| 51. |
- Fröjdh, Christer, et al.
(författare)
-
Hard X-ray imaging and particle detection with TIMEPIX3
- 2016
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE - International Society for Optical Engineering. - 9781510603271 - 9781510603288
-
Konferensbidrag (refereegranskat)abstract
- CMOS pixel electronics open up for applications with single photon or particle processing. TIMEPIX3 is a readout chip in the MEDIPIX family with the ability to simultaneously determine energy and time of interaction in the pixel. The device is fully event driven, sending out data on each interaction at a maximum speed of about 40 Mhits/s. The concept allows for off-line processing to correct for charge sharing or to find the interaction point in multi pixel events. The timing resolution of 1.56 ns allows for three dimensional tracking of charged particles in a thick sensor due to the drift time for the charge in the sensor. The experiments in this presentation have been performed with silicon sensors bonded MEDIPIX family chips with special focus on TIMEPIX3. This presentation covers basic performance of the chip, spectral imaging with hard X-rays, detection and imaging with charged particles and neutrons. Cluster identification, centroiding and charge summing is extensively used to determine energy and position of the interaction. For neutron applications a converter layer was placed on top of the sensor.
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| 52. |
- Fröjdh, Christer, et al.
(författare)
-
Processing and characterisation of an etched groove Permeable
- 1994
-
Ingår i: Physica scripta. T. - 0281-1847. ; T54, s. 56-59
-
Tidskriftsartikel (refereegranskat)abstract
- The Permeable Base Transistor (PBT) is generally considered as an interesting device for high speed applications. PBTs have been fabricated on Silicon and Gallium Arsenide by a number of groups. In this paper we reported on the fabrication of an etched groove PBT structure on 6H-SiC using Ti as contact metal for all electrodes. The devices have been characterised by DC-measurements. The transistors show the normal IV-characteristics for a such a device except for a parasitic series diode at the drain electrode. The breakdown voltage of the gate-drain diode is generally as high as around 60 V even without passivation of the sidewalls of the grooves.
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| 53. |
- Fröjdh, Christer, et al.
(författare)
-
Schottky Barriers on 6H-SiC
- 1999
-
Ingår i: Physica scripta. T. - 0281-1847. ; T79, s. 297-302
-
Tidskriftsartikel (refereegranskat)abstract
- Schottky diodes have been fabricated by deposition of Ti, Ni, Cu on epitaxial layers of p-type and n-type 6H-SiC. The fabricated devices have been characterised by CV, IV and photoelectric measurements. The results from the different characterisations are compared. The effect of incomplete ionisation of dopants and high series resistance on the results from CV-measurements is discussed. In addition to the results obtained from the experiments presented in this paper data has also been collected from other research groups in order to investigate the mechanism of Schottky barrier formation on Silicon Carbide. The results show that for a number of metals the barrier height is strongly correlated to the difference between the electron affinity of the semiconductor and the metal work function, while other metals show significant deviation from the Schottky-Mott theory.
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| 54. |
- Fröjdh, Christer, et al.
(författare)
-
Spectral resolution in pixel detectors with single photon processing
- 2013
-
Ingår i: Proceedings SPIE Optical Engineering + Applications, 2013. - : SPIE - International Society for Optical Engineering. - 9780819497024
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Pixel detectors based on photon counting or single photon processing readout are becoming popular for spectral X-ray imaging. The detector is based on deep submicron electronics with functions to determine the energy of each individual photon in every pixel. The system is virtually noiseless when it comes to the number of the detected photons. However noise and variations in system parameters affect the determination of the photon energy. Several factors affect the energy resolution in the system. In the readout electronics the most important factors are the threshold dispersion, the gain variation and the electronic noise. In the sensor contributions come from charge sharing, variations in the charge collection efficiency, leakage current and the statistical nature of the charge generation, as described by the Fano factor. The MEDIPIX technology offers a powerful tool for investigating these effects since energy spectra can be captured in each pixel. In addition the TIMEPIX chip, when operated in Time over Threshold mode, offers an opportunity to analyze individual photon interactions, thus addressing charge sharing and fluorescence. Effects of charge sharing and the properties of charge summing can be investigated using MEDIPIX3RX. Experiments are performed using both Si and CdTe detectors. In this paper we discuss the various contributions to the spectral noise and how they affect detector response. The statements are supported with experimental data from MEDIPIX-type detectors.
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| 55. |
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| 56. |
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| 57. |
- Fröjdh, Erik, et al.
(författare)
-
Depth of interaction and bias voltage dependence of the spectral response in a pixellated CdTe detector operating in time-over-threshold mode subjected to monochromatic X-rays
- 2012
-
Ingår i: Journal of Instrumentation. - 1748-0221. ; 7:3, s. Art. no. C03002-
-
Tidskriftsartikel (refereegranskat)abstract
- High stopping power is one of the most important figures of merit for X-ray detectors. CdTe is a promising material but suffers from: material defects, non-ideal charge transport and long range X-ray fluorescence. Those factors reduce the image quality and deteriorate spectral information. In this project we used a monochromatic pencil beam collimated through a 20Όm pinhole to measure the detector spectral response in dependance on the depth of interaction. The sensor was a 1mm thick CdTe detector with a pixel pitch of 110Όm, bump bonded to a Timepix readout chip operating in Time-Over-Threshold mode. The measurements were carried out at the Extreme Conditions beamline I15 of the Diamond Light Source. The beam was entering the sensor at an angle of ∌20 degrees to the surface and then passed through ∌25 pixels before leaving through the bottom of the sensor. The photon energy was tuned to 77keV giving a variation in the beam intensity of about three orders of magnitude along the beam path. Spectra in Time-over-Threshold (ToT) mode were recorded showing each individual interaction. The bias voltage was varied between -30V and -300V to investigate how the electric field affected the spectral information. For this setup it is worth noticing the large impact of fluorescence. At -300V the photo peak and escape peak are of similar height. For high bias voltages the spectra remains clear throughout the whole depth but for lower voltages as -50V, only the bottom part of the sensor carries spectral information. This is an effect of the low hole mobility and the longer range the electrons have to travel in a low field. © 2012 IOP Publishing Ltd and Sissa Medialab srl.
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| 58. |
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| 59. |
- Fröjdh, Erik, 1984-, et al.
(författare)
-
Mapping the x-ray response of a CdTe sensor with small pixels using an x-ray microbeam and a single photon processing readout chip
- 2011
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE - International Society for Optical Engineering. - 9780819487520 ; , s. Art. no. 814208-
-
Konferensbidrag (refereegranskat)abstract
- CdTe is a promising material for X-ray imaging since it has high stopping power for X-rays. However defects in the material, non ideal charge transport and long range X-ray fluorescence deteriorates the image quality. We have investigated the response of a CdTe sensor with very small pixels using an X-ray microbeam entering the sensor at a small incident angle. Effects of defects as well as depth of interaction can be measured by this method. Both electron and hole collection mode has been tested. The results show distorted electrical field around defects in the material and also shows the small pixel effect. It is also shown that charge summing can be used to get correct spectral information.
