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<jats:p>Fabrication of large-area atomically thin transition metal dichalcogenides is of critical importance for the preparation of new heterojunction-based devices. In this paper, we report the fabrication and optical investigation of large-scale chemical vapor deposition (CVD)-grown monolayer MoS<jats:sub>2</jats:sub> and exfoliated few-layer GaS heterojunctions. As revealed by photoluminescence (PL) characterization, the as-fabricated heterojunctions demonstrated edge interaction between the two layers. The heterojunction was sensitive to annealing and showed increased interaction upon annealing at 300 °C under vacuum conditions, which led to changes in both the emission peak position and intensity resulting from the strong coupling interaction between the two layers. Low-temperature PL measurements further confirmed the strong coupling interaction. In addition, defect-related GaS luminescence was observed in our few-layer GaS, and the PL mapping provided evidence of edge interaction coupling between the two layers. These findings are interesting and provide the basis for creating new material systems with rich functionalities and novel physical effects.</jats:p>

<jats:p>Ruddlesden–Popper iridium oxides have attracted considerable interest because of the many proposed novel quantum states that arise from the large spin–orbit coupling of the heavy iridium atoms in them. A prominent example is the single layer Sr<jats:sub>2</jats:sub>IrO<jats:sub>4</jats:sub>, in which superconductivity has been proposed under electron doping. However, the synthesis of Sr<jats:sub>2</jats:sub>IrO<jats:sub>4</jats:sub> high quality thin films has been a huge challenge due to the easy formation of impurities associated with different numbers of SrO layers. Thus techniques to optimize the growth of pure phase Sr<jats:sub>2</jats:sub>IrO<jats:sub>4</jats:sub> are urgently required. Here we report the deposition of high quality Sr<jats:sub>2</jats:sub>IrO<jats:sub>4</jats:sub> thin films on both insulating SrTiO<jats:sub>3</jats:sub> and conducting SrTiO<jats:sub>3</jats:sub>:Nb substrates using pulsed laser deposition assisted with reflective high-energy electron diffraction. The optimal deposition temperature of Sr<jats:sub>2</jats:sub>IrO<jats:sub>4</jats:sub> epitaxial films on SrTiO<jats:sub>3</jats:sub>:Nb substrates is about 90 °C lower than that on SrTiO<jats:sub>3</jats:sub> substrates. The electrical transports of high quality Sr<jats:sub>2</jats:sub>IrO<jats:sub>4</jats:sub> films are measured, which follow the three-dimensional Mott variable-range hopping model. The film magnetizations are measured, which show weak ferromagnetism below ∼240 K with a saturation magnetization of <jats:inline-formula> <jats:tex-math><?CDATA $\sim 0.2\,{\mu }_{{\rm{B}}}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>∼</mml:mo> <mml:mn>0.2</mml:mn> <mml:mspace width="0.25em" /> <mml:msub> <mml:mrow> <mml:mi>μ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">B</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_7_078102_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>/Ir at 5 K. This study provides applicable methods to prepare high quality 5d Sr<jats:sub>2</jats:sub>IrO<jats:sub>4</jats:sub> epitaxial films, which could be extended to other Ruddlesden–Popper phases and potentially help the future study of exotic quantum phenomena in them.</jats:p>

<jats:p>We report a large-scale, high-quality heterostructure composed of vertically-stacked graphene and two-dimensional (2D) germanium. The heterostructure is constructed by the intercalation-assisted technique. We first synthesize large-scale, single-crystalline graphene on Ir(111) surface and then intercalate germanium at the interface of graphene and Ir(111). The intercalated germanium forms a well-defined 2D layer with a 2 × 2 superstructure with respect to Ir(111). Theoretical calculations demonstrate that the 2D germanium has a double-layer structure. Raman characterizations show that the 2D germanium effectively weakens the interaction between graphene and Ir substrate, making graphene more like the intrinsic one. Further experiments of low-energy electron diffraction, scanning tunneling microscopy, and x-ray photoelectron spectroscopy (XPS) confirm the formation of large-scale and high-quality graphene/2D-germanium vertical heterostructure. The integration of graphene with a traditional 2D semiconductor provides a platform to explore new physical phenomena in the future.</jats:p>

<jats:p>Systematic investigation of InAs quantum dot (QD) growth using molecular beam epitaxy has been carried out, focusing mainly on the InAs growth rate and its effects on the quality of the InAs/GaAs quantum dots. By optimizing the growth rate, high quality InAs/GaAs quantum dots have been achieved. The areal quantum dot density is 5.9 × 10<jats:sup>10</jats:sup> cm<jats:sup>−2</jats:sup>, almost double the conventional density (3.0 × 10<jats:sup>10</jats:sup> cm<jats:sup>−2</jats:sup>). Meanwhile, the linewidth is reduced to 29 meV at room temperature without changing the areal dot density. These improved QDs are of great significance for fabricating high performance quantum dot lasers on various substrates.</jats:p>

