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Two-dimensional surface-enhanced Raman scattering (SERS) substrates have drawn intense attention due to their excellent spectral reproducibility, high uniformity and perfect anti-interference ability. However, the inferior detection sensitivity and low enhancement have limited the practical application of two-dimensional SERS substrates. To address this issue, we propose that the interaction between the MoTe2 substrate and the analyte rhodamine 6G molecules could be remarkably enhanced by the introduced p-doping effect and lattice distortion of MoTe2 via hydrogen plasma treatment. After the treatment, the SERS is greatly improved, the enhancement factor of probe molecules reaches 1.83 × 106 as well as the limit of detection concentration reaches 10−13 M. This method is anticipated to afford new enhancement probability for other 2D materials, even non-metal oxide semiconductor SERS substrates.

Topological defects in graphene induce structural and electronic modulations. Knowing exact nature of broken-symmetry states around the individual atomic defects of graphene is very important for understanding the electronic properties of this material. We investigate structural dependence on localized electronic states in the vicinity of topological defects on a highly oriented pyrolytic graphite (HOPG) surface, using scanning tunneling microscopy and spectroscopy. Several inherent topological defects on the HOPG surface and the local density of states surrounding them are explored, visualized as scattering wave-related ( 3 × 3 ) R30° superstructures and honeycomb superstructures. In addition, the superstructures observed near the grain boundary have a much higher decay length at specific sites than that reported previously, indicating far greater electron scattering on the quasi-periodic grain boundary.

We investigate the squeezed back-to-back correlation (BBC) of $D^0\!{\bar D}^0$ in relativistic heavy-ion collisions, using the in-medium mass modification calculated with a self-energy in hot pion gas and the source space-time distributions provided by the viscous hydrodynamic code VISH2+1. It is found that the BBC of $D^0\!{\bar D}^0$ is significant in peripheral Au+Au collisions at the RHIC energy. A possible way to detect the BBC in experiment is presented., 4 pages, 5 figures, will be published in Chin. Phys. Lett

A low-barrier Schottky barrier diode based on the InGaAs/InP material system is designed and fabricated with a new non-destructive dry over-etching process. By using this diode, a high-sensitivity waveguide detector is proposed. The measured maximum responsivity is over 2000 mV/mW at 630 GHz. The measured noise effective power (NEP) is less than 35 pW/Hz 0.5 at 570–630 GHz. The minimum NEP is 14 pW/Hz 0.5 at 630 GHz. The proposed high-sensitivity waveguide detector has the characteristics of simple structure, compact size, low cost and high performance, and can be used in a variety of applications such as imaging, molecular spectroscopy and atmospheric remote sensing.

Direct observation of the domain-inverted regions in LiNbO3 formed by proton exchange followed by heat treatment is performed by using transmission electron microscopy. A charged straight 180° twinning domain boundary was revealed and compared with winding domain boundaries in LiNbO3 grown by Czochralski method. Obtained results are significant to studying the mechanism of domain inversion and morphology of inversion domains.

A Schottky barrier diode with low-barrier is presented, based on which a terahertz waveguide detector working at 500–600 GHz is designed and fabricated. By using the InGaAs/InP material system, the feature of the low barrier is obtained which greatly improves the performance of the detector. The measured typical voltage responsivity is about 900 V/W at 500–560 GHz and is about 400 V/W at 560–600 GHz. The proposed broadband waveguide detector has the characteristics of simple structure, compact size, low cost and high performance, and can be used in a variety of applications such as imaging, molecular spectroscopy and atmospheric remote sensing.

We propose and experimentally demonstrate a novel all-optical non-return-to-zero differential-phase-shift-keying (NRZ-DPSK) to return-to-zero differential-phase-shift-keying (RZ-DPSK) format conversion scheme. This scheme is based on the terahertz optical asymmetric demultiplexer (TOAD). A 10 Gb/s converted RZ-DPSK signal is obtained with a wide duty cycle tuning range from 16% to 66%. For all converted RZ-DPSK signals, the receiver sensitivities at BER of 10−9 are 0.4 to 1.7 dB higher compared with the original NRZ-DPSK signal. The clear and open eye diagrams are presented to demonstrate the high quality format conversion performance. Moreover, the optical spectra show that this conversion is in a wavelength-preserving operation.

