@article{PrommesbergerBachmannDuesbergetal., author = {Prommesberger, Christian and Bachmann, Michael and D{\"u}sberg, Felix and Langer, Christoph and Ławrowski, Robert Damian and Hofmann, Martin and Pahlke, Andreas and Schreiner, Rupert}, title = {Regulation of the Transmitted Electron Flux in a Field-Emission Electron Source Demonstrated on Si Nanowhisker Cathodes}, series = {IEEE Transactions on Electron Devices}, volume = {64}, journal = {IEEE Transactions on Electron Devices}, number = {12}, publisher = {IEEE}, issn = {5128-5133}, doi = {10.1109/TED.2017.2763239}, abstract = {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.}, language = {en} } @article{LangerBomkeHausladenetal., author = {Langer, Christoph and Bomke, Vitali and Hausladen, Matthias and Ławrowski, Robert Damian and Prommesberger, Christian and Bachmann, Michael and Schreiner, Rupert}, title = {Silicon Chip Field Emission Electron Source Fabricated by Laser Micromachining}, series = {Journal of Vacuum Science \& Technology B}, volume = {38}, journal = {Journal of Vacuum Science \& Technology B}, number = {1}, publisher = {AIP Publishing}, doi = {10.1116/1.5134872}, abstract = {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.}, language = {en} } @article{BreuerBachmannDuesbergetal., author = {Breuer, Janis and Bachmann, Michael and D{\"u}sberg, Felix and Pahlke, Andreas and Edler, Simon and Langer, Christoph and Prommesberger, Christian and Ławrowski, Robert Damian and Schreiner, Rupert and Serbun, Pavel and L{\"u}tzenkirchen-Hecht, Dirk}, title = {Extraction of the current distribution out of saturated integral measurement data of p-type silicon field emitter arrays}, series = {Journal of Vacuum Science and Technology B}, volume = {36}, journal = {Journal of Vacuum Science and Technology B}, number = {5}, publisher = {AIP Publishing}, doi = {10.1116/1.5035189}, abstract = {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.}, language = {en} } @article{EdlerBachmannBreueretal., author = {Edler, Simon and Bachmann, Michael and Breuer, Janis and Dams, Florian and D{\"u}sberg, Felix and Hofmann, Martin and Jakšič, Jasna and Pahlke, Andreas and Langer, Christoph and Ławrowski, Robert Damian and Prommesberger, Christian and Schreiner, Rupert}, title = {Influence of adsorbates on the performance of a field emitter array in a high voltage triode setup}, series = {Journal of Applied Physics}, volume = {122}, journal = {Journal of Applied Physics}, doi = {10.1063/1.4987134}, abstract = {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.}, language = {en} } @article{LangerPrommesbergerŁawrowskietal., author = {Langer, Christoph and Prommesberger, Christian and Ławrowski, Robert Damian and Schreiner, Rupert and Serbun, Pavel and M{\"u}ller, G{\"u}nter and D{\"u}sberg, Felix and Hofmann, Martin and Bachmann, Michael and Pahlke, Andreas}, title = {Field emission properties of p-type black silicon on pillar structures}, series = {Journal of Vacuum Science \& Technology B}, volume = {34}, journal = {Journal of Vacuum Science \& Technology B}, number = {2}, doi = {10.1116/1.4943919}, abstract = {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.}, language = {en} } @article{BachmannDamsDuesbergetal., author = {Bachmann, Michael and Dams, Florian and D{\"u}sberg, Felix and Hofmann, Martin and Pahlke, Andreas and Langer, Christoph and Ławrowski, Robert Damian and Prommesberger, Christian and Schreiner, Rupert and Serbun, Pavel and L{\"u}tzenkirchen-Hecht, Dirk and M{\"u}ller, G{\"u}nter}, title = {Extraction of the characteristics of current-limiting elements from field emission measurement data}, series = {Journal of Vacuum Science \& Technology B}, volume = {35}, journal = {Journal of Vacuum Science \& Technology B}, number = {2}, doi = {10.1116/1.4971768}, abstract = {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.