Diagnosis of neuropsychiatric systemic lupus erythematosus by label-free serum microsphere-coupled SERS fingerprints with machine learning.

Surface-enhanced Raman spectroscopy (SERS) is a powerful optical technique for non-invasive and label-free bioanalysis of liquid biopsy, facilitating to diagnosis of potential diseases. Neuropsychiatric systemic lupus erythematosus (NPSLE) is one of the subgroups of systemic lupus erythematosus (SLE) with serious manifestations for a high mortality rate. Unfortunately, lack of well-established gold standards results in the clinical diagnosis of NPSLE being a challenge so far. Here we develop a novel Raman fingerprinting machine learning (ML-) assisted diagnostic method. The microsphere-coupled SERS (McSERS) substrates are employed to acquire Raman spectra for analysis via convolutional neural network (CNN). The McSERS substrates demonstrate better performance to distinguish the Raman spectra from serums between SLE and NPSLE, attributed to the boosted signal-to-noise ratio of Raman intensities due to the multiple optical regulation in microspheres and AuNPs. Eight statistically-significant (p-value <0.05) Raman shifts are identified, for the first time, as the characteristic spectral markers. The classification model established by CNN algorithm demonstrates 95.0% in accuracy, 95.9% in sensitivity, and 93.5% in specificity for NPSLE diagnosis. The present work paves a new way achieving clinical label-free serum diagnosis of rheumatic diseases by enhanced Raman fingerprints with machine learning.

Laser Irradiation Synthesis of AuPd Alloy with Decreased Alloying Degree for Efficient Ethanol Oxidation Reaction.

The preparation of electrocatalysts with high performance for the ethanol oxidation reaction is vital for the large-scale commercialization of direct ethanol fuel cells. Here, we successfully synthesized a high-performance electrocatalyst of a AuPd alloy with a decreased alloying degree via pulsed laser irradiation in liquids. As indicated by the experimental results, the photochemical effect-induced surficial deposition of Pd atoms, combined with the photothermal effect-induced interdiffusion of Au and Pd atoms, resulted in the formation of AuPd alloys with a decreased alloying degree. Structural characterization reveals that L-AuPd exhibits a lower degree of alloying compared to C-AuPd prepared via the conventional co-reduction method. This distinct structure endows L-AuPd with outstanding catalytic activity and stability in EOR, achieving mass and specific activities as high as 16.01 A mgPd-1 and 20.69 mA cm-2, 9.1 and 5.2 times than that of the commercial Pd/C respectively. Furthermore, L-AuPd retains 90.1% of its initial mass activity after 300 cycles. This work offers guidance for laser-assisted fabrication of efficient Pd-based catalysts in EOR.

Laser induced trace doping of Pd on Ru nanoparticles for an efficient hydrogen evolution electrocatalyst.

Improving the activity and stability of electrocatalysts for the hydrogen evolution reaction (HER) plays an essential role in the practical application of electrochemical water splitting under alkaline conditions. Here, trace Pd-doped Ru nanoparticles have been achieved using the pulsed laser ablation in liquid technology, which exhibit efficient HER catalytic performance. It is evidenced that the Pd doping amount is maintained at a trace level and increases nonlinearly with the concentration of the Pd precursor. Molecular dynamics simulations demonstrate that the trace doping of Pd is due to the slow thermal decomposition rate of the Pd precursor. This work improves the mechanistic explanation of the metal doping induced by liquid-phase laser ablation, which may promote the fabrication and application of advanced laser-based nanostructures.

Highly Selective Pd Nanosheet Aerogel Catalyst with Hybrid Strain Induced by Laser Irradiation and P Doping Postprocess.

Strain engineering of electrocatalysts provides an effective strategy to improve the intrinsic catalytic activity. Here, the defect-rich crystalline/amorphous Pd nanosheet aerogel with hybrid microstrain and lattice strain is synthesized by combining laser irradiation and phosphorus doping methods. The surface strain exhibited by the microstrain and lattice strain shifts the d-band center of the electrocatalyst, enhancing the adsorption of intermediates in the ethanol oxidation reaction and thus improving the catalytic performances. The measured mass activity, specific activity and C1-path selectivity of the Pd nanosheet aerogel are 4.48, 3.06, and 5.06 times higher than those of commercial Pd/C, respectively. These findings afford a new strategy for the preparation of highl activity and C1 pathway selective catalysts and provide insight into the catalytic mechanism of strain-rich heterojunction materials based on tunable surface strain values.

Microsphere Photonic Superlens for a Highly Emissive Flexible Upconversion-Nanoparticle-Embedded Film.

