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Wolfram Knapp

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Papers by Wolfram Knapp

Numerical investigations of hot cathode ionization gauges

Vacuum, 1998

Analytical or numerical methods for the investigation of hot cathode ionization gauges were descr... more Analytical or numerical methods for the investigation of hot cathode ionization gauges were described and discussed only rarely in the literature. This is due to various difficulties in the theoretical calculation of gauge sensitivity and other important properties. The rapid development of computer hardware gives the opportunity to apply numerical methods in the investigation of hot cathode ionization gauges. With the threedimensional numerical calculation program IONTRA3d it was possible to calculate the sensitivity and other important characteristics of hot cathode ionization gauges. The results of numerical calculations were compared with experimental data. The differences were discussed. By means of IONTRA3d it was possible to obtain results that can be achieved by experimental investigations only with large effort. These are the analysis of the distribution of electron current on the anode segments and the influence of anode support. The typical form of C-U c-Plots (with 2 maximas) was explained.

Investigations of pyroelectric crystals for vacuum electron sources and X-ray applications

2017 30th International Vacuum Nanoelectronics Conference (IVNC), 2017

The effect of pyroelectric polarization was investigated with respect to electron sources and X-r... more The effect of pyroelectric polarization was investigated with respect to electron sources and X-ray applications. Different pyroelectric Lithium Tantalate (LiTaO3) crystals were used. Main focus was the optimization of electron emission efficiency in dependence of geometrical parameters, temperature curves and vacuum pressures. The presented results and experimental experiences provide a basis for the development of novel miniaturized X-ray tubes, especially for mobile applications in X-ray fluorescence spectroscopy.

Self-focusing of electrons emitted by rectangular pyroelectric crystals: A study on geometrical conditions for optimized X-ray intensities

2018 31st International Vacuum Nanoelectronics Conference (IVNC), 2018

Pyroelectric crystals such as LiTaO3 or LiNbO3 offer the opportunity to produce X-rays with high ... more Pyroelectric crystals such as LiTaO3 or LiNbO3 offer the opportunity to produce X-rays with high energy and intensity. These pyroelectric X-ray sources may be used in XRF applications due to particular advantages. This report deals with systematic studies on the behavior of these crystals enabling an optimization of X-ray intensity. Furthermore, the focusing of electrons emitted by rectangular pyroelectric crystals has been studied.

Investigations on electrical properties and correlations to electron and X-ray energies of pyroelectric LiTaO3 and LiNbO3

2018 31st International Vacuum Nanoelectronics Conference (IVNC), 2018

The electrical properties of pyroelectric Lithium Tantalate (LiTaO3) and Lithium Niobate (LiNbO3 ... more The electrical properties of pyroelectric Lithium Tantalate (LiTaO3) and Lithium Niobate (LiNbO3 were investigated and compared to accessible X-ray energies by using the pyroelectric effect to generate X-rays. The capacitances of different crystals of varying sizes were measured and the resulting permittivities were calculated. A vacuum setup enabled a correlation to the maximum X-ray energies at a variable pressure. The presented results provide an overview of fundamental material properties and the effect on the generated difference of potential.

Energetic evaluation of the transition from field electron emission to plasma discharges with extended use of the Fowler-Nordheim plot

2017 30th International Vacuum Nanoelectronics Conference (IVNC), 2017

We report on an extended use of the Fowler-Nordheim plot for energetic evaluation of charge trans... more We report on an extended use of the Fowler-Nordheim plot for energetic evaluation of charge transfers in vacuum electronics. First results explained clearly, the transition from field electron emission to plasma discharge is physically conditioned, especially in the case of higher emission currents.

Guerickes Versuch mit den Großen Magdeburger Halbkugeln und den Pferden

Vakuum in Forschung und Praxis, 2020

ZusammenfassungDie Magdeburger Halbkugeln wurden vom deutschen Naturwissenschaftler und Bürgermei... more ZusammenfassungDie Magdeburger Halbkugeln wurden vom deutschen Naturwissenschaftler und Bürgermeister von Magdeburg, Otto von Guericke, zum Nachweis des Vakuums und der Kraft des Luftdrucks erfunden. Das Experiment mit den Großen Magdeburger Halbkugeln und den Pferden ist eines der bekanntesten und spektakulärsten Vakuumexperimente der Welt. Im Jahr 1657 war die erste Vorführung in Magdeburg, also 3 Jahre nach dem Reichstag 1654 in Regensburg. Im Beitrag wird erneut der historische Beweis dafür geliefert, basierend auf dem Briefwechsel zwischen Guericke und Schott, der diesen in seinem Buch „Technica Curiosa“ 1664 veröffentlicht hat. Das bedeutet aber auch, dass die erste Vorführung des berühmten Vakuumexperiments mit den 16 Pferden in Regensburg erst im Jahr 2004 stattgefunden hat, präsentiert von der Otto‐von‐Guericke‐Gesellschaft Magdeburg. Der Beitrag beinhaltet einige theoretische Grundlagen und praktische Erfahrungen zum Vakuumexperiment aus über 160 Vorführungen.