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| 60. |
- Fröjdh, Erik, 1984-, et al.
(författare)
-
Probing Defects in a Small Pixellated CdTe Sensor Using an Inclined Mono Energetic X-Ray Micro Beam
- 2012
-
Ingår i: 2012 IEEE NUCLEAR SCIENCE SYMPOSIUM AND MEDICAL IMAGING CONFERENCE RECORD (NSS/MIC). - : IEEE conference proceedings. - 9781467320306 - 9781467320283 ; , s. 4233-4236
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- High quantum efficiency is important in X-ray imaging applications. This means using high-Z sensor materials. Unfortunately many of these materials suffer from defects that cause non-ideal charge transport. In order to increase the understanding of these defects, we have mapped the 3D response of a number of defects in two 1 mm thick CdTe sensors with different pixel sizes (55 mu m and 110 mu m) using a monoenergetic microbeam at 79 keV. The sensors were bump bonded to Timepix read out chips. Data was collected in photon counting as well as time-over-threshold mode. The time-over-threshold mode is a very powerful tool to investigate charge transport properties and fluorescence in pixellated detectors since the signal from the charge that each photon deposits in each pixel can be analyzed. Results show distorted electrical field around the defects and indications of excess leakage current and large differences in behavior between electron collection and hole collection mode. The experiments were carried out in the Extreme Conditions Beamline I15 at Diamond Light Source.
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| 61. |
- Fröjdh, Erik, et al.
(författare)
-
Probing Defects in a Small Pixellated CdTe Sensor Using an Inclined Mono Energetic X-Ray Micro Beam
- 2013
-
Ingår i: IEEE Transactions on Nuclear Science. - 0018-9499 .- 1558-1578. ; 60:4, s. 2864-2869
-
Tidskriftsartikel (refereegranskat)abstract
- High quantum efficiency is important in X-ray imaging applications. This means using high-Z sensor materials. Unfortunately many of these materials suffer from defects that cause non-ideal charge transport. In order to increase the understanding of these defects, we have mapped the 3D response of a number of defects in two 1 mm thick CdTe sensors with different pixel sizes (55 mu m and 110 mu m) using a monoenergetic microbeam at 79 keV. The sensors were bump bonded to Timepix read out chips. Data was collected in photon counting as well as time-over-thresholdmode. The time-over-thresholdmode is a very powerful tool to investigate charge transport properties and fluorescence in pixellated detectors since the signal from the charge that each photon deposits in each pixel can be analyzed. Results show distorted electrical field around the defects, indications of excess leakage current and large differences in behavior between electron collection and hole collection mode. The experiments were carried out on the Extreme Conditions Beamline I15 at Diamond Light Source.
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| 62. |
- Fröjdh, Erik, 1984-, et al.
(författare)
-
Spectral Response in a Pixellated X-ray Imaging CdTe Detector with Single Photon Processing Readout
- 2010
-
Ingår i: Proceeddings of 2010 Nuclear Science Symposium and Medical Imaging Conference. - : IEEE conference proceedings. - 9781424491063 ; , s. 1079-1080
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The image forming process in a CdTe detector is both a function of the X-ray interaction in the material, including scattering and fluorescence, and the charge transport in the material [2]-[4]. The response of individual photons has been investigated using two pixellated CdTe image detectors with pixel pitches of 55 mu m and 110 mu m. The detectors were bonded to TIMEPIX [5] readout chips and operated in time over threshold mode (ToT). We have illuminated the sensors with monoengertic photons generated by X-ray fluorescence in metal sheets and with gamma photons from Am-241 and Cs-137. Results shows a large degradation in energy resolution caused by charge sharing and fluorescence. By summing pixels together we can correct for the charge sharing and some, but not all fluorescence.
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| 63. |
- Fröjdh, Erik, et al.
(författare)
-
X-ray absorption and charge transport in a pixellated CdTe detector with single photon processing readout
- 2011
-
Ingår i: Journal of Instrumentation. - 1748-0221. ; 6:2, s. Art. no. P02012-
-
Tidskriftsartikel (refereegranskat)abstract
- The image forming process in a CdTe detector is both a function of the X-ray interaction in the material, including scattering and fluorescence, and the charge transport in the material [2-4]. The response to individual photons has been investigated using a CdTe detector with a pixel size of 110 m m, bonded to a TIMEPIX [5] readout chip operating in time over threshold mode. The device has been illuminated with mono-energetic photons generated by fluorescence in different metals and by gamma emission from Am-241 and Cs-137. Each interaction will result in charge distributed in a cluster of pixels where the total charge in the cluster should sum up to the initial photon energy. By looking at the individual clusters the response from shared photons as well as fluorescence photons can be identified and separated. By using energies below and above the K-edges of Cd and Te the contribution from fluorescence can be further isolated. The response is analyzed to investigate the effects of both charge diffusion and fluorescence on the spectral response in the detector.
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| 64. |
- Gaynullin, Bakhram, 1967-, et al.
(författare)
-
Advanced Pressure Compensation in High Accuracy NDIR Sensors for Environmental Studies
- 2023
-
Ingår i: Sensors. - : MDPI AG. - 1424-8220. ; 23:5
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of atmospheric gas concentrations using of NDIR gas sensors requires compensation of ambient pressure variations to achieve reliable result. The extensively used general correction method is based on collecting data for varying pressures for a single reference concentration. This one-dimensional compensation approach is valid for measurements carried out in gas concentrations close to reference concentration but will introduce significant errors for concentrations further away from the calibration point. For applications, requiring high accuracy, collecting, and storing calibration data at several reference concentrations can reduce the error. However, this method will cause higher demands on memory capacity and computational power, which is problematic for cost sensitive applications. We present here an advanced, but practical, algorithm for compensation of environmental pressure variations for relatively low-cost/high resolution NDIR systems. The algorithm consists of a two-dimensional compensation procedure, which widens the valid pressure and concentrations range but with a minimal need to store calibration data, compared to the general one-dimensional compensation method based on a single reference concentration. The implementation of the presented two-dimensional algorithm was verified at two independent concentrations. The results show a reduction in the compensation error from 5.1% and 7.3%, for the one-dimensional method, to −0.02% and 0.83% for the two-dimensional algorithm. In addition, the presented two-dimensional algorithm only requires calibration in four reference gases and the storing of four sets of polynomial coefficients used for calculations.
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| 65. |
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| 66. |
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| 67. |
- Gaynullin, Bakhram, 1967-, et al.
