bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nanoscale refractory doped titanium nitride field emitters
Authors: Nardi A , Turchetti M , Britton W A , Chen Y , Yang Y , Dal Negro L , Berggren K K , Keathley P D 
Published: April 2021

Abstract
Refractory materials exhibit high damage tolerance, which is attractive for the creation of nanoscale field-emission electronics and optoelectronics applications that require operation at high peak current densities and optical intensities. Recent results have demonstrated that the optical properties of titanium nitride, a refractory and CMOS-compatible plasmonic material, can be tuned by adding silicon and oxygen dopants. However, to fully leverage the potential of titanium (silicon oxy)nitride, a reliable and scalable fabrication process with few-nm precision is needed. In this work, we developed a fabrication process for producing engineered nanostructures with gaps between 10 and 15 nm, aspect ratios larger than 5 with almost 90° steep sidewalls. Using this process, we fabricated large-scale arrays of electrically-connected bow-tie nanoantennas with few-nm free-space gaps. We measured a typical variation of 4 nm in the average gap size. Using applied DC voltages and optical illumination, we tested the electronic and optoelectronic response of the devices, demonstrating sub-10 V tunneling operation across the free-space gaps, and quantum efficiency of up to 1 × 10−3 at 1.2 μm, which is comparable to a bulk silicon photodiode at the same wavelength and three orders of magnitude higher than with nearly identical gold devices. Tests demonstrated that the titanium silicon oxynitride nanostructures did not significantly degrade, exhibiting less than 5 nm of shrinking of the average gap dimensions over few-μm2 areas after 10 h of operation. Our results will be useful for developing the next generation of robust and CMOS-compatible nanoscale devices for high-speed and low-power field-emission electronics and optoelectronics applications.
Highly conductive and transparent electrospun indium tin oxide nanofibers calcined by microwave plasma
Authors: Cheng Jun , Zhang Xi , Yang Zhuanqing , Xiang Gang 
Published: April 2021

Abstract
In this work, indium tin oxide (ITO) nanofibers have been prepared by electrospinning of polymers and post-growth microwave plasma calcination (MPC). Interestingly, compared to traditional calcination in furnace, MPC can accelerate the degradation of high polar polymers and improve adhesion of ITO nanofibers to the sapphire substrate. Further characterizations reveal that the ITO nanofibers with diameters of 100–150 nm prepared by MPC at 600 °C can reach a low sheet resistance of 269 Ω/sq and a high transmittance of 90.7% at 550 nm simultaneously, which has not been previously reported by others. Our results show that the efficient MPC method has great potential in preparation of metal-oxide nanofibers for electrical and optical applications.
An approach for estimating dosimetric uncertainties in deformable dose accumulation in pencil beam scanning proton therapy for lung cancer
Authors: Amstutz Florian , Nenoff Lena , Albertini Francesca , Ribeiro Cássia O , Knopf Antje C , Unkelbach Jan , Weber Damien C , Lomax Antony J , Zhang Ye 
Published: April 2021

Abstract
Deformable image registration (DIR) is an important component for dose accumulation and associated clinical outcome evaluation in radiotherapy. However, the resulting deformation vector field (DVF) is subject to unavoidable discrepancies when different algorithms are applied, leading to dosimetric uncertainties of the accumulated dose. We propose here an approach for proton therapy to estimate dosimetric uncertainties as a consequence of modeled or estimated DVF uncertainties. A patient-specific DVF uncertainty model was built on the first treatment fraction, by correlating the magnitude differences of five DIR results at each voxel to the magnitude of any single reference DIR. In the following fractions, only the reference DIR needs to be applied, and DVF geometric uncertainties were estimated by this model. The associated dosimetric uncertainties were then derived by considering the estimated geometric DVF uncertainty, the dose gradient of fractional recalculated dose distribution and the direction factor from the applied reference DIR of this fraction. This estimated dose uncertainty was respectively compared to the reference dose uncertainty when different DIRs were applied individually for each dose warping. This approach was validated on seven NSCLC patients, each with nine repeated CTs. The proposed model-based method is able to achieve dose uncertainty distribution on a conservative voxel-to-voxel comparison within ±5% of the prescribed dose to the ‘reference’ dosimetric uncertainty, for 77% of the voxels in the body and 66%–98% of voxels in investigated structures. We propose a method to estimate DIR induced uncertainties in dose accumulation for proton therapy of lung tumor treatments.
A novel calibration for L-shell x-ray fluorescence measurements of bone lead concentration using the strontium Kβ/Kα ratio
Authors: Gherase Mihai R , Serna Blaz , Kroeker Sarah 
Published: April 2021

