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.     

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%.     

Emission characteristics of gas-discharge ethanol-vapor plasma

Emission characteristics of a low-temperature ethanol-vapor plasma formed with the use of high-frequency and barrier discharges have been studied. The plasma emission in the spectral range of 300–700 nm was analyzed in detail. The partial pressure of the ethanol vapor was 5.7 kPa. The emission spectra of the ethanol- and argon/ethanol-vapor plasmas strongly differ. In addition, time characteristics of current and emission pulses in a high-frequency discharge in ethanol vapor are presented.     

A xenon-iodine electric discharge bactericidal lamp

We present the working characteristics of a continuous UV lamp emitting at λ=206 nm, pumped by a longitudinal glow discharge. The pressure of the working Xe-I₂ gas-vapor mixture was within 0.1–10 kPa. The power deposited in the discharge was varied within 10–130 W. The current-voltage characteristics, the emission spectra in a 200–600 nm wavelength range, the line emission intensity as a function of the power deposited in the discharge plasma, and the partial pressure of xenon in the lamp were studied. It is established that the lamp operates in the range of 206–342 nm on a resonance line of iodine at 206 nm and on the bands at 253 nm [XeI(B-X)] and 342 nm [I₂(B-X)]. Not less than half of the output UV emission power is concentrated in the bactericidal spectral interval (around λ=206 nm). The total UV emission power of the lamp reaches 6–7 W at an efficiency of ≤5%.     

Bromine-iodine excimer electric-discharge lamp with continuous UV radiation spectrum

The optical characteristics of a small-size UV lamp filled with a working mixture of xenon and krypton with bromine and iodine vapor and pumped by longitudinal electric discharge have been studied. The lamp emits a resonance atomic line of iodine I* at 206.2 nm (with a full width at half maximum of 0.10 nm) and a continuum in the range 220–390 nm, which is formed by the emission bands of diatomic molecules [XeI(B-X), XeBr(B,D-X), Br₂(B-X), I₂(B-X), and IBr(B-X)]. The optimum partial pressure of iodine vapor is 100–200 Pa, that of bromine vapor ranges from 130 to 400 Pa, and that of heavy inert gases, from 400 to 800 Pa. The average total UV output radiation power was 10–12 W at an efficiency of 10–12%.     

Shortwave krypton-bromine excimer low-pressure lamp

The emission characteristics are reported for a small short-wavelength (UV) lamp filled with a krypton-bromine mixture and pumped by longitudinal glow discharge at a 100-mm distance between electrodes in a quartz tube with an internal diameter of 14 mm. The emission spectrum is formed by the resonance atomic lines of bromine (163.3 and 157.6 nm) and the molecular lines of bromine (Br₂) and krypton bromide (KrBr). An increase in the partial pressure of bromine in the working mixture from 50 to 270 Pa is accompanied by a decrease in the intensity of emission lines due to atomic bromine and leads to the formation of VUV-UV continuum based on the molecular bands due to Br₂ and KrBr. The operation regime was optimized with respect to the glow discharge current and the gas mixture pressure and composition. The optimum partial pressure of krypton is within 500–800 Pa, and that of bromine vapor is within 100–250 Pa. The average total VUV-UV output radiation power reached 5 W at an efficiency of 8–10%.     

The effect of water vapor on the characteristics of a pulsed-periodic ultraviolet radiation source

The effect of a small admixture of water vapor on the optical characteristics of an UV radiation source using a He-air-H₂O mixture as the working medium was studied. The gas mixture was excited in a short-pulse transverse volume discharge operating at a charging voltage of U _ch ≤10 kV. As the partial pressure of helium was varied in the 10–45 kPa range at an air pressure of P(air)=130 Pa and the water vapor pressure within P(H₂O)=50–100 Pa, the main optical emission from plasma in the UV wavelength range was concentrated in a broad band peaked at λ_max=309.7 nm and was two times greater than the intensity of the base emission bands of the nitrogen molecule in this spectral range (λ=337.1 and 315.9 nm, N₂(C-B)). Adding water vapor to the He-air mixture increases the spectral range of the UV source toward shortwave region, which is related to a spontaneous decay of the products of dissociation of water molecules.     

Short-wavelength XeBr-Br gas discharge lamp

The output characteristics of a small-size gas-discharge lamp emitting in the 160–300 nm wavelength range are reported. The working medium—a mixture of xenon and bromine vapor—was excited in a longitudinal glow discharge in a quartz tube with an interelectrode distance of 100 mm. The emission spectrum is formed by the molecular lines of xenon bromide at 282 nm [XeBr(B-X)] and 220 nm [XeBr(D-X)] and the atomic resonance lines of bromine at 163.3 and 157.6 nm. An increase in the partial pressure of xenon in the working mixture from 130 to 800 Pa is accompanied by a decrease in the intensity of emission lines due to atomic bromine and an increase in the intensity of emission from xenon bromide molecules. The operation regime was optimized with respect to the energy supplied to the glow discharge and the working gas mixture pressure and composition. The optimum partial pressure of xenon is within 600–800 Pa, and that of bromine vapor, within 50–100 Pa. The average total VUV-UV output radiation power reached 7 W.     

