Development of a Static Fourier Transform Spectrometer and
Real-Time Substrates for Surface Enhanced Raman
Behzad Sardari Ghojehbeiglou
Electronics Engineering, PhD Thesis, 2017
Assoc. Prof. Dr Meriç Özcan (Thesis Advisor), Assoc. Prof. Dr Cleva Ow-Yang, Prof. Dr Ibrahim Tekin, Prof. Dr Reuf Süleymanov, Prof. Dr Necati F. Ecevit
Date & Time: July 26, 2017 – 11.00 AM
Place: FENS L058
Keywords : Static Fourier Transfrom Spectrmeter (static-FTS), Nyquist Sampling Rate, Bandpass Sampling Theorem, Surface Enhanced Raman Scattering (SERS), Electrolysis, Copper Oxide
In the first part of this thesis a novel broadband static Fourier transform spectrometer (static-FTS) configuration based on the division of the spectrum into multiple narrow-bands is proposed and implemented by combining a static-FTS and dispersive elements. The dispersive part includes a double diffraction grating structure to disperse the input spectrum in horizontal direction (to divide the input light into multiple narrow-band signals) and the static-FTS part includes a static Michelson interferometer to make different path length differences (PLD) in the vertical direction. The static Michelson interferometer is composed of a beam-splitter (BS), a flat mirror and a stair-case mirror. However, in actual setup a diffraction grating in Littrow configuration is used to realize the stair-case mirror. Using off-shelf diffraction gratings as the stair-case mirror decreases the total cost of the prototyped device. A CCD camera is used at the exit port of the static-FTS part, to record the formed interferograms.
The proposed configuration not only decreases the spectrometer size but also allows operation in the traditional spectrometer wavelength range, namely 400 nm – 1100 nm with better resolution.
This technique solves the Nyquist sampling rate issue and enables recording high resolution spectrums with regular CCDs. The proposed configuration and the method, in fact, solve the trade-off between resolution and bandwidth, and also eliminate the need for nanometer step size mirrors. An algorithm is developed to process the recorded signal and calculate the Fourier transform of the recorded interferograms on the CCD camera.
In the second part, the capability of copper oxide (CuO) nanoparticles formed on copper (Cu) electrodes by the electrolysis as a real time active substrate for surface enhanced Raman scattering (SERS) is shown. We have experimentally found that using just the ultra-pure water as the electrolyte and the Cu electrodes, ions are extracted from the copper anode form copper oxide nanoparticles of average 100 nm – 300 nm on the anode surface in matter of minutes. This anode is used in Raman experiments in real time as the nanoparticles were forming and the maximum enhancement factor (EF) of Raman signals were over five orders of magnitude. Other metal electrodes made of brass, zinc (Zn), silver (Ag) and aluminum (Al) were also tried for a possible real-time substrate for SERS applications, which except brass none of them showed this capability. Electron microscope images showed the cubic nanoparticle formation on copper and brass electrodes but none in the other metals studied.
The proposed method has some key advantages over existing SERS substrates: it’s not only a real time SERS substrate but also is a very fast, simple and a low cost technique. This technique also omits the need for an electrolyte of containing the metal ions of interest for the nanoparticle production as just the deionized or distilled water is enough. This technique also allows preparation of a large effective area as well as a uniform substrate for SERS applications