Vacuum-UV emitter using low-pressure discharge in helium-water vapor mixture

The spectral characteristics of emission from plasma of periodic-pulsed capacitive discharge in a mixture of water vapor with helium have been studied in a spectral range of 140–315 nm. Dependences of the intensity of the characteristic emission lines of hydroxy groups in He-H₂O plasma on the partial pressure of water vapor at a helium pressure of p(He) = 2.6 kPa are presented. The results provide a basis for the creation of simple sources of vacuum-UV radiation with a cheap working medium based on water vapor.     

Studying transverse volume discharge in a helium-propane mixture

The electrical properties and emission characteristics of plasma formed in a transverse volume discharge in helium-propane (He-C₆H₁₄) mixtures at a total pressure of 3–15 kPa have been studied. The spatial parameters, plasma emission spectra, and current and voltage oscillograms of the discharge, as well as the yield of carbon-containing products of propane decomposition at various pressures and compositions of the He-C₆H₁₄ gas mixture, have been determined.     

The formation of excited chlorine atoms in a low-pressure transverse volume discharge

The characteristics of a transverse volume discharge (TVD) in chlorine at low pressures (P(Cl₂)=0.1–1.5 kPa) were studied. The excited chlorine atoms were formed in a 18×2.2× (0.5–1.0) cm volume using relatively low values of the capacitor bank charging voltage (U _ch ≤ 10 kV) in the pulsed discharge voltage source. The optical emission from plasma was studied in a spectral range from 500 to 900 nm. Homogeneous TVD pulses of short duration (τ; ≤ 100 ns) obtained under these conditions are of interest for use in UV-VUV lamps employed in pulsed plasmachemical reactors for dry etching of thin films. The density of excited atomic chlorine radicals can be monitored on medium-resolution spectrometers using the ClI emission lines with λ=725, 754, and 821 (2) nm.     

The characteristics of a confined discharge in a helium-chlorine gas mixture

The electrical and optical characteristics of a confined (cage) discharge in a He-Cl₂ mixture at pressures within 0.1–1.5 kPa were studied. It was established that the negative glow plasma in this discharge is a source of wideband radiation in a wavelength range from 170 to 270 nm with the emission peaks at λ_max=195 nm [Cl₂(¹Σ?¹Π₄)], 200 nm [C1₂**, and 258 nm [Cl₂(D′-A′)]. Optimum conditions ensuring the maximum intensity of emission in the UV-VUV range due to transitions in the chlorine molecule have been established. The results are of interest from the standpoint of the development of a stationary shortwave low-pressure lamp filled with a He-Cl₂ gas mixture.     

Fine structure of carbon films deposited from a microwave low-pressure gas discharge

We have studied the conditions of synthesis and the fine structure of carbon films of various structural modifications possessing preset electrical properties. The phase diagram of polymorphous transformations is constructed for carbon films grown from the plasma of microwave discharge in low-pressure ethanol vapor. Technological factors influencing the efficiency of extracting diamondlike microcrystals from a hydrocarbon matrix have been studied. Depending on the extraction regime and initial layer thickness, the size of extracted microcrystals can vary from 10–12 to 100–120 nm, while their surface concentration may reach 1.4×10⁷ cm⁻².     

Spectra of X-ray emission from low-pressure gas discharge with runaway electrons

The spectra of X-ray emission from a low-pressure xenon discharge with runaway electrons and from a discharge in low-pressure oxygen with vanadium target have been studied. The X-ray energy spectrum from discharge can be adequately described in the framework of a theory of the intensity of continuous X-ray fluorescence.     

Electrodynamics of a low-pressure electrode microwave discharge

Results are given of self-consistent two-dimensional simulation of self-sustained steady electrode microwave discharge in a chamber at the end of central conductor of a coaxial line. The discharge parameters are calculated in the diffusion mode in hydrogen at pressures of 0.5, 2, and 8 torr and incident power of 30–200 W. The dependence of matching between the discharge chamber and delivery path on the geometric dimensions of the chamber is investigated in the presence of plasma. It is demonstrated that the length of central electrode is the key factor affecting the structure of plasma formation and its matching with the pumping wave. The maxima and minima of matching alternate when the central electrode is elongated by quarter wave. The maxima and minima of matching for the case of low pressure (< 2 torr) are shifted by λ/4 relative to those for high pressure (> 2 torr). The problem of maximal energy input to the discharge region at the end of antenna-type electrode is analyzed. It is demonstrated that a restriction exists on the maximal energy input to such a discharge (and, accordingly, on the size of plasma formation). These restrictions are associated either with the runaway of discharge toward the generator or with the ignition of discharge in the region of entry of antenna into the chamber.     

Migration healing of surface relief during the formation of nanocrystals in a microwave low-pressure gas discharge

We have studied conditions for the synthesis of nanodimensional silicon islands (quantum dots) in a microwave low-pressure gas discharge plasma on noncrystalline substrates with a weak interaction at the deposit-substrate interface. It is established that the formation of nanoislands proceeds via the leveling (healing) of depressions on the substrate surface. A mechanism of the influence of the parameters of deposition on the kinetics of formation of nanoislands is proposed.     

