Fabrication Of Detectors Research Articles

Design and Fabrication of Electrostatically Formed Nanowire Gas Sensors With Integrated Heaters

This work reports on the design and fabrication of planar gas sensors with membrane structure to allow in-situ heating capabilities crucial for enhancing gas sensing performances. The sensors are virtual nanowire field-effect transistor (FET) type devices, referred to as electrostatically formed nanowire (EFN) sensors. This work describes the design, fabrication, and performance of a 2 mm X 2 mm chip with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$850 ~\mu \text{m}$ </tex-math></inline-formula> diameter, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.5 ~\mu \text{m}$ </tex-math></inline-formula> thick membrane. The design has been analyzed using finite element simulations (FEM) and verified experimentally. The thermal efficiency of the heated membrane is found to be 10 mW to reach 400 °C, which is better than most of the reported membrane-based sensors. To improve sensitivity and for broader functionality, the sensing surface, unlike reported in most designs, is at the bottom of the membrane. The technology allows system on chip (SoC) integration and further can be used for the fabrication of handheld battery-operated gas detectors. [2021-0248]

Yttrium (Y) doped ZnO nanowire/p-Si heterojunction devices for efficient self-powered UV-sensing applications

In the current work, n-type Y-doped ZnO nanowires (n-Y:ZnO) and p-type Si heterojunctions are fabricated by employing two-step chemical bath deposition (CBD) process. The work demonstrates the systematic incorporation of Y in ZnO nanowires for achieving the low power UV response. The crystalline nature, morphology, chemical compositions of doped nanowires are studied extensively by employing XRD, FESEM, HRTEM, elemental mapping, EDS and XPS. The change in defect states due to Y incorporation has been studied in detail by using deconvoluated PL spectra. The results indicate that ZnO nanowires exhibit Zn interstitials dependent huge UV/blue luminescence and oxygen vacancy related lowest green luminescence simultaneously for selective 1% Y-doping. The best self-powered photoresponse has been achieved for 1% Y-doped ZnO nanowires/p-Si heterojunction under relatively low power UV illumination (374 nm @5 mW/cm2). More significantly, at self-powered mode, such heterojunction has been delivered a stable and fast (<1 s) photoresponse with a maximum responsivity of 225 mA/W and high On/Off ratio of ∼104. The work provides an insight into the fabrication of heterojunction UV detectors for next-generation self-powered, large area optoelectronic devices.

Statistical investigation of the large-area Si(Li) detectors mass-produced for the GAPS experiment

The lithium-drifted silicon (Si(Li)) detector developed for the General Antiparticle Spectrometer (GAPS) experiment features a thick (∼2.2 mm) sensitive layer, large (10 cm) diameter, and excellent energy resolution (∼4 keV for 20–100 keV X-rays) at a relatively high operating temperature (approximately −40 °C). Mass production of GAPS Si(Li) detectors has been performed to construct a large-volume silicon tracker for GAPS. We achieved the first success of the mass production of large-area Si(Li) detectors with a high (∼90%) yield rate. Valuable datasets related to detector fabrication, such as detector performance and manufacturing parameters, were recorded and collected during the mass production. This study analyzes the datasets using statistical methods with the aim of comprehensively examining the mass production and to gain valuable insight into the fabrication method. Sufficient uniformities of the performance parameters (leakage current and capacitance) between detectors and strips are found, demonstrating high-quality and stable mass production. We also search for correlations between detector performance and manufacturing parameters by using data-mining techniques. Conventional multivariate analysis (multiple regression analysis) and machine-learning techniques (regression tree analysis) are complementarily used, and it is found that the Li-drift process makes a significant contribution to the performance parameters of the finished detectors. Detailed investigation of the drift process is performed using environmental data, and physical interpretations are presented. Our results provide valuable insight into the fabrication methods for this kind of large-area Si(Li) detector, and encourages future projects that require large-volume silicon trackers.

Fabrication and characterization of resistance temperature detector by smart mask design

Fabrication and characterization of resistance temperature detector by smart mask design

Magnetron sputtering deposited large-scale Weyl semimetal THz detector

THz detectors are considered as a building block for a wide range of applications including THz imaging system as well as THz communication system. However, beset by low sensitivity, small effective detection area, high preparation cost and high noise equivalent power, further research still needs especially in high-performance and large-scale THz detectors. In order to fulfill this requirement, Weyl semimetal MoTe2 was chosen as the active layer due to its lower dark current and Weyl-point enhancement. Moreover, high-quality and large-scale THz MoTe2-based detectors were fabricated with an effective detection area of 1 mm × 6.3 mm by means of magnetron sputtering deposition method. With an external voltage applied, our device exhibits excellent surface plasmon polaritons effect for THz detection and demonstrates a photoresponse of 4 A/W and a noise equivalent power of 9.74 × 10-12 W Hz−1/2 under the illumination of 0.1 THz wave at room temperature. Our research paves the way to the fabrication of large-scale THz detectors, also proves that the Weyl semimetal can be an excellent candidate of high-performance material in long-wave detection.

