Hongbing Zhan

Giant optical limiting effect in Ormosil gel glasses doped with graphene oxide materials

Graphene materials have attracted interest in the field of optical limiting because of their outstanding linear and nonlinear optical (NLO) properties. However, poor solubility and agglomeration have limited the practical applications of these materials. Here, hydrophilic graphene oxide materials, including graphene oxide nanosheets (GONSs) and graphene oxide nanoribbons (GONRs) are synthesized. Using a facile sol–gel process, GONSs and GONRs are introduced into a methyltriethoxysilane modified silicate (Ormosil) glass matrix. NLO and optical limiting (OL) properties are investigated using a nanosecond Z-scan technique at 532 nm. Large OL effects of Ormosil hybrid glasses are revealed, whose optical limiting thresholds (Fth = ∼0.03 J cm−2) surpass those of corresponding suspensions by a factor of 5–20. We deduce that this behavior is mostly attributed to the combined mechanisms of nonlinear scattering and nonlinear absorption. The hybrid glasses are free of damage after hundreds of continuous laser shots with an energy of 800 μJ. These results indicate that Ormosil hybrid glasses doped with graphene oxide materials could be promising candidates for optical limiters.

Enhanced nonlinear optical properties of nonzero-bandgap graphene materials in glass matrices

The third-order nonlinear optical (NLO) properties of the nonzero-bandgap graphene materials, including graphene oxide nanosheets, graphene oxide nanoribbons, graphene quantum dots, and corresponding hybrid glasses, were investigated using ns and ps Z-scan techniques at 532 nm. The observed nonlinear absorption effects were affected by laser duration. Reverse saturable absorption was observed in the ns regime, while saturable absorption dominated in the ps regime. The NLO performance was enhanced in the hybrid glasses. These findings open up new possibilities for the practical application of graphene materials in the NLO field.

Enhanced optical limiting effects of graphene materials in polyimide

Three different graphene nanostructure suspensions of graphene oxide nanosheets (GONSs), graphene oxide nanoribbons (GONRs), and graphene oxide quantum dots (GOQDs) are prepared and characterized. Using a typical two-step method, the GONSs, GONRs, and GOQDs are incorporated into a polyimide (PI) matrix to synthesize graphene/PI composite films, whose nonlinear optical (NLO) and optical limiting (OL) properties are investigated at 532 nm in the nanosecond regime. The GONR suspension exhibits superior NLO and OL effects compared with those of GONSs and GOQDs because of its stronger nonlinear scattering and excited-state absorption. The graphene/PI composite films exhibit NLO and OL performance superior to that of their corresponding suspensions, which is attributed primarily to a combination of nonlinear mechanisms, charge transfer between graphene materials and PI, and the matrix effect.

Broadband nonlinear optical and optical limiting effects of partially unzipped carbon nanotubes

Many studies have shown that both carbon nanotubes (CNTs) and graphene are important broadband nonlinear optical (NLO) and optical limiting (OL) materials. As hybrids of CNTs and graphene, partially unzipped carbon nanotubes (PUCNTs) can be expected to exhibit superior NLO and OL effects. In this work, PUCNTs were obtained through lengthwise cutting and unraveling of multi-walled carbon nanotubes. The structure and component of PUCNTs were confirmed by transmission electron microscopy, scanning electron microscopy, powder X-ray diffraction, Fourier-transform infrared and Raman spectra. NLO and OL properties were investigated by the Z-scan technique at both 532 and 1064 nm in the nanosecond regime, in comparison with CNTs and graphene. A remarkable enhancement was observed, which can be attributed to the synergistic effect of nonlinear scattering and nonlinear absorption.

Carbon Nanotubes with Tailored Density of Electronic States for Electrochemical Applications

The density of electronic states (DOS) is an intrinsic electronic property that works conclusively in the electrochemistry of carbon materials. However, seldom has it been reported how the DOS at the Fermi level influences the electrochemical activity. In this work, we synthesized partially and fully unzipped carbon nanotubes by longitudinally unzipping pristine carbon nanotubes (CNTs). We then studied the electrochemical activity and biosensitivity of carbon materials by means of the CNTs and their derivatives to elucidate the effect of the DOS on their electrochemical performances. Tailoring of the DOS for the CNT derivatives could be conveniently realized by varying the sp(2)/sp(3) ratio (i.e., graphite concentration) through manipulating the oxidative unzipping degree. Despite the diverse electron transfer mechanisms and influence factors of the four investigated redox probes (IrCl6(2-), [Fe(CN)6](3-), Fe(3+), and ascorbic acid), the CNT derivatives exhibited consistent kinetic behaviors, wherein CNTs with a high DOS showed superior electrochemical response compared with partially and fully unzipped carbon nanotubes. For biological detection, the CNTs could simultaneously distinguish ascorbic acid, dopamine, and uric acid, while the three CNT derivatives could all differentiate phenethylamine and epinephrine existed in the newborn calf serum. Moreover, the three CNT derivatives all presented wide linear detection ranges with high sensitivities for dopamine, phenethylamine, and epinephrine.

Electric field-modulated data storage in bilayer InSe

Recently, due to the unexpectedly high carrier mobility and strongly suppressed recombination of electron–hole pairs, exfoliated atomically thin InSe has exhibited potential applications in nanoscaled electronic devices. In this study, via first-principle calculations, we have systematically investigated the crystal and electronic structures of bilayer InSe with different stacking configurations. Interestingly, the five possible stacking configurations of bilayer InSe can be categorized into two groups: Group-S with a shorter vdW interlayer distance and smaller band gap and Group-L with a longer vdW interlayer distance and larger band gap. It is highlighted that the indirect band gap bilayer InSe can be transformed into its metallic type. We have unraveled that the electronic origin of the band gap transition is derived from the electric field-induced near free-electron gas. Furthermore, a prototype data storage device based on the bilayer InSe has been proposed; this study will shed light on the design and application of bilayer InSe as well as two-dimensional material-based electronic devices in the future.

Dendritic unzipped carbon nanofibers enable uniform loading of surfactant-free Pd nanoparticles for the electroanalysis of small biomolecules

In this study, graphene nanofibers (GNF), which are a superior support material, are successfully synthesized via the dendritic unzipping of stacked-cup carbon nanofibers (SCNF). Ultrasmall Pd nanoparticles are uniformly dispersed on the GNF (Pd/GNF) via chemical reduction under mild conditions without any surfactant involved. The components and structure of Pd/GNF are evaluated via scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), Raman spectra and X-ray photoelectron spectroscopy (XPS). The characterization results indicate that the Pd nanoparticles have a uniform size of 3-6 nm without significant aggregation and the overall Pd content is about 11.2 wt% in the Pd/GNF composite. Moreover, a modified electrochemical sensor based on the Pd/GNF composite is successfully fabricated. In the two investigated redox probes (IrCl6 2- and [Fe(CN)6]3-), Pd/GNF shows a superior electrochemical response compared to the Pd nanoparticles loaded on SCNF and bare glass carbon electrode. For the detection of small biomolecules, Pd/GNF could individually or simultaneously detect ascorbic acid (AA), dopamine (DA) and uric acid (UA) through differential pulse voltammetry. The linear concentration ranges of UA, DA and AA are 0.1-1200 μM, 1-180 μM and 0.1-6000 μM, respectively.