TY - JOUR A1 - Prommesberger, Christian A1 - Bachmann, Michael A1 - Düsberg, Felix A1 - Langer, Christoph A1 - Ławrowski, Robert Damian A1 - Hofmann, Martin A1 - Pahlke, Andreas A1 - Schreiner, Rupert T1 - Regulation of the Transmitted Electron Flux in a Field-Emission Electron Source Demonstrated on Si Nanowhisker Cathodes JF - IEEE Transactions on Electron Devices N2 - We report on a method to stabilize the transmitted electron flux in a field-emission electron source using an external regulation circuit. The electron source was realized with an array of silicon (Si) nanowhiskers on the top of elongated pillar structures, a mica spacer, and an extraction grid made of Si. As for most applications, the emitted electron current from the cathode is not as crucial as the transmitted electron flux through the extraction grid toward the anode. We investigated a method which allows the regulation directly by the emitted electron flux and not merely on the cathode current. By using this method, we were able to stabilize the emitted electron flux of our electron source down to values below 1%. Simultaneously, it was shown that there is the possibility to stabilize the influencing value in the real application as well. The effectiveness of this method was demonstrated successfully with an X-ray source setup. The measured X-ray photon count rate was stabilized to a standard deviation of 0.30% at a pressure of 1 × 10 -7 mbar. Even in harsh environment of 2 × 10 -5 mbar, a stabilization of the X-ray photon count rate down to a value of 0.63% was achieved. KW - Cathodes KW - Nanostructured devices KW - Current measurement KW - Photonics KW - Electron sources KW - Emissions KW - Voltage measurement Y1 - 2017 U6 - https://doi.org/10.1109/TED.2017.2763239 SN - 5128-5133 VL - 64 IS - 12 PB - IEEE ER - TY - JOUR A1 - Langer, Christoph A1 - Bomke, Vitali A1 - Hausladen, Matthias A1 - Ławrowski, Robert Damian A1 - Prommesberger, Christian A1 - Bachmann, Michael A1 - Schreiner, Rupert T1 - Silicon Chip Field Emission Electron Source Fabricated by Laser Micromachining JF - Journal of Vacuum Science & Technology B N2 - The components for a silicon chip electron source were fabricated by laser micromachining using pulsed laser ablation and wet chemical cleaning and etching dips. The field emission electron source consists of a silicon field emission cathode with 4 × 4 conical shaped emitters with a height of 250 μm and a tip radius of about 50 nm, a 50 μm thick laser-structured mica spacer, and a silicon grid electrode with a grid periodicity of 200 μm and a bar width of 50 μm. These three components are combined to a single chip with the size of 14 × 10 mm2 and the thickness of 1 mm to form the electron source. Several of these devices were characterized in ultrahigh vacuum. Onset voltages of about 165 V and cathode currents of about 15 μA for voltages lower than 350 V were observed. Operating the electron source with an anode voltage of 500 V and an extraction grid voltage of 300 V yielded a cathode current of 4.5 μA ± 8.9%, an anode current of 4.0 μA ± 9.6%, and a corresponding grid transmittance of 89%. Regulating the anode current by the extraction grid voltage, an extremely stable anode current of 5.0 μA ± 0.017% was observed. A long-term measurement over 120 h was performed, and no significant degradation or failure was observed. KW - Ultra-high vacuum KW - Field emitter arrays KW - Etching KW - Electrical properties and parameters KW - Electron sources KW - Laser ablation KW - Laser micromachining KW - Silicon chip KW - Triodes Y1 - 2020 U6 - https://doi.org/10.1116/1.5134872 VL - 38 IS - 1 PB - AIP Publishing ER - TY - JOUR A1 - Breuer, Janis A1 - Bachmann, Michael A1 - Düsberg, Felix A1 - Pahlke, Andreas A1 - Edler, Simon A1 - Langer, Christoph A1 - Prommesberger, Christian A1 - Ławrowski, Robert Damian A1 - Schreiner, Rupert A1 - Serbun, Pavel A1 - Lützenkirchen-Hecht, Dirk T1 - Extraction of the current distribution out of saturated integral measurement data of p-type silicon field emitter arrays JF - Journal of Vacuum Science and Technology B N2 - At the moment, only complicated techniques are known for the determination of array properties of field emitter arrays such as the number of active tips, the current distribution, or the individual tip radii. In this work, a method for extracting these parameters from integral measurement data is presented. A model describing the characteristics of a single emitter, including the saturation as a function of the applied voltage and the emitter radius, is developed. It is shown that experimental data of field emitter arrays can be represented as the sum of these functions and the characteristic parameters can be fitted to field emission data of an array. Using this method, the