| 1. |
- Abbasiasl, Taher, et al.
(författare)
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Effect of intensified cavitation using poly (vinyl alcohol) microbubbles on spray atomization characteristics in microscale
- 2020
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Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 10:2
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Tidskriftsartikel (refereegranskat)abstract
- In this study, cavitating flows inside a transparent cylindrical nozzle with an inner diameter of 0.9 mm were visualized, and the effect of cavitation on atomization characteristics of emerging sprays was investigated. Different patterns of cavitating flows inside the nozzle were visualized using a high-speed camera. In-house codes were developed to process the captured images to study the droplet size distribution and droplet velocity in different flow regimes. The results show that cavitating flows at the microscale have significant effects on atomization characteristics of the spray. Two working fluids, namely, water and poly(vinyl alcohol) microbubble (PVA MB) suspension, were employed. Accordingly, the injection pressures were detected as 690 kPa, 1035 kPa, and 1725 kPa for cavitation inception, supercavitation, and hydraulic flip flow regimes in the case of water, respectively. The corresponding pressures for the aforementioned patterns for PVA MB suspension were 590 kPa, 760 kPa, and 1070 kPa, respectively. At the microscale, as a result of a higher volume fraction of cavitation bubbles inside the nozzle, there is no large difference between the cavitation numbers corresponding to cavitating and hydraulic flip flows. Although the percentage of droplets with diameters smaller than 200 μm was roughly the same for both cases of water and PVA MB suspension, the Sauter mean diameter was considerably lower in the case of PVA MBs. Moreover, higher droplet velocities were achieved in the case of PVA MBs at lower injection pressures.
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| 2. |
- Adebiyi, Abdulafeez, et al.
(författare)
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Effect of surface friction on ultrafast flame acceleration in obstructed cylindrical pipes
- 2019
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Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 9:3
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Tidskriftsartikel (refereegranskat)abstract
- The Bychkov model of ultrafast flame acceleration in obstructed tubes [Valiev et al., "Flame Acceleration in Channels with Obstacles in the Deflagration-to-Detonation Transition," Combust. Flame 157, 1012 (2010)] employed a number of simplifying assumptions, including those of free-slip and adiabatic surfaces of the obstacles and of the tube wall. In the present work, the influence of free-slip/non-slip surface conditions on the flame dynamics in a cylindrical tube of radius R, involving an array of parallel, tightly-spaced obstacles of size αR, is scrutinized by means of the computational simulations of the axisymmetric fully-compressible gasdynamics and combustion equations with an Arrhenius chemical kinetics. Specifically, non-slip and free-slip surfaces are compared for the blockage ratio, α, and the spacing between the obstacles, ΔZ, in the ranges 1/3 ≤ α ≤ 2/3 and 0.25 ≤ ΔZ/R ≤ 2.0, respectively. For these parameters, an impact of surface friction on flameacceleration is shown to be minor, only 1-4%, slightly facilitating acceleration in a tube with ΔZ/R = 0.5 and moderating acceleration in thecase of ΔZ/R = 0.25. Given the fact that the physical boundary conditions are non-slip as far as the continuum assumption is valid, the presentwork thereby justifies the Bychkov model, employing the free-slip conditions, and makes its wider applicable to the practical reality. Whilethis result can be anticipated and explained by a fact that flame propagation is mainly driven by its spreading in the unobstructed portion ofan obstructed tube (i.e. far from the tube wall), the situation is, however, qualitatively different from that in the unobstructed tubes, wheresurface friction modifies the flame dynamics conceptually.
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| 3. |
- Ahlberg Helgee, Edit, 1986, et al.
