Chemical Modifications of Graphene-Like Materials

The following sections are included:

• PREFACE
• CONTENTS

The periodic table, which clearly presents the unusual atomic configurations of all pure elements, can provide a concise overview of all the materials on Earth. These elements exhibit close relationships among the rich phenomena of physics, chemistry, and material sciences, owing mainly to their diverse multi-orbital hybridizations and spin configurations. From Group I to Group VIII, their active orbitals in condensed-matter materials only come from (s, p_x, p_y, p_z) ones, such as (2s, 2p_x, 2p_y, 2p_z), (3s, 3p_x, 3p_y, 3p_z), (4s, 4p_x, 4p_y, 4p_z), (5s, 5p_x, 5p_y, 5p_z), and (6s, 6p_x, 6p_y, 6p_z) for the Group-IV C, Si, Ge, Sn, and Pb atoms, respectively. Group I and Group VII, respectively, display the largest charge transfers and the strongest electron affinities. However, the Group-VIII inert gases only show the very chemical bondings, that is, it is very difficult to generate many mainstream compounds from such atoms. The transition-metal atoms have the outermost orbitals of 3d, 4d, 5d, and 6d, in which each d-orbital wave function is characterized by ${\text{d}}_{z^2},{\text{d}}_{x^2-y^2},{\text{d}}_{yz},{\text{d}}_{zx},{\text{d}}_{xy}$. Moreover, the rare-earth metal atoms present the active 4f and 5f orbitals,^{Refs; Refs} with the featured wave functions of $({\text{f}}_{x^3},{\text{f}}_{x{z}^2},{\text{f}}_{y{z}^2},{\text{f}}_{xyz},{\text{f}}_{z\left(x^2-y^2\right)},{\text{f}}_{x\left(x^2-y^2\right)},{\text{f}}_{x\left(x^2-3y^2\right)})$. Most of the d and f orbitals are able to generate the spin-up and/or spin-down density arrangements and thus create the ferromagnetic or antiferromagnetic configuration. The above-mentioned sp³, d⁵, and f⁷ orbitals are quite adequate for producing a super-giant superposition of various chemical bondings and spin configurations, that is, they are capable of creating many materials with greatly diversified charge and spin-density distributions. The orbital hybridizations could be divided into van der Walls interactions, covalent bondings, metallic bondings, and ionic forms, where the first, second, and third configurations might coexist in the specific regions of a condensed-matter system (e.g., stage-n graphite alkali compounds). More interestingly, the spatial charge density distribution of each isolated atom reveals a uniformly spherical form. After the formation of a crystal structure, the position-dependent chemical bonds in a primitive unit cell will determine the critical multi-orbital hybridizations and spin configurations. Concise pictures can be achieved through delicate first-principles calculations and high-resolution experimental examinations. This is very useful for developing a grand quantum quasi-particle framework. For example, first-principle simulations have successfully identified the complete orbital hybridizations in graphite metal compounds, covering the intralayer σ-sp² bonding in a planar honeycomb crystal,^Refs the interlayer van der Waals interactions between two neighboring graphitic sheets (the interlayer 2p_z–2p_z orbital hybridizations), and the interlayer host–guest metallic bondings. Furthermore, the metallic charge density distributions, respectively, belong to (I) 2s–/3s–/4s–/5s–/6s–2p_z for Li–/Na–/K–/Rb–/Cs–C bonds, (II) $({\text{d}}_{z^2},{\text{d}}_{x^2-y^2},{\text{d}}_{yz},{\text{d}}_{zx},{\text{d}}_{xy})$ for transition-metal–carbon orbital hybridizations, and (II) $\left({\text{f}}_{x^3},{\text{f}}_{x{z}^2},{\text{f}}_{y{z}^2},{\text{f}}_{xyz},{\text{f}}_{z\left(x^2-y^2\right)},{\text{f}}_{x\left(x^2-y^2\right)},{\text{f}}_{x\left(x^2-3y^2\right)}\right)-2{\text{p}}_z$ for rare-earth–carbon bondings. These critical data are very useful for fully understanding the essential quasi-particle properties and promoting the applied sciences. Their collection together can build an international database of quantum particles and will be very helpful for all scientific endeavors…

This chapter delves into the diverse chemical and physical environments encountered in materials science. It investigates the phenomena of chemical absorptions, intercalations, substitutions, decorations, heterojunctions, and physical perturbations. By examining the effects of these factors on materials, it uncovers insights into the modification and optimization of material properties for targeted applications. This comprehensive exploration equips researchers and engineers with the knowledge necessary to manipulate and enhance material behavior in specific chemical and physical environments.