Optimization of pyroelectric electron sources for the generation of x-rays for x-ray fluorescence applications

Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, 2018

X-ray fluorescence (XRF) spectroscopy is a frequently used technique for the chemical analysis of... more X-ray fluorescence (XRF) spectroscopy is a frequently used technique for the chemical analysis of materials due to several advantages such as its almost nondestructive character. Subjects of this report are investigations of the pyroelectric effect with regard to its application for the generation and acceleration of x-rays and a successive usage of radiation for XRF in materials science. In order to answer questions concerning the intensity of primary radiation and of fluorescence radiation, this paper contains several experimental investigations. Different setups and measurements have been used to increase intensity. Emission behavior of electrons has been characterized using measurements of electron current in a target positioned in front of a pyroelectric crystal as a function of the temperature of the crystal and time. Radiation has been coupled out, and its dose equivalent rate has been measured. This allowed the optimization of the working pressure of the residual gas surroun...

Elektronenfeldemission mit Nanoemitter ohne Begrenzung und Restgas-Ionisation?

Vakuum in Forschung und Praxis, 2017

Electron sources with CNT field-emitter cathodes - Design differences for lower and higher emission currents

2013 26th International Vacuum Nanoelectronics Conference (IVNC), 2013

ABSTRACT This contribution is a result of higher emission current investigations with CNT field-e... more ABSTRACT This contribution is a result of higher emission current investigations with CNT field-emitter cathodes. The emitter resistor must be considered for emission current above 5 mA. Thin and long CNT field-emitters show emission current saturation. A simple R-limited emission model is presented.

Otto von Guericke und das Abenteuer Vakuum

Vakuum in Forschung und Praxis, 2015

Grundlagenuntersuchungen zum Betriebsverhalten eines „Stabil Ion Gauge”

Vakuum in Forschung und Praxis, 1996

ABSTRACT Zusammenfassung Für ein kommerzielles Glühkatodenionisationsmanometer „Stabil Ion Gauge”... more ABSTRACT Zusammenfassung Für ein kommerzielles Glühkatodenionisationsmanometer „Stabil Ion Gauge” [1] wurden die grundlegenden Kennlinien bestimmt und ausgewertet, wobei sich ein recht eigentümlicher Verlauf der Diodenkennlinien zeigte. Durch zweidimensionale Berechnungen des elektrischen Feldes mit dem Programm „SIMION” [2] konnte eine Elektronenemission von der Rückseite der Katode als Ursache gefunden werden. Die Übereinstimmung der Feldberechnungen und der experimentellen Ergebnisse beweist nahezu zweifelsfrei, daß es sich tatsächlich um diesen Effekt handelt. Die Kennlinie von Empfindlichkeit gegen Elektronenstrom weist eine leicht fallende Tendenz auf, was sich mit der Ausbildung einer Elektronenraumladung im Gitter mit steigendem Elektronenstrom erklären läßt. Dieser Effekt wird durch den gerichteten Elektronenstrahl noch verstärkt. Die Röntgengrenze wurde mit der Alpertmethode zu 1,9.10−10 mbar und mit der Vergleichsmethode zu 1,8.10−10 mbar bestimmt. Das „Stabil Ion Gauge” weist deutlich stärkere Desorptionseffekte als die beim Vergleich benutzte Meßröhre IE 414 auf. Dies war wegen der Verwendung einer massiven Abschirmelektrode auch nicht anders zu erwarten. Der Effekt ist — in Übereinstimmung mit der Erfahrung — für Sauerstoff am größten und für Argon und Stickstoff am kleinsten. Somit erscheinen die im Hinblick auf Stabilität und Reproduzierbarkeit der Empfindlichkeit günstigen konstanten Potentialverhältnisse mit einem recht störenden Einfluß von Desorbaten an der unteren Meßgrenze sowie einer erhöhten Röntgengrenze erkauft.Summary The fundamental characteristics of a commercial “Stabil Ion Gauge” [1] as well as its x-ray limit and the influence of desorption effects on the collector current at the lower limit of pressure measurement were investigated. A strange shape of the diode characteristics of the gauge was observed. By means of two-dimensional calculations of the electrical field with the simulation program “SIMION” [2] an emission of the backside of the ribbon cathodes was determined to be the reason for that behaviour. The agreement of these calculations and the experimentally observed curves supports this thesis. The decreasing tendency of the sensitivity vs electron space charge within the anode volume with increasing electron current. This effect is intensified by the directed electron beam which originates from the ribbon cathodes. The x-ray limit was determined by the Alpert-method to 1.9.10−10 mbar and by the comparison method to 1.8.10−10 mbar. The test gauge showed larger desorption effects than the reference gauge IE414 (Leybold) which is due to the installation of a big grounded shield surrounding the whole electrode structure. In agreement with experiences the desorption effects were largest for chemical active gases like oxygen and hydrogen. Summarizing one can state that the constant potential relations within the “Stabil Ion Gauge” which are essential for stability and reproducibility of the sensitivity of ionization gauges have been achieved at the costs of a disturbing desorption effects at lower pressures and a relatively high x-ray limit.

