In this work we demonstrate that ultra-thin (5 and 15 nm) MgO transmission dynodes with sufficient high transmission electron yield (TEY) can be constructed. These transmission dynodes act as electron amplification stages in a novel vacuum electron multiplier: the Timed Photon Counter. The ultra-thin membranes with a diameter of 30 μm are arranged in a square 64-by-64-array. The TEY was determined with a scanning electron microscope using primary electrons with primary energies of 0.75-5 keV. The method allows a TEY map of the surface to be made while simultaneously imaging the surface. The TEY of individual membranes can be extracted from the TEY map. An averaged maximum TEY of 4.6±0.2 was achieved by using 1.35 keV primary electrons on a TiN/MgO bi-layer membrane with a layer thickness of 2 and 5 nm, respectively. The TiN/MgO membrane with a layer thickness of 2 and 15 nm, respectively, has a maximum TEY of 3.3±0.1 (2.35 keV). Furthermore, the effect of the electric field strength on transmission (secondary) electron emission was investigated by placing the emission surface of a transmission dynode in close proximity to a planar collector. By increasing the electric potential between the transmission dynode and the collector, from -50 V to -100 V, the averaged maximum TEY improved from 4.6±0.2 to 5.0±0.3 at a primary energy of 1.35 keV with an upper limit of 5.5 on one of the membranes.

@en

Large-area transmission dynodes were fabricated by depositing an ultra-thin continuous film on a silicon wafer with a 3-dimensional pattern. After removing the silicon, a corrugated membrane with enhanced mechanical properties was formed. Mechanical metamaterials, such as this corrugated membrane, are engineered to improve its strength and robustness, which allows it to span a larger surface in comparison to flat membranes while the film thickness remains constant. The ultra-thin film consists of three layers (Al₂O₃/TiN/Al₂O₃) and is deposited by atomic layer deposition (ALD). The encapsulated TiN layer provides in-plane conductivity, which is needed to sustain secondary electron emission. Two types of corrugated membranes were fabricated: a hexagonal honeycomb and an octagonal pattern. The latter was designed to match the square pitch of a CMOS pixel chip. The transmission secondary electron yield was determined with a collector-based method using a scanning electron microscope. The highest transmission electron yield was measured on a membrane with an octagonal pattern. A yield of 2.15 was achieved for 3.15 keV incident electrons for an Al₂O₃/TiN/Al₂O₃ tri-layer film with layer thicknesses of 10/5/15 nm. The variation in yield across the surface of the corrugated membrane was determined by constructing a yield map. The active surface for transmission secondary electron emission is near 100%, i.e. a primary electron generates transmission secondary electrons regardless of the point of impact on the corrugated membrane.

@en

The (secondary) electron emission from multilayered Al2O3/TiN membranes has been investigated with a hemispherical collector system in a scanning electron microscope for electrons with energies between 0.3 and 10 keV. These ultra-thin membranes are designed to function as transmission dynodes in novel vacuum electron multipliers. Two different types, a bi-layer and a tri-layer, have been manufactured by means of atomic-layer deposition (ALD) of aluminum oxide and sputtering of titanium nitride. The reflection and transmission electron yield (σR, σT) have been measured for both types of membranes. In comparison, the tri-layer membranes outperformed the bi-layer membranes in terms of transmission electron yield for films with the same effective thickness. The highest transmission electron yield was measured on an Al2O3/TiN/Al2O3 film with layer thicknesses of 5/2.5/5 nm, which had a maximum transmission electron yield {σ T max(E0) of 3.1 (1.55 keV). Furthermore, the bi-layer membranes have been investigated more in-depth by performing an additional measurement using a positive sample bias to separate the transmitted fraction ηT and the transmission secondary electron yield δT. The transmitted fraction was used to determine the transmission parameter p, which characterizes the interaction of primary electrons (PEs) in thin films. The transmission secondary electron yield was used to compare the energy transfer of PEs in films with different thicknesses.

