improving the performance of this technology. For example, materials such as metal oxides, nitrides, and fluorides have been demonstrated to form electron and hole selective interfaces when applied to c-Si. [1][2][3][4][5][6][7] Such an approach has potential benefits over conventional heavily doped direct-metallization approaches, including lower processing temperatures, simpler contact formation, and the removal of fundamental limitations, such as Auger recombination and free carrier absorption. [8,9] In addition, the unique interface properties of some metal compound/c-Si interfaces have even enabled novel solar cell architectures, for example, n-type c-Si cells with undoped partial rear contacts (PRCs). [10,11] This specific architecture utilizes a near-ideal surface passivation layer, such as hydrogenated silicon nitride SiN x , [12] to cover the vast majority of the rear surface which can greatly reduce the average surface recombination factor J 0 and increase the rear reflection. Only a small percentage of the area is contacted, typically < 5%, where electrons flow to be collected. An n-type undoped PRC cell structure was not previously attainable due to the tendency of n-type c-Si to form an interface potential barrier under direct metallization, which resulted in prohibitively high contact resistivity ρ c . The first successful demonstration of this cell came after a breakthrough in low resistance interfaces to n-type c-Si with a low work function LiF x /Al electrode. This contact was used to fabricate an undoped PRC cell attaining an efficiency of 20.6% with a PRC covering only ≈1% of the rear surface. [11] The next evolutionary step in this cell structure was the integration of a passivation layer at the PRC interface. This came with the introduction of a TiO x /Ca/Al contact, [10] which was found to provide both reduced surface recombination and low contact resistivity, enabling an efficiency of 21.8%. Following on from these early developments, there exist three major avenues to easily improve the electron PRC: i) reduction in the PRC interface recombination and resistivity; ii) increase in the PRC material's stability to thermal stressors; and iii) increasing the rear surface reflectivity via appropriate choice of PRC materials.This article introduces the next in this family of carrier selective interfaces, which targets the abovementioned three issues. To address this a TiO x /LiF x /Al heterocontact is developed and integrated into a PRC cell shown in Figure 1a. The

Numerous wingless arthropods as well as diverse vertebrates are capable of mid-air righting. We studied the biomechanics of the aerial righting reflex in first-instar nymphs of the stick insect Extatosoma tiaratum. After being released upside-down, insects reoriented dorsoventrally and stabilized body posture via active modulation of limb positions and associated aerodynamic torques. We identified specific reflexes for bilaterally asymmetric leg displacements which elicit body rotation and subsequently stabilize mid-air posture. Coordinated appendicular movements thus improve torsional manoeuvrability in the absence of wings, as may have characterized the initial origins of controlled aerial behaviour in arthropods. Design of small aerial or multimodal robotic vehicles may similarly benefit from use of such strategies for flight control.

Cobalt has caused much interest as an adhesion layer for copper metallization in the next generation interconnect technology. This work investigates the effects of glycine and BTA on corrosion and polishing properties of Co in the acid slurry. The potentiodynamic polarization measurement results show that glycine can increase the corrosion rate of Co. In the solution containing H 2 O 2 , adding glycine can make the Co surface smoother. In the slurry without H 2 O 2 , BTA shows good inhibition effect on Co corrosion. BTA can adsorb on the Co surface through physisorption and chemisorption, and obeys Langmuir absorption isotherm. In the acid slurry with H 2 O 2 , BTA will react with Co 2+ ions and form insoluble networked nanoparticles ([Co(II)(BTA) 2 • H 2 O] n ) on the Co surface, and induce reduction of the removal rate and static etch rate of Co.

Cobalt has emerged as a potential adhesion layer for advanced copper metallization. This work investigates the role of oxidant and inhibitor on the corrosion and polishing properties of cobalt in the acid slurry. It is found that H 2 O 2 could greatly increase the static etch rate (SER) and removal rate (RR) of cobalt. The 2-Mercaptothiazoline (2-MT) is very efficient to inhibit cobalt corrosion and reduce the SER and RR of cobalt in the acid slurry. In the glycine based slurry at pH = 5, by using 2-MT, the corrosion potential difference between Co and Cu can be reduced to a very small value.

No abstract

The synthesis and growth of hexagonal boron‐nitride crystallites at low temperature were investigated by carrying out in a lithium bromide (LiBr) melt in 600°–700°C. Transmission electron microscopy study showed that the product obtained at 650°C was composed of two‐dimensional plates having an average thickness of about 80 nm and widths from about 400 nm to several micrometers. The molten salt was found to have a strong effect on the crystal growth. The morphology of the crystallites changed from spherical particles to two‐dimensional plates when LiBr was used as a crystallization medium. Products were also characterized by X‐ray powder diffractions, Fourier Transformed infrared, FESEM/energy dispersive X‐ray spectroscopy, and selected area electron diffraction. Possible formation mechanism was also discussed.

No abstract

The thermoelectric effects of topological semimetals have attracted tremendous research interest because many topological semimetals are excellent thermoelectric materials and thermoelectricity serves as one of their most important potential applications. In this work, we reveal the transient photothermoelectric response of Dirac semimetallic Cd3As2, namely the photo-Seebeck effect and photo-Nernst effect, by studying the terahertz (THz) emission from the transient photocurrent induced by these effects. Our excitation polarization and power dependence confirm that the observed THz emission is due to photothermoelectric effect instead of other nonlinear optical effect. Furthermore, when a weak magnetic field (~0.4 T) is applied, the response clearly indicates an order of magnitude enhancement on transient photothermoelectric current generation compared to the photo-Seebeck effect. Such enhancement supports an ambipolar transport nature of the photo-Nernst current generation in Cd3As2. These results highlight the enhancement of thermoelectric performance can be achieved in topological Dirac semimetals based on the Nernst effect, and our transient studies pave the way for thermoelectric devices applicable for high field circumstance when nonequilibrium state matters. The large THz emission due to highly efficient photothermoelectric conversion is comparable to conventional semiconductors through optical rectification and photo-Dember effect.