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ABSTRACT: Purpose: To investigate the dosimetric properties of synthetic single crystal diamond based Schottky diodes under irradiation with therapeutic electron beams from linear accelerators.Methods: A single crystal diamond detector was fabricated and tested under 6, 8, 10, 12, and 15 MeV electron beams. The detector performances were evaluated using three types of commercial detectors as reference dosimeters: an Advanced Markus plane parallel ionization chamber, a Semiflex cylindrical ionization chamber, and a p-type silicon detector. Preirradiation, linearity with dose, dose rate dependence, output factors, lateral field profiles, and percentage depth dose profiles were investigated and discussed.Results: During preirradiation the diamond detector signal shows a weak decrease within 0.7% with respect to the plateau value and a final signal stability of 0.1% (1σ) is observed after about 5 Gy. A good linear behavior of the detector response as a function of the delivered dose is observed with deviations below ±0.3% in the dose range from 0.02 to 10 Gy. In addition, the detector response is dose rate independent, with deviations below 0.3% in the investigated dose rate range from 0.17 to 5.45 Gy∕min. Percentage depth dose curves obtained from the diamond detector are in good agreement with the ones from the reference dosimeters. Lateral beam profile measurements show an overall good agreement among detectors, taking into account their respective geometrical features. The spatial resolution of solid state detectors is confirmed to be better than that of ionization chambers, being the one from the diamond detector comparable to that of the silicon diode. A good agreement within experimental uncertainties was also found in terms of output factor measurements between the diamond detector and reference dosimeters.Conclusions: The observed dosimetric properties indicate that the tested diamond detector is a suitable candidate for clinical electron beam dosimetry.
Medical Physics 02/2013; 40(2):021712. · 2.83 Impact Factor
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Marco Marinelli,
E Milani,
G Prestopino,
C Verona,
G Verona-Rinati,
M Angelone,
M Pillon,
V Kachkanov,
N Tartoni,
M Benetti,
D Cannatà,
F Di Pietrantonio
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ABSTRACT: A novel beam position monitor, operated at zero bias voltage, based on high-quality chemical-vapor-deposition single-crystal Schottky diamond for use under intense synchrotron X-ray beams was fabricated and tested. The total thickness of the diamond thin-film beam monitor is about 60 µm. The diamond beam monitor was inserted in the B16 beamline of the Diamond Light Source synchrotron in Harwell (UK). The device was characterized under monochromatic high-flux X-ray beams from 6 to 20 keV and a micro-focused 10 keV beam with a spot size of approximately 2 µm × 3 µm square. Time response, linearity and position sensitivity were investigated. Device response uniformity was measured by a raster scan of the diamond surface with the micro-focused beam. Transmissivity and spectral responsivity versus beam energy were also measured, showing excellent performance of the new thin-film single-crystal diamond beam monitor.
Journal of Synchrotron Radiation 11/2012; 19(Pt 6):1015-20. · 2.73 Impact Factor
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ABSTRACT: To determine the potentialities of synthetic single crystal diamond Schottky diodes for accurate dose measurements in radiation therapy small photon beams.
The dosimetric properties of a diamond-based detector were assessed by comparison with a reference microionization chamber. The diamond device was operated at zero bias voltage under irradiation with high-energy radiotherapic photon beams. The stability of the detector response and its dose and dose rate dependence were measured. Different square field sizes ranging from 1 × 1 cm(2) to 10 × 10 cm(2) were used during comparative dose distribution measurements by means of percentage depth dose curves (PDDs), lateral beam profiles, and output factors. The angular and temperature dependence of the diamond detector response were also studied.
The detector response shows a deviation from linearity of less than ±0.5% in the 0.01-7 Gy range and dose rate dependence below ±0.5% in the 1-6 Gy∕min range. PDDs and output factors are in good agreement with those measured by the reference ionization chamber within 1%. No angular dependence is observed by rotating the detector along its axis, while ∼3.5% maximum difference is measured by varying the radiation incidence angle in the polar direction. The temperature dependence was investigated as well and a ±0.2% variation of the detector response is found in the 18-40 °C range.
