Search

Recent discoveries in the field of graphene-based heterostructures have led to the demonstration of high-performance photodetectors. However, the studies to date have been largely limited to the heterojunction with a Schottky barrier, restricted by an inevitable compromise between photoresponsivity and photodetectivity. Here, a new class of graphene-based tunneling photodetectors is introduced by inserting the Al2O3 tunneling layer between silicon and graphene. The photocarriers can tunnel through the designed insulator layer which simultaneously blocks the dark current, thus maintaining high photodetectivity with desirable photoresponsivity. We further modulate the thickness of the Al2O3 layer to explore the tunneling mechanism for the photocarriers, in which a photoresponsivity of 0.75 A/W, a high current ratio of 4.8 × 103 and a photodetectivity of 3.1 × 1012 Jones are obtained at a 13.3-nm-thick Al2O3 layer. In addition, the fabrication process is compatible with conventional semiconductor processing, providing further flexibility to large-scale integrated photodetectors with high performance.

Due to the surface plasmon induced hot electrons effect, noble metallic nanostructures as photosensitizer have been widely applied for extending the photoresponse spectra of wideband semiconductors to visible range. However, most of those researches only focused on how to extend the photoresponse spectra and to improve the hot electrons injection efficiency, few investigations about the effect of hot electrons injection process on the photocurrent transient variation. In this paper, we firstly extended the photoresponse spectra of IGZO phototransistors to visible range by decorating the channels with the Au nanoparticles (AuNPs), and then specifically investigated the influence of plasmon induced hot electrons injection process on the photocurrent by observing the photocurrent transient curve of AuNPs decorated IGZO phototransistors under different illumination conditions (405 nm, 532 nm, 658 nm). It was found that AuNPs decorated IGZO phototransistors show an overshoot peak at the rising edge (falling edge) of the photocurrent curve under 658 nm illumination (dark), while the bare IGZO phototransistors don't show this phenomenon. We proposed a dynamic transportation model of hot electrons to explain the possible reason and also found that the generation and injection efficiency of hot electrons are strongly dependent on the magnitude and location of the electric field enhancement. These findings will have a great significance for understanding the mechanism of plasmon induced hot electrons transfer process at the metallic/semiconductor interface and designing novel hot electrons based optoelectronic devices .

A high power gas terahertz laser based on L-shaped cavity was demonstrated. We, for the first time, investigated the output performances of D2O gas 385 μm THz laser by optimizing the output coupler transmittance of the L-shaped cavity both in theory and experiment. Under the pump energy of 1.6 J, the optimum output coupler transmittance was about 0.78 and the optimum gas pressure was about 500 Pa. Up to 8.4 mJ pulse energy at 385 μm was achieved at output coupler transmittance of 0.8, corresponding to a photon conversion efficiency of 43.7%. Pulse width of 120 ns, and beam quality factor M2 of 1.58 were obtained at the highest output energy. In addition, the experimental results are in agreement with the theoretical simulation results.

A modified three-level laser kinetics model for a pulsed high-power optically pumped gas terahertz laser is introduced and used to model the lasing kinetics process of a gas terahertz laser system. We, for the first time to our knowledge, investigated the time evolution dynamics process of the pump intensity, population distribution among the energy levels, pump and THz signal gain coefficient, and the THz laser intensity within the pulsed D2O gas THz laser. High-power THz pulse with peak power of about 7.4 kW and pulse width of 145 ns at wavelength of 385 μm were obtained in the simulation, using an incident pump pulse with peak power of 2.2 MW and pulse width of 110 ns. THz pulse delay of 40 ns and pulse broadening of 35 ns were quantitatively analyzed. In addition, the experimental results for the pulse profile, pulse width, pulse broadening, pulse energy, and peak power are in agreement with the theoretical simulation results.

