Journal of Physics D: Applied Physics

Levko, Dmitry; Sharma, Ashish; Raja, Laxminarayan L

doi: 10.1088/0022-3727/49/22/22LT01pmid: N/A

We present a computational modeling study of microwave plasma generated in cluster of atmospheric-pressure argon bubbles immersed in a liquid. We demonstrate that the use of microwaves allows the generation of a dense chemically active non-equilibrium plasma along the gas–liquid interface. Also, microwaves allow generation of overdense plasma in all the bubbles considered in the cluster which is possible because the collisional skin depth of the wave exceeds the bubble dimension. These features of microwave plasma generation in bubbles immersed in liquids are highly desirable for the large-scale liquid hydrocarbon reforming technologies.

Piqué, Alberto; Auyeung, Raymond C Y; Kim, Heungsoo; Charipar, Nicholas A; Mathews, Scott A

doi: 10.1088/0022-3727/49/22/223001pmid: N/A

Laser-based materials processing techniques are gaining widespread use in micro-manufacturing applications. The use of laser microfabrication techniques enables the processing of micro- and nanostructures from a wide range of materials and geometries without the need for masking and etching steps commonly associated with photolithography. This review aims to describe the broad applications space covered by laser-based micro- and nanoprocessing techniques and the benefits offered by the use of lasers in micro-manufacturing processes. Given their non-lithographic nature, these processes are also referred to as laser direct-write and constitute some of the earliest demonstrations of 3D printing or additive manufacturing at the microscale. As this review will show, the use of lasers enables precise control of the various types of processing steps—from subtractive to additive—over a wide range of scales with an extensive materials palette. Overall, laser-based direct-write techniques offer multiple modes of operation including the removal (via ablative processes) and addition (via photopolymerization or printing) of most classes of materials using the same equipment in many cases. The versatility provided by these multi-function, multi-material and multi-scale laser micro-manufacturing processes cannot be matched by photolithography nor with other direct-write microfabrication techniques and offer unique opportunities for current and future 3D micro-manufacturing applications.

Conca, A; Casper, F; Paul, J; Lehndorff, R; Jakob, G; Kläui, M; Hillebrands, B; Leven, B

doi: 10.1088/0022-3727/49/22/225001pmid: N/A

Magnetic tunnelling junctions increasingly enter the market for magnetic sensor applications. Thus, technological parameters such as the lifetime characteristics become more and more important. Here, an analysis of the lifetime characteristics of magnetic tunnelling junctions using the Weibull statistical distribution for CoFeB/MgO/CoFeB junctions is presented. The Weibull distribution is governed by two parameters, the characteristic lifetime η of the population and the shape parameter β, which gives information about the presence of an infant mortality. The suitability of the Weibull distribution is demonstrated for the description of dielectric breakdown processes in MgO-based tunnelling junctions at different voltages. A study of the dependence of the characteristic lifetime extrapolated to the low voltage regime, and the β parameter on the nominal barrier thickness and the resistance  ×  area product of the MgO barrier is shown. The influence of the RF deposition power for the MgO barrier and an annealing step on the Weibull parameters is also discussed.

Gumbs, Godfrey; Horing, N J M; Iurov, Andrii; Dahal, Dipendra

doi: 10.1088/0022-3727/49/22/225101pmid: N/A

We have developed an analytical formulation to calculate the plasmon dispersion relation for a two-dimensional layer which is encapsulated within a narrow spatial gap between two bulk half-space plasmas. This is based on a solution of the inverse dielectric function integral equation within the random-phase approximation (RPA). We take into account the nonlocality of the plasmon dispersion relation for both gapped and gapless graphene as the sandwiched two-dimensional (2D) semiconductor plasma. The associated nonlocal graphene plasmon spectrum coupled to the ‘sandwich’ system is exhibited in density plots, which show a linear mode and a pair of depolarization modes shifted from the bulk plasma frequency.

Wang, Wei; Dong, Yuan; Zhou, Qian; Tok, Eng Soon; Yeo, Yee-Chia

doi: 10.1088/0022-3727/49/22/225102pmid: N/A

The thermal stability and germanium–tin (Ge–Sn) interdiffusion properties were studied in epitaxial Ge/GeSn multiple-quantum-well (MQW) structure. No obvious interdiffusion was observed for annealing temperatures of 300 °C or below, while observable interdiffusion occurred for annealing temperatures of 380 °C and above. High-resolution x-ray diffraction was used to obtain the interdiffusion coefficient by analyzing the decrease rate of Ge/GeSn periodic satellite peaks. The interdiffusion coefficient is much higher, and the activation enthalpy of 1.21 eV is substantially lower in Ge/GeSn MQW structure than that previously reported in silicon–germanium (Si–Ge) systems. When the annealing temperature is increased to above 500 °C, Ge–Sn interdiffusion becomes severe. Some small pits appear on the surface, which should be related to Sn out-diffusion to the Ge cap layer, followed by Sn desorption from the top surface. This work provides insights into the Ge–Sn interdiffusion and Sn segregation behaviors in Ge/GeSn MQW structure, and the thermal budget that may be used for fabrication of devices comprising Ge/GeSn heterostructures.