Einfluß von Gasadsorbaten auf die Eigenschaften eines Glühkatoden‐ Ionisationsmanometers mit axialer Emission nach CHEN und SUEN

Vakuum in Forschung und Praxis, 1995

The influence of adsorbed gases on the pressure reading of the axial emission ionization gauge ac... more The influence of adsorbed gases on the pressure reading of the axial emission ionization gauge according to CHEN and SUEN [1] was investigated in the UHV pressure range. The anodes of the investigated gauges were made from molybdenum and platinum. After exposure to argon, nitrogen, oxygen and hydrogen the ion current versus time characteristic was determined during pumpdown. The pressure reading of the axial emission gauge was compared with the readings of a commercial Bayard‐Alpert gauge and an extractor gauge. After exposure to oxygen the gauge with the Mo‐anode showed the largest deviation of the pressure readings of the gauges, while the gauge with Pt‐anode showed strong deviations after oxygen and hydrogen exposure.

Transition of Electron Field Emission to Normal Glow Discharge

IEEE Transactions on Electron Devices, 2014

ABSTRACT The field emission (FE) properties of single walled carbon nanotube (SWCNT)/graphene hyb... more ABSTRACT The field emission (FE) properties of single walled carbon nanotube (SWCNT)/graphene hybrid samples were investigated for high currents in dc mode and pulsed mode with pulse-ON times between 0.2 and 400 ms and duty cycles between 1% and 80% with stainless steel anodes. Our dc measurements showed a transition to glow discharge (GD) already at currents larger than 10 mA. The pulsed (I) – (V) characteristics with up to 400-mA maximum current were limited by the cathode resistance, consisting of the emitting layer resistance and the contact resistance, which was found to be between 1.1 and 1.4 kohm . A constant-voltage behavior arises after subtracting the cathode resistance. This constant-voltage behavior, the observed glowing during FE, and time-resolved measurements give evidence for the transition of Fowler–Nordheim-type FE to FE enhanced GD. FE enables a soft transition to normal GD without the need of an ignition voltage. The buildup dynamic and the time constants of the transition to GD were evaluated and discussed. The FE and GD behaviors were also compared using copper and molybdenum anodes.

Some Studies of the Axial Emission Ionization Gauge

SHINKU, 1994

An axial emission ionization gauge with an electrode construction similar to that of J. Z. Chen a... more An axial emission ionization gauge with an electrode construction similar to that of J. Z. Chen and C. D. Suen (An axial-emission ultrahigh vacuum gauge. J. Vac. Sci. & Technol. 20(1), 88-91 (1982)) was studied experimentally with respect to its applicability as a calibration gauge for use in the UHV range. The optimum operation parameters were determined experimentally. At these values of the operation parameters the sensitivity is smaller than that in the publication of Chen and Suen. In contrast with the ionization gauge of the extractor type, the sensitivity of the modified axial emission gauge depends only very weakly on the electron current and pressure, so that its application as calibration gauge in the UHV region seems possible from this point of view. In the low-pressure region, the influence of gas exposure on the pressure reading was studied for a gauge with a molybdenum anode and one with a platinum anode. In both cases the electron-stimulated desorption (ESD) caused errors in the pressure reading. If a platinum anode was used, the influence of hydrogen was larger than that of oxygen. In the case of a molybdenum anode, the influence of oxygen was larger than that of hydrogen. This behavior is accounted for by the greater adsorption of hydrogen on platinum. The experiments on the ESD demonstrate that the axial emission gauge has a somewhat lower collection efficiency for ESD ions generated on the anode surface than for those generated by electron impact in the space surrounded by the grid. This is in conformity with some calculations of ion trajectories performed with the program SIMION.

