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Über dieses Buch

This book focuses on several areas of intense topical interest related to applied spectroscopy and the science of nanomaterials. The eleven chapters in the book cover the following areas of interest relating to applied spectroscopy and nanoscience:

· Raman spectroscopic characterization, modeling and simulation studies of carbon nanotubes,

· Characterization of plasma discharges using laser optogalvanic spectroscopy,

· Fluorescence anisotropy in understanding protein conformational disorder and aggregation,

· Nuclear magnetic resonance spectroscopy in nanomedicine,

· Calculation of Van der Waals interactions at the nanoscale,

· Theory and simulation associated with adsorption of gases in nanomaterials,

· Atom-precise metal nanoclusters,

· Plasmonic properties of metallic nanostructures, two-dimensional materials, and their composites,

· Applications of graphene in optoelectronic devices and transistors,

· Role of graphene in organic photovoltaic device technology,

· Applications of nanomaterials in nanomedicine.

Inhaltsverzeichnis

Frontmatter

Raman Spectroscopy, Modeling and Simulation Studies of Carbon Nanotubes

Abstract
This chapter focuses on two types of carbon nanotubes (CNTs): single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). CNTs are cylindrically-shaped carbon allotropes. They consist of a single layer of sp2-hybridized carbon atoms, giving it a hollow cylindrical shape. The majority of SWCNT samples have diameters on the order of ~1 nm and lengths on the order of microns to centimeters. MWCNTs are composed of concentric layers of SWCNTs nested inside one another, giving it a layered cylindrical shape. In the present chapter, we will provide a historical overview of CNTs and examine specifically their thermal properties as it relates to their applications to the semiconductor industry and nanoelectronics. The understanding of CNT chirality through the visualization of rolled-up graphene sheets will provide insight into the versatility and myriad thermo-mechanical and electrical properties of CNTs. We will focus on the use of Raman spectroscopy and Molecular Dynamics (MD) simulations to characterize and investigate the thermal characteristics of SWCNTs.
Daniel Casimir, Raul Garcia-Sanchez, Prabhakar Misra

Laser Optogalvanic Spectroscopy and Collisional State Dynamics Associated with Hollow Cathode Discharge Plasmas

Abstract
In this chapter we will discuss the laser optogalvanic effect in a discharge plasma environment, specifically associated with an iron-neon (Fe–Ne) hollow cathode lamp. The history of the optogalvanic effect will serve as an introduction to the importance of the phenomena. The theoretical model behind the optogalvanic effect will provide insight into the importance of laser optogalvanic spectroscopy as a tool for spectral characterization of the plasma processes and enhanced understanding of the collisional state dynamics associated with the discharge species in hollow cathode lamps. The present chapter will focus on transition states of neon in the Fe–Ne hollow cathode lamp. The results presented here will use, for illustrative purposes, the waveforms associated with the laser-excited optogalvanic transitions of neon: 1s4–2p3 (607.4 nm), 1s5–2p7 (621.7 nm), 1s3–2p5 (626.6 nm), 1s5–2p8 (633.4 nm) and 1s5–2p9 (640.2 nm). A comparison between the experimentally recorded optogalvanic signal waveforms and the Monte Carlo fitting routine, along with a discussion related to the variation of the (ai and bj) fitting coefficients as a function of the discharge current, will illustrate the success of our theoretical model. We will also briefly touch upon the potential applications of the optogalvanic effect at the nanoscale in fields such as graphene-based nanoelectronics and nanoplasmonics.
Michael Blosser, Xianming L. Han, Raul F. Garcia-Sanchez, Prabhakar Misra

Applications of Fluorescence Anisotropy in Understanding Protein Conformational Disorder and Aggregation

Abstract
Fluorescence spectroscopy is an ultra-sensitive multiparametric technique that provides key insights into protein conformational dynamics and size changes simultaneously. Fluorescence polarization (anisotropy) is one of the parameters related to the rotational dynamics of a fluorophore either intrinsic to the molecule or attached to a biomolecule. The anisotropy measurements can be utilized to unravel the structural and dynamical properties of biomolecules. The advantage of fluorescence anisotropy measurements is that it is a concentration-independent parameter; it can be measured either in the steady-state or in the time-resolved format. Steady-state fluorescence anisotropy provides important information about the overall size/dynamics of biomolecules, whereas the time-resolved fluorescence anisotropy can distinguish between the local and the global dynamics of a fluorophore. Therefore, the time-resolved anisotropy measurements allow one to determine the conformational flexibility as well as the size of biomolecules and assemblies. In recent years, it has been demonstrated that fluorescence anisotropy can be effectively utilized to obtain structural and dynamical information of protein-based assemblies such as aggregates, protein–lipid complexes etc. This chapter provides an overview of the applications of fluorescence anisotropy to study protein conformational disorder, misfolding and aggregation, leading to the formation of nanoscopic amyloid fibrils that are implicated in a range of human diseases.
Neha Jain, Samrat Mukhopadhyay