(författare)
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Adsorption of metal atoms at a buckled graphene grain boundary using model potentials
- 2016
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226 .- 2158-3226. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- Two model potentials have been evaluated with regard to their ability to model adsorption of single metal atoms on a buckled graphene grain boundary. One of the potentials is a Lennard-Jones potential parametrized for gold and carbon, while the other is a bond-order potential parametrized for the interaction between carbon and platinum. Metals are expected to adsorb more strongly to grain boundaries than to pristine graphene due to their enhanced adsorption at point defects resembling those that constitute the grain boundary. Of the two potentials considered here, only the bond-order potential reproduces this behavior and predicts the energy of the adsorbate to be about 0.8 eV lower at the grain boundary than on pristine graphene. The Lennard-Jones potential predicts no significant difference in energy between adsorbates at the boundary and on pristine graphene. These results indicate that the Lennard-Jones potential is not suitable for studies of metal adsorption on defects in graphene, and that bond-order potentials are preferable.
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| 4. |
- Alnoor, Hatim, et al.
(författare)
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Effect of precursor solutions stirring on deep level defects concentration and spatial distribution in low temperature aqueous chemical synthesis of zinc oxide nanorods
- 2015
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Ingår i: AIP Advances. - : AMER INST PHYSICS. - 2158-3226. ; 5:8
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Tidskriftsartikel (refereegranskat)abstract
- Hexagonal c-axis oriented zinc oxide (ZnO) nanorods (NRs) with 120-300 nm diameters are synthesized via the low temperature aqueous chemical route at 80 degrees C on silver-coated glass substrates. The influence of varying the precursor solutions stirring durations on the concentration and spatial distributions of deep level defects in ZnO NRs is investigated. Room temperature micro-photoluminesnce (mu-PL) spectra were collected for all samples. Cathodoluminescence (CL) spectra of the as-synthesized NRs reveal a significant change in the intensity ratio of the near band edge emission (NBE) to the deep-level emission (DLE) peaks with increasing stirring durations. This is attributed to the variation in the concentration of the oxygen-deficiency with increasing stirring durations as suggested from the X-ray photoelectron spectroscopy analysis. Spatially resolved CL spectra taken along individual NRs revealed that stirring the precursor solutions for relatively short duration (1-3 h), which likely induced high super saturation under thermodynamic equilibrium during the synthesis process, is observed to favor the formation of point defects moving towards the tip of the NRs. In contrary, stirring for longer duration (5-15 h) will induce low super saturation favoring the formation of point defects located at the bottom of the NRs. These findings demonstrate that it is possible to control the concentration and spatial distribution of deep level defects in ZnO NRs by varying the stirring durations of the precursor solutions.
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| 5. |
- Amiri, A., et al.
(författare)
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A replacement model to simulate the nonlinear dynamics of electro-responsive liquid crystal coatings
- 2023
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 13:3
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Tidskriftsartikel (refereegranskat)abstract
- An electric circuit replacement model is proposed to simulate the key nonlinear dynamics of electro-responsive liquid crystal polymer networks (LCNs). LCNs are known for having great potential to be integrated into smart functional surfaces due to their ability to generate various surface patterns. However, due to their complex molecular dynamics, low-order dynamic models that can accurately describe and predict their dynamic behavior are still lacking. In light of this research gap, we develop a lumped-parameter replacement model based on the observed dynamics in the experimental data and the physics of LCN dielectric properties. The unique assembly of lumped parameters in its simplest form describes the transformation of a high-frequency input voltage to a relatively slow increase in the local height of the LCN coating in between the electrodes, serving as an excitation mechanism to induce height change. The nonlinear dynamics of this height increase, as a function of both excitation frequency and voltage, is described by the proposed model. Furthermore, the comparison of the simulation results with the experimental data from LCN shows that key LCN response characteristics are captured well by the model. This model makes it possible to accurately predict and control the response of the electro-responsive LCN surfaces to obtain a predefined desired deformation pattern, which is a vital requirement for integrating them in haptic and smart surface devices.
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| 6. |
- Azina, Clio, et al.