Formation of a nano-emitter for electron field emission on a liquid metal ion source tip after solidification of the alloy

Vacuum, 2002

Liquid metal ion sources (LMISs) operating with solidified Au alloys can be used as high-intensit... more

Carbon Buckypaper field emission investigations

Vacuum, 2002

We investigated Carbon Buckypaper with respect to field emission properties, especially long-term... more We investigated Carbon Buckypaper with respect to field emission properties, especially long-term field emission stability and under well-defined stress conditions. The Carbon Buckypaper field emitters showed a threshold field strength of about 1 V mm À1 for an emission current of 1 nA. Field emission current densities of more than 10 mA cm À2 are measured for higher applied field strengths. The main focus of our current investigations is the interaction of field emission and vacuum conditions. In this contribution reproducible stress tests with controlled micro-discharges are presented. At higher emission current densities of about 100 mA cm À2 increased ionization and even luminescence out of the emission zone appears before the micro-discharges start. After arcing with micro-discharges the Carbon Buckypaper field emission has lower emission current density and lower variation range. However, the contribution demonstrates the advantages of Carbon Buckypaper as a large array electron field emitter for cold cathode applications.

Theoretical and experimental desorption investigations at ionization gauges

Vacuum, 1996

ABSTRACT We have investigated the disturbing influence of outgassing and desorption effects on th... more ABSTRACT We have investigated the disturbing influence of outgassing and desorption effects on the pressure reading of three different types of ionization gauges with different methods. The behaviour of these gauges after exposure to gases, which are important in the Ultra-High-Vacuum region, after variation of the electron current, and for different potentials of the electrodes were studied. We have also determined the influence of the grid material on the outgassing and desorption effects for the Chen-Suen gauge.General statements of the influence of desorption phenomena on the pressure reading of ionization gauges at the lower pressure limit are given.

New high capacity getter for vacuum insulated mobile LH2 storage tank systems

Vacuum, 2007

Current ''Non-evaporable getters'' (NEGs) are important for the improvement of vacuum by the help... more Current ''Non-evaporable getters'' (NEGs) are important for the improvement of vacuum by the help of metallic surface sorption of residual gas molecules. High porosity alloys or powder mixtures of Zr, Ti, Al, V, Fe and other metals are the base material for this kind of gas sorbents. The development of vacuum technologies creates new challenges for the field of getter materials. The main sorption parameters of the current NEGs, namely, pumping speed and sorption capacity, have reached certain level limits. Chemically active metals are the basis of NEGs of a new generation. The appearance of new materials with high sorption capacity at room temperature is a long-felt need. It is obvious, that chemically active metals and alloys with reactivity higher, than that of transition metals, can become this kind of materials. The potential of active metals as the strongest gas sorbents is very high. The improved getter materials allow faster pumping speed. The sticking rate on the chemically active surface is significantly higher, and sorption capacity can be increased by up to 104 times (during the lifetime of a device the entire getter material reacts with residual gases). The main structural form of the new getter concepts are spherical powders, granules and porous multi-layers. The full pumping performance takes already place at room temperature and the activation temperature can be adjusted between room temperature and 660 1C. The successful insertion of this new chemical getter pump in a mobile double-walled LH 2 tank system shows the very high sorption capacity of all relevant residual gases including H 2. This new invention opens the possibility for significant vacuum improvements especially in the field of H 2 pumping, which is an important challenge in many different vacuum devices and processes.

Control of hot-filament ionization gauge emission current: mathematical model and model-based controller

Measurement Science and Technology, 1997

ABSTRACT The lack of adequate models for feedback-controlled emission current in hot-filament cat... more ABSTRACT The lack of adequate models for feedback-controlled emission current in hot-filament cathode ionization gauges (IGs) makes it difficult to achieve precision control over a wide range of emission currents (0.01 - 10 mA). A nonlinear mathematical model for transforming the filament heating power into emission current is developed. Experimental and theoretical results are shown. An electron emission regulator is described which was designed for use in the calibration of IGs, mass spectrometers and vapour rate measurements with IGs.

Hydrogen isotope inventories in the ASDEX Upgrade tungsten coated divertor tiles

Journal of Nuclear Materials, 1999

The total hydrogen isotope inventories in the tungsten coated divertor tiles of ASDEX Upgrade wer... more The total hydrogen isotope inventories in the tungsten coated divertor tiles of ASDEX Upgrade were measured by thermal desorption spectroscopy and 7 in the near surface region w by nuclear reaction analysis. The highest amounts of deuterium (:55x103: D /m3) are measured in the inner divertor region outside the separatrix due to the formation of a GE layer on the tungsten by codeposition of deuterium with carbon. The inventories in the outer divertor 7 where erosion dominates-are generally smaller by an order of magnitude.