Nuclear Magnetic Resonance Spectroscopy in Nanomedicine

Abstract
Retaining the essentials of noninvasive measurement and deep penetration through living bodies, nuclear magnetic resonance (NMR) spectroscopy presents as a useful adjunct to the in vitro and in vivo studies of nanomedicine. This chapter is aimed at introducing basic NMR principles and certain NMR techniques relevant to the field of nanomedicine, followed by exploration of physicochemical characterization and metabolic profiles responding to treatment and development in nanomedicine.
Ping-Chang Lin

An Efficient Coupled Dipole Method for the Accurate Calculation of van der Waals Interactions at the Nanoscale

Abstract
The van der Waals (VDW) force arises from purely quantum mechanical charge fluctuations and is variously called a dispersion or London or Casimir force. This often considered as weak, yet ubiquitous, attractive interaction is important in many nanoscale systems. This chapter provides an overview of the Coupled Dipole Method (CDM), an atomistic and accurate computational method widely adopted to predict the VDW forces between dielectric nanomaterials. There is a concern about the burden of memory and computing time needed to solve eigenvalue problems by either diagonalization or iteration, which have hindered the implementation of CDM for large systems. Here, an efficient way, named trace-CDM (TCDM), is presented. TCDM uses the simple fact that the trace of a square matrix is equal to the sum of its eigenvalues and thus calculates the accurate VDW energies without solving for the eigenvalues. Four examples are solved to demonstrate the advantages of the method.
Hye-Young Kim

Adsorption of Gases in Nanomaterials: Theory and Simulations

Abstract
Physical adsorption (physisorption) is the study of atoms or molecules weakly bound to material surfaces. Physisorption-related investigations raise critical questions concerning phase transitions, fractals, wetting transitions, two-dimensional superfluidity, and Van der Waals interactions. This chapter focuses on adsorption of gases (e.g. Ar, Kr, H2, CO2, and CH4) in nanomaterials, and in particular the authors describe equilibrium properties of the gases adsorbed in carbon nanotubes, graphene and Metal Organic Frameworks (MOFs). The adsorption potential used for developing the theoretical model for studying physisorption involves the summing of two-body interactions, and several important properties of adsorbates can be obtained via simulations, namely equilibrium properties, thermal characteristics, selectivity, wetting features, and structure and phase of the adsorbed monolayer. Applications of physisorption include the separation of cryogenic gases, their storage and their use as a surface characterization tool.
M. T. Mbaye, S. M. Maiga, S. M. Gatica

Atom-Precise Metal Nanoclusters

Abstract
A nanocrystal is a crystallite with size greater than about 2 nm. Nanoclusters are non-crystalline nanoparticles that are typically small and composed of a specific number of metal atoms in the core, which are protected by a shell of ligands. Optical properties of large metal nanoparticles in external electromagnetic fields are a function of their size, free-electron density and dielectric function relative that of the surrounding medium. The ultra-small size of nanoclusters allows them to exhibit distinct quantum confinement effects, which in turn results in their discrete electronic structure and molecular-like properties, such as HOMO-LUMO electronic transitions, enhanced photoluminescence, and intrinsic magnetism, to name a few of the characteristics. Metal nanoclusters play an important bridging role between nanochemistry and molecular chemistry. A basic understanding of the structure, electronic and optical properties, as the materials evolve from the atomic state to nanoclusters to fcc-structured nanocrystals, constitutes a major evolution across length scales, and leads to fundamental insights into the correlation between the structure and key characteristics of metal nanoclusters.
Anu George, Sukhendu Mandal

Plasmonic Properties of Metallic Nanostructures, Two Dimensional Materials, and Their Composites

Abstract
The intense and highly tunable optical field enhancement provided by nanomaterials supporting plasmon resonances has diverse applications including biophotonics, terahertz spectroscopy, and subwavelength microscopy. This chapter compares plasmon resonance behavior and tunability in noble metal nanostructures with that of two dimensional and quasi-two dimensional materials including graphene, silicene, germanene, and the transition metal dichalcogenides. Plasmonic optical behavior and related advancements in two-dimensional materials functionalized by metallic nanostructures are discussed. Finally, possibilities for new directions for work on similar composite plasmonic systems are outlined.
Lauren Rast