(författare)
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Effect of titanium and zirconium carbide interphases on the thermal conductivity and interfacial heat transfers in copper/diamond composite materials
- 2019
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Ingår i: AIP Advances. - : AMER INST PHYSICS. - 2158-3226. ; 9:5
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Tidskriftsartikel (refereegranskat)abstract
- Thermal properties of metal matrix composite materials are becoming ever more relevant with the increasing demand for thermally efficient materials. In this work, the thermal conductivity and heat transfers at the interfaces of copper matrix composite materials reinforced with diamond particles (Cu/D) are discussed. The composite materials contain either ZrC or TiC interphases and exhibit, respectively, higher and lower thermal conductivities with respect to their pure Cu/D counterparts. These thermal conductivities are accounted to the presence of strong covalent bonds and increased relative densities. The role of these interphases is also discussed regarding the phonon transmission at the interfaces. (c) 2019 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
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| 7. |
- Azzouz, Hatim, et al.
(författare)
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Efficient single particle detection with a superconducting nanowire
- 2012
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 2:3
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Tidskriftsartikel (refereegranskat)abstract
- Detection of alpha- and beta-particles is of paramount importance in a wide range of applications. Current particle detectors are all macroscopic and have limited time resolution. We demonstrate a nanoscale particle detector with a small detection volume, high detection efficiency, short dead times and low dark count levels. We measure alpha- and beta-particle detection efficiencies close to unity using different sources and also demonstrate blindness towards gamma-rays. Our nanoscale detector offers particle detection measurements with unprecendented spatial resolution.
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| 8. |
- Bejhed Stjernberg, Rebecca, et al.
(författare)
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Magnetic nanobeads present during enzymatic amplification and labeling for a simplified DNA detection protocol based on AC susceptometry
- 2015
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 5:12
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic biosensors are promising candidates for low-cost point-of-care biodiagnostic devices. For optimal efficiency it is crucial to minimize the time and complexity of the assay protocol including target recognition, amplification, labeling and read-out. In this work, possibilities for protocol simplifications for a DNA biodetection principle relying on hybridization of magnetic nanobeads to rolling circle amplification (RCA) products are investigated. The target DNA is recognized through a padlock ligation assay resulting in DNA circles serving as templates for the RCA process. It is found that beads can be present during amplification without noticeably interfering with the enzyme used for RCA (phi29 polymerase). As a result, the bead-coil hybridization can be performed immediately after amplification in a one-step manner at elevated temperature within a few minutes prior to read-out in an AC susceptometer setup, i.e. a combined protocol approach. Moreover, by recording the phase angle xi = arctan(chi ''/chi'), where chi and chi '' are the in-phase and out-of-phase components of the AC susceptibility, respectively, at one single frequency the total assay time for the optimized combined protocol would be no more than 1.5 hours, often a relevant time frame for diagnosis of cancer and infectious disease. Also, applying the phase angle method normalization of AC susceptibility data is not needed. These findings are useful for the development of point-of-care biodiagnostic devices relying on bead-coil binding and magnetic AC susceptometry.
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| 9. |
- Bergström, Magnus
(författare)
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A theoretical investigation of the influence of the second critical micelle concentration on the solubilization capacity of surfactant micelles
- 2018
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Ingår i: AIP Advances. - : AMER INST PHYSICS. - 2158-3226. ; 8:5
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Tidskriftsartikel (refereegranskat)abstract
- The solubilization of hydrophobic components by surfactants that form microemulsion droplets has been investigated from a theoretical point of view. By means of combining thermodynamics of self-assembly to form small systems with bending elasticity theory, we have been able to demonstrate a strong correlation between the second critical micelle concentration (CMC2) of surfactant micelles and their solubilization capacity (sigma). The correlation may be rationalized as a consequence of all three bending elasticity constants spontaneous curvature (H-0), bending rigidity (k(c)) and saddle-splay constant ((k) over bar (c)) showing similar trends with respect to the two quantities, i.e. sigma increases and CMC2 decreases with decreasing values of k(c)H(0) and increasing values of k(c) and (k) over bar (c), respectively. As a result, we demonstrate that the solubilization capacity is predicted to always be higher for a gemini surfactant with CMC2 = 11 mM as compared with a gemini surfactant with CMC2 = 18 mM. The predicted correlation between solubilization capacity and CMC2 agrees with experimental observations showing that surfactants forming larger micelles in general have better solubilization capacity than surfactants forming smaller micelles. The theory also demonstrates, in agreement with experiments, that sigma is raised in the entire range of surfactant concentrations, below as well as aboveCMC(2), regardless of micelle size. Consequently, our theory predicts that small micelles formed below CMC2 increase in size, whereas large rodlike or wormlike micelles formed above CMC2 decrease in size, as a hydrophobic solubilizate is added to a micellar solution.