values of the radii as well as the parameters of distribution models can be determined directly. Analysis of experimental data from p-type Si emitter arrays shows that only 1–2% of the tips contribute significantly. Y1 - 2018 U6 - https://doi.org/10.1116/1.5035189 VL - 36 IS - 5 PB - AIP Publishing ER - TY - JOUR A1 - Edler, Simon A1 - Bachmann, Michael A1 - Breuer, Janis A1 - Dams, Florian A1 - Düsberg, Felix A1 - Hofmann, Martin A1 - Jakšič, Jasna A1 - Pahlke, Andreas A1 - Langer, Christoph A1 - Ławrowski, Robert Damian A1 - Prommesberger, Christian A1 - Schreiner, Rupert T1 - Influence of adsorbates on the performance of a field emitter array in a high voltage triode setup JF - Journal of Applied Physics N2 - In the present work, black-silicon field emitter arrays (FEAs) are investigated regarding the influence of residual gas pressure on the characteristics and lifetime in the high voltage triode setup. Current-voltage-characteristics at different pressure levels are recorded and show a decreasing emission current with rising pressure. This decrease can be explained by an increase of the work function and charging of the emitter surface caused by adsorbates. The emission current can be restored to its initial value by heating of the FEA up to 110 °C during active emission. With this regeneration procedure, an extended lifetime from about 20 h to 440 h at a residual gas pressure of 10−5 mbar is achieved. Y1 - 2017 U6 - https://doi.org/10.1063/1.4987134 VL - 122 ER - TY - JOUR A1 - Langer, Christoph A1 - Prommesberger, Christian A1 - Ławrowski, Robert Damian A1 - Schreiner, Rupert A1 - Serbun, Pavel A1 - Müller, Günter A1 - Düsberg, Felix A1 - Hofmann, Martin A1 - Bachmann, Michael A1 - Pahlke, Andreas T1 - Field emission properties of p-type black silicon on pillar structures JF - Journal of Vacuum Science & Technology B N2 - Arrays of black silicon field emission pillar structures were fabricated on p-type silicon substrates. Two types of samples with the same number of pillars (arrays of 10 × 10) but different pillar heights (8 and 20 μm) were prepared as well as a black silicon reference sample without pillars. The field emission properties of these cathodes were investigated both by means of integral current-voltage measurements and by field emission scanning microscopy. Samples with a pillar height of 20 μm revealed onset fields as low as 6.4 V/μm, field enhancement factors up to 800, and emission currents up to 8 μA at an applied field of 20 V/μm. Due to the p-type material, a saturation of the emission current for fields above 11 V/μm was observed. This saturation leads to a stable operation with a current fluctuation of less than ±8%. It was found that samples with a pillar height of 20 μm showed improved emission characteristics compared to samples with a pillar height of 8 μm or without pillars. The voltage maps revealed an increased emission homogeneity after a “burn-in” sequence of the sample. The current map showed that a few of the pillars dominate the emission. Integral current stability measurements were performed under different vacuum pressures, in order to investigate altered emission behavior and a potential degradation of the emitters. At pressures above 10−6 mbar, the sample starts to degrade irreversibly. Nevertheless, even after a harsh treatment over 30 min at 5 × 10−5 mbar and at an applied field of 23 V/μm, the cathode was still operating, and did not fail during further operation over 20 h at 5 × 10−8 mbar and at an applied field of 28 V/μm. Y1 - 2016 U6 - https://doi.org/10.1116/1.4943919 VL - 34 IS - 2 ER - TY - JOUR A1 - Bachmann, Michael A1 - Dams, Florian A1 - Düsberg, Felix A1 - Hofmann, Martin A1 - Pahlke, Andreas A1 - Langer, Christoph A1 - Ławrowski, Robert Damian A1 - Prommesberger, Christian A1 - Schreiner, Rupert A1 - Serbun, Pavel A1 - Lützenkirchen-Hecht, Dirk A1 - Müller, Günter T1 - Extraction of the characteristics of current-limiting elements from field emission measurement data JF - Journal of Vacuum Science & Technology B N2 - In this contribution, the authors will present an algorithm to extract the characteristics of nonideal field emission circuit elements from saturation-limited field emission measurement data. The method for calculating the voltage drop on current-limiting circuit elements is based on circuit theory as well as Newton's method. Since the only assumption the authors make on the current-limiting circuit is a connection in series, this method is applicable to most field emission data showing saturation. To be able to determine the significance of any parameter output, the uncertainties of data and extracted parameters as well as the parameter correlations are fully taken into account throughout the algorithm. N-type silicon samples with