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  • AIP Publishing  (27)
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  • AIP Publishing  (27)
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  • 1
    Online Resource
    Online Resource
    Oxygen annealing impact on β -Ga2O3 MOSFETs: Improved pinch-off characteristic and output power density
    AIP Publishing ; 2020
    In:  Applied Physics Letters Vol. 117, No. 13 ( 2020-09-28)
    Details
    In: Applied Physics Letters, AIP Publishing, Vol. 117, No. 13 ( 2020-09-28)
    Abstract: In this Letter, we present direct current (DC), small signal radio frequency (RF), and large signals with pulsed and continuous wave (CW) studies and characterization on oxygen annealed (OA) β-Ga2O3 metal-oxide-semiconductor field-effect transistors (MOSFETs) with significantly improved CW output power density (Pout) when compared to other β-Ga2O3 RF devices. The OA process is found to be useful in compensating and neutralizing the donors in the unintentionally doped (UID) buffer layer and, hence, suppressing a second depletion effect in this UID layer. The device demonstrates a peak DC drain current of 200 mA/mm, a transconductance of 11 mS/mm, and an on/off ratio of 109. Small-signal RF characterization indicates a cut-off frequency and maximum oscillation frequency (fT/fmax) of 1.8 GHz and 4.2 GHz, respectively. The device also shows an output power (Pout)/peak power added efficiency (PAE)/gain of 0.4 W/mm/10%/3.2 dB and 0.43 W/mm/12%/3.6 dB for CW and pulsed signals, respectively, at an operation frequency of 1 GHz.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    URL: Article
    DOI: 10.1063/5.0021242
    RVK:
    UA 1000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2020
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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  • 2
    Online Resource
    Online Resource
    Anisotropic shock sensitivity for β -octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine energetic material under compressive-shear loading from ReaxFF-lg reactive dynamics simulations
    AIP Publishing ; 2012
    In:  Journal of Applied Physics Vol. 111, No. 12 ( 2012-06-15)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 111, No. 12 ( 2012-06-15)
    Abstract: We report here the predictions on anisotropy of shock sensitivity and of chemical process initiation in single crystal β-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (β-HMX) using compressive shear reactive dynamics (CS-RD) model with ReaxFF-lg reactive force field. Analysis of resolved shear stress induced by uniaxial compression along three shock directions normal to (110), (011), and (010) planes leads to identify eight slip systems as candidates for shear deformation. For each of the eight slip systems, non-equilibrium reactive dynamics simulations were carried out to determine thermal, mechanical, and chemical responses to shear deformation. Shock direction normal to (010) plane exhibits large shear stress barriers arising from steric hindrance between molecules of adjacent layers leading to local dramatic energy and temperature increases under shear flow that in turn accelerate chemical bond breaking and initial product formation processes, promoting further molecular decomposition and eventually transition to detonation. This suggests that single crystal β-HMX is sensitive to shocks in direction normal to (010) plane. Shock directions normal to (110) and (011) planes reveal significantly less steric hindrance, leading to more modest energy and temperature increases followed by slower chemical reaction initiation. Thus, shock directions normal to (110) and (011) planes are less sensitive than shock direction normal to (010) plane, which agree with interpretations from currently available plate impact experiments on HMX. This validation of CS-RD and ReaxFF for characterizing sensitivity of single crystal energetic materials indicates that these methods can be applied to study sensitivity for more complex polymer bonded explosives and solid composite propellants having complex microstructures, corrugated interfaces, as well as defects.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.4729114
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2012
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 3
    Online Resource
    Online Resource
    Optimizing a rapid shutdown module for pre-polarization current in surface nuclear magnetic resonance