The obtained results indicate the investigated synthetic diamond-based detector as a candidate for small field clinical radiation dosimetry in advanced radiation therapy techniques.
Medical Physics 07/2012; 39(7):4493-501. · 2.83 Impact Factor
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ABSTRACT: X-ray and UV photovoltaic Schottky photodiodes based on single crystal diamond were recently developed at Rome “Tor Vergata” University laboratories. In this work, different rectifying metallic contact materials were thermally evaporated on the oxidized surface of intrinsic single crystal diamond grown by chemical vapor deposition. Their impact on the detection performance in the extreme UV and soft x-ray spectral regions was studied. The electrical characterization of the metal/diamond Schottky junctions was performed at room temperature by measuring the capacitance–voltage characteristics. The diamond photodiodes were then tested both over the extreme UV spectral region from 10 to 60 eV by using He-Ne DC gas discharge as a radiation source and toroidal vacuum monochromator, and in the soft x-ray range from 6 to 20 keV at the Diamond Light Source synchrotron x-ray beam-line in Harwell (UK). In both experimental setups, time response and spectral responsivity were analyzed for all the investigated Schottky contact materials. A good agreement between the experimental data and theoretical results from Monte Carlo simulations is found
Journal of Applied Physics 09/2011; 110(5):054513-054513-6. · 2.17 Impact Factor
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ABSTRACT: A study on the effect of secondary electron emission, which strongly affects the detection of extreme-UV radiation, was performed on diamond detectors. Two different structures were compared: interdigitated contacts and a transverse Schottky diode configuration. Both devices were electrically characterized by I-V measurements and their responsivity was measured in the extreme UV spectral region (20–120 nm) by using He-Ne gas discharge radiation sources and a toroidal grating vacuum monochromator. Through an ad-hoc measurement configuration, the contributions of the internal photocurrent and of the photoemission current have been analyzed and separately evaluated. The results showed that secondary electron emission, which clearly depends on the experimental conditions (e.g., external electric field, pressure, etc.), is one of the most relevant processes affecting the spectral responsivity in the extreme UV band. In particular, for interdigitated devices, extreme care must be taken in order to obtain an absolute value of their responsivity, while detectors in the transverse configuration can be shielded in such a way to avoid secondary electron current contribution and therefore provide a more correct and reliable response.
Journal of Applied Physics 07/2011; 110(1):014501-014501-8. · 2.17 Impact Factor
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A. Pietropaolo,
C. Andreani,
M. Rebai,
L. Giacomelli,
G. Gorini,
E. Perelli Cippo,
M. Tardocchi,
A. Fazzi,
G. Verona Rinati,
C. Verona, Marco Marinelli,
E. Milani,
C. D. Frost,
E. M. Schooneveld
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ABSTRACT: A novel type of fast-neutron (energy En>1 MeV) counter is presented. It is made of a fissionable natural-uranium foil faced to an intrinsic single-crystal diamond that detects the neutron-induced fission fragments escaping the uranium sheet. The fast response of the diamond is a key feature for its use at pulsed spallation neutron sources for applications in beam monitoring and spectrum measurements with mm spatial resolution. This is an important issue to be addressed in the development of beam lines dedicated to the investigation of the so-called single-event effects in electronics, such as the ChipIr instrument designed for the ISIS spallation source in the UK. Tests of the device at the ROTAX beam line at ISIS have shown its potentiality for the proposed application.
