Charged Particle Imaging Research Articles

Monolithic pixel sensors in deep-submicron SOI Technology

Monolithic pixel sensors for charged particle detection and imaging applicationshave been designed and fabricated using commercially available, deep-submicron Silicon-On-Insulator(SOI) processes, which insulate a thin layer of integrated full CMOS electronics from a high-resistivitysubstrate by means of a buried oxide. The substrate is contacted from the electronics layer through viasetched in the buried oxide, allowing pixel implanting and reverse biasing. This paper summarizes theperformances achieved with a first prototype manufactured in the OKI 0.15 μm FD-SOI process,featuring analog and digital pixels on a 10 μm pitch. The design and preliminary resultson the analog section of a second prototype manufactured in the OKI 0.20 μm FD-SOI processare briefly discussed.

Multihit two-dimensional charged-particle imaging system with real-time image processing at 1000 frames/s

A high-speed imaging system developed for two-dimensional counting of charged particles is presented. Microchannel plates coupled with a phosphor screen of a short emission lifetime (<1 micros) are used to visualize the two-dimensional positions of charged-particle impacts, and the image on the phosphor screen is captured with a 1 kHz complementary metal oxide semiconductor (CMOS) image sensor (512x512 pixels). A multistage image intensifier consisting of the first and second generation devices was used to compensate for the low sensitivity of CMOS. The centers of gravity (COG) of individual light spots in each image frame are calculated in real time by a field programmable gate array circuit. The performance of this system is tested by time-resolved photoelectron imaging (TR-PEI) of NO using (1+1(')) resonance enhanced multiphoton ionization via the A (2)Sigma(+) state with a femtosecond laser operated at 1 kHz. The new system enabled COG detection for more than ten particles in each frame at 1 kHz and achieved an extremely high degree of accuracy in the measurement of photoelectron angular distributions in TR-PEI.

Optimization of monolithic charged-particle sensor arrays

Direct-detection CMOS image sensors optimized for charged-particle imaging applications, such as electron microscopy and particle physics, have been designed, fabricated and characterized. These devices directly image charged particles without reliance on image-degrading hybrid technologies such as the use of scintillating materials. Based on standard CMOS Active Pixel Sensor (APS) technology, the sensor arrays use an 8–20 μm thick epitaxial layer that acts as a sensitive region for the generation and collection of ionization electrons resulting from impinging high-energy particles. A range of optimizations to this technology have been developed via simulation and experimental device design. These include the simulation and measurement of charge-collection efficiency vs. recombination, effect of diode area and stray capacitance vs. signal gain and noise, and the effect of different epitaxial silicon depths. Several experimental devices and full-scale prototypes are presented, including two prototypes that systematically and independently vary pixel pitch and diode area, and a complete high-resolution camera for electron microscopy optimized through experiment and simulation. The electron microscope camera has 1×1 k 2 pixels with a 5 μm pixel pitch and an 8 μm epitaxial silicon thickness.

Direct charged particle imaging sensors

CMOS image sensors optimized for charged particle imaging applications, such as electron microscopy and particle physics, have been designed and characterized. These directly image charged particles without reliance on performance-degrading hybrid technologies such as the use of scintillating materials. Based on standard CMOS active pixel sensor (APS) technology, the sensor arrays uses an 8–20 μm epitaxial layer that acts as a thicker sensitive region for the generation and collection of ionization electrons resulting from impinging high-energy particles. This results in a 100% fill factor and a far larger signal per incident electron than a standard CMOS photodiode could provide. A 512×550 pixels prototype has been fabricated and used extensively in an electron microscope, including having been used to take sample images. Temporal noise was measured to be 0.9 mV RMS, and the dynamic range was 60 dB. Power consumption at 70 frames/s is 20 mW. The full-width half-maximum of the collected ionization electron distribution was found to be 5.5 μm, yielding a spatial resolution of approximately 2.3 μm for individual incident electrons, and the modulation transfer function of the sensor at the Nyquist limit is to be 32%.

