The lack of a sizeable band gap has so far prevented graphene from building effective electronic and optoelectronic devices despite its numerous exceptional properties. Intensive theoretical research reveals that a band gap larger than 1 eV can only be achieved in sub-3 nm wide graphene nanoribbons (GNRs), but real fabrication of such ultranarrow GNRs still remains a critical challenge. Herein, we demonstrate an approach for the synthesis of ultranarrow and photoluminescent semiconducting GNRs by longitudinally unzipping single-walled carbon nanotubes. Atomic force microscopy reveals the unzipping process, and the resulting 2.2 nm wide GNRs are found to emit strong and sharp photoluminescence at ∼685 nm, demonstrating a very desirable semiconducting nature. This band gap of 1.8 eV is further confirmed by follow-up photoconductivity measurements, where a considerable photocurrent is generated, as the excitation wavelength becomes shorter than 700 nm. More importantly, our fabricated GNR field-effect transistors (FETs), by employing the hexagonal boron nitride-encapsulated heterostructure to achieve edge-bonded contacts, demonstrate a high current on/off ratio beyond 105 and carrier mobility of 840 cm2/V s, approaching the theoretical scattering limit in semiconducting GNRs at room temperature. Especially, highly aligned GNR bundles with lengths up to a millimeter are also achieved by prepatterning a template, and the fabricated GNR bundle FETs show a high on/off ratio reaching 105, well-defined saturation currents, and strong light-emitting properties. Therefore, GNRs produced by this method open a door for promising applications in graphene-based electronics and optoelectronics.

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We fabricated electrochemical metallization cells using a GaLaSO solid electrolyte, an InSnO inactive electrode and active electrodes consisting of various metals (Cu, Ag, Fe, Cu, Mo, Al). Devices with Ag and Cu active metals showed consistent and repeatable resistive switching behaviour, and had a retention of 3 and >43 days, respectively; both had switching speeds of <5 ns. Devices with Cr and Fe active metals displayed incomplete or intermittent resistive switching, and devices with Mo and Al active electrodes displayed no resistive switching ability. Deeper penetration of the active metal into the GaLaSO layer resulted in greater resistive switching ability of the cell. The off-state resistivity was greater for more reactive active metals which may be due to a thicker intermediate layer.

Seebeck measurements of n-type amorphous germanium telluride thin films (100 nm) containing oxygen and implanted with Bismuth (Bi) have been studied under dark and monochromatic light conditions from 1800 to 400 nm. The Bi-doped film has a negative Seebeck coefficient indicating its n-type nature that results from the implantation compared to the p-type undoped films. Upon illumination with monochromatic light across the near-infrared and visible region the magnitude of the measured Seebeck voltage increases (becomes more negative). This increase in Seebeck coefficient displays distinctive behaviours in different spectral regions and is caused by the inclusion of Bi ions as foreign impurities. Furthermore, the Seebeck coefficients are used to determine the film electrical properties and enable, along with complementary characterisation including X-ray photoelectron spectroscopy, electronic band diagrams to be proposed for before and after Bi ion implantation. The photo-Seebeck technique is utilised for the first time to probe the trap states created due to the implantation, providing an understanding of the mechanisms behind non-equilibrium carrier-type reversal in an amorphous system, including the modification of electronic and optoelectronic properties such as the optical bandgap.

The measurement of the Seebeck coefficient of thin film (100 nm) amorphous germanium telluride containing ~ 31% oxygen under dark conditions and when exposed to monochromatic light in the 400 nm to 1800 nm wavelength region is reported. Exposure of the films to light is found to reduce the absolute value of the Seebeck coefficient compared to that measured in the dark. Furthermore, the magnitude of this reduction displays a distinctive spectral dependence over the wavelength range covered. The observed behaviour suggests that these measurements provide a method determining the optical bandgap of thin amorphous chalcogenide films. Further analysis of the data, along with that of X-ray photoelectron spectroscopy and photoconductivity studies, is used to determine the presence of sub-bandgap defect states and their role in determining the optical response of the Seebeck coefficient.