    AIP Publishing ; 2021
    In:  Review of Scientific Instruments Vol. 92, No. 10 ( 2021-10-01)
    Details
    In: Review of Scientific Instruments, AIP Publishing, Vol. 92, No. 10 ( 2021-10-01)
    Abstract: Surface nuclear magnetic resonance (SNMR) technology is widely used for hydrological investigations. At high ambient noise levels, the use of a pre-polarization field can enhance the amplitude of the free induced decay (FID) signal. However, the spatial distribution of the pre-polarization field is inhomogeneous, and so it is vital to optimize the shutdown ramp and time for all combinations of the pre-polarization field amplitude and relative orientation. For this purpose, we designed a rapid and adiabatic shutdown circuit for pre-polarization surface nuclear magnetic resonance (PSNMR) systems. In the initial stage of the shutdown process, the magnetic field energy stored in the direct current transmitting coil is transferred to the capacitor by a semi-controlled full bridge circuit. At the end of the shutdown period, the pre-polarization current decays exponentially toward zero. The shutdown process can be controlled by adjusting the circuit parameters. The shutdown ramp and time of the designed circuit are verified through a series of simulations and experiments. As the initial voltage of the capacitor increases from 65 to 300 V, the initial amplitude of the exponential decay of the pre-polarization current increases from 15 to 48 A and the shutdown time decreases from 1.4 to 1 ms. Our design scheme provides a more reliable concept for the shutdown process in the case of multiple transmitting coils. This allows a larger gain of the FID signal to be obtained in specific PSNMR applications when pre-polarization currents with slightly different channel parameters need to be shutdown uniformly.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    URL: Article
    DOI: 10.1063/5.0064214
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2021
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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  • 4
    Online Resource
    Online Resource
    Characterization of amorphous Si-Zn-Sn-O thin films and applications in thin-film transistors
    AIP Publishing ; 2013
    In:  Applied Physics Letters Vol. 103, No. 8 ( 2013-08-19)
    Details
    In: Applied Physics Letters, AIP Publishing, Vol. 103, No. 8 ( 2013-08-19)
    Abstract: Amorphous silicon-zinc-tin-oxide (α-SZTO) thin films were prepared, and their properties were investigated physically and electrically, with an emphasis on the Si effects. An appropriate Si content in the matrix can not only achieve stable and dense films, but also suppress the formation of oxygen vacancies efficiently, due to its high oxygen bonding ability. Thin film transistors (TFTs) with α-SZTO active channel layers exhibited a field-effect mobility of around 1 cm2V−1s−1, an on/off current ratio of 107, and a subthreshold swing of 0.863 V/decade with a good long-term stability. The α-SZTO TFT is a potential candidate for electronic applications.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    URL: Article
    DOI: 10.1063/1.4818728
    RVK:
    UA 1000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2013
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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  • 5
    Online Resource
    Online Resource
    Structure and dynamics of ethane confined in silica nanopores in the presence of CO2
    AIP Publishing ; 2020
    In:  The Journal of Chemical Physics Vol. 152, No. 8 ( 2020-02-28)
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 152, No. 8 ( 2020-02-28)
    Abstract: Fundamental understanding of the subcritical/supercritical behavior of key hydrocarbon species inside nano-porous matrices at elevated pressure and temperature is less developed compared to bulk fluids, but this knowledge is of great importance for chemical and energy engineering industries. This study explores in detail the structure and dynamics of ethane (C2H6) fluid confined in silica nanopores, with a focus on the effects of pressure and different ratios of C2H6 and CO2 at non-ambient temperature. Quasi-elastic neutron scattering (QENS) experiments were carried out for the pure C2H6, C2H6:CO2 = 3:1, and 1:3 mixed fluids confined in 4-nm cylindrical silica pores at three different pressures (30 bars, 65 bars, and 100 bars) at 323 K. Two Lorentzian functions were