(författare)
-
Environmental monitoring of methane utilizing multispectral NDIR gas sensing for compensation of spectral impact from water vapor in air
- 2022
-
Ingår i: Proceedings of IEEE Sensors. - : IEEE. - 9781665484640
-
Konferensbidrag (refereegranskat)abstract
- A multispectral nondispersive infrared (NDIR) sensor was developed for simultaneous detection of methane and water vapor in air. The NDIR sensor is capable of measuring optic transmission in the CH4 absorption spectra at 3.375 μm and the H2O absorption spectra at 2.7 μm. Data from a third channel, 3.95 μm, is used as reference value for 'zero-level' calibration. The actual CH4 concentration is retrieved by adjusting the data obtained in the CH4 spectra with respect to the concentration sensed in the H2O spectra. A calibration procedure was developed and tested, which involves matching of the absorbed light energy in the CH4 and the H2O spectrum in humid reference environments. A compensation algorithm for elimination of humidity impact was developed and validated in environments with variable CH4 and H2O concentrations. By implementing the multispectral approach, and the developed algorithm, an uncertainty of 15-25 ppm relative the reference concentrations was achieved. For a concentration range valid for environmental monitoring applications this should be compared to an uncertainty of 180-200 ppm for the non-corrected CH4 concentration.
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| 68. |
- Gaynullin, Bakhram, 1967-
(författare)
-
High accuracy low-cost NDIR sensing
- 2019
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sensing gas concentrations using optical absorption offers valuable advantages over other methods ina wide variety of real-world applications from industrial processes to environmental change. One of the most rapidly developing detection techniques on the global market is the non-dispersive infrared method (NDIR). Sensors developed based on this technique satisfy a growing demand for low-cost, reliable and long-term maintenance-free solutions. The technologies available to support this field for sensor key components such as light sources, photo detectors, optic cavities, and electronic components, have advanced rapidly in recent years. This development has led to an increasing number of application fields, due to significant improvements in accuracy, sensitivity and resolution.However, this technique has limitations related to basic physical principles and sensor design performance. Variation in sensing environments’ temperature and pressure, the impact of water vapour presence and sensor component ageing are the most important interfering factors for investigation. Errors in measured values could be caused by any of these factors because they influence various sensor parts and the environment’s physical properties. The correct interpretation of error sources is one the most difficult and important tasks involved in designing stable, high-precision sensors.To facilitate investigations into measurement performance limitations, test equipment was developed along with test approaches capable of creating experimental conditions that exceed the tested sensor’ stolerances. The studied resolution limit for long-path sensors is about 100 ppb. For measurements in fresh air concentrations (approximately 400 ppm of CO2), this is equivalent to a precision of less than0.1%. The methods used to reduce possible inaccuracies due to various error sources’ impacts should possess compensatory capabilities and precisions that exceed this value.To improve the pressure compensation procedure’s performance, a complete advanced system that includes everything from a lab test bench to the supporting software and comprehensive calculation algorithm was developed. The test bench creates pressure conditions that deviate from the reference value by less than 0.2 mbar (or 0.02% of the standard pressure, 1013 mbar).One of this study’s major findings is the concentration range-independent pressure compensation method. The advanced conditions achieved with the test station also facilitated the discovery and characterisation of the sources of long-term drift in methane concentration measurement.
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| 69. |
- Gaynullin, Bakhram, 1967-, et al.
(författare)
-
Implementation of NDIR technology for selective sensing of gases with common absorption spectra
- 2023
-
Ingår i: 2023 IEEE International Instrumentation and Measurement Technology Conference (I2MTC). - : IEEE. - 9781665453837
-
Konferensbidrag (refereegranskat)abstract
- A selective algorithm for nondispersive infrared (NDIR) sensing of gases with overlapping absorption spectra was developed and evaluated in modified multichannel NDIR sensor. Measurements in the optic channel with the spectral band where two gas species (target and secondary gas) have overlapping absorption lines are complemented by additional measurements in second channel where spectral absorption for only one gas (secondary gas) is present. The real concentration for the target gas is retrieved by adjusting the absorption data obtained in the overlapping gas spectra's optic channel, with respect to the absorption data retrieved in the second optic channel that has sensitivity only for the secondary gas. An implementation example is performed by obtaining the true concentration of CH4 (as target gas) in a mixture with H2O vapor. The channel for the target gas is equipped by an optic filter with spectra at 3.375 μm where both CH4 and H2O have absorption lines. The complementary second channel provides sensing in spectra at 2.7 μm where only H2O have absorption. Data from a third channel, at 3.95 μm, is used as reference value for 'zero-level' calibration. A calibration procedure was developed and tested, which involves matching of the absorbed light energy in target and secondary channels in humid reference environments. A selective algorithm for sensing of CH4 with elimination of spectral impact from H2O was validated in environments with variable CH4 and H2O concentrations. By implementing the multispectral approach and the developed algorithm, an uncertainties of 5-10 ppm relative the reference concentrations were achieved. For the environments where selective algorithm was validated this should be compared to an uncertainty of 70-90 ppm for the non-corrected CH4 concentration.
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| 70. |
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| 71. |
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| 72. |
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| 73. |
- Jiang, Meng, 1990-, et al.
(författare)
-
A Coherent Wideband Acoustic Source Localization Using a Uniform Circular Array
- 2023
-
Ingår i: Sensors. - : MDPI. - 1424-8220. ; 23:11
-
Tidskriftsartikel (refereegranskat)abstract
- In modern applications such as robotics, autonomous vehicles, and speaker localization, the computational power for sound source localization applications can be limited when other functionalities get more complex. In such application fields, there is a need to maintain high localization accuracy for several sound sources while reducing computational complexity. The array manifold interpolation (AMI) method applied with the Multiple Signal Classification (MUSIC) algorithm enables sound source localization of multiple sources with high accuracy. However, the computational complexity has so far been relatively high. This paper presents a modified AMI for uniform circular array (UCA) that offers reduced computational complexity compared to the original AMI. The complexity reduction is based on the proposed UCA-specific focusing matrix which eliminates the calculation of the Bessel function. The simulation comparison is done with the existing methods of iMUSIC, the Weighted Squared Test of Orthogonality of Projected Subspaces (WS-TOPS), and the original AMI. The experiment result under different scenarios shows that the proposed algorithm outperforms the original AMI method in terms of estimation accuracy and up to a 30% reduction in computation time. An advantage offered by this proposed method is the ability to implement wideband array processing on low-end microprocessors.
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| 74. |
- Jiang, Meng, et al.
(författare)
-
Indoor Silent Object Localization using Ambient Acoustic Noise Fingerprinting
- 2020
-
Ingår i: 2020 IEEE International Instrumentation and Measurement Technology Conference (I2MTC). - : IEEE. - 9781728144603
-
Konferensbidrag (refereegranskat)abstract
- Indoor localization has been a popular research subject in recent years. Usually, object localization using sound involves devices on the objects, acquiring data from stationary sound sources, or by localizing the objects with external sensors when the object generates sounds. Indoor localization systems using microphones have traditionally also used systems with several microphones, setting the limitations on cost efficiency and required space for the systems. In this paper, the goal is to investigate whether it is possible for a stationary system to localize a silent object in a room, with only one microphone and ambient noise as information carrier. A subtraction method has been combined with a fingerprint technique, to define and distinguish the noise absorption characteristic of the silent object in the frequency domain for different object positions. The absorption characteristics of several positions of the object is taken as comparison references, serving as fingerprints of known positions for an object. With the experiment result, the tentative idea has been verified as feasible, and noise signal based lateral localization of silent objects can be achieved.