The optimum characteristics of a halogen lamp pumped by transverse RF discharge

We report on the optimized characteristics of a small-size bactericidal lamp pumped by transverse RF (f=1.76 MHz) discharge, operating on a system of the molecular emission bands of chlorine in a wavelength range of 195–310 nm. The spectral characteristics of the plasma emission were measured and the intensity of chlorine emission bands were studied as functions of the total pressure and partial composition of a helium-chlorine mixture. Oscillograms of the pumping current and output radiation intensity were measured and the total output radiation power was determined. It is established that the lamp radiates predominantly in a bactericidal wavelength interval on an electron-vibrational transition at 200 nm in Cl₂** molecules. The optimum partial pressures of helium and chlorine are 100–300 and 90–120 Pa, respectively. The maximum output power of UV emission from the side cylindrical surface of the lamp reached 10 W. The lamp can be used in photochemistry, ecology, genetics, and medicine.     

The emission characteristics of low-pressure water vapor discharge UV emitters

We have studied the characteristics of UV emission sources operating on low-pressure normal (H₂O) and heavy (D₂O) water vapor excited by periodic-pulsed and glow discharges. The emission in a 300–330 nm wavelength interval has been studied in detail for water vapor pressures ranging from 50 to 2500 Pa. A comparison of the characteristics of emission from discharge plasma at low (50–150 Pa) and elevated (2.0–2.5 kPa) water vapor pressures reveals significant differences in the character of emission spectra, which can be related to the different types of emitting species (hydroxy radicals versus small clusters of such radicals and water molecules). Discharge current and emission intensity pulses in the periodic-pulsed discharge regime have been measured.     

A high-frequency UV-VUV radiation source operating on a mixture of argon with chlorine molecules

We present the working optical characteristics of a short-wavelength electric-discharge lamp operating at 150–270 nm (UV-VUV spectral range). The working medium is a mixture of argon with chlorine molecules (Ar-Cl₂) excited in a high-frequency transverse discharge between a metal electrode and a semitransparent nickel grid with an interelectrode distance of 2.2 cm. The proposed UV-VUV radiation source operates on the broadened emission lines of chlorine (Cl₂) and argon chloride (ArCl) molecules, which form a continuum in the 150–270 nm wavelength range. The source operation was optimized depending on the pumping power and the pressure and composition of the Ar-Cl₂ mixture. For a discharge excitation power within 50–300 W, the optimum working media were Ar-Cl₂ mixtures with the partial pressures P(Ar) = 300?400 Pa and P(Cl₂) = 30?40 Pa. The average total output power of the UV-VUV radiation extracted from the optimized source amounted to 15 W.     

Spectroscopic diagnostics of a pulsed arc plasma in the presence of acetylene

Plasma fluxes for deposition of diamond-like carbon films were generated by the four-electrode device with graphite cathode in vacuum as well as in acetylene atmosphere at pressure of 0.2–2 Pa. Optical emission spectra of the cathodic-arc carbon plasma in a wavelength range of 400–1000 nm were studied. For observation along the plasma flow at acetylene pressures of 0.2, 0.5 and 1.0 Pa the intensity of the C₂ molecular band at 563.55 nm increases by a factor of 6, 8 and 11, respectively, in comparison with values for a vacuum discharge. When displacing the observation line from the discharge axis a sharp decrease of carbon ion emission is detected while radiation of C₂ molecules remains approximately the same. For observation across the plasma flux the emission of C₂ molecular bands predominates over carbon ions both for the vacuum discharge and the discharge in acetylene. However on acetylene addition the intensities of carbon ions and hydrogen spectral lines increase by 1.5–3 times. It was found that the gas-kinetic temperature of the plasma is about 0.1 eV.     

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.     

Bactericidal iodine lamp excited by capacitive discharge

A new capacitive discharge lamp is created in which the main contribution to the output radiation is due to the iodine atomic emission line at 206 nm. The lamp has an average output power at λ=206 nm reaching 6 W, an efficiency of 8% (with respect to the electric energy supplied to the discharge), and a working life exceeding 1700 h. The results of tests on Escherichia coli and Staphylococcus aureus bacterial cultures reliably confirmed the bactericidal action of radiation of the proposed lamp.     

Spatial distributions of the intensity of optical emission lines studied during bismuth ferrite film deposition in high-frequency discharge plasma

We have studied spatial distributions of the intensity of optical emission lines in plasma of the RF discharge in oxygen during the deposition of bismuth ferrite (BiFeO₃) films. The intensities of characteristic emission lines in the visible, near-UV and near-IR spectral ranges have been measured as functions of the distance from the probed plasma layer to the target. The intensity profiles of the emission lines of oxygen ions, oxygen atoms, and iron atoms exhibit different behavior. Differences in the spatial distributions of intensity have been also observed for the two characteristic emission lines (at 613.7 and 688.6 nm) of iron.     

