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
~ 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
> 1 μA at V
= -1 V) and high I
/I
~ 10
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 10
on-off current ratio.
The influence of transfer parameters on the final structure, morphology and electrical properties of graphene were investigated in this work. Optical microscopy and atomic force microscopy (AFM) ...images showed that a double layer of PMMA can enhance or degrade graphene quality depending on its concentration. When properly diluted (15% in anisole, resulting in a PMMA layer of 1.35%) the transfer technique using double layer PMMA produces high quality graphene with fewer PMMA residues, non-cracked surface and sheet resistance around 247ohm/square. We also investigated the influence of different baking times and temperature, and observed that the increase in baking time can degrade graphene quality thus leaving higher amounts of PMMA residues. Several works regarding graphene transfer are reported in the literature, but PMMA-based transfer processes still present challenges in yielding a clean and high quality graphene.
The electronic, optical, and magnetic properties of graphene nanoribbons (GNRs) can be engineered by controlling their edge structure and width with atomic precision through bottom‐up fabrication ...based on molecular precursors. This approach offers a unique platform for all‐carbon electronic devices but requires careful optimization of the growth conditions to match structural requirements for successful device integration, with GNR length being the most critical parameter. In this work, the growth, characterization, and device integration of 5‐atom wide armchair GNRs (5‐AGNRs) are studied, which are expected to have an optimal bandgap as active material in switching devices. 5‐AGNRs are obtained via on‐surface synthesis under ultrahigh vacuum conditions from Br‐ and I‐substituted precursors. It is shown that the use of I‐substituted precursors and the optimization of the initial precursor coverage quintupled the average 5‐AGNR length. This significant length increase allowed the integration of 5‐AGNRs into devices and the realization of the first field‐effect transistor based on narrow bandgap AGNRs that shows switching behavior at room temperature. The study highlights that the optimized growth protocols can successfully bridge between the sub‐nanometer scale, where atomic precision is needed to control the electronic properties, and the scale of tens of nanometers relevant for successful device integration of GNRs.
This work studies the growth, characterization, and device integration of 5‐atom wide armchair graphene nanoribbons (5‐AGNRs). 5‐AGNRs are synthesized under ultrahigh vacuum conditions from Br‐ and I‐substituted precursors. The authors show that I‐substituted precursors and optimized initial precursor coverage quintupled the average 5‐AGNR length. This significant length increase allows to integrate 5‐AGNRs into field‐effect transistors, showing switching behavior at room temperature.
Graphene nanoribbons (GNRs) have attracted much interest due to their largely modifiable electronic properties. Manifestation of these properties requires atomically precise GNRs which can be ...achieved through a bottom–up synthesis approach. This has recently been applied to the synthesis of width‐modulated GNRs hosting topological electronic quantum phases, with valence electronic properties that are well captured by the Su–Schrieffer–Heeger (SSH) model describing a 1D chain of interacting dimers. Here, ultralow bandgap GNRs with charge carriers behaving as massive Dirac fermions can be realized when their valence electrons represent an SSH chain close to the topological phase boundary, i.e., when the intra‐ and interdimer coupling become approximately equal. Such a system has been achieved via on‐surface synthesis based on readily available pyrene‐based precursors and the resulting GNRs are characterized by scanning probe methods. The pyrene‐based GNRs (pGNRs) can be processed under ambient conditions and incorporated as the active material in a field effect transistor. A quasi‐metallic transport behavior is observed at room temperature, whereas at low temperature, the pGNRs behave as quantum dots showing single‐electron tunneling and Coulomb blockade. This study may enable the realization of devices based on carbon nanomaterials with exotic quantum properties.
A new ultralow‐bandgap graphene nanoribbon consisting of covalently fused pyrene subunits is realized, whose charge carriers behave like massive Dirac fermions. The origin of the low bandgap derives from the periodically arranged molecular states of the pyrene units being in the limit of comparable intra‐ and inter‐Su–Schrieffer–Heeger (SSH)–dimer coupling and can be rationalized by the SSH model.