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| 75. |
- Jiang, Meng, et al.
(författare)
-
Performance Comparison of Omni and Cardioid Directional Microphones for Indoor Angle of Arrival Sound Source Localization
- 2022
-
Ingår i: Conference Record - IEEE Instrumentation and Measurement Technology Conference. - : IEEE. - 9781665483605
-
Konferensbidrag (refereegranskat)abstract
- The sound source localization technology brings the possibility of mapping the sound source positions. In this paper, angle-of-arrival (AOA) has been chosen as the method for achieving sound source localization in an indoor enclosed environment. The dynamic environment and reverberations bring a challenge for AOA-based systems for such applications. By the acknowledgement of microphone directionality, the cardioid-directional microphone systems have been chosen for the localization performance comparison with omni-directional microphone systems, in order to investigate which microphone is superior in AOA indoor sound source localization. To reduce the hardware complexity, the number of microphones used during the experiment has been limited to 4. A localization improvement has been proposed with a weighting factor. The comparison has been done for both types of microphones with 3 different array manifolds under the same system setup. The comparison shows that the cardioid-directional microphone system has an overall higher accuracy.
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| 76. |
- Kok, A., et al.
(författare)
-
Silicon sensors with pyramidal structures for neutron imaging
- 2014
-
Ingår i: Journal of Instrumentation. - 1748-0221. ; 9, s. C04011-
-
Tidskriftsartikel (refereegranskat)abstract
- Neutron detection is a valuable tool in nuclear science research, homeland security, quality assurance in nuclear plants and medical applications. Recent developments and near future instrumentations in neutron imaging have a need for sensors with high spatial resolution, dynamic range, sensitivity and background discrimination. Silicon based neutron detectors can potentially fulfil these requirements. In this work, pad and pixel detectors with pyramidal micro-structures have been successfully fabricated that should have an improved detection efficiency when compared to conventional planar devices. Titanium di-boride (TiB2) and lithium fluoride (LiF) were deposited as the neutron converters. Excellent electrical performances were measured on both simple pad and pixel detectors. A selection of pad detectors was examined by alpha spectroscopy. Measurement with thermal neutrons from a 241Am-Be source shows an improvement in relative efficiency of up to 38% when compared to conventional planar devices.
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| 77. |
- Krapohl, David, 1980-
(författare)
-
Monte Carlo and Charge Transport Simulation of Pixel Detector Systems
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is about simulation of semiconductor X-ray and particledetectors. The simulation of a novel coating for solid state neutrondetectors is discussed as well as the implementation of a simulationframework for hybrid pixel detectors.Today’s most common thermal neutron detectors are proportionalcounters, that use 3He gas in large tubes or multi wire arrays. Globalnuclear disarmament and the increase in use for homeland securityapplications has created a shortage of the gas which poses a problemfor neutron spallation sources that require higher resolution and largersensors. In this thesis a novel material and clean room compatible pro-cess for neutron conversion are discussed. Simulations and fabricationhave been executed and analysed in measurements. It has been proventhat such a device can be fabricated and detect thermal neutrons.Spectral imaging hybrid pixel detectors like the Medipix chipare the most advanced imaging systems currently available. Thesechips are highly sophisticated with several hundreds of transistors perpixel to enable features like multiple thresholds for noise free photoncounting measurements, spectral imaging as well as time of arrivalmeasurements. To analyse and understand the behaviour of differentsensor materials bonded to the chip and to improve development offuture generations of the chip simulations are necessary. Generally, allparts of the detector system are simulated independently. However, itis favourable to have a simulation framework that is able to combineMonte Carlo particle transport, charge transport in the sensor as wellas analogue and digital response of the pixel read-out electronics. Thisthesis aims to develop such a system that has been developed withGeant4 and analytical semiconductor and electronics models. Further-more, it has been verified with data from measurements with severalMedipix and Timepix sensors as well as TCAD simulations.Results show that such a framework is feasible even for imagingsimulations. It shows great promise to be able to be extended withfuture pixel detector designs and semiconductor materials as well asneutron converters to aim for next generation imaging devices.
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| 78. |
- Krapohl, David, et al.
(författare)
-
Simulation and measurement of short infrared pulses on silicon position sensitive device
- 2011
-
Ingår i: Journal of Instrumentation. - 1748-0221. ; 6:C01036
-
Tidskriftsartikel (refereegranskat)abstract
- Lateral position sensitive devices (PSD) are important for triangulation, alignment and surface measurements as well as for angle measurements. Large PSDs show a delay on rising and falling edges when irradiated with near infra-red light [1]. This delay is also dependent on the spot position relative to the electrodes. It is however desirable in most applications to have a fast response. We investigated the responsiveness of a Sitek PSD in a mixed mode simulation of a two dimensional full sized detector. For simulation and measurement purposes focused light pulses with awavelength of 850 nm, duration of 1 µs and spot size of 280 µm were used. The cause for the slopes of rise and fall time is due to time constants of the device capacitance as well as the photo- generation mechanism itself [1]. To support the simulated results, we conducted measurements of rise and fall times on a physical device. Additionally, we quantified the homogeneity of the device by repositioning a spot of light from a pulsed ir-laser diode on the surface area.
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| 79. |
- Krapohl, David, et al.
(författare)
-
Simulation of a silicon neutron detector coated with TiB 2 absorber
- 2012
-
Ingår i: Journal of Instrumentation. - 1748-0221. ; 7:1, s. Art. no. C01096-
-
Tidskriftsartikel (refereegranskat)abstract
- Neutron radiation cannot be directly detected in semiconductor detectors and therefore needs converter layers. Planar clean-room processing can be used in the manufacturing process of semiconductor detectors with metal layers to produce a cost-effective device. We used the Geant4 Monte-Carlo toolkit to simulate the performance of a semiconductor neutron detector. A silicon photo-diode was coated with vapour deposited titanium, aluminium thin films and a titaniumdiboride (TiB 2) neutron absorber layer. The neutron capture reaction 10B(n, alpha)7Li is taken advantage of to create charged particles that can be counted. Boron-10 has a natural abundance of about SI 19.8%. The emitted alpha particles are absorbed in the underlying silicon detector. We varied the thickness of the converter layer and ran the simulation with a thermal neutron source in order to find the best efficiency of the TiB 2 converter layer and optimize the clean room process. © 2012 IOP Publishing Ltd and SISSA.
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| 80. |
- Krapohl, David, 1980-, et al.
(författare)
-
Simulation of the Spectral Response of a Pixellated X-Ray Imaging Detector in Single Photon Processing Mode
- 2010
-
Ingår i: 2010 Nuclear Science Symposium and Medical Imaging Conference. - : IEEE conference proceedings.