EPL (Europhysics Letters) 06/2011; 94(6):62001. · 2.17 Impact Factor
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I. Ciancaglioni, Marco Marinelli,
E. Milani,
G. Prestopino,
C. Verona,
G. Verona-Rinati,
M. Angelone,
M. Pillon,
I. Dolbnya,
K. Sawhney,
N. Tartoni
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ABSTRACT: A synthetic multistrip single-crystal-diamond detector based on a p-type/intrinsic diamond/Schottky metal transverse configuration, operating at zero-bias voltage, was developed. The device was characterized at the Diamond Light Source synchrotron in Harwell (UK) under monochromatic high-flux X-ray beams from 6 to 20 keV and a micro-focused 10 keV beam with a spot size of ~3 μm. No significant pixel-to-pixel variation of both spectral responsivity and time response, high spatial resolution and good signal uniformity along each strip were found, suggesting the tested device structure as a promising sensor for X-ray and UV radiation imaging.
EPL (Europhysics Letters) 04/2011; 94(2):28004. · 2.17 Impact Factor
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S. Almaviva, Marco Marinelli,
E. Milani,
G. Prestopino,
A. Tucciarone,
C. Verona,
G. Verona-Rinati,
M. Angelone,
M. Pillon,
I. Dolbnya,
K. Sawhney,
N. Tartoni
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ABSTRACT: Recently, solid state photovoltaic Schottky diodes, able to detect ionizing radiation, in particular, x-ray and ultraviolet radiation, have been developed at the University of Rome “Tor Vergata.” We report on a physical and electrical properties analysis of the device and a detailed study of its detection capabilities as determined by its electrical properties. The design of the device is based on a metal/nominally intrinsic/p-type diamond layered structure obtained by microwave plasma chemical vapor deposition of homoepitaxial single crystal diamond followed by thermal evaporation of a metallic contact. The device can operate in an unbiased mode by using the built-in potential arising from the electrode-diamond junction. We compare the expected response of the device to photons of various energies calculated through Monte Carlo simulation with experimental data collected in a well controlled experimental setup i.e., monochromatic high flux x-ray beams from 6 to 20 keV, available at the Diamond Light Source synchrotron in Harwell (U.K.).
Journal of Applied Physics 02/2010; · 2.17 Impact Factor
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ABSTRACT: High performance neutron detectors sensitive to both thermal and fast neutrons are of great interest to monitor the high neutron flux produced, e.g., by fission and fusion reactors. An obvious requirement for such an application is neutron irradiation hardness. This is why diamond based neutron detectors are currently under test in some of these facilities. In this paper the damaging effects induced in chemical vapor deposition (CVD) diamond based detectors by a neutron fluence of ∼2×10<sup>16</sup> neutrons / cm <sup>2</sup> have been studied and significant changes in spectroscopic, electrical, and optical properties have been observed. The detectors are fabricated using high quality synthetic CVD single crystal diamond using the p -type/intrinsic/Schottky metal/ <sup>6</sup> L iF layered structure recently proposed by Marinelli etal [Appl. Phys. Lett. 89, 143509 (2006)], which allows simultaneous detection of thermal and fast neutrons. Neutron radiation hardness up to at least 2×10<sup>14</sup> n/ cm <sup>2</sup> fast (14 MeV) neutron fluence has been confirmed so far [see Pillon etal, (Fusion Eng. Des. 82, 1174 (2007)]. However, at the much higher neutron fluence of ∼2×10<sup>16</sup> neutrons / cm <sup>2</sup> damage is observed. The detector response to 5.5 MeV <sup>241</sup> A m α -particles still shows a well resolved α -peak, thus confirming the good radiation hardness of the device but a remarkable degradation and a significant instability with time of charge collection efficiency and energy resolution arise. Symmetric, nearly Ohmic I-V (current-voltage) characteristics have been recorded from the met-
al/intrinsic/ p -doped diamond layered structure, which before neutron irradiation acted as a Schottky barrier diode with a strong rectifying behavior. The nature and the distribution of the radiation induced damage have been deeply examined by means of cathodoluminescence spectroscopy. A more heavily damaged area into the intrinsic diamond at the same position and with the same extension of the <sup>6</sup> L iF layer has been found, the increased damage being ascribed to the highly ionizing particles produced in the <sup>6</sup> L iF layer by thermal neutrons through the nuclear reaction <sup>6</sup> L i (n,α)T .
