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Photonics
Published in Ajawad I. Haija, M. Z. Numan, W. Larry Freeman, Concise Optics, 2018
Ajawad I. Haija, M. Z. Numan, W. Larry Freeman
When n-type and p-type regions coexist in close proximity within the same semiconductor crystal, there is a transition region in which holes and electrons recombine and form a charge free zone called the depletion region. The Fermi energy must be constant across the transitions region and that forces the valence and conduction bands to shift in order to maintain charge neutrality and the lowest energy for the system in equilibrium. This is depicted in Figure 13.19.
Structure of Bipolar Junction Transistor
Published in Michael Olorunfunmi Kolawole, Electronics, 2020
A pn-junction structure constitutes a diode, as shown in Figure 3.8a. In this pn-junction structure, there exists two distinct regions, as seen in Figure 3.8b, namely: (i) the depletion region is the transition region where charge redistribution has taken place. Technically, this region is empty of free careers, and (ii) the neutral regions are those which are essentially unaffected by the charge redistribution or carrier exchange.
2/Ge Stacks
Published in Sheng-Kai Wang, 2/Ge System, 2022
In the low-temperature and high-pressure regime, the oxidation process is governed by the passive oxidation dominantly. In this regime, there will be almost no GeO desorption in the thermal process. However, in the high-temperature and low-pressure regime, the thermal process turns out to be active oxidation dominant; in other words, the substrate is merely etched by O2 to form GeO. Very important information in Figure 5.8 is that, between the passive dominant regime and the active dominant regime, there is a transition regime, in which both active oxidation and passive oxidation occur comparably and rigorously. This effect has never been predicted by the thermodynamic calculation. And it is also a special effect that has never been observed in the case of Si oxidation. The orange dashed lines are plotted by imagination based on the principle that the higher the temperature, the stronger both reaction fluxes are. Therefore, at high temperatures, this transition region becomes wider, while at low temperatures, it becomes narrower. It is worth pointing out that the active oxidation regime strongly “invades” across the thermodynamic equilibrium line at a temperature higher than 550oC because the activation oxidation flux is always irreversible; once Ge substrate is “etched” by O2 and desorbs away in terms of GeO, the desorbed GeO will not return to the original Ge substrate. Therefore, although the GeO may be re-oxidized to GeO2 somewhere other than on this substrate, the net phenomenon we observed turns out to be the etching of Ge substrate. When pO2 decreases to the regime close to UHV, the extra O2 is negligible. In this regime, almost no passive or active oxidation will occur on Ge substrate. However, for the GeO2/Ge, GeO desorption and GeO2 crystallization become dominant. Specifically, GeO desorption occurs when temperature is over 430oC in UHV, and both GeO desorption and α-quartz-like GeO2 crystallization occur at a higher temperature (> 660oC).
Near-Field Radiative Heat Transfer between $\beta-$GeSe monolayers: An ab initio study
Published in Nanoscale and Microscale Thermophysical Engineering, 2023
R. Esquivel-Sirvent, A. Gusso, F. Sánchez Ochoa
An important feature of GeSe is its strong optical anisotropy which receives contributions from all physical mechanism determining the final conductivity. As we have already seen in Figure 3 the optical phonons have a strong absorption peak in the direction of the axis, with a negligible contribution in the axis. Similarly, due to the small effective electron mass along the axis, the conductivity due to the doping is much stronger along this direction than along the axis. Finally, the anisotropy observed in the interband transition region extends to the infrared region, which impacts the NFRHT. Overall, the conductivity along the axis is much greater than that along the axis.
Reverse Flow in Submerged Journal Bearings
Published in Tribology Transactions, 2023
Shanshan Wei, Yuri Kligerman, Roman Goltsberg
Some research works theoretically studied the cavitation zone in hydrodynamic bearings. Coyne and Elrod (16) theoretically analyzed the pressure and flow conditions of the lubricating film at the rupture point in a slider bearing with the new boundary conditions of pressure continuity. It was shown that pressure variation exists in the transition region between full film and the cavitation region. This pressure variation is similar to that in the reverse flow near the end of the cavitation zone. Pan (17) studied the cavitation zone in a short submerged journal bearing with improved short bearing theory using the half film approximation. Nonconstant pressure near the end of the cavitation zone was observed. Buckholz (18) and Buckholz and others (19) analyzed the shape and location of the cavitation boundary in a similar short submerged journal bearing. A matched asymptotic theory was applied near the end of the cavitation boundary to determine the pressure distribution and also to locate the cavitation boundary. However, in refs. (16)–(19) the reverse flow near the cavitation zone was not considered.
Optical fiber strain sensor with double S-tapers
Published in Instrumentation Science & Technology, 2021
S.-C. Yan, Y. Zhao, M.-Q. Chen, Q. Liu
In Figure 1, when light transmits in the optical fiber, it is confined in the core and guided by total internal reflection. When light enters the front end of the S1-taper, a part of the light leaks into the cladding, and excites the cladding mode. When the light transmits to the back end of S1-taper, due to the special structure of the S-taper, the fundamental mode couples with the cladding mode. When the light enters the S2-taper after the transition region, the fundamental mode in the core and the cladding mode couple again. The two most dominant modes accumulate phase differences and form Mach–Zehnder interferometer. The output light intensity may be described as follows:[21,22] where I is the intensity of the interference light, I1 is the intensity of the fundamental mode transmitted in the core, I2 is the intensity of the cladding mode transmitted in the cladding, and denotes the phase difference accumulated between the two modes. The phase difference may be expressed by the following:[23] where L is the effective interference length of the sensing structure, is the difference of the effective refractive index between the cladding mode and the fundamental mode, and is the wavelength of the incident light. When the phase difference between the two modes is (2 m + 1) π and m is an integer, the wavelength of the interference fringe can be expressed by the following: