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Energy bands in AB-stacked bilayer graphene are featured by the co-presence of trigonal warping and a Mexican hat structure around each Dirac point, and electrically modulatable band edges with the modulation valley-dependent (valley-independent) in the case of in-plane (vertical) fields. This theoretical work takes into account the foregoing realistic features and exploits them for valleytronic applications. Specifically, it investigates in detail electrical valley transport in the armchair direction, in AB-stacked bilayer graphene lateral quantum structures with an interface, a single barrier, and double barriers, respectively, and demonstrates that due to the band structure features as well as an involved interplay among them, such structures harbor an interesting potential for valley filtering. An analysis of transmitted current valley polarization is provided. Optimization of the structures for the polarization is explored. The thermal effect on valley filtering is examined. Sizable polarizations of 88% (97%) and 23% (27%) at low and room temperatures, respectively, are shown to be achievable in the case of one-barrier (double-barrier) structures.

The formation of optical solitons arises from the simultaneous presence of dispersive and nonlinear properties within a propagation medium. Chip-scale devices that support optical solitons harness high field confinement and flexibility in dispersion engineering for significantly smaller footprints and lower operating powers compared to fiber-based equivalents. High-order solitons evolve periodically as they propagate and experience a temporal narrowing at the start of each soliton period. This phenomenon allows strong temporal compression of optical pulses to be achieved. In this paper, soliton-effect temporal compression of optical pulses is demonstrated on a CMOS-compatible ultra-silicon-rich nitride (USRN) waveguide. We achieve 8.7× compression of 2 ps optical pulses using a low pulse energy of ∼16 pJ, representing the largest demonstrated compression on an integrated photonic waveguide to date. The strong temporal compression is confirmed by numerical calculations of the nonlinear Schrodinger equation to be attributed to the USRN waveguide’s large nonlinearity and negligible two-photon absorption at 1550 nm.The formation of optical solitons arises from the simultaneous presence of dispersive and nonlinear properties within a propagation medium. Chip-scale devices that support optical solitons harness high field confinement and flexibility in dispersion engineering for significantly smaller footprints and lower operating powers compared to fiber-based equivalents. High-order solitons evolve periodically as they propagate and experience a temporal narrowing at the start of each soliton period. This phenomenon allows strong temporal compression of optical pulses to be achieved. In this paper, soliton-effect temporal compression of optical pulses is demonstrated on a CMOS-compatible ultra-silicon-rich nitride (USRN) waveguide. We achieve 8.7× compression of 2 ps optical pulses using a low pulse energy of ∼16 pJ, representing the largest demonstrated compression on an integrated photonic waveguide to date. The strong temporal compression is confirmed by numerical calculations of the nonlinear Schrodinger equation...

We theoretically study the valley aspect of lateral tunneling transport in valleytronic materials, using AB-stacked (Bernal-stacked) bilayer graphene as a material example. A lateral structure with multiple well/barrier interfaces is considered. A full-zone tight-binding method is employed, allowing for the study of intervalley mixing in electron states. We study the degree of tunneling current valley contrast under the condition of a source-drain bias or barrier asymmetry. For a single-barrier structure, it is found that the intervalley mixing is negligible, and the contrast is positively correlated with the barrier width and height. For a double-barrier structure, the effect of resonant tunneling is investigated. The intervalley mixing is shown to be significantly enhanced at resonant tunneling. In addition, the resonant levels are found valley split, and a proposal is given which exploits the splitting for the generation of a sizable tunneling current valley polarization. Based on a simple model using momentum-shifted thermal distribution for obliquely incident electrons, the temperature dependence of tunneling current valley polarization is also examined. An interesting crossover from the valley-orbit interaction-dominant polarization to the warping-dominant polarization is found to occur as the temperature is increased.We theoretically study the valley aspect of lateral tunneling transport in valleytronic materials, using AB-stacked (Bernal-stacked) bilayer graphene as a material example. A lateral structure with multiple well/barrier interfaces is considered. A full-zone tight-binding method is employed, allowing for the study of intervalley mixing in electron states. We study the degree of tunneling current valley contrast under the condition of a source-drain bias or barrier asymmetry. For a single-barrier structure, it is found that the intervalley mixing is negligible, and the contrast is positively correlated with the barrier width and height. For a double-barrier structure, the effect of resonant tunneling is investigated. The intervalley mixing is shown to be significantly enhanced at resonant tunneling. In addition, the resonant levels are found valley split, and a proposal is given which exploits the splitting for the generation of a sizable tunneling current valley polarization. Based on a simple model using ...

