arXiv subjects

Maria Gabriela Sales

Publications and source records attributed to Maria Gabriela Sales.

3 recordsLinked to original sources

arXiv2020

Growth kinetics and atomistic mechanisms of native oxidation of ZrS$_x$Se$_{2-x}$ and MoS$_2$ crystals

A thorough understanding of native oxides is essential for designing semiconductor devices. Here we report a study of the rate and mechanisms of spontaneous oxidation of bulk single crystals of ZrS$_x$Se$_{2-x}$ alloys and MoS$_2$. ZrS$_x$Se$_{2-x}$ alloys oxidize rapidly, and the oxidation rate increases with Se content. Oxidation of basal surfaces is initiated by favorable O$_2$ adsorption and proceeds by a mechanism of Zr-O bond switching, that collapses the van der Waals gaps, and is facilitated by progressive redox transitions of the chalcogen. The rate-limiting process is the formation and out-diffusion of SO$_2$. In contrast, MoS$_2$ basal surfaces are stable due to unfavorable oxygen adsorption. Our results provide insight and quantitative guidance for designing and processing semiconductor devices based on ZrS$_x$Se$_{2-x}$ and MoS$_2$, and identify the atomistic-scale mechanisms of bonding and phase transformations in layered materials with competing anions.

cond-mat.mtrl-sci↗

arXiv2020

Thermal Stability of Hafnium Zirconium Oxide on Transition Metal Dichalcogenides

Ferroelectric oxides interfaced with transition metal dichalcogenides (TMDCs) offer a promising route toward ferroelectric-based devices due to lack of dangling bonds on the TMDC surface leading to a high-quality and abrupt ferroelectric/TMDC interface. In this work, the thermal stability of this interface is explored by first depositing hafnium zirconium oxide (HZO) directly on geological MoS2 and as-grown WSe2, followed by sequential annealing in ultra-high vacuum (UHV) over a range of temperatures (400-800 °C), and examining the interface through X-ray photoelectron spectroscopy (XPS). We show that the nucleation and stability of HZO grown through atomic layer deposition (ALD) varied depending on functionalization of the TMDC, and the deposition conditions can cause tungsten oxidation in WSe2. It was observed that HZO deposited on non-functionalized MoS2 was unstable and volatile upon annealing, while HZO on functionalized MoS2 was stable in the 400-800 °C range. The HZO/WSe2 interface was stable until 700 °C, after which Se began to evolve from the WSe2. In addition, there is evidence of oxygen vacancies in the HZO film being passivated at high temperatures. Lastly, X-ray diffraction (XRD) was used to confirm crystallization of the HZO within the temperature range studied.

cond-mat.mtrl-sci↗

arXiv2019

MoS2 Impurities: Chemical Identification and Spatial Resolution of Bismuth Impurities in Geological Material

Molybdenum disulfide (MoS2) is the most widely studied transition metal dichalcogenide (TMDC) material, in part because it is a natural crystal present in the earth, thus making it abundant and easily accessible. Geological MoS2 has been used in various studies that look at incorporating MoS2 into devices for nanoelectronics and optoelectronics. However, variations in the electronic properties of a single MoS2 surface are known to exist due to defects that are intrinsic to natural MoS2. This work reports the presence of bismuth impurities in MoS2 with concentrations high enough to be detected by X-ray photoelectron spectroscopy (XPS). These concentrations are further corroborated with inductively coupled plasma optical emission spectroscopy (ICP-OES). Localization of these bismuth clusters is shown using XPS-mapping, and the cluster size is determined to be on the order of tens of microns. This work provides important insights into the nature of impurities that are known to exist in MoS2.

cond-mat.mtrl-sci↗