氧化钨纳米线气敏传感器的制备及其室温NO_2敏感特性

纳米结构的氧化钨有高比表面积和气体吸附能力,在气体传感器领域得到了广泛研究.本文采用磁控溅射金属钨薄膜和两步热氧化工艺在二氧化硅衬底上生长出氧化钨纳米线.通过改变第二步氧化温度,研究退火温度对氧化钨纳米线气敏特性的影响.采用扫描电子显微镜、X射线衍射仪、X射线光电子能谱分析仪和透射射电子显微镜表征材料的微观特性和晶体结构,利用静态配气法测试气敏性能.研究结果表明,经过退火处理后氧化钨纳米线密度略微降低,300℃比400℃退火后的氧化钨结晶性差,对应的表面态含量多,有利于室温气体敏感性.测试NO_2的气敏性能,经过对比得出300℃退火温度下制备的氧化钨纳米线在室温下表现出较很好的气敏响应,对6 ppm(1 ppm=10~(-6))NO_2达到2.5,对检测极限0.5 ppm NO_2响应达1.37.氧化钨纳米线在室温下表现出反常的P型响应,是因为氧化钨纳米线表面被氧气吸附形成反型层,空穴取代电子成为主要载流子所致.     

Room temperature NO_2-sensing properties of hexagonal tungsten oxide nanorods

Hexagonal WO_3 nanorods were synthesized through a facile hydrothermal method. The nanorods properties were investigated by scanning electron microscope(SEM), transmission electron microscope(TEM), energy dispersive spectroscopy(EDS), and x-ray diffraction(XRD). The NO_2-sensing performances in terms of sensor response, response/recovery times and repeatability at room temperature were optimized by varying the heat treatment temperature of WO_3 nanorods. The optimized NO_2sensor(400-℃-annealed WO_3 nanorods) showed an ultra-high sensor response of 3.2 and short response time of 1 s to 5-ppm NO_2. In addition, the 400-℃-annealed sample exhibited more stable repeatability.Furthermore, dynamic responses measurements of annealed samples showed that all the annealed WO_3 nanorods sensors presented p-type behaviors. We suppose the p-type behavior of the WO_3 nanorods sensor to be that an inversion layer is formed in the space charge layer when the sensor is exposed to NO_2 at room temperature.Therefore, the 400-℃-annealed WO_3 nanorods sensor is one of the most energy conservation candidates to detect NO_2 at room temperature.     

钒掺杂W18O49纳米线的室温p型电导与NO2敏感性能

钨氧化物纳米线在高灵敏度低功耗气体传感器中极具应用潜力, 且通过掺杂改性可进一步显著改善其敏感性能. 本文以WCl₆为钨源, NH₄VO₃为掺杂剂, 采用溶剂热法合成了钒掺杂的W₁₈O₄₉纳米线. 利用扫描电镜、透射电镜、X射线衍射、X射线光电子能谱仪表征了纳米线的微结构, 并利用静态气敏性能测试系统评价了掺杂纳米线的NO₂敏感性能. 研究结果表明: 五价钒离子受主掺杂进入氧化钨晶格结构, 抑制了纳米线沿轴向的生长并导致了纳米线束的二次集聚; 室温下, 钒掺杂W₁₈O₄₉纳米线接触NO₂气体后表现出反常的p型响应特性; 随工作温度逐渐升高至约110 ℃时, 发生从p型到n型的电导特性转变; 该掺杂纳米线气敏元件对浓度低至80 ppb (1 ppb=10^-9) 的NO₂气体具有明显的室温敏感响应和良好的响应稳定性. 分析并探讨了钒掺杂W₁₈O₄₉纳米线的高室温敏感特性及其p-n电导转型机理, 认为钒掺杂W₁₈O₄₉纳米线在室温下的良好敏感响应及反常p型导电性与掺杂纳米线表面高密度非稳表面态诱导的低温气体强吸附有关. 关键词： 氧化钨 纳米线 气体传感器 室温灵敏度     

Fabrication of CoFe_2O_4 ferrite nanowire arrays in porous silicon template and their local magnetic properties

CoFe_2O_4 ferrite nanowire arrays are fabricated in porous silicon templates. The porous silicon templates are prepared via metal-assisted chemical etching with gold(Au) nanoparticles as the catalyst. Subsequently, CoFe_2O_4 ferrite nanowires are successfully synthesized into porous silicon templates by the sol–gel method. The magnetic hysteresis loop of nanowire array shows an isotropic feature of magnetic properties. The coercivity and squareness ratio(M_r/M_s) of ensemble nanowires are found to be 630 Oe(1 Oe = 79.5775 A·m~(-1) and 0.4 respectively. However, the first-order reversal curve(FORC) is adopted to reveal the probability density function of local magnetostatic properties(i.e., interwire interaction field and coercivity). The FORC diagram shows an obvious distribution feature for interaction field and coercivity. The local coercivity with a value of about 1000 Oe is found to have the highest probability.     

