K. Xu

Chinese Academy of Sciences, Peping, Beijing, China

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Publications (80)118.57 Total impact

  • Microscopy (Oxford 11/2015; 64(suppl 1):i58-i58. DOI:10.1093/jmicro/dfv170
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    Y Bi · X Han · K Xu · H Zhong ·

    European journal of vascular and endovascular surgery: the official journal of the European Society for Vascular Surgery 07/2015; 50(4). DOI:10.1016/j.ejvs.2015.04.037 · 2.49 Impact Factor
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    ABSTRACT: Different content of Er ions implanted GaN were prepared and annealed at different temperature and atmosphere. The effect mechanism of annealing temperature and atmosphere were investigated. The results show that as the Er ions dose was 1×1015 cm-2, the luminescence intensity is the strongest. When the Er ions dose is 5×1015 cm-2, the luminescence quenching could be observed. ©, 2015, Rengong Jingti Xuebao/Journal of Synthetic Crystals. All right reserved.
    Rengong Jingti Xuebao/Journal of Synthetic Crystals 06/2015; 44(6):1569-1574.
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    ABSTRACT: An apparently different effect of excitonic luminescence has been observed on the Ga-/N-faces of a free-standing HVPE GaN. The neutral donor-bound exciton ( D 2 0 X) emission of the N-face is only dominant at lower temperature as compared with that of the Ga-face. Moreover, the temperature-related ratio of the peak intensity of D 2 0 X to X A n=1 (a free exciton) is found to be about 2.8, which is in coincidence with the ratio of the average dislocation density of the N-face to the Ga-face confirmed by Cathodoluminiscence images. These details could provide useful information for the design of GaN-based and related devices.
    Optical Materials Express 03/2014; 4(3). DOI:10.1364/OME.4.000553 · 2.84 Impact Factor
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    ABSTRACT: A detailed study on electrical and optical inhomogeneity in N-face GaN grown by hydride vapor phase epitaxy is presented. There are two distinctive regions with non-homogeneous electrical and optical properties in N-face of GaN revealed by wet etching, Raman and cathodoluminescence. One region exclusively exhibited stronger donor–acceptor pair emission and higher carrier concentration due to impurity incorporation. A strong red-shift of near band edge emission of ∼24 meV was also observed owing to additional carrier concentration. Furthermore, the activation energy difference of the etching process between the two regions is ∼0.12 eV. The distinctive etching topography was probably due to the difference of surface potentials related to the level of carrier concentration in GaN.
    Journal of Crystal Growth 06/2013; 372:43–48. DOI:10.1016/j.jcrysgro.2013.03.018 · 1.70 Impact Factor
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    ABSTRACT: Two types of GaN-based ultraviolet (UV) photodetectors were fabricated by using NiAu and Ga-doped ZnO (GZO) as electrode materials, respectively. Dark current-voltage and photoresponse characteristics of the devices were investigated. It is found that in addition to the ∼365 nm cut-off response of GaN, an enhanced responsivity at around 250 nm is achieved for the GZO/GaN photodetectors. Photo absorption measurements provide proof that the efficient deep UV absorption occurs in the solar blind spectral zone. Transmission electron microscopy observations reveal the existence of nanostructures in the GZO thin film. Such nanostructures could be responsible for the deep UV photoresponse.
    Applied Physics Letters 05/2013; 102(21). DOI:10.1063/1.4808381 · 3.30 Impact Factor
  • X J Su · K Xu · Y Xu · G Q Ren · J C Zhang · J F Wang · H Yang ·
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    ABSTRACT: A study on brittle cracking in GaN films processed by laser lift-off is presented. Two kinds of cracks were found in the N-polar face of GaN after the laser lift-off process, namely perpendicular cracks along the {1 −1 0 0} planes and lateral cracks along the (0 0 0 −1) plane, respectively. Single-shot laser damage is studied to understand the cracking mechanism. The damage morphology indicates that the GaN material on the edge of the laser ablation area experiences three loading modes: shear stress PS, longitudinal compressive stress PL and transverse tensile stress PT. Under shock PL, lateral cracks likely appear and extend from the illuminated region along the interface in mode I. Furthermore, two different kinds of perpendicular cracks were found, namely shear cracks (PC I) and deflection cracks (PC II). A strong PS gives rise to PC I while a cooperative action of PL and PT results in PC II. In addition, there exist a critical effective spot size dPth and a critical ratio of the laser spot size dL to the effective spot size dP, when cracks occur over them.