-
Konferensbidrag (refereegranskat)abstract
- X-ray imaging with spectral resolution, “Color X-ray imaging” is a new imaging technology that is currently attracting a lot of attention. It has however been observed that the quality of spectral response is degraded as the pixel size is reduced. This is an effect of charge sharing where the signal from a photon absorbed close to the border between two pixels is shared between pixels. This effect is caused by both diffusion during the charge transport and X-ray fluorescence in heavy detector materials. In order to understand the behavior of pixellated detectors with heavy detector materials operating in single photon processing mode, we have simulated the X-ray interaction with the sensor and the transport of the charge to the readout electrode using a Monte Carlo model for the X-ray interaction and a drift diffusion model for the charge transport. By combining these models, both signal and noise properties of the detector can be simulated.
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| 81. |
- Krapohl, David, 1980-, et al.
(författare)
-
Validation of Geant4 Pixel Detector Simulation Framework by Measurements with the Medipix Family Detectors
- 2016
-
Ingår i: IEEE Transactions on Nuclear Science. - 0018-9499 .- 1558-1578. ; 63:3, s. 1874-1881
-
Tidskriftsartikel (refereegranskat)abstract
- Monte Carlo simulations are an extensively used tool for developingand understanding radiation detector systems. In this work, we usedresults of several chips and readout modes of the Medipix detector family to validatea Geant4 based pixel detector framework, developed in our group, thatis capable of simulating particle tracking, charge transport in thesensor material and different readout schemes. We experimentally verifiedthe simulation with different detector geometries in terms of pixelpitch and size as well as sensor material and sensor thickness. Thesingle pixel mode (SPM) and charge summing mode (CSM) in Medipix3 were evaluated with fluorescenceand synchrotron radiation. The integration of the charge sensitiveamplifier functionality in the simulation framework allowed to simulatethe time-over-threshold mode of the Timepix chip.Simulation and measurement have been compared in terms of spectralresolution using threshold scans in photon counting mode (Medipix3) and time over thresholdmode (Timepix). Furthercomparisons were done using X-ray tube spectra and beta decay to covera broad energy range. Additionally, TCAD simulations are performedas a comparison to a well-established simulation method. The resultsshow good agreement between simulation and measurement.
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| 82. |
- Lars, Herrnsdorf, et al.
(författare)
-
Point Dose Profile Measurments using Solid State Detectors in Characterization of Computed Tomograhy Systems
- 2009
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elesevier. - 0168-9002 .- 1872-9576. ; 607:1, s. 223-225
-
Tidskriftsartikel (refereegranskat)abstract
- Existing solid-state detectors for point dose measurements are typically mounted in a package with a high Z material acting as the back contact causing unsymmetrical response. In the Computed Tomography (CT) dose profile application this is a major drawback. A new silicon detector has been constructed without this disturbing element. The new detector has been mounted in a cylindrical tube and its characteristics are presented in this paper. The conclusion is that this new detector design is a major improvement for correct dose and dose profile measurements in CT systems.
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| 83. |
- Ljungberg, K., et al.
(författare)
-
Buried Cobalt Silicide Layers in Silicon Created by Wafer Bonding
- 1994
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 141:10, s. 2829-2833
-
Tidskriftsartikel (refereegranskat)abstract
- A buried conductive layer in silicon has been created using wafer bonding technique, with a cobalt interfacial layer.Co-coated silicon wafers were brought into contact with either similar or uncoated wafers at room temperature. CoSi2 wasthen formed through a solid-phase reaction, during an anneal at 700 to 900°C. A 700 Å buried CoSi2-layer, with a resistivityof approximately 21 µ cm, was achieved. Good adhesion, as measured by tensile strength testing, between the wafers wasachieved. Transmission electron microscopic investigations (Co-coated wafer bonded to bare silicon) showed that thesilicide has not grown into the opposite wafer, and that an amorphous layer exists between the silicide and the siliconsurface. The presence of such a layer has been confirmed by electrical characterization.
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| 84. |
- Manuilskiy, Anatoliy, et al.
(författare)
-
Compact Multi Channel Optical Fourier Spectrometer
- 2006
-
Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE - International Society for Optical Engineering. - 9780819464934 ; , s. U34-U43
-
Konferensbidrag (refereegranskat)abstract
- In this work are shown the principle, first experimental results and a model design of a new type of multi channel Fourier transform (FT) spectrometer for visible (VIS) and infrared (IR) region operating in real time. The main principle of this spectrometer is that measured collected and collimated optical radiation passes through a linear array or matrix of optical Fabry-Perot interferometers. Each interferometer is placed in front of and close to each element of the array detector. By processing the signal the spectrum of the optical radiation can be extracted. This design does not require intermediate optics between interferometer and array detector and allows for a reliable and extremely compact construction. Production cost can be low when a simple wedge type interferometer is integrated with existing array or matrix detectors, e.g. CCD camera. One other benefit is that the shape of the interferometer determines whether the spectrometer is suitable for measuring wide spectra radiation or has the ability to discriminate optical coherent radiation. Experimental results achieved for VIS and NIR range of spectra are promising. The principals of this design can be used for a variety of applications besides as a spectrometer. For example warning systems for lasers and restricted coherency sources and also filtering of optical signals and for measuring the spectral content working in a wide spectral range.
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| 85. |
- Manuilskiy, Anatoliy, et al.
(författare)
-
Multi Channel Array Interferometer-Fourier Spectrometer
- 2006
-
Ingår i: 2006 Northern Optics Conference Proceedings. - New York : IEEE. - 9781424404353 ; , s. 1-6
-
Konferensbidrag (refereegranskat)abstract
- The characterization and design of a Fourier transform spectrometer, which enables the integration of a multi channel interferometer with a detector unit in order to create a compact device is presented in this paper. It operates within a wide spectral range from visible to NIR, contains no moving parts and is resistible to mechanical and climatic conditions. Such a design with an array or matrix detector can be used for spectroscopy with a partially coherent or white optical source depending on the shape of the optical interferometer. A reasonable spectral resolution of the order of 20-50 cm-1 can be achieved over a 1 µm wavelength range when using a 512 pixel detector array. A design model for characterization of the quasi integrated device, where a multi channel interferometer was mechanically attached and which contained a gap to the detector elements, was used. The experimental results are promising and suggest a variety of different directions for the development and application of these types of integrated spectrometers.
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| 86. |
- Manuilskiy, Analoliy, et al.
(författare)
-
New concept of compact optical Fourier-Transform spectrometer
- 2006
-
Ingår i: 2006 IEEE SENSORS, VOLS 1-3. - : IEEE. - 9781424403752 ; , s. 408-411
-
Konferensbidrag (refereegranskat)abstract
- Here is presented a new concept of a compact optical Fourier-transform spectrometer (FT) working in a wide spectral range in real time and containing no moving parts. Most of the existing FT spectrometers consist of optics to create an image of the interference pattern on the detector plane. The concept presented here does not require these optical components because interferometer consists of multi channel Fabry Perot interferometer with stepped or gradually changing thickness attached directly to the detector array or detector matrix. As a result this allows complete integration of the interferometer with the detector together to one of the main spectrometer units. Two types of these spectrometers were simulated and experimentally tested. The first type with the wedge interferometer is suitable for analysis of optical radiation with partially coherent radiation and exhibits higher resolution and response to coherent radiation and lower response for non coherent radiation. Second one with cylindrically shaped interferometer suitable for spectroscopy with white sources shows lower spectral resolution. Both types of the spectrometers were tested from 0.6µm to 2µm with a 256pixels extended InGaAs array detector.
