Al3O3N纳米线的制备与表征

在H2+Ar混合气氛中加入少许N2+O2气氛，采用直流电弧等离子体法制备了Al3O3N纳米线.用XRD，SEM，TEM，HRTEM测定了纳米线的成分、形貌特征、显微结构等.Al3O3N纳米线直径分布为25—110nm，长度达55μm.Al3O3N纳米线是尖晶石结构.另外，对Al3O3N纳米线的生长机理进行了研究. 关键词： 纳米线 等离子体 纳米结构陶瓷 尖晶石结构     

高质量单壁纳米碳管的CVD法合成及催化剂酸碱性对碳管生长的影响

采用燃烧法制备了Fe/Mo/MgO催化剂,用化学气相沉积法在1000℃下催化裂解甲烷制得了单壁纳米碳管.实验结果表明,550℃下焙烧的催化剂效果最好,适宜的酸碱性应该是催化剂具有较高活性的原因.用扫描电镜、透射电镜、高分辨透射电镜、热重分析和拉曼光谱等方法对制备的纳米碳管粗产品进行了表征.结果表明,该产物确为高质量单壁纳米碳管,其形态基本都以束状存在,且单壁纳米碳管直径分布较窄(0.85～1.22nm);对反应气氛的考察表明,CH4/N2=50/300为最佳,该气氛下所制得粗产物中单壁碳管的含量接近40%,经稀盐酸室温处理后,碳管含量可达到75%以上.     

热效应对纳米焊接界面结构的影响（英文）

采用分子动力学方法深入研究热效应对纳米焊接界面结构的影响。具体分析了碳管直径和时间的变化对界面结构的影响规律,并详细给出了1530K下的焊接过程。结果表明,除碳管(5,5)外,碳管(6,6),(7,7),(9,9),(11,11)中纳米线形成的时间分别为13.8,14.6,17.5,19.6ps。纳米线是由单根或多根Ni原子链组成,碳管(6,6),(7,7),(9,9),(11,11)中Ni原子链数分别为1,3,7和16。界面结构包括内部焊接和外部焊接。内部焊接的临界直径由碳管(6,6)决定,其值为0.814nm。在同一时刻,大直径的碳管可获得更大的外部接触长度。外部接触长度的增长速率随碳管直径的增加而增大,接触长度的最大增长速率可达0.013nm/ps。最后确定了界面结构形成临界温度,发现对于相同直径碳管,外部焊接的临界温度高于内部焊接的临界温度,临界温度与碳管直径无关。     

Al3O3N纳米线的制备与表征

在H2+Ar混合气氛中加入少许N2+O2气氛,采用直流电弧等离子体法制备了Al3O3N纳米线.用XRD,SEM,TEM,HRTEM测定了纳米线的成分、形貌特征、显微结构等.Al3O3N纳米线直径分布为25-110 nm,长度达5.5μm.Al3O3N纳米线是尖晶石结构.另外,对Al3O3N纳米线的生长机理进行了研究.     

催化剂比例对单壁碳纳米管制备的影响

采用电弧放电法以Y/Ni为催化剂制备了单壁碳纳米管 ,研究了不同催化剂比例对制备产物的影响。获得了不同激发波长下 (476 5～ 1 0 6 4nm)单壁碳纳米管的拉曼光谱 ,采用图表法对径向呼吸模的谱峰进行了认定。结果表明 :样品中碳管的直径分布在 1 2～ 1 6nm之间 ,直径在 1 43nm附近的碳管居多。催化剂的比例只是影响碳管的产额 ,对其直径分布的影响很小     

热效应对纳米焊接界面结构的影响

采用分子动力学方法深入研究热效应对纳米焊接界面结构的影响。具体分析了碳管直径和时间的变化对界面结构的影响规律,并详细给出了1530 K下的焊接过程。结果表明,除碳管(5,5)外,碳管(6,6),(7,7),(9,9),(11,11)中纳米线形成的时间分别为13.8, 14.6, 17.5, 19.6 ps。纳米线是由单根或多根Ni原子链组成,碳管(6,6),(7,7),(9,9),(11,11)中Ni原子链数分别为1,3,7和16。界面结构包括内部焊接和外部焊接。内部焊接的临界直径由碳管(6,6)决定,其值为0.814 nm。在同一时刻,大直径的碳管可获得更大的外部接触长度。外部接触长度的增长速率随碳管直径的增加而增大,接触长度的最大增长速率可达0.013 nm/ps。最后确定了界面结构形成临界温度,发现对于相同直径碳管,外部焊接的临界温度高于内部焊接的临界温度,临界温度与碳管直径无关。     

催化剂对热蒸发CVD法生长β-Ga2O3纳米材料的结构及发光特性的影响

用热蒸发CVD法制备了β-Ga2O3纳米材料,探讨了Au催化剂对纳米结构和形貌的影响,并研究了其光致发光特性。X射线衍射(XRD)分析显示产物为单斜结构的β-Ga2O3。扫描电子显微镜(SEM)测试表明:Au催化剂颗粒尺寸较小时,制备的产物为尺度均匀的β-Ga2O3纳米线,宽度小于100 nm,长度为几微米至几十微米;增加催化剂颗粒尺寸时,制备出的β-Ga2O3纳米结构的尺度变大,形貌由纳米线逐步形成纳米带、片等形状。β-Ga2O3纳米结构在波长516 nm处有很强的绿光发光带,而且随着催化剂颗粒尺寸的增加,发光强度和峰位"红移"现象逐渐减弱。     

CVD法制备碳纳米管的TG-DTA研究--温度对CVD法制备碳纳米管的影响

基于碳纳米管粗产品中无定形碳和不同直径碳纳米管对氧的反应活性的差异 ,通过差热 -热重 (TG DTA)方法 ,结合透射电镜 (TEM)和X射线衍射 (XRD)的测试结果 ,研究了合成温度对以乙炔气体为碳源 ,用CVD法制备碳纳米管的石墨化程度、碳纳米管直径以及直径分布的影响 .结果表明 :反应中 ,由于催化剂Co/SiO2中活性组分 (Co)微晶随合成温度的升高而增大 ,导致所制备的碳纳米管的直径增大 ,从 2 0～ 30nm (6 5 0℃ )增加到 30～ 5 0nm (75 0℃ ) .碳纳米管的石墨化程度随着反应温度的升高而增加 .XRD实验结果还表明 ,当合成温度从 6 5 0℃增加到 85 0℃时 ,2θ值从 2 5 .8°增加到 2 6 .8°,(0 0 2 )晶面的层间距从 3.45 减小到 3.32 ,即随着合成温度的升高 ,碳纳米管 (0 0 2 )晶面的层间距减小 .通过DTA放热峰的峰温和半峰宽的分析得出 ,无定形碳的放热峰峰温Tp<380℃ ,其含量随着温度的升高而减小 .碳纳米管的DTA放热峰的峰温Tp 随着碳纳米管的直径和石墨化的程度的增加而升高 ,半峰宽随着碳纳米管的直径的分布范围增大而增宽 .低温 (6 5 0℃ )有利于生成直径小且均匀的多层碳纳米管 (2 0～ 30nm) ,而高温 (大于 75 0℃ )则有利于生成直径大的多层碳纳米管 (大于 30～5 0nm) .     

表面活性剂辅助固相法合成碘化银纳米线束与光谱表征

卤化银具有光致变色特性,广泛应用于光致变色玻璃,照相感光乳剂等。作为一种光信息载体,具有记录和保存光信息的功能,它还是一类重要的半导体光催化剂,有着广泛的应用。以AgNO3与KI为原料,在非离子表面活性剂聚乙二醇(PEG-400)存在条件下,进行室温固相反应,合成了碘化银纳米线束。采用XRD,TEM和SEM等测试手段对产物结构和形貌进行表征,结果表明,产物为一维碘化银纳米线束,其直径在80～100nm之间,长度约为20μm,长径比>200。表面活性剂PEG-400在碘化银纳米线束的形成过程中起到了软模板剂的作用,诱导产物纳米晶沿着某一特定方向定向有序生长从而生成纳米线束。该方法消除了水对反应过程的影响,操作简单,成本较低,对碘化银纳米线束的制备技术研究具有重要意义。     

高定向石墨表面金纳米粒子和金纳米线的研究

利用真空沉积方法在高定向石墨(HOPG)基底上直接制备了粒径分布较小的金纳米粒子.超高真空扫描隧道显微镜(STM)研究发现,在74℃退火后,表观直径为2.5?nm的金纳米粒子在HOPG基底上形成了排列均匀的准一维纳米粒子链,并且此金纳米粒子链结构稳定.在122℃退火后,不同粒径的金纳米粒子在HOPG基底表面上聚合长大形成了准一维金纳米线.这一发现为制备由金粒子组成的有序纳米结构开辟了探索途径.     

