Qi-Dai Chen

Common Origin of Green Luminescence in Carbon Nanodots and Graphene Quantum Dots

Carbon nanodots (C-dots) synthesized by electrochemical ablation and small molecule carbonization, as well as graphene quantum dots (GQDs) fabricated by solvothermally cutting graphene oxide, are three kinds of typical green fluorescence carbon nanomaterials. Insight into the photoluminescence origin in these fluorescent carbon nanomaterials is one of the important matters of current debates. Here, a common origin of green luminescence in these C-dots and GQDs is unraveled by ultrafast spectroscopy. According to the change of surface functional groups during surface chemical reduction experiments, which are also accompanied by obvious emission-type transform, these common green luminescence emission centers that emerge in these C-dots and GQDs synthesized by bottom-up and top-down methods are unambiguously assigned to special edge states consisting of several carbon atoms on the edge of carbon backbone and functional groups with C═O (carbonyl and carboxyl groups). Our findings further suggest that the competition among various emission centers (bright edge states) and traps dominates the optical properties of these fluorescent carbon nanomaterials.

Curvature‐Driven Reversible In Situ Switching Between Pinned and Roll‐Down Superhydrophobic States for Water Droplet Transportation

Artifi cial superhydrophobic surfaces [ 1–10 ] with water contact angles (CAs) greater than 150 ° have been intensively investigated due to their unique “anti-water” property that could be utilized in a wide range of applications. [ 11–13 ] Recent development of intelligent devices, such as microfl uidic switches and biomedicine transporters, makes strong demands on surface wettability control, therefore, responsive surfaces have become a signifi cant issue for superhydrophobic studies. Up to now, various smart surfaces have been successfully developed as reversible switches for wettability control through a micronanostructured surface on a responsive material. [ 14–25 ] These unique tunings of surface wettability greatly contributed to refi ned control of surface wettability. With the thorough understanding of superhydrophobic phenomenon, superhydrophobic surfaces have been classifi ed into fi ve states [ 26 ] according to the details of CA hysteresis, which have been well verifi ed on different samples based on experimental results. [ 1 , 8 , 27–29 ]

Ferrofluids for Fabrication of Remotely Controllable Micro‐Nanomachines by Two‐Photon Polymerization

Miniaturized smart machines with micro-nanometer sized moving parts have now been utilized for on-site, in vivo sensing, monitoring, analysis and treatment in narrow enclosure, harsh environment, and even inside human body. [ 1–10 ] Despite the fact that a vast majority of currently available micromachines are produced with silicon by lithography, represented by Si: MEMS (silicon microelectromechanical systems) technique, a recent trend of the fi eld resorts to polymers. [ 11 ] As a designable three-dimensional micro-nanoprocessing method, two-photon photopolymerization (TPP) of photopolymers provides a novel route for fabricating micro-nanomechines with higher spatial resolution and smaller size. [ 12–14 ] However, introduction of driven force to these tiny devices for precise micro-manipulation constitutes the main problem for the advanced applications of these micro-nanomachines, for example, remote control is indispensable for intelligent micromachine that may be placed in blood vessels for health care. It is therefore of great importance to fi nd novel fabricative and driven techniques for making functional micronanomachines with precise motion control. Magnetic force drive technique which has been widely applied in macroscopical instruments would be an ideal method for remote control due to its simple, mind, safe and non-contact properties. [ 15–18 ] However, up to now, magnetic force is still not properly applied to remote control of micro-nanomachines for accomplishing desired task. Possible reason for this gap would be the lack of nanotechnology of appending magnetic components to existing micro-nanomachines, or to photopolymer precursors for laser fabrication. Generally, magnetic components such as nanoparticles which usually behave inorganic properties are really diffi cult to be introduced into polymeric carriers in a highly dispersed, largely doped fashion without signifi cant phase separation. [ 19 ] If magnetic nanomaterials can be homogeneously, largely and stably embedded in photopolymerizable resin through a simple method, magnetic force controllable micro-nanomachines would be fabricated accordingly.

Time-resolved fluorescence study of aggregation-induced emission enhancement by restriction of intramolecular charge transfer state.

