Theoretical Analysis of Interference Nanolithography of Surface Plasmon Polaritons without a Match Layer

Interference nanolithography techniques based on long-range surface plasmon polaritons （LR-SPP） are hardly ever achieved by experiments at present. One key reason is that suitable liquid materials are difflcult to find as the match layer connects the metal film and the resist. We redesign a Kretschmann-Raether structure for interference lithography. A polymer layer is coated under the metal film, and an air layer is placed between the polymer layer and the resist layer. This design not only avoids the above-mentioned question of the match layer, but also can form a soft contact between the polymer layer and the resist layer and can protect the exposure pattern. Simulation results confirm that a device with an appropriately thick polymer layer can form high intensity and contrast interference fringes with a critical dimension of about λ/7 in the resist. In addition, the fabrication of the device is very easy.     

光刻对准中干涉条纹相位解析研究

针对光刻对准中双光栅产生的具有多频率的干涉条纹,提出了一种基于二维解析小波变换进行条纹分析的方法。该方法首先通过二维小波变换的多尺度对条纹的多频率进行分析,并通过解析小波基函数将条纹的幅度与相位进行分离,最终通过二维小波脊方法提取出与偏移量相关的相位。在相位提取的同时通过二维小波脊所处点的角度分布来移除封闭条纹处理中常见的相位符号不确定性。数值模拟与实验验证了该方法的可行性并与传统的基于频域的相位分析方法进行了对比分析。结果表明,该方法能在获得所需相位信息的同时较好地滤除掉由光路抖动引起的噪声,具有很强的适应性。     

表面等离激元体干涉制备纳米光子晶体的模拟分析

利用表面等离激元短波长和近场增强效应的特性,用多束P偏振态相干光激发表面等离激元(SPPs),并优化干涉光刻的曝光参数,可获得高分辨率、高对比度周期性纳米结构.阐述了多束SPPs干涉法制备纳米光子晶体的原理,并得到了干涉场强度分布随光束增加的关系.随着干涉SPPs数目的增加,干涉场会复杂变化,对此进行了计算机模拟.模拟了三束SPPs和六束SPPs干涉的强度分布,并分析了调制技术干涉曝光结果,该方法适合光电子器件中大范围亚波长的周期性孔阵或点阵结构的制作以及纳米量级光子晶体的的制作,并可以有效降低制作成本.     

Nanolithography Considerations for Multi-Passband Grating Filters

The placement accuracy and resolution of direct-write patterning tools, in particular the atomic force microscope (AFM), is considered for application to fabricating multi-passband integrated optical niters. Because of its simpler fabrication a grating structure is proposed that consists of identical stripes that are non-periodically spaced. The recently developed pseudorandom encoding method from the field of computer generated holography is modified to effectively assign analog reflectances at each point along the grating by selective withdrawal and offsetting of the stripes from a periodic spacing. An example filter designed by this method has two 1.5 nm bandwidth passbands and –23 dB of rejection for lightly coupled stripes. As with single band filters, the passbands broaden as the coupling increases. A calculation of the coupling coefficient of stripes on a fundamental mode, slab waveguide indicate that stripes on the order of 100 nm in depth and width support low insertion loss, multipassband filtering applications at visible wavelengths. Lines of these dimensions patterned with an AFM on (110) silicon indicates the feasibility of fabricating these filters. These conclusions are specific to current AFM’s that are limited to writing fields of 100 μm. Increased rejection and decreased passband widths will result from incorporating precise field stitching into future AFM’s.     

四激光束干涉光刻制造纳米级孔阵的理论分析

为提供一个在大范围内曝光出深亚微米甚至纳米级周期性密集图形的廉价的方法,研究了四激光束干涉光刻的原理,分析了干涉曝光的结果,并进行了计算机模拟.用现有的光源,如442 nm、365 nm、248 nm、193 nm激光,曝光得到的图形的临界尺寸容易做到180～70 nm.具有实际上无限制的焦深和容易实现的大视场.适合硅基CCDs、平场显示器的场发射电极阵列等光电子器件中大范围内超亚微米级的周期性孔阵或点阵结构图形的制作.     

High-Contrast Imaging of Nano-Channels Using Reflection Near-Field Scanning Optical Microscope Enhanced by Optical Interference

We demonstrated a contrast enhancement in a near-field scanning optical microscope (NSOM) by optical interference with an aperture probe in reflection (illumination-collection) mode operation. We observed a NiO film deposited on a sapphire substrate and clearly visualized 2-nm-deep nano-channel structures on the surface of the film. The reflection NSOM enhanced by optical interference is quite a promising instrument for high-resolution optical detection and estimation of low-contrast nanostructures.     

