High I on/I off current ratio graphene field effect transistor: the role of line defect

Low-cost graphite and double-gate FET-based label-free biosensor for dopamine sensing to detect neural diseases

The manuscript proposes biosensors for detecting different concentrations of neurotransmitters named dopamine, which have a critical role in the human body's neurological, hormonal, and renal systems. In this work, the primary focus is to detect dopamine, whose disorder levels cause many neurological disabilities such as Alzheimer's and Parkinson's disease. In the present work, the simulation of two different structures has been studies: a) a graphite-based structure and b) a double gate TFET structure for detecting dopamine using TCAD Silvaco software. The proposed device utilizes a graphite-based structure with respective work functions of the used materials and studies the change in ON current (ION sensing factor is calculated for simulation study for VGS = 0.8 V). The cavity is increased to 800 µm for graphite-based biosensors for improved sensitivity. The graphite-based biosensors can detect up to 13.3 nM concentration of dopamine. Experimental electrochemical analysis results verify the proposed graphite-based biosensors' sensitivity for different dopamine concentrations. Another double gate field effect transistor (FET) biosensor has also been investigated for the detection of dopamine. The effective dielectric constant has been calculated using Bruggeman's model to check the sensitivity of double gate FET-based sensors for varying dopamine and uric acid concentrations. The sensitivity is increased with the increase of dopamine concentration percentage.

Silica Particle-Mediated Growth of Single Crystal Graphene Ribbons on Cu(111) Foil

The authors report the growth of micrometer-long single-crystal graphene ribbons (GRs) (tapered when grown above 900 °C, but uniform width when grown in the range 850 °C to 900 °C) using silica particle seeds on single crystal Cu(111) foil. Tapered graphene ribbons grow strictly along the Cu<101> direction on Cu(111) and polycrystalline copper (Cu) foils. Silica particles on both Cu foils form (semi-)molten Cu-Si-O droplets at growth temperatures, then catalyze nucleation and drive the longitudinal growth of graphene ribbons. Longitudinal growth is likely by a vapor-liquid-solid (VLS) mechanism but edge growth (above 900 °C) is due to catalytic activation of ethylene (C₂ H₄ ) and attachment of C atoms or species ("vapor solid" or VS growth) at the edges. It is found, based on the taper angle of the graphene ribbon, that the taper angle is determined by the growth temperature and the growth rates are independent of the particle size. The activation enthalpy (1.73 ± 0.03 eV) for longitudinal ribbon growth on Cu(111) from ethylene is lower than that for VS growth at the edges of the GRs (2.78 ± 0.15 eV) and for graphene island growth (2.85 ± 0.07 eV) that occurs concurrently.

A new photodetector structure based on graphene nanomeshes: an ab initio study

Recent experiments suggest graphene-based materials as candidates in future electronic and optoelectronic devices. In this paper, we propose to investigate new photodetectors based on graphene nanomeshes (GNMs). Density functional theory (DFT) calculations are performed to gain insight into electronic and optical characteristics of various GNM structures. To investigate the device-level properties of GNMs, their current-voltage characteristics are explored by DFT-based tight-binding (DFTB) in combination with non-equilibrium Green's function (NEGF) methods. Band structure analysis shows that GNMs have both metallic and semiconducting properties depending on the arrangements of perforations. Also, absorption spectrum analysis indicates attractive infrared peaks for GNMs with semiconducting characteristics, making them better photodetectors than graphene nanoribbon (GNR)-based alternatives. The results suggest that GNMs can be potentially used in mid-infrared detectors with specific detectivity values that are 100-fold that of graphene-based devices and 1000-fold that of GNR-based devices. Hence, the special properties of graphene combined with the quantum feathers of the perforation makes it suitable for optical devices.

Effects of high-k gate dielectrics on the electrical performance and reliability of an amorphous indium-tin-zinc-oxide thin film transistor (a-ITZO TFT): an analytical survey

This study is a numerical simulation obtained by using Silvaco Atlas software to investigate the effect of different types of dielectric layers, inserted between the channel and the gate, on the performance and reliability of an a-ITZO TFT. Replacing the SiO2 oxide layer with a high-k dielectric layer gives the concept of the electrical thickness, known by the equivalent oxide thickness (EOT) in which the physical thickness (PT) can be increased to improve the device reliability without increasing the effective thickness of the gate dielectric. A range of different high-k dielectric materials was suggested. For low-k SiO2 (k = 3.9), the electrical parameters extracted are: Ci = 3.45 × 10-8 F cm-2, Ion = 2.23 × 10-6 A, Ioff = 2.17 × 10-13 A, Ion/Ioff = 1.02 × 107, EOT = 100 nm, VT = -0.61 V, μFE = 29.75 cm2 V-1 s-1, SS = 7.91 × 10-2 V per decade and Von = -0.95 V. Replacing SiO2 by a high-k dielectric material, such as SrTiO3 (k = 300), leads to effects similar to the effects of reducing the physical thickness of the gate dielectric but without actually reducing this physical thickness. This allows improving the outputs of the a-ITZO TFT as it leads to an increase in Ci, Ion and Ion/Ioff to the values Ci = 2.66 × 10-6 F cm-2, Ion = 2.86 × 10-4 A, and Ion/Ioff = 8.80 × 109, respectively, and the decrease in EOT, Ioff, VT, μFE, SS and Von to the values EOT = 1.3 nm, Ioff = 3.25 × 10-14 A, VT = -0.428 V, μFE = 26.66 cm2 V-1 s-1, SS = 6.12 × 10-2 V per decade and Von = -0.75 V, respectively, without leakage effects.

Effects of Divacancy and Extended Line Defects on the Thermal Transport Properties of Graphene Nanoribbons

The effects of divacancy, including isolated defects and extended line defects (ELD), on the thermal transport properties of graphene nanoribbons (GNRs) are investigated using the Nonequilibrium Green's function method. Different divacancy defects can effectively tune the thermal transport of GNRs and the thermal conductance is significantly reduced. The phonon scattering of a single divacancy is mostly at high frequencies while the phonon scattering at low frequencies is also strong for randomly distributed multiple divacancies. The collective effect of impurity scattering and boundary scattering is discussed, which makes the defect scattering vary with the boundary condition. The effect on thermal transport properties of a divacancy is also shown to be closely related to the cross section of the defect, the internal structure and the bonding strength inside the defect. Both low frequency and high frequency phonons are scattered by 48, d5d7 and t5t7 ELD. However, the 585 ELD has almost no influence on phonon scattering at low frequency region, resulting in the thermal conductance of GNRs with 585 ELD being 50% higher than that of randomly distributed 585 defects. All these results are valuable for the design and manufacture of graphene nanodevices.