}, language = {en} } @inproceedings{LangerHausladenPrommesbergeretal., author = {Langer, Christoph and Hausladen, Matthias and Prommesberger, Christian and Ławrowski, Robert Damian and Bachmann, Michael and D{\"u}sberg, Felix and Pahlke, Andreas and Shamonin (Chamonine), Mikhail and Schreiner, Rupert}, title = {Field emission current investigation of p-type and metallized silicon emitters in the frequency domain}, series = {International Vacuum Nanoelectronics Conference (IVNC), 31st, 2018, Kyoto, Japan}, booktitle = {International Vacuum Nanoelectronics Conference (IVNC), 31st, 2018, Kyoto, Japan}, publisher = {IEEE}, doi = {10.1109/IVNC.2018.8520127}, pages = {1-2}, abstract = {We investigated two different field emitter arrays consisting of 10×10 p-type and 10×10 undoped Au-coated high aspect ratio silicon tips. The I-V characterization of the p-type sample showed a pronounced saturation for voltages higher than 500 V and a maximum emission current of 39 nA. The metallized sample revealed a FN-like emission up to several μA. The metallized and the p-type sample operating below the saturation region showed high current fluctuations of ±16\%. Whereas, the metallized sample with current regulation and the p-type sample in the saturation yielded a current stability of ±0.4\% and ±0.3\%, respectively. Investigations in the frequency domain revealed the for field emission typical 1/f-noise. By operating in the saturation region (p-type sample) or using an emission current regulation (metallized sample) the noise level was reduced by at least 20 dB. Finally, the p-type sample was illuminated by a light emitting diode to increase and modulate the emission current in the saturation region. The emission current was increased by a factor of 3.7 to 145 nA. With this configuration we emulated an unstable emission behavior and evaluated the performance of our emission current regulation circuit.}, language = {en} } @inproceedings{BachmannDamsDuesbergetal., author = {Bachmann, Michael and Dams, Florian and D{\"u}sberg, Felix and Hofmann, Martin and Pahlke, Andreas and Langer, Christoph and Ławrowski, Robert Damian and Prommesberger, Christian and Schreiner, Rupert}, title = {Extraction of the characteristics of limiting elements from field emission measurement data}, series = {29th International Vacuum Nanoelectronics Conference (IVNC), 2016, 11-15 July, Vancouver, BC, Canada}, booktitle = {29th International Vacuum Nanoelectronics Conference (IVNC), 2016, 11-15 July, Vancouver, BC, Canada}, publisher = {IEEE}, issn = {2380-6311}, doi = {10.1109/IVNC.2016.7551474}, pages = {81 -- 82}, abstract = {In this contribution we will present an algorithm to extract the characteristics of non-Fowler-Nordheim (FN) circuit elements from saturation limited field emission (FE) measurement data. The method for calculating the voltage drop on limiting circuit elements is based on circuit theory as well as Newton's method. Since no assumption on the limiting circuit is made, this method is applicable to any FE data showing saturation. To be able to determine the significance of any parameter output, the uncertainties of data and extracted parameters are fully taken into account throughout the algorithm. External serial resistors and a limiting p-doped substrate are analyzed, where the latter shows a diode-like behavior.}, language = {en} } @inproceedings{BachmannDamsDuesbergetal., author = {Bachmann, Michael and Dams, Florian and D{\"u}sberg, Felix and Hofmann, Martin and Pahlke, Andreas and Langer, Christoph and Ławrowski, Robert Damian and Prommesberger, Christian and Schreiner, Rupert}, title = {Control of the electron source current}, series = {International Vacuum Nanoelectronics Conference (IVNC), 30th, 2017, Regensburg}, booktitle = {International Vacuum Nanoelectronics Conference (IVNC), 30th, 2017, Regensburg}, publisher = {IEEE}, doi = {10.1109/IVNC.2017.8051550}, pages = {66 -- 67}, abstract = {A control circuit to stabilize the flux of electrons transmitted through an extractor electrode is presented. By controlling the emission current a fluctuation with a standard deviation of 0.015\% is observed. However, the achievable stability of the transmitted electron current is limited due to a variation of the extraction grid current ratio showing a standard deviation of 4.33\%. By regulating the difference of the emission current and the extraction grid current an improved stability of the transmitted electron current down to a standard deviation of 0.280\% is observed. Even with operation at 2 × 10 -5 mbar a standard deviation of 0.558\% is achieved.