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Non-planar nanomaterials and heterojunctions based on semiconducting oxides


Author: Ababii Nicolai
Degree:doctor of engineering
Speciality: 05.27.03 - Quantum Electronics and Optoelectronics
Year:2022
Scientific adviser: Oleg Lupan
doctor habilitat, associate professor (docent)
Institution: Technical University of Moldova

Status

The thesis was presented on the 1 July, 2022 at the meeting of the Scientific Council and now it is under consideration of the National Council.

Abstract

Adobe PDF document3.33 Mb / in romanian
Adobe PDF document2.79 Mb / in english

Thesis

CZU [620.22+539.2]:621.315.592.4(043)

Adobe PDF document 14.11 Mb / in romanian
206 pages


Keywords

CuO, nanotechnologies, nanomaterials, heterojunctions, gas sensor

Summary

Thesis structure: The thesis was realised at the Technical University of Moldova (TUM), Center for Nanotechnologies and Nanosensors (CNN), Department of Microelectronics and Biomedical Engineering (DMBE). It is written in Romanian language and consists of introduction, 5 chapters, general conclusions and recommendations, bibliography with 297 references, 119 pages of basic text, 51 figures and 1 table. The obtained results were published in 27 scientific papers, including: 2 patents; 10 peer-review papers in international journals listed ISI and SCOPUS database (two of which have an Impact Factor: 17.881); 1 article in journals from the National Register of specialized journals; 14 papers presented, revised and published in proceeding of National and International Conferences.

Aim of the study: consists in obtaining non-planar nanomaterials, heterostructures, and heterojunctions based on semiconductor oxides, CuO/Cu2O, TiO2/CuO/Cu2O, Fe2O3 - CuO/Cu2O, CuO-Cu2O/ZnO:Al and Al2O3/CuO, through cost-effective methods and technologies; identification of nanomaterials and heterostructures with sensitivity and selectivity to gases (H2) and volatile organic compounds (VOC: acetone, n-butanol, ethanol and 2-propanol); obtaining sensor structures stable at high relative humidity based on developed nanomaterials and heterostructures.

Objectives: research of the sensor properties of nanomaterials and heterostructures based on: (i) TiO2/CuO/Cu2O films and their functionalization; (ii) 3D printed Fe2O3 - CuO/Cu2O heterostructures; (iii) CuO-Cu2O/ZnO:Al heterostructures; (iv) Al2O3/CuO heterostructures with a stable response at high relative humidity; advanced physico-chemical analysis and characterization of properties; stability research at high relative humidity.

Scientific novelty and originality: ensuring long-term stability of response, regulating selective sensitivity, as well as improving the gas and VOC response of TiO2, CuO/Cu2O, TiO2/CuO/Cu2O, CuO-Cu2O/ZnO:Al and Al2O3/CuO nanomaterials and heterostructures. For the first time, heterostructures of CuO/Cu2O and Fe2O3 - CuO/Cu2O were obtained by the 3D printing method and investigated their properties. Through the techniques of SEM, XRD, Raman, TEM, HRTEM, SAED, EDX and XPS, research was performed to determine the quality and characteristics of obtained nanomaterials and heterostructures. Calculations (DFT) of heterojunctions, by simulating the interaction of gas/VOCs molecules with the surface of modeled structures were performed to model the proposed detection mechanisms and to understand the effects and phenomena that occurs at the surface and interface of heterojunctions developed in this thesis.

The solved scientific and research problem is to identify nanomaterials and heterojunctions with sensitivity and selectivity to gases (H2) and VOCs (acetone, n-butanol, ethanol and 2-propanol) and to obtain stability at high relative humidity.

The theoretical significance and applicative value of the work are based on the deepening and elaboration of physico-chemical mechanisms for detecting gases/VOCs and UV radiation by nanomaterials and heterostructures developed based on TiO2, CuO/Cu2O, TiO2/CuO/Cu2O, Fe2O3 - CuO/Cu2O, CuO-Cu2O/ZnO:Al and Al2O3/CuO, as well as the presentation of practical applications for sensitive and selective detection of hydrogen, ethanol, acetone, n-butanol and 2-propanol gases/vapors with stability of response over time and at high relative humidity. The models of the proposed detection mechanisms were supported by the calculations of the elaborated functional theory, in combination with DFT simulations, by simulating the interaction of gas/VOCs molecules with the surface of heterojunctions.

Implementation of scientific results. The scientific results were partially implemented in the instructive-educational process carried out within TUM, and in the elaboration of the undergraduate theses of the students within the MBE Department, Subsequently, based on the acquired scientific results, it was possible to obtain an act for the implementation of innovative research at the Faculty of CIM, TUM, as well as two patents.