VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY PHAM BA LICH ADSORPTION OF TOXIC GASES ON GRAPHENE/SiO2 AND GRAPHENE/h-BN MASTER'S THESIS LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY __________________ PHAM BA LICH ADSORPTION OF TOXIC GASES ON GRAPHENE/SiO2 AND GRAPHENE/h-BN MAJOR: NANOTECHNOLOGY CODE: 8440140.11QTD RESEARCH SUPERVISORS: Dr. DINH VAN AN Dr. PHUNG THI VIET BAC Hanoi, 2020 LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com ACKNOWLEDGEMENTS I do thank to all people who helped me and supported me during the completion of this report. Foremost, I especially would love to express my hearty appreciation toward Dr.
Dinh Van An – my first supervisor and Dr. Phung Thi Viet Bac – my second supervisor for their continuous support, conscientious guidance, wonderful inspiration, and providing me with an excellent atmosphere during my thesis. I would also like to acknowledge Prof. Morikawa Yoshitada, Assoc.
Ikutaro Hamada at Osaka University for their kind supports during my internship in Japan. I am gratefully indebted to them for their very valuable comments and supervision on this research topic. My sincere thanks also go to Ms. Ta Thi Luong, Mr.
Pham Trong Lam, and Mr. Ngoc Thanh for their helpful instruction when learning how to use DFT and VASP. I also want to thank other lab mates and lab secretaries for all their kind supports. Last but not least, I am grateful to staff of Vietnam Japan University, Osaka University, and the Japanese International Cooperation Agency for their support with kindness.
LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com TABLE OF CONTENTS Page INTRODUCTION .1 CHAPTER 1: LITERATURE REVIEW. Heterostructure of Graphene/Hexagonal boron nitride (G/h-BN). Heterostructure of Graphene/Silicon dioxide (G/SiO2). Physisorption mechanism of gas sensor.11 CHAPTER 2: COMPUTATIONAL METHODS AND MODELS.
Density Functional Theory (DFT). The Kohn-Sham (KS) Method. The Local-Density Approximation (LDA). VASP – Vienna Ab initio Simulation Package.
Implemented computational scheme. Unit cell of the graphene/substrate heterostructure. Supercell of the graphene/substrate heterostructure. Positions for adsorption of toxic gases on G/h-BN and G/α-SiO2 .28 CHAPTER 3: RESULTS AND DISCUSSION.
Study and fabrication the Graphene/substrate heterostructures. The mismatch property between graphene and substrates. Adsorption of different gases on Graphene/h-BN. CO2 on graphene/h-BN.
CO on graphene/h-BN. NO on graphene/h-BN. NO2 on graphene/h-BN. NH3 on graphene/h-BN.
H2O on graphene/h-BN. Selectivity and sensitivity of gas adsorption on G/h-BN. Adsorption of CO and NO gases on Graphene/α-SiO2 .53 LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com LIST OF TABLES Page Table 1. Physical properties among graphite, SiO2, and h-BN.
The optimization results of AB stacking pattern with C on top B. The optimization results of AB stacking pattern with C on top N. Comparison of lattice mismatch with other articles. Comparison with various DFT simulation methods.
Adsorption energy and adsorptive distance for CO2 on G/h-BN. Adsorption properties from optimization of CO/G/h-BN in four sites. Adsorption properties from optimization of NO/G/h-BN in four sites. Adsorption properties from optimization of NO2/G/h-BN in four sites.
Adsorption properties from optimization of NH3/G/h-BN in four sites. Adsorption properties from optimization of H2O/G/h-BN in four sites. A comparison of adsorption energies of gases on G/h-BN. A comparison of adsorption energies of gases on G/α-SiO2 .50 LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com LIST OF FIGURES Page Figure 1.
Structure of monolayer of graphene and its applications. Structure and properties of other graphene’s derivatives. Structure and physical properties of other 2D materials. Topology and charge density map of G/h-BN and G/SiO2.