varying external serial resistors are analyzed. All results show a good agreement to the nominal resistor values. Additionally, several p-type samples are analyzed, showing a diodelike behavior. The extracted current-limiting characteristics of the p-type samples are in good agreement with a pn-junction model. The stability of the emission current of the p-type samples is measured by constant voltage measurements and compared to the extracted current-limiting characteristics. The application of the algorithm to measurement data shows that the given algorithm is a valuable tool to analyze field emission measurement data influenced by nonemissive processes. Y1 - 2017 U6 - https://doi.org/10.1116/1.4971768 VL - 35 IS - 2 ER - TY - JOUR A1 - Prommesberger, Christian A1 - Langer, Christoph A1 - Ławrowski, Robert Damian A1 - Schreiner, Rupert T1 - Investigations on the long-term performance of gated p-type silicon tip arrays with reproducible and stable field emission behavior JF - Journal of Vacuum Science & Technology B N2 - The authors report on the fabrication and characterization of p-type Si tip arrays with an integrated gate electrode for applications as field emission electron sources. After the reactive ion etching of the emitters, the combined thermal dry and wet oxidation was used for both the sharpening of the emitters and for the realization of an enhanced insulation layer. Au was evaporated in a self-aligned process as gate electrode. Arrays of 16 Si tips were fabricated with tip heights of about 3 μm and tip radii of about 20 nm with integrated gate electrode concentrically positioned ≈2 μm below the tip apex. Integral measurements with an additional anode showed improved field emission properties with a reproducible and stable emission behavior. A fast activation of the tips, low onset voltages of about 30 V, and moderate field emission currents up to 0.55 μA were noticed. The field emission parameters were calculated using the Fowler–Nordheim characteristics. A pronounced saturation regime was observed, and current fluctuations of less than ±1% were investigated for 30 min. Long-term measurements were carried out for a period of more than 8 h. In the first 6 h of operation, the authors observed a drift of the emission current from 0.35 to 0.55 μA caused by an increased emission surface. Y1 - 2017 U6 - https://doi.org/10.1116/1.4972519 VL - 35 IS - 1 ER - TY - JOUR A1 - Ławrowski, Robert Damian A1 - Hausladen, Matthias A1 - Buchner, Philipp A1 - Schreiner, Rupert T1 - Silicon Field Emission Electron Source With Individually Controllable Single Emitters JF - IEEE Transactions on Electron Devices N2 - An electron source with an array of individually controllable single tips allows the observation of each emitter current simultaneously as well as the measurement of the integral current. Furthermore, the initial activation process of the individual tips and current distribution of the source can be examined. The Si cathode consists of an array of 2 x 2 conically shaped emitter structures on a borosilicate glass substrate. The emitters were fabricated by laser micromachining and wet etching. Integral field emission (FE) measurements were performed in a diode configuration in a vacuum chamber at pressures of about 10(-9) mbar with a self-aligned Si extraction grid, due to adjustment pins. The total emission current was regulated to a predefined value (4.0, 10, 20, 40, and 50 mu A) by an external regulating circuit and recorded individually during the measurement. The onset voltage for a current of 1 nA varied between 320 and 430 V. The voltage conversion factor is in the range of 7.6 x 10(4) cm(-1) to 1.3 x 10(5) cm(-1). Constant currentmeasurementsover a longer periodof time (1800 values with a sample rate of 0.5 Hz) were performed and show a total current fluctuation less than 0.6% due to the regulation circuit. Despite the stable total current in regulated operation, it was observed that the individual emitters fluctuate up to 75% for low (similar to 10(-8) A) and 5% for high (similar to 10(-5) A) currents. KW - Current distribution KW - current limiters KW - electron emission KW - electron sources KW - silicon-on-insulator Y1 - 2021 U6 - https://doi.org/10.1109/TED.2021.3093374 VL - 68 IS - 8 SP - 4116 EP - 4122 PB - IEEE ER - TY - JOUR A1 - Bachmann, Michael A1 - Düsberg, Felix A1 - Pahlke, Andreas A1 - Edler, Simon A1 - Schels, Andreas A1 - Herdl, Florian A1 - Ławrowski, Robert Damian A1 - Schreiner, Rupert T1 - High current silicon nanowire field emitter arrays JF - Journal of Vacuum Science & Technology B N2 - Arrays of n-doped silicon nanowire field emitters with a high aspect ratio are realized by a novel dry etching technique. Compared to the high current silicon emitters in the literature, the