Numerical investigations of hot cathode ionization gauges

Vacuum, 1998

Analytical or numerical methods for the investigation of hot cathode ionization gauges were descr... more Analytical or numerical methods for the investigation of hot cathode ionization gauges were described and discussed only rarely in the literature. This is due to various difficulties in the theoretical calculation of gauge sensitivity and other important properties. The rapid development of computer hardware gives the opportunity to apply numerical methods in the investigation of hot cathode ionization gauges. With the threedimensional numerical calculation program IONTRA3d it was possible to calculate the sensitivity and other important characteristics of hot cathode ionization gauges. The results of numerical calculations were compared with experimental data. The differences were discussed. By means of IONTRA3d it was possible to obtain results that can be achieved by experimental investigations only with large effort. These are the analysis of the distribution of electron current on the anode segments and the influence of anode support. The typical form of C-U c-Plots (with 2 maximas) was explained.

Investigations of pyroelectric crystals for vacuum electron sources and X-ray applications

2017 30th International Vacuum Nanoelectronics Conference (IVNC), 2017

The effect of pyroelectric polarization was investigated with respect to electron sources and X-r... more The effect of pyroelectric polarization was investigated with respect to electron sources and X-ray applications. Different pyroelectric Lithium Tantalate (LiTaO3) crystals were used. Main focus was the optimization of electron emission efficiency in dependence of geometrical parameters, temperature curves and vacuum pressures. The presented results and experimental experiences provide a basis for the development of novel miniaturized X-ray tubes, especially for mobile applications in X-ray fluorescence spectroscopy.

Self-focusing of electrons emitted by rectangular pyroelectric crystals: A study on geometrical conditions for optimized X-ray intensities

2018 31st International Vacuum Nanoelectronics Conference (IVNC), 2018

Pyroelectric crystals such as LiTaO3 or LiNbO3 offer the opportunity to produce X-rays with high ... more Pyroelectric crystals such as LiTaO3 or LiNbO3 offer the opportunity to produce X-rays with high energy and intensity. These pyroelectric X-ray sources may be used in XRF applications due to particular advantages. This report deals with systematic studies on the behavior of these crystals enabling an optimization of X-ray intensity. Furthermore, the focusing of electrons emitted by rectangular pyroelectric crystals has been studied.

Investigations on electrical properties and correlations to electron and X-ray energies of pyroelectric LiTaO3 and LiNbO3

2018 31st International Vacuum Nanoelectronics Conference (IVNC), 2018

The electrical properties of pyroelectric Lithium Tantalate (LiTaO3) and Lithium Niobate (LiNbO3 ... more The electrical properties of pyroelectric Lithium Tantalate (LiTaO3) and Lithium Niobate (LiNbO3 were investigated and compared to accessible X-ray energies by using the pyroelectric effect to generate X-rays. The capacitances of different crystals of varying sizes were measured and the resulting permittivities were calculated. A vacuum setup enabled a correlation to the maximum X-ray energies at a variable pressure. The presented results provide an overview of fundamental material properties and the effect on the generated difference of potential.

Energetic evaluation of the transition from field electron emission to plasma discharges with extended use of the Fowler-Nordheim plot

2017 30th International Vacuum Nanoelectronics Conference (IVNC), 2017

We report on an extended use of the Fowler-Nordheim plot for energetic evaluation of charge trans... more We report on an extended use of the Fowler-Nordheim plot for energetic evaluation of charge transfers in vacuum electronics. First results explained clearly, the transition from field electron emission to plasma discharge is physically conditioned, especially in the case of higher emission currents.

Guerickes Versuch mit den Großen Magdeburger Halbkugeln und den Pferden

Vakuum in Forschung und Praxis, 2020

ZusammenfassungDie Magdeburger Halbkugeln wurden vom deutschen Naturwissenschaftler und Bürgermei... more ZusammenfassungDie Magdeburger Halbkugeln wurden vom deutschen Naturwissenschaftler und Bürgermeister von Magdeburg, Otto von Guericke, zum Nachweis des Vakuums und der Kraft des Luftdrucks erfunden. Das Experiment mit den Großen Magdeburger Halbkugeln und den Pferden ist eines der bekanntesten und spektakulärsten Vakuumexperimente der Welt. Im Jahr 1657 war die erste Vorführung in Magdeburg, also 3 Jahre nach dem Reichstag 1654 in Regensburg. Im Beitrag wird erneut der historische Beweis dafür geliefert, basierend auf dem Briefwechsel zwischen Guericke und Schott, der diesen in seinem Buch „Technica Curiosa“ 1664 veröffentlicht hat. Das bedeutet aber auch, dass die erste Vorführung des berühmten Vakuumexperiments mit den 16 Pferden in Regensburg erst im Jahr 2004 stattgefunden hat, präsentiert von der Otto‐von‐Guericke‐Gesellschaft Magdeburg. Der Beitrag beinhaltet einige theoretische Grundlagen und praktische Erfahrungen zum Vakuumexperiment aus über 160 Vorführungen.

