Graphene Nanofilms Research Articles

Multilayer Graphene/Epitaxial Silicon Near‐Infrared Self‐Quenched Avalanche Photodetectors

Abstract2D materials and their heterostructures exhibit considerable potential in the development of avalanche photodetectors (APDs) with high gain, response, and signal‐to‐noise ratio. These materials hold promise in addressing inherent technical challenges associated with APDs, such as low light absorption coefficient, elevated noise current, and substantial power consumption due to high bias resulting in only moderate current gain. In this work, a macro‐assembled graphene nanofilm (nMAG)/epitaxial silicon (epi‐Si) vertical heterostructure photodetector with a responsivity of 0.38 A W−1 and a response time of 1.4 µs is reported. The photodetectors use high‐quality nMAG as the absorption layer and a lightly‐doped epi‐Si layer as the multiplication region under the avalanche mode to provide a high responsivity (2.51 mA W−1) and detectivity (2.67 × 109 Jones) at 1550 nm, which can achieve high‐resolution imaging. In addition, the APD displays a weak noise level and an avalanche gain of M = 1123. It can work with relatively low avalanche turn‐on voltages and achieve self‐quenching by switching from illumination to dark during avalanche multiplication, with a real‐time data transfer rate of 38 Mbps in near‐infrared light communication data links. The proposed structure enables the fabrication of high‐performance APDs in the infrared range using complementary‐metal‐oxide‐semiconductor (CMOS)‐compatible processes.

Physical and Electrical Properties of Spray Coating Graphene Films: The Effect of Solution Concentration

Graphene nanofilms were deposited by the spray coating method at different concentrations (0.05, 0.1, 0.2, 0.3, 0.4, and 0.5 g) and prepared at 120°C. The prepared nanofilms were characterized in terms of their structural, morphological, optical, and electrical properties. The results confirm the formation of high-purity and high-crystallinity graphene nanofilms with a layered nanosheet morphology. The X-ray diffraction pattern shows the presence of pure graphene with (002) crystal planes. SEM Images show that the intended graphene films are symmetrical with few wrinkles on their surface. The graphene films show semi-transparent behavior with a maximum transmission of 50%. Raman spectroscopy shows that the relative intensity, position, and shape of the G and 2D Raman peaks change with the number of graphene layers. The electrical conductivity increases with temperature, and the conductivity can be further increased depending on the metal or metal oxide functionalization. The electrical conductivity of the graphene film deposited at a concentration of 0.3 g was significantly higher than the values reported for other concentrations. The results of this study suggest that the physical and electrical properties of spray-coated graphene films can be optimized by controlling the solution concentration, which could have potential applications in transparent conductive films.

Plasmon resonance-enhanced graphene nanofilm-based dual-band infrared silicon photodetector

Graphene-based photodetectors have attracted much attention due to their unique properties, such as high-speed and wide-band detection capability. However, they suffer from very low external quantum efficiency in the infrared (IR) region and lack spectral selectivity. Here, we construct a plasmon-enhanced macro-assembled graphene nanofilm (nMAG) based dual-band infrared silicon photodetector. The Au plasmonic nanostructures improve the absorption of long-wavelength photons with energy levels below the Schottky barrier (between metal and Si) and enhance the interface transport of electrons. Combined with the strong photo-thermionic emission (PTI) effect of nMAG, the nMAG–Au–Si heterojunctions show strong dual-band detection capability with responsivities of 52.9 mA/W at 1342 nm and 10.72 mA/W at 1850 nm, outperforming IR detectors without plasmonic nanostructures by 58–4562 times. The synergy between plasmon–exciton resonance enhancement and the PTI effect opens a new avenue for invisible light detection.

Flexible Large-Area Graphene Films of 50–600 nm Thickness with High Carrier Mobility

HighlightsLarge-area production of self-standing graphene nanofilm (~ 20 cm) through a clean ‘substrate replacement’ strategy.Realizing highly crystalline graphene nanofilms without micro-gasbags by introducing polymers.The graphene nanofilms demonstrate a solid light–matter interaction (photoelectric conversion in the mid-infrared and electromagnetic interference (EMI) shielding in X-band) with performance beyond state-of-the-art graphene/silicon diodes and EMI materials.

