Rm Gd Research Articles

Development of ultra-pure gadolinium sulfate for the Super-Kamiokande gadolinium project

Abstract This paper reports the development and detailed properties of about 13 metric tons of gadolinium sulfate octahydrate, $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$, which has been dissolved into Super-Kamiokande (SK) in the summer of 2020. We evaluate the impact of radioactive impurities in $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$ on diffuse supernova neutrino background searches and solar neutrino observation and confirm the need to reduce radioactive and fluorescent impurities by about three orders of magnitude from commercially available high-purity $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$. In order to produce ultra-high-purity $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$, we have developed a method to remove impurities from gadolinium oxide, Gd2O3, consisting of acid dissolution, solvent extraction, and pH control processes, followed by a high-purity sulfation process. All of the produced ultra-high-purity $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$ is assayed by inductively coupled plasma mass spectrometry and high-purity germanium detectors to evaluate its quality. Because of the long measurement time of high-purity germanium detectors, we have employed several underground laboratories for making parallel measurements including the Laboratorio Subterráneo de Canfranc in Spain, Boulby in the UK, and Kamioka in Japan. In the first half of production, the measured batch purities were found to be consistent with the specifications. However, in the latter half, the $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$ contained one order of magnitude more 228Ra than the budgeted mean contamination. This was correlated with the corresponding characteristics of the raw material Gd2O3, in which an intrinsically large contamination was present. Based on their modest impact on SK physics, they were nevertheless introduced into the detector. To reduce 228Ra for the next stage of gadolinium loading to SK, a new process has been successfully established.

Preparation and characterization of nanosphere and nanorod Gd2O3:Tb3+ by polyol route.

Nanorod and nanosphere ${{\rm Gd}_2}{{\rm O}_3}\!:\!{{\rm Tb}^{3 + }}$Gd2O3:Tb3+ particles were synthesized from chloride precursors ${{\rm GdCl}_3}$GdCl3 and ${{\rm TbCl}_3}$TbCl3 by NaOH addition in a diethylene glycol medium. The nanospheres and the nanorods of ${{\rm Gd}_2}{{\rm O}_3}\!:\!{{\rm Tb}^{3 + }}$Gd2O3:Tb3+ were tunably obtained by adjusting the addition speed of NaOH. The structure, morphologies, and the luminescence properties of nanorod and nanosphere ${{\rm Gd}_2}{{\rm O}_3}\!:\!{{\rm Tb}^{3 + }}$Gd2O3:Tb3+ were characterized by x-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, and fluorescence spectrometry, respectively. The results confirmed that the structure of nanorod and nanosphere ${{\rm Gd}_2}{{\rm O}_3}\!:\!{{\rm Tb}^{3 + }}$Gd2O3:Tb3+ is cubic ${{\rm Gd}_2}{{\rm O}_3}$Gd2O3, and the luminescence of nanospheres is more intense than that of nanorods. The low cytotoxicity measured by the MTT method indicated the good biocompatibility of the samples.

An Assessment of Step Patterned Gate Oxide Superjunction Trench MOSFET for Potential Benefits

A 600 V-class step patterned gate oxide trench (SPGOT) superjunction vertical device incorporating gate engineering is proposed in this paper. An $$n^{+}$$ polysilicon gate is segregated into three steps of varied length and oxide thickness. To improve the device performance, the gate oxide in the SPGOT structure is narrow towards the source and wide towards the drain. This modification increases the gate–source capacitance, indicating higher transconductance, and reduces gate–drain capacitance, suggesting lower switching delay. The gate length is optimized to achieve enhanced performance indicators. Electrical performance is investigated and analyzed using 2-D numerical simulations. The optimized results reveal 9.7% and 26.14% reduction in specific resistance ( $$R_{\rm on} {\cdot} A$$ ) and gate–drain charge ( $$Q_{\rm GD}\cdot A$$ ), respectively, without any reduction in breakdown voltage. The engineered gate structure further exhibits a 43% and a 33.2% improvement in switching delay and figure of merit ( $$R_{\rm on}\cdot A$$ × $$Q_{\rm GD}\cdot A$$ ), respectively, over a conventional device.

