Vacuum Ultraviolet Lamp Research Articles

A VUV Photoionization Aerosol Time-of-Flight Mass Spectrometer with a RF-Powered VUV Lamp for Laboratory-Based Organic Aerosol Measurements

A vacuum ultraviolet (VUV) photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS) has been developed for real-time, quantitative chemical analysis of organic particles in laboratory environments. A nozzle of ∼ 0.12 mm orifice combined with an aerodynamic lens assembly and a three stage differential pumping system is used to sample particles at atmospheric pressure. The particles are vaporized on a thermal heater, and then the nascent vapor is photoionized by light generated with a RF-powered VUV lamp. A 0.41 V/cm electric field is used to drive the ions from the ionization region into the ion extraction region where a positive electric pulse repels the ions into a reflectron mass spectrometer. The mass resolution of the spectrometer is ∼ 350 and the detection limit is ∼ 400 μ m 3 . The signal intensities observed are linear with the mass concentration of aerosols. Oleic acid particles are well quantified with an uncertainty of 15% in mass concentrations ranging from 3.9 mg/m 3 to 392 mg/m 3...

Demonstration of a VUV Lamp Photoionization Source for Improved Organic Speciation in an Aerosol Mass Spectrometer

In recent years, the Aerodyne Aerosol Mass Spectrometer (AMS) has become a widely used tool for determining aerosol size distributions and chemical composition for non-refractory inorganic and organic aerosols. All AMSs to date have used a combination of flash thermal vaporization and 70 eV electron impact (EI) ionization. However, EI causes extensive fragmentation and mass spectra of organic aerosols are difficult to deconvolve because they are composites of the overlapping fragmentation patterns of a multitude of species. In this manuscript we present an approach to gain more information about organic aerosol composition by employing the softer technique of vacuum ultraviolet (VUV) ionization in a Time-of-Flight AMS (ToF-AMS). Our novel design allows for alternation between photoionization (PI) and EI within the same instrument on a timescale of minutes. Thus, the EI-based quantification capability of the AMS is retained while improved spectral interpretation is made possible by combined analysis of the...

New vacuum ultraviolet lamps for gas analysis

The designs of vacuum ultraviolet lamps offering a high stability, their basic specifications, and acceptance tests are described.

Single Photon Ionization Time-of-Flight Mass Spectrometry with a Pulsed Electron Beam Pumped Excimer VUV Lamp for On-Line Gas Analysis: Setup and First Results on Cigarette Smoke and Human Breath

Single-photon ionization (SPI) using vacuum ultraviolet (VUV) light produced by an electron beam pumped rare gas excimer source has been coupled to a compact and mobile time-of-flight mass spectrometer (TOFMS). The novel device enables real-time on-line monitoring of organic trace substances in complex gaseous matrixes down to the ppb range. The pulsed VUV radiation of the light source is employed for SPI in the ion source of the TOFMS. Ion extraction is also carried out in a pulsed mode with a short time delay with respect to ionization. The experimental setup of the interface VUV light source/time-of-flight mass spectrometer is described, and the novel SPI-TOFMS system is characterized by means of standard calibration gases. Limits of detection down to 50 ppb for aliphatic and aromatic hydrocarbons were achieved. First on-line applications comprised real-time measurements of aromatic and aliphatic trace compounds in mainstream cigarette smoke, which represents a highly dynamic fluctuating gaseous matrix. Time resolution was sufficient to monitor the smoking process on a puff-by-puff resolved basis. Furthermore, human breath analysis has been carried out to detect differences in the breath of a smoker and a nonsmoker, respectively. Several well-known biomarkers for smoke could be identified in the smoker's breath. The possibility for even shorter measurement times while maintaining the achieved sensitivity makes this new device a promising tool for on-line analysis of organic trace compounds in process gases or biological systems.

Single-Photon Ionization Quadrupole Mass Spectrometry with an Electron Beam Pumped Excimer Light Source

The application of soft ionization methods for mass spectrometry (MS), such as single-photon ionization (SPI) using vacuum ultraviolet (VUV) light, provides powerful analytical instrumentation for real-time on-line monitoring of organic substances in gaseous matrixes. A compact and mobile quadrupole mass spectrometer (QMS) system using a novel electron beam pumped rare gas VUV lamp for SPI has been developed for on-line analysis of organic trace compounds (ppb concentrations). The VUV radiation of the light source is employed for SPI in the ion source of the QMS. The concept of the interfacing of the VUV light source with the QMS is described and the SPI-QMS is characterized. On-line detection limits down to 50 ppb for benzene, toluene, and m-xylene were achieved. The instrument is well suited for continuous measurements of aromatic and aliphatic trace compounds and can therefore be used for on-line monitoring of trace compounds in dynamically fluctuating process gases. First measurements of gas standards, petrochemical samples, and on-line monitoring of automotive exhaust are presented.