Structure of h-BN. Configurations of (a) α-quartz and (b) cristobalite of SiO2. Schematic mechanism of gas sensor and its signal measurement. Flow chart of the solution procedure of DFT.
Two different AB-stacking patterns of G/h-BN. G/α-SiO2 heterostructure with (a) side view and (b) top view of G/SiO2. Electron distribution of G/h-BN heterostructure with C on top B. Band structure of G/h-BN and DOS of (a) h-BN, (b) graphene and (c) total system.
Optimized configuration and electronic density of G/α-SiO2 using revPBE-vdW. Yellow in (c) presents the locations of the electron cloud. Three adsorption sites and gas molecule orientations on G/h-BN. Different adsorption sites on G/α-SiO2.
Atomic structures of all configurations for CO2 molecule adsorbed on G/h-BN. DOS of CO2 before and after adsorption on G/h-BN. Partial DOS of a carbon on graphene mainly interacted with CO2 before and after adsorption. Adsorption of CO molecule on G/h-BN in four different sites.
Molecular orbital of CO (1) and DOS of CO before adsorption (2). DOS of CO before and after adsorption on G/h-BN. Partial DOS of a carbon on graphene mainly interacted with CO before and after adsorption. Adsorption of NO molecule on G/h-BN in four different sites.
MO of NO molecule (1) and DOS of NO before adsorption (2). DOS of NO before and after adsorption on G/h-BN. Adsorption of NO2 molecule on G/h-BN in four different sites. MO of NO2 molecule (1) and DOS of NO2 before adsorption (2).
DOS of NO2 before and after adsorption on G/h-BN. Adsorption of NH3 molecule on G/h-BN .43 LUAN VAN CHAT LUONG download : add luanvanchat@agmail. MO of NH3 molecule (1) and DOS of NH3 before adsorption (2). DOS of NH3 before and after adsorption on G/h-BN.
Adsorption of H2O molecule on G/h-BN in four different sites. MO of H2O molecule (1) and DOS of H2O before adsorption (2). DOS of H2O before and after adsorption on G/h-BN. Adsorption energy and distance of each gas on G/h-BN from z-axis scanning.
Adsorption of CO and NO on G/α-SiO2 in top and hollow sites .50 LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com LIST OF ABBREVIATIONS 2D Two-dimensional DFT Density Functional Theory DOS Density Of State FET Field Effect Transistor G/h-BN Graphene/hexagonal Boron Nitride G/SiO2 Graphene/Silicon Dioxide HOMO Highest Occupied Molecular Orbitals KS Kohn-Sham LUMO Lowest Unoccupied Molecular Orbitals MO Molecular Orbital VSEPR Valance Shell Electron Pair Repulsion theory vdW Van der Waals LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com INTRODUCTION Recently, graphene, a two-dimensional (2D) monolayer of graphite, has drawn a great interest in public due to its potential electrical properties. It can serve as a core material in nano-electronic appliances. One of the most fascinating application of carbon-based material such as graphene is in gas sensors detecting gases on the atmosphere with a high sensitivity. Accordingly, the high mobility of carrier’s behavior of graphene may provide essential clues for gas adsorption properties.
Current research efforts are mostly directed at the detection and remedy of air pollution by anthropogenic activities. Nonetheless, an issue with the high sensitivity of graphene with gas adsorption is that the selectivity in the study of gas adsorption is quite questionable. Hence, for the purpose of enhancing the selectivity of gas adsorption’s study, several novel approaches have been adopted by doping method, structural defect method, or substrate introduction. In this study, the substrate introduction on graphene is take into consideration to ameliorate the selectivity of pristine graphene.
Heterostructure of graphene and a vdW interactive substrate has been studied and reported such as a second graphene layer, MoS2, SiO2 or h-BN in order to open band gap of graphene and help improve its electrical properties. It is demonstrated that a considerable improvement in chemical stability of graphene supported on such substrates. Therefore, hybrid structures of graphene with a substrate are of pivotal importance for both theoretically fundamental studies as well as applications of graphene. Additionally, the booming of electrical waste disposal is a critical problem for scientists and environmentalists.