Preparation and room temperature NO_2-sensing performances of porous silicon/V_2O_5nanorods

In this paper, porous silicon/V₂O₅ nanorod composites are prepared by a heating process of as-sputtered V film on porous silicon (PS) at 600 ℃ for different times (15, 30, and 45 min) in air. The morphologies and crystal structures of the samples are investigated by field emission scanning electron microscope (FESEM), x-ray diffractometer (XRD), x-ray photoelectron spectroscopy (XPS), and Raman spectrum (RS). An improved understanding of the growth process of V₂O₅ nanorods on PS is presented. The gas sensing properties of samples are measured for NO₂ gas of 0.25 ppm～3 ppm at 25 ℃. We investigate the effects of the annealing time on the NO₂-sensing performances of the samples. The sample obtained at 600 ℃ for 30 min exhibits a very strong response and fast response-recovery rate to ppm level NO₂, indicating a p-type semiconducting behavior. The XPS analysis reveals that the heating process for 30 min produces the biggest number of oxygen vacancies in the nanorods, which is highly beneficial to gas sensing. The significant NO₂ sensing performance of the sample obtained at 600 ℃ for 30 min probably is due to the strong amplification effect of the heterojunction between PS and V₂O₅ and a large number of oxygen vacancies in the nanorods.     

银纳米颗粒/多孔硅复合材料的制备与气敏性能研究

采用双槽电化学腐蚀法以电阻率为10-15 Ω·cm的p型<100>晶向的单晶硅片制备了孔径约为1.5 μm, 孔深约为15-20 μm的p型多孔硅, 并以此多孔硅作为基底采用无电沉积法通过调控沉积时间在其表面沉积了不同厚度的银纳米颗粒薄膜. 采用扫描电子显微镜和X 射线衍射仪表征了银纳米颗粒/多孔硅复合材料的形貌和微观结构, 结果表明银纳米颗粒较均匀的分布于多孔硅的表面上且沉积时间对产物的形貌有重要影响. 采用静态配气法在室温下研究了银纳米颗粒/多孔硅复合材料对NH₃的气敏性能. 气敏测试结果表明沉积时间对产物的气敏性能影响较大. 当沉积时间较短时, 适量银纳米颗粒掺杂的多孔硅复合材料由于其较高的比表面积以及特殊的形貌和结构, 对NH₃气体表现出较高的灵敏度、优良的响应/恢复性能. 室温下, 其对50 ppm 的NH₃气体的气敏灵敏度可以达到5.8左右.     

光照对HF/Fe(NO3)3溶液中制备硅纳米线的作用研究

以不同掺杂浓度的单晶n型硅为衬底、金属银为催化剂、硝酸铁作为氧化剂制备硅纳米线, 系统研究了光照对不同硝酸铁浓度条件下用化学腐蚀法制备硅纳米线的作用. 研究发现, 不同掺杂浓度的硅衬底, 光照对硅纳米线长度的影响明显不同. 通过对比硅纳米线的长度, 发现光照对硅纳米线的形成兼具促进和溶解作用, 并分别从能带结构、电化学表征和光致发光等方面对这两种作用的形成机理进行了深入讨论.     

基于电学调制相消法和高功率蓝光LD的离轴石英增强光声光谱NO2传感器设计和优化

使用中心波长为450 nm的高功率多模蓝光激光管(LD)作为激励光源, 结合电学调制相消法和离轴石英增强光声光谱(QEPAS)配置, 设计了一款高灵敏二氧化氮传感器. 电学调制相消法使离轴QEPAS传感器的背景噪声降低至1/269, 在标准大气压和1 s积分时间下, 获得的探测灵敏度为4.5 ppb, 对应的归一化噪声等效吸收系数(1σ )为2.2×10^-8 cm^-1·W/Hz^1/2. 延长积分时间到46 s, 灵敏度能够进一步下降到0.34 ppb. 气体流速对该传感器的影响也被研究.     

