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Bottom-up assembled nanomaterials and nanostructures allow for the studies of rich and unprecedented quantum-related and mesoscopic transport phenomena. However, it can be difficult to quantify the correlations between the geometrical or structural parameters obtained from advanced microscopy and measured electrical characteristics when they are made into macroscopic devices. Here, we propose a strategy to connect the nanomaterial morphologies and the device performance through a Monte Carlo device model and apply it to understand the scaling trends of bottom-up synthesized armchair graphene nanoribbon (GNR) transistors. A new nanofabrication process is developed for GNR transistors with channel length down to 7 nm. The impacts of the GNR spatial distributions and the device geometries on the device performance are investigated systematically through comparison of experimental data with the model. Through this study, challenges and opportunities of transistor technologies based on bottom-up synthesized GNRs are pinpointed, paving the way to the further improvement of the GNR device performance for future transistor technology nodes.

Covalent organic frameworks are an emerging class of covalently linked polymers with programmable lattices and well-defined nanopores. Developing covalent organic frameworks with both high porosity and excellent charge transport properties is crucial for widespread applications, including sensing, catalysis, and organic electronics. However, achieving the combination of both features remains challenging due to the lack of overarching structure-property correlations. Here, we report a strategy toward covalent organic frameworks with tunable dimensionality. The concept relies on splicing one-dimensional charge-conducting channels to form extended networks with tailorable substitution patterns. Such dimensional evolution and substitution control enable fine-tuning of electronic band structure, charge mobility, and porosity. According to surface-area characterization, high-frequency terahertz photoconductivity measurements, and theoretical calculations, the transition from one-dimensional to para-linked two-dimensional networks furnishes a substantial increase in surface area and a decrease in local charge mobility. The latter feature is assigned to substitution-induced electronic band flattening. A subtle balance of surface area (947 m2·g−1) and local charge mobility (49 ± 10 cm2·V−1·s−1) is achieved through the rational design of meta-linked analogs with mixed one-dimensional and two-dimensional superior nature. This work provides fundamental insights and new structural knobs for the design of conductive covalent organic frameworks. The design of covalent organic frameworks featuring high porosity and excellent charge transfer properties is crucial for widespread applications. Here, the authors report covalent organic frameworks with tunable dimensionality allowing to fine-tune their electronic band structure, charge mobility, and porosity. [ABSTRACT FROM AUTHOR]

Bottom-up synthesized graphene nanoribbons and graphene nanoribbon heterostructures have promising electronic properties for high-performance field-effect transistors and ultra-low power devices such as tunneling field-effect transistors. However, the short length and wide band gap of these graphene nanoribbons have prevented the fabrication of devices with the desired performance and switching behavior. Here, by fabricating short channel (L ch ~ 20 nm) devices with a thin, high-κ gate dielectric and a 9-atom wide (0.95 nm) armchair graphene nanoribbon as the channel material, we demonstrate field-effect transistors with high on-current (I on > 1 μA at V d = -1 V) and high I on /I off ~ 105 at room temperature. We find that the performance of these devices is limited by tunneling through the Schottky barrier at the contacts and we observe an increase in the transparency of the barrier by increasing the gate field near the contacts. Our results thus demonstrate successful fabrication of high-performance short-channel field-effect transistors with bottom-up synthesized armchair graphene nanoribbons.Graphene nanoribbons show promise for high-performance field-effect transistors, however they often suffer from short lengths and wide band gaps. Here, the authors use a bottom-up synthesis approach to fabricate 9- and 13-atom wide ribbons, enabling short-channel transistors with 105 on-off current ratio.

Thermally‐induced dehydrogenative coupling of polyphenylenes on metal surfaces is an important technique to synthesize π ${\pi }$ ‐conjugated carbon nanostructures with atomic precision. However, this protocol has rarely been utilized to fabricate structurally defined carbon nanosheets composed of sp‐ and sp2‐hybridized carbon atoms. Here, we present the synthesis of butadiyne‐linked hexabenzocoronenes (HBCs) on Au(111) surfaces as core‐expanded graphdiynes. The reaction started from hexa(4‐ethylphenyl)benzene, which undergoes dehydrogenation toward hexa(4‐vinylphenyl)benzene, followed by planarization to hexabenzocoronene, coupling between the vinyl groups, and further dehydrogenation. In addition to butadiyne linkages, benzene groups were also found as another type of linker. The reaction sequences were monitored by scanning tunneling microscopy and bond‐resolved non‐contact atomic force microscopy, which disclose the structures of intermediates and final products. In combination with density functional theory simulations, the key steps from ethyl substituents to butadiyne and benzene linkers were elucidated. This is a new on‐surface synthesis of core‐expanded graphdiynes with unprecedented electronic properties. [ABSTRACT FROM AUTHOR]

Functionalizing graphene beyond its intrinsic properties has been a key concept since the first successful realization of this archetype monolayer system. While various concepts, such as doping, co-doping, and layered device design, have been proposed, the often complex structural and electronic changes are often jeopardizing simple functionalization attempts. Here, we present a thorough analysis of the structural and electronic properties of co-doped graphene via Raman spectroscopy as well as magneto-transport and Hall measurements. The results highlight the challenges in understanding its microscopic properties beyond the simple preparation of such devices. It is discussed how co-doping with N and B dopants leads to effective charge-neutral defects acting as short-range scatterers, while charged defects introduce more long-range scattering centers. Such distinct behavior may obscure or alter the desired structural as well as electronic properties not anticipated initially. Exploring further the preparation of effective pn-junctions, we highlight step by step how the preparation process may lead to alterations in the intrinsic properties of the individual layers. Importantly, it is highlighted in all steps how the inhomogeneities across individual graphene sheets may challenge simple interpretations of individual measurements. [ABSTRACT FROM AUTHOR]

Ionic discotic liquid crystals combine ion conduction with fluid, yet ordered, liquid crystal phases at ambient temperature, making them suitable nanomaterials for ion transport and energy storage. A series of Janus-type hexa-peri-hexabenzocoronenes (HBCs) with ionic (sulfonate) groups covalently bonded to the HBC core, and tetraalkylammonium counterions (sizes from 0.15 to 0.95 nm) are synthesized and investigated with respect to the self-assembly and ion dynamics. We find that the counterion size affects the nanoscale self-assembly and ionic conductivity in opposite ways. Smaller counterions act as structure formers, whereas larger ones act as structure breakers. The latter exhibits the highest ion dc-conductivity. We quantify the effect of Coulomb interactions on the self-assembly, the glass temperature Tg (which was found to vary by 30 K), and the dc-conductivity (varying by 4 orders of magnitude). The precise synthesis of tailor-made ionic discotic liquid crystals with the HBC core and the characterization of their physical properties revealed that ion-conduction and nanoscale self-assembly in HBCs can be modulated by tuning electrostatic interactions, e.g., by adjusting the size of counterions. [ABSTRACT FROM AUTHOR]