Abstract

Objective. Lead (Pb) is a well-known toxic element. In vivo bone Pb concentration measurement is a long-term exposure metric complementary to blood Pb concentration measurement which is a metric of recent exposure. In vivo human tibia bone Pb measurements using Pb K-shell or L-shell x-ray fluorescence (KXRF or LXRF) emissions were developed in the 1980s. KXRF bone Pb measurements using Cd-109 gamma rays and coherent-to-fluorescence ratio to account for differences between phantom and in vivo measurements, was employed in human studies. Bone Pb LXRF method employed x-ray tubes. However, calibration procedures using ultrasound measurements of the soft tissue thickness (STT) proved inaccurate. Approach. In this study, bone and soft tissue (ST) phantoms simulated in vivo bone Pb measurements. Seven plaster-of-Paris cylindrical bone phantoms containing 1.01 mg g−1 of strontium (Sr) were doped with Pb in 0, 8, 16, 29, 44, 59, and 74 μg g−1 concentrations. Polyoxymethylene (POM), resin, and wax were each used to fabricate four ST phantoms in the approximate 1–4 mm thickness range. Pb LXRF measurements were performed using a previously developed optimal grazing incidence position method. Main results. Linear attenuation coefficients measurements of ST materials indicated that POM and resin mimicked well attenuation of Pb x-rays in skin and adipose tissue, respectively. POM and resin data indicated a bone Pb detection limit of 20 μg g−1 for a 2 mm STT. Derived relationships between the Pb concentration, Pb LXRF and Sr K
β
/K
α
ratio data did not require STT knowledge. Applied to POM and resin data, the new calibration method yielded unbiased results. Significance. In vivo bone Pb measurements in children were suggested following considerations of radiation dose, STT, detectability and distribution of Pb and Sr in bone. This research meets with the concerns regarding the negative effects of low levels of Pb exposure on neurodevelopment of children.
Trapped upper hybrid waves as eigenmodes of non-monotonic background density profiles
Authors: Senstius M G , Nielsen S K , Vann R G L 
Published: April 2021

Abstract
Non-monotonic plasma density structures such as blobs and magnetic islands give rise to trapped upper hybrid (UH) waves. Trapped UH waves which satisfy Bohr–Sommerfeld quantization can be thought of as eigenmodes of a cavity. Using fully kinetic particle-in-cell simulations, we verify the existence of these UH eigenmodes and demonstrate their significance as only eigenfrequencies become unstable to three-wave interactions. The eigenmodes can be excited through parametric decay instabilities (PDIs) of an X-mode pump wave at approximately twice the UH frequency, as could be the case for a gyrotron beam traversing a blob in a magnetically confined fusion plasma. We derive a closed expression for the wavenumber of UH waves, which is accurate both close to the UH layer and to the electron cyclotron resonance. This allows for fast analysis of eigenmodes in a non-monotonic structure. An expression for the amplification of PDI daughter waves in an inhomogeneous plasma is extended to a decay region where the first several derivatives vanish. From the amplification in a convective PDI, we estimate the growth rate of the absolute PDI involving the trapped waves. We show that the excitation of eigenmodes through PDIs in our simulations are indeed absolute rather than convective due to the trapping of the daughter waves. Additionally, we show that only eigenmodes get excited through the PDIs, and that we are able to predict the growth rates of the daughter waves and how they scale with the pump wave intensity. This is evidence supporting a fundamental assumption of analytical theory describing low threshold strong scattering observed in magnetically confined fusion experiments during second harmonic electron cyclotron resonance heating (ECRH). Such low threshold instabilities can degrade ECRH performance but also offer novel uses for ion heating or as diagnostics.
Observation of quasi-coherent density fluctuation in scrape-off layer enhancing boundary transport in high-

βN

hybrid plasmas on DIII-D
Authors: Hong R , Rhodes T L , Li Z-Y , Wang H , Zeng L , Barada K , Wang G , Watkins J G , Peebles W A 
Published: April 2021

