A novel approach to leverage the extraordinary properties of graphene for designing thin film strain sensors is demonstrated. Graphene nanosheets (GNS) are produced from graphite by a liquid phase exfoliation (LPE) method using water along with
Liquid-phase exfoliation (LPE) is a promising and scalable technique to produce low-cost dispersible nanosheets of graphene and nano-graphite for electronic, optoelectronics, and photonics applications. Fundamental information about how LPE affects the electrical properties is lacking. Here, a relationship is provided between the morphology of nano-graphite flakes resulting from LPE and cascade centrifugation to the charge-carrier transport properties. A range of process parameters, such as centrifuge force and exfoliation solvent, are employed, leading to a range of flake sizes. Morphology is characterized by scanning electron microscopy, atomic force microscopy and optical profilometry. Raman spectroscopy is used to confirm morphology, crystallite size, and chemical properties. Terahertz time-domain spectroscopy with a Drude-Smith conduction model provides the charge-carrier concentration and scattering times from AC conductivity. Carrier concentration increases with a reduction in flake area, potentially resulting from the introduction of electronic defect states at the edge of the nano-crystallites. Meanwhile, the carrier scattering time decreases with decreased flake size, similarly due to this self-doping that increases the carrier-carrier scattering. The approach and results serve as a foundation for understanding the processing-dependent electrical characteristics of LPE flakes and nanosheets.
more » « less- NSF-PAR ID:
- 10488467
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optical Materials Express
- Volume:
- 14
- Issue:
- 2
- ISSN:
- 2159-3930
- Format(s):
- Medium: X Size: Article No. 505
- Size(s):
- ["Article No. 505"]
- Sponsoring Org:
- National Science Foundation
More Like this
-
Printed Strain Sensors Using Graphene Nanosheets Prepared by Water‐Assisted Liquid Phase Exfoliationmore » « less
Abstract N ‐methylpyrrolidinone (NMP) as cosolvents. It is found that the water‐NMP solvent system enhances the exfoliation yield and the stability of the GNS dispersion, thereby lowering the number of defects in the GNS basal plane. Both LPE‐based GNS and reduced graphene oxide (RGO) are synthesized for fabricating thin film strain sensors and for comparison purposes. Detailed micro‐Raman, X‐ray photoelectron spectroscopy, and transmission electron microscopy studies indicate that the as‐produced GNS exhibits lower defects than RGO nanosheets. The strain sensing study reveals that strain sensors fabricated using low‐defect GNS exhibit enhanced electrical and electromechanical properties, including higher electrical conductivity, lower noise floor, and more stable electromechanical response as compared to RGO‐based sensors. -
α-RuCl3 is a layered transition metal halide that possesses a range of exotic magnetic, optical, and electronic properties including fractional excitations indicative of a proximate Kitaev quantum spin liquid (QSL). While previous reports have explored these properties on idealized single crystals or mechanically exfoliated samples, the scalable production of α-RuCl3 nanosheets has not yet been demonstrated. Here, we perform liquid-phase exfoliation (LPE) of α-RuCl3 through an electrochemically assisted approach, which yields ultrathin, electron-doped α-RuCl3 nanosheets that are then assembled into electrically conductive large-area thin films. The crystalline integrity of the α-RuCl3 nanosheets following LPE is confirmed through a wide range of structural and chemical analyses. Moreover, the physical properties of the LPE α-RuCl3 nanosheets are investigated through electrical, optical, and magnetic characterization methods, which reveal a structural phase transition at 230 K that is consistent with the onset of Kitaev paramagnetism in addition to an antiferromagnetic transition at 2.6 K. Intercalated ions from the electrochemical LPE protocol favorably alter the optical response of the α-RuCl3 nanosheets, enabling large-area Mott insulator photodetectors that operate at telecommunications-relevant infrared wavelengths near 1.55 μm. These photodetectors show a linear photocurrent response as a function of incident power, which suggests negligible trap-mediated recombination or photothermal effects, ultimately resulting in a photoresponsivity of ≈2 mA/W.more » « less
-
