Surface plasmonic effect of nanoparticle-like silver nanostructure on the high responsivity of visible/infrared silver-based heterojunction photodetector

The fabrication of a silver (Ag) based photodetector on a silicon dioxide/p-silicon (SiO₂/p-Si) substrate using direct current (DC) magnetron sputtering is demonstrated. The proposed method deposits a nanoparticle-like Ag thin film that favours the photoconduction mechanism under light illumination at 468?nm and laser illumination at 660 and 980?nm. The thin film is characterized using scanning electron microscope (SEM), energy dispersive x-ray (EDX), x-ray diffraction (XRD), Raman scattering, photoluminescence (PL) and ultraviolet–visible (UV–VIS) analysis. Current–voltage (I–V) analysis and the calculated rectifying ratio (RR) suggests the establishment of good Schottky contacts for incident light/laser at 468, 660 and 980?nm, with good responsivity towards light and laser illumination in the forward and reverse DC bias regions. The responsivity increases as the wavelength decreases from 980?nm → 660?nm → 468?nm, with the highest responsivity of 213.7?mAW^?1 at 468?nm indicating better photoconduction at low light powers.     

Development of Laboratory Experimental System to Clarify Solar Wind Charge Exchange Mechanism with TES Microcalorimeter

Significant fraction of the cosmic diffuse soft X-ray emission (0.1–1?keV) is caused by the Solar Wind Charge eXchange (SWCX) process between the solar wind ion (C ^q+, N ^q+, O ^q+ etc.) and the interplanetary neutral matter. It is difficult to identify spectral features of SWCX with the spectral resolution of existing X-ray astronomy satellites. We are developing a laboratory experimental system with transition edge sensor (TES) X-ray microcalorimeters, in order to clarify the SWCX mechanism. This experiment is designed to measure Charge eXchange (CX) X-rays using Electron Cyclotron Resonance Ion Source (ECRIS) that generates multi-charged ions. Emission lines (O_VIII: 2p→1s; 654?eV) by CX between O⁸⁺ and neutral He atom is aimed to be measured with energy resolution better than 10?eV. The TES microcalorimeter is cooled by a double-stage adiabatic demagnetization refrigerator (DADR), however, our TES microcalorimeter are not working potentially due to magnetic field contamination. This paper reports our experimental system, present results, and future prospects.     

A Robust and Conductive Black Tin Oxide Nanostructure Makes Efficient Lithium‐Ion Batteries Possible

SnO₂‐based lithium‐ion batteries have low cost and high energy density, but their capacity fades rapidly during lithiation/delithiation due to phase aggregation and cracking. These problems can be mitigated by using highly conducting black SnO_2?x , which homogenizes the redox reactions and stabilizes fine, fracture‐resistant Sn precipitates in the Li₂O matrix. Such fine Sn precipitates and their ample contact with Li₂O proliferate the reversible Sn → Li _x Sn → Sn → SnO₂/SnO_2?x cycle during charging/discharging. SnO_2?x electrode has a reversible capacity of 1340 mAh g^?1 and retains 590 mAh g^?1 after 100 cycles. The addition of highly conductive, well‐dispersed reduced graphene oxide further stabilizes and improves its performance, allowing 950 mAh g^?1 remaining after 100 cycles at 0.2 A g^?1 with 700 mAh g^?1 at 2.0 A g^?1. Conductivity‐directed microstructure development may offer a new approach to form advanced electrodes.     

Effects of packaging SrI2(Eu) scintillator crystals

Recent renewed emphasis placed on gamma-ray detectors for national security purposes has motivated researchers to identify and develop new scintillator materials capable of high energy resolution and growable to large sizes. We have discovered that SrI₂(Eu) has many desirable properties for gamma-ray detection and spectroscopy, including high light yield of ∼90,000 photons/MeV and excellent light yield proportionality. We have measured <2.7% FWHM at 662 keV with small detectors (<1 cm³) in direct contact with a photomultiplier tube, and ∼3% resolution at 662 keV is obtained for 1 in.³ crystals. Due to the hygroscopic nature of SrI₂(Eu), similar to NaI(Tl), proper packaging is required for field use. This work describes a systematic study performed to determine the key factors in the packaging process to optimize performance. These factors include proper polishing of the surface, the geometry of the crystal, reflector materials and windows. A technique based on use of a collimated ¹³⁷Cs source was developed to examine light collection uniformity. Employing this technique, we found that when the crystal is packaged properly, the variation in the pulse height at 662 keV from events near the bottom of the crystal compared to those near the top of the crystal could be reduced to <1%. This paper describes the design and engineering of our detector package in order to improve energy resolution of 1 in.³-scale SrI₂(Eu) crystals.     