Porous silicon templates for electrodeposition of nanostructures

We report the fabrication and characterization of porous silicon templates for electrodeposition of high aspect ratio one-dimensional metallic nanostructures (nanowires/nanoparticles) in them. Even though nanostructures/nanowires in the past have been fabricated in alumina, polymer or silica templates, the advantages of this approach are the possibility for seamless integration of nanostructures with other silicon components, and silicon based sensors because of better physical and electrical interconnection between the nanostructure and the silicon substrate. In this work, fabrication and characterization of nanowires/nanostructures such as single-segment Ni–Fe and Au and two-segment Ni–Fe/Au electrodeposited in the porous silicon template are presented. The templates with ordered and controlled nanometer-sized pores, 40 nm and 290 nm in diameter, were created through porous Si etching. The morphology, composition and structural characteristics of the template and of the single-segment Ni–Fe and Au and two-segment Ni–Fe/Au nanostructures of diameter 275±25 nm, length up to 100 μm and pitch of 1 μm were analyzed using scanning electron microscopy and X-ray diffraction techniques. The micrographs confirm that the plating parameters have a strong influence on morphology and composition of the structures. Further, the Ni–Fe images show the formation of both vertical and branched nanowires along with nanoparticles, from breakage/discontinuous growth of nanowires. Ni–Fe nanostructures were further analyzed for temperature-dependent magnetization and magnetization vs. magnetic field measurements using a commercial physical property measurement system. They reveal no magnetic anisotropy of the nanostructures probably due to a balance between ‘reduced’ shape anisotropy from branched and rough pore surfaces and magnetocrystalline anisotropy. PACS 61.46.+w; 75.75.+a; 81.07.-b; 81.16.Be     

多孔ZnO微米球的制备及其优异的丙酮敏感特性

以六水合硝酸锌、尿素为原料,以六亚甲基四胺为表面活性剂,利用水热法合成了多孔氧化锌微米球.通过X射线衍射仪、扫描电子显微镜和吸附仪对样品的结构、形貌、比表面积和孔径进行了表征.利用所得多孔微米球氧化锌制备了气敏元件,并对其气敏特性进行了测试.结果表明:在280℃的工作温度下,表面多孔氧化锌微米球气敏元件对50 ppm的丙酮气体的灵敏度为26.8,响应时间和恢复时间分别约为4 s和10 s,并具有良好的选择性.     

Eu掺杂Si纳米线的光致发光特性

利用Si(111)衬底, 以Au-Al为金属催化剂, 基于固-液-固生长机理, 在温度为1100℃, N₂气流量为1.5 L/min、生长时间为30–90 min等工艺条件下, 制备了直径约为100 nm、长度为数微米的高密度、均匀分布、大面积的Si纳米线(～10¹⁰ cm^-2). 对Si纳米线进行了Eu掺杂, 实验研究了不同长度的Si纳米线以及不同掺杂温度、掺杂时间等工艺参数对Eu离子红光发射的影响, 利用扫描电子显微镜和X射线衍射仪对Si纳米线表面形貌和Eu掺杂后Si纳米线的结晶取向进行了测量和表征; 室温下利用Hitachi F-4600型荧光分光光度计对样品的激发光谱和发射光谱进行了测试和分析. 结果表明: 在Si纳米线生长时间为30 min、掺杂温度为1000℃、 最佳激发波长为395 nm时, 样品最强荧光波长为619 nm (⁵D₀→⁷F₂); 同时, 还出现了576 nm (⁵D₀→⁷F₀), 596 nm (⁵D₀→⁷F₁), 658 nm (⁵D₀→⁷F₃)和708 nm (⁵D₀→⁷F₄)四条谱带.     

宽带腔增强吸收光谱法测量大气NO2定标方法研究

非相干宽带腔增强吸收光谱法定量探测大气痕量气体浓度需要准确定标。以定量探测大气NO₂为目的,建立了基于蓝色发光二极管光源的非相干宽带腔增强吸收光谱测量系统,研究了(1)仅使用浓度已知的NO₂吸收光谱、(2)同时使用浓度已知的NO₂和纯氧气中氧气二聚体O₂-O₂吸收光谱、(3)利用纯氮气和纯氦气的瑞利散射消光差异等三种方法,分别获取非相干宽带腔增强吸收光谱在430～490 nm波段的镜片反射率定标曲线。三种方法得到的镜片反射率最大值对应波长均约为460 nm,但这些最大值存在一定差异,分别为0.999 25,0.999 33和0.999 37。利用NO₂样气吸收测量对比了三种定标方法,发现方法(1)与另外两种方法的测量结果不一致性分别约为14%和19%,而后两种方法所测结果的不一致性仅为4%。测量结果表明,NO₂标准气体浓度的不准确性以及壁损耗等因素恶化了方法(1)的定标精度,应尽量避免使用该定标方法。通过对实际大气中NO₂和O₂-O₂在440～485 nm波段内的同时测量,进一步验证了非相干宽带腔增强吸收光谱法的高灵敏度以及所用标定方法的有效性。     