The generation of broadband light within the telecommunication band has been instrumental to the design and characterization of advanced optical devices and systems. In this paper, stimulated degenerate four-wave mixing of an ultra-silicon rich nitride waveguide is investigated using a pulsed pump at 1.555 μm and incoherent broadband sources emitting in the 1.65 μm wavelength region as a signal. The waveguide possesses a large nonlinear parameter of 330 W−1/m as well as anomalous dispersion, required for phase matched parametric processes. The broadband idler ranging from 1.43 μm to 1.52 μm is generated using a coupled peak power of 4.6 W, spanning ∼100 nm at the −20 dB level, which is sufficient to cover parts of the E- and S-bands. The spectral span of the generated idler also agrees well with the calculation based on the phase-matching condition governing degenerate four-wave mixing. Cascaded incoherent four-wave mixing is also observed. Using a supercontinuum pump spanning from 1.1 to 1.7 μm with a co...

We present the design, fabrication, and characterization of photonic crystal waveguides (PhCWs) on an ultra-silicon-rich nitride (USRN) platform, with the goal of augmenting the optical nonlinearities. The design goals are to achieve an optimized group index curve on the PhCW band edge with a non-membrane PhCW with symmetric SiO2 undercladding and overcladding, so as to maintain back-end CMOS compatibility and better structural robustness. Linear optical characterization, as well as nonlinear optical characterization of PhCWs on ultra-silicon-rich nitride is performed at the telecommunication wavelengths. USRN's negligible two-photon absorption and free carrier losses at the telecommunication wavelengths ensure that there is no scaling of two-photon related losses with the group index, thus maintaining a high nonlinear efficiency. Self-phase modulation experiments are performed using a 96.6 μm PhCW. A 1.5π phase shift is achieved with an input peak power of 2.5 W implying an effective nonlinear parameter ...

Spin-dependent tunnel junctions, Co/Al2O3/Co (CoFe)/NiFe, were fabricated to investigate the effect of the additional Co (CoFe) interlayer on tunneling magnetoresistance. The quality of the junction was examined with a cross-sectional image generated by high-resolution transmission electron microscopy, and an electron energy loss spectra map. For junctions with a Co (CoFe) interlayer in the top electrode thinner than 0.8 nm (1.0 nm), the tunneling magnetoresistance ratio increases with interlayer thickness. For junctions with a 0.8–2.0 nm Co (1.0–2.0 nm CoFe) interlayer in the top electrode, the tunneling magnetoresistance ratio reaches the maximum value of 2.16 (4.45) times that without any Co (CoFe) interlayer in the top electrode. The increase in the tunneling magnetoresistance ratio may be attributed to the increased effective ferromagnetic electrode polarization and the various spin-flip scattering factors.

We studied strain‐induced band splittings of ZnSe/GaAs and Zn1−xMnxSe/GaAs epilayers of 0.064–3 μm thickness by reflectance and polarized photoluminescence. Polarized photolumi‐ nescence was found particularly useful in optical transition identification. The spectacular difference in magnetic field sensitivity of heavy hole and light hole exciton in ZnMnSe is also very helpful in transition identification. The evaluated heavy‐light hole band splitting is in general accordance with previous data. An exceptionally strong variation of the strain with epilayer thickness is observed in the thickness range 0.5–2 μm.

