Shouvik Banerjee

Stacked Graphene-Al2O3 Nanopore Sensors for Sensitive Detection of DNA and DNA–Protein Complexes

We report the development of a multilayered graphene-Al(2)O(3) nanopore platform for the sensitive detection of DNA and DNA-protein complexes. Graphene-Al(2)O(3) nanolaminate membranes are formed by sequentially depositing layers of graphene and Al(2)O(3), with nanopores being formed in these membranes using an electron-beam sculpting process. The resulting nanopores are highly robust, exhibit low electrical noise (significantly lower than nanopores in pure graphene), are highly sensitive to electrolyte pH at low KCl concentrations (attributed to the high buffer capacity of Al(2)O(3)), and permit the electrical biasing of the embedded graphene electrode, thereby allowing for three terminal nanopore measurements. In proof-of-principle biomolecule sensing experiments, the folded and unfolded transport of single DNA molecules and RecA-coated DNA complexes could be discerned with high temporal resolution. The process described here also enables nanopore integration with new graphene-based structures, including nanoribbons and nanogaps, for single-molecule DNA sequencing and medical diagnostic applications.

Electrochemistry at the Edge of a Single Graphene Layer in a Nanopore

We study the electrochemistry of single layer graphene edges using a nanopore-based structure consisting of stacked graphene and Al(2)O(3) dielectric layers. Nanopores, with diameters ranging from 5 to 20 nm, are formed by an electron beam sculpting process on the stacked layers. This leads to a unique edge structure which, along with the atomically thin nature of the embedded graphene electrode, demonstrates electrochemical current densities as high as 1.2 × 10(4) A/cm(2). The graphene edge embedded structure offers a unique capability to study the electrochemical exchange at an individual graphene edge, isolated from the basal plane electrochemical activity. We also report ionic current modulation in the nanopore by biasing the embedded graphene terminal with respect to the electrodes in the fluid. The high electrochemical specific current density for a graphene nanopore-based device can have many applications in sensitive chemical and biological sensing, and energy storage devices.

Measurements of hot‐electron conduction and real‐space transfer in GaAs‐AlxGa1−xAs heterojunction layers

Measurements of the current‐voltage characteristics of GaAs‐AlxGa1−xAs heterojunction layers are reported. The experimental results are consistent with the idea of real‐space transfer of the electrons out of the GaAs into the AlxGa1−xAs under hot‐electron conditions. Current saturation and negative differential resistance are observed as predicted by Monte Carlo simulations.

Hydrodynamic loading and viscous damping of patterned perforations on microfabricated resonant structures

We examined the hydrodynamic loading of vertically resonating microfabricated plates immersed in liquids with different viscosities. The planar structures were patterned with focused ion beam, perforating various shapes with identical area but varying perimeters. The hydrodynamic loading of various geometries was characterized from resonant frequency and quality factor. In water, the damping increased linearly with the perimeter at 45.4 × 10−3 Ns/m2, until the perforation’s radius was 123% ± 13% of the depth of penetration of fluid’s oscillation. The added mass effect decreased with perforations and recovered to the level of un-perforated structures when the perforation’s radius became smaller than the depth of penetration.

Tip-Based Nanofabrication of Arbitrary Shapes of Graphene Nanoribbons for Device Applications

Graphene nanoribbons (GNRs) have promising applications in future nanoelectronics, chemical sensing and electrical interconnects. Although there are quite a few GNR nanofabrication methods reported, a rapid and low-cost fabrication method that is capable of fabricating arbitrary shapes of GNRs with good-quality is still in demand for using GNRs for device applications. In this paper, we present a tip-based nanofabrication method capable of fabricating arbitrary shapes of GNRs. A heated atomic force microscope (AFM) tip deposits polymer nanowires atop a CVD-grown graphene surface. The polymer nanowires serve as an etch mask to define GNRs through one step of oxygen plasma etching similar to a photoresist in conventional photolithography. Various shapes of GNRs with either linear or curvilinear features are demonstrated. The width of the GNR is around 270 nm and is determined by the width of the depositing polymer nanowire, which we estimate can be scaled down 15 nms. We characterize our TBN-fabricated GNRs using Raman spectroscopy and I-V measurements. The measured sheet resistances of our GNRs fall within the range of 1.65 kΩ/□-1 - 2.64 kΩ/□-1, in agreement with previously reported values. Furthermore, we determined the high-field breakdown current density of GNRs to be approximately 2.94×108 A/cm2. This TBN process is seamlessly compatible with existing nanofabrication processes, and is particularly suitable for fabricating GNR based electronic devices including next generation DNA sequencing technologies and beyond silicon field effect transistors.

Graphene nanopores for nucleic acid analysis

Solid-state nanopores are being widely investigated as potential tools for DNA sequencing and early detection of diseases. We review our recent work in the formation of nanopores in graphene embedded in thin layers of dielectrics for sensitive, controllable, and low-noise detection of bio-molecules. We also discuss applications in medical diagnostics.

Nanopore sensors for DNA analysis

Solid-state nanopore sensors are promising devices for single DNA molecule detection and sequencing. This paper presents a review of our work on solid-state nanopores performed over the last decade. In particular, here we discuss atomic-layer-deposited (ALD)-based, graphene-based, and functionalized solid state nanopores.