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| 10. |
- Bondarenko, Artem, 1992-, et al.
(författare)
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Stochastic dynamics of strongly-bound magnetic vortex pairs
- 2017
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Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 7:5
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that strongly-bound spin-vortex pairs exhibit pronounced stochastic behaviour. Such dynamics is due to collective magnetization states originating from purely dipolar interactions between the vortices. The resulting thermal noise exhibits telegraph-like behaviour, with random switching between different oscillation regimes observable at room temperature. The noise in the system is further studied by varying the external field and observing the related changes in the frequency of switching and the probability for different magnetic states and regimes. Monte Carlo simulations are used to replicate and explain the experimental observations.
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| 11. |
- Buermans, J., et al.
(författare)
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Triple Langmuir probe calibration in TOMAS ECRH plasma
- 2023
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 13:5
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Tidskriftsartikel (refereegranskat)abstract
- In the TOMAS device, a triple Langmuir probe is used to measure the electron temperature and density. The accuracy of this measurement depends on correct determination of the effective collecting area of the probe, which depends on complex plasma transport processes. The probe can be calibrated by electron cyclotron resonance heating experiments using the cut-off density of the ordinary wave (O-wave). This threshold only depends on the frequency of the injected wave, and the occurrence of this phenomenon is clearly visible in the temperature evolution. The value of density is consequently known at this point and can be used to calibrate the density measurements of the triple Langmuir probe.
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| 12. |
- Capriata, Corrado Carlo Maria, et al.
(författare)
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Grain structure influence on synchronized two-dimensional spin-Hall nano-oscillators
- 2023
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 13:5
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Tidskriftsartikel (refereegranskat)abstract
- Nanoconstriction spin-Hall nano-oscillators (NC-SHNOs) are excellent devices for a wide variety of applications, from RF communication to bio-inspired computing. NC-SHNOs are easy to fabricate in large arrays, are CMOS compatible, and feature a narrow linewidth and high output power. However, in order to take full advantage of the device capabilities, a systematic analysis of the array behavior with respect to the number and dimensions of oscillators, the temperature of operation, and the influence of layer quality is needed. Here, we focus on micromagnetic simulations of 2 x 2 and 4 x 4 NC-SHNO arrays with single oscillators separated by up to 300 nm. We observe a synchronization scheme that allows for column-wise selection of the oscillation frequency for a larger pitch. However, for smaller pitches, a coherent oscillation volume was observed, and this volume included both the constrictions and extended beyond that region. A local variation in the exchange coupling in the active oscillator region was investigated by placing physical grains in the free magnetic layer, and it was shown to influence both the stable current range and the resulting frequency and output power. De-coupling the oscillators along rows or columns could provide higher power due to more favorable phase shifts between oscillators. Our investigation helps in achieving a deeper understanding of the intrinsic working principles of NC-SHNO arrays and how they reach fully synchronized states, and this will help to expand non-conventional computing capabilities.
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| 13. |
- Cuadra, Jorge, 1982, et al.