We report on the mid-infrared (MIR) and terahertz (THz) wave spectra of D2O gas pumped using a fundamental transverse mode transversely excited atmospheric CO2 laser with an emission wavelength of 9.26 μm. We obtain MIR emission lines at center wavelengths of 9.262, 9.491, and 9.752 μm, which correspond to the vibrational-energy-level-transition lines of D2O. We observe an intense THz stimulated Raman emission line of 385 μm and a weak cascade-transition line of 359 μm for transitions from rotational levels 422 to 413 and 413 to 404 in the first-excited vibration state of the D2O molecule gas. We establish a four-energy-level system for modeling the laser kinetics of the dual-wavelength (385 and 359 μm) superradiation THz laser. For the optically pumped D2O gas 385 μm THz laser, in considering the cavity effect and insertion loss of a THz cavity oscillator, an approximation treatment of the THz laser kinetics can be made based on a three-energy-level system.

Objective:This was a 12-week randomized, placebo-controlled trial to assess the efficacy of quetiapine monotherapy in the treatment of posttraumatic stress disorder (PTSD).Method:Eighty patients were randomly assigned to treatment with either quetiapine or placebo. The primary outcome measure was the Clinician-Administered PTSD Scale (CAPS). Secondary efficacy measures included the CAPS subscales, the Davidson Trauma Scale, the Positive and Negative Syndrome Scale (PANSS), the Clinical Global Impressions (CGI) scales for severity of Illness and improvement, the Hamilton Depression Rating Scale (HAM-D), and the Hamilton Anxiety Rating Scale (HAM-A). Safety measurements included adverse events, vital signs, the Abnormal Involuntary Movement Scale, the Barnes Akathisia Scale, the Simpson-Angus Scale, and the Arizona Sexual Experiences Scale.Results:After a 1-week placebo run-in, quetiapine was started at a daily dosage of 25 mg and increased to a maximum of 800 mg; the average was 258 mg (range, 50–800 mg). ...

There have been many investigations performed for color filtering based on surface plasmon resonances in recent years. However, research results on color filters integrated on the silicon-based photodetectors are infrequently reported. At present, problems including low light transmission, wide full width at half maximum (FWHM), and poor color tunability exist in the light filters integrated on the silicon-based photodetectors. We propose and numerically demonstrate a light filter with the periodic nanostructure and dielectric multi-layers integrated on the silicon substrate. Continuously tunable transmission visible spectra (400 ∼ 760 nm) are applied for the proposed filters. Hybrid resonant modes including plasmonic resonances and waveguide modes result in the extraordinary light transmission in the proposed filters. The simulations indicate that the integrated filter has more than 75% transmission and less than 25 nm full width at half maximum (FWHM) of the transmission curve for the destined wavelength. The proposed filter provides a solution for the combination of color filters with the silicon-based photosensors like CMOS photodiodes.

We propose the utilization of a light-modulated scanning tunneling microscope (LM-STM) to study the plasmonenhanced photoemission and tunneling effect between metal tip and Au nanostructures on conductive substrate. The periodic Au nanorods are fabricated by electron beam lithography (EBL) and the topography is imaged using atom force microscopy (AFM) and STM. With irradiation of continuous lasers at 532 and 805 nm, the performance of electron tunneling emission is measured under STM’s ramp mode. We show that, by exciting localized surface plasmon resonances (LSPRs), a tiny laser intensity of around 1 W/cm2 along with a bias voltage less than 50 mV can activate a significantly enhanced tunneling current. This method has the potential for analyzing electron energy states and transport characteristics of surface plasmon.

Employing the edge effect and localized surface plasmon resonance effect, an enhanced photoemission is obtained from a carbon nanotube (CNT) arrays modified with gold nanoparticles. Compared with the unpatterned CNTs, the quantum efficiency of patterned CNTs is improved from 3.69×10−6 to 1.85×10−5. After modification with gold nanoparticles, the quantum efficiency of patterned CNTs is further raised to 4.98×10−5. This work makes CNTs as a promising material for the high stability and high efficiency photocathode.

We demonstrate the possibility for integrating field emitters with two-dimensional (2D) graphene for directly transferred vacuum nanoelectronics. Improved field emission (FE) properties were revealed with few-layer graphene (FLG) decorated with gold nanoparticles (Au NPs). An in situ field emission measurement on the local graphene film was applied, achieving a maximum current density of 37.8 mA cm−2. The graphene–Au NP nanocomposite retains a turn-on electric field of 3.84 V μm−1, which is much lower than the pristine graphene, and the emission has been proved to be very stable. With graphene directly transferred onto a pre-prepared structure, we demonstrate the possibility of improving the efficiency of manufacturing large scale nano-devices with high-precision integration. The direct transferred vacuum devices are supposed to combine the advantages of vacuum nano-electronics with individual access, high integration density or nano-precision, offering promising features for future vacuum integrated applications.