Journal of Applied Physics 11/2009; · 2.17 Impact Factor
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M. G. Donato,
G. Messina,
G. Verona Rinati,
S. Almaviva,
G. Faggio, Marco Marinelli,
E. Milani,
G. Prestopino,
S. Santangelo,
P. Tripodi,
C. Verona
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ABSTRACT: In this work, the characteristics of the edge emission of a homoepitaxial diamond sample grown by chemical vapor deposition (CVD) are reported. Photoluminescence has been excited at 220 nm by using a tunable optical parametric oscillator laser, giving ∼5 ns wide laser pulses. The temperature of the sample has been decreased from room temperature down to 30 K. Free exciton emission and its phonon replicas have been observed at all the temperatures explored. Excitonic lifetime shows a nonmonotonic dependence on the sample temperature. Luminescence at low temperatures from electron-hole drops at approximately 5.18 eV has been observed for the first time in CVD diamond.
Journal of Applied Physics 10/2009; · 2.17 Impact Factor
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ABSTRACT: We report on a new solid state dosimeter based on chemical vapor deposition (CVD) single crystal diamond fabricated at Roma "Tor Vergata" University laboratories. The dosimeter has been specifically designed for direct neutron dose measurements in boron neutron capture therapy (BNCT). The response to thermal neutrons of the proposed diamond dosimeter is directly due to (10)B and, therefore, the dosimeter response is directly proportional to the boron absorbed doses in BNCT. Two single crystal diamond detectors are fabricated in a p-type/intrinsic/metal configuration and are sandwiched together with a boron containing layer in between the metallic contacts (see Fig.1). Neutron irradiations were performed at the Frascati Neutron Generator (FNG) using the 2.5 MeV neutrons produced through the D(d,n)(3)He fusion reaction. Thermal neutrons were then produced by slowing down the 2.5 MeV neutrons using a cylindrical polymethylmethacrylate (PMMA) moderator. The diamond dosimeter was placed in the center of the moderator. The products of (10)B(n,alpha)Li nuclear reaction were collected simultaneously giving rise to a single peak. Stable performance, high reproducibility, high efficiency and good linearity were observed.
Applied radiation and isotopes: including data, instrumentation and methods for use in agriculture, industry and medicine 04/2009; 67(7-8 Suppl):S183-5. · 1.09 Impact Factor
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ABSTRACT: Diamond exhibits many properties such as an outstanding radiation hardness and fast response time both important to design detectors working in extremely radioactive environments. Among the many applications these devices can be used for, there is the development of a fast and radiation hard neutron detector for the next generation of fusion reactors, such as the International Thermonuclear Experimental Reactor project, under construction at Cadarache in France. A technology to routinely produce electronic grade synthetic single crystal diamond detectors was recently developed by our group. One of such detectors, with an energy resolution of 0.9% as measured using an <sup>241</sup> A m α particle source, has been heavily irradiated with 14.8 MeV neutrons produced by the Frascati Neutron Generator. The modifications of its spectroscopic properties have been studied as a function of the neutron fluence up to 2.0×10<sup>14</sup> n/ cm <sup>2</sup> . In the early stage of the irradiation procedure an improvement in the spectroscopic performance of the detector was observed. Subsequently the detection performance remains stable for all the given neutron fluence up to the final one thus assessing a remarkable radiation hardness of the device. The neutron damage in materials has been calculated and compared with the experimental results. This comparison is discussed within the nonionizing energy loss (NIEL) hypothesis, which states that performance degradation is proportional to NIEL.
