Excited-State Hydroxide Ion Release From a Series of Acridinol Photobases

The excited-state heterolysis of acridinol-based derivatives leads to the release of the OH- ion and the formation of the corresponding acridinium cations. To evaluate the parameters that control the reaction barriers, the kinetics of excited-state OH- release from a series of acridinol photobases were studied using transient absorption spectroscopy. The rate constants were obtained in three solvents (methanol, butanol, and isobutanol), and the data were modeled using Marcus theory. The intrinsic reorganization energies obtained from these fits were found to correlate well with the solvent reorganization energies calculated using dielectric continuum model, suggesting that the excited-state OH- release occurs along the solvent reaction coordinate. Furthermore, the ability of acridinol photobases to photoinitiate chemical reactions was demonstrated using the Michael reaction between dimethylmalonate and nitrostyrene

Recharging process of commercial floating-gate MOS transistor in dosimetry application

We investigated the recharging process of commercial floating gate device (EPAD) during the six different dose rates and ten irradiation cycles with the highest dose rate. Dose rate dependence of the floating gate dosimeter was observed from 1 Gy/h to 26 Gy/h (H2O). There is no change of the dosimetric characteristic with a constant dose rate of 26 Gy/h for ten cycles. The absorbed dose does not affect the drift of the threshold voltage readings after the irradiation steps. The reprogramming characteristic is not degrading with the absorbed dose for the ten irradiation cycles, giving the promising potential in the application for dosimetric purposes

Modified direct orthodontic bonding metod: Effectiveness in orthodontic therapy: A retrospective clinical study

Background: The aim of the study was to determine the percentage of bond failures of placed brackets with a modified direct method in patients of both genders, different ages and malocclusion types during 12 months of initial bonding. Material and Methods: The retrospective clinical study covered the period from November 2019 to December 2022 and included thirty patients with an average age of 17.07±5.35 8 males,(average age 18.77±7.87), and 22 females, (average age 16.45±4.17) who met the criteria. A total of 600 brackets with a 0.022" slot size (Mini Sprint ® , Forestadent, Germany) were placed by a modified direct method using thin paste adhesive (Reliance Light Bond™, Itasca, USA) by one operator. The observation of bond failures lasted 12 months. Results: The total number of bond failures was 10 (1.67%), where eight patients (26,7%) experienced unwanted debonding. The number of failed brackets in relation to age and malocclusion did not show statistical significance. There was a clinical difference between the genders, in 18.2% of women and in 50% of men. Statistical significance in number of failed brackets was not significant (HR=0.343; 95% CI: 0.084-1.394; p=0.135). Conclusion: The modified direct bonding method did not show differences at the level of age, gender and type of malocclusion, but it can be one of the methods of choice during direct bonding

Radiation sensitive MOSFETs irradiated with various positive gate biases

The RADiation sensitive metal-oxide-semiconductor field-effect-transistors (RADFETs) were irradiated with gamma rays up to absorbed dose of 110 Gy(H2O). The results of threshold voltage, VT, during irradiation with various positive gate biases showed the increase in VT with gate bias. The threshold voltage shift, ΔVT, during irradiation was fitted very well. The contributions of both the fixed traps (FTs) and switching traps (STs) during radiation on ΔVT were analyzed. The results show the significantly higher contribution of FTs than STs. A function that describes the dependence of threshold voltage shift and its components on gate bias was proposed, which fitted the experimental values very well. The annealing at the room temperature without gate bias of irradiated RADFETs was investigated. The recovery of threshold voltage, known as fading, slightly increase with the gate bias applied during radiation. The ΔVT shows the same changes as the threshold voltage component due to fixed states, ΔVft, while there is no change in the threshold voltage component due to switching traps, ΔVst