Abstract
We report the observation of a quasi-coherent fluctuation (QCF) by the Doppler backscattering system in the scrape-off layer (SOL) region of the DIII-D tokamak. This QCF is observed in high power, high performance hybrid plasmas with near double-null divertor shape during the electron cyclotron heating period. This mode is correlated with a steepened SOL density profile, and leads to significantly elevated particle and heat fluxes between edge localized modes. The SOL QCF is a long-wavelength ion-scale fluctuation (

k

θ

ρ

s

≈
0.2

–0.4 and

k

r

ρ

s

≈
0.03

), and propagates in the ion diamagnetic direction in the plasma frame. Its radial expanse is about 1.5–2 cm, well beyond the typical width of heat flux λ

q
on DIII-D. Also, the SOL QCF does not show any clear dependence on the effective SOL collisionality, and thus may raise issues on the control of plasma-material interactions in low collisionality plasmas in which the blob-induced transport is reduced. A linear simulation using BOUT++ with a five-field reduced model is performed and compared with experimental observations. In simulation results, an interchange-like density perturbation can be driven by the SOL density gradient, and its peak location and the radial width of the density perturbation are in agreement with the experimental observations.
Formation and evolution of post-solitons following a high intensity laser-plasma interaction with a low-density foam target
Authors: Blackman David R , Adak Amitava , Singh Prashant K , Lad Amit D , Chatterjee Gourab , Ridgers Christopher P , Del Sorbo Dario , Trines Raoul M G M , Robinson A P L , Nazarov Wigen , Ravindra Kumar G , Pasley John 
Published: April 2021

Abstract
The formation and evolution of post-solitons has been discussed for quite some time both analytically and through the use of particle-in-cell (PIC) codes. It is however only recently that they have been directly observed in laser-plasma experiments. Relativistic electromagnetic (EM) solitons are localised structures that can occur in collisionless plasmas. They consist of a low-frequency EM wave trapped in a low electron number-density cavity surrounded by a shell with a higher electron number-density. Here we describe the results of an experiment in which a 100 TW Ti:sapphire laser (30 fs, 800 nm) irradiates a

0.03

g
c

m

−
3

TMPTA foam target with a focused intensity

I

l

=
9.5
×

10

17

W
c

m

−
2

. A third harmonic (

λ

p
r
o
b
e

≃
266

nm) probe is employed to diagnose plasma motion for 25 ps after the main pulse interaction via Doppler-Spectroscopy. Both radiation-hydrodynamics and 2D PIC simulations are performed to aid in the interpretation of the experimental results. We show that the rapid motion of the probe critical-surface observed in the experiment might be a signature of post-soliton wall motion.
Effect of the toroidal flow and flow shear on the m/n

=

2/1 tearing mode in J-TEXT tokamak
Authors: Shao Junren , Liu Hai , Xu Yuhong , Chen Zhipeng , Wang Tong , Cheng Jun , Wang Xianqu , Huang Jie , Liu Haifeng , Zhang Xin , Xu Kangzhong , Tang Changjian 
Published: April 2021

Abstract
The effect of the toroidal flow and flow shear on the m/n

=

2/1 tearing mode (TM) has been investigated in J-TEXT tokamak, where m and n are the poloidal and toroidal mode numbers. It is found that the toroidal flow increment is linearly modulated by the bias current/return current. The frequency of the 2/1 TM is also found to be proportional to the toroidal flow during the bias phase, which is consistent with the theoretical expectation. The electron diamagnetic drift frequency is almost constant before and during the bias phase. Moreover, the statistical analysis shows that the saturated island width of the TM is more correlated to the toroidal flow amplitude than the flow shear, which reveals that the effect of the TM depends on the magnitude of the toroidal flow rather than the flow shear. This result may illustrate the process of the 2/1 TM controlled by the electrode biasing, and suggests that changing the magnitude of toroidal flow is a possible method for stabilizing the TM.
Effects of energetic particles on the density-gradient-driven collisionless trapped electron mode instability in tokamak plasmas
Authors: Hussain M S , Guo Weixin , Wang Lu 
Published: April 2021

