Application of Wavelet Analysis on Transient Rlectivity in Ultra-thin Films

Applications of wavelet analysis in ultra-thin film transient reflectivity (TR) measurements have been investigated. Advantages of utilizing different localized wavelet bases, in position and time, have been addressed on the residual TR signals. Morse wavelets have been used to obtain information from the abrupt oscillatory modes in the signal, which are not distinguishable with conventional methods such as Fourier transforms. These abrupt oscillatory modes are caused by the surface, interface, or any short-lived oscillatory modes which are suppressed in the TR signal in ultra-thin films. It is demonstrated that by choosing different Morse wavelets, information regarding different oscillatory modes in the TR signal of a heterostructure thin film is achievable. Moreover, by performing wavelet analysis on multiferroic heterostructures, oscillatory modes with very close energy ranges are easily distinguishable. For illustration, residuals of the TR signals have been obtained by a pumpprobe setup in reflectivity mode on La0.7Sr0.3MnO3/SrTiO3 and BaTiO3/La0.7Sr0.3MnO3/SrTiO3 samples, where sufficient signal to noise ratios have been achieved by taking multiple scans. The residual signals have been analyzed with Morse wavelets, and multiple oscillatory modes with close energy ranges have been observed and distinguished. This approach can isolate the location of various oscillatory modes at the surface, interface and in the bulk of the heterostructure sample

Excitonic AND Logic Gates on DNA Brick Nanobreadboards

A promising application of DNA self-assembly is the fabrication of chromophore-based excitonic devices. DNA brick assembly is a compelling method for creating programmable nanobreadboards on which chromophores may be rapidly and easily repositioned to prototype new excitonic devices, optimize device operation, and induce reversible switching. Using DNA nanobreadboards, we have demonstrated each of these functions through the construction and operation of two different excitonic AND logic gates. The modularity and high chromophore density achievable via this brick-based approach provide a viable path toward developing information processing and storage systems

Low-Operating-Voltage Organic Transistors Made of Bifunctional Self-Assembled Monolayers

International audienceSelf-assembled monolayers (SAMs) are molecular assemblies that spontaneously form on an appropriate substrate dipped into a solution of an active surfactant in an organic solvent. Organic field-effect transistors are described, built on an SAM made of bifunctional molecules comprising a short alkyl chain linked to an oligothiophene moiety that acts as the active semiconductor. The SAM is deposited on a thin oxide layer (alumina or silica) that serves as a gate insulator. Platinum-titanium source and drain electrodes (either top- or bottom-contact configuration) are patterned by using electron-beam (e-beam) lithography, with a channel length ranging between 20 and 1000 nm. In most cases, ill defined current-voltage (I-V) curves are recorded, attributed to a poor electrical contact between platinum and the oligothiophene moiety. However, a few devices offer well-defined curves with a clear saturation, thus allowing an estimation of the mobility: 0.0035 cm2V-1 s-1 for quaterthiophene and 8 × 10-4 cm2V-1 s-1 for terthiophene. In the first case, the on-off ratio reaches 1800 at a gate voltage of -2 V. Interestingly, the device operates at room temperature and very low bias, which may open the way to applications where low consumption is required