Stacked floating gate MOSFET as a passive dosimeter

Introduction. The approach to increase the sensitivity of semiconductor radiation dosimeter with a stacked design was presented for the thick oxide pMOS transistors, also known as RadFETs (A. Kelleher et al., IEEE transactions on nuclear science 42, 1995). The sensitivity is increasing with the number of RadFETs in stacked structure, but there were limitations because of the diode reverse breakdown voltage during readout current (B. O’Connell et al., In Proceedings of the Third European Conference on Radiation and its Effects on Components and Systems, 1995). Further improvement of the stacked RadFETs device enables detecting a minimum absorbed dose of less than 50 Gy for a 20 V power supply (B. O’Connell et al., Fifth European Conference on Radiation and Its Effects on Components and Systems, 1999). Floating gate MOSFET is a modified structure of MOSFET with another polysilicon gate surrounded by oxide. The advantages of the floating gate MOSFET as a radiation dosimeter are that it does not require thick oxide fabrication and the highest sensitivity is for the zero-bias at the control gate during irradiation (S. Ilić et al., Sensors 20 (11), 2020). Experimental setup. Commercial floating gate MOSFETs designed by Advanced Linear Devices Inc. were used in this paper. Four transistors were connected in the stacked structure (drain and control gate are shorted and connected to the source of the next stacked transistor), and their threshold voltage drift values were measured before and after each irradiation portion with the same conditions. The experiment was performed at the Institute of Nuclear Sciences “Vinča”, Belgrade, Serbia. Radiation source Co-60 was used for irradiation of the components, with the following portions of the absorbed dose (Si): 10 Gy, 10 Gy, 10 Gy, 20 Gy, 50 Gy, 400 Gy, 500 Gy, 4 mGy, 45 mGy, 50 mGy, respectively (absorbed dose was 100 mGy in total). All measurements were performed in a test fixture with triax cables by Keithley 2636A Source Measure Unit. During irradiation, all stacked transistors were zero-biased. Results. Observing the threshold voltage drift of the four stacked floating gate MOS transistors, we noticed that the stack of two transistors has the most stable reading values over time (smallest drift). Considering this, we analyzed only two stacked floating gate MOS transistors as a passive dosimeter for the low doses. The results show that it is possible to detect the first portion of 10 Gy at which the sensitivity of the two stacked transistors is 23 V/Gy. For the next same portion, the sensitivity is 17 V/Gy, while for the third, the value is 7 V/Gy. However, for the next 20 Gy, there is a tiny shift, and the sensitivity is only 1 V/Gy. Decreased sensitivity with absorbed dose is a feature of the floating gate MOSFET that has been observed before for much higher doses (S. Ilić et al., Sensors 20 (11), 2020). There is a large overlap in the threshold voltage drift values for the next four radiation portions. However, for the last two largest portions, 45 and 50 mGy, there is a significant threshold voltage shift with no overlapping, and thus it is possible to determine the sensitivity of 0.0226 and 0.0214 V/Gy, respectively. Conclusions. Using a floating gate MOSFET as a low-dose passive dosimeter is possible, but recharging the floating gate and reusing this device for higher total ionizing doses should be investigated.X JUBILEE International Conference on Radiation in Various Fields of Research : RAD 2022 (Spring Edition) : book of abstracts; June 13-17, 2022; Herceg Novi, Montenegr

Power silicon carbide schottky diodes as current mode ?-radiation detectors

In this paper, the feasibility of using commercial power Silicon Carbide (SiC) Schottky diodes as a current mode ?-radiation detector have been examined. Diodes with almost identical electric characteristics are purchased from two different manufacturers, On Semiconductor and RoHM. They have been tested under gamma radiation exposure from a Co-60 source. The current response during irradiation has been measured for various dose rates with reversed diode bias. Investigated range of dose rates was from 0.258 Gy/h to 26.312 Gy/h, and reverse diode bias values were 10 V, 20 V, 50 V, 100 V and 200 V. Tested Schottky diodes produce stable current response for the investigated dose rates. Although the manufacturers are different, the results show that the dosimetric characteristics of these diodes have an excellent match. Sensitivity was proportional to the applied reverse bias voltage. A simple power-law can very well describe the dependence of measured radiation-induced current on dose rate

Sensitivity and fading of irradiated RADFETs with different gate voltages

The radiation-sensitive field-effect transistors (RADFETs) with an oxide thickness of 400 nm are irradiated with gate voltages of 2, 4 and 6 V, and without gate voltage. A detailed analysis of the mechanisms responsible for the creation of traps during irradiation is performed. The creation of the traps in the oxide, near and at the silicon/silicon-dioxide (Si/SiO2) interface during irradiation is modelled very well. This modelling can also be used for other MOS transistors containing SiO2. The behaviour of radiation traps during postirradiation annealing is analysed, and the corresponding functions for their modelling are obtained. The switching traps (STs) do not have significant influence on threshold voltage shift, and two radiation-induced trap types fit the fixed traps (FTs) very well. The fading does not depend on the positive gate voltage applied during irradiation, but it is twice lower in case there is no gate voltage. A new dosimetric parameter, called the Golden Ratio (GR), is proposed, which represents the ratio between the threshold voltage shift after irradiation and fading after spontaneous annealing. This parameter can be useful for comparing MOS dosimeters