An Improved ZnMoO4 Scintillating Bolometer for the Search for Neutrinoless Double Beta Decay of 100Mo

We present a prototype scintillating bolometer for the search for neutrinoless double β decay of ¹⁰⁰Mo, consisting of a single ≈5?g ZnMoO₄ crystal operated aboveground in the 20–30?mK temperature range. The scintillation light is read out by two thin Ge bolometers. The phonon signals are collected by NTD Ge thermistors. The ZnMoO₄ crystal was grown with an advanced method (low-thermal-gradient Czochralski technique) and after purification of molybdenum. The results are very encouraging: the intrinsic energy resolution of the heat channel is ≈800?eV FWHM, the α/β rejection factor (crucial for background suppression) is better than 99.9% in the region of interest for double β decay (≈3?MeV), and the radiopurity of ZnMoO₄ looks substantially improved with respect to previous devices.     

Large barium fluoride detectors

Big BaF₂ crystals of 1–2 1 volume and up to 15 cm thickness were investigated with respect to their application as gamma-ray detectors. In particular, we were interested in the light transmission in the UV region, and the energy and time resolution. We found that an energy resolution of ～ 12% (662 keV) and a time resolution of ～ 0.4 ns (⁶⁰Co, 300 keV threshold) can be obtained simultaneously. For these features, BaF₂ is superior to NaI or BGO in cases where good timing is essential. Gamma-rays and alpha particles can be clearly discriminated; as for the latter the fast component does not show up in the scintillation light.     

Design and Fabrication of the Second-Generation KID-Based Light Detectors of CALDER

The goal of the cryogenic wide-area light detectors with excellent resolution project is the development of light detectors with large active area and noise energy resolution smaller than 20 eV RMS using phonon-mediated kinetic inductance detectors (KIDs). The detectors are developed to improve the background suppression in large-mass bolometric experiments such as CUORE, via the double readout of the light and the heat released by particles interacting in the bolometers. In this work we present the fabrication process, starting from the silicon wafer arriving to the single chip. In the first part of the project, we designed and fabricated KID detectors using aluminum. Detectors are designed by means of state-of-the-art software for electromagnetic analysis (SONNET). The Al thin films (40 nm) are evaporated on high-quality, high-resistivity (>?10 kΩ cm) Si(100) substrates using an electron beam evaporator in a HV chamber. Detectors are patterned in direct-write mode, using electron beam lithography (EBL), positive tone resist poly-methyl methacrylate and lift-off process. Finally, the chip is diced into 20?×?20 mm² chips and assembled in a holder OFHC (oxygen-free high conductivity) copper using PTFE support. To increase the energy resolution of our detectors, we are changing the superconductor to sub-stoichiometric TiN (TiN_x) deposited by means of DC magnetron sputtering. We are optimizing its deposition by means of DC magnetron reactive sputtering. For this kind of material, the fabrication process is subtractive and consists of EBL patterning through negative tone resist AR-N 7700 and deep reactive ion etching. Critical temperature of TiN_x samples was measured in a dedicated cryostat.     

Utilization of a ZnS(en)0.5 photocatalyst hybridized with a CdS component for solar energy conversion to hydrogen

Photocatalytic solar energy conversion to chemical energy attracts great attention due to its high potential in harvesting renewable energy for the future. A ZnS(en)_0.5 photocatalyst hybridized with a CdS component was synthesized by solvothermal and precipitation methods to compare the effect of preparation methods on photocatalytic performance. The highest hydrogen production rate (559 μmol g^?1 h^?1) was achieved from a solvothermally synthesized ZnS(en)_0.5?CdS composite at 80 wt% of CdS content under standard 1-sun-irradiation condition (1000 W/m²). Photocatalytic hydrogen production rates from ZnS(en)_0.5?CdS photocatalysts were highly associated with degrees of charge separation, crystallinity, reduction power, and light absorption. By comparing two different routes for the synthesis of ZnS(en)_0.5?CdS photocatalysts, solvothermally-fabricated material was shown to have a higher photocatalytic activity compared with material fabricated by a precipitation method. This improvement may be due to its excellent crystalline and charge-separation characteristics.     