required to fit the spectra, corresponding to fast and slow translational motions. No localized motions (rotations and vibrations) were detected. Higher pressures resulted in hindrances of the diffusivity of C2H6 molecules in all systems investigated. Pore size was found to be an important factor, i.e., the dynamics of confined C2H6 is more restricted in smaller pores compared to the larger pores used in previous studies. Molecular dynamics simulations were performed to complement the QENS experiment at 65 bars, providing supportive structure information and comparable dynamic information. The simulations indicate that CO2 molecules are more strongly attracted to the pore surface compared to C2H6. The C2H6 molecules interacting with or near the pore surface form a dense first layer (L1) close to the pore surface and a second less dense layer (L2) extending into the pore center. Both the experiments and simulations revealed the role that CO2 molecules play in enhancing C2H6 diffusion (“molecular lubrication”) at high CO2:C2H6 ratios. The energy scales of the two dynamic components, fast and slow, quantified by both techniques, are in very good agreement. Herein, the simulations identified the fast component as the main contributor to the dynamics. Molecule motions in the L2 region are mostly responsible for the dynamics (fast and slow) that can be detected by the instrument.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.5134451
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2020
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 6
    Online Resource
    Online Resource
    Planar Hall effect in PtSe2
    AIP Publishing ; 2020
    In:  Journal of Applied Physics Vol. 127, No. 5 ( 2020-02-07)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 127, No. 5 ( 2020-02-07)
    Abstract: In this study, we report on the planar Hall transport study of type-II Dirac semimetal PtSe2 microflakes. The remarkable anisotropic magnetoresistance (AMR) and giant planar Hall resistance (PHR) are observed while tilting the magnetic field away from the current direction in the sample plane. Both AMR and PHR oscillate with the in-plane angle between the magnetic field and current, and the oscillation period is π. The angular dependence of AMR and PHR can be perfectly described by the theoretical formulas. The physical mechanism behind the observed AMR and PHR may have resulted from the classical orbital magnetoresistance.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.5133809
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2020
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 7
    Online Resource
    Online Resource
    A fractal power-law approach for investigating the interactions between reservoir microstructure and gas migration
    AIP Publishing ; 2023
    In:  Physics of Fluids Vol. 35, No. 1 ( 2023-01-01)
    Details
    In: Physics of Fluids, AIP Publishing, Vol. 35, No. 1 ( 2023-01-01)
    Abstract: As one of the most significant clean energy sources, the migration characteristics and extraction processes of coalbed methane (CBM) have been extensively studied. The structural distribution and evolutionary characteristics of reservoir fractures, as the main conduit for gas migration, significantly affect the permeability and gas production. However, few models have been able to quantitatively and accurately explore reservoir micro–macro interactions under coupled thermal-fluid–solid effects. This work develops a new highly coupled model based on the widely adopted power-law function to quantify reservoir thermal conduction effect, gas pressure evolution, reservoir deformation, in situ stress, the adsorption–desorption effect, and reservoir microstructure evolution. Three parameters are adopted to quantitatively characterize the reservoir structure: (1) fracture power index αf (to characterize the fracture density), (2) fracture length ratio rf (to characterize the fracture size), and (3) the maximum fracture length l. The results demonstrate that the fractal network is a special kind of network in the power-law length distribution. The proposed power-law seepage model is able to accurately characterize the evolution of reservoir microstructure and the impact of microevolution on extraction under multi-field coupling effects, compared to the traditional power-law model. The proposed model can provide a good theoretical and practical support for the study of CBM migration and extraction.