Journal of Applied Physics 10/2008; · 2.17 Impact Factor
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Marco Marinelli,
E. Milani,
G. Prestopino,
A. Tucciarone,
C. Verona,
G. Verona-Rinati,
M. Angelone,
D. Lattanzi,
M. Pillon,
R. Rosa,
E. Santoro
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ABSTRACT: Thermal neutron flux monitors were fabricated using chemical vapor deposited single crystal diamond in a p -type/intrinsic/metal/ <sup>6</sup> Li F layered structure. They were placed 80 cm above the core midplane of a 1 MW research fission reactor, where the maximum neutron flux is 2.2×10<sup>9</sup> neutrons / cm <sup>2</sup> s . Good stability and reproducibility of the device response were observed over the whole reactor power range. A 150 000 counts / s count rate was measured at the maximum reactor power with no degradation of the detector signal. As the multiple pile-up process due to the slow readout electronics is accounted for, an excellent linearity of the diamond response is observed.
Applied Physics Letters 05/2007; · 3.84 Impact Factor
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ABSTRACT: Pulsed x-ray dose measurements have been carried at maximum x-ray energies from 40 to 120 KeV out by using a single crystal epitaxial diamond sample grown by chemical vapor deposition (CVD). Delivered doses were between 0.1 and 10 mGy and pulse duration times between 0.01 and 0.5 s. Values of dose linearity index very close to 1 (between 1.02 and 1.07) at increasing x-ray energies and pulse decay times between 15 and 20 ms were obtained. The reproducibility was very good with no memory effects. CVD homoepitaxial diamond results to be very promising for x-ray diagnostic applications.
Applied Physics Letters 04/2006; 88(15):151901-151901-3. · 3.84 Impact Factor
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ABSTRACT: The possibility to realize a high sensitive thermocouple by means of boron doped chemical vapour deposition (CVD) diamond
was investigated. The thermoelectric power of p-type diamond, grown by plasma enhanced CVD was studied for films of electrical resistivity in the 0.2–40Ωcm range in order
to asses the dependence of thermocouple sensitivity on the doping level. The p-type diamond films were prepared by CH3OH+B2O3 vapour addition to a 1% CH4–H2 gas mixture during the growth. The conductive films were then tested tracing the I–V characteristic in order to study the
conduction properties of the films. An appropriate experimental setup was built to evaluate the thermoelectric properties
of the grown samples for different temperatures imposed between two ends of the samples. Firstly, the output voltage was measured
maintaining a reference temperature of 273K at one end and varying the second temperature between 275.5 and 360.5K. A constant
value of the temperature drop of 5K was then used for an accurate evaluation of the thermoelectric properties of the diamond
films for different value of the average temperature. The measurements provided values of thermoelectric power in the range
0.3–0.6mV/K while conductivity increases. These values showed different decreasing behaviour with increasing temperature
for different resistivity of the sample. In particular, more relevant changes in thermoelectric power were measured for high
resistive samples.
Microsystem Technologies 01/2006; 12(4):365-368. · 0.93 Impact Factor
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ABSTRACT: High-quality single-crystal diamond films were homoepitaxially grown by chemical vapor deposition onto low cost high-pressure high-temperature diamond substrates. The transport properties of the obtained samples were studied by photoresponse characterization. Fast ultraviolet (5 ns) laser pulses at 215 nm were used as a probe. The time evolution of the photoinduced current was observed to closely reproduce the laser pulse shape, thus indicating a time response lower than the adopted laser pulse duration. Very stable and reproducible response was measured, so that neither priming nor memory effects are observed. However, a minor slow component shows up in the charge-integrated sample response, whose temperature dependence was investigated in a −25–+50 °C range. A systematic speed up of this slow component of the sample signal is observed, indicating the presence of shallow centers producing trapping-detrapping effects. The experimental results are discussed in the framework of a trapping-detrapping model affecting the charge transport mechanism and an activation energy of Ea = 0.4 eV was derived for the shallow trapping centers.