Cyano-substituted oligo (alpha-phenylenevinylene)-1,4-bis(R-cyano-4-diphenylaminostyryl)-2,5-diphenylbenzene (CNDPASDB) molecules are studied in solution and aggregate state by time-resolved fluorescence techniques. CNDPASDB exhibits a strong solvent polarity dependent characteristic of aggregation-induced emission (AIE). By time-dependent spectra, the gradual transition from local excited state to intramolecular charge transfer state with the increasing solvent polarity is clearly resolved. The transition time in high polarity solvent DMF is very fast, around 0.5 ps, resulting in a low fluorescence quantum yield. While in aggregate state, the intramolecular torsion is restricted and the local environment becomes less polar. Thus, the intramolecular charge transfer state is eliminated and efficient AIE occurs.

Moisture‐Responsive Graphene Paper Prepared by Self‐Controlled Photoreduction

A facile and cost-effective preparation of moisture-responsive graphene bilayer paper by focused sunlight irradiation is reported. The smart graphene paper shows moisture-responsive properties due to selective adsorption of water molecules, leading to controllable actuation under humid conditions. In this way, graphene-based moisture-responsive actuators including a smart claw, an orientable transporter, and a crawler paper robot are successfully developed.

High numerical aperture microlens arrays of close packing

Closed-packed high numerical aperture (NA) microlens arrays (MLA) are highly desirable for high resolution imaging and high signal-to-noise-ratio detection in micro-optical and integrated optical applications. However, realization of such devices remains technically challenging. Here, we report high quality fabrication of curved surfaces and MLAs by taking the full advantage of surface self-smoothing effect by creating highly reproducible voxels and by adopting an equal-arc scanning strategy. MLA of approximately 100% fill ratio and NA of 0.46, much greater than those ever reported, 0.13, is demonstrated, whose excellent optical performance was approved by the sharp focusing and high resolution imaging.

Exciton diffusion and charge transfer dynamics in nano phase-separated P3HT/PCBM blend films.

Exciton quenching dynamics has been systematically studied in pristine P3HT and nano phase separated P3HT/PCBM blend films under various excitation intensities by femtosecond fluorescence up-conversion technique. The behaviors of excitons in the films can be well described by a three-dimensional diffusion model. The small diffusion length and large charge transfer radius indicate that excitons reach the interface most likely by the delocalization of the excitons in P3HT fibrillar at a range of 4.8-9 nm so that the excitons can quickly delocalize in the P3HT domain to reach the interface (instead of by diffusion).

Flexible Nanowiring of Metal on Nonplanar Substrates by Femtosecond‐Laser‐Induced Electroless Plating

However,thelithographicrouteshowsstrongdemandsonthesurfaceflatnessofeachlayerin the multilevel chip architectures. To meet the processingnature of lithography, a global planarization of interlayermetals by chemical–mechanical polishing is therefore neededto reduce the interval between the metal layer and thephotomask, and to guarantee exposure resolution when wiresreachthesub-300nmscale.Two-photonabsorption(TPA)hasalso been tried for the fabrication of metal microstructures byusing suitable salt solutions as the metal source and photo-sensitive molecules as the photoinitiator.

Solving Efficiency–Stability Tradeoff in Top‐Emitting Organic Light‐Emitting Devices by Employing Periodically Corrugated Metallic Cathode

The introduction of a periodic corrugation into TOLEDs is demonstrated to be effective in relieving the tradeoff between device stability and efficiency, through the cross coupling of the SPPs associated with the Ag cathode and the microcavity modes. The thickness of the Ag cathode for the corrugated TOLEDs was increased from 20 to 45 nm, and both the device lifetime and efficiency are significantly improved. The figure shows a schematic cross section of a red TOLED with periodic microstructure and an operating TOLED with both corrugated and planar area.

Remote manipulation of micronanomachines containing magnetic nanoparticles

We report remote manipulation of micronanomachines containing magnetic nanoparticles. Surface-modified Fe(3)O(4) nanocrystals were synthesized as doping agents of the photopolymerizable resin, which was pinpoint written by femtosecond laser-induced two-photon photopolymerization to create microsprings. Owing to the nature of superparamagnetism of Fe(3)O(4) nanoparticles, force exerted to the microsprings relies sensitively on the field gradient of the external ferromagnet, and various motions like elongation, bending, and swing are achieved in a well-controllable remote manner. As a noncontact, sensitive, easy, and environmentally friendly approach, the magnetic driving of micronanomachines may play an important role for nano and biological applications.