Design and fabrication of single photon detector with ultra-large area superconducting nanowire array

&lt;sec&gt;Superconducting nanowire single-photon detector (SNSPD) is one of the most mainstream single-photon detectors at present, which possesses excellent comprehensive performance, including low time jitter, high efficiency, low dark count, and wide spectrum. However, the traditional single-pixel SNSPD suffers a lack of spatial resolution and a small photosensitive surface, which becomes a bottleneck associated with optical coupling efficiency. In addition, a single-pixel detector has no ability to resolving the photon number, whose working speed cannot be further improved due to the existence of dead time. While array devices can make up for the above deficiencies. Therefore, the development of a large-area SNSPD array is the key to free-space photon detection and other applications. In recent years, the relevant researches have been conducted and great progress has been achieved. However, the large-area SNSPD array is facing some intractable problems, including complex process, low yield, and difficult fabrication, owing to the photosensitive surface consisting of a large number of superconducting nanowires. Photons imaging is verified with this device. At present, in the existing studies mainly used is the three-dimensional technology with complicated process steps to fabricate large array SNSPDs. How to simplify the process has become a research focus.&lt;/sec&gt;&lt;sec&gt;In this work, we design an ultra-large area nanowire array structure and propose an innovative plane process. Taking advantage of the property that the electron beam resists HSQ (hydrogen silsesquioxane polymer) forming a silicon oxide electrical isolation layer after exposure, we fabricate a large array SNSPD with a simplified two-dimensional process and realize dimensionality reduction for the traditional three-dimensional process of a multilayer structure. By measurement in parallel, the devices enjoy high yield with no bad points found. In addition, a full-superconducting electrode is adopted in our design to reduce the thermal effect of resistors. We add series and parallel resistors in the pixels to divide the bias current evenly and expand the array scale optionally. At the same time, we also offer the design details of array SNSPDs, the related simulation of hot spots to verify the rationality of the design, the optimization of the preparation conditions of array devices, measurement scheme formulation, and other related work.&lt;/sec&gt;&lt;sec&gt;This work provides an idea for designing and fabricating ultra-large array SNSPD, which is expected to be applied to the fabrication of megapixel array SNSPDs. Combined with an efficient readout circuit, a focal plane photon detection and imaging system with both a large field of view and high sensitivity can be realized.&lt;/sec&gt;

Synthesis of CdZnTeSe single crystals for room temperature radiation detector fabrication: mitigation of hole trapping effects using a convolutional neural network

Synthesis of CdZnTeSe single crystals for room temperature radiation detector fabrication: mitigation of hole trapping effects using a convolutional neural network

Design and fabrication of superconducting single-photon detector operating in 5–10 μm wavelength band

