Ballistic InAs Nanowire Transistors

Ballistic transport of electrons at room temperature in top-gated InAs nanowire (NW) transistors is experimentally observed and theoretically examined. From length dependent studies, the low-field mean free path is directly extracted as ∼150 nm. The mean free path is found to be independent of temperature due to the dominant role of surface roughness scattering. The mean free path was also theoretically assessed by a method that combines Fermi’s golden rule and a numerical Schrödinger–Poisson simulation to determine the surface scattering potential with the theoretical calculations being consistent with experiments. Near ballistic transport (∼80% of the ballistic limit) is demonstrated experimentally for transistors with a channel length of ∼60 nm, owing to the long mean free path of electrons in InAs NWs

High-Performance Single Layered WSe₂ p-FETs with Chemically Doped Contacts

We report high performance p-type field-effect transistors based on single layered (thickness, ∼0.7 nm) WSe₂ as the active channel with chemically doped source/drain contacts and high-κ gate dielectrics. The top-gated monolayer transistors exhibit a high effective hole mobility of ∼250 cm²/(V s), perfect subthreshold swing of ∼60 mV/dec, and <i>I</i>_ON/<i>I</i>_OFF of >10⁶ at room temperature. Special attention is given to lowering the contact resistance for hole injection by using high work function Pd contacts along with degenerate surface doping of the contacts by patterned NO₂ chemisorption on WSe₂. The results here present a promising material system and device architecture for p-type monolayer transistors with excellent characteristics

Highly Uniform and Stable n‑Type Carbon Nanotube Transistors by Using Positively Charged Silicon Nitride Thin Films

Air-stable n-doping of carbon nanotubes is presented by utilizing SiN_<i>x</i> thin films deposited by plasma-enhanced chemical vapor deposition. The fixed positive charges in SiN_<i>x</i>, arising from ⁺SiN₃ dangling bonds induce strong field-effect doping of underlying nanotubes. Specifically, an electron doping density of ∼10²⁰ cm^–3 is estimated from capacitance voltage measurements of the fixed charge within the SiN_<i>x</i>. This high doping concentration results in thinning of the Schottky barrier widths at the nanotube/metal contacts, thus allowing for efficient injection of electrons by tunnelling. As a proof-of-concept, n-type thin-film transistors using random networks of semiconductor-enriched nanotubes are presented with an electron mobility of ∼10 cm²/V s, which is comparable to the hole mobility of as-made p-type devices. The devices are highly stable without any noticeable change in the electrical properties upon exposure to ambient air for 30 days. Furthermore, the devices exhibit high uniformity over large areas, which is an important requirement for use in practical applications. The work presents a robust approach for physicochemical doping of carbon nanotubes by relying on field-effect rather than a charge transfer mechanism

Tanshinones Inhibit Amyloid Aggregation by Amyloid‑β Peptide, Disaggregate Amyloid Fibrils, and Protect Cultured Cells

The misfolding and aggregation of amyloid-β (Aβ) peptides into amyloid fibrils is regarded as one of the causative events in the pathogenesis of Alzheimer’s disease (AD). Tanshinones extracted from Chinese herb Danshen (Salvia Miltiorrhiza Bunge) were traditionally used as anti-inflammation and cerebrovascular drugs due to their antioxidation and antiacetylcholinesterase effects. A number of studies have suggested that tanshinones could protect neuronal cells. In this work, we examine the inhibitory activity of tanshinone I (TS1) and tanshinone IIA (TS2), the two major components in the Danshen herb, on the aggregation and toxicity of Aβ_1–42 using atomic force microscopy (AFM), thioflavin-T (ThT) fluorescence assay, cell viability assay, and molecular dynamics (MD) simulations. AFM and ThT results show that both TS1 and TS2 exhibit different inhibitory abilities to prevent unseeded amyloid fibril formation and to disaggregate preformed amyloid fibrils, in which TS1 shows better inhibitory potency than TS2. Live/dead assay further confirms that introduction of a very small amount of tanshinones enables protection of cultured SH-SY5Y cells against Aβ-induced cell toxicity. Comparative MD simulation results reveal a general tanshinone binding mode to prevent Aβ peptide association, showing that both TS1 and TS2 preferentially bind to a hydrophobic β-sheet groove formed by the C-terminal residues of I31-M35 and M35-V39 and several aromatic residues. Meanwhile, the differences in binding distribution, residues, sites, population, and affinity between TS1-Aβ and TS2-Aβ systems also interpret different inhibitory effects on Aβ aggregation as observed by in vitro experiments. More importantly, due to nonspecific binding mode of tanshinones, it is expected that tanshinones would have a general inhibitory efficacy of a wide range of amyloid peptides. These findings suggest that tanshinones, particularly TS1 compound, offer promising lead compounds with dual protective role in anti-inflammation and antiaggregation for further development of Aβ inhibitors to prevent and disaggregate amyloid formation

Hole Contacts on Transition Metal Dichalcogenides: Interface Chemistry and Band Alignments

MoO_<i>x</i> shows promising potential as an efficient hole injection layer for p-FETs based on transition metal dichalcogenides. A combination of experiment and theory is used to study the surface and interfacial chemistry, as well as the band alignments for MoO_<i>x</i>/MoS₂ and MoO_<i>x</i>/WSe₂ heterostructures, using photoelectron spectroscopy, scanning tunneling microscopy, and density functional theory. A Mo⁵⁺ rich interface region is identified and is proposed to explain the similar low hole Schottky barriers reported in a recent device study utilizing MoO_<i>x</i> contacts on MoS₂ and WSe₂

MoS₂ P‑type Transistors and Diodes Enabled by High Work Function MoO_<i>x</i> Contacts

The development of low-resistance source/drain contacts to transition-metal dichalcogenides (TMDCs) is crucial for the realization of high-performance logic components. In particular, efficient hole contacts are required for the fabrication of p-type transistors with MoS₂, a model TMDC. Previous studies have shown that the Fermi level of elemental metals is pinned close to the conduction band of MoS₂, thus resulting in large Schottky barrier heights for holes with limited hole injection from the contacts. Here, we show that substoichiometric molybdenum trioxide (MoO_<i>x</i>, <i>x</i> < 3), a high work function material, acts as an efficient hole injection layer to MoS₂ and WSe₂. In particular, we demonstrate MoS₂ p-type field-effect transistors and diodes by using MoO_<i>x</i> contacts. We also show drastic on-current improvement for p-type WSe₂ FETs with MoO_<i>x</i> contacts over devices made with Pd contacts, which is the prototypical metal used for hole injection. The work presents an important advance in contact engineering of TMDCs and will enable future exploration of their performance limits and intrinsic transport properties

Nanoscale InGaSb Heterostructure Membranes on Si Substrates for High Hole Mobility Transistors

As of yet, III–V p-type field-effect transistors (p-FETs) on Si have not been reported, due partly to materials and processing challenges, presenting an important bottleneck in the development of complementary III–V electronics. Here, we report the first high-mobility III–V p-FET on Si, enabled by the epitaxial layer transfer of InGaSb heterostructures with nanoscale thicknesses. Importantly, the use of ultrathin (thickness, ∼2.5 nm) InAs cladding layers results in drastic performance enhancements arising from (i) surface passivation of the InGaSb channel, (ii) mobility enhancement due to the confinement of holes in InGaSb, and (iii) low-resistance, dopant-free contacts due to the type III band alignment of the heterojunction. The fabricated p-FETs display a peak effective mobility of ∼820 cm²/(V s) for holes with a subthreshold swing of ∼130 mV/decade. The results present an important advance in the field of III–V electronics