@en

For decades, photomultiplier tubes (PMTs) have been the most common choice in single photon detection, covering the spectral range from deep-ultraviolet to nearinfrared. PMT is a vacuum tube with three crucial components: photocathode, chain of dynodes and anode. At the photocathode, photons are converted to electrons in a photoelectric effect, after which they are directed to the dynodes chain. The material and geometry of dynodes are chosen to efficiently amplify the charge through the secondary electron emission (in reflection mode). Finally, created avalanche of electrons is collected and measured by the anode. Timed Photon Counter (TiPC) is a novel vacuum-based photomultiplier proposed to overcome limitations of PMTs in terms of size, speed, spatial resolution and operation in the presence of magnetic field. The key novelty of TiPC is a tynode – a large-size array of ultra-thin, free-standing membranes which, in contrast to dynodes, multiply electrons in the transmission mode. Due to the short and straight crossing paths of electrons between subsequent tynodes, the time resolution of the TiPC can be in the order of 10 -12 s. The set of tynodes is placed under the photocathode, and on top of a CMOS detecting chip. With such design, TiPC represents a light, compact and ultra-fast photodetecting device with a high relevance for solid state, atomic and molecular physics experiments, medical imaging and 3D optical imaging. The focus of this thesis is microelectromechanical systems (MEMS) fabrication of the tynodes. To our knowledge, this is the first time MEMS technology is employed as a powerful tool for the production of large arrays of free-standing membranes, with thicknesses of only a few nanometers, to be used in photodetection. Detailed analysis in terms of mechanical, optical, electrical and structural properties were performed in order to discern the most suitable material for the TiPC application among the investigated candidates. The transmission SEY (TSEY) of the released tynodes is analysed with a dedicated setup, specifically developed in our group, inserted in a scanning electron microscope (SEM). Low pressure chemical vapour deposition (LPCVD) was employed as a technique to grow silicon nitride (SiN) tynodes with varied layout, elemental stoichiometry and thicknesses in the range from 25 to 40 nm. Due to its inability to produce good-quality films with thicknesses lower than 20 nm, LPCVD was replaced by atomic layer deposition (ALD). It was found that SiN performs poorly in terms of secondary electron emission (SEE), and we selected Al2O3 (alumina) as the next tynode material. The ALD of alumina is investigated in the temperature range from 300 down to 100 °C, with the goal to determine its viability in the coating of temperature-sensitive substrates such as photoresist. We demonstrated the fabrication of 5 – 25 nm-thick ALD alumina tynodes which exhibited moderately high TSEY. Apart from SiN and alumina, other materials subjected to SEE analysis in this work were: chemical vapour deposited (CVD) ultrananocrystalline diamond (UNCD), monocrystalline silicon and LPCVD silicon carbide (SiC). Applying atomic layer deposited magnesium oxide (MgO) as the tynode material resulted in a transmission secondary electron yield (TSEY) of up to 5.5, by which it proved to be the most efficient electron multiplier among materials taken into account in this work. During the fabrication of tynodes, SEE films were exposed to different MEMS processing steps, and thus inevitably undewent a surface modification which alters the SEE properties. On that account, we conducted a study on the ALD MgO films subjected to various chemical and thermal treatments and explored the methods to further enhance their SEE. For the final application in the TiPC, stacked tynodes should provide the focusing of electrons. To meet this requirement, the emission film was grown on a pre-patterned substrate, which enabled hemi-spherical shape of the released membranes. Finally, for the vertical stacking and alignment of the tynodes, steps for the formation of V-grooves were added in the standard fabrication flowchart. @en

In this work we have developed a prototype gaseous pixel detector by combining a micromegas grid with a Timepix3 chip for the readout. The micromegas foil supported by a matrix of pillars about 50 μm high was manually placed on top the chip. By placing a cathode foil above the chip an ionisation detector was created with a drift gap of 13.5 mm. The Timepix3 chip, thanks to the simultaneous measurement of the time-of-arrival (ToA) and charge via time-over-threshold (ToT) allows corrections to remaining timewalk effects, improving further the position resolution along the drift direction. We present the timewalk correction for Timepix3 chip obtained with real data from a particle beam and its impact on the tracking performance. The results obtained show a significant improvement on the position resolution for single-hits and tracks along the drift direction compared to previous experiments.

@en