Application of Graphene Within Optoelectronic Devices and Transistors

Abstract
Scientists are always yearning for new and exciting ways to unlock graphene’s true potential. However, recent reports suggest this two-dimensional material may harbor some unique properties, making it a viable candidate for use in optoelectronic and semiconducting devices. Whereas on one hand, graphene is highly transparent due to its atomic thickness, the material does exhibit a strong interaction with photons. This has clear advantages over existing materials used in photonic devices such as Indium-based compounds. Moreover, the material can be used to ‘trap’ light and alter the incident wavelength, forming the basis of the plasmonic devices. We also highlight upon graphene’s nonlinear optical response to an applied electric field, and the phenomenon of saturable absorption. Within the context of logical devices, graphene has no discernible band-gap. Therefore, generating one will be of utmost importance. Amongst many others, some existing methods to open this band-gap include chemical doping, deformation of the honeycomb structure, or the use of carbon nanotubes (CNTs). We shall also discuss various designs of transistors, including those which incorporate CNTs, and others which exploit the idea of quantum tunneling. A key advantage of the CNT transistor is that ballistic transport occurs throughout the CNT channel, with short channel effects being minimized. We shall also discuss recent developments of the graphene tunneling transistor, with emphasis being placed upon its operational mechanism. Finally, we provide perspective for incorporating graphene within high frequency devices, which do not require a pre-defined band-gap.
F. V. Kusmartsev, W. M. Wu, M. P. Pierpoint, K. C. Yung

The Versatile Roles of Graphene in Organic Photovoltaic Device Technology

Abstract
This chapter discusses the potential applications of graphene in the realization of efficient and stable organic optoelectronic devices, especially flexible solar cells. With the introduction of the prospects of graphene and functionalized graphene in modifying the performance characteristics of organic solar cells, the chapter evolves into assessing the prospects of realizing all carbon photovoltaic devices. The combination of unique, yet tunable, electrical and optical properties of graphene, makes it a highly sought after candidate for various technologically important applications in optoelectronics. Graphene has been identified as a suitable replacement for the highly expensive, brittle and less abundant indium tin oxide, as the transparent electrode material for optoelectronic device applications. The best graphene-based transparent conducting films show very low sheet resistance of 20 Ω/sq and high transparency around 90 % in the visible spectrum, making it a better choice compared to the commonly used transparent conductors including indium tin oxide (ITO) and zinc oxide (ZnO). The absence of energy band gap in graphene has originally limited its applications in optoelectronic devices. This problem has since been solved with the advent of graphene nanoribbons (GNRs) and functionalized graphenes. Functionalized graphenes and GNRs have extended the use of graphene as hole and electron transport layers in organic/polymer light emitting diodes and organic solar cells by the suitable tuning of the band gap energy. Blending dispersions of functionalised graphene with the active layers in photovoltaic devices has been found to enhance light absorption and enable carrier transport efficiently. Graphene layers with absorption in the entire visible region can be fine-tuned to be incorporated into the active layers of organic solar cells. Finally the synthesis conditions of GNRs and the functionalized graphenes can be optimized to achieve the required structural, optical and electrical characteristics for venturing into developing all carbon-based cost-effective organic solar cells with improved efficiency.
Jayalekshmi Sankaran, Sreekanth J. Varma

Nanomaterials in Nanomedicine

Abstract
Nanomedicine refers to the applications of nanotechnology to the field of medicine. Nanomaterials have led to the development of novel devices for the early detection of malignant tumors, as well as significant enhancements in efficient drug, gene and protein delivery mechanisms to targeted sites in the human body. As nanoparticles become increasingly smaller in size, they also present the potential for harming certain organs of the body. Safety issues involving nanoparticles need to be solved using in vivo techniques. Research in nanomedicine has improved biological therapies, such as vaccination, cell therapy and gene therapy. A particular kind of colloidal nanoparticle, called the liposome, which has properties similar to a red blood cell, has viscoelastic properties that make it extremely useful for a variety of applications in the pharmaceutical and consumer product sectors of the global market. Liposomes have been clinically established as efficient nanosystems for targeted drug delivery. Their efficacy has been demonstrated in reducing systemic effects and toxicity, as well as in attenuating drug clearance. The Maxwell Spring-Dashpot model has been reviewed for liposomes and the viscoelastic exponential equation shown to fit the liposome data. The relevance of this study is to the increasing use of viscoelastic characteristics of liposomes for efficient drug delivery and targeted destruction of malignant tumors. Nanobiotechnology has the potential to facilitate the integration of diagnostics with therapeutics, and in turn lead to personalized medicine tailored for a specific individual.
Francis Mensah, Hailemichael Seyoum, Prabhakar Misra
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