Topological Crystalline Insulator SnTe/Si Vertical Heterostructure Photodetectors for High-Performance Near-Infrared Detection

Due to the gapless surface state and narrow bulk band gap, the light absorption of topological crystalline insulators covers a broad spectrum ranging from terahertz to infrared, revealing promising applications in new generation optoelectronic devices. To date, the photodetectors based on topological insulators generally suffer from a large dark current and a weaker photocurrent especially under the near-infrared lights, which severely limits the practical application of devices. Owing to the lower excitation energy of infrared lights, the photodetection application of topological crystalline insulators in the near-infrared region relies critically on understanding the preparation and properties of their heterostructures. Herein, we fabricate the high-quality topological crystalline insulator SnTe film/Si vertical heterostructure by a simple physical vapor deposition process. The resultant heterostructure exhibits an excellent diode characteristic, enabling the construction of high-performance near-infrared photodetectors. The built-in electric field at SnTe/Si interface enhances the absorption efficiency of near-infrared lights and greatly facilitates the separation of photogenerated carriers, making the device capable of operating as a self-driven photodetector. The as-grown SnTe film acts as the hole transport layer in heterostructure photodetectors, promoting the transport of holes to electrode and reducing electron-hole recombination effectively. These merits enable the SnTe/Si heterostructure photodetector to have a high responsivity of 2.36 AW^-1, a high detectivity of 1.54 × 10¹⁴ Jones, and a large bandwidth of 10⁴ Hz in the near-infrared wavelength, which makes the detector have a promising market in novel device applications.

Third-harmonic generation from gold nanowires of rough surface considering classical nonlocal effect

We demonstrate that the nonlocal dielectric response of metal, comparing with the traditional local model, will significantly boost the third-order harmonic generation (THG) from gold nanowires of rough surface by a factor of several orders of magnitude. The enhancement is probably due to the penetrated field into the fine nanostructures on the metal surface in nonlocal model. The anisotropy THG efficiency versus the angle of incidence is also demonstrated due to the inhomogeneous surface morphology. The possible ways to verify the nonlocal effect to the THG are demonstrated. The results have a general significance in explaining the experimental observations.

Investigation of Two Kinds of Periodical Surface Structures Induced by Femtosecond Laser on the Surface of Titanium Plate

Two kinds of laser-induced periodical structures observed on metal titanium plate irradiated by femtosecond laser (fs-laser) are reported, including the fs-laser-induced concentric rings and periodical subwavelength ripples. The rings can be produced only when the titanium target is located before the focal plane. The period and distribution of the rings stay almost fixable with the change of laser fluence and pulse number. The average cross section area (ACSA) is introduced to investigate the material removal behavior with the growth of the rings. The rings grow with the accumulation of laser pulses and the increase of the laser fluence, but the growth rate will be moderated with the increase of the pulse number. The ripples are obtained in an annular region when powerful multi-pulses irradiate on the target surface. The ripple period varies with laser fluence and location. And the annular region migrates outward when the laser fluence increases. We suggest that the formations of ripples are attributed to the propagation of the laser-stimulated surface plasma wave (SPW) on the air/ti interface. The dependence of the ripple period on the pulse fluence calculated by the SPW model agrees well with our experimental observation. The investigation improves the understanding of the two kinds of periodical surface structures both in their appearances and mechanisms.

Dense AuNP/MoS2 hybrid fabrication on fiber membranes for molecule separation and SERS detection

Synthesis of uniform and dense metal nanostructures on the whole exposed fiber, instead of simply on the membrane surface, is necessary for controllable separation and sensitive SERS detection.

Theoretical design of a surface plasmon resonance sensor with high sensitivity and high resolution based on graphene–WS2 hybrid nanostructures and Au–Ag bimetallic film

We proposed a high sensitivity and a high resolution surface plasmon resonance sensor composed of graphene–WS₂ hybrid nanostructure and Au–Ag bimetallic-layers film.