}, language = {en} } @article{BachmannDuesbergPahlkeetal., author = {Bachmann, Michael and D{\"u}sberg, Felix and Pahlke, Andreas and Edler, Simon and Schels, Andreas and Herdl, Florian and Ławrowski, Robert Damian and Schreiner, Rupert}, title = {High current silicon nanowire field emitter arrays}, series = {Journal of Vacuum Science \& Technology B}, volume = {40}, journal = {Journal of Vacuum Science \& Technology B}, number = {1}, publisher = {AIP Publishing}, doi = {10.1116/6.0001639}, abstract = {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.}, language = {en} } @inproceedings{ŁawrowskiBachmannSchreiner, author = {Ławrowski, Robert Damian and Bachmann, Michael and Schreiner, Rupert}, title = {Field Emission Arrays from Graphite Fabricated by Laser Micromachining}, series = {34th International Vacuum Nanoelectronics Conference (IVNC): 7/5/2021 - 7/9/2021, Lyon, France}, booktitle = {34th International Vacuum Nanoelectronics Conference (IVNC): 7/5/2021 - 7/9/2021, Lyon, France}, publisher = {IEEE}, isbn = {978-1-6654-2589-6}, doi = {10.1109/IVNC52431.2021.9600736}, pages = {1 -- 2}, abstract = {Arrays of 4x4 conical shaped emitters were directly structured by laser micromaching. Assembled as an electron source with a spacer and Si-grid, they were investigated by means of IV-measurement in ultra-high vacuum. The IV-measurements of the sample show integral emission currents up to 10 µA at a voltage of 1000 V (11 MV/m). Initially, an ideal FN-behaviour is noticeable. The deviation for higher voltage values in the FN-plot is caused by the change of the work function, which was proven by numerical calculations.}, language = {en} } @inproceedings{LangerŁawrowskiPrommesbergeretal., author = {Langer, Christoph and Ławrowski, Robert Damian and Prommesberger, Christian and Dams, Florian and Serbun, Pavel and Bachmann, Michael and M{\"u}ller, G{\"u}nter and Schreiner, Rupert}, title = {High aspect ratio silicon tip cathodes for application in field emission electron sources}, series = {2014 27th International Vacuum Nanoelectronics Conference (IVNC), 6-10 July 2014, Engelberg, Switzerland}, booktitle = {2014 27th International Vacuum Nanoelectronics Conference (IVNC), 6-10 July 2014, Engelberg, Switzerland}, publisher = {IEEE}, doi = {10.1109/IVNC.2014.6894824}, pages = {222 -- 223}, abstract = {Precisely aligned arrays of sharp tip structures on top of elongated pillars were realized by using an improved fabrication process including an additional inductively-coupled-plasma reactive-ion etching step. Arrays of n-type and p-type silicon with 271 tips have been fabricated and investigated. Those structures have a total height of 5-6 µm and apex radii less than 20nm. Integral field emission measurements of the arrays yielded low onset-fields in the range of 8-12V=µm and field enhancement factors between 300 and 700. The I-E curves of n-type structures showed the usual Fowler-Nordheim behaviour, whereas p-type structures revealed a significant saturation region due to the limited number of electrons in the conduction band and a further carrier depletion effect caused by the pillar. The maximum integral current in the saturation region was 150 nA at fields above 30V=µm. An excellent stability of the emission current of less than ± 2\% fluctuation was observed in the saturation region. For n-type Si a maximum integral current of 10 µA at 24V=µm and an average current stability with a fluctuation of ± 50\% were measured.