The Rasnik 3-point alignment system, widely applied in particle physics experiments and in the instrumentation of gravitational wave experiments, can be used as N-point alignment system by'leap frog' N individual 3-point systems. The conceptual implementation of Rasnik chains in C³ is presented. Then, the proper operation of a laser diode and a CMOS image sensor in liquid nitrogen has been verified. Finally, next plans for testing a small but complete system, immersed in liquid nitrogen, are presented.

The Rasnik system is a 3-point optical displacement monitor with sub-nanometer precision. The CCD-Rasnik alignment system was developed in 1993 for monitoring the alignment of the muon chambers of the ATLAS Muon Spectrometer at CERN. Since then, the development has continued as new CMOS imaging pixel chips became available. In this work the system processes and parameters that limit the precision are studied. We conclude that the spatial resolution of Rasnik is only limited by the quantum fluctuations of the photon flux arriving at the pixels of the image sensor. The results of two Rasnik systems are compared to results from simulations, which are in good agreement. The best spatial resolution obtained was 7 pm/Hz. Finally, some applications of high-precision Rasnik systems are set out.

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.

The effect of doping in Si3N4 membranes on the secondary electron yield is investigated using Monte Carlo simulations of the electron-matter interactions. The effect of the concentration and the distribution of the doping in silicon rich silicon nitride membranes is studied by using the energy loss function as obtained from ab initio density functional theory calculations in the electron scattering models of the Monte Carlo simulations. An increasing doping concentration leads to a decreasing maximum secondary electron yield. The distribution of the doped silicon atoms can be optimised in order to minimize the decrease in yield.

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.

The Rasnik alignment system was developed initially in 1983 for the monitoring of the alignment of the muon chambers of the L₃ Muon Spectrometer at CERN. Since then, the development has continued as new opto-electronic components become available. Rasnik systems are 3-point optical displacement monitors and their precision ranges from below nanometers to several micrometers, depending on the design and requirements of the systems. A result, expressed in the range/precision ratio of 2 × 10⁶, is presented. According to the calculations of the Cram'er-Rao limit, and by means of MonteCarlo simulations, a typical Rasnik image should have enough information to reach deep sub-nanometer precision. This paper is an overview of the technological developments and achievements since Rasnik was applied in high energy physics experiments.

This study reports on the secondary electron emission (SEE) performance of atomic layer deposited MgO films, with thicknesses in the range from 5 to 25 nm, for the application in the Timed Photon Counter. In this novel, photodetector MgO is utilized as a material for the fabrication of ultrathin transmission dynodes (tynodes). Two different types of PECVD silicon oxide films are applied on top of MgO, in order to protect it against etching steps in the fabrication of tynodes and also as a prevention against aging. Applicability of these two materials as capping films is evaluated in terms of achieved secondary electron yield (SEY) of MgO after their removal. Emission of secondary electrons is known to depend on numerous physical and chemical properties of the material, such as surface roughness and chemical composition. On that account, morphological and structural properties of modified MgO are determined by atomic force microscope and x-ray photoelectron spectrometer and linked to the changes in SEE behavior. The authors demonstrate that the application of a suitable capping layer followed by its removal provides an SEY of 6.6, as opposed to the value of 4.8 recorded from the as-deposited MgO film. Furthermore, in a following experiment, they showed that annealing of MgO films at high temperatures (up to 1100 °C) significantly improved the secondary electron emission, elevating the SEY to 7.2.

In this paper we demonstrate the fabrication of large arrays of ultrathin freestanding membranes (tynodes) for application in a timed photon counter (TiPC), a novel photomultiplier for single electron detection. Low pressure chemical vapour deposited silicon nitride (Si _x N _y ) and atomic layer deposited alumina (Al₂O₃) with thicknesses down to only 5 nm are employed for the membrane fabrication. Detailed characterization of structural, mechanical and chemical properties of the utilized films is carried out for different process conditions and thicknesses. Furthermore, the performance of the tynodes is investigated in terms of secondary electron emission, a fundamental attribute that determines their applicability in TiPC. Studied features and presented fabrication methods may be of interest for other MEMS application of alumina and silicon nitride as well, in particular where strong ultra-thin membranes are required.

By placing, in vacuum, a stack of transmission dynodes (tynodes) on top of a CMOS pixel chip, a single free electron detector could be made with outstanding performance in terms of spatial and time resolution. The essential object is the tynode: an ultra thin membrane, which emits, at the impact of an energetic electron on one side, a multiple of electrons at the other side. The electron yields of tynodes have been calculated by means of GEANT-4 Monte Carlo simulations, applying special low-energy extensions. The results are in line with another simulation based on a continuous charge-diffusion model. By means of Micro Electro Mechanical System (MEMS) technology, tynodes and test samples have been realized. The secondary electron yield of several samples has been measured in three different setups. Finally, several possibilities to improve the yield are presented.

In this work we demonstrate how a novel single free electron detector 'Timed Photon Counter' (TiPC) may benefit from ultra-thin MgO transmission dynodes (tynodes). These membranes are fabricated through MEMS process technologies, with atomic layer deposition (ALD) as the most apt technique for growing films of good quality, with excellent control over thicknesses and extremely low surface roughness. Large area arrays of ultra-thin (5-25 nm) free-standing MgO membranes are fabricated and characterized to determine the optimal thickness for application of ALD MgO in TiPC. Supremacy of MgO over other materials previously considered, such as SiN, Al₂O₃, SiC, Si is verified. The exceptional mechanical (low stress in particular, -200 MPa), chemical and electrical properties of MgO make this material a very attractive candidate for numerous MEMS applications, as the MEMS transmission dynodes in the timed photon counter.

Secondary electron emission materials are reviewed with the aim of providing guidelines for the future development of novel transmission dynodes. Materials with reflection secondary electron yield higher than three and transmission secondary electron yield higher than one are tabulated for easy reference. Generations of transmission dynodes are listed in the order of the invention time with a special focus on the most recent atomic-layer-deposition synthesized transmission dynodes. Based on the knowledge gained from the survey of secondary election emission materials with high secondary electron yield, an outlook of possible improvements upon the state-of-the-art transmission dynodes is provided.