(författare)
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Hybrid dielectric waveguide spectroscopy of individual plasmonic nanoparticles
- 2017
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226 .- 2158-3226. ; 7:7, s. Article no: 075207 -
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Tidskriftsartikel (refereegranskat)abstract
- Plasmonics is a mature scientific discipline which is now entering the realm of practical applications. Recently, significant attention has been devoted to on-chip hybrid devices where plasmonic nanoantennas are integrated in standard Si 3 N 4 photonic waveguides. Light in these systems is usually coupled at the waveguide apexes by using multiple objectives and/or tapered optical fibers, rendering the analysis of spectroscopic signals a complicated task. Here, we show how by using a grating coupler and a low NA objective, quantitative spectroscopic information similar to standard dark-field spectroscopy can be obtained at the single-nanoparticle level. This technology may be useful for enabling single-nanoparticle studies in non-linear excitation regimes and/or in complex experimental environments, thus enriching the toolbox of nanophotonic methods.
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| 14. |
- Derek, Vedran, et al.
(författare)
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Micropatterning of organic electronic materials using a facile aqueous photolithographic process
- 2018
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Ingår i: AIP Advances. - : AMER INST PHYSICS. - 2158-3226. ; 8:10
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Tidskriftsartikel (refereegranskat)abstract
- Patterning organic semiconductors via traditional solution-based microfabrication techniques is precluded by undesired interactions between processing solvents and the organic material. Herein we show how to avoid these problems easily and introduce a simple lift-off method to pattern organic semiconductors. Positive tone resist is deposited on the substrate, followed by conventional exposure and development. After deposition of the organic semiconductor layer, the remaining photoresist is subjected to a flood exposure, rendering it developable. Lift-off is then performed using the same aqueous developer as before. We find that the aqueous developers do not compromise the integrity of the organic layer or alter its electronic performance. We utilize this technique to pattern four different organic electronic materials: epindo-lidione (EPI), a luminescent semiconductor, p-n photovoltaic bilayers of metal-free phthalocyanine and N, N-dimethyltetracarboxylic diimide, and finally the archetypical conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT). The result of our efforts is a facile method making use of well-established techniques that can be added to the toolbox of research and industrial scientists developing organic electronics technology. (c) 2018 Author(s).
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| 15. |
- Dhaka, Veer, et al.
(författare)
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Protective capping and surface passivation of III-V nanowires by atomic layer deposition
- 2016
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Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- Low temperature (similar to 200 degrees C) grown atomic layer deposition (ALD) films of AlN, TiN, Al2O3, GaN, and TiO2 were tested for protective capping and surface passivation of bottom-up grown III-V (GaAs and InP) nanowires (NWs), and top-down fabricated InP nanopillars. For as-grown GaAs NWs, only the AlN material passivated the GaAs surface as measured by photoluminescence (PL) at low temperatures (15K), and the best passivation was achieved with a few monolayer thick (2 angstrom) film. For InP NWs, the best passivation (similar to 2x enhancement in room-temperature PL) was achieved with a capping of 2nm thick Al2O3. All other ALD capping layers resulted in a de-passivation effect and possible damage to the InP surface. Top-down fabricated InP nanopillars show similar passivation effects as InP NWs. In particular, capping with a 2 nm thick Al2O3 layer increased the carrier decay time from 251 ps (as-etched nanopillars) to about 525 ps. Tests after six months ageing reveal that the capped nanostructures retain their optical properties. Overall, capping of GaAs and InP NWs with high-k dielectrics AlN and Al2O3 provides moderate surface passivation as well as long term protection from oxidation and environmental attack.
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| 16. |
- Diesen, Elias, et al.
(författare)
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Accuracy of XAS theory for unraveling structural changes of adsorbates : CO on Ni(100)
- 2020
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 10:11
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Tidskriftsartikel (refereegranskat)abstract
- Studying surface reactions using ultrafast optical pump and x-ray probe experiments relies on accurate calculations of x-ray spectra of adsorbates for the correct identification of the spectral signatures and their dynamical evolution. We show that experimental x-ray absorption can be well reproduced for different binding sites in a static prototype system CO/Ni(100) at a standard density functional theory generalized-gradient-approximation level of theory using a plane-wave basis and pseudopotentials. This validates its utility in analyzing ultrafast x-ray probe experiments. The accuracy of computed relative core level binding energies is about 0.2 eV, representing a lower limit for which spectral features can be resolved with this method. We also show that the commonly used Z + 1 approximation gives very good core binding energy shifts overall. However, we find a discrepancy for CO adsorbed in the hollow site, which we assign to the significantly stronger hybridization in hollow bonding than in on-top.