Femtosecond time-resolved charged particle imaging studies of the ultraviolet photodissociation of the NO dimer

Ultraviolet photodissociation dynamics of the NO dimer into NO(Α)+NO(Χ) in a supersonic molecular beam is studied by femtosecond pump-probe charged particle imaging. Time-resolved photoelectron imaging reveals that photoionization from the Franck–Condon region of the excited state(s) reaches vibrationally excited states of the NO dimer cation, resulting in spontaneous fragmentation into NO+NO+ even at the shortest pump-probe time delays. The corresponding photoelectron energy distribution extending up to more than 1 eV above the ionization threshold indicates a large structural difference between the dimer cation and the photoexcited neutral state. From the isotropic photoelectron distribution, this state is assigned to a valence state rather than a Rydberg state. The characteristic photoelectron distribution and also the small NO dimer ion signal vanish within 200 fs. In the same time the photoelectron image rapidly evolves from an almost isotropic distribution into an anisotropic one characteristic for ionization from the 3s Rydberg state of the NO dimer that is adiabatically correlated with the NO(Α)+NO(Χ) fragments. Time-resolved photoion imaging used to measure the translational energy release in the NO(Α)+NO(Χ) dissociation channel reveals that at least one of the fragments, most likely NO(Χ), has an inverted vibrational state distribution. The strong vibrational excitation is in qualitative agreement with a large structural change of the NO dimer in the excited state from the neutral ground state, which presumably involves excitation of the NO stretching vibration in the dimer.

Performance of large area Micro Pixel Chamber

A novel gaseous two-dimensional imaging detector “Micro Pixel Chamber (μ-PIC)” has been developed. This detector is based on double sided printed circuit board (PCB). We have developed large area (10 cm×10 cm) μ -PICs with 65536 pixel anodes of 400 μm pitch on a 100 μm thick insulating substrate. Achieved energy resolution was 30% (FWHM) at 5.9 keV , and a gas gain of 7000 was obtained with argon ethane (8:2) gas mixture. This gain is high enough to detect minimum ionizing particles with such a small electrode pitch. Although several discharges occurred during 65 h continuous operation, the detectors have kept stable operation with high gain. The μ-PIC is a useful detector for many applications e.g. X-ray, gamma ray, and charged particle imaging. The micro electrode structure allows us to measure directions of primary electrons due to incident X-rays or gamma rays, which provide a strong method for X-ray polarimetry and gamma-ray imaging.

Dark current reduction in stacked-type CMOS-APS for charged particle imaging

A stacked CMOS-active pixel sensor (APS) with a newly devised pixel structure for charged particle detection has been developed. At low operation temperatures (<200 K), the dark current of the CMOS-APS is determined by the hot carrier effect. A twin well CMOS pixel with a p-MOS readout and n-MOS reset circuit achieves low leakage current as low as 5/spl times/10/sup -8/ V/s at the pixel electrode under liquid nitrogen temperature of 77 K. The total read noise floor of 0.1 mV/sub rms/ at the pixel electrode was obtained by nondestructive readout correlated double sampling (CDS) with the CDS interval of 21 s.

Development of micro pixel chamber

The novel gaseous detector “Micro Pixel Chamber (μ-PIC)” has been developed for X-ray, gamma-ray and charged particle imaging. The μ-PIC is made based on a double-sided printing circuit board, by which a large size detector could be produced easily. The operation tests were performed successfully using a 3 cm×3 cm μ -PIC with a 0.4 mm pitch. The gas gain and stability were measured in these tests. There is neither gain reduction nor discharge between anode and cathode at a gain of 10 3 for 5 days continuous operation. Also, no gain decrease was observed up to 10 7 cps(counts per second)/mm 2 intense X-ray irradiation.

A new design of the gaseous imaging detector: Micro Pixel Chamber

The novel gaseous detector “Micro Pixel Chamber (Micro PIC)” has been developed for X-ray, gamma-ray and charged particle imaging. This detector consists of double sided printing circuit board (PCB). The stable operation of Micro PIC is realized by thick substrate and wide anode strips. One of the most outstanding feature is the process of production and the cost. The base technology of producing Micro PIC is same as producing PCB, then detector with large detection area (more than 10 cm×10 cm ) can be made by present technology. Our first tests were performed using a 3 cm×3 cm detection area with a readout of 0.4 mm pitch. The gas gain and stability were measured in these tests. The gas gain of 10 4 was obtained using argon ethane (8:2) gas mixture. Also, there was no discharge between anodes and cathodes in the gain of 10 3 during two days of continuous operation. Although some discharges occurred in the higher gain (approximately 10 4), no critical damage on the detector was found.