Large Size Czochralski Growth and Scintillation Properties of

The 3 inch size Mg co-doped ${\rm Ce}:{\rm Gd}_{3} {\rm Al}_{2}{\rm Ga}_{3} {\rm O}_{12}$ single crystals were prepared by the Czochralski (Cz) method. Absorption and luminescence spectra were measured together with several other scintillation characteristics, namely the scintillation decay and light yield to reveal the effect of Mg co-doping. The timing resolution measurement for a pair of $3 \times 3 \times 3\;\hbox{mm}^3$ size GAGG:Ce.Mg scintillator crystals was performed using Si-PMs.

Characterization Method of SiC-JFET Interelectrode Capacitances in Linear Region

In order to study switching waveforms of a SiC-JFET, its interelectrode capacitances evolution is necessary when the power device is in linear region. In this paper, the reverse transfer capacitance $C_{\rm gd}$ is at first characterized by the multiple-current-probe method and afterwards validated by the measurement with an impedance analyzer. The output capacitance $C_{\rm oss}$ is measured by the same method and compared with the single-pulse characterization, which shows a huge increase of the apparent capacitance values in linear region. The influence of the power transistor internal gate resistor is thus studied, revealing the interelectrode capacitances measurement difficulties when the power device is in linear region. The characterization results are allowed to finely model the power transistor of which the switching behaviors are validated with the measurement in a buck converter.

Influence of the Gate Height Engineering on the Intrinsic Parameters of UDG-MOSFETs With Nonquasi Static Effect

This paper presents the results of a systematic theoretical investigation on the impact of gate height on the analog and radio-frequency (RF) performances of underlap-FinFET devices. The conventional underlap-FinFETs offer lower on current $(I_{\rm on} )$ and higher distributed channel resistance $(R_{\rm ch} )$ . This paper shows that a higher gate height improves both $I_{\rm on} $ and $R_{\rm ch} $ due to higher gate side-wall fringing fields. In this paper, the various figure of merits (FOMs) for analog applications of the underlap-FinFETs such as drain current $(I_{\rm ds} )$ , transconductance $(g_{m} )$ , transconductance generation factor $(g_{m} /I_{\rm ds} )$ , output resistance $(R_{o} )$ , and intrinsic gain $(g_{m} R_{o} )$ are systematically analyzed for different values of gate height and reported. The RF FOMs studied include intrinsic capacitances $(C_{\rm gs} , C_{\rm gd} )$ and resistances $(R_{\rm gs} , R_{\rm gd} )$ , transport delay $(\tau _{m} )$ , cutoff frequency $(\,f_{T} )$ , and the transit frequency of maximum available power gain $(\,f_{\rm MAX} )$ . This paper clearly demonstrates that the gate height is a critical technology parameter in improving the analog performance of underlap-FinFETs.

High-Performance Enhancement-Mode Al<sub>2</sub>O<sub>3</sub>/AlGaN/GaN-on-Si MISFETs With 626 MW/<inline-formula> <tex-math notation="LaTeX">$\mathrm{cm}^{2}$ </tex-math></inline-formula> Figure of Merit

In this paper, the partial gate recess for performance improvement of enhancement-mode (E-mode) GaN power devices is experimentally demonstrated. The gate recess with a careful control of the recess depth was performed with an optimized recessed barrier thickness of ~1.5 nm that is thin enough to completely deplete the 2-D electron gas channel in the gate region. Meanwhile, the remaining barrier preserves the as-grown quantum well of the heterostructure physically intact and thus, effectively mitigates the lattice damage caused by gate recess. The fabricated E-mode Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /AlGaN/GaN MISFETs deliver a threshold voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> ) of +1.5 V. The maximum drain current density (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D,max</sub> ) and transconductance (G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m,max</sub> ) are 693 mA/mm and 166 mS/mm, respectively. The MISFETs with an L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GD</sub> of 10 μm feature an OFF-state breakdown voltage of 860 V at a leakage current of 1 μA/mm. The corresponding specific ON-resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON,sp</sub> ) is as low as 1.18 mΩ·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> yielding a high-power figure of merit of 626 MW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . In comparison with the reference MOSFETs by fully gate recess, the respectably improved device performance of the MISFETs attributes to the enhanced electron mobility achieved by the partial gate recess.

Characterization of Oxygen Accumulation in Indium-Tin-Oxide for Resistance Random Access Memory

In this letter, we report the oxygen accumulation effect and its influence on resistive switching for gadolinium-doped silicon dioxide $({\rm Gd}{:}{\rm SiO}_{2})$ resistance random access memory (RRAM). We find that oxygen absorbance by indium-tin-oxide electrode affects the conduction current mechanism, and remarkably modifies the device performance of RRAM devices. By current fitting, Schottky emission can be observed in both low and high resistance states, from which conduction model is proposed to clarify the oxygen accumulation phenomenon. Reliability tests, including endurance and high temperature retention are further carried out, evaluating the significance of oxygen accumulation effect in redox reaction for RRAM devices.