    Journal of Physics D Applied Physics 05/2013; 46(20):205103. DOI:10.1088/0022-3727/46/20/205103 · 2.72 Impact Factor
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    Y Bi · H Zhong · K Xu · Y Ni · X Qi · Z Zhang · W Li ·
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    ABSTRACT: OBJECTIVES: To modify the method for creating an abdominal aortic aneurysm in rabbits, and to study its performance. MATERIALS AND METHODS: A total of 24 New Zealand white rabbits were induced topically with 10 μl of porcine elastase (0, 0.1, 5 and 10 units μl(-1)) to define the optimal concentration (groups A-D). Twelve aneurysms were induced with 10 units μl(-1) of 10 μl elastase to serve as a follow-up group (group E) to serve as a follow-up. A 1.5-cm aortic segment was isolated and induced with elastase solution for 30 min. RESULTS: All animals in groups D and E developed AAA by day 5. Aneurysms in Group E were stable over 100 days. Partial destruction to disappearance of elastic lamellae and smooth muscle cells (SMCs) was seen in elastase-treated animals by day 5. Regenerated elastin and proliferated SMCs were present in group E. Matrix metalloproteinases 2 and 9 and RAM11 showed strong expression in group D, but expression decreased in group E after day 15. CONCLUSIONS: The rabbit AAA model induced via topical application of porcine elastase at 10 units μl(-1) for 30 min appears easy and simple, with shorter induction and more rapid aortic dilation. The model is stable over 100 days and is useful to study the formation and progress of AAAs.
    European journal of vascular and endovascular surgery: the official journal of the European Society for Vascular Surgery 12/2012; 45(2). DOI:10.1016/j.ejvs.2012.11.015 · 2.49 Impact Factor
  • Y Tang · L Kong · F Wu · F Womer · W Jiang · Y Cao · L Ren · J Wang · G Fan · H P Blumberg · K Xu · F Wang ·
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    ABSTRACT: Background: Convergent studies provide support for abnormalities in the structure and functioning of the prefrontal cortex (PFC) and the amygdala, the key components of the neural system that subserves emotional processing in major depressive disorder (MDD). We used resting-state functional magnetic resonance imaging (fMRI) to examine potential amygdala-PFC functional connectivity abnormalities in treatment-naive subjects with MDD. Methods: Resting-state fMRI data were acquired from 28 individuals with MDD and 30 healthy control (HC) subjects. Amygdala-PFC functional connectivity was compared between the MDD and HC groups. Results: Decreased functional connectivity to the left ventral PFC (VPFC) from the left and right amygdala was observed in the MDD group, compared with the HC group (p < 0.05, corrected). Conclusions: The treatment-naive subjects with MDD showed decreased functional connectivity from the amygdala to the VPFC, especially to the left VPFC. This suggests that these connections may play an important role in the neuropathophysiology of MDD at its onset.
    Psychological Medicine 11/2012; 43(9):1-7. DOI:10.1017/S0033291712002759 · 5.94 Impact Factor
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    W Li · K Xu · H Zhong · Y Ni · Y Bi ·
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    ABSTRACT: To evaluate the feasibility and safety of a new unibody branched stent-graft for reconstruction of the canine aortic arch. Twenty adult hybrid dogs were used for the experiments. Ten dogs were implanted with single-branched stent-grafts; the other ten dogs were implanted with double-branched stent-grafts. The stent-grafts were implanted transluminally via the abdominal aorta. The branched limbs were caught and pulled into supra-aortic vessels using gooseneck snare wires introduced via the axillary arteries. The animals were euthanized 4 months after implantation. One of the ten dogs implanted with a single-branched stent-graft died from failure of the implantation procedure, and two of the ten dogs implanted with double-branched stent-grafts died from failure of the procedure and excessive blood loss. After month 4, the remaining unibody branched stent-grafts were patent and did not migrate. This new unibody branched stent-graft could be used to reconstruct the aortic arch. This is a total endovascular technique, and compared to other branched stent-grafts appears to be safer and easier to implant.
    European journal of vascular and endovascular surgery: the official journal of the European Society for Vascular Surgery 05/2012; 44(2):139-44. DOI:10.1016/j.ejvs.2012.05.015 · 2.49 Impact Factor
  • Yu Ji · Yan Li · J. Wu · F.Z. Zhang · K. Xu · W. Li · X.B. Hong · J.T. Lin ·