Optimization of pyroelectric electron sources for the generation of x-rays for x-ray fluorescence applications

Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, 2018

X-ray fluorescence (XRF) spectroscopy is a frequently used technique for the chemical analysis of... more X-ray fluorescence (XRF) spectroscopy is a frequently used technique for the chemical analysis of materials due to several advantages such as its almost nondestructive character. Subjects of this report are investigations of the pyroelectric effect with regard to its application for the generation and acceleration of x-rays and a successive usage of radiation for XRF in materials science. In order to answer questions concerning the intensity of primary radiation and of fluorescence radiation, this paper contains several experimental investigations. Different setups and measurements have been used to increase intensity. Emission behavior of electrons has been characterized using measurements of electron current in a target positioned in front of a pyroelectric crystal as a function of the temperature of the crystal and time. Radiation has been coupled out, and its dose equivalent rate has been measured. This allowed the optimization of the working pressure of the residual gas surroun...

Elektronenfeldemission mit Nanoemitter ohne Begrenzung und Restgas-Ionisation?

Vakuum in Forschung und Praxis, 2017

Electron sources with CNT field-emitter cathodes - Design differences for lower and higher emission currents

2013 26th International Vacuum Nanoelectronics Conference (IVNC), 2013

ABSTRACT This contribution is a result of higher emission current investigations with CNT field-e... more ABSTRACT This contribution is a result of higher emission current investigations with CNT field-emitter cathodes. The emitter resistor must be considered for emission current above 5 mA. Thin and long CNT field-emitters show emission current saturation. A simple R-limited emission model is presented.

Otto von Guericke und das Abenteuer Vakuum

Vakuum in Forschung und Praxis, 2015

Grundlagenuntersuchungen zum Betriebsverhalten eines „Stabil Ion Gauge”

Vakuum in Forschung und Praxis, 1996

ABSTRACT Zusammenfassung Für ein kommerzielles Glühkatodenionisationsmanometer „Stabil Ion Gauge”... more ABSTRACT Zusammenfassung Für ein kommerzielles Glühkatodenionisationsmanometer „Stabil Ion Gauge” [1] wurden die grundlegenden Kennlinien bestimmt und ausgewertet, wobei sich ein recht eigentümlicher Verlauf der Diodenkennlinien zeigte. Durch zweidimensionale Berechnungen des elektrischen Feldes mit dem Programm „SIMION” [2] konnte eine Elektronenemission von der Rückseite der Katode als Ursache gefunden werden. Die Übereinstimmung der Feldberechnungen und der experimentellen Ergebnisse beweist nahezu zweifelsfrei, daß es sich tatsächlich um diesen Effekt handelt. Die Kennlinie von Empfindlichkeit gegen Elektronenstrom weist eine leicht fallende Tendenz auf, was sich mit der Ausbildung einer Elektronenraumladung im Gitter mit steigendem Elektronenstrom erklären läßt. Dieser Effekt wird durch den gerichteten Elektronenstrahl noch verstärkt. Die Röntgengrenze wurde mit der Alpertmethode zu 1,9.10−10 mbar und mit der Vergleichsmethode zu 1,8.10−10 mbar bestimmt. Das „Stabil Ion Gauge” weist deutlich stärkere Desorptionseffekte als die beim Vergleich benutzte Meßröhre IE 414 auf. Dies war wegen der Verwendung einer massiven Abschirmelektrode auch nicht anders zu erwarten. Der Effekt ist — in Übereinstimmung mit der Erfahrung — für Sauerstoff am größten und für Argon und Stickstoff am kleinsten. Somit erscheinen die im Hinblick auf Stabilität und Reproduzierbarkeit der Empfindlichkeit günstigen konstanten Potentialverhältnisse mit einem recht störenden Einfluß von Desorbaten an der unteren Meßgrenze sowie einer erhöhten Röntgengrenze erkauft.Summary The fundamental characteristics of a commercial “Stabil Ion Gauge” [1] as well as its x-ray limit and the influence of desorption effects on the collector current at the lower limit of pressure measurement were investigated. A strange shape of the diode characteristics of the gauge was observed. By means of two-dimensional calculations of the electrical field with the simulation program “SIMION” [2] an emission of the backside of the ribbon cathodes was determined to be the reason for that behaviour. The agreement of these calculations and the experimentally observed curves supports this thesis. The decreasing tendency of the sensitivity vs electron space charge within the anode volume with increasing electron current. This effect is intensified by the directed electron beam which originates from the ribbon cathodes. The x-ray limit was determined by the Alpert-method to 1.9.10−10 mbar and by the comparison method to 1.8.10−10 mbar. The test gauge showed larger desorption effects than the reference gauge IE414 (Leybold) which is due to the installation of a big grounded shield surrounding the whole electrode structure. In agreement with experiences the desorption effects were largest for chemical active gases like oxygen and hydrogen. Summarizing one can state that the constant potential relations within the “Stabil Ion Gauge” which are essential for stability and reproducibility of the sensitivity of ionization gauges have been achieved at the costs of a disturbing desorption effects at lower pressures and a relatively high x-ray limit.