Formation of large-area stretchable 3D graphene–nickel particle foams and their sensor applications

3D graphene/nickel particles (Gr–NiP) foams, fabricated using CVD and stamp-transfer processes, are used for stretchable sensor applications. The NiP, covered by Gr layers, are useful for the 3D nanostructures and separated from each other for the stretchable application.

Controlled-layer and large-area MoS2 films encapsulated Au nanoparticle hybrids for SERS

In this work, a facile and effective method for controlled-layer and large-area MoS₂ films encapsulated Au nanoparticle hybrids is developed. With accurate Ar plasma treatment time control, the large-area MoS₂ layers can be obtained from monolayer to trilayer. The fabricated MoS₂@Au NPs with higher surface area exhibit excellent Raman enhanced effect for aromatic organic molecules (rhodamine 6G and crystal violet) and achieve the best when the monolayer MoS₂@AuNPs was obtained. The limit of detection is found to be as low as 1 × 10^-10 M. The MoS₂@AuNPs was characterized by SEM, EDS, AFM, Raman spectroscopy, UV-Vis, XRD and HRTEM.

WS2 as a saturable absorber for Q-switched 2 micron lasers

We prepared WS₂ nanosheets by using the thermal decomposition method and demonstrated for the first time its nonlinear saturable absorption property at around 2 μm. With the as-prepared WS₂ nanosheets as saturable absorber (SA), a passively Q-switched Tm:LuAG laser was realized successfully, and 660 ns laser pulses with an average output power of 1.08 W and pulse peak power of 26 W at a repetition rate of 63 kHz were obtained for an incident pump power of 7 W. Our experimental results definitely demonstrate that WS₂ could be a kind of promising SA for solid-state 2 μm lasers.

Substrate Considerations for the Formation of the Graphene-CNTs Hybrid on the Dielectric Substrate

Graphene-carbon nanotube (CNT) hybrid materials are directly synthesized on an unpolished SiO₂ substrate by the use of a chemical vapor deposition (CVD) system with a two-temperature reactor. The two-temperature reactor utilized here proves more efficient than that of the one-temperature reactor. Potential candidate substrates for the formation of the graphene-CNT hybrid materials are discussed in detail. SEM and Raman results demonstrate that the unpolished SiO₂ base is the most fitting substrate for the graphene-CNT hybrid CVD growth. These results open the way for direct and high-efficiency production of graphene-CNT hybrid materials with high conductivity and transmittance.

A sensitive 2D plasmon ruler based on Fano resonance

In this paper, we designed a 2D distance and rotation angle plasmon ruler based on Fano resonance of a trimer nanostructure, which consists of a concentric square nanoring–disk and an outside nanorod (CSRDR).

Graphene-Based Flexible and Transparent Tunable Capacitors

We report a kind of electric field tunable transparent and flexible capacitor with the structure of graphene-Bi1.5MgNb1.5O7 (BMN)-graphene. The graphene films with low sheet resistance were grown by chemical vapor deposition. The BMN thin films were fabricated on graphene by using laser molecular beam epitaxy technology. Compared to BMN films grown on Au, the samples on graphene substrates show better quality in terms of crystallinity, surface morphology, leakage current, and loss tangent. By transferring another graphene layer, we fabricated flexible and transparent capacitors with the structure of graphene-BMN-graphene. The capacitors show a large dielectric constant of 113 with high dielectric tunability of ~40.7 % at a bias field of 1.0 MV/cm. Also, the capacitor can work stably in the high bending condition with curvature radii as low as 10 mm. This flexible film capacitor has a high optical transparency of ~90 % in the visible light region, demonstrating their potential application for a wide range of flexible electronic devices.