Atomically precise graphene nanoribbons (GNRs) are a promising emerging class of designer quantum materials with electronic properties that are tunable by chemical design. However, many challenges ...remain in the device integration of these materials, especially regarding contacting strategies. We report on the device integration of uniaxially aligned and non-aligned 9-atom wide armchair graphene nanoribbons (9-AGNRs) in a field-effect transistor geometry using electron beam lithography-defined graphene electrodes. This approach yields controlled electrode geometries and enables higher fabrication throughput compared to previous approaches using an electrical breakdown technique. Thermal annealing is found to be a crucial step for successful device operation resulting in electronic transport characteristics showing a strong gate dependence. Raman spectroscopy confirms the integrity of the graphene electrodes after patterning and of the GNRs after device integration. Our results demonstrate the importance of the GNR-graphene electrode interface and pave the way for GNR device integration with structurally well-defined electrodes.
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Bottom-up synthesis of graphene nanoribbons (GNRs) has significantly advanced during the past decade, providing various GNR structures with tunable properties. The synthesis of chiral GNRs, however, ...has been underexplored and only limited to (3,1)-GNRs. We report herein the surface-assisted synthesis of the first heteroatom-doped chiral (4,1)-GNRs from the rationally designed precursor 6,16-dibromo-9,10,19,20-tetraoxa-9a,19a-diboratetrabenzoa,f,j,operylene. The structure of the chiral GNRs has been verified by scanning tunneling microscopy, noncontact atomic force microscopy, and Raman spectroscopy in combination with theoretical modeling. Due to the presence of oxygen–boron–oxygen (OBO) segments on the edges, lateral self-assembly of the GNRs has been observed, realizing well-aligned GNR arrays with different modes of homochiral and heterochiral inter-ribbon assemblies.
Recent progress in the on-surface synthesis of graphene nanoribbons (GNRs) has given access to atomically precise narrow GNRs with tunable electronic band gaps which makes them excellent candidates ...for room temperature switching devices such as field-effect transistors (FET). However, in spite of their exceptional properties, significant challenges remain for GNR processing and characterization. This contribution addresses some of the most important challenges, including GNR fabrication scalability, substrate transfer, long-term stability under ambient conditions, and ex situ characterization. We focus on 7- and 9-atom-wide armchair graphene nanoribbons (i.e., 7-AGNR and 9-AGNR) grown on 200 nm Au(111)/mica substrates using a high throughput system. Transfer of both 7- and 9-AGNRs from their Au growth substrate onto various target substrates for additional characterization is accomplished utilizing a polymer-free method that avoids residual contamination. This results in a homogeneous GNR film morphology with very few tears and wrinkles, as examined by atomic force microscopy. Raman spectroscopy indicates no significant degradation of GNR quality upon substrate transfer and reveals that GNRs have remarkable stability under ambient conditions over a 24 month period. The transferred GNRs are analyzed using multiwavelength Raman spectroscopy, which provides detailed insight into the wavelength dependence of the width-specific vibrational modes. Finally, we characterize the optical properties of 7- and 9-AGNRs via ultraviolet–visible (UV–vis) spectroscopy.
Photodetectors utilizing graphene field‐effect transistors sensitized by colloidal quantum dots exhibit high responsivities under infrared light illumination. Precise, microscopic spatial control ...over quantum dot deposition is required to gain deeper insight into device mechanisms, optimize device performance, and enable new device architectures and applications. The latter may eventually include photodetectors with subwavelength device dimensions. Here, infrared photodetectors are fabricated by electrohydrodynamic nanoprinting of colloidal PbS quantum dots onto graphene field‐effect transistors with varying quantum dot layer thicknesses on a single substrate, demonstrating the potential of the method for realizing small footprint detectors with high spatial resolution. Remarkably, while the responsivity of the photodetectors increases with increasing layer thicknesses up to 130 nm, the noise current is found to be independent of the layer thickness. In addition, the responsivity and noise current are both linearly dependent on the applied drain voltage and drain current. As a result, the specific detectivity is independent of the drain voltage, and the detector can be operated at lower drain voltages thus reducing power consumption. Finally, specific detectivities of at least 109 Jones at 1200 nm are obtained, without degradation of the charge carrier mobilities in graphene from the electrohydrodynamic printing.
Novel device concepts for infrared light detection combine colloidal quantum dots with graphene field‐effect transistors thus avoiding sophisticated semiconductor growth technology. The development of electrohydrodynamic nanoprinting provides precise control over material deposition and is herein used in the device fabrication of colloidal PbS quantum dot–graphene field‐effect transistors for infrared light detection.
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