Scintillating Bolometers for Double Beta Decay Search

In the field of Double Beta Decay searches the possibility to have high resolution detectors in which a very large part of the natural background can be discriminated with respect to the tiny expected signal, results very appealing. This very interesting possibility can be fulfilled in the case of a scintillating crystal bolometer containing a DBD emitter whose transition energy exceeds the one of the natural 2615 keV gamma line of ²⁰⁸Tl. We present the results achieved in the development of bolometric light detectors for double beta searches. The detectors are 1 mm thick germanium disk coated with a layer of SiO₂ in order to increase the light collection. The adopted temperature sensors are NTD Ge thermistors optimized to work at temperatures between 9 and 13 mK. A light detector with a considerable large area (35 cm²) was constructed and run in a test measurement. A 140 g CdWO₄ crystal (¹¹⁶Cd has a DBD transition energy of 2802 keV) was operated as bolometer and the scintillation light was read by the light detector. The excellent results combined with extreme easy light detector assembly represent the first tangible proof demonstrating the feasibility of this kind of technique.      

Development of Metallic Magnetic Calorimeters for High Precision Measurements of Calorimetric 187Re and 163Ho Spectra

The measurement of calorimetric spectra following atomic weak decays, beta?(β) and electron capture (EC), of nuclides having a very low Q-value, can provide an impressively high sensitivity to a non-vanishing neutrino mass. The achievable sensitivity in this kind of experiments is directly connected to the performance of the used detectors. In particular an energy resolution of a few eV and a pulse formation time well below 1?μs are required. Low temperature Metallic Magnetic Calorimeters (MMCs) for soft X-rays have already shown an energy resolution of 2.0?eV FWHM and a pulse rise-time of about 90?ns for fully micro-fabricated detectors. We present the use of MMCs for high precision measurements of calorimetric spectra following the β-decay of ¹⁸⁷Re and the EC of ¹⁶³Ho. We show results obtained with detectors optimized for ¹⁸⁷Re and for ¹⁶³Ho experiments respectively. While the detectors equipped with superconducting Re absorbers have not yet reached the aimed performance, a first detector prototype with a Au absorber having implanted ¹⁶³Ho ions already shows excellent results. An energy resolution of 12?eV FWHM and a rise time of 90?ns were measured.     

Elastic strain at the solid-solid interface in intergrowth structures : A novel example of partial structure refinement by HREM

The solid-solid interface in recurrent intergrowth structures formed by oxides of the general formula (Bi₂O₂)²⁺(A_m?1M_mO_3m+1)^2? has been investigated by high resolution electron microscopy (HREM). Matching of experimental and computer-simulated high resolution images has enabled a partial structure refinement which throws light on the presence and the nature of elastic strain in the intergrowths.     

Heterovalent cation substitutions in the layered compound YBaCuFeO<Subscript>5 + δ</Subscript>

(Y,M)BaCuFeO_{5 + δ} (M = Ce, Ca, Na), Y(Ba,K)CuFeO_{5 + δ}, YBa(Cu,Co)FeO_{5 + δ}, YBaCu(Fe,M)O_{5 + δ} (M = Zn, Nb), (Y,Ca)BaCu(Fe,Zn)O_{5 + δ}, and (Y,Ca)(Ba,La)Cu(Fe,Zn)O_{5 + δ} solid solutions have been prepared by ceramic processing techniques and have been characterized by x-ray diffraction, IR absorption spectroscopy, and thermal expansion and electrical conductivity (σ) measurements in air at temperatures from 300 to 1100 K. It is shown that, in the range 650–700 K, the linear thermal expansion coefficient of the (Y,M)BaCuFeO_{5 + δ} phases rises from (11–12) × 10^?6 to (14–15) × 10^?6 K^?1, while that of the YBa(Cu,Co)FeO_{5 + δ} solid solution decreases from 18 × 10^?6 to 14 × 10^?6 K^?1. The conductivity data (an increase in σ upon Ca²⁺ → Y³⁺ and Zn²⁺ → Fe³⁺ substitutions and a reduction in σ upon Ce⁴⁺ → Y³⁺ and Nb⁵⁺ → Fe³⁺ substitutions) demonstrate that the transport properties of YBaCuFeO_{5 + δ} can be tuned by electron-hole doping.     