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| 17. |
- Dmitriev, Yurij A., et al.
(författare)
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H/D isotope effect observed in the isotropic Fermi contact interaction of formyl radical : Experimental and theoretical analysis of the inter- and intra-molecular dynamics
- 2020
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Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 10:12
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Tidskriftsartikel (refereegranskat)abstract
- An unexpected deficit of the computed hyper fine coupling constant in normal formyl HCO radicals, compared to that expected based on the proton to deuteron gyromagnetic ratio of the DCO species, was observed in experimental electron paramagnetic resonance studies of HCO and DCO radicals in a CO solid matrix at cryogenic conditions. Still, the matrix was found to have only a small effect on the anisotropic parts of the magnetic parameter tensors. The underlying isotope effect between the lighter proton and the heavier deuteron on the motional dynamics was verified and elucidated by quantum chemical calculations. The experimental results obtained within a temperature range of 1.4 K–4.2 K require special attention due to the tunneling motions of the molecule and its constituent particles. The effect from vibrational, rotational, and librational motion observed in the molecular states of formyl as a probe, averaged over the dynamics of the low temperature CO matrix isolation, reveals a clear proton isotope effect under both classical and quantum conditions.
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| 18. |
- Eklund, Per, et al.
(författare)
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Epitaxial growth of by reactive high-power impulse magnetron sputtering
- 2014
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 4:1
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Tidskriftsartikel (refereegranskat)abstract
- Al2O3 was deposited by reactive high-power impulse magnetron sputtering at 600 C onto pre-deposited Ti2AlC(0001) thin films on Al2O3(0001) substrates. The Al2O 3 was deposited to a thickness of 65 nm and formed an adherent layer of epitaxial γ-Al2O3(111) as shown by transmission electron microscopy. The demonstration of epitaxial growth of γ-Al 2O3 on Ti2AlC(0001) open prospects for growth of crystalline alumina as protective coatings on Ti2AlC and related nanolaminated materials. The crystallographic orientation relationships are γ-Al2O3(111)//Ti2AlC(0001) (out-of-plane) and Al2O3//Ti2AlC(112̄0)γ-Al 2O3(22̄0)// Ti 2 AlC (112̄0) (in-plane) as determined by electron diffraction. Annealing in vacuum at 900 C resulted in partial decomposition of the Ti2AlC by depletion of Al and diffusion into and through the γ-Al2O3 layer.
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| 19. |
- Eklund, Per, et al.
(författare)
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Epitaxial growth of gamma-Al2O3 on Ti2AlC(0001) by reactive high-power impulse magnetron sputtering
- 2014
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Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 4:1, s. 017138-
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Tidskriftsartikel (refereegranskat)abstract
- Al2O3 was deposited by reactive high-power impulse magnetron sputtering at 600 degrees C onto pre-deposited Ti2AlC(0001) thin films on alpha-Al2O3(0001) substrates. The Al2O3 was deposited to a thickness of 65 nm and formed an adherent layer of epitaxial gamma-Al2O3(111) as shown by transmission electron microscopy. The demonstration of epitaxial growth of gamma-Al2O3 on Ti2AlC (0001) open prospects for growth of crystalline alumina as protective coatings on Ti2AlC and related nanolaminated materials. The crystallographic orientation relationships are gamma-Al2O3(111)//Ti2AlC(0001) (out-of-plane) and gamma-Al2O3(2 (2) over bar0)//Ti2AlC(11 (2) over bar0) (in-plane) as determined by electron diffraction. Annealing in vacuum at 900 degrees C resulted in partial decomposition of the Ti2AlC by depletion of Al and diffusion into and through the gamma-Al2O3 layer.
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| 20. |
- Elamain, Omaima Abubakr, et al.
