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<jats:p>We demonstrated an AlGaN/GaN high electron mobility transistor (HEMT) namely double-<jats:italic>V</jats:italic> <jats:sub>th</jats:sub> coupling HEMT (DVC-HEMT) fabricated by connecting different threshold voltage (<jats:italic>V</jats:italic> <jats:sub>th</jats:sub>) values including the slant recess element and planar element in parallel along the gate width with N<jats:sub>2</jats:sub>O plasma treatment on the gate region. The comparative studies of DVC-HEMT and Fin-like HEMT fabricated on the same wafer show significantly improved linearity of transconductance (<jats:italic>G</jats:italic> <jats:sub>m</jats:sub>) and radio frequency (RF) output signal characteristics in DVC-HEMT. The fabricated device shows the transconductance plateau larger than 7 V, which yields a flattened <jats:italic>f</jats:italic> <jats:sub>T</jats:sub>/<jats:italic>f</jats:italic> <jats:sub>max</jats:sub>-gate bias dependence. At the operating frequency of 30 GHz, the peak power-added efficiency (PAE) of 41% accompanied by the power density (<jats:italic>P</jats:italic> <jats:sub>out</jats:sub>) of 5.3 W/mm. Furthermore, the proposed architecture also features an exceptional linearity performance with 1-dB compression point (<jats:italic>P</jats:italic> <jats:sub>1 dB</jats:sub>) of 28 dBm, whereas that of the Fin-like HEMT is 25.2 dBm. The device demonstrated in this article has great potential to be a new paradigm for millimeter-wave application where high linearity is essential.</jats:p>

<jats:p>Poly(3,4-ethylenedioxythiophene) (PEDOT) has proved its quite competitive thermoelectric properties in flexible electronics with its excellent electrical and mechanical properties. Since the early discovery of PEDOT, considerable experimental progress has been achieved in optimizing and improving the thermoelectric properties as a promising organic thermoelectric material (OTE). Among them, theoretical research has made significant contributions to its development. Here the basic physics of conductive PEDOT are reviewed based on the combination of theory and experiment. The purpose is to provide a new insight into the development of PEDOT, so as to effectively design and preparation of advanced thermoelectric PEDOT material in the future.</jats:p>

<jats:p>An atomic-level controlled etching (ACE) technology is invstigated for the fabrication of recessed gate AlGaN/GaN high-electron-mobility transistors (HEMTs) with high power added efficiency. We compare the recessed gate HEMTs with conventional etching (CE) based chlorine, Cl<jats:sub>2</jats:sub>-only ACE and BCl<jats:sub>3</jats:sub>/Cl<jats:sub>2</jats:sub> ACE, respectively. The mixed radicals of BCl<jats:sub>3</jats:sub>/Cl<jats:sub>2</jats:sub> were used as the active reactants in the step of chemical modification. For ensuring precise and controllable etching depth and low etching damage, the kinetic energy of argon ions was accurately controlled. These argon ions were used precisely to remove the chemical modified surface atomic layer. Compared to the HEMTs with CE, the characteristics of devices fabricated by ACE are significantly improved, which benefits from significant reduction of etching damage. For BCl<jats:sub>3</jats:sub>/Cl<jats:sub>2</jats:sub> ACE recessed HEMTs, the load pull test at 17 GHz shows a high power added efficiency (PAE) of 59.8% with an output power density of 1.6 W/mm at <jats:italic>V</jats:italic> <jats:sub>d</jats:sub> = 10 V, and a peak PAE of 44.8% with an output power density of 3.2 W/mm at <jats:italic>V</jats:italic> <jats:sub>d</jats:sub> = 20 V in a continuous-wave mode.</jats:p>