Comparison of High-$\kappa~{\rm Gd}_{2}{\rm O}_{3}$ and ${\rm GdTiO}_{3}~\alpha$-InGaZnO Thin-Film Transistors

In this paper, we compared the structural and electrical properties of high- κ Gd2O3 and GdTiO3 gate dielectrics for an amorphous indium-gallium-zinc oxide ( α-IGZO) thin-film transistor (TFT) application. In comparison with the Gd2O3 dielectric, the α-IGZO TFT featuring the GdTiO3 dielectric exhibited better electrical characteristics in terms of a large field effect mobility of 26.9 cm2/Vs, a low threshold voltage of 0.04 V, a high ION/IOFF ratio of 1.2×108, and a low subthreshold swing of 200 mV/decade. We attribute these results to the incorporation of Ti into the Gd2O3 film, forming a smooth surface and thus reducing density of interface states at the oxide/channel interface. In addition, the stability of threshold voltage on high- κ Gd2O3 and GdTiO3 a-IGZO TFTs was studied under positive gate bias stress.

Gd3+ rattling triggered by a “weak” M–I transition at 140–160 K in the Ce1−xGdxFe4P12 (x ≈ 0.001) skutterudite compounds: An ESR study

AbstractIn this work we report electron spin resonance (ESR) measurements in the semiconducting ${\rm Ce}_{1 - x} {\rm Gd}_x {\rm Fe}_4 {\rm P}_{12}$ ($x \approx 0.001$) filled skutterudite compounds. Investigation of the temperature (T) dependence of the ESR spectra and relaxation process suggests, that in the T‐interval of 140–160 K, the onset of a “weak” metal–insulator (M–I) transition takes place due to the increasing density of thermally activated carriers across the semiconducting gap of $\approx 1500$ K. In addition, the observed low‐T fine and hyperfine structures start to collapse at $T \approx 140\,{\rm K}$ and is completely absent for T ≳ 160 K. We claim that the increasing carrier density is able to trigger the rattling of the Gd3+ ions which in turn is responsible, via a motional narrowing mechanism, for the collapse of the ESR spectra.

High-Temperature Microwave Performance of Submicron AlGaN/GaN HEMTs on SiC

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The effect of temperature on the small-signal radio-frequency (RF) performance of submicron AlGaN/GaN high-electron-mobility transistors on SiC has been studied from room temperature (RT) up to 600 K. A relation between ambient and channel temperatures has been established by means of finite-element simulations. The thermal behavior of the intrinsic parameters <formula formulatype="inline"><tex Notation="TeX">$C_{\rm gs}$</tex></formula>, <formula formulatype="inline"><tex Notation="TeX">$C_{\rm gd}$</tex></formula>, <formula formulatype="inline"><tex Notation="TeX">$g_{m, {\rm int}}$</tex></formula>, and <formula formulatype="inline"><tex Notation="TeX">$g_{\rm ds}$</tex></formula> has been extracted accurately from RF measurements by means of the small-signal equivalent circuit. Main dc parameters <formula formulatype="inline"><tex Notation="TeX">$(I_{D}, g_{m, {\rm ext}})$</tex></formula> show reductions close to 50% between RT and 600 K, mainly due to the decrease in the electron mobility and drift velocity. In the same range, <formula formulatype="inline"><tex Notation="TeX">$f_{T}$</tex></formula> and <formula formulatype="inline"><tex Notation="TeX">$f_{\max}$</tex> </formula> suffer a 60% decrease due to the reduction in <formula formulatype="inline"><tex Notation="TeX">$g_{m, {\rm ext}}$</tex> </formula> and a slight increase of <formula formulatype="inline"><tex Notation="TeX">$C_{\rm gs}$</tex></formula> and <formula formulatype="inline"><tex Notation="TeX">$C_{\rm gd}$</tex></formula>. An anomalous thermal evolution of <formula formulatype="inline"><tex Notation="TeX">$C_{\rm gd}$</tex></formula> at low <formula formulatype="inline"><tex Notation="TeX">$I_{D}$ </tex></formula> has been identified, which is indicative of the presence of traps. </para>