Construction of anti-swelling circuit board-like activated graphene oxide lamellar nanofilms with functionalized heterostructured 2D nanosheets

The assembly of 2D nanosheets into graphene nanofilm is attracting great interests because of their distinctive properties. However, it remains a big challenge to break through the unfixed interlayer channels caused by swelling for selective separation. In this study, novel activated graphene oxide lamellar nanofilms fixed by functionalized heterostructured MEA-C3N4 nanosheets with superior anti-swelling ability were successfully synthesized via post-synthesis activation (PSA) and alignment oriented slow deposition (AOSD). Different from traditional cross-linking by random packing, the structure-directed g-C3N4 nanosheets can not only be immobilized on activated GO to eliminate unstable interlayer structures by forming strong ionic and covalent bondings, but also act as building block to organize circuit board-like structure with highly interconnected microporosity by varying the thickness of electrical layer and the deposition rate. The strong interactions generated between building blocks reinforced the stability of interlayer sub-nanochannels and greatly suppressed swelling during cross-flow filtration for at least 120 h, in which the difference of interlayer spacing in dry condition and in water was as low as 0.2 Å. The prepared nanofilms with unique structure exhibited ultrahigh rejection (≥99.5%) toward low molecular weight organic matters. Meanwhile, due to the unique circuit board-like structure, very high water permeance (25.6 L m-2h-1 bar-1) and competitive rejection (91.0 %) for Na2SO4 were achieved, surpassing most reported GO-based or commercial nanofiltration membranes. Importantly, the permselectivity of constructed nanofilms can easily be adjusted by varying the space and type of intercalated nanosheets. The results indicate that this promising route will offer more opportunities in the synthesis of various 2D membranes with oriented structure for versatile applications.

Enhanced Electrical Conductivity and Tensile Strength of Cu/Single-Layer Graphene/Cu Nanomaterials

Copper (Cu) is widely used for electrical conduction but the inherent resistive heating not only wastes significant amounts of energy but also creates severe reliability issues; therefore, how to increase copper’s electrical conductivity has been a goal with a long history. Although nanometer-thin graphene has been regarded with great potential to increase copper’s conductive performance, published results are far from expectations and the quest remains about the actual enhancement efficiency of graphene. Here, we demonstrated that single-layer graphene in a Cu-sandwiched Cu/graphene/Cu composite structure fabricated by combining chemical vapor deposition (CVD) of graphene with magnetron sputtering deposition of copper can significantly increase annealed Cu’s electrical conductivity and strength at the same time. With a graphene content of less than 0.0008 vol % (a single-layer graphene sandwiched by 260 nm sputtering copper and 45 μm copper foil), the resultant electrical conductivity is about 110% of the annealed copper foil. In addition, the tensile strength is about 187% of the annealed copper. The converted enhancement efficiency per unit volume fraction of graphene is about a factor of 125 for the electrical conductivity and about a factor of 1096 for the tensile strength, respectively. The increased electrical conductivity and strength of Cu/graphene/Cu-sandwiched composite is attributed to the soundness of single-layer graphene obtained from the CVD growth, the graphene quality retention through the sputtering deposition process, and the good interfacial bonding formed between graphene and copper nanofilms that materializes band gap tuning by doping.

Recoverable Patterning of Macro-Assembled Graphene Nanofilms

Recoverable Patterning of Macro-Assembled Graphene Nanofilms

Structure formation and physical-mechanical properties of Al-Mg alloy with microadditions of graphene

Composites based on Al-Mg alloy, reinforced with graphene nanofilms, were obtained by in situ synthesis under a layer of salt melt. Using SEM and HRTEM, the morphological and dimensional characteristics of the structural components of composites with different contents of graphene were studied. An experiment on dynamic compression of composites by the Kolsky method was carried out, dynamic properties were measured, and the evolution of a cast structure during high-speed deformation was considered. For the first time, the dynamic properties of composites under loading by plane shock waves have been determined. The dynamic properties of aluminum matrix composites are compared depending on the properties of the non-reinforced alloy.