Abstract
We investigate analytically the effects of energetic particles (EPs) on the instability of the density-gradient-driven collisionless trapped electron mode (CTEM) through linear gyrokinetic theory and bounce kinetic theory in tokamak plasmas. The effects of EPs, including fusion-born alpha particles and neutral-beam-injection-driven beam ions, on the CTEM instability are compared for the dynamic model with slowing-down (SD) and equivalent Maxwellian (EM) equilibrium EP distribution functions and dilution model. It is found that the density-gradient-driven CTEM instability in the long wavelength regime can be further destabilized by EPs mainly due to the downshift in the real frequency of the mode by dilution effects. This is attributed to more resonant electrons around the smaller phase velocity of the drift wave and the consequent stronger excitation of CTEM instability. The growth rate is slightly higher for the dilution model as compared to that for the dynamic model since the Landau damping effects of EPs are neglected in the dilution model. Moreover, there is no significant difference in the growth rate between the cases of SD and EM equilibrium EP distribution functions, except for the case of alpha particles and with relatively higher electron temperature.
A non-twisting flux tube for local gyrokinetic simulations
Authors: Ball Justin , Brunner Stephan 
Published: April 2021

Abstract
Local gyrokinetic simulations use a field-aligned domain that twists due to the magnetic shear of the background magnetic equilibrium. However, if the magnetic shear is strong and/or the domain is long, the twist can become so extreme that it fails to properly resolve the turbulence. In this work, we derive and implement the ‘non-twisting flux tube,’ a local simulation domain that remains rectangular at all parallel locations. Convergence and runtime tests indicate that it can calculate the heat flux more efficiently than the conventional flux tube. For one test case, it was 30 times less computationally expensive and we found no case for which it was more expensive. It is most advantageous when the magnetic shear is high and the domain includes at least two regions of turbulent drive (e.g. stellarator simulations, pedestal simulations, tokamak simulations with several poloidal turns). Additionally, it more accurately models the inboard midplane when the magnetic shear is large. Lastly, we show how the non-twisting flux tube can be generalized to allow further optimization and control of the simulation domain.
On the quasi-stationary approach to solve the electron Boltzmann equation in pulsed plasmas
Authors: Tejero-del-Caz A , Guerra V , Pinhão N , Pintassilgo C D , Alves L L 
Published: April 2021

Abstract
This work analyzes the temporal evolution of the electron kinetics in dry-air plasmas (80% N2: 20% O2), excited by electric-field pulses with typical rise-times of 10−9 and 10−6 s, applied to a stationary neutral gaseous background at pressures of 105, 133 Pa and temperature of 300 K. The study is based on the solution of the electron Boltzmann equation (EBE), adopting either (i) a time-dependent formulation that considers an intrinsic time evolution for the electron energy distribution function (EEDF), assuming the classical two-term expansion and a space-independent exponential temporal growth of the electron density; or (ii) a quasi-stationary approach, where the time-independent form of the EBE is solved for different values of the reduced electric-field over the duration of the pulse. The EBE was solved using the LisbOn KInetics Boltzmann solver (LoKI-B), whose original capabilities were extended to accept time-dependent non-oscillatory electric fields as input data. The role of electron–electron collisions, under specific conditions, is also reported and discussed. The simulations show that the quasi-stationary approach gives solutions similar to the time-dependent formulation for rise-times longer than the characteristic evolution time of the EEDF, i.e. 20 ns at 105 Pa and 20 μs at 133 Pa, meaning that a quasi-stationary description is possible in a high-collisionality situation and long rise-times (e.g. microsecond pulses at atmospheric pressure), failing for faster rise-times (e.g. nanosecond pulses for both pressures considered here).
Transient analysis of graphene-based on-chip interconnects using closed-form MRA model
Authors: Kumar Amit , Kaushik Brajesh Kumar 
Published: April 2021

Abstract
As interconnects in very-large-scale-integration technology shrinks into the sub-22 nm regime, carbon nanotubes, graphene nanoribbons (GNRs), and Cu-GNRs are emerging as potential replacements for conventional copper on-chip interconnects. This paper presents an matrix-rational-approximation (MRA) model for the fast transient analysis of graphene-based on-chip interconnects. The proposed model’s key feature is that it allows the mathematical representation of the transfer function matrix of on-chip graphene-based interconnect networks in the frequency-domain using closed-form rational functions. The network’s rational functions coefficients are derived from per-unit-length parameters and predetermined coefficients of the Padé approximation. The graphene-based network’s time-domain model is directly obtained from the rational function frequency-domain model without any numerical integration techniques. This makes the proposed MRA model more numerically efficient than conventional simulation program with integrated circuit emphasis (SPICE) models. The results obtained using the proposed model show less than 1% error when compared with HSPICE simulations, ensuring the proposed model’s excellent accuracy. A wide eye-height of 0.8137 V and eye-width of 219.87 ps are obtained for the eye-diagram analysis of multilayer graphene nanoribbon lines at 4 Gbps.
High-speed short-wave infrared Si-based GeSn MQW phototransistor: an alternative to existing photodetectors
Authors: Kumar Harshvardhan 
Published: April 2021