Einfluß von Gasadsorbaten auf die Eigenschaften eines Glühkatoden‐ Ionisationsmanometers mit axialer Emission nach CHEN und SUEN

Vakuum in Forschung und Praxis, 1995

The influence of adsorbed gases on the pressure reading of the axial emission ionization gauge ac... more The influence of adsorbed gases on the pressure reading of the axial emission ionization gauge according to CHEN and SUEN [1] was investigated in the UHV pressure range. The anodes of the investigated gauges were made from molybdenum and platinum. After exposure to argon, nitrogen, oxygen and hydrogen the ion current versus time characteristic was determined during pumpdown. The pressure reading of the axial emission gauge was compared with the readings of a commercial Bayard‐Alpert gauge and an extractor gauge. After exposure to oxygen the gauge with the Mo‐anode showed the largest deviation of the pressure readings of the gauges, while the gauge with Pt‐anode showed strong deviations after oxygen and hydrogen exposure.

Transition of Electron Field Emission to Normal Glow Discharge

IEEE Transactions on Electron Devices, 2014

ABSTRACT The field emission (FE) properties of single walled carbon nanotube (SWCNT)/graphene hyb... more ABSTRACT The field emission (FE) properties of single walled carbon nanotube (SWCNT)/graphene hybrid samples were investigated for high currents in dc mode and pulsed mode with pulse-ON times between 0.2 and 400 ms and duty cycles between 1% and 80% with stainless steel anodes. Our dc measurements showed a transition to glow discharge (GD) already at currents larger than 10 mA. The pulsed (I) – (V) characteristics with up to 400-mA maximum current were limited by the cathode resistance, consisting of the emitting layer resistance and the contact resistance, which was found to be between 1.1 and 1.4 kohm . A constant-voltage behavior arises after subtracting the cathode resistance. This constant-voltage behavior, the observed glowing during FE, and time-resolved measurements give evidence for the transition of Fowler–Nordheim-type FE to FE enhanced GD. FE enables a soft transition to normal GD without the need of an ignition voltage. The buildup dynamic and the time constants of the transition to GD were evaluated and discussed. The FE and GD behaviors were also compared using copper and molybdenum anodes.

Some Studies of the Axial Emission Ionization Gauge

SHINKU, 1994

An axial emission ionization gauge with an electrode construction similar to that of J. Z. Chen a... more An axial emission ionization gauge with an electrode construction similar to that of J. Z. Chen and C. D. Suen (An axial-emission ultrahigh vacuum gauge. J. Vac. Sci. & Technol. 20(1), 88-91 (1982)) was studied experimentally with respect to its applicability as a calibration gauge for use in the UHV range. The optimum operation parameters were determined experimentally. At these values of the operation parameters the sensitivity is smaller than that in the publication of Chen and Suen. In contrast with the ionization gauge of the extractor type, the sensitivity of the modified axial emission gauge depends only very weakly on the electron current and pressure, so that its application as calibration gauge in the UHV region seems possible from this point of view. In the low-pressure region, the influence of gas exposure on the pressure reading was studied for a gauge with a molybdenum anode and one with a platinum anode. In both cases the electron-stimulated desorption (ESD) caused errors in the pressure reading. If a platinum anode was used, the influence of hydrogen was larger than that of oxygen. In the case of a molybdenum anode, the influence of oxygen was larger than that of hydrogen. This behavior is accounted for by the greater adsorption of hydrogen on platinum. The experiments on the ESD demonstrate that the axial emission gauge has a somewhat lower collection efficiency for ESD ions generated on the anode surface than for those generated by electron impact in the space surrounded by the grid. This is in conformity with some calculations of ion trajectories performed with the program SIMION.

