[en] Carbon foil time pick-up detectors are widely used in pairs in ion beam applications as time-of-flight detectors. These detectors are suitable for a wide energy range and for all ions but at the lowest energies the tandem effect limits the achievable time of flight and therefore the energy resolution. Tandem effect occurs when an ion passes the first carbon foil of the timing detector and its charge state is changed. As the carbon foil of the first timing detector has often a non-zero voltage the ion can accelerate or decelerate before and after the timing detector. The combination of different charge state properties before and after the carbon foil now induces spread to the measured times of flight. We have simulated different time pick-up detector orientations, voltages, ions and ion energies to examine the tandem effect in detail and found out that the individual timing detector orientation and the average ion charge state have a very small influence to the magnitude of the tandem effect. On the other hand, the width of the charge state distribution for particular ion and energy in the first carbon foil, and the carbon foil voltage contributes linearly to the magnitude of the tandem effect. In the simulations low energy light ion trajectories were observed to bend in the electric fields of the first timing gate, and the magnitude of this bending was studied. It was found out that 50–150 keV proton trajectories can even bend outside the second timing gate

[en] Er₂O₃ thin films were grown onto Si(1 0 0) and soda lime glass substrates by atomic layer deposition (ALD) from Er(thd)₃ (thd 2,2,6,6-tetramethyl-3,5-heptanedione) and ozone precursors. Temperature range studied was 200-450 deg. C where a region of constant growth rate for Er₂O₃ (ALD window) was observed at 250-375 and 275-350 deg. C on Si(1 0 0) and soda lime glass, respectively. Within the ALD window, the growth rates of Er₂O₃ films deposited onto Si(1 0 0) and soda lime glass were 0.25 and 0.20 A (cycle)^-1, respectively. Films were polycrystalline, cubic Er₂O₃, and their preferred orientation changed from (4 0 0) to (2 2 2) as the deposition temperature was raised above 325 deg. C. Below 250 deg. C, the films were amorphous. The surface morphology studies by AFM revealed that the films were very smooth (rms=0.3-1.4 nm), when deposited within the ALD window. Time-of-flight elastic recoil detection (TOF-ERD) analyses were carried out to determine stoichiometry and impurity levels and they proved the films to be nearly stoichiometric Er₂O₃ with some hydrogen, carbon and fluorine as impurities. Within the ALD window, the hydrogen, carbon and fluorine contents were in the order of 1.7-4.0, 0.5-1.8 and 0.7-1.7 at.%, respectively

[en] A versatile system to capture and analyze signals from multi channel plate (MCP) based time-of-flight detectors and ionization based energy detectors such as silicon diodes and gas ionization chambers (GIC) is introduced. The system is based on commercial digitizers and custom software. It forms a part of a ToF-ERDA spectrometer, which has to be able to detect recoil atoms of many different species and energies. Compared to the currently used analogue electronics the digitizing system provides comparable time-of-flight resolution and improved hydrogen detection efficiency, while allowing the operation of the spectrometer be studied and optimized after the measurement. The hardware, data acquisition software and digital pulse processing algorithms to suit this application are described in detail.

[en] Stoichiometric HfO₂ films were atomic layer deposited from HfI₄ and HfCl₄ at 300 deg. C on p-Si(1 0 0) substrates. Water was in both cases used as an oxygen precursor. The films consisted dominantly of monoclinic HfO₂ phase. Additional tetragonal HfO₂ could be detected only in the films grown from HfCl₄. Effective permittivities were frequency-independent and varied in the range of 12-14, without clear dependence on the precursor used. Oxide rechargeable trap densities were relatively high for the films grown from HfCl₄. The films grown from HfI₄ were more resistant against breakdown. The films grown from either precursor contained 0.4 at.% of halide residues and 1.0-1.5 at.% hydrogen. Annealing in forming gas at 400 deg. C did not affect the film composition. The growth rate was somewhat more stable in the HfI₄ based process

