Eighty years have passed since Langmuir's first use of the word 'plasma' for describing ionized media. On this occasion we would like to present selected recent results on the application of Langmuir probes to diagnose plasma jet systems. To demonstrate the versatility of the Langmuir probe method we give examples of measurements of the spatial distribution of the plasma parameters as well as their temporal dependence in cases when the plasma jet system operates in a pulsed regime. A part of this paper is devoted to introducing the Langmuir probe technique, especially with regard to its application under conditions when collisions between the charged and neutral particles in the probe sheath cannot be neglected and when the electron energy distribution function in plasma cannot be approximated by a Maxwellian one. In the experimental part we present Langmuir probe measurement of low-pressure and atmospheric-pressure plasma jet systems that are currently used for experiments with deposition of materials with special properties.Most of the experimental results presented in this paper are original data. However, in order to fill in the picture we have used in the case of a barrier-torch discharge three figures that have already been published.
Summary: The atmospheric plasma jet system was investigated for deposition of oxide layers on polymer (kapton) substrates. The plasma in the system was excited by an RF power source working in pulse modulated mode. This modulation allowed exciting high density plasma in the active part of the duty cycle and simultaneously keeping the neutral gas in the plasma jets at the substrate sufficiently cold, thus protecting the kapton substrate from thermal damage. The atmospheric plasma jet system was tested in two configurations: as single jet system and as linear multi‐jet system with four equivalent jets. The plasma in the system was investigated by means of impedance measurements. A calibrated capacitive voltage probe and a Rogowski current coil were used for direct measurement of voltage and current RF waveforms, respectively. From these data the power deposited in the discharge and the plasma column impedance were estimated. The real part of plasma impedance was used for electron concentration ne estimation. It was found that the electron concentration in the plasma jet was about 2 × 1013 cm−3. The atmospheric plasma jet source was used for low temperature deposition of conductive oxide (ZnO) thin films on kapton, silicon and quartz glass substrates. As growth precursors for ZnO films, Zn‐acetylacetonate vapors were used. Deposited ZnO films on both kapton and quartz glass contained hexagonal crystalline phase. They were optically transparent and had an electrical conductivity σ ≈ 10−1–100 S · cm−1.
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