VUV Single-Photon Ionization Ion Trap Time-of-Flight Mass Spectrometer for On-Line, Real-Time Monitoring of Chlorinated Organic Compounds in Waste Incineration Flue Gas

In this work, a sensitive and robust vacuum ultra-violet (VUV) single-photon ionization (SPI) ion trap time-of-flight mass spectrometer (VUV-SPI-IT-TOFMS) for on-line, realtime monitoring of chlorinated organic compounds in waste incineration flue gas has been newly developed. The fragment-free SPI technique with 121.6-nm VUV lamp irradiated by a microwave generator and the quadrupole ion trap to accumulate and select analyte ions were combined with a reflectron time-of-flight mass spectrometer to detect chlorinated organic compounds at trace level. This measuring system was tuned up to detect dioxins precursors with the aim at an application to monitoring trace level toxic substances in flue gases from incinerator furnaces. As a result, this technology has made it possible to analyze trichlorobenzene (T3CB), a dioxin precursor, in 18 s with a sensitivity of 80 ng/m3-N (10 pptv) using the selective accumulation of analyte substances and separation of interfering substances in the ion trap. Moreover, the first field test of the continuous monitoring T3CB in an actual waste incineration flue gas had been done for 7 months. The results show that this system has an exceeding robust performance and is able to maintain the high sensitivity in analyzing T3CB for long months of operation.

Photocatalytic degradation of phenols in aqueous solution under irradiation of 254 and 185 nm UV light

The photocatalytic decomposition and mineralization of 4-chlorophenol (4-CP), hydroquinone and 4-nitrophenol (4-NP) in aqueous solution were investigated using two kinds of low-pressure mercury lamps: one was UV (ultraviolet) lamp emitting at 254 nm and the other was VUV (vacuum ultraviolet) lamp emitting at both 254 and 185 nm. VUV irradiation led to the most efficient degradation of the organics. Different mechanisms of photocatalysis and photolysis under VUV irradiation were observed. The degradation rate was subjected to the molecular structures of the substrates. 4-CP was easy to be decomposed, while hydroquinone was easy to be mineralized. However 4-NP was difficult to be decomposed or mineralized. VUV was efficient for decomposition of refractory compounds, such as nitrophenols, and the catalyst was efficient for TOC removal.

Experimental and theoretical investigations of a low-pressure He–Xe discharge for lighting purpose

Low-pressure cylindrical dc glow discharges in a mixture of helium and 2% xenon are studied by experiment and self-consistent modeling. They can be used for the design of mercury-free vacuum ultraviolet sources and fluorescent lamps for publicity lighting. Experimental diagnostics of the column plasma includes measurements of the axial electric field strength and of the axis densities of the four lowest excited states of xenon. The electric field is determined from probe measurements. The particle densities are derived from the results of tunable diode laser absorption spectroscopy. Experimental investigations are assisted by a self-consistent analysis of the dc positive column plasma. A comparison between calculated and measured values of the axial electric field strength and the densities of excited xenon atoms is presented and discussed. The validated model is used for optimization of the discharge conditions by variation of the discharge current, gas pressure, and tube radius with respect to the radiation power and efficiency of the 147 nm resonance line of xenon. The discussion includes an analysis of the power budget of the column plasma.

Direct, etching of GaAs Crystal Excited by a Vacuum UltravioletLamp

A successful direct, etching system excited by a vacuum ultraviolethollow-cathode lamp is reported. The result shows that the facility cantransfer a mesh pattern exactly and directly to n-type GaAs wafer,which is the same as that direct, etched by synchrotron radiation.

Single photon ionization (SPI) via incoherent VUV-excimer light: robust and compact time-of-flight mass spectrometer for on-line, real-time process gas analysis.