Self-organization of five species in a cyclic competition game

Cyclic competition game models, particularly the “rock–paper–scissors” model, play important roles in exploring the problem of multi-species coexistence in spatially ecological systems. We propose an extended “rock–paper–scissors” game to model cyclic interactions among five species, and find that two of the five can coexistent when biodiversity disappears, which is different from the “rock–paper–scissors” game. As the number of fingers is five, we named the new model the “fingers” game, where the thumb, forefinger, middle finger, ring finger, and little finger cyclically dominate their subsequent species and are dominated by their former species. We investigate the “fingers” model in two ways: direct simulations and nonlinear partial differential equations. An important finding is that the number of species in a cyclic competition game has an influence on the emergence of biodiversity. To be specific, the “rock–paper–scissors” model is in favor of maintaining biodiversity in comparison with the “fingers” model when the variables (population size, reproduction rate, selection rate, and migration rate) are the same. It is also shown that the mobility and reproduction rate can promote or jeopardize biodiversity.     

Experimental study on downstep in Chinese intonation

Downstep in pitch contour of Chinese Putonghua is examined using subtly designed sentences by controlling tone combinations. The results show both automatic and nonautomatic downstep phenomena exist in Chinese. In non-automatic downstep, low tones compress downwards the pitch range of the following syllables. and the main influence of downstep is on topline. Low tone not only lower the topline behind it, but also raise the high tones before it, the effects are compatible with each other. In automatic downstep, the topline of pitch contour in intonational phrase is presented as a linear downtrend, but it differs among speakers due to the effect of personal stress practice. In comparison with downstep phenomenon in other tone or non-tone languages, the downstep ratio in Chinese is not constant, and the domain of downstep is not limited within the adjacent tones.     

Contrastive analysis on tone between Putonghua and Taiwan Mandarin

The differences of the pitch and duration of Chinese syllables between Putonghua （PTH） and Taiwan Mandarin （TM） were studied. The speech materials to be used are not only isolated syllables, but also sentences. The results reveal that： For the isolated syllables, T1 and T2 in TM are influenced by Minnan dialect, therefore their pitch are lower than those in PTH. T3 is fall-rise in PTH, while it is fall in TM. Moreover, the syllable duration sequence for different tone is T3〉T2〉T1〉T4 in PTH, while it is T1〉T2〉T3〉T4 in TM. For the syllables in sentences, T2 is mid-rise in PTH, while it is mid-level in TM. And the T3 is longer than T4 but shorter than T1 or T2 in PTH, while it is the shortest in TM. Furthermore the effects of prosodic phrase boundary on duration for different tones are almost the same in PTH, but the lengthening part of T1 or T2 is longer than that of T3 or T4 in TM.     

Abelian-Higgs phase of SU(2) QCD and glueball energy

It is shown that SU(2) QCD admits an dual Abelian-Higgs phase, with a Higgs vacuum of a type-Ⅱ superconductor. This is done by using a connection decomposition for the gluon field and the random-direction approximation. Using a bag picture with soft wall, we presented a calculational procedure for the glueball energy based on the recent proof for wall-vortices [Nucl. Phys. B 741(2006)1].     

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.     

Real-time restoration of rotational blurred image using gradient-loading

The key to the restoration of rotational motion blurred image is how to restore the image under a low cost and to correct the irreversibility of the degradation function matrix.Based on the special qualities of degradation function matrix and precise deduction in space-domain, we present a new approach using gradient-loading for restoration of rotational blurred image.By easily adding a gradient operator, the irreversibility of the original matrix is corrected and can be applied for inverse filtering then.Gradientloading is the optimized approach which combines the advantages of both the approaches using constrained least square filtering and traditional diagonal-loading.Compared with the approach using least square filtering, its peak signal-to-noise ratio (PSNR) is improved from 3.18 to 6.46dB, while the computing time is reduced to 1/2-1/3.Experimental results demonstrate the effectiveness, noise-resistibility, robustness, and low complexity of this approach, which make it more suitable for real-time environment.     

Signal generation in an isotropic medium in scanning electron acoustic microscope

Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122： 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM （Scanning Electron Acoustic Microscopy） signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α （α is the radius of the focused electron beam）. Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally.     

All-Optical Logic Device Using Bent Nonlinear Tapered Y-Junction Waveguide Structure

We propose an all-optical logic device made of a bent tapered Y-junction waveguide with a Kerr-type nonlinear interface. It could provide an AND gate, OR gate, and exclusive-OR (XOR) gate. We could obtain different transmission results by adjusting the bending angle. The numerical simulation results show that the device functions as AND, OR, and XOR gates.     

Real-time, continuous-wave terahertz imaging by a pyroelectric camera

Real-time, continuous-wave terahertz (THz) imaging is demonstrated. A 1.89-THz optically-pumped farinfrared laser is used as the illumination source, and a 124 × 124 element room-temperature pyroelectric camera is adopted as the detector. With this setup, THz images through various wrapping materials are shown. The results show that this imaging system has the potential applications in real-time mail and security inspection.