<jats:p>Thermoelectric (TE) energy harvesting can effectively convert waste heat into electricity, which is a crucial technology to solve energy concerns. As a promising candidate for energy conversion, poly(3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT:PSS) has gained significant attention owing to its easy doping, high transparency, and solution processability. However, the TE performance of PEDOT:PSS still needs to be further enhanced. Herein, different approaches have been applied for tuning the TE properties: (i) direct dipping PEDOT:PSS thin films in ionic liquid; (ii) post-treatment of the films with concentrated sulfuric acid (H<jats:sub>2</jats:sub>SO<jats:sub>4</jats:sub>), and then dipping in ionic liquid. Besides, the same bis(trifluoromethanesulfonyl)amide (TFSI) anion and different cation salts, including 1-ethyl-3-methylimidazolium (EMIM<jats:sup>+</jats:sup>) and lithium (Li<jats:sup>+</jats:sup>), are selected to study the influence of varying cation types on the TE properties of PEDOT:PSS. The Seebeck coefficient and electrical conductivity of the PEDOT:PSS film treated with H<jats:sub>2</jats:sub>SO<jats:sub>4</jats:sub>EMIM:TFSI increase simultaneously, and the resulting maximum power factor is 46.7 μW⋅m<jats:sup>−1</jats:sup>⋅K<jats:sup>–2</jats:sup>, which may be attributed to the ionic liquid facilitating the rearrangement of the molecular chain of PEDOT. The work provides a reference for the development of organic films with high TE properties.</jats:p>

<jats:p>High-performance organic composite thermoelectric (TE) materials are considered as a promising alternative for harvesting heat energy. Herein, composite films of poly (3,4-ethyienedioxythiophene):poly(styrene sulfonate)/single-walled carbon nanotubes (PEDOT:PSS/SWCNTs) were fabricated by utilizing a convenient solution mixing method. Thereafter, the as-prepared hybrid films were treated using sulfuric acid (H<jats:sub>2</jats:sub>SO<jats:sub>4</jats:sub>) to further optimize the TE performance. Film morphological studies revealed that the sulfuric acid treated PEDOT:PSS/SWCNTs composite samples all possessed porous structures. Due to the successful fabrication of highly conductive networks, the porous nano-architecture also exhibited much more excellent TE properties when compared with the dense structure of the pristine samples. For the post-treated sample, a high power factor of 156.43 μW⋅m<jats:sup>−1</jats:sup>⋅K<jats:sup>–2</jats:sup> can be achieved by adjusting the content of CNTs, which is approximately 3 orders of magnitude higher than that of the corresponding untreated samples (0.23 μW⋅m<jats:sup>−1</jats:sup>⋅K<jats:sup>–2</jats:sup>). Besides, the obtained films also showed excellent mechanical flexibility, owing to the porous nanostructure and the strong <jats:italic>π</jats:italic>–<jats:italic>π</jats:italic> interactions between the two components. This work indicates that the H<jats:sub>2</jats:sub>SO<jats:sub>4</jats:sub> treatment could be a promising strategy for fabricating highly-flexible and porous PEDOT:PSS/SWCNTs films with high TE performances.</jats:p>

<jats:p>Phonon anomalies have been reported in iron-pnictide superconductors indicating a diverse interplay between different orders in the materials. Here, we report Raman scattering measurements on Sr(Fe<jats:sub>1–<jats:italic>x</jats:italic> </jats:sub>Co<jats:sub> <jats:italic>x</jats:italic> </jats:sub>)<jats:sub>2</jats:sub>As<jats:sub>2</jats:sub> (<jats:italic>x</jats:italic> = 0 and <jats:italic>x</jats:italic> = 0.04) single crystals in the <jats:italic>B</jats:italic> <jats:sub>2<jats:italic>g</jats:italic> </jats:sub> symmetry with respect to a 1 Fe unit cell. Upon cooling, we observe a larger split (13 cm<jats:sup>−1</jats:sup>) of <jats:italic>E<jats:sub>g</jats:sub> </jats:italic> Raman phonon modes pertaining to in-plane Fe and As displacements as the crystals undergo the tetragonal-to-orthorhombic structural phase transition, although a considerable split (9 cm<jats:sup>−1</jats:sup>) has been reported in Ba(Fe<jats:sub>1–<jats:italic>x</jats:italic> </jats:sub>Co<jats:sub> <jats:italic>x</jats:italic> </jats:sub>)<jats:sub>2</jats:sub>As<jats:sub>2</jats:sub>. Furthermore, the splitting of <jats:italic>E<jats:sub>g</jats:sub> </jats:italic> phonon modes is strongly reduced upon doping. We perform an order-parameter analysis revealing a similar doping dependence of <jats:italic>E<jats:sub>g</jats:sub> </jats:italic> phonon splitting as reported in other compounds of the 122 family, indicating these phonon anomalies widely exist in 122 iron-based superconductors and might share the same mechanisms.</jats:p>