&lt;sec&gt;High-performance mid-wave and long-wave infrared single-photon detectors not only have significant research value in the fields of infrared astronomy and defense technology, but also are the challenges in the field of single-photon detection technology. Superconducting nanowire single-photon detectors (SNSPDs) have shown excellent performances in the near-infrared band. However, how to further improve the cutoff wavelength &lt;i&gt;λ&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; is a topic of widespread concern. In this paper, the method of improving &lt;i&gt;λ&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; by regulating the superconducting disorder is discussed, and a detector with an operating wavelength band of 5–10 μm is designed and fabricated.&lt;/sec&gt;&lt;sec&gt;The studies show that the multiplication and diffusion behaviors of the quasiparticles always occur during the photon detection events, although the microscopic photodetection mechanism of SNSPD still lacks a perfect theoretical explanation. Therefore, the theoretical analysis mainly considers the influence of the quasiparticles in this paper, and the mathematical formula of the detection cutoff wavelength &lt;i&gt;λ&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; can be obtained based on the phenomenological quasiparticle diffusion model. Furthermore, the disorder-dependent superconducting phase transition temperature &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt;, superconducting energy gap &lt;i&gt;Δ&lt;/i&gt;, and electron thermalization time &lt;i&gt;τ&lt;/i&gt;&lt;sub&gt;th&lt;/sub&gt; are also considered, in order to obtain more precise results.&lt;/sec&gt;&lt;sec&gt;Theoretical analysis suggests that the increase in the sheet resistance &lt;i&gt;R&lt;/i&gt;&lt;sub&gt;s&lt;/sub&gt;, which evaluates the disorder strength, will help to increase &lt;i&gt;λ&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt;. For example, when the nanowire width is kept at 30 nm and &lt;i&gt;R&lt;/i&gt;&lt;sub&gt;s&lt;/sub&gt; &gt; 380 Ω/square, it can be deduced that &lt;i&gt;λ&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; is larger than 10 μm.&lt;/sec&gt;&lt;sec&gt;Experimentally, the active area of the device consists of a straight superconducting nanowire with a length of 10 μm and a width of 30 nm, so that it can effectively reduce the probability of the defects on the nanowire and avoid the current crowding effect. We fabricate a 30 nm-wide Mo&lt;sub&gt;0.8&lt;/sub&gt;Si&lt;sub&gt;0.2&lt;/sub&gt; mid infrared SNSPD, which has a cutoff wavelength &lt;i&gt;λ&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; no more than 5 μm, the effective strength of the disorder－the film sheet resistance &lt;i&gt;R&lt;/i&gt;&lt;sub&gt;s&lt;/sub&gt; = 248.6 Ω/square. For comparison, the sheet resistance, which is controlled by the film thickness, increases to about 320 Ω/square in this experiment.&lt;/sec&gt;&lt;sec&gt;It is demonstrated that the Mo&lt;sub&gt;0.8&lt;/sub&gt;Si&lt;sub&gt;0.2&lt;/sub&gt; detector with &lt;i&gt;R&lt;/i&gt;&lt;sub&gt;s &lt;inline-formula&gt;&lt;tex-math id="Z-20221216014812-1"&gt;\begin{document}$ \sim $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20221594_Z-20221216014812-1.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20221594_Z-20221216014812-1.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;&lt;/sub&gt;320 Ω/square can achieve saturated quantum efficiency at a wavelength of 6 μm. Furthermore, 53% quantum efficiency at a wavelength of 10.2 μm can be obtained when the detector works at a bias current of 0.9&lt;i&gt;I&lt;/i&gt;&lt;sub&gt;SW&lt;/sub&gt; (&lt;i&gt;I&lt;/i&gt;&lt;sub&gt;SW&lt;/sub&gt; is the superconducting transition current), and it can theoretically reach a maximum value of 92% if the compression of switching current is excluded. Therefore, it can be predicted that the disorder regulation may become another efficient approach to designing high-performance mid-wave and long-wave infrared SNSPDs, in addition to the optimization of the superconducting energy gap and the cross section of superconducting nanowire.&lt;/sec&gt;&lt;sec&gt;However, the continuous increase in the disorder will cause both the superconducting phase transition temperature &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;c&lt;/sub&gt; and &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;SW&lt;/sub&gt; of the detector to decrease from the viewpoint of detector fabrication and application. This downward trend is especially pronounced when the nanowire width is ultranarrow, which is not conducive to the signal readout of the detector. Thus, exploring the optimal disorder regulation technology and balancing the relationship among the operating temperature, the signal-to-noise ratio, and the cutoff wavelength will have key scientific and application value for the development of high-performance mid-wave and long-wave infrared SNSPDs.&lt;/sec&gt;

Fabrication of morphine detector based on quartz@Au-layer biosensor

Biosensors analytical devices consist of a diagnostic element with a physical converter that can be very useful for analyzing biomarkers on site. The biosensor oscillator was made from a 20 MHz piezoelectric modified gold nano-layer. The response of this biosensor was based on the frequency change resulting from the effect of morphine on the anti-morphine monoclonal antibody.The level of the biosensor was studied with the FE-SEM and XRD analysis. Also, the comparison of the frequency response of this system at temperatures of 5 °C, 25 °C, and 45 °C shows that this system is stable at different temperatures. This device measured the concentration of morphine in both open and closed modes. The results showed that the device has a limit of detection (LOD) of 0.25 ng.mL-1 and the limit of quantification (LOQ) of 0.25–2500 ng.mL-1. The detection of this platform is fast (460 s) with a small volume of sample (1 µL), which showed that the server is compatible with what is required in clinical measurements.