In this study, rose-like nickel oxide (NiO) nanoparticles with diameters of 400–500 nm are prepared on ITO glass substrates by simple electrodeposition in NiSO46H2O solution at room temperature followed by oxidation in air. Scanning electron microscopy, x-ray diffraction and a transmission electron microscope are used for analyses of the NiO nanoparticles. The ethanol gas sensitivity of these nanoparticles is studied. The results indicate that the rose-like NiO nanoparticles could be used for the fabrication of ethanol gas sensors to monitor the low concentration of ethanol gas in air. Furthermore, at 5 ppm, the NiO nanorose-based sensors show a high response to ethanol (Rg/Ra = 8.4).

The 'plug & play' quantum key distribution system is the most stable and the earliest commercial system in the quantum communication field. Jones matrix and Jones calculus are widely used in the analysis of this system and the improved version, which is called the auto-compensating quantum key distribution system. Unfortunately, existing analysis has two drawbacks: only the auto-compensating process is analyzed and existing systems do not fully consider laser phase affected by a Faraday mirror (FM). In this work, we present a detailed analysis of the output of light pulse transmitting in a plug & play quantum key distribution system that contains only an FM, by Jones calculus. A similar analysis is made to a home-made auto-compensating system which contains two FMs to compensate for environmental effects. More importantly, we show that theoretical and experimental results are different in the plug & play interferometric setup due to the fact that a conventional Jones matrix of FM neglected an additional phase π on alternative polarization direction. To resolve the above problem, we give a new Jones matrix of an FM according to the coordinate rotation. This new Jones matrix not only resolves the above contradiction in the plug & play interferometric setup, but also is suitable for the previous analyses about auto-compensating quantum key distribution.

In diffusion to blue light-emitting diode (LED) wafers is performed by the inductive coupled plasma (ICP) treatment of a covering layer of indium tin oxide (ITO) on the wafer surface. The electrical property of the p-type contact is improved and the redshift of photoluminescence (PL) from the InGaN quantum well of the wafer is found. Measurements by x-ray photoelectron spectroscopy (XPS) demonstrate that In atoms have diffused into p-GaN. Reflectance spectra of the sample surface reveal the variation caused by the ICP treatment. A model of compensation of the in-plane strain of the InGaN layer is used to explain the redshift of the PL data. Finally, LEDs are fabricated by using as-grown and ICP-treated wafers and their properties are compared. Under an injection current of 20 mA, LEDs with ICP-induced In doping show a decrease of 0.3V in the forward voltage and an increase of 23% in the light output, respectively.

A 330–500 GHz zero-biased broadband monolithic integrated tripler is reported. The measured results show that the maximum efficiency and the maximum output power are 2% and 194 μW at 348 GHz. The saturation characteristic test shows that the output 1 dB compression point is about −8.5 dBm at 334 GHz and the maximum efficiency is obtained at the point, which is slightly below the 1 dB compression point. Compared with the conventional hybrid integrated circuit, a major advantage of the monolithic integrated circuit is the significant improvement of reliability and consistency. In this work, a terahertz monolithic frequency multiplier at this band is designed and fabricated.

Emission properties of self-assembled green-emitting InGaN quantum dots (QDs) grown on sapphire substrates by using metal organic chemical vapor deposition are studied by temperature-dependent photoluminescence (PL) measurements. As temperature increases (15–300 K), the PL peak energy shows an anomalous V-shaped (redshift—blueshift) variation instead of an S-shaped (redshift—blueshift—redshift) variation, as observed typically in green-emitting InGaN/GaN multi-quantum wells (MQWs). The PL full width at half maximum (FWHM) also shows a V-shaped (decrease—increase) variation. The temperature dependence of the PL peak energy and FWHM of QDs are well explained by a model similar to MQWs, in which carriers transferring in localized states play an important role, while the confinement energy of localized states in the QDs is significantly larger than that in MQWs. By analyzing the integrated PL intensity, the larger confinement energy of localized states in the QDs is estimated to be 105.9 meV, which is well explained by taking into account the band-gap shrinkage and carrier thermalization with temperature. It is also found that the nonradiative combination centers in QD samples are much less than those in QW samples with the same In content.

A tunable grating-coupled external cavity (EC) laser is realized by employing a GaN-based laser diode as the gain device. A tuning range of 4.47 nm from 403.82 to 408.29 nm is achieved. Detailed investigations reveal that the injection current strongly influences the performance of the EC laser. Below the free-running lasing threshold, EC laser works stably. While above the free-running lasing threshold, a Fabry—Perot (F-P) resonance peak in the emission spectrum and a smooth kink in the output power-injection current characteristic curve are observed, suggesting the competition between the inner F-P cavity resonance and EC resonance. Furthermore, the tuning range is found to be asymmetric and occurs predominantly on the longer wavelength side. This is interpreted in terms of the asymmetric gain distribution of GaN-based quantum well material.

