

Abstract

This plenary talk will focus on discussing room temperature magnetic ordering of very small carbon dots (CDs), mat-like polyaniline nanofibers (Mat-PANI), and a composite comprising CDs and Mat-PANI (CDs@Mat-PANI), the latter containing a small fraction (less than 1 wt%) of CDs. It will explore the saturation magnetization (M_S) of CDs, Mat-PANI, and CDs@Mat-PANI at increasing temperatures, from 5 K to 300 K, revealing a systematic decreasing trend, with a huge synergic effect demonstrated in the CDs@Mat-PANI system. The impressive M_S enhancement in the CDs@Mat-PANI system (about 200% at 5 K and 40% at 300 K) will be discussed in terms of an electron transfer mechanism from Mat-PANI imine nitrogen atoms to the encapsulated CDs. Changes in M_S values revealed that a substantial electron density is transferred to the CDs at low (5 K) as well as at high (300 K) temperatures, which is supported by observation of CDs photoluminescence (PL) redshift while within the CDs@Mat-PANI system. Band-bending and bandgap-renormalization calculations are claimed suitable to predict the observed redshift at higher (300 K) temperature as a result of the electron transfer mechanism, which is in excellent agreement with the PL data. Raman, x-ray diffraction, and x-ray photoelectron spectroscopy data are used to support the electron transfer mechanism as well as the strong interaction of CDs with PANI within the CDs@Mat-PANI system, which doubles the crystalline domain size of Mat-PANI while reducing the tensile strain from about one third.