Two-dimensional (2D) materials, particularly black phosphorus (bP), have demonstrated themselves to be excellent candidates for high-performance infrared photodetectors and transistors. However, high-quality bP can be obtained only via mechanical exfoliation from high-temperature- and high-pressure-grown bulk crystals and degrades rapidly when exposed to ambient conditions. Here, we report solution-synthesized and air-stable quasi-2D tellurium (Te) nanoflakes for short-wave infrared (SWIR) photodetectors. We perform comprehensive optical characterization via polarization-resolved transmission and reflection measurements and report the absorbance and complex refractive index of Te crystals. It is found that this material is an indirect semiconductor with a band gap of 0.31 eV. From temperature-dependent electrical measurements, we confirm this band-gap value and find that 12 nm thick Te nanoflakes show high hole mobilities of 450 and 1430 cm V s at 300 and 77 K, respectively. Finally, we demonstrate that despite its indirect band gap, Te can be utilized for high-performance SWIR photodetectors by employing optical cavity substrates consisting of Au/AlO to dramatically increase the absorption in the semiconductor. By changing the thickness of the AlO cavity, the peak responsivity of Te photoconductors can be tuned from 1.4 μm (13 A/W) to 2.4 μm (8 A/W) with a cutoff wavelength of 3.4 μm, fully capturing the SWIR band. An optimized room-temperature specific detectivity ( D*) of 2 × 10 cm Hz W is obtained at a wavelength of 1.7 μm.

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There is an emerging need for semiconductors that can be processed at near ambient temperature with high mobility and device performance. Although multiple n-type options have been identified, the development of their p-type counterparts remains limited. Here, we report the realization of tellurium ( Te) thin films through thermal evaporation at cryogenic temperatures for fabrication of high-performance wafer-scale p-type field-effect transistors (FETs). We achieve an effective hole mobility of 35 cm 2 V -1 s -1 , on/off current ratio of ~10 4 and subthreshold swing of 108 mVdec -1 on an 8 nm thick film. High-performance Te p-FETs are fabricated on a wide range of substrates including glass and plastic, further demonstrating the broad applicability of this material. Significantly, 3D circuits are demonstrated by integrating multi-layered transistors on a single chip using sequential lithography, deposition and lift-off processes. Finally, various functional logic gates and circuits are demonstrated.

for help with the experiments. Reviewer information Nature thanks Hua Zhang and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Two well-defined amphiphilic asymmetric macromolecular brushes, one bearing hydrophilic poly(ethylene glycol) (PEO) and hydrophobic polystyrene (PS) side chains on poly(glycidyl methacrylate) (PGMA) backbone and the other bearing pendant PEO and poly(styrene-block-N-isopropylacrylamide) (PS-b-PNIPAM) block copolymer side chains, were synthesized by grafting from approach based on a combination of click chemistry and in situ reversible addition−fragmentation chain transfer (RAFT) polymerization. PGMA backbone was synthesized by atom transfer radical polymerization (ATRP), and a polymer backbone with pendant hydroxyl and azide groups (PGMA−OH/N3) was obtained after ring-opening reaction of the epoxide rings on PGMA. RAFT chain transfer agent (CTA) was introduced to the polymer backbone by facile click reaction between alkyne-terminated RAFT CTA and PGMA−OH/N3. PEO side chains were grafted onto the polymer backbone by esterification between carboxyl end group of PEO and hydroxyl group on the polymer backbone; PS or PS-b-PNIPAM side chains were prepared by RAFT polymerization. Gel permeation chromatograph, FTIR and 1H NMR results all indicated successful synthesis of well-defined amphiphilic asymmetric macromolecular brushes. The self-assembly of the macromolecular brushes in solutions was also investigated in this research. Asymmetric macromolecular brushes with PEO and PS side chains self-assembled into vesicle structures in methanol. PS side chains were in the walls of the vesicles, and PEO side chains were in the coronae. The average size of the structure increased with PS chain length. The macromolecular brushes with PEO and PS-b-PNIPAM block copolymer side chains were able to self-assemble into vesicles in aqueous solution. Temperature exerted a significant effect on the morphology of the structures. At a temperature above lower critical solution temperature (LCST) of PNIPAM, the size of the vesicles decreased due to the shrinking of PNIPAM blocks in the corona.

Two-dimensional (2D) noble-metal dichalcogenides exhibit exceptionally strong thickness-dependent bandgaps, which can be leveraged in a wide variety of device applications. A detailed study of their optical (e.g., optical bandgaps) and electrical properties (e.g., mobilities) is important in determining potential future applications of these materials. In this work, we perform detailed optical and electrical characterization of 2D PdSe 2 nanoflakes mechanically exfoliated from a single-crystalline source. Layer-dependent bandgap analysis from optical absorption results indicates that this material is an indirect semiconductor with bandgaps of approximately 1.37 and 0.50 eV for the monolayer and bulk, respectively. Spectral photoresponse measurements further confirm these bandgap values. Moreover, temperature-dependent electrical measurements of a 6.8-nm-thick PdSe 2 flake-based transistor show effective electron mobilities of 130 and 520 cm 2 V À1 s À1 at 300 K and 77 K, respectively. Finally, we demonstrate that PdSe 2 can be utilized for shortwave infrared photodetectors. A room-temperature specific detectivity (D Ã) of 1.8 Â 10 10 cm Hz 1/2 W À1 at 1 lm with a band edge at 1.94 lm is achieved on a 6.8-nm-thick PdSe 2 flake-based photodetector.

Carboxyl groups at the periphery of reduced graphene oxide (RGO) sheets are converted to amine groups by reaction with N-hydroxysuccinimide and 1,3-diaminopropane, and a free-radical polymerization initiator is anchored to the RGO sheets. Poly(acrylamide) (PAM) polymer brushes on RGO sheets (RGO/PAM) are synthesized by in situ free-radical polymerization. The heavy metals, Pb(II), and the benzenoid compounds, methylene blue, (MB) were selected and adsorbed by RGO/PAM composites, and the adsorption capacity of RGO/PAM for Pb(II) and MB was measured. The experimental data of RGO/PAM isotherms for Pb(II) and MB followed the Langmuir isotherm model. The RGO/PAM displays adsorption capacities as high as 1000 and 1530 mg/g for Pb(II) and MB, respectively, indicating RGO/PAM is a good adsorbent for the adsorption of Pb(II) and MB. The adsorption kinetics of Pb(II) and MB onto RGO/PAM can be well fitted to the pseudo-second-order model. The adsorption processes of Pb(II) and MB onto RGO/PAM are spontaneous at 298, 308, and 318 K.

Exfoliated graphene oxide (GO) sheets with hydrophilic functional groups on the surface were prepared by the oxidation of graphite. Because of the hydrophilic groups on the sheets and the hydrophobic carbon surface, GO sheets were located at the oil-water interface and could be used as a stabilizer in Pickering emulsions. After the Pickering emulsion polymerization of styrene, PS colloidal particles with GO sheets on the surface were prepared. The size of the GO sheets exerts an important influence on the preparation of PS colloidal particles. Small GO sheets located at the liquid-liquid interface and GO-stabilized PS colloidal particles were prepared; however, for large GO sheets, smaller PS colloidal particles prepared on the GO surface were observed. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) were used to characterize the structure and morphology of the colloidal particles. TEM, SEM, and XPS results all suggest the successful preparation of GO-stabilized PS colloidal particles.