We study the statistical properties of leaders in growing networks with age. A leader of a network is defined as the node with the largest degree and the age of the node is trivially labeled by its index, i.e., the time it joins the network. As networks evolve with the addition of new nodes connecting to old ones with the possibility that is proportional to the index of the target, we investigate both the average number and index of leaders as well as the degree distribution of nodes. The average number of leaders first increases quickly with time and then saturates to a finite value and the average index of leaders increases algebraically with time. Both features result from the degree distribution with an exponential tail. Analytical calculations based on the rate equation are verified by numerical simulations.

Laser lift-off (LLO), by which GaN is separated from sapphire, is demonstrated to be a promising technique for advanced GaN-based optoelectronic devices. Its physical insight, however, is still not fully understood. We study systematically the effect of laser pulse width on the LLO process and the property of GaN. To estimate accurately the temperature distribution and the decomposed thickness of GaN, fluctuation in the pulse laser energy is taken into account. It is found that the temperature at the interface is increased in a higher speed for a narrower pulse width. In addition, less damage to the GaN film is expected for a narrower pulse width owing to the smaller heated area, lower transient temperature and lower N2 vapor pressure encountered during LLO. Some experimental results reported in literature are explained well. Our results are useful in understanding the effect of laser pulse width and can be taken as references in LLO of GaN/sapphire structures.

A generalized parallel-plate dielectric waveguide (G-PPDW) is proposed as a new guiding medium for terahertz wave. A theoretical analysis of the transmission characteristics for the TE modes of this generalized structure is performed. Equations are presented for the field components, dispersion, power ratio, transmission loss and characteristic impedance as functions of the operating frequencies, dimensions and material constants. In the case of the lowest-order mode TE10, design curves covering frequencies and dimensions for the given material constants in the THz region are presented. The theoretical results of transmission characteristics obtained from these equations are verified by the finite-element method with a good agreement. The investigation results show that by selecting proper dimensions and dielectric materials, G-PPDW can be used to guide THz waves efficiently with high power confinement and low attenuation. These outstanding properties may open up a way to many important applications for THz integrated circuits and systems.

Specimens of silicon carbide (6H-SiC) were irradiated with 5 MeV Kr ions (84Kr19+) for three fluences of 5×1013, 2 ×1014 and 1× 1015 ions/cm2, and subsequently annealed at room temperature, 500°C, 700°C and 1000°C, respectively. The strain of the specimens was investigated with high resolution XRD and different defect evolution processes are revealed. An interpretation of the defect evolution and migration is given to explain the strain variation. The mechanical properties of the specimens were studied by using a nano-indentation technique in continuous stiffness measurement (GSM) mode with a diamond Berkovich indenter. For specimens irradiated with fluences of 5×1013 or 2×1014 ions/cm2, hardness values exceed that of un-implanted SiC. However, hardness sharply degrades for specimens irradiated with the highest fluence of 1×1015 ions/cm2. The specimens with fluences of 5×1013 and 2×1014 ions/cm2 and subsequently annealed at 700°C and 500°C, respectively, show the maximum hardness value.

Data taken with ACT2 and ACT3 between 1995 and 1997 are used to search for 0.1 s bursts of TeV gamma ray from evaporating primordial black holes (PBHs). There is no evidence for such bursts in the dataset. Using the result, the upper limit of 3×108pc-3yr-1 on the rate-density of evaporating PBHs is set in the vicinity of the solar system at a 99% confidence level.

Quantum cryptography allows the establishing of a highly confidential sequence of random bits between two parties who share no secret information in advance. Its security is guaranteed by the basic laws of quantum mechanics rather than mathematical difficulty. An experimental system based on a novel protocol for quantum cryptography using only two nonorthogonal photon polarization states is implemented. The photon sources are two semiconductor laser diodes operated at 680 nm, their light pulses which are heavily attenuated to far below one photon per pulse are employed to encode the key. Gated single photon detection technique is used to minimize the dark count effect of the photon multiplier tube. Key establishing rate of 40 b/s and error rate of 2.1% are obtained. Compared with other systems, our system has the simplest experimental setup.