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    ABSTRACT: A method of 40 GHz phase stable short pulses generation is experimentally demonstrated. It is based on a dual parallel Mach–Zehnder modulator (DPMZM) driven by only one electrical sinusoidal clock and two cascaded phase modulators. The generated pulses are characterized with full-width-at-half-maximum pulse width of 1.9 ps, extinction ratio of 27 dB, timing jitter of 36 fs and signal to noise ratio over 30 dB. The high quality and phase stability of the pulses are further experimentally verified in a 4 × 40 GBaud differential quadrature phase shift keying (DQPSK) optical-time-division-multiplexing (OTDM) system.
    Optics Communications 04/2012; 285(7):1964–1969. DOI:10.1016/j.optcom.2011.12.071 · 1.45 Impact Factor
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    ABSTRACT: Indium-rich InGaN epitaxial layers with a p-i-n structure were grown pseudomorphically on a strain-relaxed InGaN template to reduce structural strain induced by lattice mismatch. We applied a nano-sculpting process to improve the crystal quality of the strain-relaxed InGaN template. The results show that the nano-sculpting process can suppress effectively the threading dislocation generation and improves significantly the I-V characteristic of the InGaN p-i-n structure. This InGaN template technique with nano-sculpting process shows great potential for future applications in indium-rich InGaN optic-electron devices.
    Optics Express 03/2012; 20(7):8093-9. DOI:10.1364/OE.20.008093 · 3.49 Impact Factor
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    ABSTRACT: A study on the bound states of Fe impurities in GaN by ultraviolet photoluminescence (PL) emissions is presented. Two elusive PL lines were observed at 3.463 eV (L1) and 3.447 eV (L2), respectively. The intensities of the two lines are proportional to the Fe concentration. The temperature dependence of L1 and L2 revealed acceptor-like and strong localized characteristic, respectively. Furthermore, Raman analysis indicated that L2 is correlated to an exciton bound to a nitride-vacancy (VN) related complex, i.e., [Fe2+-VN]. By co-doping with Si, the [Fe2+-VN]-related bound state will enable the spin-coupling between isolated iron ions.
    Applied Physics Letters 01/2012; 100(4). DOI:10.1063/1.3679133 · 3.30 Impact Factor
  • Yu Ji · Y. Li · J. Wu · F. Z. Zhang · K. Xu · W. Li · X. B. Hong · J. T. Lin ·
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    ABSTRACT: We demonstrate 40-GHz phase stable short optical pulses generation using an electroabsorption modulator and cascaded phase modulators. The pulses are characterized with a small pedestal, $\sim$ 2.1-ps pulsewidth, an extinction ratio larger than 23 dB, timing jitter less than 60 fs, and an optical signal-to-noise ratio over 40 dB over 30-nm tuning range. The high quality and phase stability of the pulses are further experimentally verified in a 4$\,\times\,$ 40 GBaud differential quadrature phase-shift-keying (DQPSK) optical-time-division-multiplexing (OTDM) system.
    IEEE Photonics Technology Letters 01/2012; 24(1):64-66. DOI:10.1109/LPT.2011.2172406 · 2.11 Impact Factor
  • L. Li · B. Wu · J. Qiu · Y. Li · H. Guo · Y. Zuo · X. Hong · Y. Dai · K. Xu · J. Wu · J. Lin ·
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    ABSTRACT: We demonstrate a photonic logic gate for RZ-PolSK signals based on bidirectional FWM in HNLF. Multi-function, such as XOR, ̄AB, ̄AB, XNOR, AND, NOR, half-subtracter, half-adder, comparator and decoder, are simultaneously implemented.
  • M Cui · T F Zhou · M R Wang · J Huang · H J Huang · J P Zhang · K Xu · H Yang ·
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    ABSTRACT: A comprehensive temperature characterization method based on the GaNE2-high Raman mode and sapphire ruby R fluorescence lines from Raman spectra was developed to analyse the thermal distribution and heat transfer process of high-power flip-chip InGaN/GaN LEDs (FC LEDs). Our analysis demonstrated that in addition to the known problem that the edges of mesa were always the hottest point of FC LEDs, which was due to the current crowding effect, a noteworthy temperature difference was first observed between the sapphire substrate and n-GaN when the injection current was above 300 mA. A 'heat reservoir' was suggested to occur at the interface between the sapphire and n-GaN due to poor thermal conductivity of sapphire when a large amount of heat from the hottest spot cannot be effectively transferred to the Si mount via the active region under high injection currents.
    Journal of Physics D Applied Physics 08/2011; 44(35):355101. DOI:10.1088/0022-3727/44/35/355101 · 2.72 Impact Factor
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    J.F. Tao · H. Cai · A.B. Yu · Q.X. Zhang · J. Wu · K. Xu · J.T. Lin · G.Q. Lo · D.L. Kwong · A.Q. Liu ·