}, language = {en} } @article{BachmannDuesbergLangeretal., author = {Bachmann, Michael and D{\"u}sberg, Felix and Langer, Christoph and Herdl, Florian and Bergbreiter, Lukas and Dams, Florian and Miyakawa, Natuski and Eggert, Tobias and Pahlke, Andreas and Edler, Simon and Prommesberger, Christian and Ławrowski, Robert Damian and Hausladen, Matthias and Schreiner, Rupert}, title = {Vacuum-sealed field emission electron gun}, series = {Journal of Vacuum Science \& Technology B}, volume = {38}, journal = {Journal of Vacuum Science \& Technology B}, number = {2}, publisher = {AIP Publishing}, doi = {10.1116/1.5139316}, abstract = {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.}, language = {en} } @article{ŁawrowskiBachmannSchreiner, author = {Ławrowski, Robert Damian and Bachmann, Michael and Schreiner, Rupert}, title = {Field emission arrays from graphite fabricated by laser micromachining}, series = {Journal of Vacuum Science \& Technology B}, volume = {40}, journal = {Journal of Vacuum Science \& Technology B}, number = {2}, publisher = {AIP Publishing}, doi = {10.1116/6.0001547}, abstract = {Laser micro structuring allows the manufacturing of conical shaped emitters on a graphitized carbon substrate without any additional treatment. Integral field emission measurements were performed in a diode configuration with a 50 µm mica spacer and a metalized Si-grid in a vacuum chamber at pressures of about 10-9 mbar. Emission currents up to 10 µA at a voltage of 1000 V (11 MV/m) with a positive current drift were observed for an array of 16 emitters. A strong modification of the emitter tip is noticeable after individual measurements. A comparable alteration of the surface is also achieved by an electrochemical treatment of the samples with a potassium hydroxide solution. However, the IV-measurements of such samples show higher onset voltages, but also higher integral emission currents. For all arrays an ideal FN behaviour is only noticeable at applied voltages below 625 V (7 MV/m). Numerical calculations indicate that the deviation in the FN-plot for higher voltage values is caused by the change of the effective work function.}, language = {en} } @inproceedings{ŁawrowskiLangerPrommesbergeretal., author = {Ławrowski, Robert Damian and Langer, Christoph and Prommesberger, Christian and Dams, Florian and Bachmann, Michael and Schreiner, Rupert}, title = {Fabrication and simulation of silicon structures with high aspect ratio for field emission devices}, series = {2014 27th International Vacuum Nanoelectronics Conference (IVNC), 6-10 July 2014, Engelberg, Switzerland}, booktitle = {2014 27th International Vacuum Nanoelectronics Conference (IVNC), 6-10 July 2014, Engelberg, Switzerland}, publisher = {IEEE}, doi = {10.1109/IVNC.2014.6894805}, pages = {193 -- 194}, abstract = {To obtain higher field enhancement factors of Si-tip structures, we present an improved fabrication process utilizing reactive-ion etching (RIE) with an inductively coupled plasma (ICP). In our design, a pillar under the tips is realized by a combination of RIE with ICP. With adjusted power settings (≈ 240 W) and step times (<; 5 s), vertical slopes with a low roughness of approximately 10 nm to 20 nm are possible. The remaining silicon is oxidized thermally to sharpen the emitters. A final tip radius of R <; 20 nm is obtained for the tips of the emitters. The pillar height HP can be mainly adjusted by the duration of the ICP-etching step. A total emitter height of H ≈ 6 μm with a pillar height of HP ≈ 5 μm is achieved. Simulations with COMSOL Multiphysics® are applied to calculate the field enhancement factor β. A two-dimensional model is used in rotational symmetry. In addition to the previous model, a pillar with a varying diameter {\O}P and height HP is added. A conventional emitter (H = 1 μm and R = 20 nm) placed on a pillar of the height HP ≈ 5 μm approximately results in a three times higher β-factor (β≈ 105). By decreasing the diameter {\O}P a slight increase of the β-factor is observed. However, the aspect ratio of the emitter mainly influences on the β-factor.