Monolithic Integration of Vertical Thin-Film Transistors in Nanopores for Charge Sensing of Single Biomolecules.

We propose and fabricate solid-state nanopore devices that monolithically integrate solution-gated, vertical thin-film transistors (TFTs) inside the nanopores for charge-based sensing of translocating biomolecules. The TFTs consist of zinc oxide semiconductor channels and aluminum oxide gate dielectrics, which are both conformally deposited along the inner surfaces of the nanopores via atomic layer deposition. The resultant TFT channel lengths and nanopore diameters both reach the ∼10 nm range. In translocation experiments using λ-DNAs or bovine serum antibody (BSA) proteins, the TFT-nanopore devices demonstrate concurrent detection of the ion conductance blockade signals and modulation signals in the TFT electrical current. The TFT signals show opposite signs for the negatively charged DNAs and positively charged BSAs as well as staircase signal shapes that correspond to the folding and knotting of λ-DNAs. Further experiments under various electrical biases and solution ionic strengths show that the ion blockade signals and the TFT signals have different dependence upon these experimental conditions. The TFT signals are analyzed to be consistent with the field effect sensing of the biomolecular charge, and the induced mirror charge is estimated from the signal amplitudes. This study could be a step forward to achieve charge-based single-biomolecular technology for basic research as well as for biosensing applications. It may also stimulate the development of TFT technologies for conformal integration of semiconductor electronics at the front end of nanostructures.

Low-Temperature Growth of Two-Dimensional Layered Chalcogenide Crystals on Liquid.

The growth of high-quality two-dimensional (2D) layered chalcogenide crystals is highly important for practical applications in future electronics, optoelectronics, and photonics. Current route for the synthesis of 2D chalcogenide crystals by vapor deposition method mainly involves an energy intensive high-temperature growth process on solid substrates, often suffering from inhomogeneous nucleation density and grain size distribution. Here, we first demonstrate a facile vapor-phase synthesis of large-area high-quality 2D layered chalcogenide crystals on liquid metal surface with relatively low surface energy at a growth temperature as low as ∼100 °C. Uniform and large-domain-sized 2D crystals of GaSe and GaxIn1-xSe were grown on liquid metal surface even supported on a polyimide film. As-grown 2D GaSe crystals have been fabricated to flexible photodetectors, showing high photoresponse and excellent flexibility. Our strategy of energy-sustainable low-temperature growth on liquid metal surface may open a route to the synthesis of high-quality 2D crystals of Ga-, In-, Bi-, Hg-, Pb-, or Sn-based chalcogenides and halides.

Large scale growth and characterization of atomic hexagonal boron nitride layers.

Hexagonal boron nitride (h-BN), a layered material similar to graphite, is a promising dielectric. Monolayer h-BN, so-called "white graphene", has been isolated from bulk BN and could be useful as a complementary two-dimensional dielectric substrate for graphene electronics. Here we report the large area synthesis of h-BN films consisting of two to five atomic layers, using chemical vapor deposition. These atomic films show a large optical energy band gap of 5.5 eV and are highly transparent over a broad wavelength range. The mechanical properties of the h-BN films, measured by nanoindentation, show 2D elastic modulus in the range of 200-500 N/m, which is corroborated by corresponding theoretical calculations.

Atomic layers of hybridized boron nitride and graphene domains.

Two-dimensional materials, such as graphene and monolayer hexagonal BN (h-BN), are attractive for demonstrating fundamental physics in materials and potential applications in next-generation electronics. Atomic sheets containing hybridized bonds involving elements B, N and C over wide compositional ranges could result in new materials with properties complementary to those of graphene and h-BN, enabling a rich variety of electronic structures, properties and applications. Here we report the synthesis and characterization of large-area atomic layers of h-BNC material, consisting of hybridized, randomly distributed domains of h-BN and C phases with compositions ranging from pure BN to pure graphene. Our studies reveal that their structural features and bandgap are distinct from those of graphene, doped graphene and h-BN. This new form of hybrid h-BNC material enables the development of bandgap-engineered applications in electronics and optics and properties that are distinct from those of graphene and h-BN.