Raman Spectroscopy and its Application in Nanostructures

Shu-Lin Zhang

• Publisher: Wiley
• Year: 2012
• Print ISBN:
  9780470686102
• eBook ISBN:
  9781119966784
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Spectroscopy & Spectrum Analysis

Raman Spectroscopy and its Application in Nanostructures is an original and timely contribution to a very active area of physics and materials science research. This book presents the theoretical and experimental phenomena of Raman spectroscopy, with specialized discussions on the physical fundamentals, new developments and main features in low-dimensional systems of Raman spectroscopy.

In recent years physicists, materials scientists and chemists have devoted increasing attention to low-dimensional systems and as Raman spectroscopy can be used to study and analyse such materials as carbon nanotubes, quantum wells, silicon nanowires, etc., it is fast becoming one of the most powerful and sensitive experimental techniques to characterize the qualities of such nanostructures.

Recent scientific and technological developments have resulted in the applications of Raman spectroscopy to expand. These developments are vital in providing information for a very broad field of applications: for example in microelectronics, biology, forensics and archaeology. Thus, this book not only introduces these important new branches of Raman spectroscopy from both a theoretical and practical view point, but the resulting effects are fully explored and relevant representative models of Raman spectra are described in-depth with the inclusion of theoretical calculations, when appropriate.

Part I

Fundamentals of Raman Spectroscopy

Chapter 1

Basic Knowledge of Raman Spectroscopy

The term “Raman spectroscopy” is an abbreviation of “Raman scattering spectroscopy”. Basic knowledge of Raman spectroscopy can be gained by understanding the meaning of three words: “spectroscopy”, “scattering”, and “Raman”.

1.1 Spectrum and Spectroscopy

Spectroscopy can be considered in three parts: theory, experiment, and application. These will be described in more detail later. In this section, only spectrum are discussed.

1.1.1 Optical Spectrum

A band of colors is called a “spectrum”. The rainbow, as shown in Figure 1.1a (see color Plate 1 for the original Figure 1.1), is one example of a spectrum. A spectrum is usually one recorded by an artificial dispersive element called a spectrograph, as shown in Figure 1.1 b.

Figure 1.1 Examples of spectra: (a) a rainbow: (b) a scheme of spectra by a dispersive element prism

1.1.2 Classification of Spectra

1.1.2.1 Classification Based on Optical Effects

When a medium is illuminated by light, the interaction between the light and the medium produces many kinds of optical effects and phenomena. Figure 1.2 shows some examples of major optical effects.

Figure 1.2 Different optical effects caused by interaction between light and a medium. Reprinted from S.-L. Zhang, Raman Spectroscopy and Low-dimensional nanoscale Semiconductors, Science Press, (2008)

The spectrum is a record of all the optical effects. As such, the spectra can be divided into many types, based on the different optical effects such as reflection, transmission, absorption, emission (fluorescence, luminescence), and scattering spectra. All of these spectra help us to understand the kind of interactions and the inner structure and motion of the medium. For example, the measurement and understanding of atomic spectra led to the elucidation of the atom's inner structure and played a key role in the establishment and development of quantum theory.

This book concentrates on discussion of scattering spectra. Light scattering based on fundamental and broad ideas is introduced in detail in the next section.

1.1.2.2 Classification Based on Spectral Parameters

The spectrum, as a record of optical effects mentioned above, reflects the dependence of electromagnetic radiation intensity on its relevant parameters.

The radiation intensity, I, can be expressed as

(1.1)

where E is the electric field given by

(1.2)

where ω, k, r, t, and E₀ are the measured frequency (the reciprocal of wavelength λ), wave vector (representing the propagating direction), position vector, time, and the amplitude of the electric field, respectively. These are the only relevant parameters in the measurement of spectra.

Depending on the spectral parameter of interest, the measured spectra can be classified into different categories. With respect to different excited light wavelengths λ₀, spectra with spectral intensity I on the rest of the parameters ω, k, r, t, and E₀ have been classified as:

• Visible and non-visible excited spectra: these spectra are excited by visible and non-visible light, respectively. The non-visible excited spectra are further divided into ultraviolet (UV), infrared (IR), and Terahertz (THz, λ = 0.1
  
  1 mm) excited spectra, and so on.
• Visible and non-visible spectra: the recorded spectral wavelength λ is localized in the visible and non-visible range. The non-visible spectra are further divided into the UV, IR, and THz spectra, and so on.
• Spontaneous and stimulated spectra: these spectra are due to spontaneous and stimulated radiation, respectively.
• Linear and non-linear spectra: the spectral intensity I depends on the first- and high-order of parameters E_0, respectively.
• Single- and multi-order spectra: these are the spectra at the single- and multiple-folded frequency ω of the Raman mode_, respectively.
• Angle distributed spectrum: this is the dependence of spectral intensity I with respect to the direction of the parameter r of the measured position, that is, the propagating direction of spectral light, or the direction of parameter k.
• Polarized and non-polarized spectrum: this spectrum is measured under excitation by polarized light and detection in a fixed polar direction, that is, in the direction that excited and recorded E are both fixed.
• Steady state and transient (time resolved) spectra: this is the spectral intensity I with respect to the parameter t at a long and very short duration, respectively (Figure 1.3 a,b).
• Far- and near-field spectra: this is the measured spectral intensity I in the region of magnitude of the position parameter r
  
  λ (light wavelength) and
  
  λ, respectively.
• Frequency and image spectra: the former records the spectral intensity I variation with spectral parameters, ω, and the latter is the spectral intensity I distribution at a single wavelength at various sample positions, r₀ (Figure 1.3 c).
  Figure 1.3 Examples of various kinds of spectra: (a) Steady Raman spectrum of CCl₄. Reprinted from S.-L. Zhang, Raman Spectroscopy and Low-dimensional nanoscale Semiconductors, Science Press, (2008). (b) Transient spectra of ring-breathing mode of cyclohexane under shock compression. The solid and dashed lines show the fitted Lorentzian function and the separated peaks, respectively [2]. Reprinted from in A. Matsuda, G. Kazutaka and K. Kondo, Time-resolved Raman spectroscopy of benzene and cyclohexane under laser-driven shock compression, Phys Rev B, 65, 174116 (2002) with permission of the American Physical Society. (c) Image of spectral line of unstained and live HeLa cells [3]. Reprinted from A. Zumbusch, G. P. Holtom, and S. X. Xie, Three-Dimensional Vibrational Imaging by Coherent Anti-Stokes Raman Scattering, Phys Rev Let...

Table of contents

• Cover
• Description of the Cover
• Title Page
• Copyright
• Preface
• Acknowledgements
• Part I: Fundamentals of Raman Spectroscopy
• Part II: Study of Nanostructures by Raman Spectroscopy
• Appendix I: Electromagnetic Waves and Lasers
• Appendix II: Standard Spectral Lines
• Appendix III: Raman Tensors
• Appendix IV: Constitution, Polarity, and Symmetry Structure of Crystals
• Appendix V: Brillouin Zones, Vibration Modes, and Raman Spectra of Typical Ordinary and Semiconducting Crystals
• Appendix VI: Physical Parameters, Constants, and Units
• Index
• Colour Plates