Increasing upconversion luminescence (UCL) to overcome the intrinsically low conversion efficiency of upconversion nanoparticles (UCNPs) poses a fundamental challenge. Photonic nanostructures are the efficient approaches for UCL enhancement by tailoring the local electromagnetic fields. Unfortunately, such nanostructures are sensitive to environmental conditions, and the regulation strength is varied in flexible applications. Here, we report giant UCL enhancement from a flexible UCNP-embedded film coupled with a microsphere photonic superlens (MPS), by which the enhancement ratio of UCL is over 104-fold under 808 nm excitation down to 0.72 mW. The enhancement pathways of MPS-enhanced UCL are attributed to Mie-resonant nanofocusing for high excitation-photon density, optical whispering-gallery modes (WGMs) for fast radiative decay, and the directional antenna effect for far-field emission confinement. The contribution of optical resonance in the MPS to suppressing the phonon-induced nonradiative transition and thermal quenching is experimentally validated. The UCL quantum yield is therefore improved by 3-fold to 4.20% under 120 mW/cm2 near-infrared excitation, consistent with the enhancement ratio via the Purcell effect of WGMs. Furthermore, the MPS demonstrates the robust optical regulation capability toward flexible applications, opening up new opportunities for facilitating multiphoton upconversion in wearable optoelectrical devices for nanoimaging, biosensing, and energy conversion in the future.

Highly Efficient Heavy Atom Free Room Temperature Phosphorescence by Host-Guest Doping.

Recently, there has been remarkable progress of the host-guest doped pure organic room-temperature phosphorescence (RTP) materials. However, it remains a great challenge to develop highly efficient host-guest doping systems. In this study, we have successfully developed a heavy atom free pure organic molecular doped system (benzophenone-thianthrene, respectively) with efficient RTP through a simple host-guest doping strategy. Furthermore, by optimizing the doping ratios, the host-guest material with a molar ratio of 100:1 presented an efficient RTP emission with 46% quantum efficiency and a long lifetime of up to 9.17 ms under ambient conditions. This work will provide an effective way to design new organic doping systems with RTP.

Current-Induced Thermal Tunneling Electroluminescence in a Single Highly Compensated Semiconductor Microrod.

Here we demonstrate a novel and robust mechanism, termed as "current-induced Joule heating activated thermal tunneling excitation," to achieve electroluminescence (EL) by the hot electron-hole-pair recombination in a single highly compensated semiconductor microrod. The radiative luminescence is electrically excited under ambient conditions. The current-induced Joule heating reduces the thermal tunneling excitation threshold of voltage down to 8 V and increases the EL efficiency ~4.4-fold at 723 K. We interpret this novel phenomenon by a thermal tunneling excitation model corrected by electric-induced Joule heating effect. The mechanism is confirmed via theoretical calculation and experimental demonstration, for the first time. The color-tunable EL emission is also achieved by regulation of donor concentration. This work opens up new opportunities for design of novel multi-color light-emitting devices by homogeneous defect-engineered semiconductors in future.

Mechanical properties tailoring of topology optimized and selective laser melting fabricated Ti6Al4V lattice structure.

This paper investigates the effect of porosity and unit cell size variation in topology optimized (TOP) and selective laser melting (SLM) fabricated Ti6Al4V lattice structure on the mechanical properties including compressive strength, failure mechanism and dynamic elastic modulus. Meanwhile, mathematical relations between mechanical properties and geometric parameters are obtained based on Gibson-Ashby model. The results show that both ultimate compressive strength (σ = 23∼498 MPa) and dynamic elastic modulus (E = 3.5∼55.47 GPa) of TOP lattice structures gradually decrease with the increase in porosity and unit cell size. The analysis combining experimental and numerical results indicates that TOP lattice structures are elastic-brittle porous material and have two failure mechanisms. The numerical predicted stress-strain curves are compared with the experimental ones. The numerical models incorporating the Johnson-Cook damage model could predict the slip direction of 45° failure band and ultimate compressive strength. Classical Gibson-Ashby model was used to predict the relation between relative density and mechanical properties of lattice structures. The exponential factors (n) of fitted models are obviously affected by unit cell size, which are determined by the number of unit cells in compressive test and SLM manufacturability in dynamic elastic modulus test. A 3D Modulus-Density-Unit Cell Size model is innovatively proposed, which can provide theoretical basis of tailoring orthopedic implant filled with functional gradient TOP lattice structures.

