Ke-Qin Zhang

Broadband optical scattering in coupled silicon nanocylinders

In this work, we demonstrate the broadband scattering of light waves incident on coupled silicon nanocylinders. First, it is shown that both electric and magnetic resonances are observed in a single silicon nanocylinder. By using two silicon nanocylinders, we next construct a silicon nanodimer. Thereafter, the original electric and magnetic resonances of the single nanocylinder shift and form hybrid resonant modes in the dimer; meanwhile, a new magnetic resonant mode emerges at a longer wavelength. Consequently, the silicon nanodimer exhibits a broadband scattering response that originates from optically magnetic interactions between dimeric silicon nanocylinders. Furthermore, the scattering bandwidth further increases upon using a silicon nanotrimer. This broadband optical response in silicon nanocylinders is demonstrated via their scattering spectra, and the magnetic interaction is verified by examining the spatial distributions of electromagnetic fields and the retrieved permittivity and permeability o...

Temperature-dependent strain relaxation of the AlGaN barrier in AlGaN∕GaN heterostructures with and without Si3N4 surface passivation

The temperature dependence of strain relaxation in Al0.22Ga0.78N layers, with and without a Si3N4 surface passivation layer, was investigated at temperatures from room temperature to 813K using high-resolution x-ray diffraction. A small strain relaxation occurs in the unpassivated Al0.22Ga0.78N layers at high temperature. After passivating, an additional in-plane tensile strain and an initial increase of the residual tensile strain with increasing temperature were observed in Al0.22Ga0.78N layers, and at higher temperatures the residual tensile strain only decreases slightly in the 100-nm-thick Al0.22Ga0.78N layer, but a pronounced strain relaxation occurs in the 50-nm-thick one. The degree of strain relaxation of the passivated 50-nm-thick Al0.22Ga0.78N layer increases by about 33%, which results in the two-dimensional electron gas concentration reduction of about 16% at the whole temperature range in our measurements.

Oscillations in electrochemical deposition of zinc

The effect of annealing treatment and thermal cycling on the phase transformation behaviour of Ni - Mn - Ga alloy prepared by arc melting technology has been investigated. The results show that the main transformation parameters decrease in a few initial thermal cycles, and then stabilise with further cycling. The transformation temperature interval decreases with an increase of annealing temperature. As cast material exhibits a columnar grain microstructure, while annealed material exhibits coarsened grains with clearly martensitic plates. When the alloy is annealed at 1073 K, both the martensite start temperature M-s and the austenite finish temperature A(f) decrease, while the martensite finish temperature M-f and the austenite start temperature A(s) increase with an increase in annealing time. This implies that the chemical order degree of the parent phase increases with increasing annealing time, which causes the chemical driving force for martensitic transformation to decrease.

H3O+-dependent morphological change in the electrochemical deposition of iron

Abstract By in situ optical microscopy and scanning electron microscopy, we investigate the morphology of the iron electrodeposit grown at different H 3 O + concentration in the electrolyte. The chemical composition of the electrodeposit is analyzed by X-ray diffraction and Mossbauer spectroscopy. It seems that the morphological transitions observed in this system do not relate to the oxidation/passivation of the metallic deposit during the growth. The possible origin of the dependence of deposit morphology on the H 3 O + in the electrolyte is discussed.

GaN1−xPx ternary alloys with high P composition grown by metal-organic chemical vapor deposition

GaN1-xPx ternary alloys with high P compositions were deposited on sapphire substrates by means of metal-organic chemical vapor deposition. Depth profiles of the elements indicate that the maximum P/N composition ratio is about 17% and a uniform distribution of the P atoms in the alloys is achieved. 2theta/omega XRD spectra demonstrate that the (0002) peak of the GaN1-xPx alloys shifts to smaller angle with increasing P composition. From the photoluminescence (PL) spectra, the red shifts to the bandedge emission of GaN are determined to be 73, 78, 100 and 87 meV for the GaN1-xPx alloys with the P/N composition ratios of 3%, 11%, 15% and 17%, respectively. No PL peak related to GaP is observed, indicating that the phase separation between GaN and GaP is well suppressed in our GaN1-xPx samples

Cavity modes with optical orbital angular momentum in a metamaterial ring based on transformation optics.

In this work, we theoretically study the cavity modes with transverse orbital angular momentum in metamaterial ring based on transformation optics. The metamaterial ring is designed to transform the straight trajectory of light into the circulating one by enlarging the azimuthal angle, effectively presenting the modes with transverse orbital angular momentum. The simulation results confirm the theoretical predictions, which state that the transverse orbital angular momentum of the mode not only depends on the frequency of the incident light, but also depends on the transformation scale of the azimuthal angle. Because energy dissipation inevitably reduces the field amplitude of the modes, the confined electromagnetic energy and the quality factor of the modes inside the ring are also studied in order to evaluate the stability of those cavity modes. The results show that the metamaterial ring can effectively confine light with a high quality factor and maintain steady modes with the orbital angular momentum, even if the dimension of the ring is much smaller than the wavelength of the incident light. This technique for exploiting the modes with optical transverse orbital angular momentum may provides a unique platform for applications related to micromanipulation.

Raman studies of phosphorus incorporation in GaN1-xPx alloys

Raman spectra for a series of high phosphorus compositional GaN1−xPx alloys, with phosphorus composition ratio up to 15%, grown by means of light-radiation heating, low-pressure metalorganic chemical vapor deposition have been investigated. The Raman spectra of GaN1−xPx alloys, recorded in backscattering geometry, exhibit four vibrational modes at 256, 314, 377, and 428 cm−1 compared with an undoped GaN sample. Those modes are assigned to the so-called quasilocal mode induced by P in GaN, disorder-activated scattering, and gap modes related to the Ga–P bond vibrations, respectively. The frequency of the A1(LO) mode is found to redshift, but the trend of the redshift weakens with larger x. This redshift is attributed to the effects of alloying and strain. Furthermore, the weakening trend of redshift with larger x illuminates that substitutional P atoms in the GaN1−xPx alloy are gradually getting saturated.

Temperature dependence of strain in Al/sub x/Ga/sub 1-x/N/GaN heterostructures

The temperature dependence of strain in a 50-nm- and a 100-nm-thick Al/sub 0.2/Ga/sub 0.8/N/GaN heterostructures were investigated at temperatures 300-800 K. The results show that the temperature behavior of the in-plane strain in the 50-nm-thick AlGaN layer is different to that in the 100-nm-thick AlGaN layer. There exists an initial energy barrier to the strain relaxation for the 50-nm-thick Al/sub 0.22/Ga/sub 0.78/N/GaN heterostructure. Meanwhile, for both the 50-nm-and 100-nm-thick AlGaN layers the strain relaxation becomes saturated at the high temperature segment, although the temperature at the point of saturation is different. The total strain relaxation is less than 5% for both the 50-nm- and 100-nm-thick Al/sub 0.22/Ga/sub 0.78/N layers at whole temperature range in our measurements.