Development of novel flexible black silicon

We report a new type of black silicon: flexible black silicon. A silicon-on-insulator (SOI) wafer is irradiated by automatically scanning a femtosecond laser and then split by etching out the SOI silica middle layer. Large-area, uniform micro spikes on the surface of a very thin flexible silicon layer are obtained. The black silicon shows good flexibility and optical properties. The absorption spectrum of the flexible black silicon is as high as 97% in the visible and insensitive to the change of the incident angle of the light, which makes it a potential good candidate as an absorber for the solar-thermo generator.     

Control of resonant peak depths of tunable long-period fiber gratings using overcoupling

We present a method to reduce changes in the resonant peak depth of a long-period fiber grating (LPFG) as the resonant band is tuned by varying the external refractive index. We theoretically analyze the effects of the initial coupling strength on the peak depth change as external refractive index is varied. By controlling the initial coupling strength, it is experimentally demonstrated that an optimum peak depth can be obtained over a range of operating wavelengths that will maximize the sensitivity and stability of LPFG based sensors and tunable filters.     

Experimental realization of self-guiding unidirectional electromagnetic edge states

We present an experimental demonstration of self-guiding electromagnetic edge states existing along the zigzag edge of a honeycomb magnetic photonic crystal. These edge states are shown to possess unidirectional propagation characteristics that are robust against various types of defects and obstacles. In particular, they allow for the unidirectional transport of electromagnetic energy without requiring an ancillary cladding layer.     

Tuning the metal-insulator transition in manganite films through surface exchange coupling with magnetic nanodots

In strongly correlated electronic systems, the global transport behavior depends sensitively on spin ordering. We show that spin ordering in manganites can be controlled by depositing isolated ferromagnetic nanodots at the surface. The exchange field at the interface is tunable with nanodot density and makes it possible to overcome dimensionality and strain effects in frustrated systems to greatly increasing the metal-insulator transition and magnetoresistance. These findings indicate that electronic phase separation can be controlled by the presence of magnetic nanodots.     

Mn-Cu合金成分对去合金化法制备纳米多孔铜的影响

 采用电弧熔炼制备出前驱体Mn-Cu合金,在稀盐酸溶液中自由腐蚀去合金化,制备出具有双连续结构的纳米多孔铜。研究了前驱体合金的成分对纳米多孔铜微观结构及Mn的选择性腐蚀程度的影响。结果表明：前驱体Mn-Cu合金的Cu原子分数为43%时,其去合金化受到抑制,存在明显的未完全去合金化的岛状结构;前驱体Mn-Cu合金的Cu原子分数为32%～23%时,可完全去合金化,形成平均孔径尺寸为20～100 nm,平均系带尺寸为30～80 nm,具有双连续结构的纳米多孔铜;前驱体Mn-Cu合金的Cu原子分数低至20%时,去合金化后存在大量裂纹,形成纳米颗粒聚集体。纳米多孔铜中存在少量的残余Mn,残余Mn的原子分数随着前驱体合金Mn原子分数的增高而降低。实验表明腐蚀液浓度对纳米多孔铜形貌也存在影响。     

W波段磁控管型高次谐波潘尼管的研究与设计北大核心CSCD

针对在高频率、高效率、低磁场及低电压工作方面具有自身独特优势的磁控管型高次谐波潘尼管进行了研究与设计。通过对磁控管型谐振系统的研究,指出了工作在高次谐波时谐振系统设计与谐波次数选择的问题。在此基础上完成了对采用11腔、工作在2π模式的高次谐波潘尼管的设计。3维粒子仿真和优化的结果表明:该器件可以在磁场为0.379T、工作电压为30kV、工作电流为1A、横纵速度比为2的条件下,在W波段(99.1GHz)得到8.6kW的功率输出,相应的束波转换效率达28.7%。     

风速对空气源热泵翅片管换热器结霜特性影响

针对风速对空气源热泵翅片管室外换热器结霜特性的影响进行了实验研究.实验结果表明,结霜量随风速的增加不是成线形增长,在风速为1.3m/s时结霜量最小.霜层厚度随着风速的增加反而减小,而翅片管换热器的最大换热量随着风速的增加而增加.     

Investigation on F–B–S tri-doped nano-TiO<Subscript>2</Subscript> films for the photocatalytic degradation of organic dyes

F–B–S tri-doped titanium dioxide thin films on common glass were prepared by a modified sol–gel method, in which tetrabutyl titanate (Ti(OC₄H₉)₄) was chosen as the precursor and boric acid (H₃BO₃), sodium fluoride (NaF), and thiourea (N₂H₄CS) were employed as boron, fluorine, and sulfur sources, respectively. The microstructure and optical property were characterized by X-ray diffraction, high-resolution field emission scanning electron microscopy, N₂ adsorption–desorption isotherms, photoluminescence spectrum, and UV–Vis diffraction reflectance spectroscopy. The photocatalytic performances were evaluated by decomposition of organic dyes in solution. The experimental results revealed that the F–B–S tri-doped TiO₂ thin film was composed of uniform round-like nano-particles with the size range of 5–8 nm. F–B–S tri-doping not only significantly promoted the UV-induced photodecomposition activities of TiO₂ films but also extended the optical response of TiO₂ red shift to visible light region, herein improving the visible light-induced degradation of organic dyes. The improvement mechanism by F–B–S tri-doping was also discussed.     

High-power diode-end-pumped Tm：YAP and Tm：YLF slab lasers

Diode-end-pumped continuous-wave(CW) Tm:YAP and Tm:YLF slab lasers are demonstrated. The a-cut Tm:YAP and Tm:YLF slabs with doping concentrations of 4 at.-% and 3.5 at.-%,respectively,are pumped by fast-axis collimated laser diodes at room temperature. The maximum CW output powers of 72 and 50.2 W are obtained from Tm:YAP and Tm:YLF,respectively,while the pump power is 220 W,corresponding to the slope efficiencies of 37.9% and 26.6%,respectively.     

Single-molecule surface-enhanced Raman scattering of R6G in aqueous environment under non-resonance conditions

The single-molecule surface-enhanced Raman scattering(SERS) spectra of Rhodamine 6G(R6G) in an aqueous environment under non-resonance conditions are studied.Series of spectra are recorded in timemapping mode,and intensity fluctuations of SERS signals and spectral diffusion are observed.The correlations between the presence frequency of SERS spectra and number of hot spots as well as the quantity of molecules in scattering volume are examined thoroughly.The results indicate that only molecules located at hot spots produce good signal-to-noise ratio Raman spectra and the origin of fluctuating SERS signals are mainly ascribed to the movement of hot spots.