Mechanism of cerium(III) oxidation with ozone in sulfuric acid solutions

The kinetics of Ce(III) oxidation with ozone in 0.1–3.2 M H₂SO₄ solutions was studied by spectrophotometry. The reaction follows the first-order rate law with respect to each reactant. The rate constant k slightly increases with an increase in the acid concentration, which is associated with an increase in the O₃/O ₃ ^? oxidation potential. The activation energy in the range 17–35°C is 46 kJ mol^?1. With excess Ce(III), the stoichiometric coefficient Δ[Ce(IV)]/Δ[O₃] increases from 1.6 to 2 in going from 0.1 to 1–3.2 M H₂SO₄. The extent of the Ce(III) oxidation is 78% in 0.1 M H₂SO₄ and reaches 82% in 1 M H₂SO₄. The ozonation involves the reactions Ce(III) + O₃ → Ce(IV) + O ₃ ^? , O ₃ ^? + H⁺ → HO₃, HO₃ → OH + O₂, OH + HSO ₄ ^? → H₂O + SO ₄ ^? , OH + Ce(III) → OH^? + Ce(IV), and SO ₄ ^? + Ce(III) → SO_4/2? + Ce(IV). Low stoichiometric coefficient of the Ce(III) oxidation is associated with the hydrolysis of Ce(IV). The excited Ce(IV) ion arising from oxidation of Ce(III) with OH radical forms with the hydrolyzed Ce(IV) ion a dimer whose decomposition yields Ce(III) and H₂O₂. After the ozonation termination, Ce(IV) is relatively stable in sulfuric acid solution, with only 5–7% of Ce(IV) disappearing in 24 h.     

Ultra-stable high-precision Mössbauer spectroscopy of photochromic centers in Fe:SrTiO3

Normal state and optically-pumped state Mössbauer spectra have been studied to identify photochromic centers in irondoped SrTiO₃. The type and proportion of the centers are dependent on impurity concentration. The 3 and 1.5 atomic percent doped materials have optically inactive centers: Fe³⁺  V_O, Fe³⁺  V_O(e) and Fe³⁺  V_O(2e). The 0.2 and 0.05 atomic percent doped materials weakly indicate the following centers on exposure to blue light centered around 400 nm: Fe³⁺ → Fe⁴⁺ and Fe³⁺  V_O → Fe³⁺  V_O(e), the confidence level for the assignment from computer-fitted spectra being only 65 percent.     

Electron emission from solid surfaces stimulated by electric field and heterogeneous chemical reaction

A method for monitoring the process of electron accommodation during chemical reactions at the gas-solid (metal, semiconductor) interface is proposed. It is established that the tunneling electron current from a solid surface (Ni, Cu, Si steel) increases by a factor of 10³–10⁵ when a heterogeneous chemical reaction (H+H→H₂) proceeds on the surface. Autooscillations of the reaction-stimulated tunneling current have been observed. A method of investigation of the structure of surface catalytic centers on a nanometer resolution level is proposed.     

A detection system for energetic light heavy ions

A light heavy ion detection system which consists of a gas-filled ionization chamber (IC) connected to a scattering chamber via a time-of-flight (TOF) system has been constructed. The entrance window of the IC has an area of 14 × 40 cm², the active depth is 115 cm. Filled with CF₄ at a pressure of 350 Torr, the energy range for ¹²C and ⁴⁰Ar is 5–20 MeV/A and 6–30 MeV/A, respectively. The TOF system consists of two parallel plate avalanche counters with a flightpath of 70 cm in between. The IC has been tested with ¹²C ions at an energy of 39 MeV. The energy resolution of the IC (1.1%) is mainly determined by the energy straggling in the foils of the TOF system and the ionization chamber. The energy-loss resolution is 3.5%, the horizontal position resolution varies between 6 and 20 mm and the vertical position resolution is 2 mm. The time resolution of the TOF system ranges from 800 ps for ⁴He at 5.0 MeV, to 280 ps for ²⁸Si at 55 MeV.     