Defect-induced photocurrent gain for carbon nanofilm-based broadband infrared photodetector

Broad-spectrum detection and large-scale integration are the inevitable trends in the current evolution of infrared photodetectors. New materials were integrated with existing platforms to further improve the performance of infrared photodetectors. Here, we reported a defective macro-assembled graphene nanofilm (D-nMAG)/Silicon (Si) photodetector using trap-assisted gain to optimize the photoelectric response. This wafer-scale environmentally friendly carbon material can be easily compatible with the complementary-metal-oxide-semiconductor (CMOS) technical. Noteworthy, the defective states in D-nMAG trap carriers and then enter the conduction (CB) and valence band (VB) again to be thermalized, generating a gain in photocurrent. Thus, our D-nMAG-based line array image sensor exhibits high-resolution infrared imaging of the target. This device displays a high responsivity at room temperature within a broad-spectrum region, i.e., 0.156 A/W @ 900 nm in the near-infrared (NIR) region and 3.7 mA/W @ 4 μm in the mid-infrared (MIR) region. Our work provides a carbon nanofilm for IR detection at a broad-spectrum region, with tunable defective structure, uniform thickness, and wafer-scale production.

Macroscopic assembled graphene nanofilms based room temperature ultrafast mid‐infrared photodetectors

AbstractGraphene with linear energy dispersion and weak electron–phonon interaction is highly anticipated to harvest hot electrons in a broad wavelength range. However, the limited absorption and serious backscattering of hot‐electrons result in inadequate quantum yields, especially in the mid‐infrared range. Here, we report a macroscopic assembled graphene (nMAG) nanofilm/silicon heterojunction for ultrafast mid‐infrared photodetection. The assembled Schottky diode works in 1.5–4.0 μm at room temperature with fast response (20–30 ns, rising time, 4 mm2 window) and high detectivity (1.6 × 1011 to 1.9 × 109 Jones from 1.5 to 4.0 μm) under the pulsed laser, outperforming single‐layer‐graphene/silicon photodetectors by 2–8 orders. These performances are attributed to the greatly enhanced photo‐thermionic effect of electrons in nMAG due to its high light absorption (~40%), long carrier relaxation time (~20 ps), low work function (4.52 eV), and suppressed carrier number fluctuation. The nMAG provides a long‐range platform to understand the hot‐carrier dynamics in bulk 2D materials, leading to broadband and ultrafast MIR active imaging devices at room temperature.image

A highly effective and reusable platinum nanoblock based on graphene/ polyamino acid nanofilms for 4-nitrophenol degradation

To develop Pt nanomaterials with facile approach is of great significance for the improvement of their catalytic properties for organic pollutants degradation. In this study, we report a simple in-situ reduction strategy to prepare Pt nanoblocks based on graphene/ polyamino acid self-assembly nanofilms. Polyamino acid modified graphene nanofilms severed as the nanoreactor and reducing agent for further fabrication of Pt nanoblocks. The as-prepared complex efficiently transformed 4-nitrophenol into 4-aminophenol completely within 4.5 min (kapp is 0.962 min−1) and kept good long-term stability. We expect this work to offer a new valuable insight for facile preparation of Pt materials as efficient and recyclable catalysts for water pollution remediation.

Propagation and localization of phonons in graphite and graphene nanofilms

The nature of flexural rigidity of graphene monolayers and the formation of the quasi-flexural modes in graphite and graphene nanofilms is explained. It is shown, that in the major part of the band of quasi-continuous spectrum, quasi-flexural modes do not practically couple with the modes polarized in the plane of the layer. The frequencies of the propagone zone are determined for the phonons with various polarizations. The existence of a high-frequency propagation zone is demonstrated for quasi-flexural phonons. The conditions for the formation of quasi-local vibrations and boson peaks are analyzed for modes with different polarization. The conditions for the formation of the quasi-local vibrations and boson peaks in the modes of different polarization are analyzed.