manufacturing process is much simpler and requires only a single photolithography step and two dry etching steps. The cathodes realized with this method exhibit a total current of 20 mA from an active area of 4×4 mm2, which is significantly higher than that for most known structures made from silicon and also represents good performance in comparison with other emitter types, e.g., carbon nanotubes. In addition to characterization in ultrahigh vacuum, measurements at 10−5 mbar are performed and compared with our recent silicon emitters. Compared to these cathodes, the structures with the nanowires exhibit at least two orders of magnitude higher current-carrying capability. Y1 - 2022 U6 - https://doi.org/10.1116/6.0001639 VL - 40 IS - 1 PB - AIP Publishing ER - TY - JOUR A1 - Remskar, Maja A1 - Hüttel, Andreas K. A1 - Shubina, Tatiana V. A1 - Seabaugh, Alan A1 - Fathipour, Sara A1 - Ławrowski, Robert Damian A1 - Schreiner, Rupert T1 - Confinement Related Phenomena in MoS2 Tubular Structures Grown from Vapour Phase JF - Israel Journal of Chemistry N2 - We review recently discovered phenomena observed in the MoS2 tubular structures, which were synthesized by a lasting chemical transport reaction nearly at chemical equilibrium. Such MoS2 nanotubes are distinguished by low density of structural defects, thin walls and a high aspect ratio, which intrinsically provide a confined, edge-free geometry. Quantum confinement with single electron conductance was recorded and a bright exciton photoluminescence with appearance of whispering gallery modes was observed. In addition, the field-effect transistors and field emitters based on single MoS2 nanotubes were demonstrated. These discoveries revitalize research of MoS2 curved structures grown from vapour phase, which were reported several decades ago. Y1 - 2021 U6 - https://doi.org/10.1002/ijch.202100100 SN - 1869-5868 VL - 62 IS - 3-4 SP - 1 EP - 11 PB - Wiley ER - TY - JOUR A1 - Bachmann, Michael A1 - Düsberg, Felix A1 - Langer, Christoph A1 - Herdl, Florian A1 - Bergbreiter, Lukas A1 - Dams, Florian A1 - Miyakawa, Natuski A1 - Eggert, Tobias A1 - Pahlke, Andreas A1 - Edler, Simon A1 - Prommesberger, Christian A1 - Ławrowski, Robert Damian A1 - Hausladen, Matthias A1 - Schreiner, Rupert T1 - Vacuum-sealed field emission electron gun JF - Journal of Vacuum Science & Technology B N2 - A compact vacuum-sealed field emission electron gun with an operation voltage below 5 kV is presented. With a 150 nm thick pyrolytic carbon membrane, a transmission of 40% at 5 kV is obtained. For more than 2500 h of continuous operation at an emission current of 100 nA, no significant increase (<50V ) and almost no degradation were found. From this measurement, a lifetime of more than 10 000 h at continuous operation with approximately a linear increase of the extraction voltage from about 545 V to about 730 V is predicted. This electron source enables application of field emitter arrays in poor vacuum or even ambient pressure. ACKNOWLEDGMENT This work was supported by the German Federal Ministry for Economic Affairs and Energy under Project No. ZF4081502GM8. C.P., R.L., M.H., and R.S. were supported by Grant No. ZF4562901GM8. Y1 - 2020 U6 - https://doi.org/10.1116/1.5139316 VL - 38 IS - 2 PB - AIP Publishing ER - TY - JOUR A1 - Langer, Christoph A1 - Prommesberger, Christian A1 - Ławrowski, Robert Damian A1 - Dams, Florian A1 - Schreiner, Rupert T1 - Simulation and Fabrication of Silicon Field Emission Cathodes for Cold Electron Sources JF - Advanced Materials Research N2 - We report on the simulation and fabrication of nanostructured silicon surfaces for field emission (FE) applications, e.g. ionization sensors and x-ray tubes. For the design and optimization of field-emitting silicon structures, the influence of the geometric parameters like tip height, apex radius, aperture angle and curvature shape on the field enhancement factor was investigated by simulation using finite element method. A universal geometric model which describes the real geometry of our silicon structures sufficiently accurate was taken for modeling a variety of different silicon tip structures as well as ridge structures. While a high dependency of the field enhancement on the aspect ratio and the aperture angle was found, the simulations show that the elliptic curvature affects the field enhancement only marginally. Finally, an improved process for fabrication of such silicon structures on n-type as well as p-type substrate is described, using reactive ion etching with adjustable anisotropy, wet thermal oxidation and wet etching. KW - field emission cathodes KW - field enhancement factor KW - silicon field emitter Y1 - 2014 U6 - https://doi.org/10.4028/www.scientific.net/amr.1024.48 VL - 1024 SP - 48 EP - 51 ER -