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    ABSTRACT: In this paper, an optical switch driven by the optical force is demonstrated based on Nanoelectromechanical system (NEMS) technology. The switch consists of a Mach-Zehnder interferometer (MZI) and a ring resonator. One of the MZI arms is suspended to enable optical switching by optical force induced displacement. The optical force is introduced by injecting a control light into the ring resonator. It has a switching contrast of 16 dB and a response time of 0.2 μs, which is 10<sup>3</sup> times faster than the traditional millimeter-scaled optical switches. It has potential applications in the high speed optical-packet-switching communications and the silicon-photonic integrated circuits.
    Solid-State Sensors, Actuators and Microsystems Conference (TRANSDUCERS), 2011 16th International; 07/2011
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    ABSTRACT: This paper reports a silicon-based micromachined optical power detector with on-chip measurement ability. The optical power is detected by an integrated electron-tunneling displacement transducer, in which optical force is employed as the bridge between optical energy and mechanical energy transition. Compared with the traditional optical power detectors, which are based on photo absorption, the proposed optical power detector has advantages of small size (0.08 mm × 0.3 mm), low thermal noise (0.03 V/°C), large measurement range (>;20 mW) and wavelength independence. Therefore, it has potential applications as high-speed detecting element in silicon-based photonic chips and lab-on-chip systems.
    Solid-State Sensors, Actuators and Microsystems Conference (TRANSDUCERS), 2011 16th International; 07/2011
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    ABSTRACT: The dislocation multiplication and movement mechanism in GaN single crystals has been studied using nanoindentation and cathodoluminescence. Dislocation loops can multiply and move from plane to plane by cross-slip, thus producing a wide plastic deformation in GaN during indentation. This mechanism is further supported by the remarkable movement of indentation induced dislocations during annealing. Furthermore, the so-called pop-in events, in which the indenter suddenly enters deeper into the material without the application of any additional force, can be better understood by considering the cross-slip mechanism.
    Applied Physics Letters 06/2011; 98(22-98):221906 - 221906-3. DOI:10.1063/1.3593381 · 3.30 Impact Factor
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    J-L Yu · S Yang · Q Luo · H-L Wang · B Wang · Y-Y Qu · K Xu ·
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    ABSTRACT: This study investigated and summarized endovascular therapeutic strategies for intracranial ruptured aneurysms associated with arteriovenous malformations (AVMs). Between June 2005 and June 2009, we identified 16 aneurysms in 14 hemorrhagic cases of intracranial AVM using digital subtraction angiography (DSA). Of the 16 aneurysms, 14 were ruptured and two were unruptured. Aneurysms were classified as types I to IV, and were treated. Aneurysm treatment was followed by AVM treatment via various therapies, including embolization, gamma knife radiotherapy, or follow-up and observation to reduce the risk of aneurysm rupture or intracranial hemorrhage. Over a follow-up period ranging from six months to one year, none of the patients had aneurysm ruptures or intracranial hemorrhage. Most (13/14) patients had a Glasgow Outcome Scale (GOS) score of 5, and one patient had a score of 4. Sixteen aneurysms were treated successfully, as confirmed by DSA examination, and no AVMs re-grew. Clinical therapeutic strategies for intracranial ruptured aneurysms associated with AVMs should include aneurysm treatment first to reduce the risk of rupture and intracranial hemorrhage, eventually leading to a better prognosis.
    Interventional Neuroradiology 03/2011; 17(1):78-86. · 0.78 Impact Factor

Publication Stats

511 Citations
118.57 Total Impact Points


  • 2009-2014
    • Chinese Academy of Sciences
      • Institute of Semiconductors
      Peping, Beijing, China
  • 2012
    • Guangzhou Medical University
      Feng-t’ien, Liaoning, China
  • 2006-2012
    • Beijing University of Posts and Telecommunications
      • State Key Laboratory of Information Photonics and Optical Communications
      Peping, Beijing, China
    • Peking University
      • State Key Laboratory for Artificial Microstructure and Mesoscopic Physics
      Peping, Beijing, China
  • 2011
    • Jilin University
      Yung-chi, Jilin Sheng, China
  • 2007
    • Nanjing Medical University
      • Department of Endocrinology
      Nan-ching, Jiangsu Sheng, China