Graphene Nanofilms/Silicon Near-Infrared Avalanche Photodetectors

Graphene/silicon Schottky junction diodes have been extensively studied and widely used in photodetection. However, limited to the low light absorption of single-layer graphene and bandgap of silicon, graphene/silicon devices exhibit low quantum efficiency in the infrared region. Here, we demonstrate a high-performance near-infrared Schottky diode by integrating silicon with the macroscopic assembled graphene nanofilms (nMAG). Because of the intense light absorption, low work function, and long carrier lifetime of nMAG, the device shows a detection spectra range up to 1870 nm with the responsivity of 0.4 mA/W and response speed of 371 ns. By driving the device into avalanche multiplication, 10⁴-10⁵ of avalanche gain has been obtained, and the responsivity at 1870 nm increases to 10 A/W. The device structure in this report could be compatible with the semiconductor process so that silicon-based infrared photodetectors with high performance and low cost could be potentially realized.

P-Si/Macro-Assembled Graphene/n-Si Heterojunction Near-Infrared Photodetector

p-type silicon (p-Si)/macro-assembled graphene nanofilm (nMAG)/n-type silicon (n-Si) heterojunction is utilized to fabricate near-infrared photodetector. Dual built-in electric fields were established in the same direction at the p-Si/nMAG and nMAG/n-Si heterojunctions, providing an enhanced electron-hole separation ability. The p-Si/nMAG/n-Si device has realized responsivities of 90 mA/W and 45 mA/W under 900 nm and 1064 nm illumination at room temperature and corresponding external quantum efficiency (EQE) of 11.8% and 5.2%, respectively, which is 30% and 45% higher than that of the single-junction nMAG/n-Si device. In this work, we applied two-dimensional (2D) carbon materials combined with monocrystalline silicon to explore complementary metal-oxide-semiconductor (CMOS) process-compatible device fabrication techniques, which paves the way to develop low-cost and large-scale near-infrared carbon-based photodetectors.

Multifunctional Macroassembled Graphene Nanofilms with High Crystallinity.

A "cooling-contraction" method to separate large-area (up to 4.2cm in lateral size) graphene oxide (GO)-assembled films (of nanoscale thickness) from substrates is reported. Heat treatment at 3000°C of such free-standing macroscale films yields highly crystalline "macroassembled graphene nanofilms" (nMAGs) with 16-48nm thickness. These nMAGs present tensile strength of 5.5-11.3GPa (with ≈3µm gauge length), electrical conductivity of 1.8-2.1 MS m-1 , thermal conductivity of 2027-2820 W m-1 K-1 , and carrier relaxation time up to ≈23ps. As a demonstration application, an nMAG-based sound-generator shows a 30 µs response and sound pressure level of 89dB at 1 W cm-2 . A THz metasurface fabricated from nMAG has a light response of 8.2% for 0.159 W mm-2 and can detect down to 0.01ppm of glucose. The approach provides a straightforward way to form highly crystallized graphene nanofilms from low-cost GO sheets.

Oil-water self-assembly engineering of Prussian blue/quantum dots decorated graphene film for wearable textile biosensors and photoelectronic unit

Integrating functional components into graphene film is crucial for taking full advantage of graphene and manufacturing film-based devices. However, most graphene film-based system acts specialized property with complicated fabricated process, limiting further application. Herein, a highly compatible graphene nanofilm, decorated by electroactive Prussian blue (PB) and photoelectric responsive quantum dots (QDs), has been prepared via a simple and effective oil-water (O/W) self-assembly engineering. Interestingly, this graphene film could be transferred on various substrates for flexible application. As a result, PB and QDs have played a synergic effect with reduced graphene oxide (rGO) matrix, respectively, acquiring both excellent electrochemical sensing behaviors and extremely enhanced photocurrent generation compared with pure QDs film under simulated solar light. Furthermore, impressive biosensing performance has been obtained by enzyme-modified PB-rGO-QDs film. Additionally, proposed film-based wearable textile H2O2 sensor possesses high sensitivity of 53.8 µA mM−1 cm−2, while developed wearable glucose biosensor exhibits good performance, with a sensitivity of 37.24 µA mM−1 cm−2. Significantly, wearable devices of PB-rGO-QDs films on textile have established flexible bending lifetime over thousands of cycles, accompanying with stable sensor and photoelectronic properties. Prospectively, PB-rGO-QDs films would provide an efficient strategy of multi-components self-assembly for broadening the application of graphene and developing wearable biosensing/photoelectronic devices.