The adsorption of manganese and chromium on graphene is investigated using first principles based on density functional theory. The binding energy, optimal geometric structures, band structure, density of states, charge density, and charge density difference, spin distribution, and magnetic moment of each adatom-adsorbed graphene system are calculated in detail. The calculated results show that the most stable adsorption positions of both Mn and Cr on graphene are hollow sites. The calculated adsorption of all systems illustrates strong hybridization between transition metal adatoms and graphene, as well as metallic behavior. Besides, the positive magnetic moment shows that the Mn- and Cr-adsorbed graphenes have ferromagnetic configurations. The electronic and magnetic properties of Mn- and Cradsorbed graphenes reveal that the transition metal-adsorbed graphene systems have potential for applications in the future.

Lanthanum (La) and cerium (Ce) atom-adsorbed graphene systems are investigated for a thorough understanding of the strongly coupling effects associated with the very complicated quasi-particle 4f orbital charges and spin configurations, such as the significant covalent bonds of C-sp3 and La-5d5/Ce-4f7 orbitals and their non-magnetic/ferromagnetic spin configurations. Their quasi-particle behaviors are expected to present a sharp contrast with those observed in alkalizations, oxidations, and halogenations.

Through the quasi-particle framework implemented using VASP calculations, the structural, electronic, and optical properties of 4d transition-metal intercalated graphite were investigated and discussed.

The rare-earth metal atoms of Pd and Pu with 5f orbitals are outstanding candidates for fully exploring the significant decoration effects owing mainly to their seven types of probability functions. The highly complicated orbital hybridizations and spin configurations closely related to the C–Pd/C–Pu, C–C, and Pd–Pd/Pu–Pu bonds are fully examined under a unified framework.

The 5d transition metal guest-atom substituted graphene systems extensively change the featured properties of condensed-matter systems. Significant chemical bonds of C–C and C–M (where M is W, Os, Ir, or Pt) are formed by single and multi-hybridizations. W-, Os-, and Pt-substituted graphenes form narrow-bandgap semiconductors, with a range of 0.21–0.4 eV, while Ir substitution results in a semi-metal with a bandgap of 0.04 eV. Moreover, the magnetic properties are exposed to W- and Ir-substituted graphenes. The geometric, electronic, magnetic, and optical characteristics are essentially discussed in this book chapter.

This study investigates the electronic and magnetic properties of 4f-rare earth metal substitutions in graphene monolayers using first-principles calculations. The incorporation of rare earth metals into the graphene lattice modifies its electronic structure and introduces a significant bandgap, enabling potential semiconductor device applications. The presence of 4f electrons leads to localized magnetic moments, offering possibilities for spintronic applications. Hybridized states between the carbon atoms and 4f orbitals generate unique electronic and magnetic phenomena, including magnetic anisotropy and spin polarization. This research provides insights into the design of graphene-based materials with tailored functionalities, facilitating their implementation in future electronic and spintronic devices.

Graphene is a popular, truly two-dimensional material, possessing a cone-like energy structure near the Fermi level, and is treated as a gapless semiconductor. Its unique properties have motivated researchers to find applications for it. The gapless feature limits the development of graphene nanoelectronics. Making one-dimensional strips of graphene nanoribbons (GNRs) could be one of the more promising routes for modulating the electronic and optical properties of graphene. These properties are highly sensitive to the edge and width of the nanoribbons. The tunability of electronic and optical properties further implies the possibility of applying GNRs. However, the dangling bonds at ribbon edges remain an open issue in GNR systems. Various passivation techniques that could change the physical properties at the ribbon edge are available. This work considers 5d transition-metal elements as guest atoms at the edges. The geometric structure, energy bands, density of states, charge distribution, and optical transitions are discussed.

This study explores the decoration of graphene nanoribbons with 5f rare-earth elements and investigates their impact on the electronic, magnetic, and optical properties. Using first-principles calculations, we demonstrate that the incorporation of 5f elements induces significant changes in the nanoribbons’ electronic structure, leading to localized electronic states within the bandgap. The presence of 5f electrons also introduces magnetic moments, while the hybridization between carbon atoms and 5f orbitals gives rise to unique electronic and magnetic phenomena. Additionally, we examine the optical properties, including absorption and emission spectra, providing insights into potential optoelectronic applications. This research advances our understanding of the design and development of graphene nanoribbon-based materials with tailored electronic, magnetic, and optical functionalities.

