Local phonon imaging of AlN nanostructures with nanoscale spatial resolution.

We demonstrate local phonon analysis of single AlN nanocrystals by two complementary imaging spectroscopic techniques: tip-enhanced Raman scattering (TERS) and nano-Fourier transform infrared (nano-FTIR) spectroscopy. Strong surface optical (SO) phonon modes appear in the TERS spectra with their intensities revealing a weak polarization dependence. The local electric field enhancement stemming from the plasmon mode of the TERS tip modifies the phonon response of the sample, making the SO mode dominate over other phonon modes. The TERS imaging allows the spatial localization of the SO mode to be visualized. We were able to probe the angle anisotropy on the SO phonon modes in AlN nanocrystals with nanoscale spatial resolution. The excitation geometry and the local nanostructure surface profile determine the frequency position of SO modes in nano-FTIR spectra. An analytical calculation explains the behaviour of SO mode frequencies vs. tip position with respect to the sample.

Determination of the Thermodynamic Parameters of DNA Double Helix Unwinding with the Help of Mechanical Methods.

For the first time, rupture event scanning (REVS) procedure based on quartz crystal microbalance (QCM) and involving only mechanical action was used to determine the height of the energy barrier for dsDNA unwinding. Melting point was determined with the help of this procedure. To determine the thermodynamic parameters including enthalpy, DNA denaturation was represented as a unimolecular process. This allowed us to recover the energy profiles from the experimental data obtained by force measurements at different scanning times (reaction times) for different temperatures. The thus obtained results were compared with the data obtained with the help of another mechanical method, namely, atomic force microscopy. The mechanism of DNA unwinding in QCM-based experiments through the unzipping mode, as proposed by us in previous works, was confirmed. Thus, we demonstrated that REVS procedure may be used to assess the thermodynamic parameters of dsDNA unwinding.

Temperature dependence of unwinding forces between complementary oligonucleotides.

Rupture Event Scanning (REVS) was used to study oligonucleotide unwinding under mechanical load. Oligonucleotide melting temperature was successfully estimated using this method. To estimate the enthalpy of reaction, we represented denaturation process as a unimolecular reaction. This gave us the possibility to recover the force profile from the experimental data obtained in force measurements at different scanning time (reaction time) for different temperatures.