    Type of Medium: Online Resource
    ISSN: 1070-6631 , 1089-7666
    URL: Article
    DOI: 10.1063/5.0129025
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2023
    detail.hit.zdb_id: 1472743-2
    detail.hit.zdb_id: 241528-8
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  • 8
    Online Resource
    Online Resource
    Field-free switching of magnetization induced by spin–orbit torque in Pt/CoGd/Pt thin film
    AIP Publishing ; 2022
    In:  Applied Physics Letters Vol. 120, No. 25 ( 2022-06-20)
    Details
    In: Applied Physics Letters, AIP Publishing, Vol. 120, No. 25 ( 2022-06-20)
    Abstract: All-electric control of magnetism is essential for the future ultralow-power memory and logic spintronic applications. Here, we report a highly efficient way to realize field-free current-induced switching of magnetization in ferrimagnetic CoGd, which is deposited with composite target. The critical switching current density is as low as ∼1 × 107 A/cm2. Without any gradient designs, our CoGd film intrinsically exhibits extraordinary titled magnetic anisotropy and bias-fields. The field-free switching of magnetizations can be achieved by applying current pulses in x or y directions. We further establish a coupled ferrimagnetic macrospin model subjected to the Landau–Lifshitz–Gilbert–Slonczewski equation, and the theoretical results agree with experiments well. All these results suggest that deposition with composite target is the optimal route to fabricate a high performance spin–orbit torque device, which provides multiple routes to achieve field-free, deterministic, and low-consumption magnetization switching.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    URL: Article
    DOI: 10.1063/5.0092513
    RVK:
    UA 1000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2022
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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  • 9
    Online Resource
    Online Resource
    Particle dynamics in compressible turbulent vertical channel flows
    AIP Publishing ; 2023
    In:  Physics of Fluids Vol. 35, No. 8 ( 2023-08-01)
    Details
    In: Physics of Fluids, AIP Publishing, Vol. 35, No. 8 ( 2023-08-01)
    Abstract: In this work, we carry out direct numerical simulations of particle suspensions in the compressible turbulent vertical channel (TVC) flows with Mach number Ma = 1.5 and particle Stokes number St = 1–100. The compressibility effect is considered in the particle dynamic model for the first time in the study of compressible particle-laden wall turbulence. We find that in both incompressible and compressible flow, gravity weakens the wall-normal and spanwise fluctuations of particle velocities as the Stokes number increases. However, compared to the incompressible flow case, the compressible effect amplifies the mean velocity, fluctuations of velocity, and slip velocity of particle in the streamwise direction. The wall-normal and spanwise fluctuations of particle velocities are augmented by the compressible effect in the channel core region. Moreover, in the core region, the effect of fluid compressibility on the wall-normal and spanwise fluctuations of particle velocities attenuates as the Stokes number increases, indicating a competition between the compressible effect and the particle inertia effect. We, furthermore, conduct the quadrant analysis of the local fluctuation velocities of fluid at particle positions and observe preferential distributions in the second and the fourth quadrants at y+ = 12.5–13.5. For compressible TVC flows, the pattern of probability distributions is more elongated, and the percentage is slightly higher in the second and fourth quadrants than that of incompressible flows. This observation implies that more particles locate in the ejection and sweep events in compressible flows than that in incompressible flows, which is anticipated to influence the particle wall-normal transport.
    Type of Medium: Online Resource
    ISSN: 1070-6631 , 1089-7666
    URL: Article
    DOI: 10.1063/5.0155642
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2023
    detail.hit.zdb_id: 1472743-2
    detail.hit.zdb_id: 241528-8
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  • 10
    Online Resource
    Online Resource
    Near infrared quantum cutting in heavy Yb doped Ce0.03Yb3xY(2.97−3x)Al5O12 transparent ceramics for crystalline silicon solar cells
    AIP Publishing ; 2010
    In:  Journal of Applied Physics Vol. 107, No. 4 ( 2010-02-15)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 107, No. 4 ( 2010-02-15)
    Abstract: Near infrared (NIR) quantum cutting involving the conversion of an absorbed blue photon into two NIR photons emission has been realized in heavy Yb doped Ce0.03Yb3xY(2.97−3x)Al5O12 (x=0.1, 0.25, and 0.5) transparent ceramics. Upon the 467 nm excitation, the energy transfer process was dominated by the cooperative downconversion from the 5d1 state of one Ce3+ ion to the F25/2 state of two Yb3+ ions. The influence of the Ce4+–Yb2+ charge transfer state (CTS) should not contribute much to the energy transfer process for the large energy gap between Ce3+:5d1 and the CTS. The calculated quantum yield of Yb3+ for the x=0.25 sample without concentration quenching was 175.4%.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.3298907
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2010
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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