[en] Low energy heavy ion elastic recoil detection work has been carried out in Jyväskylä since 2009 using home made timing detectors, a silicon energy detector and a timestamping data acquisition setup forming a time-of-flight–energy telescope. In order to improve the mass resolution of the setup a new energy detector was designed to replace the silicon solid state detector, which suffered from radiation damage and had poor resolution for heavy recoils. In this paper the construction and operation of an isobutane filled gas ionization chamber with a 14 × 14 mm² 100 nm thick silicon nitride window are described. In addition to greatly improved energy resolution for heavy ions, the detector is also able to detect hydrogen recoils simultaneously in the energy range of 100–1000 keV. Additionally the detector has position sensitivity by means of timing measurement, which can be performed without compromising the performance of the detector in any other way. The achieved position sensitivity improves the depth resolution near the surface

[en] Carbon foil time pick-up detectors used in the time-of-flight measurements of MeV energy ions have been studied in connection to time-of-flight-energy spectrometer used for heavy ion elastic recoil detection analysis. In experimental coincident TOF-E data characteristic halos are observed around light element isobars, and the origin of these halos were studied. The experimental data indicated that these halos originate from single electron events occurring before the electron multiplication in the microchannel plate. By means of electron trajectory simulations, this halo effect is explained to originate from single electron, emitted from the carbon foil, hitting the non-active area of the microchannel plate. This electron creates a secondary electron from the surface and which ends up to the microchannel plate pore, is multiplied and create now a detectable signal. Other general timing gate parameters such as wire-to-wire spacing of the grids, acceleration potential of the 1st grid and the mirror grid potential gradient were also studied in order to improve the detector performance

[en] A new time-of-flight elastic recoil detection spectrometer has been built, and initially the main effort was focused in getting good timing resolution and high detection efficiency for light elements. With the ready system, a 154 ps timing resolution was recorded for scattered 4.8 MeV ⁴He²⁺ ions. The hydrogen detection efficiency was from 80% to 20% for energies from 100 keV to 1 MeV, respectively, and this was achieved by having an additional atomic layer deposited Al₂O₃ coating on the first timing detector’s carbon foil. The data acquisition system utilizes an FPGA-card to time-stamp every time-of-flight and energy event with 25 ns resolution. The different origins of the background events in coincident time-of-flight-energy histograms have been studied and explained. The built system has proved to be able to routinely depth profile films thinner than 10 nm

[en] Hafnium tetraiodide and oxygen were used as precursors for atomic layer deposition of hafnium dioxide (HfO₂) thin films on silicon substrates at temperatures of 400-750 deg. C. At 500-750 deg. C the growth rate ranged from 0.11 to 0.12 nm/cycle and, within the experimental uncertainty, did not depend on the substrate temperature. With the decrease of the substrate temperature from 500 to 400 deg. C, however, the growth rate decreased to 0.035 nm/cycle. All films contained monoclinic HfO₂. In addition, some amount of cubic, tetragonal or orthorhombic phase was observed in thinner films, particularly in those deposited at lower substrate temperatures and lower oxygen doses. The relative dielectric constant of the films measured at the frequency of 500 kHz reached 16

[en] Hf-Si-O mixture films were fabricated by atomic layer deposition at 400 deg. C on Si(1 0 0) substrates. The deposition sequence for one hafnium silicon oxide submonolayer comprises surface reactions between Si(OC₂H₅)₄ and HfCl₄, followed by the hydrolysis step in order to effectively remove the residual ligands. The effective permittivity, leakage current, and capacitance-voltage behavior depended on the hafnium/silicon ratio and on the oxide/silicon interface quality. The dielectric quality can be modulated for various configurations of stacked layers with different hafnium to silicon ratios

[en] The detection efficiency of recoils with masses ranging from H up to Nb at energies from 0.05 to 1 MeV per nucleon has been investigated for Time-of-Flight Energy Elastic Recoil Detection (ToF-E ERD) systems. It is observed that the detection efficiency for the ToF-E detector telescope depends on the stopping power in the carbon foils, which in turn relies upon the recoil mass and energy. Furthermore, the limits of this behaviour depend on the setting of the discriminator thresholds. The detection efficiency of a time detector could be fitted to a universal curve that can be described by a simple empirical formula as a function of recoil electronic stopping power in the carbon foil. This formula can be used to predict the detection efficiency by recoil energy for N, O and other elements, for which it may not be easy to prepare suitable reference samples containing only that element