Confined assembly of ultrathin nanoporous nitrogen-doped graphene nanofilms with dual metal coordination chemistry

SummaryGraphene oxide (GO) nanosheets with unique structure have received much attention in providing opportunity for high-performance membranes in separation. However, the rational design of ultrathin graphene membranes with controlled structures remains a big challenge. Here, we report a methodology to synthesize dual metal-coordinated ultrathin nanoporous graphene nanofilms by tailoring well-aligned nanocrystals as building blocks on heteroatom-doped GO nanosheets with tunable architectures. Manipulation of metal nitrate as bifunctional dopants realizes N-doping of graphene oxide and preferential growth of α-Mn2O3 nanocrystals. Generation of Mn-O-C bond during cross-linking greatly strengthens the stability of membranes for long-term steady operation. Meanwhile, because of spatial confinement effects and high binding energy, N-doped reduced GO nanosheets are desirable supports to construct numerous Mn-N-C bonds, thus generating artificial nanopores to significantly increase nanochannels for ultrafast mass transport. Moreover, the size-selective permeability of ultrathin nanoporous GO-based nanofilms can be optimized by managing the types of metal source for target coordination.

Low dimensional features of graphene nanostructure stability and vibrational characteristics (Review)

The densities of phonon states and their related vibrational thermodynamic characteristics, such as heat capacity, root-mean-square displacement of atoms, and thermal expansion, are calculated and analyzed at the microscopic level for graphite and graphene nanoformations, such as nanofilms and nanotubes. The simulation model is based on experimental data without a priori assumptions as to the nature and potentials of interatomic interactions, and is compared to them only after, which yields a good agreement. The quasi-flexural and torsional modes, which are inherent to graphene nanotubes, are considered and their contribution to the low temperature vibrational characteristics are analyzed. The impact that extended defects, such as graphite intercalation with transition metals, step-edges on graphene nanofilms, and edges of a graphene single layer on a substrate, have on the phonon spectrum and vibrational characteristics is analyzed. The calculated results are compared to the experimental data.

Solid–Liquid Interdiffusion Bonding of Cu–Sn–Cu Interconnection and Sealing for High-Temperature Pressure Sensor Based on Graphene

Cu–Sn–Cu solid–liquid interdiffusion (SLID) bonding for high-temperature pressure sensors based on graphene has been investigated. Square bumps with a length of $160~\mu \text{m}$ and an 80- $\mu \text{m}$ -wide sealing ring were simultaneously fabricated by the evaporation process. The die surface was treated with Ar (5% H2) plasma before bonding. Chip-level bonding was performed at 260 °C for 15 min with a pressure of 9.13 MPa under N2 atmosphere. Pure Sn and Cu6Sn5 have been exhausted completely, and the as-bonded interface only contains three layers of Cu–Cu3Sn–Cu, with no serious Sn overflow. The average shear strength of 50.6 MPa and an excellent leak rate of around 2.64 $\times 10^{-4}$ Pa $\cdot $ cm3/s are achieved. The resistance measurements are similar to the theoretical estimation. After high-temperature storage (HTS) at 300 °C for 10 h, the average shear strength slightly decreases to 46.7 MPa and the leak rate increases to 1.01 $\times 10^{-3}$ Pa $\cdot $ cm3/s. More importantly, there is no degeneration of the graphene nanofilm during electrical measurement in the bonding process and HTS test. It is concluded that Cu–Sn–Cu SLID bonding is appropriate for high-temperature pressure sensors based on graphene.

Synthesis and Characteristics of Polyaniline (PANI) Filled by Graphene (PANI/GR) nano-Films

In this research polyaniline (PANI) was synthesized by using chemical oxidative polymerization method. The structural properties of polyaniline nano films pure and filled by graphene (GR) at different weight percentage of graphene like (1%, 3% and 5%) were investigated. The nano films prepared by using spin coating technique and deposited on glass substrate at room temperature. The structural and surface morphology of the nano films are evaluated by FT-IR, XRD and AFM. The results showed that FT-IR spectra of pure PANI is similar to tha spectra of PANI/GR composites, While the results of XRD singular that the PANI has amorphous nature, As well as the results of AFM for all nano films of pure PANI and filled by graphene(PANI/GR) composites showed that Roughness average (Ra), Root mean square (Rms) value and average grain size (G.S) increase with increasing addition of GR ratio.