Kunming Institute of Physics

Kunming, China

Kunming Institute of Physics

Kunming, China
SEARCH FILTERS
Time filter
Source Type

Tang L.,Hong Kong Polytechnic University | Tang L.,Kunming Institute of Physics | Ji R.,Kunming Institute of Physics | Li X.,Yunnan Normal University | And 8 more authors.
ACS Nano | Year: 2014

Material that can emit broad spectral wavelengths covering deep ultraviolet, visible, and near-infrared is highly desirable. It can lead to important applications such as broadband modulators, photodetectors, solar cells, bioimaging, and fiber communications. However, there is currently no material that meets such desirable requirement. Here, we report the layered structure of nitrogen-doped graphene quantum dots (N-GQDs) which possess broadband emission ranging from 300 to >1000 nm. The broadband emission is attributed to the layered structure of the N-GQDs that contains a large conjugated system and provides extensive delocalized π electrons. In addition, a broadband photodetector with responsivity as high as 325 V/W is demonstrated by coating N-GQDs onto interdigital gold electrodes. The unusual negative photocurrent is observed which is attributed to the trapping sites induced by the self-passivated surface states in the N-GQDs. © 2014 American Chemical Society.


Yang Z.,National University of Singapore | Yao L.,Kunming Institute of Physics | Lian Y.,National University of Singapore
IEEE Journal of Solid-State Circuits | Year: 2012

This paper presents a 0.5-V 1.5-bit double-sampled δσ modulator for audio applications. Unlike existing double-sampled designs, the proposed double-sampled δσ modulator employs an input-feedforward topology to reduce internal signal swings, thereby relaxing design requirements for the low-voltage building blocks and reducing distortion. Moreover, in order to avoid instability and noise shaping degradation, the proposed architecture restores the noise transfer function (NTF) of the double-sampled modulator to its single-sampled equivalent with the help of compensation loops. In the circuit implementation, the proposed fully-differential amplifier adopts an inverter output stage and a common-mode feedback (CMFB) circuit with a global feedback loop in order to reduce power consumption. A resistor-string-reference switch matrix based on a direct summation quantizer is used to simplify the analog compensation loop. The chip prototype has been fabricated in a 0.13-μm CMOS technology with a core area of 0.57 mm . The measured results show that when operating from a 0.5-V supply and clocked at 1.25 MHz, the modulator achieves a peak signal-to-noise and distortion ratio (SNDR) of 81.7 dB, a peak signal-to-noise ratio (SNR) of 82.4 dB and a dynamic range (DR) of 85.0 dB while consuming 35.2 μW for a 20-kHz signal bandwidth. © 2012 IEEE.


Zhang J.,National University of Singapore | Lian Y.,National University of Singapore | Yao L.,Kunming Institute of Physics | Shi B.,Institute for Infocomm Research
IEEE Journal of Solid-State Circuits | Year: 2011

The design of a low-voltage low-power fourth-order single-bit continuous-time Delta-Sigma modulator is presented in this paper for audio applications. The modulator employs an input-feedforward topology in order to reduce internal signal swings, thus relaxes the linearity and slew rate requirements on amplifiers leading to low-voltage operation and low-power consumption. The energy efficiency is further improved by embedding the summation of feedforward paths into the quantizer. For low-voltage operation, a gain-enhanced fully-differential amplifier and a body-driven rail-to-rail input CMFB circuit are developed. The modulator, implemented in a 0.13-μm standard CMOS technology with a core area of 0.11 mm2, achieves an 82-dB dynamic range (DR), and a 79.1-dB peak signal-to-noise and distortion ratio (SNDR) over a 20-kHz signal bandwidth. The power consumption of the modulator is 28.6 μW under a 0.6-V supply voltage. The achieved performance make it one of the best among state-of-the-art sub-1-V modulators in terms of two widely used figures of merit. © 2011 IEEE.


Tang L.,Hong Kong Polytechnic University | Tang L.,Kunming Institute of Physics | Ji R.,Kunming Institute of Physics | Li X.,Yunnan Normal University | And 2 more authors.
Journal of Materials Chemistry C | Year: 2013

The doping of carbon-based materials is of great importance due to its ability to modulate their optical, electrical and optoelectronic properties. Nitrogen-doped graphene quantum dots (N-GQDs) have received significant attention due to their superior electrocatalytic activity, optical properties and biocompatibility. The energy-level structure of N-GQDs remains unknown, which hinders the development of N-GQDs for various applications. Here, we report a one-pot synthesis method to prepare large-quantity N-GQDs at room temperature and atmospheric pressure under a prolonged reaction time. Using this approach, we can effectively dope N into the N-GQDs. As revealed by electron energy loss spectroscopy, N-doping introduces a new energy level into the electronic structure, which is responsible for tuning the optical properties of the N-GQDs. © 2013 The Royal Society of Chemistry.


Tang L.,Hong Kong Polytechnic University | Tang L.,Kunming Institute of Physics | Ji R.,Kunming Institute of Physics | Cao X.,Texas Tech University | And 8 more authors.
ACS Nano | Year: 2012

Figure Persented: Glucose-derived water-soluble crystalline graphene quantum dots (GQDs) with an average diameter as small as 1.65 nm (∼5 layers) were prepared by a facile microwave-assisted hydrothermal method. The GQDs exhibits deep ultraviolet (DUV) emission of 4.1 eV, which is the shortest emission wavelength among all the solution-based QDs. The GQDs exhibit typical excitation wavelength-dependent properties as expected in carbon-based quantum dots. However, the emission wavelength is independent of the size of the GQDs. The unique optical properties of the GQDs are attributed to the self-passivated layer on the surface of the GQDs as revealed by electron energy loss spectroscopy. The photoluminescence quantum yields of the GQDs were determined to be 7-11%. The GQDs are capable of converting blue light into white light when the GQDs are coated onto a blue light emitting diode. © 2012 American Chemical Society.