Formation of a nano-emitter for electron field emission on a liquid metal ion source tip after solidification of the alloy

Vacuum, 2002

Liquid metal ion sources (LMISs) operating with solidified Au alloys can be used as high-intensit... more

Carbon Buckypaper field emission investigations

Vacuum, 2002

We investigated Carbon Buckypaper with respect to field emission properties, especially long-term... more We investigated Carbon Buckypaper with respect to field emission properties, especially long-term field emission stability and under well-defined stress conditions. The Carbon Buckypaper field emitters showed a threshold field strength of about 1 V mm À1 for an emission current of 1 nA. Field emission current densities of more than 10 mA cm À2 are measured for higher applied field strengths. The main focus of our current investigations is the interaction of field emission and vacuum conditions. In this contribution reproducible stress tests with controlled micro-discharges are presented. At higher emission current densities of about 100 mA cm À2 increased ionization and even luminescence out of the emission zone appears before the micro-discharges start. After arcing with micro-discharges the Carbon Buckypaper field emission has lower emission current density and lower variation range. However, the contribution demonstrates the advantages of Carbon Buckypaper as a large array electron field emitter for cold cathode applications.

Theoretical and experimental desorption investigations at ionization gauges

Vacuum, 1996

ABSTRACT We have investigated the disturbing influence of outgassing and desorption effects on th... more ABSTRACT We have investigated the disturbing influence of outgassing and desorption effects on the pressure reading of three different types of ionization gauges with different methods. The behaviour of these gauges after exposure to gases, which are important in the Ultra-High-Vacuum region, after variation of the electron current, and for different potentials of the electrodes were studied. We have also determined the influence of the grid material on the outgassing and desorption effects for the Chen-Suen gauge.General statements of the influence of desorption phenomena on the pressure reading of ionization gauges at the lower pressure limit are given.

New high capacity getter for vacuum insulated mobile LH2 storage tank systems

Vacuum, 2007

Current ''Non-evaporable getters'' (NEGs) are important for the improvement of vacuum by the help... more Current ''Non-evaporable getters'' (NEGs) are important for the improvement of vacuum by the help of metallic surface sorption of residual gas molecules. High porosity alloys or powder mixtures of Zr, Ti, Al, V, Fe and other metals are the base material for this kind of gas sorbents. The development of vacuum technologies creates new challenges for the field of getter materials. The main sorption parameters of the current NEGs, namely, pumping speed and sorption capacity, have reached certain level limits. Chemically active metals are the basis of NEGs of a new generation. The appearance of new materials with high sorption capacity at room temperature is a long-felt need. It is obvious, that chemically active metals and alloys with reactivity higher, than that of transition metals, can become this kind of materials. The potential of active metals as the strongest gas sorbents is very high. The improved getter materials allow faster pumping speed. The sticking rate on the chemically active surface is significantly higher, and sorption capacity can be increased by up to 104 times (during the lifetime of a device the entire getter material reacts with residual gases). The main structural form of the new getter concepts are spherical powders, granules and porous multi-layers. The full pumping performance takes already place at room temperature and the activation temperature can be adjusted between room temperature and 660 1C. The successful insertion of this new chemical getter pump in a mobile double-walled LH 2 tank system shows the very high sorption capacity of all relevant residual gases including H 2. This new invention opens the possibility for significant vacuum improvements especially in the field of H 2 pumping, which is an important challenge in many different vacuum devices and processes.

Control of hot-filament ionization gauge emission current: mathematical model and model-based controller

Measurement Science and Technology, 1997

ABSTRACT The lack of adequate models for feedback-controlled emission current in hot-filament cat... more ABSTRACT The lack of adequate models for feedback-controlled emission current in hot-filament cathode ionization gauges (IGs) makes it difficult to achieve precision control over a wide range of emission currents (0.01 - 10 mA). A nonlinear mathematical model for transforming the filament heating power into emission current is developed. Experimental and theoretical results are shown. An electron emission regulator is described which was designed for use in the calibration of IGs, mass spectrometers and vapour rate measurements with IGs.

Hydrogen isotope inventories in the ASDEX Upgrade tungsten coated divertor tiles

Journal of Nuclear Materials, 1999

The total hydrogen isotope inventories in the tungsten coated divertor tiles of ASDEX Upgrade wer... more The total hydrogen isotope inventories in the tungsten coated divertor tiles of ASDEX Upgrade were measured by thermal desorption spectroscopy and 7 in the near surface region w by nuclear reaction analysis. The highest amounts of deuterium (:55x103: D /m3) are measured in the inner divertor region outside the separatrix due to the formation of a GE layer on the tungsten by codeposition of deuterium with carbon. The inventories in the outer divertor 7 where erosion dominates-are generally smaller by an order of magnitude.