<jats:p>We investigate the spin to charge conversion phenomena in Y<jats:sub>3</jats:sub>Fe<jats:sub>5</jats:sub>O<jats:sub>12</jats:sub>/Pt/Co<jats:sub>1–<jats:italic>x</jats:italic> </jats:sub>Tb<jats:sub> <jats:italic>x</jats:italic> </jats:sub>/Pt multilayers by both the spin pumping and spin Seebeck effects. We find that the spin transport efficiency is irrelevant to magnetization states of the perpendicular magnetized Co<jats:sub>1–<jats:italic>x</jats:italic> </jats:sub>Tb<jats:sub> <jats:italic>x</jats:italic> </jats:sub> films, which can be attributed to the symmetry requirement of the inverse transverse spin Hall effect. Furthermore, the spin transmission efficiency is significantly affected by the film concentration, revealing the dominant role of extrinsic impurity scattering caused by Tb impurity. The present results provide further guidance for enhancing the spin transport efficiency and developing spintronic devices.</jats:p>

<jats:p>We theoretically and experimentally studied the Gilbert damping evolution of both acoustic and optical magnetic resonance modes in the layered flake CrCl<jats:sub>3</jats:sub> with an external magnetic field <jats:italic>H</jats:italic> applied in plane. Based on a Lagrangian equation and a Rayleigh dissipation function, we predicted that the resonance linewidth Δ<jats:italic>H</jats:italic> as a function of microwave frequency <jats:italic>ω</jats:italic> is nonlinear for both acoustic and optical modes in the CrCl<jats:sub>3</jats:sub> flake, which is significantly different from the linear relationship of Δ<jats:italic>H</jats:italic> ∝ <jats:italic>ω</jats:italic> in ferromagnets. Measuring the microwave transmission through the CrCl<jats:sub>3</jats:sub> flake, we obtained the <jats:italic>ω</jats:italic>–<jats:italic>H</jats:italic> dispersion and damping evolution Δ<jats:italic>H</jats:italic>–<jats:italic>ω</jats:italic> for both acoustic and optical modes. Combining both our theoretical prediction and experimental observations, we concluded that the nonlinear damping evolution Δ<jats:italic>H</jats:italic>–<jats:italic>ω</jats:italic> is a consequence of the interlayer interaction during the antiferromagnetic resonance, and the interlayer Gilbert dissipation plays an important role in the nonlinear damping evolution because of the asymmetry of the non-collinear magnetizaiton between layers.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The realization of perpendicular magnetization and perpendicular exchange bias (PEB) in magnetic multilayers is important for the spintronic applications. NiO(<jats:italic>t</jats:italic>)/[Ni(4 nm)/Pt(1 nm)]<jats:sub>2</jats:sub> multilayers with varying the NiO layer thickness <jats:italic>t</jats:italic> have been epitaxially deposited on SrTiO<jats:sub>3</jats:sub> (001) substrates. Perpendicular magnetization can be achieved when <jats:italic>t</jats:italic> &lt; 25 nm. Perpendicular magnetization originates from strong perpendicular magnetic anisotropy (PMA), mainly resulting from interfacial strain induced by the lattice mismatch between the Ni and Pt layers. The PMA energy constant decreases monotonically with increasing <jats:italic>t</jats:italic>, due to the weakening of Ni (001) orientation and a little degradation of the Ni–Pt interface. Furthermore, significant PEB can be observed though NiO layer has spin compensated (001) crystalline plane. The PEB field increases monotonically with increasing <jats:italic>t</jats:italic>, which is considered to result from the thickness dependent anisotropy of the NiO layer.</jats:p>

<jats:p>Effects of Nb<jats:sub>2</jats:sub>O<jats:sub>5</jats:sub> dopant on the radiation response of barium gallo-germanate (BGG) glass are studied mainly by electron paramagnetic resonance and absorption spectroscopy. Owing to the Nb<jats:sup>5+</jats:sup>↔Nb<jats:sup>3+</jats:sup> interconversion in doped samples, formations of Ge-related non-bridging oxygen hole center and Ge-related electron center defects after <jats:italic>γ</jats:italic>-ray irradiation are inhibited. Thereby, Nb<jats:sub>2</jats:sub>O<jats:sub>5</jats:sub> dopant can enhance radiation resistance of BGG glass, and 1.0% Nb<jats:sub>2</jats:sub>O<jats:sub>5</jats:sub> concentration is the best.</jats:p>