Non-adiabatic effects in chemistry revealed by time-resolved charged-particle imaging

Recent advances in photoelectron and photoion imaging techniques are reviewed. The general background to photofragmentation spectroscopy and, in particular, the information that can be extracted from laboratory and molecular frame photoproduct angular distributions are briefly discussed. Recent technological advances to the photofragment imaging experiment first introduced by Chandler and Houston, such as velocity mapping and event counting, are also described. The main focus of the review is devoted to time-resolved imaging applications in which femtosecond pump?probe techniques are combined with charged particle imaging. We survey the recent literature and describe a number of applications; in particular we show how pump?probe photoelectron imaging can be used to follow intersystem crossing in molecules such as pyrazine, and we also show how the transfer of nuclear coherences can be followed with this technique. We discuss how time-resolved pump?probe photofragment imaging can be used to follow unimolecular decomposition of free radicals with small reaction barriers and we show how this can lead to non-statistical behaviour as a result of restricted rovibrational coupling. Finally, we describe recent applications of pump?probe Coulomb explosion imaging which has the potential to image directly the nuclear wavefunction throughout the course of a chemical reaction. The review closes with some brief conclusions and pointers for future work.

Non-adiabatic effects in chemistry revealed by time-resolved charged-particle imaging

Non-adiabatic effects in chemistry revealed by time-resolved charged-particle imaging

A monolithic active pixel sensor for charged particle tracking and imaging using standard VLSI CMOS technology

A novel Monolithic Active Pixel Sensor (MAPS) for charged particle tracking made in a standard CMOS technology is proposed. The sensor is a photodiode, which is readily available in a CMOS technology. The diode has a special structure, which allows the high detection efficiency required for tracking applications. The partially depleted thin epitaxial silicon layer is used as a sensitive detector volume. Semiconductor device simulation, using either ToSCA based or 3-D ISE-TCAD software packages shows that the charge collection is efficient, reasonably fast (order of 100 ns), and the charge spreading limited to a few pixels only. A first prototype has been designed, fabricated and tested. It is made of four arrays each containing 64×64 pixels, with a readout pitch of 20 μm in both directions. The device is fabricated using standard submicron 0.6 μm CMOS process, which features twin-tub implanted in a p-type epitaxial layer, a characteristic common to many modern CMOS VLSI processes. Extensive tests made with soft X-ray source ( 55Fe) and minimum ionising particles (15 GeV/ c pions) fully demonstrate the predicted performances, with the individual pixel noise (ENC) below 20 electrons and the Signal-to-Noise ratio for both 5.9 keV X-rays and Minimum Ionising Particles (MIP) of the order of 30. This novel device opens new perspectives in high-precision vertex detectors in Particle Physics experiments, as well as in other application, like low-energy beta particle imaging, visible light single photon imaging (using the Hybrid Photon Detector approach) and high-precision slow neutron imaging.

High resolution imaging for charged particles using CR-39 and atomic force microscopy

Recently Atomic Force Microscopy (AFM) has been used for a readout of Solid State Nuclear Track Detectors (SSNTD). In this technique, the SSNTD is etched for very short time and scanned by an AFM to observe track etch pits. Etch pits of several hundred nm in diameter can be observed. We applied this technique to charged particle imaging using CR-39. CR-39 plates were etched for about 5 min in 27% NaOH solution at 70°C. Then very small etch pits were measured. A typical diameter of etch pits was below 1 μm and a typical etch pit depth was about several hundred nm. The obtained image has demonstrated a position resolution of less than 100 nm. Ion microbeam profiles were also measured by the system.

Factors affecting image formation in accelerator-based fast neutron radiography

Fast neutrons can be generated with accelerators via various reactions. The reactions 7Li(p,n) 7Be and D(d,n) 3He were employed for this study to generate neutrons at various energies. Radiographs of different materials have been produced and analysed in terms of contrast and resolution. Monte Carlo methods have been used to evaluate the physical factors determining the image quality in these practical situations. In each case the theoretical and experimental values were compared. A series of gamma-ray radiographs generated using a Co-60 source provided an experimental benchmark for comparison with fast neutron radiographs. The neutron radiographs were generated as a function of fast neutron producing reaction (neutron energy spectrum), scintillator type and thickness, charged particle energy, imaging geometry and sample material. Both a CCD camera operating at room temperature and cooled CCD were used in the imaging process.

