THz Spectroscopy:
THz region of spctra (1 THz = 1012 Hz= 1 ps-1) is a very important tool to study the nano-materials. Nano-materials (nano-particle, nano-tubes, nano-wire) have attracted attention due to their fascinating opto-electrical properties specially in the high frequency regime due to space confinement of electronic wave function. Decrease of grain dimensions increase the role of surfaces which dramatically alter the complex dielectric and transport properties of nano-materials. THz spectroscopy being a non-contact probe eliminates any chance of errors due to resistive connecting leads. The conductivity of nano-materials are extracted from the composite conductivity using effective medium models (Bruggeman Model or Maxwell-Garnett Model) and are modeled using Drude or Drude-Smith Models and the corresponding scattering times and plasma frequency can be obtained. Coherent phonon modes of spherical small diameter (< 10 nm) nano-particles lie in the THz frequency region. Vibrational modes are extracted from complex dielectric function and modeled using conventional superposition of a number of Lorentz oscillator model. A distinct advantage of coherent THz pulses is that the amplitude and phase of the electric field can be measured directly, because the THz fields are coherent with the femto-second pulses from which they are generated. Using THz time domain spectroscopy (THz-TDS), both the real and imaginary parts of the response functions, Such as the dielectric function ε(ω) = ε1(ω) + iε2(ω), are obtained directly without the need for Kramers-Kronig transforms. The THz response can also be expressed in terms of absorption α (ω) and refractive index n (ω), or as the optical conductivity, σ(ω) ≡ σ1(ω) + iσ2(ω) = iωε0[1-ε(ω)]. The conductivity σ (ω) describes the current response, J(ω) = σ(ω)E(ω) of a many-body system to an electric field, an ideal tool to study conducting systems.
THz spectroscopy provides information on the hydration structure around biological important molecules. We can easily probe the collective hydrogen bond dynamics of water around hydrophilic, hydrophobic & electrolytes. The vibrational modes of large molecules with many functional groupings, including many biologic molecules that have broad resonances at THz frequencies.mTHz spectroscopy is a useful non-contact, non-invasive tool. It also does not need any probe molecules. Thus there is no chance of accidentally damaging the biomolecules or the nanostructure or modifying any of its properties.
"Research is what I'm doing when I don't know what I'm doing." - Wernher von Braun