Scintillation Characteristics of ${\rm Ce}:{\rm Gd}_{2}{\rm Si}_{2}{\rm O}_{7}$ (Ce 2.5–30 mol%) Single Crystals Prepared by the Floating Zone Method

Cerium-doped gadolinium pyrosilicate single crystals Ce:Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> (Ce:GPS) with various Ce concentrations of 2.5-30 mol% with respect to the total rare-earth sites were prepared by the floating zone method. Their scintillation performances were investigated under irradiation of gamma rays of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">137</sup> Cs. The Ce concentration dependence of scintillation characteristics and high-performance scintillation characteristics were obtained: 3-6 times greater light output than that of BGO single crystals, rapid decay, and good energy resolutions of 5.1-8.4%. Furthermore, X-ray diffraction patterns of Ce:GPS revealed Ce concentration dependence of the crystal structure of Ce:GPS.

Magnetic excitations in the geometrically frustrated pyrochlore antiferromagnetGd2Sn2O7studied by electron spin resonance

The spin dynamics in the geometrically frustrated pyrochlore antiferromagnet $\rm Gd_2Sn_2O_7$ is studied by means of the electron spin resonance. In the ordered phase ($T_N = 1$ K), we have detected three gapped resonance modes. Their values agree well with the developed spin-wave theory which takes into account the Heisenberg nearest-neighbor exchange, the single-ion anisotropy and the long-range dipolar interactions. The theory also predicts a fourth lowest-frequency gap, which lies beyond the experimental range of frequencies, but determines the exponential decrease of the specific heat at low temperature.

A Physics-Based Modeling of Interelectrode MOS Capacitances of Power MOSFET and IGBT

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The conventional and widespread modeling of interelectrode capacitances of power <emphasis emphasistype="smcaps">mosfet</emphasis> and insulated gate bipolar transistor is based on a single dipolar representation of the electric charge induced in the intercellular drain region. In this paper, it is proved by some experimental tests that this representation, symbolized by the gate transfer capacitance <formula formulatype="inline"><tex Notation="TeX">$C_{{\rm GD}}$</tex></formula>, may not be physics-based, especially under negative gate polarization. Then, it is demonstrated that interelectrode MOS capacitances are fundamentally of three-port coupling origin. A physical capacitive model, available for both gate capacitance and gate transfer capacitance, is detailed, implemented in a simulation software, and compared with experiment. </para>

Defect structure of oxide ferroelectrics—valence state, site of incorporation, mechanisms of charge compensation and internal bias fields

The defect structure of aliovalent transition-metal and rare-earth functional centers in ferroelectric perovskite oxides is characterized by means of multifrequency electron paramagnetic resonance spectroscopy, assisted by density-functional theory calculations. The review is mainly focused on lead zirconate titanate (Pb[Zr x Ti1−x ]O3, PZT) compounds. However, where available also results on ferroelectric ’lead-free’ compounds are discussed. The results include the formation of charged $({\rm Fe}'_{\rm Zr,Ti}-V_{\rm O}^{\bullet \bullet})^{\bullet}$ defect dipoles, causing internal bias fields, multivalence manganese centers, acceptor-type copper functional centers creating isolated oxygen vacancies that promote ionic conductivity, as well as ${\rm Gd}_{\rm Pb}^{\bullet}$ donor-type centers. Moreover, the impact of the defect structure on macroscopic material properties is discussed.

Superconducting properties of Ce-substituted TaSr2(Gd,Ce)2 $${\rm Cu}_2{\rm O}_y$$

A layered cuprate TaSr2\({\rm Gd}_{1+x}\)\({\rm Ce}_{1-x}\)Cu2\({\rm O}_y\) for x = 0.4–0.8 has been successfully synthesized by solid state reaction. X-ray powder diffraction analysis indicates that nearly all the peaks from the samples can be indexed to a single phase of Ta-1222. The sample with nominal composition TaSr2Gd1.6Ce0.4Cu2\({\rm O}_y\) showed a tetragonal structure with lattice parameters a = 3.858 A, c = 28.81 A with space group most likely I4/mmm. The TaSr2\({\rm Gd}_{1+x}\)\({\rm Ce}_{1-y}\)Cu2\({\rm O}_y\) compound exhibits a narrow superconducting region near x = 0.6 with Tc-onset = 30 and Tc-zero=10 K as determined by d.c. electrical resistance versus temperature measurements.