WS(2)/fluorine mica (FM) saturable absorbers for all-normal-dispersion mode-locked fiber laser

The report firstly propose a new WS(2) absorber based on fluorine mica (FM) substrate. The WS(2) material was fabricated by thermal decomposition method. The FM was stripped into one single layer as thin as 20 μm and deposited WS(2) on it, which can be attached to the fiber flank without causing the laser deviation. Similar to quartz, the transmission rate of FM is as high as 90% at near infrared wavelength from one to two micrometers. Furthermore, FM is a highly elastic material so that it is not easy to break off even its thickness was only 20 μm. On the contrary, quartz is hard to be processed and easy to break off when its thickness is less than 100 μm. Compared to organic matrix such as polyvinyl alcohol (PVA), FM has higher softening temperature, heat dissipation and laser damage threshold than those of organic composites. In our work, the modulation depth (MD) and non-saturable losses (NLs) of this kind of saturable absorber were measured to be 5.8% and 14.8%, respectively. The WS(2)/FM absorber has a high damage threshold of 406 MW/cm(2), two times higher than that of WS(2)/PVA. By incorporating the saturable absorber into Yb-doped fiber laser cavity, a mode-locked fiber laser was achieved with central wavelength of 1052.45 nm. The repetition rate was 23.26 MHz and the maximum average output power was 30 mW. The long term stability of working was proved to be good too. The results indicate that WS(2)/FM film is a practical nonlinear optical material for photonic applications.

Graphene/Cu nanoparticle hybrids fabricated by chemical vapor deposition as surface-enhanced Raman scattering substrate for label-free detection of adenosine

We present a graphene/Cu nanoparticle hybrids (G/CuNPs) system as a surface-enhanced Raman scattering (SERS) substrate for adenosine detection. The Cu nanoparticles wrapped by a monolayer graphene shell were directly synthesized on flat quartz by chemical vapor deposition in a mixture of methane and hydrogen. The G/CuNPs showed an excellent SERS enhancement activity for adenosine. The minimum detected concentration of the adenosine in serum was demonstrated as low as 5 nM, and the calibration curve showed a good linear response from 5 to 500 nM. The capability of SERS detection of adenosine in real normal human urine samples based on G/CuNPs was also investigated and the characteristic peaks of adenosine were still recognizable. The reproducible and the ultrasensitive enhanced Raman signals could be due to the presence of an ultrathin graphene layer. The graphene shell was able to enrich and fix the adenosine molecules, which could also efficiently maintain chemical and optical stability of G/CuNPs. Based on the G/CuNPs system, the ultrasensitive SERS detection of adenosine in varied matrices was expected for the practical applications in medicine and biotechnology.

Facile synthesis 3D flexible core-shell graphene/glass fiber via chemical vapor deposition

Direct deposition of graphene layers on the flexible glass fiber surface to form the three-dimensional (3D) core-shell structures is offered using a two-heating reactor chemical vapor deposition system. The two-heating reactor is utilized to offer sufficient, well-proportioned floating C atoms and provide a facile way for low-temperature deposition. Graphene layers, which are controlled by changing the growth time, can be grown on the surface of wire-type glass fiber with the diameter from 30 nm to 120 um. The core-shell graphene/glass fiber deposition mechanism is proposed, suggesting that the 3D graphene films can be deposited on any proper wire-type substrates. These results open a facile way for direct and high-efficiency deposition of the transfer-free graphene layers on the low-temperature dielectric wire-type substrates.

PACS

81.05.U-; 81.07.-b; 81.15.Gh.

Direct growth of graphene on quartz substrates for label-free detection of adenosine triphosphate

We demonstrate that continuous, uniform graphene films can be directly synthesized on quartz substrates using a two-temperature-zone chemical vapor deposition system and that their layers can be controlled by adjusting the precursor partial pressure. Raman spectroscopy and transmission electron microscopy confirm the formation of monolayer graphene with a grain size of ∼100 nm. Hall measurements show a room-temperature carrier mobility above 1500 cm2 V(-1) s(-1). The optical transmittance and conductance of the graphene films are comparable to those of transferred metal-catalyzed graphene. The method avoids the complicated and skilled post-growth transfer process and allows the graphene to be directly incorporated into a fully functional biosensor for label-free detection of adenosine triphosphate (ATP). This device shows a fast response time of a few milliseconds and achieves a high sensitivity to ATP molecules over a very wide range from 0.002 to 5 mM.