An excimer emitter with pumping by barrier discharge in mixtures of zink diiodide vapors with inert gases

An experimental investigation is performed of the output characteristics of an excimer lamp utilizing mixtures of zinc diiodide vapors with inert gases and excited by a barrier discharge (BD) with the repetition rate of sine voltage pulses f ≤ 130 kHz. Radiation spectra of BD plasma in the range of 200–900 nm with resolution of 0.05 nm are studied, as well as the time characteristics of voltage and current and the dependence of radiation intensity on the composition of mixtures. The radiation of ZnI(B–X) excimer molecules is revealed with a maximum at λ = 602 nm, as well as of I ₂ ^* excimer molecules, lines of inert gases, and, in mixtures with xenon, of XeI* excimer molecules. The composition and pressure of gas components of mixture are optimized. It is found that the most intense radiation of ZnI* in binary mixtures is observed when helium or neon is used as buffer gas. The specific average radiation power in the visible range is 23 mW/cm².     

A planar excimer-halogen radiation source pumped by transverse RF discharge

We present the characteristics of a planar source of wideband shortwave radiation pumped by transverse RF (f=1.76 MHz) discharge in a Kr/Xe/Cl₂ mixture (P≤500 Pa). The spectral characteristics of the plasma emission were studied in the wavelength interval of 130–600 nm. The oscillograms of the voltage, current, and output radiation intensity and the diagrams of the output power depending on the gas pressure, partial composition of the working gas mixture, and discharge power are presented. It is established that the source produces emission predominantly in the spectral interval of 170–330 nm, representing a system of the molecular emission bands XeCl(D, B-X), KrCl(B-X), Cl₂(D′-A′), and Cl₂**. For a maximum output power in the UV-VUV range, the optimum working gas mixture is Kr/Xe/Cl₂ with the partial pressures P(Kr)/P(Xe)/P(Cl₂)=150–200/150–200/20–40 Pa. The maximum power irradiated within a solid angle of 4π via two output holes with a total area of S≤ 100 cm² reaches 30–40 W. In the region of a threshold with respect to the transverse discharge initiation, there are narrow peaks of plasma emission that are probably related to the jumps in the density of electrons and the positive and negative ions at the boundary between the plasma and the RF discharge layer.     

Spectroscopic study of an electrode microwave discharge in argon and argon-hydrogen mixtures

The results of an optical emission spectroscopy study of low-pressure microwave induced discharge in argon, argon-hydrogen (0.9% H₂) and hydrogen-argon (5% Ar) mixture are reported. At four different pressures the Boltzman plot of relative ArI line intensities is used to measure electron excitation temperature, which was close to 3000 K in argon and in argon-hydrogen mixture discharges. The spatial distributions of light emission from argon and hydrogen-argon discharges are recorded with CCD camera and compared with spectroscopically observed spatial distributions of the ArI 415.8 nm line intensity in argon and the H_β line intensity in hydrogen-argon mixture at three different pressures. The variation of light intensity with pressure for argon lines ArI 842.5 nm, ArI 750.3 nm and ArI 419.8 nm as well as for hydrogen H_β line is also studied. For high- and low-lying energy levels in argon and in argon-hydrogen mixture, a different dependence of spectral line intensity upon gas pressure is detected. In hydrogen-argon mixture, a non-linear decrease of argon and hydrogen spectral line intensity with an increase of gas pressure is observed.     

脉冲调制射频容性耦合SiH/C2H4/Ar放电的发射光谱诊断

本文采用发射光谱法诊断了低气压下氩气(Ar)、硅烷(SiH4)及乙烯(C2H4)混合气体(SiH4/C2H4/Ar)脉冲调制射频放电等离子体特性,利用了Ar发射光谱中的五条谱线通过Boltzmann斜率法计算了电子激发温度,研究了占空比、调制频率、功率及气压等对电子激发温度和谱线相对强度的影响.     

A water-vapor electric-discharge vacuum ultraviolet source

The optical emission from a longitudinal dc glow discharge in water vapors (P=0.05–2.5 kPa) was studied in a wavelength range of λ=130–350 nm. It is shown that the discharge in low-pressure water vapors can be used as a source of the vacuum UV (VUV) radiation in the 140–190 nm wavelength range. As the vapor pressure was increased to 2.5 kPa, the emission intensity decreased by one-two orders of magnitude and the main peaks shifted to λ=286 and 306–315 nm. The bands of optical emission from the products of water decomposition agree in position with the emission band edges of the hydroxyl molecule. The obtained results are important for the development of a simple water-vapor electric-discharge VUV source.