Etiología de la Esclerosis Múltiple

2.8 Fourier Transform Infrared Spectroscopy (FTIR)

Infrared spectroscopy yields similar and complementary information to Raman spectroscopy. This technique utilises the infrared region of the electromagnetic spectrum, which is characterized by having a lower frequency and a longer wavelength compared with

three sections known as near , mid

, 2.5–25μm) is the most commonly studied segment as it contains

Raman cell in (A) the fully assembled stage and in (B) an enlarged area showing the separate components (expanded, not in scale)

2.8 Fourier Transform Infrared Spectroscopy (FTIR)

Infrared spectroscopy yields similar and complementary information to Raman spectroscopy. This technique utilises the infrared region of the electromagnetic spectrum, which is characterized by having a lower frequency and a longer wavelength compared with visible light. The infrared region can b

three sections known as near , mid

μm) is the most commonly studied segment as it contains

Raman cell in (A) the fully assembled stage and in (B) an enlarged area showing the separate components (expanded, not in scale)

2.8 Fourier Transform Infrared Spectroscopy (FTIR)

Infrared spectroscopy yields similar and complementary information to Raman spectroscopy. This technique utilises the infrared region of the electromagnetic spectrum, which is characterized by having a lower frequency and a longer

visible light. The infrared region can b three sections known as near , mid and far-

μm) is the most commonly studied segment as it contains

Chapter 2.

Raman cell in (A) the fully assembled stage and in (B) an enlarged area showing the separate components (expanded, not in scale)

2.8 Fourier Transform Infrared Spectroscopy (FTIR)

Infrared spectroscopy yields similar and complementary information to Raman spectroscopy. This technique utilises the infrared region of the electromagnetic spectrum, which is characterized by having a lower frequency and a longer

visible light. The infrared region can b -infrared. The mid

μm) is the most commonly studied segment as it contains

Chapter 2. Characteri

Raman cell in (A) the fully assembled stage and in (B) an enlarged area showing the separate components (expanded, not in scale)

2.8 Fourier Transform Infrared Spectroscopy (FTIR)

Infrared spectroscopy yields similar and complementary information to Raman spectroscopy. This technique utilises the infrared region of the electromagnetic spectrum, which is characterized by having a lower frequency and a longer

visible light. The infrared region can b

infrared. The mid-infrared region (4000

μm) is the most commonly studied segment as it contains

Characterisation Techniques

Raman cell in (A) the fully assembled stage and in (B) an enlarged area showing the separate components (expanded, not in scale).

Infrared spectroscopy yields similar and complementary information to Raman spectroscopy. This technique utilises the infrared region of the electromagnetic spectrum, which is characterized by having a lower frequency and a longer visible light. The infrared region can be subdivided into infrared region (4000

μm) is the most commonly studied segment as it contains

ation Techniques

Raman cell in (A) the fully assembled stage and in (B) an enlarged area

Infrared spectroscopy yields similar and complementary information to Raman spectroscopy. This technique utilises the infrared region of the electromagnetic spectrum, which is characterized by having a lower frequency and a longer e subdivided into infrared region (4000–

information regarding the fundamental vibration and associated vibrational structure of a specific sample.

Infrared spectroscopy relies upon the fact that materials have specific frequencies where they vibrate and these correspond to discrete energy levels. A change in permanent dipole is required for a vibrational mode in a material to be IR active. An IR spectrum of a sample is recorded by focussing a beam of infrared light at the specimen. For the purpose of this thesis a Fourier transform infrared (FTIR) spectrophotometer was used. This method operates by having a moving mirror, which alters the distribution of the infrared light as it passes through the interferometer. The signal which is recorded represents the light output as a function of mirror position, specifically referred to the interferogram. This raw data is turned into the final spectrum (light output versus infrared wavelength or wavenumber) using a Fourier transform method. Comparison is then made with reference material. All IR experiments reported in this thesis were carried out on a Nicolet 6700 FT-IR system, which is located in a nitrogen filled glove-box, to protect the air-sensitive samples from any moisture or air contamination.

Prior to each experiment a reference spectrum was recorded in order to correct the final spectra for background effects. Pellets were prepared by grinding a small amount of the specimen together with caesium iodide and placed in a mechanical

Chapter 2. Characterisation Techniques

2.9 Photoelectron Spectroscopy

X-ray photoelectron spectroscopy (XPS) is a powerful technique for surface analysis. It provides both qualitative and quantitative information on the elements present on a given surface (except for H and He), by illuminating the surface under investigation with X-ray radiation and analysing the ejected electrons, as a consequence of the photoelectric effect.

The physics of this process can be effectively described by the following:

஻ ௄ (8)

where EB is the binding energy of the electron in the atom, which depends on the type of atom and its chemical environment. The energy of the X-ray excitation

source, is given by the known value hν, and EK is the kinetic energy of the emitted electron which is measured by the spectrometer. Thus Eb is obtained from hν, known, andEK, measured8.

A typical XP spectrum consists of a series of discrete lines of different intensities over a background due to inelastic scattering, the intensity of which decreases with decreasing binding energy. Each of these lines is characterised by a position (eV), a full width at half maximum (FWHM) (eV) and an intensity (cps).

The peak position is related to the orbitals from which the electrons are emitted and the intensity is correlated to the amount of material present. By comparison with tabulated data it is possible to identify the element present in the spectrum and the surrounding environment.

The composition of the sample can be determined by quantitative analysis and by mathematically fitting the data. For this work CasaXPS software was used.

For the purpose of this thesis, XPS has been employed to investigate the surface composition of TiO2electrodes at different charges. The instrument used is a Kratos Axis Ultra high resolution XPS, equipped with monochromatic aluminum X-ray

source (hν = 1486.69 eV), charge neutraliser and a hemispherical analyzer equipped

with a Delay-Line detector (DLD) and multichannel plate. All the experiments reported in this thesis were performed in the Sasol laboratories in St Andrews.

2.10 Electrochemical Characterisation

2.10.1 Basic principles of Electrochemical Energy Storage and

Conversion

In an electrochemical cell, the chemical energy, which is the Gibbs free energy associated with the cell reaction, is converted into electrical energy and vice versa. The energy –providing processes are the redox reactions taking place at the interface electrode with the electrolyte9.