Transmission electron microscopy has been used to observe Al segregation around the threading dislocations in Al0.1Ga0.9N and Al0.3Ga0.7N grown by metalorganic chemical vapor deposition on 6H–SiC. Dislocation lines were found to have up to 70% more Al concentration than those regions free of dislocations in the matrix. The Al-depleted regions around the dislocations are shown to be within a few nanometers from the dislocation lines. The results also show that more Al segregate to edge dislocations than to screw ones.

The correlation between the exchange field of NiFe/NiMn and the phase transformation of NiMn was investigated. Transmission electron microscopy (TEM) dark-field images, contributed by the order phase of NiMn, were used to identify the location and volume fraction of the order phase. TEM selected area diffraction patterns showed the (110) superlattice diffraction rings of NiMn, verifying the existence of the order phase in the annealed samples. The order volume fraction can be calculated by the dark field image contributed by the (110) diffraction. The exchange field increased almost linearly with increasing order volume fraction. Energy dispersive x-ray spectroscopy attached to TEM indicated that Mn diffused into NiFe for annealing at 280 °C, leading to a larger coercivity and small coercivity squareness. Part of the NiMn still maintains the paramagnetic phase even after annealing at 280 °C.

The atomic configuration of irradiation-induced planar defects in single crystal 3C-SiC at high irradiation temperatures was shown in this research. A spherical aberration corrected scanning transmission electron microscope provided images of individual silicon and carbon atoms by the annular bright-field (ABF) method. Two types of irradiation-induced planar defects were observed in the ABF images including the extrinsic stacking fault loop with two offset Si-C bilayers and the intrinsic stacking fault loop with one offset Si-C bilayer. The results are in good agreement with images simulated under identical conditions.

ZnS nanotubes were synthesized using wet-chemistry method. These nanotubes appear to be extremely unstable under electron beam irradiation. Time dependent transmission electron diffraction patterns disclose the appearance of additional diffraction spots that belong to ZnO, with the prolonged e-beam irradiation duration. The experimental results suggest that displacement damage followed by oxidation is mainly responsible for the structural degradation of these ZnS nanotubes.

Self-assembled In1−xMnxAs quantum dots (0.19⩽x⩽0.45) have been grown on GaAs (100) substrates by low-temperature molecular beam epitaxy. The microstructure analysis revealed that the uniformly distributed In1−xMnxAs dots have a zinc blende structure as x⩽0.38. Furthermore, all samples exhibit ferromagnetic state at 5K, and their Curie temperatures range from 260to340K varying with x. These (In, Mn)As quantum dots are promising for room-temperature spintronic devices.

Different sizes of three-dimensional PbSe quantum dots have been synthesized for the study of orbital magnetic susceptibilities. Two types of orbital susceptibilities have been found, including the Curie susceptibility and finite-size corrections to the Landau susceptibility. The Curie term of a quantum dot manifests itself in the temperature dependence of magnetic susceptibility at low temperatures, while the field dependence of differential susceptibility at high temperatures shows finite-size corrections to the Landau susceptibility. Both of the two kinds of orbital susceptibility, estimated per quantum dot, show linear dependence on the size.

A detailed study of the interface properties as well as the thermal stability has been done for the Co/Al–O/CoFe/NiFe magnetic tunnel junction, by using high resolution transmission electron microscopy equipped with energy dispersive x-ray spectrum. The Al behaves more stable against thermal annealing compared with the Fe, Co, Ni, and O elements. The reduction of the tunnel magnetoresistance ratio for the low annealing temperature (200 °C) may be caused by the spin flip scattering at oxide ion, rather than by the change in magnetic properties. The annealing at higher temperatures (300 °C and 400 °C) results in a strong interdiffusion, and in turn the disappearance of the magnetoresistance due to the shortcut of the junction.