Ultraviolet luminescence enhancement of planar wide bandgap semiconductor film by a hybrid microsphere cavity/dual metallic nanoparticles sandwich structure.

Here we report a novel hybrid structure composing of microsphere array (MA), Al nanoparticles (Al-NPs), ZnO thin film (luminescence layer), Au nanoparticles (Au-NPs), and substrate (sapphire) for ultraviolet (UV) luminescence enhancement of planar wide bandgap semiconductor film. The plasmonic sandwich structure of Al-NPs/ZnO/Au-NPs boosts the hot electron state density in the conduction band by electron trapping from deep-defect level of ZnO and localized surface plasmon resonances (LSPRs) coupling around dual metallic NPs, enhancing UV emission and suppressing visible emission efficiently. The dielectric microsphere array capping on the plasmonic sandwich structure further increases UV emission intensity via photonic nanojets, optical whispering-gallery modes (WGMs), and directional antenna effect, by which the interaction between photon and exciton is strengthened. The contribution of microsphere cavity coupling with LSPRs to UV luminescence enhancement is therefore revealed. The maximum enhancement ratio of up to two orders of magnitude (~250-fold) is achieved by the optimized 5.06-µm-diameter-MA/Al-NPs/ZnO/Au-NPs/sapphire structure and the UV emission is highly directional with a divergent angle of ~5°. The present work provides a simple and easily-prepared structure incorporating optical WGMs and LSPRs to manipulate UV luminescence of planar wide-bandgap semiconductors for potential optoelectronic applications.

Controllable plasmon-induced catalytic reaction by surface-enhanced and tip-enhanced Raman spectroscopy.

The controllable catalytic reaction plays a pivotal role in heterogeneous catalysis. Surface-enhanced Raman scattering (SERS) and tip enhanced Raman spectroscopy (TERS) are considered promising techniques for the study of catalytic reactions due to the highly localized sensitivity of SERS and the nanoscale spatial resolution of TERS. Herein, Ag/Au composite films were employed as catalyst for in situ monitoring of the catalytic reaction of 4­nitrobenzenethiol (4NBT) to p, p'­dimercaptoazobenzene (DMAB). The catalytic reaction of 4NBT adsorbed on Au film can be manipulated at the nanoscale using TERS by controlling the height between the tip-apex and the sample surface in Ag tip-Au substrate geometry. According to finite difference time domain (FDTD) simulations, the 'hot electron' induced by the localized surface plasmon is sufficient for promoting the catalytic reaction. These findings provide a novel way for controllable graph drawing of molecules at the nanoscale level.

Parametric study on photoluminescence enhancement of high-quality zinc oxide single-crystal capping with dielectric microsphere array.

A dielectric microsphere is a multifunctional platform to manipulate light in microscale by nanofocusing, optical whispering gallery resonance, and unidirectional antenna. Dielectric microsphere arrays (MSAs) have demonstrated the capability for photoluminescence (PL) and Raman enhancement without plasmonics. In this work, we investigate the effects of excitation power, tilting angle, and temperature on PL enhancement of high-quality zinc oxide (ZnO) single-crystal capping with fused silica MSAs. The microsphere diameter is optimized to 3.5-5.5 µm, achieving the maximum UV-PL enhancement ratio of intensity (ERI) up to tenfold by strong focusing and unidirectional antenna effects. Under the excitation power <0.2 mW, the incident light focused by the MSA increases the localized exciton state density for a higher ERI of ∼15-fold. The angle-sensitive PL intensity from the MSA enhancer provides a simple approach achieving unidirectional UV emission from planar ZnO. The 16-fold enhancement for UV-PL near 130°C is also demonstrated, for the first time, owing to thermal ionization of hydrogen-related donor that increases free-exciton concentration. The high temperature stability and reproducibility of PL enhancement up to 400°C promote the nonplasmonic MSAs superior to surface plasmon-related metal nanostructures for ZnO-based highly efficient luminescence and highly sensitive photon detection above room temperature.

Flexible Microsphere-Embedded Film for Microsphere-Enhanced Raman Spectroscopy.