Fast on-line detection of organic compounds from complex mixtures, such as industrial process gas streams, require selective and sensitive analytical methods. One feasible approach for this purpose is the use of mass spectrometry (MS) with a selective and soft (fragment-free) ionization technique, such as chemical ionization (CI) or photo ionization (PI). Single photon ionization (SPI) with vacuum ultraviolet (VUV) light is a particularly sof tionization technique, well-suited for detection of both aromatic and aliphatic species. Problematic, however, is the generation of the VUV light. In general, the vacuum ultraviolet (VUV) light sources for SPI-MS are based either on lasers (e.g., 118-nm radiation generated by frequency-tripling of the third harmonic of a Nd:YAG laser) or on conventional VUV lamps, such as deuterium lamps. Althoughthe laser-based techniques are very sophisticated and expensive, the conventional lamps have serious drawbacks regarding their optical parameters, such as low-output power, low spectral power density, and broad emission bands. In this work, a novel excimer VUV light source, in which an electron beam is used to form rare gas excimer species, is used. The excimer VUV light sourceproduces brilliant and intense VUV light. The novel VUV light source was coupled to a compact and mobile time-of-flight mass spectrometer (TOFMS). A special interface design, including optical (VUV optics) as well as electronic measures (e.g., pulsed ion extraction) was realized. The use of the excimer VUV lamp for SPI will allow the realization of very compact, rugged, and sensitive SPI-TOFMS devices, which preferably will be adapted for process analytical application or monitoring issues (e.g., chemical warfare detection). The excimer VUV-lamp technology delivers VUV light with a good beam quality and high-output power at low costs. Furthermore, it allows changing the emitted wavelength as well as the bandwidth of the excimer VUV lamp in t he 100-200-nm region by changing the gas filling. Consequently, SPI-TOFMS with an excimer light source is a fast detection technique that can be used for online monitoring, for example, in environmental studies or industrial manufacturing processes. In this paper, technology and characteristics of the new excimer light source, as well as the combination with the TOFMS, are presented. Furthermore, a first characterization of the SPI-TOFMS instrument, regarding analytical parameters such as detection limits and selectivity, is given. This includes a discussion of potential improvements that probably will be achievable within a future prototype genertation. Finally, first applications of the system for on-line measurement of organic trace species in a complex gas mixture (here, motorcycle exhaust gas) are presented.

1.5 kW high-peak-power vacuum ultraviolet flash lamp using a pulsed silent discharge of krypton gas

A 1.5 kW high-peak-power discharge lamp with short emission duration of 140 ns has been developed in the vacuum ultraviolet spectral region. Our numerical calculation ensured that the peak emission at 147 nm was due to singlet excimers (1Σ), which were mainly produced via electron-collisional mixing of triplet excimers (3Σ).

X-ray photoelectron spectroscopy investigations of ultrathin layers grown by ultraviolet-assisted oxidation of SiGe

X-ray photoelectron spectroscopy (XPS) investigations of the composition and chemical bonding of layers grown on Si 0.8Ge 0.2 samples at 300 °C by a vacuum ultraviolet (VUV)-assisted dry oxidation process have been performed. The VUV source was an array of three Xe 2 ∗ excimer VUV lamps emitting at 172 nm, a power density of around 25 mW/cm 2. XPS investigations showed that the layers grown for shorter periods of time contain mostly SiO 2 with a very low percent of GeO 2. Most of Ge atoms initially present in the surface SiGe layer were segregated and accumulated at the interface between the grown oxide and remaining SiGe. Angle-resolved XPS showed that the formed GeO 2 was buried under the grown SiO 2 layer and located adjacent to the remaining SiGe layer. When the grown SiO 2 layer reached a thickness around ∼70 Å and the fraction of Ge accumulated in the segregated layer was more than double the initial value, a sudden increase in Ge oxidation rate was observed.

134 nm vacuum ultraviolet emission using an Ar/Kr gas mixture excited by a quasi-continuous-wave gas jet discharge

We have developed a vacuum ultraviolet (VUV) lamp at 134 nm with a quasi-point emission geometry using a quasi-continuous-wave (cw) gas jet discharge of an Ar/Kr gas mixture. We have unambiguously identified a new emission continuum centered at 134 nm as a transition of Ar-Kr hetero-nuclear excimers (ArKr*). The VUV emission power of the 134 nm continuum was 10 mW at 21 atm of the total Ar/Kr stagnation gas pressure, at a Kr concentration of 0.1%. Characteristic energy transfer between atoms and dimers plays an important role for the efficient production of ArKr* in such a gas jet discharge.

Ultrathin silicon dioxide films grown by photo-oxidation of silicon using 172 nm excimer lamps

We report the low temperature growth of ultrathin SiO2 films on crystalline Si by photo-oxidation with an array of Xe2∗ excimer vacuum ultraviolet (VUV) lamps operating at a wavelength of 172nm. Ultrathin layers from 1.2 to 3.3nm thickness were grown at time intervals from 5 to 40min at 100–400°C at an O2 pressure of 1000mbar. Growth rates of up to 0.2nmmin−1 have been achieved at 400°C, while the chemical bonding of the films has been analysed by Fourier transform infrared (FTIR) spectroscopy and found to be SiO2. The as-grown 3.3nm films exhibited good dielectric properties, comparible to SiO2 films of identical thickness, grown by RTP at 800°C.

