The plasma density (n e ) profile, rotational (T rot ) and vibrational (T vib ) temperatures, and their dependence on the RF power (500-1500 W) and gas pressure (50-500 mTorr) is investigated in a high to very high frequency (VHF) (162 MHz) capacitively coupled nitrogen plasma excited by a multi-tile electrode (tiles) system. The density profile is measured in the mid-plane of the discharge using a resonance hairpin probe, and the rotational and vibrational temperatures are measured at both tile centre and tile-tile boundary using optical emission spectroscopy. It is observed that the plasma density increases monotonically with a rise in RF power and decreases with an increase in the operating gas pressure. At a low gas pressure (50 mTorr), plasma density profile shows a maximum at the tile centre and a minimum at the tile-tile boundary, whereas, at high gas pressure tile-edge effects are observed. Measured rotational temperature (∼350-450 K) is slightly above room temperature for both positions and independent of RF power and operating gas pressure. Vibrational temperature is in the range of ∼6500-9400 K, and increases with RF power, analogue to the plasma density. It is noticed that the plasma uniformity can be substantially improved, to better than 90%, by changing the power-pressure matrix. A large difference between measured vibrational and rotational gas temperature suggests that the plasma produced by VHF multi-tile electrode is under highly non-equilibrium condition and thus highly efficient to produce unique gas phase chemistry.

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Ensuring food safety in various steps along the entire food value chain is crucial to prevent undesired and harmful substances entering the food humans consume. Pesticides and antifungal agents used during growth, processing or along the logistic chain from the field to the consumer can be toxic causing a range of symptoms from stomach pain to the death of the consumer even at trace levels of concentrations. To prevent dangerous contaminants from entering the food chain governmental restrictions on a large number of components have been established and are tightly monitored. For a large number of tests complex and sophisticated equipment is required along with time consuming sample preparation steps, not permitting instantaneous sampling of the specimen at the point of measurement or in a timely manner. High costs and poor reproducibility of commercially available substrates have so far limited the successful application of surface enhanced Raman scattering (SERS) measurements along the food value chain. The use of an affordable handheld Raman instrument with affordable, mass-producible and reproducible SERS substrates will be described in the frame of the contribution with respect to requirements imposed at various stages along the food value chain.

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