A modified transmission line model with the equivalent capacitors is proposed to describe extraordinary optical transmission (EOT) of the sub-wavelength slit with different inner walls. The equivalent capacitors can effectively explain the discontinuity of the interface at which the surface wave propagates. The transmittance calculated with this model is in accordance with finite difference time domain (FDTD) calculations. This modified analytical model provides a methodology to analyze the transmission properties of sub-wavelength slits with different inner walls. The results show that if well-designed and manufactured, sub-wavelength curved slits have the ability to enhance the optical transmission in the visible region or the infrared region.

A new laser kinetics model (LKM) of gas Terahertz (THz) laser has been improved and the output characteristics of a pulse gas 385 μm THz laser have been simulated and compared with the associated experimental data. Pump absorption coefficient (PAC) and pulse profile were determined using the experimental method, which provided reliable reference basis for approximated treatment of the model. The equations were solved numerically by the Runge–Kutta numerical method and some THz output characteristics, such as output power, pulse shape and pulse energy were theoretically investigated. The simulation and experimental results are in good agreement.

We present a novel periodic sub-wavelength metallic grating with parabolic walls fabricated on the silica substrate. With finite difference time domain (FDTD) simulation, we find that the grating not only can realize broadband transmission in the visible range with TM-polarized incidence, but also can achieve higher transmission efficiency with TE-polarized light incidence. The transmission properties of the proposed grating strongly depend on the geometric parameters including the period, the thickness, the entrance width, and the exit width. The transmission spectra can be manipulated by tuning the parameters of the parabolic-wall grating. Transmission line theorem and the interaction between the surface plasmon waves on the slit walls are introduced to explain broadband extraordinary optical transmission of the grating proposed in this paper.

Due to its atomically ultrathin morphology and superior optoelectronic properties, graphene has been broadly studied and utilized in phototransistors, photoconductors, or heterojunction nanostructures. However, in practical devices, the disadvantages of graphene should be concerned for its high dark current, very low on/off ratio, and high-priced fabrication cost. We report the photodetecting of the graphene/insulator/silicon heterojunction. The insulator layer is optimized to achieve balanced optoelectronic properties in terms of an Iph/Idark ratio of 4.17 × 103, a responsivity of 35 mA W−1, and a detectivity of 6.39 × 1010 Jones at a wavelength of 658 nm, with low operating voltage and static power dissipation (0.84 nW). Besides, response speed and degradation in the environment are tested. The mechanisms are revealed and analyzed by I-V measurements.

The semiconductor laser is the important part in the semiconductor laser frequency standard. The quality of light frequency standard depends on line width and stability of laser. Semiconductor laser is very sensitive to environmental changes, such as the temperature, humidity and so on. The driving voltage and circuit and the temperature compensation are significant to laser output stability. The paper put forward a novel method to drive the semiconductor laser based on constant voltage source. The experimental results show that the circuit is simple, reliable, and high-precision. After improvement, the driving source of laser can promise parameters: constant-current range is from 0 to 250 mA, and the drift of current is less than 10 −6 , and stability is 10 −5 . The drift of frequency of laser drive with the circuit is within 10 −5 nm.

Improved field emission properties are demonstrated based on the multidimensional graphene-carbon nanotube (G-CNT) emitters decorated with gold nanoparticles (AuNPs). Chemical vapor deposition and screen printing are adopted to prepare the complex structures of G-CNT emitters. The AuNPs decoration of the emitters is implemented by the thermal evaporation and rapid thermal annealing of the Au film. Experimental results reveal that the proposed field emitters can supply a peak current of >17 mA with the current density of 556.05 mA/cm $^{2}$ . G-CNTs retain the turn-ON electric field that is $\mu \text{m}$ , and the emission has been proved to be very stable.

A novel method for laser beam straightness error measurements based on common-path compensation is proposed. The basic principle of the method is described and the math-model is established. Furthermore, the influence of laser beam drift on straightness error measurements is analyzed. The experimental results show that the measurement accuracy can be greatly improved by using the common-path compensation for laser beam drift.