The early stages of MgO epitaxy on lattice-matched Cr 0.7Mo 0.3(001)

We have investigated the structure and morphology of thin epitaxial overlayers of MgO on lattice-matched interlayers of Cr 0.7Mo 0.3 grown on MgO(001) substrates. Lattice matching results in unstrained MgO epitaxial films with short- and long-range structural order of comparable quality to those of buffer layers of MgO grown on MgO(001) under optimized step-flow growth conditions. In addition, the structural coherence of the oxide/metal interface is excellent due to lattice matching, in contrast to lattice-mismatched systems. However, MgO does not grow in a perfectly laminar fashion on Cr 0.7Mo 0.3 due to surface and interface free-energy imbalances; thin MgO films exhibit mean roughnesses of ∼ 4 A ̊ with terrace widths of several hundred Å. Nevertheless, the use of lattice-matched conducting interlayers between a bulk oxide substrate and an epitaxial thin film of the same material allows high-quality insulting oxides to be prepared on conducting substrates. This approach in turn permits the full arsenal of charged-particle spectroscopic, diffraction and imaging probes to be applied to investigations of the surface science of insulators.

Epitaxial growth of MgO on lattice-matched Cr xMO 1−x(001)

We describe the MBE growth and structural characterization of ultrathin layers of epitaxial MgO on Cr xMO 1−x ( x ≈ 0.65 ). The metal alloy was grown as an epitaxial film on high-quality MgO(001) substrates. This kind of epitaxy produces unstrained MgO surfaces of very high structural quality on a conducting substrate. Such materials will enable definitive investigations of surface structure and reactivity using charged-particle spectroscopy, diffraction, and imaging. The role of lattice matching is discussed and shown to be very important.

Computed tomography and advanced X-ray and charged-particle imaging: 38798 Martz, H.; Brase, J.; Azevedo, S.; Ryon, R. Lawrence Livermore National Laboratory, California (United States), UCID-21263, DE88-003728, 19 pp. (17 Sep. 1987)

Computed tomography and advanced X-ray and charged-particle imaging: 38798 Martz, H.; Brase, J.; Azevedo, S.; Ryon, R. Lawrence Livermore National Laboratory, California (United States), UCID-21263, DE88-003728, 19 pp. (17 Sep. 1987)

Computed tomography and advanced X-ray and charged-particle imaging 38798 Martz, H.; Brase, J.; Azevedo, S.; Ryon, R. Lawrence Livermore National Laboratory, California (United States), UCID-21263, DE88-003728, 19 pp. (17 Sep. 1987)

Computed tomography and advanced X-ray and charged-particle imaging 38798 Martz, H.; Brase, J.; Azevedo, S.; Ryon, R. Lawrence Livermore National Laboratory, California (United States), UCID-21263, DE88-003728, 19 pp. (17 Sep. 1987)

Rapid Detection and Size Determination of PuO2 Particles Using a Charged-particle Imaging Video Monitor System

A charged-particle imaging video monitor system was constructed and applied to video imaging of the position profile of PuO2 particles on filter paper. The imaging video monitor system consists of a detector head, a silicon intensifier target (SIT) camera, a video frame memory, and a personal computer. The system can display the distribution image of PuO2 particles becoming gradually clearer on a video monitor. The integrated image that is transferred to the computer is analyzed quantitatively for the radioactivity of each PuO2 particle deposited on the filter paper. The system can not only rapidly distinguish PuO2 particle contamination from Rn daughter products, but can also determine the size distribution of the PuO2 particles.

Charged-particle imaging video monitor system

A charged-particle imaging video monitor system was constructed for video imaging of the distributions of alpha-emitting and low-energy beta-emitting nuclides. The imaging video monitor system consists of a detector head, a silicon intensifier target (SIT) camera, a video frame memory, and a personal computer. The system can display not only the scintillation image due to radiation on the video monitor, but also the integrated video image becoming gradually clearer on another video monitor. The integrated image is transferred to a personal computer for image processing. The distortion of the image is about 5%, and the spatial resolution is about 2 line pairs (lp) mm−1.