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| 87. |
- Mattsson, Claes, 1978-
(författare)
-
Design, Fabrication and Optimization of Thermal Radiation Detectors Based on Thin Polymer Membranes
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The number of applications in which infrared radiation sensors are used is increasing. In some applications, the cost of the sensor itself is an issue, and simple solutions are thus required. In this thesis, the investigations have related to the use of thin polymer membranes in thermal infrared sensors, such as bolometers and thermopiles. Infrared sensors are usually subcategorized into photonic sensors and thermal sensors. For detection of infrared radiation using a photodetector, there is a requirement for low band-gap material. The need of cooling makes infrared photodetectors rather expensive, and not an alternative for low-cost applications. In thermal sensors, the heat generated from the incident infrared radiation is converted into an electrical output by means of a heat sensitive element. Thermal sensors operate at room temperature, which makes them a low-cost alternative. The basic structure of thermal sensors consists of a temperature sensitive element connected to a heat sink through a structure with low thermal conductance. It is common to use thin membranes of Silicon or Silicon Nitride as thermal insulation between the heat sink and the sensitive element. In comparison, polymers have a thermal conductance that is lower than in these materials, and this increases the generated temperature in the sensitive element. A polymer such as SU-8 has a low thermal conductivity and is applied using a spin coater. This reduces the number of complex processing steps. This thesis presents a new application of SU-8 as a closed membrane in a thermal sensor. The concept was initially demonstrated by fabricating a nickel bolometer and titanium/nickel thermopile structure with a 5 µm SU-8 / SiO2 membrane. However, for the sensor responsivity to be able to compete with commercial thermal sensors the structures, some optimization was required. Since the thermopile generates its own voltage output and requires no external bias, the optimizations were focused on this structure. There exist a number available software tools for thermal simulation of components. However, to the author’s best knowledge, there exist no tool for design optimization of thermopiles with closed membranes. An optimization tool using iterative thermal simulations was developed and evaluated. A new thermopile structure, based on the optimization results, was both fabricated and characterized. Using an infrared laser with a small spot, the measured responsivity of the manufactured thermopile was higher than that of a commercial sensor. In the case of a defocused spot and for longer wavelengths, the infrared absorption in the absorption layer reduces and degrades the responsivity. The thermopile was further evaluated as a sensor in a carbon dioxide meter application based on the NDIR principle. An increase in the CO2 concentration demonstrated a clear decrease in the thermopile voltage response, as was expected. By normalizing the voltage response and comparing it with a commercial sensor, this showed that the SU-8 based thermopile is relatively more sensitive to changes in the CO2 concentration.
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| 88. |
- Mattsson, Claes, 1978-, et al.
(författare)
-
Design of a Micromachined Thermopile Infrared Sensor with a Self-Supported SiO2/SU-8 Membrane
- 2008
-
Ingår i: IEEE Sensors Journal. - Piscataway, USA : IEEE. - 1530-437X .- 1558-1748. ; 8:12, s. 2044-2052
-
Tidskriftsartikel (refereegranskat)abstract
- In the infrared region of the spectrum thermoelectric detectors such as the thermopile, are extensively used. These detectors rely on the well-known Seebeck effect, in which there is a direct conversion of thermoelectric differentials into electrical voltage. The temperature difference over thermocouple junctions is in general, created by forming a thin membrane connected to the silicon bulk. In many existing thermopiles, materials such as Si and Si3N4 have been used as membrane. These materials suffer from relatively high thermal conductivity, which lowers the membrane temperature and reduces the sensitivity of the detector. A material such as SU-8 2002 has a much lower thermal conductivity and is applied using standard photolithographic processing steps. This work presents thermal simulations regarding the use of SU-8 2002 as a thermal insulating membrane as compared to Si and Si3N4. The simulation results presented show that the temperature increase in a 5 µm SiO2/SU-8 membrane is about 9% higher than in a 1 µm Si3N4 membrane, despite the membrane thickness being increased by a factor of 5. A thermopile consisting of 196 serially interconnected Ti/Ni thermocouples positioned on a 5 µm SiO2/SU-8 2002 membrane has been fabricated. The sensitivity of the fabricated device has been evaluated in the infrared region, using a 1.56 µm IR laser and a xenon arc lamp together with a monochromator. The measurement results show a sensitivity of approximately 5 V/W over the wavelength range between 900 - 2200 nm. Measurements performed in a vacuum chamber show that the sensitivity of the detector could be increased by more than a factor of 3 by mounting the detector in a vacuum sealed capsule.
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| 89. |
- Mattsson, Claes, et al.
(författare)
-
Development of an infrared thermopile detector with a thin self-supporting SU-8 membrane
- 2007
-
Ingår i: Proceedings of IEEE Sensors. - New York : IEEE conference proceedings. - 9781424412624 ; , s. 836-839
-
Konferensbidrag (refereegranskat)abstract
- In this paper we present the development and characterization of thermopile detector on a 4 mum thin self-supporting membrane made of the epoxy based photoresist SU-8. The membrane is realized using silicon bulk micromachining techniques. In many existing thermopile detectors, a temperature difference over the thermocouple junctions is achieved by connecting a thin membrane of either Si or Si3N4 to a silicon bulk. These materials suffer from relatively high thermal conductivity, which lowers the sensitivity of the detector. A material such as SU-8 has much lower thermal conductivity and is applied using standard photolithographic processing steps. Simulation results are presented which verifies SU-8 as a better choice than Si and Si3N4 when used as thermal insulating membrane in a thermopile detector. A thermopile consisting of 196 series coupled Ti/Ni thermocouples has been fabricated. Results from measurements are presented, showing a sensitivity of 5.6 V/W and a noise equivalent power (NEP) of 9.9 nW/radicHz.
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| 90. |
- Mattsson, Claes, 1978-, et al.