VUV and UV Florescence and Absorption Studies of Tb3+ and Tm3+ Trivalent Ions in LiYF4 Single Crystal Hosts

Abstract

The laser induced fluorescence spectra of LiYF₄:Tb³⁺ (YLF:Tb) and LiYF₄:Tm³⁺ (YLF:Tm) single crystals, pumped by an F₂ pulsed discharge molecular laser at 157 nm, were obtained in the vacuum ultraviolet (VUV) and ultraviolet (UV) regions of the spectrum, at room temperature. A number of new fluorescence peaks were observed for the first time. They were assigned to the dipole allowed transitions 4f⁷5d → 4f⁸ and 4f¹¹5d → 4f¹² of Tb³⁺ and Tm³⁺ ions respectively. The absorption spectra of the same crystal samples in the VUV and UV regions were taken as well. The edge (onset) and the energy of the states with 4f^{N ? 1}5d configuration were determined.     

Tunable acousto-optic spectral imager for atmospheric composition measurements in the visible spectral domain

We describe a new spectral imaging instrument using a TeO₂ acousto-optical tunable filter (AOTF) operating in the visible domain (450-900?nm). It allows for fast (～1 second), monochromatic (FWHM ranges from 0.6?nm at 450?nm to 3.5?nm at 800?nm) picture acquisition with good spatial resolution. This instrument was designed as a breadboard of the visible channel of a new satellite-borne atmospheric limb spectral imager, named the Atmospheric Limb Tracker for the Investigation of the Upcoming Stratosphere (ALTIUS), that is currently being developed. We tested its remote sensing capabilities by observing the dense, turbulent plume exhausted by a waste incinerator stack at two wavelengths sensitive to NO₂. An average value of 6.0±0.4×10¹⁷ molecules?cm^-2 has been obtained for the NO₂ slant column density within the plume, close to the stack outlet. Although this result was obtained with a rather low accuracy, it demonstrates the potential of spectral imaging by using AOTFs in remote sensing.     

Application of CLTD’s for High Resolution Mass Identification and for Stopping Power Measurements of Heavy Ions

An array of calorimetric low temperature detectors (CLTD’s) for energy sensitive detection of heavy ions was combined with time-of-flight (TOF) detectors to obtain a detector system for high resolution mass identification of low energy heavy ions. In addition the same setup was used to prove the ability of CLTD’s to be used in electronic stopping power measurements for heavy ions in matter. Experiments with 50?MeV ⁶³Cu and ⁶⁵Cu ions at the tandem accelerator at the MPI at Heidelberg, and with 25 to 250?MeV ²³⁸U ions at the UNILAC accelerator at GSI at Darmstadt have been performed. For ^63,65Cu at 50?MeV a mass resolution of Δm(FWHM)=0.9?amu, and for ²³⁸U in an energy range of 65 to 150?MeV a resolution of Δm(FWHM)=1.28?amu, was obtained. The results for stopping powers of ²³⁸U in carbon and gold are presented and compared with theoretical predictions and data from the literature.     

A Novel Type of Absorber Presenting a Constant Detection Efficiency for up to 25 keV X-Ray Photons

A novel type of absorber, dedicated to cryogenic detectors, was conceived to reach a high and constant intrinsic detection efficiency (>98%) for up to 25?keV X-ray photons. The absorber consists of two layers having a different atomic number?Z. The role of the first layer (large?Z) is to make negligible the transmission through the absorber; while the second layer (medium?Z) has to reabsorb the escape photons from the first layer. A?metallic magnetic calorimeter was realized with an Au-Ag absorber. The required thicknesses of both layers were determined using Monte Carlo simulation of the efficiency. To show the advantages of such a detector, its efficiency and its energy resolution are compared to the efficiency and energy resolution of a gold absorber using a ²⁴¹Am source.