The manufacture of a variety of chemically single- use gas sensors is one of typical examples of this. In order to solve that issue, the physisorption of adsorbates is necessary for the gas adsorption mechanism. Furthermore, the introduction of a substrate below graphene is still based on mainly vdW interactions, so that graphene and substrate could be really promising for achieving the requirement for green studies. LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com In this work, the adsorption of gases including five toxic gases CO2, CO, NO, NO2, NH3, and water vapor H2O adopted for hygrometer (humidity sensor) on two constructed heterostructures (G/h-BN and G/SiO2) were investigated on particular sites (Top, Hollow, and Bridge).
To fully understand the adsorption mechanism of toxic gases on hybrid structures, DOS analysis was conducted. The aims here were to (1) analyze the optimal positions in gas adsorption, (2) rationalize the adsorption properties (adsorption energy and adsorptive distance) of gases on heterostructures, (3) decipher the adsorption mechanism by exploiting DOS diagram and (4) analyze the selectivity and sensitivity of constructed materials. LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com CHAPTER 1: LITERATURE REVIEW 1. Graphene material Graphene, silicene, germanene, phosphorene, hexagonal boron nitride (h-BN), molybdenum disulphide (MoS2), graphitic structures of carbon nitride (g-C3N4), and zinc oxide (g-ZnO) [12] which are typical representatives of two-dimensional (2D) ultrathin materials have recently exploited on a wide range of applications such as electrical appliances.
As far as graphene was concerned, a 2D sp2-bonded carbon monolayer, has drawn tremendous attention owing to its notable electronic and mechanical properties [14]. It is known to have remarkable electronic properties, such as a high carrier mobility [8][19], but the absence of a band gap restricts its applications of large-off current and high on-off ratio for graphene-based electronic devices [14].1 illustrates the structure of monolayer of graphene and its applications [23]. Structure of monolayer of graphene and its applications Initially, it was believed before the accomplishment of experimental fabrication of graphene that strict 2D crystals could be difficult to stabilize from 3 LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com theoretical and experimental perspectives due to the effects of thermal expansion. Nevertheless, in 2004, a single layer of carbon in atoms-level thickness was fabricated by Geim and Novoselov using micromechanical exfoliation and studied the electronic field effect and carried out a series of studies [8].
On the other hand, graphene oxide and its reduced form are graphene’s derivatives and are all semiconductors but with lower carrier mobility (Fig. Structure and properties of other graphene’s derivatives In comparison with other 2D materials (Fig.3) [12], graphene is considered to be an excellent sensor material with high conductivity, electron mobility and the gapless and approximately linear electron dispersion around the Fermi level. Although graphene exhibits a very promising material with excellent electronic properties, there will be quite questionable to adopt graphene into sensors using nano- electric devices [19]. Therefore, the introduction of the substrates such as h-BN and SiO2 can be an innovative way to help open up the band gap of graphene, thereby enhancing the sensor properties of graphene.
4 LUAN VAN CHAT LUONG download : add luanvanchat@agmail. Structure and physical properties of other 2D materials Figure 1. Topology and charge density map of G/h-BN and G/SiO2 A comparison of topology of G/h-BN and G/SiO2 is depicted in Fig. It is clear that while a similar lattice structure of graphene with both h-BN and SiO2 is seen, h-BN seems to have a smooth surface without any charge traps and 5 LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com SiO2 surface is usually impure and uneven.
The surface optical phonon energy of h- BN is two-fold magnitude greater than that of SiO2 [4]. It indicates that G/h-BN will have a better performance compared with G/SiO2. Heterostructure of Graphene/Hexagonal boron nitride (G/h-BN) Hexagonal boron nitride (h-BN) is a representative of 2D material with a wide band gap. Hexagonal boron nitride (h-BN) is called “white graphene”, consists of alternative boron and nitrogen atoms in a sp2-hybridized 2D honeycomb arrangement and 2D h-BN monolayer is isolated from bulk BN (Fig.
The bond length of B-N is around 1. The interaction between boron and nitrogen is basically a covalent bond.