Applied Physics Letters 11/2005; 87(22):222101-222101-3. · 3.84 Impact Factor
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ABSTRACT: The growth conditions and the detection properties of a homoepitaxial diamond film, deposited in Roma “Tor Vergata” University Laboratories by microwave chemical vapor deposition on a high-pressure high-temperature single-crystal substrate are reported. An energy resolution as low as 1.1% was achieved when irradiating the device with 5.5 MeV α-particles. The dependence of the charge collection efficiency and the energy resolution on the applied voltage are reported as well. A clear saturation plateau was observed in both curves. Preliminary results with 14.8 MeV neutron irradiation are reported, showing a well separated (n,α0) reaction peak.
Applied Physics Letters 05/2005; 86(21):213507-213507-3. · 3.84 Impact Factor
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ABSTRACT: High-quality single-crystal diamond films, homoepitaxially grown by microwave chemical vapor deposition, have been used to produce diamond-based photodetectors. Such devices were tested over a very wide spectral range, from the extreme ultraviolet (UV) (20 nm) up to the near IR region (2400 nm). An optical parametric oscillator tunable laser was used to investigate the 210–2400 nm spectral range in pulse mode. In this region, the spectral response shows a UV to visible contrast of about 6 orders of magnitude. A time response shorter than 5 ns, i.e., the laser pulse duration, was observed. By integrating the pulse shape, a minor slow component was evidenced, which can be explained in terms of trapping–detrapping effects. Extreme UV gas sources and a toroidal grating vacuum monochromator were used to measure the device response down to 20 nm in continuous mode. In particular, the extreme UV He spectrum was measured and the He II m, 30.4 nmand He I 58.4 nm emission lines were clearly detected. The measured time response of 0.2 s is totally due to the instrumental readout time constants. In both experimental setups an extremely good stability and reproducibility of the device response were obtained, whereas no persistent photoconductivity nor undesirable pumping effects were observed.
Applied Physics Letters 05/2005; 86(19):193509-193509-3. · 3.84 Impact Factor
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ABSTRACT: Defects limiting the movement of charge carriers in polycrystalline chemical vapor deposition (CVD) diamond films are located within the grains or in grain boundaries. Their geometrical distribution in the sample is different and is usually unknown. We present here a method to quantitatively evaluate the concentration and distribution of in-grain and grain-boundary located active carrier traps. Since the impact of these two kinds of defects on the performance of CVD diamond based devices is different, it is possible to obtain the defect distribution by measuring the response of diamond alpha particle detectors as a function of film thickness. The Hecht theory, describing the efficiency of a semiconductor particle detector, has been modified to take into account the polycrystalline nature of CVD diamond. This extended Hecht model was then used to fit experimental data and extract quantitative information about the defect distribution.
Applied Physics Letters 02/2005; · 3.84 Impact Factor
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ABSTRACT: A method is presented to selectively characterize the traps involved in the pumping procedure of diamond films. The pumping process strongly reduces the concentration of active carrier trapping centers, leading to an enhancement of electronic properties of such material, and is obtained by irradiating the diamond films with ionizing radiation. Since the improved transport properties lead to an increased efficiency when diamond films are used as radiation detectors, valuable information on this process can be obtained by analyzing the response of diamond based particle detectors. For this purpose a high-quality diamond film was grown by microwave chemical vapor deposition and a particle detector was realized. Its response to a 5.5-MeV 241Am α-particles was measured after successive annealing steps performed at different temperatures in the 180–228 °C range. Before each annealing curve at a given temperature, the detector was driven to the pumped state through β-particle irradiation. The efficiency versus annealing time curves evidence a thermally induced detrapping, confirming the pumping mechanism as a filling and consequent passivation of defects. The analysis of the decay time of the detector efficiency as a function of temperature allows the determination of the activation energy of these defects, which is Ea = 1.62±0.15 eV. © 2003 American Institute of Physics.
Applied Physics Letters 11/2003; 83(18):3707-3709. · 3.84 Impact Factor