}, language = {en} } @inproceedings{BachmannDamsDuesbergetal., author = {Bachmann, Michael and Dams, Florian and D{\"u}sberg, F. and Hofmann, Martin and Pahlke, Andreas and Langer, Christoph and Ławrowski, Robert Damian and Prommesberger, Christian and Schreiner, Rupert}, title = {Stability investigation of high aspect ratio n-type silicon field emitter arrays}, series = {2015 28th International Vacuum Nanoelectronics Conference (IVNC), 13-17 July 2015, Guangzhou, China}, booktitle = {2015 28th International Vacuum Nanoelectronics Conference (IVNC), 13-17 July 2015, Guangzhou, China}, publisher = {IEEE}, doi = {10.1109/IVNC.2015.7225584}, pages = {204 -- 205}, abstract = {Electron sources based on silicon field emitter arrays, produced in processes based on semiconductor technology, are good candidates for a miniaturized X-ray source. A key parameter for this application is the stability of the X-ray photon flux and, thus, the emission current. In the present work we have investigated the influence of the residual gas pressure and a resistor in series on the emission stability of a high aspect ratio n-type silicon emitter array with hybrid extraction electrode. An increase of current fluctuations was found for pressures above 10-6 mbar. High resistances in series to the emitter array alter the emission characteristics, but greatly suppress spikes in the emission current and improve its stability. This, however, strongly depends on the bias point. The field enhancement factor is not affected by the resistance. In a long term measurement the emission current was found to be constant after an initial phase of degradation.}, language = {en} } @article{ŁawrowskiPirkerKanekoetal., author = {Ławrowski, Robert Damian and Pirker, Luka and Kaneko, Keita and Kokubo, Hiroki and Bachmann, Michael and Ikuno, Takashi and Remskar, Maja and Schreiner, Rupert}, title = {Field emission from nanotubes and flakes of transition metal dichalcogenides}, series = {Journal of Vacuum Science and Technology B}, volume = {38}, journal = {Journal of Vacuum Science and Technology B}, number = {3}, publisher = {AIP Publishing}, doi = {10.1116/1.5140474}, pages = {032801}, abstract = {Transition metal dichalcogenides such as MoS2 and WS2 are low-dimensional semiconductor materials. MoS2 and WS2 nanotubes and flakes were grown by a chemical transport reaction under a temperature gradient. I2 was used as a transport agent for previously synthesized MoS2 and WS2, respectively. These multilayered nanotubes are indirect bandgap semiconductors with a bandgap depending on their diameter. WS2 flakes were prepared by the sulfurization of thin WOx flakes. To increase the field enhancement of such low-dimensional structures by a higher aspect ratio, two approaches were examined: (a) the MoS2 and WS2 nanotubes were attached individually by a focused ion beam with Pt on dry etched n-type Si pillars and (b) the WS2 flakes were grown directly on the surface of the (n-type and p-type) Si pillars. Integral field emission measurements were performed in a diode configuration with a 50 μm mica spacer in a vacuum chamber at pressures of about 10-9 mbar. At a voltage of 900 V (18 MV/m), the integral emission current from the nanotubes is up to 11 μA for the lateral mounted MoS2 and about 1.3 μA (1.0 μA) for the upright mounted WS2 (MoS2). The onset voltage for a current of 1 nA is about 550 V for MoS2 and 500 V for WS2, respectively. The voltage conversion factor is in the range of 6 × 104-8 × 104 cm-1 for the nanotubes. The mounted MoS2 flakes show a field emission current of about 6 μA at 18 MV/m in contrast to the directly grown WS2 flakes, which show a pronounced saturation regime and, therefore, a lower emission current of about 0.5 μA is reached at 1500 V (25 MV/m). The WS2 flakes show a two times higher (1 × 105 cm-1) voltage conversion factor in comparison to the MoS2 flakes (5 × 104 cm-1). The extracted characteristics of the current-limiting part show a difference in the behavior of the extracted current-limiting characteristics between the lateral (linear) and upright mounted (exponential) nanotubes and the MoS2 flakes. In contrast, the WS2 flakes show charge carrier depletion effects.