Ultrathin ferroelectrics hold great promise for modern miniaturized sensors, memories, and optoelectronic devices. However, in most ferroelectric materials, polarization is destabilized in ultrathin films by the intrinsic depolarization field. Here we report robust in-plane ferroelectricity in fewlayer tin sulfide (SnS) 2D crystals that is coupled anisotropically to lattice strain. Specifically, the intrinsic polarization of SnS manifests as nanoripples along the armchair direction due to a converse piezoelectric effect. Most interestingly, such nanoripples show an odd-and-even effect in terms of its layer dependence, indicating that it is highly sensitive to changes in inversion symmetry. Ferroelectric switching is demonstrated in field-effect transistor devices fabricated on ultrathin SnS films, in which a stronger ferroelectric response is achieved at negative gate voltages. Our work shows the promise of 2D SnS in ultrathin ferroelectric field-effect transistors as well as nanoscale electromechanical systems.

Lead halide perovskites have shown great potential in photovoltaic and photocatalytic fields. However, the toxicity of lead impedes their wide application. Herein composites of lead-free halide perovskite Cs 2 AgBiBr 6 supported on nitrogen-doped carbon (N-C) materials were synthesized successfully through a facile one-pot method for the first time. Without deposition of noble metals as the cocatalyst, the optimal composite Cs 2 AgBiBr 6 /N-C (Cs 2 AgBiBr 6 /N-C-140) exhibits outstanding photocatalytic performance with a high hydrogen evolution rate of 380 μmol g −1 h −1 under visible light irradiation (λ ≥ 420 nm), which is about 19 times faster than that of pure Cs 2 AgBiBr 6 and 4 times faster than that of physically mixed Cs 2 AgBiBr 6 /N-C-140, respectively. The Cs 2 AgBiBr 6 /N-C-140 composite also displays high stability with no significant decrease after six cycles of repeated hydrogen evolution experiments. The addition of N-C with a high surface area helps to prevent aggregation of Cs 2 AgBiBr 6 NPs and provides more pathways for the migration of photoinduced carriers. The nitrogen dopant can facilitate photoinduced electron transfer from Cs 2 AgBiBr 6 to N-C to result in spatially separated electrons and holes with prolonged electron time and greatly enhance the photocatalytic performance. This study indicates that Cs 2 AgBiBr 6 -based perovskite materials are promising candidates for photocatalytic hydrogen evolution.

We propose a new strip/slot hybrid waveguide with double slots, which exhibits a flat and low dispersion over a 1098-nm bandwidth with four zero-dispersion wavelengths. Dispersion of dual-slot silicon waveguide is mainly determined by mode transition from a strip mode to a slot mode rather than by material dispersion. Dispersion tailoring is investigated by tuning different structural parameters of waveguides. Moreover, nonlinear coefficient of dual-slot silicon waveguide and phase-matching condition in FWM are both explored in detail. The dual-slot waveguide can be used to generate supercontinuum with bandwidth extending up to 1630 nm pumped by femtosecond pulses. This waveguide will have a great potential for ultrabroadband signal processing applications from near-infrared region to mid-infrared region.

High‐performance organic heterojunction phototransistors are fabricated using highly ordered copper phthalocyanine (CuPc) and para‐sexiphenyl (p‐6P) thin films. The p‐6P thin film plays an important role on the performance of CuPc/p‐6P heterojunction phototransistors. It acts as a molecular template layer to induce the growth of highly ordered CuPc thin film, which dramatically improves the charge transport and decreases the grain boundaries. On the other hand, the p‐6P thin film can form an effective heterojunction with CuPc thin film, which is greatly helpful to enhance the light absorption and photogenerated carriers. Under 365 nm ultraviolet light irradiation, the ratio of photocurrent and dark current and photoresponsivity of CuPc/p‐6P heterojunction phototransistors reaches to about 2.2 × 104 and 4.3 × 102 A W−1, respectively, which are much larger than that of CuPc phototransistors of about 2.7 × 102 and 7.3 A W−1, respectively. A detailed study carried out with current sensing atomic force microscopy proves that the photocurrent is predominately produced inside the highly ordered CuPc/p‐6P heterojunction grains, while the photocurrent produced at the boundaries between grains can be neglected. The research provides a good method for fabricating high‐performance organic phototransistors using a combination of molecular template growth and organic heterojunction.

Cp′ 2 LnR(THF) (Cp′ ) C 5 H 4 CH 3 ) reacted with phenyl isocyanate to form the PhNCO insertion products [Cp′ 2 Ln(OC(R)NPh)] 2 [R ) n-butyl, Ln ) Sm (1), Dy (2), Er (3); R ) R-naphthyl, Ln ) Dy (4)]. It was found that an excess of PhNCO did not affect the nature of the final complexes, a single insertion only being observed and excess PhNCO forming a cyclotrimer (5). The reaction of Cp′HoCl 2 (THF) 3 with Bu n Li and subsequently with 2 equiv of PhNCO in THF gave Ho[OC(Bu n )NPh)] 3 ( 6) and [Cp′ 2 Ho(OC(Bu n )NPh)] 2 (7), which can be rationalized by the rearrangement reaction of the di-insertion product Cp′Ho[OC(Bu n )-NPh] 2 (THF) x . The structures of 1, 4‚THF, 5‚THF and 7 were determined by X-ray diffraction, revealing an unusual bonding mode of the amido groups arising from the insertion of PhNCO into the Ln-C σ-bonds and that the O.C.N fragment of the OC(R)NPh ligand acts as both a bridging and side-on chelating group.