<jats:p>Thermal conductivity is an important material parameter of silicon when studying the performance and reliability of devices or for guiding circuit design when considering heat dissipation, especially when the self-heating effect becomes prominent in ultra-scaled MOSFETs. The cross-plane thermal conductivity of a thin silicon film is lacking due to the difficulty in sensing high thermal conductivity in the vertical direction. In this paper, a feasible method that utilizes an ultra-fast electrical pulse within <jats:inline-formula> <jats:tex-math> <?CDATA $20{\rm{\mu }}{\rm{s}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>20</mml:mn> <mml:mi mathvariant="normal">μ</mml:mi> <mml:mi mathvariant="normal">s</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_7_078105_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> combined with the hot strip technique is adopted. To the best of our knowledge, this is the first work that shows how to extract the cross-plane thermal conductivity of sub-50 nm (30 nm, 17 nm, and 10 nm) silicon films on buried oxide. The ratio of the extracted cross-plane thermal conductivity of the silicon films over the bulk value is only about 6.9%, 4.3%, and 3.8% at 300 K, respectively. As the thickness of the films is smaller than the phonon mean free path, the classical heat transport theory fails to predict the heat dissipation in nanoscale transistors. Thus, in this study, a ballistic model, derived from the heat transport equation based on extended-irreversible-hydrodynamics (EIT), is used for further investigation, and the simulation results exhibit good consistence with the experimental data. The extracted effective thermal data could provide a good reference for precise device simulations and thermoelectric applications.</jats:p>

<jats:p>Bilayer graphene quantum dots with rotational stacking faults (RSFs) having different rotational angles were studied. Using the first-principles calculation, we determined that these stacking faults could quantitatively modulate the magnetism and the distribution of spin and energy levels in the electronic structures of the dots. In addition, by examining the spatial distribution of unpaired spins and Bader charge analysis, we found that the main source of magnetic moment originated from the edge atoms of the quantum dots. Our research results can potentially provide a new path for producing all-carbon nanodevices with different electrical and magnetic properties.</jats:p>

<jats:p>The crystallization behavior and mechanism of CaO–Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>–MgO–SiO<jats:sub>2</jats:sub> (CAMS)-based diopside glass ceramics with nano-ZrO<jats:sub>2</jats:sub> nucleators and CeO<jats:sub>2</jats:sub> agents have been investigated. The use of nanoscale ZrO<jats:sub>2</jats:sub> as nucleators is favorable to the crystallization of glass ceramic at a relatively lower temperature due to the reduction of the activation energy, while the activation energy is increased after adding the CeO<jats:sub>2</jats:sub> agent. The microstructure and orientation have been analyzed by scanning electron microscopy and electron backscatter diffraction. Two discernible layers are observed, featured in glass and crystalline phases, respectively. Remarkably textured polycrystalline diopsides are verified for the samples (A and B) free of CeO<jats:sub>2</jats:sub> agents, with <jats:italic>c</jats:italic>-axes perpendicular to the interface of the two layers. Comparatively, the <jats:italic>c</jats:italic>-axes of diopside grains of the sample (C) with CeO<jats:sub>2</jats:sub> agents are proved to be parallel to the interface. Nanocrystals are detected in the vicinity of the interface for sample C.</jats:p>

<jats:p>Polarized red, green, and blue light emitting diodes (LEDs) are successfully fabricated using polyfluorene and its derivatives, namely, poly (9,9-dioctylfluorene) (PFO), poly (9,9-dioctylfluorene-co-benzothiadiazole) (F8BT), and poly (triphenylamine-<jats:italic>co</jats:italic>-4,7-di(thiophen-2-yl)benzo[<jats:italic>c</jats:italic>][1,2,5]thiadiazole-<jats:italic>co</jats:italic>-benzo[<jats:italic>c</jats:italic>]thiadiazole-<jats:italic>co</jats:italic>-9,9-dioctyl-9<jats:italic>H</jats:italic>-fluorene) (Red F). Rubbed hole transport layer poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) is employed in the devices as the alignment layer to achieve fully monodomain alignment in all polymer layers. Red F is blended with F8BT to realize the polarized electroluminescence of red light (dichroic ratio ∼3.3), despite having no liquid crystallinity itself. Comparing PFO/F8BT blend to F8BT, higher efficiency of polarized emission is found due to the energy transfer. All the polarized LEDs exhibit pronounced dichroism and efficient polarized emission compared to the non-alignment regular devices.</jats:p>

<jats:p>The structural, electronic, and adsorption properties of Li/Na ions on graphene decorated by epoxy groups are investigated by first-principles calculations based on density functional theory. Our results show that the concentration of epoxy groups remarkably affects the structural and electronic properties of graphene. The bandgaps change monotonically from 0.16 eV to 3.35 eV when the O coverage increases from 12.5% to 50% (O/C ratio). Furthermore, the highest lithiation potential of 2.714 V is obtained for the case of graphene oxide (GO) with 37.5 % O coverage, while the highest sodiation potential is 1.503 V for GO with 12.5% O coverage. This clearly demonstrates that the concentration of epoxy groups has different effects on Li and Na storage in GO. Our results provide a new insight into enhancing the Li and Na storage by tuning the concentration of epoxy groups on GO.</jats:p>

<jats:p>High chemical reactivity, large volume changes, and uncontrollable lithium dendrite growth have always been the key problems of lithium metal anodes. Coating has been demonstrated as an effective strategy to protect the lithium metal. In this work, the effects of polyacrylonitrile (PAN)-based coatings on electrodeposited lithium have been studied. Our results show that a PAN coating layer provides uniform and dendrite-free lithium deposition as well as better cycling performance with carbonate electrolyte. Notably, heat treatment of the PAN coating layer promotes the formation of larger deposit particle size and higher coulombic efficiency (85%). The compact coating layer of heat-treated PAN with a large Young modulus (82.7 GPa) may provide stable protection for the active lithium. Improved homogeneity of morphology and mechanical properties of heat-treated PAN contribute to the larger deposit particles. This work provides new feasibility to optimize the polymer coating through rational modification of polymers.</jats:p>