}, language = {en} } @inproceedings{SerbunPorshynMuelleretal., author = {Serbun, Pavel and Porshyn, Vitali and M{\"u}ller, G{\"u}nter and Mingels, Stephan and L{\"u}tzenkirchen-Hecht, Dirk and Bachmann, Michael and D{\"u}sberg, Felix and Dams, Florian and Hofmann, Martin and Pahlke, Andreas and Prommesberger, Christian and Langer, Christoph and Ławrowski, Robert Damian and Schreiner, Rupert}, title = {Field emission behavior of Au-tip-coated p-type Si pillar structures}, series = {29th International Vacuum Nanoelectronics Conference (IVNC), 2016, 11-15 July, Vancouver, BC, Canada}, booktitle = {29th International Vacuum Nanoelectronics Conference (IVNC), 2016, 11-15 July, Vancouver, BC, Canada}, publisher = {IEEE}, issn = {2380-6311}, doi = {10.1109/IVNC.2016.7551516}, pages = {181 -- 182}, abstract = {Precisely aligned high-aspect-ratio (HAR) silicon tip arrays were fabricated using enhanced reactive ion etching with an inductively-coupled-plasma followed by a sharpening oxidation. A gold thin film was then sputtered only on the tips of the HAR structures. Field-emission (FE) properties from Au-coated HAR p-Si tip array cathodes have been systematically investigated by means of field emission scanning microscopy (FESM). A rather high efficiency of the HAR Si structures (71\% at 550 V), but limited homogeneous FE with currents of 1-600 nA might be correlated with the varying geometry of the tips and the presence of oxides. I-V measurements of single Au-coated HAR emitters revealed activation effects and the saturation current region at 3 nA. An increase of the saturation current by 4 orders of magnitude was observed during 20 hours of conditioning at constant voltage, which finally resulted in nearly reproducible FN curves with a ß-factor of 473. An excellent stability of the emission current of less than 1 \% was obtained during the additional long-time conditioning at constant voltage. Optical switching under halogen lamp illumination resulted in at least 2 times higher saturation currents and showed a linear dependence of the FE current on the light color temperature.}, language = {en} } @inproceedings{SchreinerLangerPrommesbergeretal., author = {Schreiner, Rupert and Langer, Christoph and Prommesberger, Christian and Ławrowski, Robert Damian and Dams, Florian and Bachmann, Michael and D{\"u}sberg, F. and Hofmann, Martin and Pahlke, Andreas and Serbun, Pavel and Mingels, Stephan and M{\"u}ller, G{\"u}nter}, title = {Semiconductor field emission electron sources using a modular system concept for application in sensors and x-ray-sources}, series = {2015 28th International Vacuum Nanoelectronics Conference (IVNC), 13-17 July 2015, Guangzhou, China}, booktitle = {2015 28th International Vacuum Nanoelectronics Conference (IVNC), 13-17 July 2015, Guangzhou, China}, publisher = {IEEE}, doi = {10.1109/IVNC.2015.7225572}, pages = {178 -- 179}, abstract = {Semiconductor field emitters are suitable candidates for applications, which require a very stable field emission (FE) current and a high emission uniformity over the entire emission area. By using different materials and geometries, we are able to vary the FE characteristics within a wide range. Each specific application requires its own optimized design for the cathode as well as for the other parts of the FE electron source. To meet as many of these requirements as possible while using only a limited number of different prefabricated components, we established a modular system concept for our FE electron source. This allows the implementation of almost every cathode material. For first characterizations, we used gated p-type Si cathodes with 16 tips. We obtained stable FE currents of 0.4 μA for a grid-potential of 400 V and a gate potential of 100 V. Almost 100\% of the electrons are emitted towards the grid-electrode. Parasitic leakage paths, as well as the electron emission towards the gate-electrode can be neglected. Approximately 10\% of the electrons are transmitted through the grid and reach the external anode. This is in good agreement with the optical transmission through the grid-mesh.}, language = {en} }