Spray‐Stencil Lithography Enabled Large‐Scale Fabrication of Multispectral Colloidal Quantum‐Dot Infrared Detectors

AbstractInfrared HgTe colloidal quantum dots (CQDs) are attracting great interest due to their synthesis scalability, mechanical flexibility, wide spectrum tunability, and excellent photoelectric properties. However, traditional HgTe CQD infrared detector fabrication methods such as drop casting and spin coating cannot achieve spatial control of patterned CQD films, which limits their sensing range to just single waveband and greatly hinders the realization of pixelated or multispectral CQD detectors. In this paper, an efficient spray‐stencil lithography technique is demonstrated for the scalable fabrication of multichannel HgTe CQD infrared detectors that can respond to different spectral ranges. Uniform and smooth CQD films can be deposited on rigid, flexible, and curved substrates up to 4 inch wafer. Both photoconductive and photovoltaic infrared HgTe CQD detectors are fabricated with peak D* above 1011 Jones across short‐wave and mid‐wave regions and show infrared imaging with noise equivalent temperature difference down to 26.7 mK. Flexible multispectral detectors with six channels are fabricated by the proposed spray‐stencil lithography method, and experimentally demonstrate spectral sensing and chemical analysis capability. It is believed that the proposed fabrication method provides a reliable scheme for the production of high‐performance multispectral CQD infrared detector arrays.

Laser-induced novel ohmic contact formation for effective charge collection in diamond detectors

In this study, we employed an authentic process for the device fabrication of diamond detectors, wherein thin, highly conductive surface layers were processed in bulk diamond substrate using a nanosecond-pulsed excimer laser with liquid-immersion irradiation. The incorporation of high-concentration phosphorus dopants at 40 nm under the irradiated surface characterized the irradiated areas with much lower electrical resistivity, which was adequate for demonstrating ohmic contacts even with the tungsten probe heads at room temperature. In particular, a low activation energy (<54 meV) of irradiated surfaces enabled space-charge-free build-up effects between the diamond film and external connection. Moreover, the electrical characterization revealed an improved carrier-collection efficiency that was more than three orders of magnitude greater than that of typical Ti/Au diamond ohmic contacts, including a high-response speed of the current pulse to irradiation burst. The laser treatment of diamond films displayed promising results for the fabrication of diamond detectors with minimum power consumption, fastest process rate, and highest visible-light detection that could maintain smooth and stable charge transport. The process allowed selective, patterned doping of the diamond surface, which could be electrically contacted more readily. Furthermore, they could be operated at high temperatures and in radiation-harsh environments with sustainable efficiency.

Terahertz detector utilizing a SiO2/Graphene/SiO2 sandwich suspended at the feed of a planar antenna

We report on the fabrication of a terahertz detector utilizing a SiO2/graphene/SiO2 sandwich suspended at the planar antenna feed. This design of the detector aims to enhance its sensitivity via weakening of the heat sink between graphene’s phonons and those of the substrate. We achieve complete suspension of the sandwich only in case of a low fill-factor of the antenna feed area. Evaluated DC parameters of the samples are consistent with those reported in the literature. The fabrication process developed is suitable for implementing the detector proposed for signal frequencies up to several terahertz.

Fabrication of silicon PIN diode with SiGe junction for soft x-ray detector using low-temperature technology

In this paper, a low-temperature technology was introduced for the fabrication of PIN photodiode. A double dielectric oxide layers were prepared by nitric acid oxidation and PECVD, respectively. The selective epitaxial growth of SiGe thin layers, which were in-situ doped in a reactive thermal chemical vapor deposition system, were applied for the preparation of PN junction and high-low junction. A SiNx passivation layer combined with a post-annealing was adopted to lower the reverse current. The temperature was controlled below 450 °C for the whole fabrication process. Finally, the reverse current of 0.7 nA was achieved at room temperature for our 5 mm-diameter PIN detector and the energy resolution of 240 eV was obtained at 5.9 keV, −60 °C. The results indicated that the low-temperature technology is suitable for the fabrication of high quality PIN detector, and the cost can be reduced effectively.

Research of a Compact MEMS-Based Integrated Detector for X-Band Application: Theory, Design, Fabrication, and Measurement

This study investigated various types of Micro-Electro- mechanical Systems (MEMS)-based detectors, which enabled the derivation of a general formula via microwave network analysis. Multiple microwave parameters were measured and converted into a problem involving N-port network structural design with the derived formula. Furthermore, a compact integrated detector was proposed by removing a redundant power divider. Additionally, one processing circuit was designed to compensate for the output voltages from the detector and calculate the microwave parameters. The detector fabrication process is compatible with GaAs monolithic microwave integrated circuit (MMIC) process. Experimental results indicate that the revised detector is at least 35% smaller than that obtained using existing methods. This approach can detect multiple parameters, including frequency, power, and phase detection on a monolithic chip.