Suspended graphene (SG) membranes could enable strain-engineering of ballistic Dirac fermion transport and eliminate the extrinsic bulk disorder by annealing. When freely suspended without contact to any substrates, graphene could be considered as the ultimate two-dimensional (2D) morphology, leading to special field characteristics with the 2D geometrical effect and effectively utilized as an outstanding structure to explore the fundamental electronic or optoelectronic mechanism. In this paper, we report field emission characterization on an individual suspended few-layer graphene. A controllable wet transfer method is used to obtain the continuous and suspended graphene membrane on interdigitated gold electrodes. This suspended structure displays an overall field emission from the entirely surface, except for the variation in the emitting positions, acquiring a better enhancement than the exfoliated graphene on the conventional flat substrate. We also observe the transition process from space charge flow at low bias to the Fowler-Nordheim theory at high current emission regime. It could enable theoretical and experimental investigation of the typical electron emission properties of the 2D regime. Numerical simulations are also carried out to study the electrical properties of the suspended structure. Further improvement on the fabrication would realize low disorder, high quality, and large-scale suspended graphene devices.

This paper reports the fabrication of bulk molybdenum field emitter arrays with integrated, self-aligned gates. Based on molybdenum deep reactive ion etching, the fabrication process is significantly simplified compared with that of conventional Spindt-type arrays. In the present structures, the distance between the gate and emitter has been precisely controlled by the thickness of SiO2 dielectric layer. In this work, current densities of 84mA/cm2 were produced from a uniform array of 2500 tips covering a total emission area of just 1 mm2, driven at gate-emitter voltages of just 120 V. Compared to diode-type emitters we reported elsewhere [1], the emission current densities increased by 240 times to 33.6nA/tip, owing to the extractor gates. Further scaling down of the pitch to may lead to an increase of the current densities to several A/cm2, which is very promising for high-current cathode applications such as X-ray sources.

The triangulation measurement is a kind of active vision measurement. The laser triangulation displacement is widely used with advantages of non-contact, high precision, high sensitivity. The measuring error will increase with the nonlinear and noise disturbance when sensors work in large distance. The paper introduces the principle of laser triangulation measurement and analyzes the measuring error and establishes the compensation error. Spot centroid is extracted with digital image processing technology to increase noise-signal ratio. Results of simulation and experiment show the method can meet requirement of large distance and high precision.

Laser collimation technology is widely applied in the positioning and measurement. The accuracy is affected by the laser beam drift, so laser beam drift compensation is necessary. Effective compensation depends on the characteristics analysis of laser beam drifts. Spectrums and values of noise signals caused by electronic noise, laser source, and environment, are analyzed in detail. The characteristics of various types of noise signals are gained and the effectiveness of low-pass filter and mean process are verified and compared. This study will provide support for separation of various types of signals and compensation of beam drifts.

The heterojunction between metal and silicon (Si) is an attractive route to extend the response of Si-based photodiodes into the near-infrared (NIR) region, so-called Schottky barrier diodes. Photons absorbed into a metallic nanostructure excite the surface plasmon resonances (SPRs), which can be damped non-radiatively through the creation of hot electrons. Unfortunately, the quantum efficiency of hot electron detectors remains low due to low optical absorption and poor electron injection efficiency. In this study, we propose an efficient and low-cost plasmonic hot electron NIR photodetector based on a Au nanoparticle (Au NP)-decorated Si pyramid Schottky junction. The large-area and lithography-free photodetector is realized by using an anisotropic chemical wet etching and rapid thermal annealing (RTA) of a thin Au film. We experimentally demonstrate that these hot electron detectors have broad photoresponsivity spectra in the NIR region of 1200-1475 nm, with a low dark current on the order of 10-5 A cm-2. The observed responsivities enable these devices to be competitive with other reported Si-based NIR hot electron photodetectors using perfectly periodic nanostructures. The improved performance is attributed to the pyramid surface which can enhance light trapping and the localized electric field, and the nano-sized Au NPs which are beneficial for the tunneling of hot electrons. The simple and large-area preparation processes make them suitable for large-scale thermophotovoltaic cell and low-cost NIR detection applications.