Abstract
This work demonstrates high-performance vertical GeSn multiple quantum well (MQW) heterojunction phototransistors (HPTs) on Si substrates for short-wave infrared (SWIR) applications. Estimated results show a strong dependence on the number of QWs (N), incident optical power

P

in

and capture parameter

β

. Enhanced carrier and gain confinement cause an increase in responsivity of the device with the QWs in the base layer. However, the frequency performance of the device degrades with more QWs due to the increased forward transit time. On the other hand, the 3 dB cut-off frequency

f

T

is the highest for the lower value of

β

. In addition, the detectivity and responsivity of the device decrease with an increase in incident optical power due to the change in base potential. The calculated results show that the 3 dB cut-off

f

T

and maximum operating frequency

f

max

are

>
18

GHz

and

>
0.147

THz

, respectively for N = 1 at 300 K. The detectivity and noise equivalent power are

∼

10
9

cm

H

z

1

/

2

/

W

and

<

10

−
12

WH

z

−
1

/

2

, respectively for N = 3 at 300 K under 0.4 applied bias voltage. These promising results of the presented GeSn MQW HPT can pave the way for efficient low-noise high-speed photodetection applications under a low applied bias voltage.
Superconducting nanowire single-photon detector made of ultrathin γ-Nb4N3 film for mid-infrared wavelengths
Authors: Pan Yiming , Zhou Hui , Zhang Lu , Li Hao , Tang Yan , Yu Huiqin , Si Mengting , You Lixing , Wang Zhen 
Published: April 2021

Abstract
Superconducting nanowire single-photon detectors (SNSPDs) made of ultrathin δ-NbN films have been widely applied in both visible and infrared wavelengths. For mid-infrared (MIR) wavelengths, SNSPDs made of tungsten silicide films with a lower critical temperature were reported up to 9.9 μm wavelength. In this study, we demonstrate the potential of NbN-SNSPDs for use in MIR applications. SNSPDs made of γ-Nb4N3 films (critical temperature of 5.1 K for 6.5 nm thick films) instead of δ-NbN films were fabricated. The dependence of the normalized detection efficiency on the bias current indicated a clear trend toward a saturated plateau for wavelengths up to 2145 nm. The calculated cut-off wavelengths indicated the possibility of using γ-Nb4N3 SNSPDs for longer MIR wavelengths.
First-order kinetics bottleneck during photoinduced ultrafast insulator–metal transition in 3D orbitally-driven Peierls insulator CuIr2S4
Authors: Naseska M , Sutar P , Vaskivskyi Y , Vaskivskyi I , Vengust D , Svetin D , Kabanov V V , Mihailovic D , Mertelj T 
Published: April 2021

Abstract
The spinel-structure CuIr2S4 compound displays a rather unusual orbitally-driven three-dimensional Peierls-like insulator–metal transition. The low-T symmetry-broken insulating state is especially interesting due to the existence of a metastable irradiation-induced disordered weakly conducting state. Here we study intense femtosecond optical pulse irradiation effects by means of the all-optical ultrafast multi-pulse time-resolved spectroscopy. We show that the structural coherence of the low-T broken symmetry state is strongly suppressed on a sub-picosecond timescale above a threshold excitation fluence resulting in a structurally inhomogeneous transient state which persists for several-tens of picoseconds before reverting to the low-T disordered weakly conducting state. The electronic order shows a transient gap filling at a significantly lower fluence threshold. The data suggest that the photoinduced-transition dynamics to the high-T metallic phase is governed by first-order-transition nucleation kinetics that prevents the complete ultrafast structural transition even when the absorbed energy significantly exceeds the equilibrium enthalpy difference to the high-T metallic phase.