DNA condensations on mica surfaces induced collaboratively by alcohol and hexammine cobalt

We performed systematic studies of λ-DNA condensation on mica surfaces induced by alcohol and hexammine cobalt (III) [Co(NH(3))(6)(3+)] using atomic force microscopy (AFM). The critical condensation concentration for [Co(NH(3))(6)(3+)] was found to be about 10 microM; the DNA molecules extended freely on mica when the concentration was below the critical value. The morphology of condensed DNA became more compact with increasing concentration. At about 500 microM [Co(NH(3))(6)(3+)] concentration, no condensation patterns could be observed due to charge inversion of the compact structures resulting in failure of adhesion to the positively charged surfaces. The critical concentration for alcohol was about 15% (v/v). At this concentration, a few intramolecular loops could be observed in the AFM images. With increasing ethanol concentration the condensation pattern became more complicated ranging from flower-like to pancake-like. When the solution contained both alcohol and hexammine cobalt (III), DNA condensation patterns could be observed even when the concentrations of the two condensation agents were lower than their critical values. We observed this phenomenon by adding mixtures of 10% alcohol and 8 microM hexammine cobalt (III) to DNA solutions. The condensation patterns were more compact than those of the condensation agents separately. Typical toroids were found at an appropriate alcohol and hexammine cobalt (III) concentration. The collaborative condensation phenomenon was analyzed by electrostatic interaction and charge neutralization.

Temporal and spatial evolution of Si atoms in plasmas produced by a nanosecond laser ablating silicon carbide crystals

Optical emission spectroscopy (OES) was used to study the evolution behavior of the neutral Si atoms in the plasma produced by nanosecond pulsed-laser beam irradiating on SiC crystal targets. The OES measurements indicated that the electron temperature and density in the plasma had maximum values around a region about 2mm from the target surface. Based on the temporal and spatial evolution of the spectral line at 633.19 nm originating from excited Si atoms, it was found that these Si atoms have short decay times and long range spatial distribution in vacuum. At the initial growth stage of SiC thin films using pulsed-laser deposition (PLD) technique, these Si atoms were found possibly to arrive at the Si substrate to form defects near the SiC/Si interface. By comparing the OES result measured in vacuum and that measured in ambient air, it was deduced that by properly adjusting the background gas species and pressure, the quality of the films prepared by PLD technique may be improved.

The influence of permanent magnetic field therapy on wound healing in suction lipectomy patients: a double-blind study

The authors present their experience with the healing influence of permanent magnets on postoperative wounds. The responses of 20 patients who underwent suction lipectomy and postoperative negative magnetic field therapy were studied in a double-blind fashion. Magnets in the form of patches (10 patients) or sham magnet patches (10 patients) were placed over the operative region in each of the patients. Pain, edema, and discoloration (ecchymosis) were evaluated at 1, 2, 3, 4, 7, and 14 days postoperatively. Our results show that the treatment group had significant reductions in pain on postoperative days 1 through 7, in edema on days 1 through 4, and in discoloration on days 1 through 3 when compared with the control group. These results demonstrated that commercially available magnets have a positive influence on the postoperative healing process in suction lipectomy patients.

[Analysis of the properties of plasma produced by pulsed laser ablation of metal Al at different ambient pressures]

A time and space resolved diagnostic technique was used to study the properties of plasma produced by a pulsed laser on an Al target irradiated at different ambient pressures. The velocities of projected particles were measured. The projected ranges for 1-10keV AI2+ ions ejecting into ambient gas at different pressures were calculated in theory. The calculated results can explain the observed experimental phenomena successfully.

Loss of circadian behavioral rhythms and per RNA oscillations in the Drosophila mutant timeless

Eclosion, or emergence of adult flies from the pupa, and locomotor activity of adults occur rhythmically in Drosophila melanogaster, with a circadian period of about 24 hours. Here, a clock mutation, timeless (tim), is described that produces arrhythmia for both behaviors. The effects of tim on behavioral rhythms are likely to involve products of the X chromosome-linked clock gene period (per), because tim alters circadian oscillations of per RNA. Genetic mapping places tim on the left arm of the second chromosome between dumpy (dp) and decapentaplegic (dpp).