This study explores the electronic and structural properties of heterojunctions formed by mono-/bi-layers of graphene on a silver (Ag) (111) substrate. Using first-principles calculations, we investigate the influence of the Ag(111) substrate on graphene’s electronic structure and interfacial properties. Our findings highlight the significant modifications in the band structure, including the emergence of interface states and a bandgap opening. We also examine the charge transfer phenomena and its impact on electrical conductivity and carrier mobility. Additionally, we investigate the optical properties, such as absorption spectra and excitonic behavior, offering insights into potential optoelectronic applications. This research advances our understanding of graphene-silver heterostructures for the design and development of novel electronic and optoelectronic devices.

This study investigates the electronic and structural properties of heterojunctions formed by mono-/bi-layers of graphene on a cerium oxide (CeO₂) substrate. By utilizing first-principles calculations, we analyze the effects of the CeO₂ substrate on graphene’s electronic structure and interfacial properties. The presence of the CeO₂ substrate induces significant modifications in the band structure, including the formation of interface states and changes in the bandgap. The interfacial bonding and lattice matching play crucial roles in determining the heterojunction’s electronic behavior. Furthermore, we examine the charge transfer phenomena and its influence on electrical conductivity and carrier mobility. This research provides insights into the design and optimization of graphene-based devices on CeO₂ substrates for potential electronic and optoelectronic applications.

A first-principles study of the structural diversity and optoelectronic properties of the small penta-graphene (PG) quantum dots (PGQDs) of various sizes is performed. The stability and optoelectronic properties of the PGQDs are investigated under the effects of chemical modifications. PGQDs are edge-functionalized by Si, P, O, and F atoms. Furthermore, PGQDs are also doped with B and P atoms. An increase in the size of the PGQDs leads to a decrease in their bandgaps. All edge-functionalized structures are stable with strong electronic quantization and exhibit semiconducting properties, except for the P-edge functional structure (metallic nature). There is a semiconductor–metal transition with some doped structures. We did not observe absorption peaks in the visible region for hydrogen-passivated PGQDs. However, some absorption peaks appear in this region for edge-passivated or doped PGQDs. There are changes in the electronic properties of PGQD samples containing the impurities B, P, or BP, which also causes a shift in the peak of the spectrum to the visible region from the ultraviolet region of the corresponding pure sample because of various hybridization effects in PG (sp² and sp³) and PGQDs with edge passivation and atom doping. A solid optical polarization effect occurs with some structures, e.g., H-36-B1P2 and F-ZZ-36. This represents its significant asymmetry and anisotropy compared to the other structures. The enhanced reactivity and the controllable electronic properties by size change, edge passivation, and doping make PGQDs ideal for new nanodevice applications.

Graphene quantum dot (GQD), a zero-dimensional material with size less than 10 nm, is a newly developed member of the graphene family. GQDs have become highly promising materials in various applications, including catalysis, bioimaging, energy conversion, and storage, owing to their unique physicochemical properties, such as excellent photoluminescence, biocompatibility, low toxicity, easy fabrication, and edge effect. Additionally, oxygen-containing functional groups such as −COOH, −COC-, −OH, −CHO, and −OCH₃ play a crucial role in the structure of GQD_s. Oxygen is located in different edges and the basal plane of GQD_s. The unique architecture of oxygen inside the structure of GQDs and the outstanding properties and performance of GQDs provide a powerful impetus to use GQD_s as a promising material with applicability in various fields. In this chapter, we describe the possible structure, application, and critical role of the oxygen-containing functional group on the essential properties and application of GQD_s. Finally, we provide a brief outlook to point out the issues that need to settle for further development.

A series of density functional theory calculations was performed to understand the bonding and interaction of hydrogen adsorption on two-dimensional (2D) silicon carbide (SiC). The converged energy results pointed out that the H atom can sufficiently bond to 2D SiC at the top sites (atop Si and C), of which the most stable adsorption site is T_Si. The vibrational properties, along with the zero-point energy, were incorporated into the energy calculations to further understand the phonon effect of the adsorbed H. Most of the 2D SiC structure deformations caused by the H atoms were found at the adsorbent atom along the vertical axis. For the first time, five SiC defect formations, including the quadrilateral-octagon linear defect (8-4), the silicon interstitial defect, the divacancy (4-10-4) defect, the divacancy (8-4-4-8) defect, and the divacancy (4-8-8-4) defect, were investigated. The linear defect (8-4) has the lowest formation energy and is most likely to form. This study could be an interesting step toward future applications of hydrogen energy.