Atmospheric pressure photoionization: an ionization method for liquid chromatography-mass spectrometry

Atmospheric pressure photoionization (APPI) has been successfully demonstrated to provide high sensitivity to LC-MS analysis. A vacuum-ultraviolet lamp designed for photoionization detection in gas chromatography is used as a source of 10-eV photons. The mixture of samples and solvent eluting from an HPLC is fully evaporated prior to introduction into the photoionization region. In the new method, large quantities of an ionizable dopant are added to the vapor generated from the LC eluant, allowing for a great abundance of dopant photoions to be produced. Because the ion source is at atmospheric pressure, and the collision rate is high, the dopant photoions react to completion with solvent and analyte molecules present in the ion source. Using APPI, at an LC flow rate of 200 microL/min, it is possible to obtain analyte signal intensities 8 times as high as those obtainable with a commercially available corona discharge-atmospheric pressure chemical ionization source.

Titanium dioxide films prepared by photo-induced sol–gel processing using 172 nm excimer lamps

We report the growth of single- and multilayer films of titanium dioxide (TiO2) on Si(100) substrates at low temperature by a new photo-induced sol–gel process. Polymeric TiO2 sols prepared by the hydrolysis and condensation of titanium isopropoxide were spin-coated on the silicon substrate and then irradiated by an Xe∗2 excimer vacuum ultraviolet (VUV) lamp operating at a wavelength of 172nm. Films with thicknesses between 10 and 200nm were achieved readily by this technique. The effects of spin speed, irradiation time and substrate temperature on the films formed have been studied. The chemical bonding changes in the thin films were analysed by Fourier transform infrared spectroscopy (FTIR), while thickness and refractive indices were determined by ellipsometry. FTIR confirmed the removal of H2O and OH groups after VUV irradiation for 10min at 300°C. The refractive index reached a value of 2.4, which compares favourably with the value of 2.58 recorded for the bulk material, while optical transmittance values in the visible region of the spectrum between 85 and 95% were obtained on quartz substrates.

Generation of intense excimer radiation from high-pressure hollow cathode discharges

By reducing the diameter of the cathode opening in a hollow cathode discharge geometry to values on the order of 100 μm, we were able to operate these discharges in noble gases in a direct current mode up to atmospheric pressure. High-pressure discharges in xenon were found to be strong sources of excimer radiation. Highest intensities at a wavelength of 172 nm were obtained at a pressure of 400 Torr. At this pressure, the vacuum ultraviolet (VUV) radiant power of a single discharge operating at a forward voltage of 220 V and currents exceeding 2 mA reaches values between 6% and 9% of the input electrical power. The possibility to form arrays of these discharges allows the generation of flat panel VUV lamps with radiant emittances exceeding 50 W/cm2.

A vacuum ultraviolet flash lamp with extremely broadened emission spectra

We have developed a vacuum ultraviolet (VUV) flash lamp using a binary rare gas mixture excited by a pulsed silent discharge. In a Kr/Xe silent discharge, the VUV emission spectral width was extended up to 26 nm full width at half-maximum (FWHM) at a center wavelength of 162 nm. According to kinetic analyses, such a spectral extension in mixed rare gases is attributed to the simultaneous emissions from heteronuclear rare gas excimers (KrXe*) and homonuclear rare gas excimers (Kr2* and Xe2*).

Low Thermal Budget Processing Of Organic Dielectrics

AbstractLow dielectric constant organic materials are ideal for use as interconnect dielectrics forintegrated circuits. As compared to silicon dioxide, organic dielectrics with K <3.84 reducepower dissipation, crosstilk and RC delays in interconnects. Curing is essential afterdeposition of these materials to initiate polymerization reactions and form films of desirableelectrical properties. For high performance and reliability, low thermal budget processing isa necessity. Rapid isothermal processing (RIP) based on the use of dual spectral sources isa potential technique to lower the thermal budget. In this paper, we demonstrate the role ofphotoeffects in the curing of polyimide films (K∼2.6) using a rapid isothermal processor witha dual spectral source (Tungsten Halogen and vacuum ultra violet (VUV) lamps) as a sourceof optical and thermal energy. Lamp configurations that allowed a greater availability of ultraviolet and vacuum ultra violet photons on the film to initiate physical and chemical processesallowed a lower curing temperature to achieve the same level of immidization. Furthermore, these samples also gave the lowest leakage current and film stress. Therefore, the rapidheating and cooling features of rapid isothermal processing in conjunction with lowerprocessing temperature through the use of high energy photons to enhance surface reactionsgive superior film properties

Photo-excited removal of native oxide on a silicon wafer in NF 3 gas using a VUV Xe lamp

Photo-excited removal of native oxide on a silicon substrate in NF 3 gas has been investigated at room temperature using a vacuum ultraviolet Xe lamp. In pure NF 3 at a pressure of 0.2 Torr, the oxide layer has been partly removed, and etching of the silicon substrate has also occured. When NF 3 has been diluted with H 2, the formation of a thin layer has been observed, which has been characterized as (NH 4) 2SiF 6. This layer has been removed by heating the substrate up to 100°C leaving a smooth silicon surface without native oxide. Possible reaction mechanisms are discussed.