Radiation Hardness Property of Ultra-Fast 3D-Trench Electrode Silicon Detector on N-Type Substrate.

The radiation fluence of high luminosity LHC (HL-LHC) is predicted up to 1 × 1016 1 MeV neq/cm2 in the ATLAS and CMS experiments for the pixel detectors at the innermost layers. The increased radiation leads to the degradation of the detector properties, such as increased leakage current and full depletion voltage, and reduced signals and charge collection efficiency, which means it is necessary to develop the radiation hard semiconductor devices for very high luminosity colliders. In our previous study about ultra-fast 3D-trench electrode silicon detectors, through induced transient current simulation with different minimum ionizing particle (MIP) hitting positions, the ultra-fast response times ranging from 30 ps to 140 ps were verified. In this work, the full depletion voltage, breakdown voltage, leakage current, capacitance, weighting field and MIP induced transient current (signal) of the detector after radiation at different fluences will be simulated and calculated with professional software, namely the finite-element Technology Computer-Aided Design (TCAD) software frameworks. From analysis of the simulation results, one can predict the performance of the detector in heavy radiation environment. The fabrication of pixel detectors will be carried out in CMOS process platform of IMECAS based on ultra-pure high resistivity (up to 104 ohm·cm) silicon material.

A carbon dioxide detector fabrication with screen printing technique for use in airplanes

Purpose From the beginning of aviation history, fire has been a serious problem for aircrafts. The purpose of this study is to provide a reference document on current risks and proposed reductions for smoke and fire incidents in commercial transport aircrafts. For this purpose, metal oxide carbon dioxide (CO2) detector was produced with the screen printing technique to detect CO2 and carbon monoxide gases from the sensors required to observe the occurrence of fire that may occur in the aircraft and to take the necessary steps to control it. Design/methodology/approach The screen printing technique was used as the gas sensor production technique for the produced sensor and tin oxide was used as the metal oxide in the produced samples. The samples produced were examined under the gases with specified gas detecting properties, and it was concluded that they can be used simultaneously with smoke detectors to increase the detection reliability and decrease the alarm time with the smoke detectors currently used in today's passenger aircrafts. Findings When the electrical characteristics of the sensor made were examined, it was observed that it meets the requirements of the Federal Aviation Administration and European Aviation Safety Agency standards (the fire should be detected within 1 min), and the false alarm situation experienced in the smoke sensors used today can be eliminated. Originality/value There is no other sensor than the smoke detectors that are used for fire detection in cargo section, lavatories and avionic compartment on aircrafts. With this study, the gas detecting feature of the produced samples was examined under the specified gases, and it was concluded that they can be used simultaneously with smoke detectors to increase detection reliability and decrease alarm time as compared to with the smoke detectors currently used in today's passenger aircrafts.

Graphene Suspension from Modified Electrochemical Exfoliation of Graphite

Graphene has emerged as one of the most exciting materials since its discovery in 2004. Graphene is a term used for one to ten layers of sp2 hybridized carbon atoms arranged in a hexagonal pattern. Monolayer graphene is the building block of all graphitic structures and has high electron mobility, high thermal conductivity, high specific surface area, extremely high resistance to gas permeation and high optical transmittance. These exceptional properties make monolayer graphene attractive for potential applications as a catalyst or catalyst support in direct methanol fuel cells (DMFC), proton exchange membrane fuel cells (PEMFC), electrode in lithium-ion batteries, supercapacitors, as well as in thermally and electrically conductive sensors. AB-stacked bilayer and trilayer graphene have applications in the electronic industry, such as fabrication of field-effect transistors (FEts) and light detectors, due to an induced bandgap in the presence of an applied electric field. In addition, graphene finds major applications in the optoelectronic industry, such as electrode materials in solar cells, supercapacitors and transparent LCDs.Graphene is traditionally synthesized using the simple mechanical exfoliation of graphite, which is not scalable, or from chemical vapour deposition of a carbon source on a suitable substrate, which is both a complex and an expensive method. Hence, a scalable and economic graphene synthesis method is needed to harness the remarkable properties of graphene. The electrochemical exfoliation of graphite provides a promising route for the bulk production of graphene because it provides graphene flakes with the largest size and a smaller defect density than the well-known chemical synthesis methods such as Hummer or modified Hummer processes. The large size flakes resulting from electrochemical exfoliation are suitable for scalable electronic device fabrication methods. Electrochemical exfoliation proceeds via intercalation of the ions present in the electrolyte and is followed by the subsequent expansion and later exfoliation of graphite. However, this strategy produces graphene with a scatter in the layer numbers. A polydisperse suspension of graphene is undesirable because the electronic properties of graphene change with the number of layers. The intermediate graphite intercalation compounds are formed by the insertion of intercalants between the layers of the graphite host material. The intercalants can be atoms, ions or molecules. Graphite intercalation occurs in stages where the stage number indicates the number of graphene layers between the two nearest intercalant layers. In the present study, a modified electrochemical exfoliation route of graphite is explored, which proceeds through the exfoliation of a stage pure graphite intercalation compound followed by low-intensity ultrasonication. The modified electrochemical exfoliation of graphite is capable of providing a monodisperse graphene suspension