Two-dimensional monolayer pentagonal silicon dicarbide (pSiC₂) and its one-dimensional nanoribbon derivative (pSiC₂ NR) possess novel electronic properties, possibly leading to many potential applications. In this chapter, we have systematically investigated the structural, electronic, and transport properties of pSiC2NRs using chemical function and strain engineering. The energy gaps of the pSiC₂ NRs (ZZ-ribbon, ZA-ribbon, AA-ribbon, and SS-ribbon) are created mainly owing to the competition in the edge structures, finite-size confinements, and asymmetry of chemical bonds in the tetrahedral lattice or chemical modification. By applying uniaxial tensile or compressive strain, it is possible to modulate the physical properties of pSiC₂NRs, which subsequently change the transport behavior of the carriers. Interestingly, the pentagon network of SS-pSiC₂NRs is still maintained, but the bond length along the strained direction undergoes a large change. The electronic band structure and bandgap are strongly affected by the uniaxial compressive strain. The evolution of bandgap versus strain is linear. The I–V characteristic of SS-pSiC₂NR seems to be more sensitive to compressive strain than stretch strain. The ultrahigh and strain-modulated carrier mobility in monolayer penta-SiC₂ may lead to many novel applications in high-performance electronic devices. Furthermore, the unusual properties of the pSiC₂ nanoribbons render them with great potential for applications in optoelectronic devices, especially in photovoltaics.

The hydrogen adsorption on pristine germanene is studied using ab initio calculations. By performing a converged density functional theory calculation, we find the nearly degenerated nature of hydrogen on the top sites (H_T1 and H_T2), where H_T1 is the most stable site. The adsorption of hydrogen atoms leads to local germanene structural changes. The localized surface curvature and the zero-point energy of hydrogen, which have not been studied to date for the 2D germanene, are investigated. We also demonstrate the properties of germanene defects via four obtained defects: Stone–Wales (55-77), divacancies (77-555-6 and 555-7), and pentagon-heptagon linear defect (5-7). The lowest formation energy of the pentagon-heptagon linear defect is shown for the first time in this study.

This chapter discusses the diverse applications of semiconductor materials in agriculture, 3D printing, biology, and electronic/optical devices. Semiconductors play a vital role in precision farming, 3D printing functional components, biosensors, and electronic/optical devices such as transistors, solar cells, LEDs, and lasers. These materials have revolutionized resource management, additive manufacturing, diagnostics, and advanced technology, enhancing various industries and improving quality of life.

The first-principles methods, phenomenological models, and experimental observations present a number of merits and drawbacks under a grand quasi-particle framework. How to solve open issues by establishing their strong partnerships is one of the near-future research focuses. Obviously, the mainstream materials are outstanding candidates in developing more wide, broad and high viewpoints.

The current book is successful in expanding a grand quantum quasiparticle framework though delicate first-principles calculations and analyses of the chemical modifications of mainstream materials. The strong partnerships between phenomenological models and experimental observations are established in detail. All significant orbitals from the outermost (s, p_x, p_y, p_z), five types of 3d/4d/5d/6d and seven types of 4f/5f are thoroughly identified to dominate the multi-/single-orbital hybridizations and ferromagnetic/antiferromagnetic spin configurations under chemical adsorptions, intercalations, substitutions, decorations, and heterojunctions. The concise pictures of physics and chemistry directly reflect the featured quasi-particle properties: the position-dependent crystal symmetries, the atom- and spin-dominated band structures, the spatial charge/spin-density distributions, the atom- and spin-decomposed magnetic moments, the atom-, orbital-, and spin-decomposed densities of states, and the prominent absorption peaks associated with the photon–orbital couplings. The drastic changes in orbital probability distributions (the dramatic transformations between the spherical and highly non-uniform charge densities) and the merged van Hove singularities are very useful in verifying the critical mechanisms in chemical bonds. A number of potential applications and open issues are discussed in detail. The basic and applied sciences require close combinations, especially for functional chips with many semiconducting components. Similar studies could be generalized to other mainstream materials, e.g., binary semiconductor compounds and ternary lithium oxides/sulfides, solar cells, and hydrogen energies. The time-dependent intermediate crystal phases of cathode/electrolyte/anode materials in ion-based batteries need to be thoroughly investigated under the first-principles method and molecular dynamics. Theoretical models are urgently needed to explain stationary ion transports. Their near-future researches can greatly promote the quasi-particle development in a series of published books and be helpful for the establishment of an international quantum quasi-particle center…

The following section is included:

• INDEX