Li X.,Yunnan Normal University | Lau S.P.,Hong Kong Polytechnic University | Tang L.,Hong Kong Polytechnic University | Tang L.,Kunming Institute of Physics | And 2 more authors.
Journal of Materials Chemistry C | Year: 2013

Multicolour emission is realized in chlorine-doped GQDs (Cl-GQDs) prepared by a facile hydrothermal method using fructose and hydrochloric acid as source materials. The average diameter of a Cl-GQD is about 5.4 nm with 2 at.% Cl. The emission colour of the Cl-GQDs can be tuned successively from blue to white, orange, green and red simply by varying the excitation wavelength between 300 and 600 nm. The multicolour emission from the Cl-GQDs can be attributed to Cl doping, which introduces additional energy levels between C π and C π*. The multicolour Cl-GQDs should find applications in bioimaging and optoelectronic devices. © 2013 The Royal Society of Chemistry.


Yan S.-Y.,Kunming Institute of Physics | Li Q.-Y.,Kunming Institute of Physics | Rong B.-L.,Kunming Institute of Physics
Journal of Chinese Mass Spectrometry Society | Year: 2014

In order to create the detection method o methyl alcohol with low detection limit and high precision, kinds of 15 trace elements including Li, Na, K, Ca, Al, Mo, Sb, W in methyl alcohol were determined by inductively coupled plasma-mass spectrometry (ICP-MS). The results show that the linear correlative coefficients are in the range of 0.999 8-1.000. The contents of impurity elements are lower than 0.5 μg/L in methyl alcohol. The results of testing are accurate, the recoveries of the elements are 92%-105%, the relative standard deviation(RSD) is less than 4% and the precision of testing is high. The detection limit of method is low, which is in the range of 0.000 5-0.010 0 μg/L. This method is rapid and accurate, which can determine 15 trace elements in high purity methyl alcohol.


Li X.,Yunnan Normal University | Lau S.P.,Hong Kong Polytechnic University | Tang L.,Hong Kong Polytechnic University | Tang L.,Kunming Institute of Physics | And 2 more authors.
Nanoscale | Year: 2014

Sulphur-doped carbon-based materials have attracted a great deal of interest because of their important applications in the fields of oxygen reduction reactions, hydrogen storage, supercapacitors, photocatalysts and lithium ion batteries. Here, we report a new member of sulphur-doped carbon-based materials, i.e. sulphur doped graphene quantum dots (S-GQDs). The S-GQDs were prepared by a hydrothermal method using fructose and sulphuric acid as source materials. Absorption and photoluminescence investigations show that inter-band crossings are responsible for the observed multiple emission peaks. The incorporation of ∼1 at% of S into the quantum dots can effectively modify the electronic structure of the S-GQDs by introducing S-related energy levels between π and π* of C. The additional energy levels in the S-GQDs lead to efficient and multiple emission peaks. This journal is © the Partner Organisations 2014.


Xia M.,Kunming Institute of Physics | Chen X.,Kunming Institute of Physics
International Journal of Refrigeration | Year: 2010

This paper analyzes resonant frequency of the moving magnet linear compressor of Stirling cryocooler. The CFD (Computational Fluid Dynamics) and FEM (Finite Element Method) are used for the analysis of resonant frequency with FLUENT 6.2 and ANSYS 11.0 and an experiment is designed for testing the resonant frequency of moving magnet linear compressor. Results from simulations and experiments showed that the resonant frequency of the moving magnet linear compressors is affected by the machine spring, the gas spring, the magnet spring, and the mass of moving assembly, while the resonant frequency of the moving coil linear compressors is only affected by the machine spring, the gas spring, and the mass of moving assembly. © 2010 Elsevier Ltd and IIR.


Yao L.,Kunming Institute of Physics
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

Photo current integration is the key to improve the performance of a thermal imaging system. By integrating the photo current in the capacitance, the signal-to-noise ratio of the system is greatly improved. Theoretically, the maximum integration time of a thermal imaging system is the frame time of the system. However, due to the low well capacity of the readout integrated circuit, the integration time of the photo current is often shorter than the frame time of the system. To increase the well capacity of the readout circuit is one of the main research topics in thermal imaging system. The super-framing technique can overcome the restriction by reading-out the detector signal in a rate higher than the frame rate and then integrating the signal outside the IRFPA. As the signal integration is carried out outside the pixel, the integration time is no longer restricted. The key of the super-framing technique is the transmission of the signal in high readout rate. The digital readout circuit by integrating the analog-to-digital converter (ADC) array on the readout circuit chip becomes more and more popular with the development of CMOS technologies. Since the digital signal can be transferred outside the chip in a GS/s rate without any concern on noise and distortion, the super-framing technique based on digital readout circuit is advantageous over the analog solution. © 2014 SPIE.

Loading Kunming Institute of Physics collaborators
Loading Kunming Institute of Physics collaborators