(författare)
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Periodic pattern formation in an achiral bent core nematic
- 2018
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Ingår i: Aip Advances. - : AIP Publishing. - 2158-3226. ; 8:9
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Tidskriftsartikel (refereegranskat)abstract
- We investigated a periodic flexoelectric domain pattern, which appeared as regular parallel stripes in an achiral bent core nematic liquid crystal when dc electric field was applied. We found that such a pattern was first formed at the substrate surface and took place in sandwich cells with a gap larger than 2 mu m. The field-induced periodic pattern was preserved in the field-off state by a polymer network formed in the cell and was found to exhibit a polar as well as a linear electro-optic response due to in-plane switching of the sample optic axis. A comparison between this response and the one obtained in short cholesteric liquid crystals, aligned in ULH (uniform lying helix) texture, and short pitch ferroelectric liquid crystals, respectively, suggested that a heliconical molecular order is most probably formed in the field-induced periodic stripe pattern, with the helix axis orthogonal to the stripes. To our knowledge, this is the first experimental evidence of field-induced chiral-symmetry breaking in the flexoelectric periodic stripe pattern in achiral bent core nematic, resulting in heliconical molecular order, resembling the one of twist-bend (TB) nematic phase in this kind of nematics. (C) 2018 Author(s).
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| 21. |
- Eriksson, Martin O., et al.
(författare)
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Recombination processes in Mg doped wurtzite InN films with p- and n-type conductivity
- 2019
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Ingår i: AIP Advances. - : AMER INST PHYSICS. - 2158-3226. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Obtaining high quality, wurtzite InN films with p-type conductivity is a challenge, and there is limited information about the photoluminescence (PL) characteristics of such films. In this study, we present a comprehensive PL study and discuss in detail the recombination processes in Mg-doped InN films with varying Mg concentrations. We find that at low Mg-doping of 1x10(18) cm(-3), which yields p-type conductivity, the PL in InN is spatially inhomogeneous. The latter is suggested to be associated with the presence of n-type pockets, displaying photoluminescence at 0.73 eV involving electrons at the Fermi edge above the conduction band edge. Increasing the Mg concentration to 2.9x10(19) cm(-3) in p-type InN yields strong and spatially uniform photoluminescence at 0.62 eV and 0.68 eV visible all the way to room temperature, indicating homogeneous p-type conductivity. An acceptor binding energy of 64 meV is determined for the Mg acceptor. Further increase of the Mg concentration to 1.8x10(20) cm(-3) leads to switching conductivity back to n-type. The PL spectra in this highly doped sample reveal only the emission related to the Mg acceptor (at 0.61 eV). In the low-energy tail of the emission, the multiple peaks observed at 0.54 - 0.58 eV are suggested to originate from recombination of carriers localized at stacking faults. (C) 2019 Author(s).
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| 22. |
- Fan, W., et al.
(författare)
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Investigation of magnetization dynamics damping in Ni80Fe20/Nd-Cu bilayer at room temperature
- 2018
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Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 8:5
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Tidskriftsartikel (refereegranskat)abstract
- Focusing on the Ni80Fe20 (Py)/Nd-Cu bilayers, the magnetization dynamic damping from spin pumping effect is investigated systematically by doping itinerant Cu in rear earth metal Nd. Various Ta/Py/Nd1-xCux/Ta/Si films with x = 0%, 16%, 38%, 46% and 58% are prepared by magnetron sputtering. For every content of Cu, the thickness of Nd-Cu layer is changed from 1 nm to 32 nm. The damping coefficient increases with increasing the thickness of Nd-Cu layer, which shows the trend of the spin pumping behavior. Also, with increasing Cu concentration in the Nd-Cu layer, the damping coefficient decreases, implying that the spin-orbit coupling in Nd-Cu layer is indeed cut down by high itinerant of Cu dopants. It is interesting that the spin diffusion length (λSD) in the Nd-Cu layer for different Cu dopants is not found to increase monotonously.
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| 23. |
- Fu, Chaochao, et al.