Dielectric microspheres with extraordinary microscale optical properties, such as photonic nanojets, optical whispering-gallery modes (WGMs), and directional antennas, have drawn interest in many research fields. Microsphere-enhanced Raman spectroscopy (MERS) is an alternative approach for enhanced Raman detection by dielectric microstructures. Unfortunately, fabrication of microsphere monolayer arrays is the major challenge of MERS for practical applications on various specimen surfaces. Here we report a microsphere-embedded film (MF) by immersing a highly refractive microsphere monolayer array in the poly(dimethylsiloxane) (PDMS) film as a flexible MERS sensing platform for one- to three-dimensional (1D to 3D) specimen surfaces. The directional antennas and wave-guided whispering-gallery modes (WG-WGMs) contribute to the majority of Raman enhancement by the MFs. Moreover, the MF can be coupled with surface-enhanced Raman spectroscopy (SERS) to provide an extra >10-fold enhancement. The limit of detection is therefore improved for sensing of crystal violet (CV) and Sudan I molecules in aqueous solutions at concentrations down to 10-7 M. A hybrid dual-layer microsphere enhancer, constructed by depositing a MF onto a microsphere monolayer array, is also demonstrated, wherein the WG-WGMs become dominant and boost the enhancement ratio >50-fold. The present work opens up new opportunities for design of cost-effective and flexible MERS sensing platforms as individual or associated techniques toward practical applications in ultrasensitive Raman detection.

Sandwich-structure-modulated photoluminescence enhancement of wide bandgap semiconductors capping with dielectric microsphere arrays.

Here we investigated the effect of substrate and film thickness on photoluminescence (PL) enhancement of wide bandgap semiconductor (i.e. ZnO) by dielectric microsphere array/luminescence film/substrate (MLS) sandwich structures. The PL enhancement channels in the sandwich structure were revealed, for the first time, including the focusing property of microsphere array (MSA) distinctly enhancing free-exciton recombination, anti-reflection effect of MSA increasing excitation cross-section area, MLS-supported TW-/SW-WGMs inducing ASE and Purcell's effect, and optical directional antenna effect for high equivalent NA of objective lens as well as out-coupling efficiency. The enhancement ratio of intensity (ERI) for ZnO UV-PL from free-exciton recombination in the sandwich structure was found to be strongly dependent upon the refractive index of substrate and luminescence film thickness. In order to achieve high ERI for PL emission, the refractive index of substrate should differ from luminescence film and the film thickness needs to be chosen to support WGMs in the sandwich structure. The maximum ERI beyond one order of magnitude for ZnO UV-PL was therefore predicted theoretically and validated experimentally, where 11.25-fold UV PL enhancement ratio was achieved in ~650-nm-thick ZnO film grown on SiC substrate and capped with 5.06-µm-diameter MSA. The ERI could further be increased by improving above-mentioned enhancement channels. The present work provides a novel platform to manipulate light by low-loss dielectric microstructures for enhancing photon-matter interaction, which would be employed for other semiconductors achieving energy-saving luminescence and high-sensitivity photoelectric detection in future.

Freeform microlens array homogenizer for excimer laser beam shaping.

We presented a novel technique to design microlens optical beam homogenizing system for excimer lasers. As a new approach by applying freeform surface microlens array, the homogenizer can yield somehow superior beam shaping results with larger but less microlens units than conventional method. With new concept and design, the diffraction effects at the microlens apertures can be reduced substantially. Large scale and highly uniform beam profile can be realized at a relative nearby working distance after beam shaping. This is hard to achieve by conventional method. Our design method takes the real spatial energy characteristics of the excimer laser beam as the design basis, and combined with feasible optimization method. The design method is demonstrated as a real instance based, on a 193 nm ArF excimer laser in our laboratory. Moreover, to verify the effectiveness of our method, the designed freeform microlens array homogenizer has been fabricated and tested experimentally. The experimental optical performance of the homogenizer coincides well with the theoretical simulation.

Free-Standing Undoped ZnO Microtubes with Rich and Stable Shallow Acceptors.

Fabrication of reliable large-sized p-ZnO is a major challenge to realise ZnO-based electronic device applications. Here we report a novel technique to grow high-quality free-standing undoped acceptor-rich ZnO (A-ZnO) microtubes with dimensions of ~100 µm (in diameter) × 5 mm (in length) by optical vapour supersaturated precipitation. The A-ZnO exhibits long lifetimes (>1 year) against compensation/lattice-relaxation and the stable shallow acceptors with binding energy of ~127 meV are confirmed from Zn vacancies. The A-ZnO provides a possibility for a mimetic p-n homojunction diode with n(+)-ZnO:Sn. The high concentrations of holes in A-ZnO and electrons in n(+)-ZnO make the dual diffusion possible to form a depletion layer. The diode threshold voltage, turn-on voltage, reverse saturated current and reverse breakdown voltage are 0.72 V, 1.90 V, <10 µA and >15 V, respectively. The A-ZnO also demonstrates quenching-free donor-acceptor-pairs (DAP) emission located in 390-414 nm with temperature of 270-470 K. Combining the temperature-dependent DAP violet emission with native green emission, the visible luminescence of A-ZnO microtube can be modulated in a wide region of colour space across white light. The present work opens up new opportunities to achieve ZnO with rich and stable acceptors instead of p-ZnO for a variety of potential applications.

