Intrinsic stability of an HBT based on a small signal equivalent circuit model

Intrinsic stability ofthe heterojunction bipolar transistor （HBT） was analyzed and discussed based on a small signal equivalent circuit model. The stability factor of the HBT device was derived based on a compact T-type small signal equivalent circuit model of the HBT. The effect of the mainly small signal model parameters of the HBT on the stability of the HBT was thoroughly examined. The discipline of parameter optimum to improve the intrinsic stability of the HBT was achieved. The theoretic analysis results of the stability were also used to explain the experimental results of the stability of the HBT and they were verified by the experimental results.

Structure, magnetic properties, and thermal stability of Sm(1-x)Tm_xCo_5compounds

Structure, magnetic properties, and thermal stability of ternary Sm1-xTmxCo5 compounds were studied via X-ray diffraction（XRD）, thermal magnetic analysis（TMA）, and magnetic measurements. XRD results show that all the compounds have a main phase of hexagonal CaCu5-type crystal structure with small amount of impurity phases; increasing Tm content is associated with contraction of the hexagonal unit cell in the direction of the c axis and expansion of the a and b parameters. TMA results indicate that the Curie temperature（TC） of Sm1-xTmxCo5 compounds gets higher with the increase in Tm content.Magnetic measurements show that both the magnetic anisotropy field（HA） and the magnetization at an applied field of 7 T（M7 T） decrease with the increase of Tm content. However, the thermal stability of both the HAand M7 Tof all the Tm doped compounds is remarkably improved compared with that of the pure SmCo5 compound, leading to the result that both the M7 Tand HAof Sm0.8Tm0.2Co5 .2are higher than those of SmCo5 compound at 473 K, which indicates the good potential of Tm doped compound in the practical applications at elevated temperature.

Negative Charge Management to Make Fragile Bonds Less Fragile toward Electrons for Robust Organic Optoelectronic Materials

The operational stability of organic(opto)electronic devices largely depends on the intrinsic stability of organic materials on service.For organic light-emitting diode(OLED)materials,a key parameter of their intrinsic stability is the bond-dissociation energy of the most fragile bond(BDE_(f)).Although rarely involved,many OLED molecules have the lowest BDE_(f) in anionic states[BDE_(f)(−)∼1.6–2.5 eV],which could be a fatal short-slab for device stability.Herein,we separated BDE_(f)(−)from other parameters and confirmed the clear relationship between BDE_(f)(−),intrinsic material stability and device lifetime.Based on thermodynamic principles,we developed a general and effective strategy to greatly improve BDE_(f)(−)by introducing a negative charge manager within the molecule.The manager must combine an electron-withdrawing group(EWG)with a delocalizing structure,so that it can firmly confine the negative charge and hinder the charge redistribution toward fragile bonds.Consequently,the use of this manager can substantially promote BDE_(f)(−)by∼1 eV for various fragile bonds and outperform the effect reported from solely employing EWGs or delocalizing structures.This effect was verified in typical phosphine-oxide and carbazole derivatives and backed up by newly designed molecules with multiple fragile bonds.This strategy provides a new way to transform vulnerable building blocks into robust organic(opto)electronic materials and devices.

Exceptionally shear-stable and ultra-strong Ir-Ni-Ta high-temperature metallic glasses at micro/nano scales

Ir-Ni-Ta metallic glasses(MGs)exhibit an array of superior high-temperature properties,making them attractive for applications at high temperatures or in harsh environments.However,Ir-Ni-Ta bulk MGs are quite brittle and often fracture catastrophically even before plastic yielding,significantly undercutting their high-strength advantage.Here,we show that the Ir-Ni-Ta MGs are not intrinsically brittle,but rather malleable when the feature size is reduced to micro/nano-scales.All tested Ir-Ni-Ta MG micropillars with a diameter ranging from~500 nm to~5μm display a large plastic strain above 25%(the maximum up to 35%),together with a yield strength up to 7 GPa,well exceeding the strength recorded in most metallic materials.The intrinsic shear stability of Ir-Ni-Ta MGs,as characterized by the normalized shear displacement during a shear event,is much larger than those malleable Zr-and Cu-based MGs.Our results suggest that Ir-Ni-Ta MGs are excellent candidates for micro/nanoscale structural applications used at high-temperature or extreme conditions.