Lithium indium diselenide — An advanced material for neutron detection

This paper describes the synthesis, crystal growth, detector fabrication, radiation hardening studies, MCNP modeling, and characterization of lithium indium diselenide or LiInSe2. This newly-developed room-temperature thermal neutron detector has semiconducting and scintillating properties and it is suitable for neutron detection application. LiInSe2 was synthesized starting from elemental Li, In, Se in two steps due to high reactivity of Li. A single crystal of LiInSe2 was grown using the Vertical Bridgman method. The room temperature band gap was found to be 2.8eV using optical absorption measurements. Bulk resistivity was measured at ∼5 × 1011 Ωcm. Photoconductivity measurements of LiInSe 2 wafers identified a peak in the photocurrent around 445 nm. Nuclear radiation detectors were fabricated from single crystal wafer and the responses to alpha particles at various biases were measured. The mobility-lifetime product was estimated. Gamma irradiation studies were performed with calculated absorbed doses ranging from 0.2126 to 21,262 Gy. The characterization of the two wafers for their scintillator performance was conducted after each irradiation. The gamma irradiation produced a reduction of the light yield that translated to a lower channel number for the centroid of alpha detection spectra. It also showed a considerable reduction of the decay time after the first irradiation. These are the first studies on gamma radiation hardening with this material.

Characterization of superconducting NbTiN films using a dispersive Fourier transform spectrometer

We have built a terahertz dispersive Fourier transform spectrometer [Birch, Microchim. Acta 93, 105–122 (1987)] to study frequency properties of superconducting films used for fabrication of THz detectors. The signal reflected from the tested film is measured in time domain, which allows to separate it from the other reflections. The complex conductivity of the film depends on frequency and determines the reflection coefficient. By comparing the film reflection in the superconducting state (temperature is below Tc) with the reflection of the normal state, we characterize the film quality at terahertz frequencies. The method was applied to 70 and 200 nm thick Nb films on a silicon wafer and to 360 nm thick NbTiN films on silicon and quartz wafers. The strong-coupling coefficient, α, was found to be 3.52 for Nb and 3.71–4.02 for the NbTiN films. The experimental results were fitted using extended Mattis-Bardeen theory [Noguchi et al., Phys. Procedia 36, 318–323 (2012)] and show good agreement.

Modulation of electronic properties of MoS2 thin films by benzyl viologen treatment for IR detection

In this research, benzyl viologen (BV) is incorporated to enhance the n-type carriers in rapid thermally grown MoS2 thin films. A (002) oriented XRD peak, around 2θ = 14.1°, has been observed in BV treated MoS2 thin films. Raman spectra depicted the presence of two characteristics peaks around 389 cm−1 and 408 cm−1 corresponding to E12g and A1g modes of MoS2, respectively. The ideality factor and built-in voltage for the MoS2/Si heterojunction, treated with 25 mM and 6 coats of BV solution, were found to be 1.27 and 0.30 V, respectively for annealing temperature of 300 °C. The carrier concentration, calculated from Mott-Schottky analysis, is found to rise with the increase in BV concentration and annealing temperature up to 300 °C. The BV treated MoS2/Si heterojunction revealed the current On/Off ratio, rise and fall time of 520, 1.9 s and 1.7 s, respectively for the exposure of 940 nm IR light. With 850 nm IR illumination, the current On/Off ratio, rise and fall time decreased to 322, 1.4 s and 1.3 s, respectively. The results obtained provide the preliminary information for the fabrication of efficient next generation IR detectors.