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Tunable Phase Shifter Based on Few-Layer Graphene Flakes
摘要： This letter presents a voltage-controlled tunable phase shifter based on few-layer graphene. The phase shifter consists of a stub-loaded line, composed of a microstrip line with a stub attached to it through a taper and graphene pad. The bias voltage applied to the graphene pad determines a variation of graphene resistance, which eventually causes the phase change. Without any voltage bias, graphene exhibits high resistance, thus isolating the stub and leading to a low phase shift. As the bias voltage is increased, graphene resistance is lowered, the effect of the stub is more pronounced, and the phase shift is increased. A prototype operating in the frequency range from 5 to 6 GHz has been designed and tested. The measured maximum phase shift obtained is 40°, and the corresponding degradation of the insertion loss is 3 dB.
关键词： tunable microwave devices,graphene,phase shifter,Few-layer graphene
更新于2025-09-23 15:22:29
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Graphite to Graphene: Green Synthesis Using Opuntia ficus-indica
摘要： Green synthesis promotes partial or total substitution of chemicals that are potentially harmful to the environment with more friendly ones and is also concerned with decreasing energy consumption. In this study, commercial graphite (1.0 g) was mixed with Opuntia ficus-indica (Ofi) (1.0 ml) and 50 ml deionized water in a glass beaker. The mixture was sonicated in an ultrasonic bath for 30 min at room temperature. Subsequently, the supernatant was transferred to a glass substrate and dried. To characterize the graphitic nanostructure, we used Raman spectroscopy, x-ray diffraction (XRD) analysis, x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). Raman spectroscopy was used to characterize the crystal structure. The ratio of the relative intensity of the G and 2D peaks in the Raman spectrum followed by deconvolution of the 2D band suggested that four and five layers of graphene were formed. The XRD profile showed a strong decrease in the (002) peak intensity with a thickness of 0.34 nm characterizing the graphite structure. The C:O ratio measured by XPS showed a degree of oxidation comparable to reports on few-layer graphene (FLG), and AFM images showing the roughness of the sheets revealed small steps of 1 nm with length of about 100 nm. Structural and morphological properties were analyzed by TEM. We found thin graphene layers of about one micron in extent; at 10-nm scale, structures of two, three, four, and five layers were identified. These results suggest that this method can be used for synthesis of FLG via an environmentally friendly route without use of acids or strong chemical oxidants.
关键词： few-layer graphene,sonication,Opuntia ficus-indica,Green synthesis
更新于2025-09-19 17:15:36
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - The Highly Tunable Graphene Ring Modulator
摘要： We propose a ring modulator based on few-layer graphene. The shift of resonance wavelength can be enlarged to 20.3 nm and a large extinction ratio of 15.5 dB can be obtained.
关键词： Few-layer graphene,Ring modulator,Large tunability
更新于2025-09-16 10:30:52
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Morphology-selective preparation and formation mechanism of few-layer graphene on Cu substrate by liquid-phase pulsed laser ablation
摘要： This paper presented a morphology-selective preparation and formation mechanism of few-layer graphene (FLG) on a Cu substrate by pulsed laser ablation in liquid. It is a simple and controllable route to grow FLG directly on the surface of a copper foil at ambient temperature and normal pressure, which does not need other precursor materials. FLG with 3–10 layers of thickness and continuous hundreds of micrometers in lateral size is obtained. The morphology and structure of FLG were investigated by using a Raman spectrometer, scanning electron microscope, high-resolution transmission electron microscope, and atomic force microscope. The formation mechanism of FLG and the role of the plasma-produced carbon species are put forward based on the interaction between the laser, material, and substrate. Our finding, the direct deposition of FLG on the Cu substrate by pulsed laser ablation in liquid, will open a door to apply this green route to the production of FLG with controlled morphology.
关键词： formation mechanism,Cu substrate,morphology-selective preparation,few-layer graphene,liquid-phase pulsed laser ablation
更新于2025-09-16 10:30:52
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The Electrical Property of Large Few Layer Graphene Flakes Obtained by Microwaves Assisted Exfoliation of Expanded Graphite
摘要： Few layer graphene (FLG) was synthesized by (cid:2)-wave assisted exfoliation of expanded graphite in toluene with an overall yield from c.a. 7% to 20%. A significant difference in the absorption of (cid:2)-waves by the expanded graphite and toluene allowed a rapid heating of the medium. The number of FLG sheets varies from 3 to 12, while the lateral size of the sheets exceeds few (cid:2)ms. The obtained FLG exhibits very low resistance with average value of 1.6 k(cid:3) (500 (cid:3) minimum) which is comparable to that of high quality graphenes synthesized by CVD methods, and lower than numbers of exfoliated graphenes.
关键词： (cid:2)-waves,electrical properties,expanded graphite,few layer graphene,resistance.,liquid exfoliation
更新于2025-09-11 14:12:44
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Direct Liquid Phase Exfoliation of Graphite to Produce Few-Layer Graphene by Microfluidization
摘要： Graphene has attracted a great number of attentions due to the excellent physical and chemical properties. For the convenience of investigations and applications, it is crucial to produce the grapheme with high-quality and high-yield by an easy-obtained method. In this research, a promising method is demonstrated to produce a high-concentration few-layer graphene (FLG) dispersion by direct micro?uidization in water/surfactant systems. The effects of surfactant selection, chamber pressure and micro?uidization cycles on the graphitic material exfoliation ef?ciency are systematically studied. The FLG concentration and the quality of the as-prepared FLG were determined by a series of characterizations. The graphene dispersions, with an average lateral size of 0.6 (cid:2)m and a few-layer structure, were stabilized by surfactants at a high concentration of up to 1.7 mg/mL and = 0.07–0.56, C/O ～ 19(cid:3)36) within a processing time of a few hours. This method should facilitate the mass production of high-quality graphene by liquid-phase exfoliation and promote the industrial application of graphene.
关键词： High Concentration,Few-Layer Graphene,Micro?uidization,Liquid Phase Exfoliation,Aqueous Graphene Dispersion
更新于2025-09-09 09:28:46
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Structure stability of few-layer graphene under high electric field
摘要： The stability of material structure is the key factor to determine its service capacity and lifetime. The structure evolution of vertical few-layer graphene (FLG) under high electric field was directly observed in situ TEM. The structure stability of FLG depends on its crystallinity and edge morphology. The vertical FLG without pinhole defects can sustain an electrostatic field beyond 58.5 V/nm. The vertical FLG with pinhole defects disintegrated from top to bottom due to field evaporation and the critical electrostatic field weaken to 17.4 V/nm. The vertical FLG with curly layer perpendicular to the electric field stretched and slid at the edge due to the layer sliding and the critical fracture electrostatic field of it was low to 7.5 V/nm which is an order of magnitudes small than that of the curly layer parallel to the electrostatic field of 24.7 V/nm. Those results were the first direct observation of the nano-structure evolution of FLG under high electric field. It helps to understand the deterioration mechanism of FLG under high electric field in free space and provides guidance for the high electric field applications such as field electron emitter and scanning tunneling microscopy.
关键词： Few-layer graphene,Layer sliding,Field evaporation,Structure stability,High electric field
更新于2025-09-04 15:30:14