(författare)
-
Experimental evaluation of a thermopile detector with SU-8 membrane, in a carbon dioxide meter setup
- 2009
-
Ingår i: IEEE Sensors Journal. - 1530-437X .- 1558-1748. ; 9:12, s. 1633-1638
-
Tidskriftsartikel (refereegranskat)abstract
- Continuous control of the carbon dioxide levels in the ventilation systems in office buildings and public schools has been shown to increase productivity and save money. However, these measurement systems require further developments in order to be more cost effective. This paper presents an evaluation of an Al/Bi thermopile detector with a 4 µm thin SiO2/SU-8 membrane in a CO2 meter application using the NDIR (Non-Dispersive Infrared Technology). The system consists of an 11 cm aluminum tube, used as the sample chamber and in which a light source and a thermopile detector with a 4.26 µm optical bandpass filter are positioned on its opposite sides. The light source is pulsed with a frequency of 0.5 Hz. The voltage response of the Al/Bi thermopile is measured for different CO2 concentrations, and, as expected according to the Lambert-Beer law, there is an exponential decrease in the measured intensity. The absolute response is about 50 % lower than for a commercial HMS J21 thermopile from Heimann Sensor GmbH. In relative terms, on the other hand, the Al/Bi thermopile is more sensitive for changes in the CO2 concentration. At 7500 ppm, the voltage response has decreased to 40 % of the reference response measured in the nitrogen atmosphere.
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| 91. |
- Mattsson, Claes, 1978-, et al.
(författare)
-
Fabrication and characterization of a design optimized SU-8 thermopile with enhanced sensitivity
- 2009
-
Ingår i: Measurement science and technology. - : IOP. - 0957-0233 .- 1361-6501. ; 20:11, s. 115202-
-
Tidskriftsartikel (refereegranskat)abstract
- In the infrared wavelength region, thermopiles are an important type of detectors. A major advantage of thermopiles is their non-cooling requirement. Depending on the applied absorption layer, their responsivity is often rather flat within a large wavelength region. This work presents the fabrication and characterization of a sensitivity and design optimized thermopile detector with a 4 µm self-supported SiO2/SU-8 membrane. The structure consists of 240 series interconnected thermocouple junctions obtained by a metal evaporation and lift-off. Two metal combinations have been evaluated, namely, nickel/titanium and aluminium/bismuth. Series resistances of 76 k and 283 k were measured for the Ni/Ti thermopile and the Al/Bi thermopile respectively. For the Al/Bi thermopile a responsivity of 60 V/W was achieved using a 1.56 µm fibre coupled diode laser with a power of 3.5 mW. Using a white light source with a radiation flux of 0.45 W/mm2 a voltage response of 68 V mm2/W was measured for the Al/Bi thermopile. The time constant of the characterized detectors was calculated as being 70 ms, using the pulsed IR laser.
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| 92. |
- Mattsson, Claes, 1978-
(författare)
-
Fabrication and Characterization of Photon Radiation Detectors
- 2007
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis involves a study the fabrication and characterization of photon radiation detectors. The focus has been to develop and improve the performance of optical measurement systems, but also to reduce their cost. The work is based on the study of two types of detectors, the position sensitive detector and the thermal detector. Infrared detectors are usually subcategorized into photonic detectors and thermal detectors. In the thermal detectors, heat generated from the incident infrared radiation is converted into an electrical output by some sensitive element. The basic structure of these detectors consists of a temperature sensitive element connected to a heat sink through a thermally isolating structure. Thin membranes of Silicon and Silicon nitride have been commonly used as thermally insulation between the heat sink and the sensitive elements. However, these materials suffer from relatively high thermal conductivity, which lowers the response of the detector. The fabrication of these membranes also requires rather advanced processing techniques and equipment. SU-8 is an epoxy based photoresist, which has low thermal conductivity and requires only standard photolithography. A new application of SU-8 as a self-supported membrane in a thermal detector is presented. This application is demonstrated by the fabrication and characterization of both an infrared sensitive thermopile and a bolometer detector. The bolometer consists of nickel resistances connected in a Wheatstone bridge configuration, whereas the thermopile uses serially interconnected Ti/Ni thermocouple junctions. The position sensitive detectors include the lateral effect photodiodes and the quadrant detectors. Typical applications for these detectors are distance measurements and as centering devices. In the quadrant detectors, the active region consists of four pn-junctions separated by a narrow gap. The size of the active region in these detectors depends on the size of the light spot. In outdoor application, this spot size dependence degrades the performance of the four-quadrant detectors. In this thesis, a modified four-quadrant detector having the pn-junctions separated by a larger distance has been fabricated and characterized. By separating the pn-junctions the horizontal electric filed in the active region is removed, making the detector spot size insensitive. Linearity of the lateral effect photodiodes depends on the uniformity of the resistive layer in the active region. The introduction of mechanical stress in an LPSD results in a resistance change mainly due to resistivity changes, and this affects the linearity of the detector. Measurements and simulations, where mechanical stress is applied to LPSDs are presented, and support this conclusion.
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| 93. |
- Mattsson, Claes, et al.
(författare)
-
Fabrication and evaluation of a thermal sensor formed on a thin photosensitive epoxy membrane with low thermal conductivity
- 2008
-
Ingår i: PROCEEDINGS OF THE 17TH INTERNATIONAL VACUUM CONGRESS/13TH INTERNATIONAL CONFERENCE ON SURFACE SCIENCE/INTERNATIONAL CONFERENCE ON NANOSCIENCE AND TECHNOLOGY. - : Institute of Physics (IOP). ; , s. 082048-
-
Konferensbidrag (refereegranskat)abstract
- This article present the fabrication and development of a thin metal film bolometer IR detector connected in a Wheatstone bridge configuration. The bolometer is constructed on a 4 μm thin self-supported SU-8 2002 membrane. A polymer material such as SU-8 has low thermal conductivity and is applied using standard photolithographic processing step, and this could increase detector sensitivity and lower the production cost. Thermal simulation results are presented, which verifies SU-8 as a better choice of materials compared to common membrane materials such as Si and Silicon nitride. Measurements on the fabricated nickel resistance bolometer on SU-8 2002 membrane show a sensitivity of 9.3 V/W when radiated by an IR laser with a wavelength of 1.56 μm.
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| 94. |
- Mattsson, Claes, et al.
(författare)
-
Manufacturing and characterization of a modified four-quadrant position sensitive detector for out-door applications
- 2004
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : ELSEVIER SCIENCE BV. - 0168-9002 .- 1872-9576. ; 531:1-2, s. 134-139
-
Tidskriftsartikel (refereegranskat)abstract
- Position sensing detectors (PSDs) are useful in many applications such as vibration, displacement and triangulation measurements. In this paper we have constructed a novel structure, which has higher inter-electrode resistance than a lateral effect PSD and is more robust to atmospheric turbulence than a conventional four-quadrant PSD (Nuclear Instruments and Methods in Physics Research A 466 (2001) 183). The detector structure is useful for applications with detector windows less than 0.5 x 0.5 mm(2), but the nonlinearity is the main concern for a detector of that size. Without any corrections for non-linearity the standard deviation of the error is 9 mum (2.2%). Using a simple analytical expression and a 2-d correction-function stored in a look-up table the positioning error is reduced to 6 (1.5%) and 2 (0.5%) mum, respectively.
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| 95. |
- Mattsson, Claes, 1978-, et al.