Interesting polarization-independent SERS detection performance induced by the rotation symmetry of multiparticle nanostructures.

In this work, on the basis of finite difference time domain simulations and group theory, by employing regular nanosphere trimers as the main examples, we analyse and discuss the polarization-independent surface enhanced Raman scattering (SERS) phenomenon arising from the rotation symmetry of coined metallic nanomultimers. The results demonstrate why the rotationally symmetrical nanomultimers can show polarization-independent SERS performance. Because of the dramatically hybridized polarization-independent SERS performance over the whole 360° range, rotationally symmetrical coined metal nanomultimers, such as regular trimers, regular triangular tetramers and regular pentamers, are reliable and reproducible SERS substrates, which have the potential for convenient and flexible practical SERS detection without the need for optimally incident polarization outside the laboratory setting.

Self-assembled dielectric microsphere array enhanced Raman scattering for large-area and ultra-long working distance confocal detection.

Here we report enhanced confocal Raman detection with large-area and ultra-long working distance by capping dielectric microsphere array. Microspheres have been found to provide three channels for Raman scattering enhancement, including localized photonic nanojets, directional antenna effects, and whispering-gallery modes. The maximum enhancement ratio of Raman intensity is up to 14.6 using 4.94-µm-diameter polystyrene (PS) microspheres. Investigation on the directional antenna effect of microsphere reveals that the microsphere array confines electromagnetic (EM) waves to a narrow distribution with small divergent angles, by which the signal-to-noise ratio is retained and the offset of focal plane position from sample surface can be up to ± 7.5 mm. The present work reduces the requirement of focusing in confocal Raman detection and hence makes the large-area detection possible via rapid mapping. It opens up a simple approach for high-sensitivity Raman detection of 3D-structured surface.

Ten-fold enhancement of ZnO thin film ultraviolet-luminescence by dielectric microsphere arrays.

Here we report strong enhancement in ultraviolet-photoluminescence (UV-PL) of ZnO thin films (grown on a SiC substrate) covered by monolayer dielectric fused silica or polystyrene microspheres with diameters ranging from 0.5 to 7.5 µm. The excited light scatted in the film is collected by the microspheres to stimulate whispering gallery modes, by which the internal quantum efficiency of spontaneous emission is enhanced. Meanwhile, the microsphere monolayer efficiently couples emitted light energy from the luminescent film to the far-field for PL detection. A UV-PL enhancement up to 10-fold via a 5-µm-diameter microsphere monolayer is experimentally demonstrated in this work. The unique optical property of microsphere in photoluminescence (PL) enhancement makes them promising for high-sensitivity PL measurements as well as design of photoelectric devices with low loss and high efficiency.

Rapid fabrication of patterned high-performance conductor poly (vinylidene fluoride) surfaces using a 248nm excimer laser.

This work describes a method for rapidly and conveniently fabricating high-performance conductive patterns on poly (vinylidene fluoride) substrates using a 248 nm excimer laser. It shows that the artificial active centre, created by laser direct etching technique, could facilely control the formation of modified layer, avoiding the laser threshold in processing. Using the etching lines to structure the nonconductive paths, the controllable patterns can be formed in selective areas through the designed photo-mask when 248nm laser irradiation. The modified layer exhibits a high-grade electrical conductivity of 2.80 Ω(-1)cm(-1) increased by 13 orders of magnitude, and the considerable improvement in conductivity could be attributed to the carbon enrichment, especially the structural formation of C-C.

Investigation of room temperature UV emission of ZnO films with different defect densities induced by laser irradiation.

We studied the room temperature UV emission of ZnO films with different defect densities which is fabricated by KrF laser irradiation process. It is shown room temperature UV photoluminescence of ZnO film is composed of contribution from free-exciton (FX) recombination and its longitudinal-optical phonon replica (FX-LO) (1LO, 2LO). With increase of the defect density, the FX emission decreased and FX-LO emission increased dramatically; and the relative strengths of FX to FX-LO emission intensities determine the peak position and intensity of UV emission. What is more, laser irradiation with moderate energy density could induce the crystalline ZnO film with very flat and smooth surface. This investigation indicates that KrF laser irradiation could effectively modulate the exciton emission and surface morphology, which is important for the application of high performance of UV emitting optoelectronic devices.