Liquid phase exfoliation (LPE) is a method that can be used to produce bulk quantities of two-dimensional (2D) nanosheets from layered van der Waals (vdW) materials. In recent years, LPE has been applied to several non-vdW materials with anisotropic bonding to produce nanosheets and platelets, but it has not been demonstrated for materials with strong isotropic bonding. In this paper, we demonstrate the exfoliation of boron carbide (B 4 C), the third hardest known material, into ultrathin nanosheets. B 4 C has a structure consisting of strongly bonded boron icosahedra and carbon chains, but does not have anisotropic cleavage energies to suggest that it can be readily cleaved into nanosheets. B 4 C has been widely studied for its very high melting point, high mechanical strength, and chemical stability, as well as its zero- and one-dimensional nanostructured forms. Herein, ultrathin nanosheets are successfully prepared by sonication of B 4 C powder in organic solvents and are characterized by microscopy and spectroscopy. Density functional theory (DFT) simulations reveal that B 4 C can be cleaved along several different crystallographic planes with similar energetic favourability, facilititated by an unexpected mechanism of breaking boron icosahedra and forming new boron-rich cage structures at the surface. Atomic force microscopy (AFM) shows that the nanosheets produced by LPE are as thin as 5 nm, with an average thickness of 31.4 nm and average area of 16 000 nm 2 . Raman spectroscopy shows that many of the nanosheets exhibit additional carbon-rich peaks that change with laser irradiation, which are attributed to atomic rearrangements and amorphization at the nanosheet surfaces, consistent with the diverse cleavage planes. High-resolution transmission electron microscopy (HRTEM) demonstrates that many different cleavage planes exist among the exfoliated nanosheets, in agreement with DFT simulations. This work elucidates the exfoliation mechanism of 2D B 4 C and suggests that LPE can be applied to generate nanosheets from a variety of non-layered and non-vdW materials.more » « less
-
more » « less
Abstract The thermoelectric properties of semiconducting polymers are influenced by both the carrier concentration and the morphology that sets the pathways for charge transport. A combination of optical, morphological, and electrical characterization is used to assess the effect of the role of disorder on the thermoelectric properties of thin films of poly(3‐hexylthiophene) (P3HT) doped with 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ). Controlled morphologies are formed by casting blends of regioregular (RR‐P3HT) and regiorandom (RRa‐P3HT) and then subsequently doped with F4TCNQ from the vapor phase. Optical spectroscopy and X‐ray scattering show that vapor phase doping induces order in the disordered regions of thin films and increases the long‐range connectivity of the film. The thermoelectric properties are assessed as a function of composition and it is shown that while the Seebeck coefficient is affected by structural ordering, the electrical conductivity and power factor are more strongly correlated with the long‐range connectivity of ordered domains.
-
more » « less
Abstract Few‐layer black phosphorus (BP) has emerged as one of the most promising candidates for post‐silicon electronic materials due to its outstanding electrical and optical properties. However, lack of large‐scale BP thin films is still a major roadblock to further applications. The most widely used methods for obtaining BP thin films are mechanical exfoliation and liquid exfoliation. Herein, a method of directly synthesizing continuous BP thin films with the capability of patterning arbitrary shapes by employing ultrafast laser writing with confinement is reported. The physical mechanism of confined laser metaphase transformation is understood by molecular dynamics simulation. Ultrafast laser ablation of BP layer under confinement can induce transient nonequilibrium high‐temperature and high‐pressure conditions for a few picoseconds. Under optimized laser intensity, this process induces a metaphase transformation to form a crystalline BP thin film on the substrate. Raman spectroscopy, atomic force microscopy, and transmission electron microscopy techniques are utilized to characterize the morphology of the resulting BP thin films. Field‐effect transistors are fabricated on the BP films to study their electrical properties. This unique approach offers a general methodology to mass produce large‐scale patterned BP films with a one‐step manufacturing process that has the potential to be applied to other 2D materials.