(författare)
-
Thermal simulation and design optimization of a thermopile infrared detector with SU-8 membrane
- 2009
-
Ingår i: Journal of Micromechanics and Microengineering. - : IOP Publishing. - 0960-1317 .- 1361-6439. ; 19:5, s. 055016-
-
Tidskriftsartikel (refereegranskat)abstract
- Simulation and optimization tools are commonly used in the design phase of advanced electronics devices. In this work, we present a thermal simulation and design optimization tool for infrared thermopile detectors based on a closed membrane structure. The tool can be used to simulate and optimize thermopile detectors with an arbitrary number of design parameters. The optimization utilizes the Nelder–Mead and the adaptive simulated annealing optimization algorithms to maximize the system performance. A thermopile detector with an SU-8-based closed membrane and metal–metal thermocouples has been simulated and optimized. Based on the results generated by the tool, an optimized detector has been fabricated and characterized. The results from the measurements presented are in good agreement with the simulation results.
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| 96. |
- Nilsson, Charlotta, et al.
(författare)
-
Characterisation of a pre-cell hit detector to be used in single cell irradiation experiments at the Lund Nuclear Microprobe
- 2008
-
Ingår i: Nuclear Instruments & Methods in Physics Research. Section B: Beam Interactions with Materials and Atoms. - Amsterdam : Elsevier BV. - 0168-583X .- 1872-9584. ; 266:21, s. 4808-4815
-
Tidskriftsartikel (refereegranskat)abstract
- This paper describes the characterisation of an ultra-thin silicon semicondoctor Delta E detector to be used as a pre-cell ion hit detector in single ion experiments on individual, living cells. The characteristics of interest for this specific application are the hit detection efficiency, which has to be close to 100% to enable bombardment with either a single ion or a counted number of ions, the beam spreading, which should be as small as possible to maintain the targeting accuracy, and the vacuum tightness, since the detector is intended, if possible, to be used simultaneously as vacuum window. The hit detection efficiency was shown to be above 99% when detecting alpha particles or 2 MeV protons, the increase in beam size was about 1 mu m and the vacuum tightness was comparable to that of the Si3N4 wafer which is normally used as vacuum window, thus the Delta E detector fulfils the main criteria to function properly as a single ion hit detector. (C) 2008 Elsevier B.V. All rights reserved.
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| 97. |
- Nilsson, Charlotta, et al.
(författare)
-
Evaluation of a pre-cell hit detector for the future single ion hit facility in Lund
- 2006
-
Ingår i: Nuclear Instruments & Methods in Physics Research. Section B: Beam Interactions with Materials and Atoms. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 249:1-2, s. 924-927
-
Tidskriftsartikel (refereegranskat)abstract
- Currently, a single ion hit facility, for irradiation of single cells with single, light MeV ions is under development at the Lund Nuclear Microprobe. In this paper, a novel approach to the ion detection issue is presented. A silicon detector, a type utilized at other facilities for post-cell ion detection, has been investigated as a possible option for pre-cell hit detection. If proven successful, this detector could possibly also be used simultaneously as vacuum window. The first experiments carried out on the 9 mu m thick silicon detector, with an area of 4 mm(2), have been aimed at investigations of signal-to-noise ratio and efficiency. The results thus far reveal a low noise level and a noise distribution, which is well separated from the signal peak. However, the efficiency remains a problem, since at present it is far from the required 100%.
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| 98. |
- Niskanen, Ilpo, et al.
(författare)
-
Determination of nanoparticle size using Rayleigh approximation and Mie theory
- 2019
-
Ingår i: Chemical Engineering Science. - : Elsevier. - 0009-2509 .- 1873-4405. ; 201, s. 222-229
-
Tidskriftsartikel (refereegranskat)abstract
- Accurate determination of the size of nanoparticles has an important role in many different scientific and industrial purposes, such as in material, medical and environment sciences, colloidal chemistry and astrophysics. We describe an effective optical method to determine the size of nanoparticles by analysis of transmission and scattering of visible spectral range data from a designed UV-Vis multi-spectrophotometer. The size of the nanoparticles was calculated from the extinction cross section of the particles using Rayleigh approximation and Mie theory. We validated the method using polystyrene nanospheres, cellulose nanofibrils, and cellulose nanocrystals. A good agreement was achieved through graphical analysis between measured extinction cross section values and theoretical Rayleigh approximation and Mie theory predictions for the sizes of polystyrene nanospheres at wavelength range 450-750 nm. Provided that Rayleigh approximation's forward scattering (FS)/back scattering (BS) ratio was smaller than 1.3 and Mie theory's FS/BS ratio was smaller than 1.8. A good fit for the hydrodynamic diameter of nanocellulose was achieved using the Mie theory and Rayleigh approximation. However, due to the high aspect ratio of nanocellulose, the obtained results do not directly reflect the actual cross-sectional diameters of the nanocellulose. Overall, the method is a fast, relatively easy, and simple technique to determine the size of a particle by a spectrophotometer. Consequently, the method can be utilized for example in production and quality control purposes as well as for research and development applications.
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| 99. |
- Niskanen, Ilpo, et al.
(författare)
-
Determination of relative solids concentration in homogeneous dual component pulp-filler suspension by multi-spectrophotometer
- 2020
-
Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 35:1, s. 71-77
-
Tidskriftsartikel (refereegranskat)abstract
- The concentration of fibers and fillers in the pulp suspension is an important parameter in the monitoring process. This paper proposes a versatile optical measurement system to estimate the concentration of a solids mixture in water. The geometry used in a multi-spectrophotometer (MSM) enables the controlled observation of transmission, and forward scattering light from the suspension in the UV-visible spectral range. We have developed the new fibers mixing system which gives a homogenous distribution of the fines and fillers making it possible to increase the reproducibility and accuracy of the measurement. The data analysis is based on the Beer-Lambert law and CIELAB color space equations. The results show that the proposed method is accurate for measuring the fines and filler concentrations in multicomponent suspensions.
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| 100. |
- Niskanen, Ilpo, et al.
(författare)
-
Determining the complex refractive index of cellulose nanocrystals by combination of Beer-Lambert and immersion matching methods
- 2019
-
Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier BV. - 0022-4073 .- 1879-1352. ; 235, s. 1-6
-
Tidskriftsartikel (refereegranskat)abstract
- Nanocelluloses have received significant interest due to their unique structural, mechanical, and optical properties. Nanocellulose refractive indices can be used to indicate many crucial characteristics, such as crystallinity, transparency, and purity. Thus, accurate measurement is important. This study describes a new method to determine the wavelength dependent complex refractive index of cellulose nanocrystals (CNCs) by the measurement of light transmittance with a spectrophotometer. The data analysis is based on a combination of the Beer-Lambert and immersion liquid matching equations. The immersion liquid method's main advantage is that it is independent of particle shape and size. Moreover, the measurement is easy and relatively quick to perform. The present procedure is not restricted to the nanocellulose and could potentially be applied to other nanomaterials, such as hyphenate nanoparticle-based, lignin nanoparticles, nanopigments, biological entities, structural elements of dielectric metamaterials, and nanoparticle-based composites.
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