Self-consistent model of a low-pressure rf capacitive discharge

A simple self-consistent model of a low-pressure rf capacitive discharge is formulated. Effects associated with stochastic heating of the electrons and the nonlocal nature of the electric field are taken into account. The relations obtained can be used for a qualitative analysis of the main features of these low-pressure discharges. The results of the numerical calculations show good agreement with available experimental data. Pis’ma Zh. Tekh. Fiz. 23, 39–45 (January 12, 1997)     

Chemical micropatterning of polymeric cell culture substrates using low-pressure hydrogen gas discharge plasmas

Micropatterned cell cultures will allow a new quality of bioartificial systems. Here, an approach to chemical micropatterning of polymer substrates is presented, which is completely based on low pressure gas discharge processes. Well expressed micropatterned cell cultures on polystyrene and poly (ether ether ketone) were obtained with many different cell types. No impairment of typical cell behavior was observed.     

A high-power low-pressure iodine lamp pumped by glow discharge

We present the working characteristics of a high-power UV-VUV electric-discharge lamp filled with a working mixture of helium and iodine vapor (He-I₂) at a low pressure (0.1–1.5 kPa) and pumped by a dc glow discharge at a power of 15–200 W. The power of the total output UV radiation and the main emission peak at λ = 206.2 nm were studied as dependent on the electric power supplied to the glow discharge and on the partial pressure of helium in the He-I₂ mixture. The emission characteristics of the glow discharge plasma were studied in the spectral range from 200 to 350 nm. In this range, the lamp is operating predominantly on a resonance emission line of excited iodine atoms (λ = 206.2 nm, FWHM = 0.10–0.12 nm) and on a system of electronic-vibrational bands of excited iodine molecules with the main peak at λ = 342 nm. The contribution of the resonance emission due to excited iodine atoms to the total UV emission from the glow discharge plasma does not exceed 50%. The optimum partial pressure of helium is within 400–800 Pa. The total UV radiation power of the lamp operating in the optimum regime reaches 25 W at an efficiency of η ≤15%.     

Nonuniform microwave discharge in a nitrogen-hydrogen mixture

The method of optical emission spectroscopy is used to investigate the influence of additions of hydrogen on the emission characteristics of a highly nonuniform electrode microwave discharge in nitrogen at a pressure of 1 torr. It is demonstrated that the pattern of the influence made by hydrogen addition (zero to 50% with respect to flow rate of hydrogen) on the intensity of emission bands of nitrogen is different in different parts of the discharge. It is further observed that the influence of hydrogen on the vibrational distribution of nitrogen molecules in the C ³Π _u state is different C3?uin different parts of the discharge. Analysis is made of various processes involving hydrogen, which affect the emission of nitrogen bands. An inference is made that ion conversion is an important mechanism of such influence. One-dimensional simulation is performed in view of these processes, and it is demonstrated that the experimentally observed effects may be associated with this mechanism.     

Equilibrium discharge from a nozzle of a mixture of an ideal gas and a condensing vapor

Within the framework of the theory of ideal gases, an examination is made of equilibrium discharge of a mixture of a gas and a condensing vapor from a nozzle. The basic equations describing discharge are presented, as well as the results of calculations of the discharge from a nozzle of a mixture of air and water vapor.     

Characteristics and plasma parameters of a short-wavelength low-pressure discharge lamp

We have studied the working optical characteristics and electron kinetic coefficients of a short-wavelength, electric discharge exciplex-halogen UV-VUV lamp employing a mixture of argon and chlorine with a total pressure of P = 0.5–10 kPa. The lamp operates on a system of broadened electron-vibrational bands of ArCl (175 nm) and chlorine (200, 258 nm) molecules, which overlap to form a continuum in the spectral range of 160–260 nm. It is established that the optimum mixtures are those with p(Ar) − p(Cl₂) = (2–4)−(0.15–0.30) kPa. The average output power of the short-wavelength radiation is 1–2 W at an efficiency of ∼5%. The electron energy distribution functions (EDFs) and the discharge plasma parameters have been calculated by solving the Boltzmann equation for a gas mixture with the experimentally determined optimum composition in the range of E/P values from 1 to 200 V/(cm Torr), where E is the electric field strength and P is the total gas pressure. Using the obtained EDFs, the electron transport characteristics, specific discharge power losses for the main elementary processes, and rate constants of electron processes are determined.     

Cathode layer characteristics of a low-pressure glow discharge in argon and nitrogen

Cathode layer characteristics were experimentally determined for a glow discharge in argon and nitrogen in a broad range of gas pressures. A normal glow discharge regime is observed only provided that the gas ionization takes place in the anode layer (on the right of the inflection point in the glow discharge initiation curve). Importance of using a correct method for the normal cathode voltage drop is emphasized.     

An axisymmetric electric discharge as a means for remote heating of gas and for ignition of combustible gas mixture

Experimental and theoretical investigations are performed of gasdynamic phenomena accompanying a ring electric discharge excited in air at atmospheric pressure. It is experimentally demonstrated that the discharge generates a toroidal (three-dimensional) shock wave which cumulatively converges toward the axis. A mathematical model is constructed, which describes the process of focusing of the toroidal shock wave. The results of measurements of shock-wave processes accompanying the discharge are in good agreement with the calculation results; this enables one to estimate the gas temperature which may be attained in the region of cumulative convergence at some distance from the ring center. Results are given of first experiments in the excitation of a ring shock wave in a combustible gas mixture (stoichiometric mixture of CH₄:O₂).     

Alpha-gamma transition in RF capacitive discharge in low-pressure oxygen

We report the recorded current-voltage characteristics of a RF capacitive discharge in oxygen. Low-frequency oscillations of the plasma potential in a kilohertz frequency range are observed to accompany the transition of the discharge from a weak- (α-) to a strong-current (γ-) regime in the low-pressure range. The weak-current regime of the RF capacitive discharge is observed within the pressure range limited not only from the medium pressure side but also from the lower-pressure one. Electron temperature and plasma density are registered with a probe technique.