Ce掺杂Si纳米线的制备及其蓝光发射特性

以抛光和“金字塔”织构表面的单晶Si(100)为衬底,分别以Au和Au-Al为金属催化剂,在温度为1 100 ℃、N₂气流量为1 500 sccm、生长时间为15～60 min等工艺条件下,制备了直径约为50～200 nm、长度为数微米至数十微米和不同分布的Si纳米线。然后,利用CeO₂粉末为掺杂剂,在温度为1 100～1 200 ℃、N₂流量为1 000 sccm、掺杂时间为30～60 min等工艺条件下对Si纳米线进行Ce掺杂。实验研究了不同Si纳米线长度、密度和分布等对Ce3+蓝光发射的影响。室温下利用Hitachi F-4600型荧光分光光度计对样品的激发光谱和发射光谱进行了测试和分析,同时利用FLS920全功能型荧光光谱仪对样品的荧光量子效率进行了测试。结果表明,在Si纳米线生长时间为30 min、织构表面和密度相对较低时以及最佳激发光波长为328 nm时,样品发射光波长为405 nm(5d→2F_5/2)荧光强度较大,实现了强的蓝光发射,其荧光量子效率达到了65.57%。通过光谱功率分布和CIE-1931标准公式进行计算,Ce掺杂Si纳米线样品的色坐标为(0.16, 0.03);发光强度大,量子效率高使其在照明、显示等领域有着潜在的应用价值,同时对Si纳米线在发光领域的研究和应用具有一定的参考价值。     

WO3/Pt复合薄膜的制备及其光电催化性能

导电玻璃作为基底水热法生长了WO₃纳米棒,通过电沉积法改变沉积Pt的时间(40 s,80 s,120 s),以WO₃纳米棒为基底沉积得到不同的WO₃/Pt复合薄膜样品。通过X射线衍射分析和扫描电子显微镜等测试手段将WO₃纳米棒薄膜和WO₃/Pt复合薄膜样品进行表征。结果表明成功制备了WO₃/Pt复合薄膜样品。漫反射结果显示WO₃/Pt复合薄膜与WO₃薄膜相比具有更强的光吸收。交流阻抗谱显示WO₃/Pt复合薄膜与WO₃纳米棒薄膜相比增强了电荷转移效率。利用光电流、光电催化对WO₃/Pt复合薄膜进行光电性能测试,结果表明WO₃/Pt复合薄膜相较于单一WO₃薄膜光电流活性更高和光电催化活性更强,并且沉积时间为80 s的WO₃/Pt复合薄膜显示最为优异的光电流和光电催化性能。同时,沉积时间为80 s的WO₃/Pt复合薄膜的光电催化性能优于其光催化和电催化性能。     

硅纳米线/氧化钒纳米棒复合材料的制备与气敏性能研究

采用纳米球光刻和金属辅助刻蚀法以p型单晶硅片制备了硅纳米线阵列, 并以此作为基底, 通过溅射不同时长的金属钒薄膜并进行热退火氧化处理, 制备出硅纳米线/氧化钒纳米棒复合材料. 采用扫描电子显微镜和X射线衍射仪表征了该复合材料的微观特性, 结果表明该结构增大了材料的比表面积, 有利于气体传感, 并且镀膜时间对后续生长的氧化钒纳米棒形貌有明显影响. 采用静态配气法在室温下测试了该复合材料对NO₂的气敏性能, 气敏测试结果表明沉积钒膜的时间对复合材料的气敏性能影响较大. 当选择合适的镀膜时间时, 适量氧化钒纳米棒增加了材料表面积并形成大量pn结结构, 相比纯硅纳米线对NO₂气体的灵敏度有明显提升, 且在室温下表现出优良的选择性. 同时, 对气敏机理做了定性解释, 认为硅纳米线与氧化钒纳米棒之间形成的pn结及能带结构在接触NO₂ 时的动态变化是其气敏响应提升的主要机制.     

Synthesis and room-temperature NO_2 gas sensing properties of a WO_3 nanowires/porous silicon hybrid structure

We report on the fabrication and performance of a room-temperature NO2 gas sensor based on a WO3 nanowires/porous silicon hybrid structure. The W18O49 nanowires are synthesized directly from a sputtered tungsten film on a porous silicon （PS） layer under heating in an argon atmosphere. After a carefully controlled annealing treatment, WO3 nanowires are obtained on the PS layer without losing the morphology. The morphology, phase structure, and crystallinity of the nanowires are investigated by using field emission scanning electron microscopy （FESEM）, X-ray diffractometer （XRD）, and high-resolution transmission electron microscopy （HRTEM）. Comparative gas sensing results indicate that the sensor based on the WO3 nanowires exhibits a much higher sensitivity than that based on the PS and pure WO3 nanowires in detecting NO2 gas at room temperature. The mechanism of the WO3 nanowires/PS hybrid structure in the NO2 sensing is explained in detail.     