(författare)
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Understanding the microwave annealing of silicon
- 2017
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Ingår i: AIP Advances. - : AMER INST PHYSICS. - 2158-3226. ; 7:3
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Tidskriftsartikel (refereegranskat)abstract
- Though microwave annealing appears to be very appealing due to its unique features, lacking an in-depth understanding and accurate model hinder its application in semiconductor processing. In this paper, the physics-based model and accurate calculation for the microwave annealing of silicon are presented. Both thermal effects, including ohmic conduction loss and dielectric polarization loss, and non-thermal effects are thoroughly analyzed. We designed unique experiments to verify the mechanism and extract relevant parameters. We also explicitly illustrate the dynamic interaction processes of the microwave annealing of silicon. This work provides an in-depth understanding that can expedite the application of microwave annealing in semiconductor processing and open the door to implementing microwave annealing for future research and applications.
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| 24. |
- Fu, Jie, et al.
(författare)
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Ab initio molecular dynamics study of fluid H2O-CO2 mixture in broad pressure-temperature range
- 2017
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 7:11
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Tidskriftsartikel (refereegranskat)abstract
- Properties of H2O and CO2 fluid and their mixtures under extreme pressures and temperatures are poorly known yet critically important in a number of applications. Several hundreds of first-principles molecular dynamics (FPMD) runs have been performed to obtain the pressure-volume-temperature (P-V-T) data on supercritical H2O, CO2, and H2O-CO2 mixtures. The pressure-temperature (P-T) range are from 0.5 GPa to 104 GPa (48.5 GPa for CO2) and from 600 K to 4000 K. Based on these data, we evaluate several existing equations of state (EOS) for the fluid H2O, CO2, and H2O-CO2 mixture. The results show that the EOS for H2O from Belonoshko et al. [Geochim. Cosmochim. Acta 55, 381-387; Geochim. Cosmochim. Acta 55, 3191-3208; Geochim. Cosmochim. Acta 56, 3611-3626; Comput. Geosci. 18, 1267-1269] not only can be used in the studied P-T range but also is accurate enough to be used for prediction of P-V-T data. In addition, IAPWS-95 EOS for H2O shows excellent extrapolation behavior beyond 1.0 GPa and 1273 K. However, for the case of CO2, none of the existing EOS produces data in agreement with the FPMD results. We created new EOS for CO2. The precision of the new EOS is tested by comparison to the calculated P-V-T data, fugacity coefficient of the CO2 fluid derived from high P-T experimental data as well as to the (very scarce) experimental volumetric data in the high P-T range. On the basis of our FPMD data we created a new EOS for H2O-CO2 mixture. The new EOS for the mixture is in reasonable agreement with experimental data.
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- Gandhi, Hemi H., et al.
(författare)
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Chalcogen-hyperdoped germanium for short-wavelength infrared photodetection
- 2020
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Ingår i: AIP Advances. - : AMER INST PHYSICS. - 2158-3226. ; 10:7
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Tidskriftsartikel (refereegranskat)abstract
- Obtaining short-wavelength-infrared (SWIR; 1.4 mu m-3.0 mu m) room-temperature photodetection in a low-cost, group IV semiconductor is desirable for numerous applications. We demonstrate a non-equilibrium method for hyperdoping germanium with selenium or tellurium for dopant-mediated SWIR photodetection. By ion-implanting Se or Te into Ge wafers and restoring crystallinity with pulsed laser melting induced rapid solidification, we obtain single crystalline materials with peak Se and Te concentrations of 10(20) cm(-3) (10(4) times the solubility limits). These hyperdoped materials exhibit sub-bandgap absorption of light up to wavelengths of at least 3.0 mu m, with their sub-bandgap optical absorption coefficients comparable to those of commercial SWIR photodetection materials. Although previous studies of Ge-based photodetectors have reported a sub-bandgap optoelectronic response only at low temperature, we report room-temperature sub-bandgap SWIR photodetection at wavelengths as long as 3.0 mu m from rudimentary hyperdoped Ge:Se and Ge:Te photodetectors.
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