Dry etching of ternary metal carbide TiAlC via surface modification using floating wire-assisted vapor plasma.

Dry etching of ternary metal carbides TiAlC has been first developed by transferring from wet etching to dry etching using a floating wire (FW)-assisted Ar/ammonium hydroxide vapor plasma. FW-assisted non-halogen vapor plasma generated at medium pressure can produce high-density reactive radicals (NH, H, and OH) for TiAlC surface modifications such as hydrogenation and methylamination. A proposed mechanism for dry etching of TiAlC is considered with the formation of the volatile products from the modified layer.

Two-step breakdown of a SiN membrane for nanopore fabrication: Formation of thin portion and penetration.

For the nanopore sensing of various large molecules, such as probe-labelled DNA and antigen-antibody complexes, the nanopore size has to be customized for each target molecule. The recently developed nanopore fabrication method utilizing dielectric breakdown of a membrane is simple and quite inexpensive, but it is somewhat unsuitable for the stable fabrication of a single large nanopore due to the risk of generating multiple nanopores. To overcome this bottleneck, we propose a new technique called "two-step breakdown" (TSB). In the first step of TSB, a local conductive thin portion (not a nanopore) is formed in the membrane by dielectric breakdown. In the second step, the created thin portion is penetrated by voltage pulses whose polarity is opposite to the polarity of the voltage used in the first step. By applying TSB to a 20-nm-thick SiN membrane, a single nanopore with a diameter of 21-26 nm could be fabricated with a high yield of 83%.

Slowing single-stranded DNA translocation through a solid-state nanopore by decreasing the nanopore diameter.

To slow the translocation of single-stranded DNA (ssDNA) through a solid-state nanopore, a nanopore was narrowed, and the effect of the narrowing on the DNA translocation speed was investigated. In order to accurately measure the speed, long (5.3 kb) ssDNA (namely, ss-poly(dA)) with uniform length (±0.4 kb) was synthesized. The diameters of nanopores fabricated by a transmission electron microscope were controlled by atomic-layer deposition. Reducing the nanopore diameter from 4.5 to 2.3 nm slowed down the translocation of ssDNA by more than 16 times (to 0.18 µs base(-1)) when 300 mV was applied across the nanopore. It is speculated that the interaction between the nanopore and the ssDNA dominates the translocation speed. Unexpectedly, the translocation speed of ssDNA through the 4.5 nm nanopore is more than two orders of magnitude higher than that of double-stranded DNA (dsDNA) through a nanopore of almost the same size. The cause of such a faster translocation of ssDNA can be explained by the weaker drag force inside the nanopore. Moreover, the measured translocation speeds of ssDNA and dsDNA agree well with those calculated by molecular-dynamics (MD) simulation. The MD simulation predicted that reducing the nanopore diameter to almost the same as that of ssDNA (i.e. 1.4 nm) decreases the translocation speed (to 1.4 µs base(-1)). Narrowing the nanopore is thus an effective approach for accomplishing nanopore DNA sequencing.