Desheng Zhao

“Soft” bulk metallic glasses based on cerium

CeAlNiCu alloys can be readily cast into glassy rods with up to 5mm in diameter. The Ce-based bulk metallic glasses (BMGs) exhibit a wide supercooled region up to 78K, very low glass transition temperature (Tg=359K), melting temperature (Tm=637K), and Debye temperature (θD=144K). Ultrasonic measurements demonstrate that these Ce-based BMGs are very soft, having the lowest elastic moduli in known BMGs. These features suggest that the “soft” BMGs are an ideal model system for investigating physical problems in glass transition, supercooled liquid and melt states, and have potential applications as a functional material as well.

Glass forming properties of Zr-based bulk metallic alloys

The compositions of Zr41Ti14Cu12Ni10Be23 and Zr55Ni10Cu20Al15 bulk metallic glasses, were modified by the addition of other elements, such as Nb, Fe, Mg, Y, Ta, and C. The modified alloys also exhibit excellent glass forming ability. The glass transition temperature (Tg), crystallization temperature (Tx), and offset melting temperature (Tl) of the composition modified Zr-based alloys were determined by differential temperature analysis. The results show that the Tg, Tx, and Tl are all sensitive to the composition. The undercooled temperature from Tl to Tx,ΔTl defined by ΔTl=Tl−Tx, has a stronger correlation with the reduced glass transition temperature Trg (Trg=Tg/Tl) than that of ΔTx (ΔTx=Tx−Tg).

Formation and properties of Zr48Nb8Cu14Ni12Be18 bulk metallic glass

Zr48Nb8Cu14Ni12Be18 bulk metallic glass (BMG) with excellent glass-forming ability was prepared by water quenching method. The BMG exhibits high glass transition temperature Tg and onset crystallization temperature Tx, compared with Zr41Ti14Cu12.5Ni10Be22.5 BMG. The crystallization processes, change of elastic constants, and density and hardness in the crystallization process were studied by using X-ray diffraction, differential scanning calorimetry and acoustic method. The shear modulus, Poisson ratio, density and hardness are found to be sensitive to the crystallization process. A striking softening of long-wavelength transverse acoustic phonons in the BMG relative to its crystallized state is observed. The linear expansion coefficient, determined by a dilatometer method, is αTG=1.04×10−5 K−1 (300–656 K) for the BMG and αTC=1.11×10−5 K−1 (356–890 K) for the crystalline alloy. The Mie potential function and the equation of state of the BMG are determined from the expansion coefficient and acoustic experiments.

Unusual diamagnetic response in PrAlNiCuFe metallic glass

An unusual diamagnetic response is observed in a Pr60Al10Ni10Cu16Fe4 bulk metallic glass (BMG) during the zero-field-cooled (ZFC) magnetization measurement. The ZFC magnetization of the BMG is found to reverse its direction at low temperature and becomes diamagnetic, whereas the field-cooled branch remains positive. This apparent diamagnetism is ascribed to the specific couple between the ferromagnetic nanoparticles and the amorphous matrix in low fields. Besides, in superconductors, a giant diamagnetic response is unusual in magnetic materials. Therefore, it may simulate scientific and technological interest.

Wafer-Level Light Emitting Diode (WL-LED) Chip Simplified Package for Very-High Power Solid-State Lighting (SSL) Source

A simplified packaging process was successfully developed for a wafer-level light emitting diode (WL-LED) chip aiming at very-high power solid-state lighting (SSL) applications. Compared with the traditional chip-on-board (COB) technology, WL-LED chip not only greatly simplifies the packaging process but also enables the lighting source more compact. The fabricated blue WL-LED SSL source with a record-high light output power of 305 W exhibits ~30% wall plug efficiency at an input electrical power of 1026 W.

A Double-Gate AlGaN/GaN HEMT With Improved Dynamic Performance

In this letter, a double-gate AlGaN/GaN high electron mobility transistor operated in a synchronized switching mode is demonstrated, and improved dynamic performances are obtained. The additional gate sits on top of the conventional gate and stretches 2/4 μm to the source/drain electrodes, respectively. A positive voltage pulse is applied to the top gate and is synchronized with the ON-OFF switching pulse applied to the conventional gate. Such a double-gate driving method significantly improves the dynamic performances of the device. Moreover, it allows us to investigate the dynamic on-resistance in the drift region in detail.