X射线光电子能谱法研究硅纳米线的能带结构

制备了氧辅助热分解法,以一氧化硅为原料,以氩气为载气,维持管内压强为1000Pa,在高温炉中于1250℃下反应5 h后得到硅纳米线。硅纳米线经5%氢氟酸水溶液处理5 min后,与1×10-3 mol·L-1的氯化金溶液中反应5 min,在硅纳米线的表面上修饰了金纳米粒子,用X射线粉末衍射表征了产物的结构,同时观察到单质硅和金的XRD图谱;用电子扫描和透射显微镜观察了产物的形貌,表明氧辅助方法可制得大量均匀的硅纳米线,修饰在硅纳米线上的金纳米点形状整齐,尺寸均匀,平均直径约8 nm;并用X射线光电子能谱分析了修饰过程中能带结构的变化。结果表明,金纳米粒子表面带负电,它在施主能级和受主能级上都有电子存在;由于氧杂质的存在,硅纳米线的费米能级移向价带顶。     

闪烁晶体的发光研究进展

概述了近年来闪烁体发光研究的进展,主要介绍用于未来高能物理实验的新型闪烁体发光机理研究,选取我们在研BaF₂,BaF₂:RE,CeF₃以及PbWO₄中的一些新进展。重点谈及三点:(1)在BaF₂的“价带^→芯带”跃迁发光研究基础上进行稀土(Gd³⁺-Eu³⁺)掺杂时观察到的量子剪裁以及对多光子发光的新思考;(2)CeF₃晶体发光的级联能量传递中,Ce³⁺(290nm发射带)与缺陷发光中心(340nm发射带)间能量传递及其传递效率的温度依赖;(3)PbWO₄晶体的发光中心研究中,提出以“WO₄^-2+O_i”绿光中心替代“WO³+F”中心观点的依据。同时也简介了医用闪烁体的最新进展。     

过渡金属Cu、Cr掺杂TiO2表面氧化性气体NO2光学气敏传感特性

采用密度泛函理论（DFT）体系广义梯度近似（GGA）第一性原理平面波超软赝势方法,分析锐钛矿型TiO₂（101）表面吸附NO₂分子光学气敏传感的微观机理.结果表明：Cu和Cr原子易于掺入TiO₂（101）表面,掺杂表面能稳定地吸附NO₂分子且吸附后光学性质发生显著变化.表面吸附NO₂分子后,Cu掺杂TiO₂（101）表面对分子的吸附能最大,吸附后结构更稳定,分子与表面的距离最短.通过分析差分电荷密度和电荷布居数发现,NO₂分子与基底表面间发生电荷转移,转移电子数目：Cu掺杂表面 > Cr掺杂表面 > 无掺杂表面.对比吸收光谱和反射光谱发现,在Cu掺杂表面吸附分子后,光学性质变化最明显,说明表面与吸附分子间氧化还原能力是决定光学气敏传感性能的核心因素.在过渡金属中,Cu与Cr都有4s价电子结构,其4s电子降低了材料表面氧空位的氧化性,增加了其还原性.对于氧化性气体,可以提升表面与分子的氧化还原作用,而Cu的4s电子更加活泼,从而光学气敏传感特性更加明显.因此,Cu掺杂的TiO₂对氧化性气体是一种较好的光学气敏传感材料.     

Several nonlinear phenomena in Er3 doped silica optical fibers

Experimental researches on frequency upconverted processes in Er³⁺ and Er³⁺/Yb³⁺-doped silica optical fibers are reported. These processes include frequency upconverted fluorescent light at wavelength of 466 (468) nm in Er³⁺/GeO₂/SiO₂ (Er³⁺/A1³⁺/GeO₂/SiO₂) optical fibers and at wavelengths of 467, 546, and 667 nm in Yb³⁺/Er³⁺/GeO₂/SiO₂ optical fibers pumped by CW 1064 nm radiation, second harmonic generation (1064 nm-532 nm) with high peak power conversion efficiencies in Er³⁺ and Er³⁺/Yb³⁺-doped optical fibers, and 977 nm resonance enhanced antistokes of stimulated four-photon mixing in an Er³⁺ doped optical fiber pumped by high peak power 1064 nm radiation.