Goto, Daisuke; Hijikata, Yasuto

doi: 10.1088/0022-3727/49/22/225103pmid: N/A

We have attempted to establish a unified theory of SiC oxidation by reproducing all the SiC oxide growth rates on the (0 0 0 1) Si-face, (1 1 0) a-face and (0 0 0 ) C-face at various oxidation temperatures and oxide partial pressures. Growth rates were calculated using the Si and C emission model and were confirmed to fully reproduce the observed data when an enhanced surface oxide growth rate was added to the previously defined growth rate. The parameters deduced from the calculations indicated that the activation energy for the initial interfacial reaction rate corresponds to the number of Si back-bond(s) on the crystalline surface. Although the C emission ratio was found to have no significant dependence on the surface orientation, the Si emission ratio varied significantly and so likely determines the oxide growth rate. The densities of Si and C interstitials at the SiC-oxide interface were simulated both on the oxide and SiC substrate sides, and the optimal oxidation sequence is discussed in terms of the formation of the interface state.

Bai, Zhen; Zhang, Jun; Zhong, Huihuang; Zhang, Dian; Meng, Dong

doi: 10.1088/0022-3727/49/22/225104pmid: N/A

Coaxial O-type Cerenkov devices usually operate in the quasi-TEM or TM01 mode, but the power capacity characteristics of these modes in coaxial slow-wave structures (SWSs) have not been published thus far. This paper presents numerical studies of the power capacity characteristics of the quasi-TEM and TM01 modes in coaxial SWSs. The results suggest that the power capacity of the TM01 mode is not significantly higher than that of the quasi-TEM mode, unless the distance between the inner and outer conductors is less than a critical value. A comparison of the power capacities of the TM01 mode in coaxial and hollow SWSs is reported for the first time. When the distance between the inner and outer conductors of coaxial SWSs is small enough or the outer radius is large enough, the power capacity of the TM01 mode in coaxial SWSs is higher than that of the TM01 mode in hollow SWSs with the same outer radius.

Xie, Mubiao; Zhu, Guoxian; Pan, Rongkai; Li, Dongyu; Hou, Dejian

doi: 10.1088/0022-3727/49/22/225105pmid: N/A

Novel yellow-emitting phosphors LiLa9(SiO4)6O2: 0.05Eu, xTb (x  =  0, 0.01, 0.03, 0.02, 0.04, 0.06, 0.08, 0.10) were prepared by a solid-state reaction in a CO-reducing atmosphere. The excitation and emission spectra, and the fluorescence decays were measured and discussed in detail. The fluorescence spectra results of sample LiLa9(SiO4)6O2: 0.05Eu reveal that still a small amount of Eu3+ ions are detected in the LiLa9(SiO4)6O2 host. The introduction of Tb3+ ions can enhance the emission intensity of LiLa9(SiO4)6O2: 0.05Eu under near-ultraviolet light excitation but they do not vary the emission color much. The results indicate that the yellow-emitting phosphors LiLa9(SiO4)6O2: Eu, Tb can be considered as potential phosphor-converted materials for n-UV white light-emitting diodes.

Beyene, Girum A; Tobin, Isaac; Juschkin, Larissa; Hayden, Patrick; O’Sullivan, Gerry; Sokell, Emma; Zakharov, Vassily S; Zakharov, Sergey V; O’Reilly, Fergal

doi: 10.1088/0022-3727/49/22/225201pmid: N/A

Extreme ultraviolet (EUV) light generation by hybrid laser-assisted vacuum arc discharge plasmas, utilizing Sn-coated rotating-disc-electrodes, was investigated. The discharge was initiated by localized ablation of the liquid tin coating of the cathode disc by a laser pulse. The laser pulse, at 1064 nm, was generated by Nd:YAG lasers with variable energy from 1 to 100 mJ per pulse. The impact of shortening the laser pulse from 7 ns to 170 ps on the EUV generation has been investigated in detail. The use of ps pulses resulted in an increase in emission of EUV radiation. With a fixed discharge energy of ~4 J, the EUV conversion efficiency tends to plateau at ~2.4  ±  0.25% for the ps laser pulses, while for the ns pulses, it saturates at ~1.7  ±  0.3%. Under similar discharge and laser energy conditions, operating the EUV source with the ps-triggering resulted also in narrower spectral profiles of the emission in comparison to ns-triggering. The results indicate an advantage in using ps-triggering in laser-assisted discharges to produce brighter plasmas required for applications such as metrology.

Liu, Lipeng; Becerra, Marley

doi: 10.1088/0022-3727/49/22/225202pmid: N/A

A 2D numerical simulation of the transition from stable positive glow corona to streamers in coaxial cylindrical configuration is presented. The hydrodynamic model with several convection-dominated continuity equations together with Poisson equation are solved with consideration of the ionization layer. The transition from a stable positive glow corona produced under a DC voltage to streamers is investigated under a sudden change of the applied voltage. The critical rate of rise of voltage required for the transition from positive glow to streamer corona is evaluated with a voltage ramp. By introducing either physical or numerical instabilities into the model, streamers with filamentary structures are observed, which produce a sudden increase of the discharge current by more than two orders of magnitude. It is also found that the surface electric field of the corona-generating conductor deviates from the onset electric field, casting doubts about the validity of Kaptzov’s approximation to evaluate the transition from stable glow to streamers.