Imaging for Borehole Wall by a Cylindrical Linear Phased Array

A new ultrasonic cylindrical linear phased array （CLPA） transducer is designed and fabricated for the borehole wall imaging in petroleum logging based on the previous theoretical researches. First, the CLPA transducer, which is made up of numbers of the piezoelectric elements distributed on the surface of a cylinder uniformly, is designed and fabricated. By transmitting and receiving acoustic waves with 16 active elements and using different groups of the elements under the control of the electric system, the CLPA can scan all areas of the borehole wall dynamically and rapidly without a traditional mechanism around the borehole axis. Then, the theoretical and experimental investigations are conducted in detail for the borehole wall scanning and imaging by the steel pipe and casing borehole with defects distributed in different shapes and directions. It is shown by experiments that the CLPA transducer has good focusing characteristic and good resolution for the borehole wall imaging in acoustic logging.     

Double-mode Two-photon Absorption and Enhanced Photon Antibunching Due to Interference

Inspired by results of interfering signal and idler from a nondegenerate parametric amplifier we investigate the photon statistics of the resulting field after interference of two components subjected to double-mode two-photon absorption. This absorption process leads to a strong correlation of the participating modes, which can be used to generate fields with photon antibunching in interference experiments. In addition the photon number can be made small, which produces enhanced antibunching.     

双光栅衍射场的干涉效应

双光栅衍射场的干涉效应既具有理论研究价值又具有很实际的应用价值.本文利用波前相因子分析法,推导出了双余弦光栅夫琅禾费衍射场的理论结果;分析了当两个光栅在横向有相对运动时,各级衍射斑光强的变化规律.通过实验观测映证了光强变化与数值计算结果是一致的.这一理论结果是双光栅衍射类实验设计的基础,而这类实验可以用于测量微小振动的振幅和频率.     

金纳米颗粒阵列基底的化学置换制备及其表面增强拉曼散射特性研究

表面增强拉曼(SERS)作为一种分析手段,具有高灵敏度、高选择性、高重复性、非破坏性等优点,在过去的几十年中,被广泛应用在成分检测、环境科学、生物医药及传感器等领域。其中以金、银等贵金属纳米颗粒薄膜在表面增强拉曼(SERS)活性基底方面得到了更为广泛的应用。SERS技术一个关键的因素是如何制设计并备具有大面积、高增强能力及高重复性、可循环使用的SERS基底。通常,贵金属纳米颗粒规则阵列结构的单元颗粒电磁增强特性及其颗粒间的电磁耦合增强特性的综合作用可大力提升SERS基底的探测性能。然而,利用传统微纳米加工方法如光刻、电子束光刻等方法制备得到的贵金属纳米阵列结构的表面粗糙度不够理想。结合光刻与化学置换方法制备金纳米颗粒四方点阵列孔洞结构,并研究其作为SERS基底的电磁增强特性。具体研究利用光刻法在硅衬底上制备了规则排列的四方点阵列孔洞结构,用磁控溅射在其表面镀上金属铁膜;接着在衬底上旋涂浓度为1.893 8 mol·L-1的氯金酸液膜,在孔洞内铁和氯金酸发生置换反应,进而孔洞生成金纳米颗粒,最终得到金纳米颗粒四方点阵SERS活性基底。采用罗丹明6G(R6G)分子作为探测分子测试不同金纳米颗粒阵列结构基底的SERS谱。实验结果表明,随着化学置换反应时间的延长,金纳米颗粒排列更加紧凑有序,SERS谱增强性能更好。     

Beamforming for a Flexible Acoustic Array

A method is considered for processing the signal received by a flexible acoustic array bent in such a way that random phase shifts exceeding 2π occur between the receiving elements. It is shown that these phase shifts can be filtered out if the random bends of the array are characterized by a low-frequency spatial spectrum. The efficiency of the method is tested by numerical modeling.     

Nanolithography with metastable helium atoms in a high-power standing-wave light field

We have created periodic nanoscale structures in a gold substrate with a lithography process using metastable triplet helium atoms that damage a hydrophobic resist layer on top of the substrate. A beam of metastable helium atoms is transversely collimated and guided through an intense standing-wave light field. Compared to commonly used low-power optical masks, a high-power light field (saturation parameter of 10⁷) increases the confinement of the atoms in the standing wave considerably, and makes the alignment of the experimental setup less critical. Due to the high internal energy of the metastable helium atoms (20 eV), a dose of only one atom per resist molecule is required. With an exposure time of only eight minutes, parallel lines with a separation of 542 nm and a width of 100 nm (one-eleventh of the wavelength used for the optical mask) are created.PACS 32.80.Lg; 39.25.+k; 81.16.Nd     

Coherent Array of White-Light Continuum Generated by Microlens Array

We generated a white-light continuum array by directing femtosecond laser pulses into a liquid with a microlens array. Experimental evidence demonstrates that the spatial coherence is high within a single light source in the array. We also confirmed that all the light sources in the white-light continuum array are mutually coherent. We found that the simple self-phase modulation model cannot explain this high coherence between the white continuum sources.     

Bragg Scattering of Surface Waves by a Photo-Induced Array

A pattern of spots of light projected on to a semiconductor wafer creates an array of scatterers that can diffract millimeter-wavelength surface waves through 90° in agreement with the expression for Bragg reflection.     

Enhanced Field Emission of Composite Au Nanostructured Network on Si Nanoporous Pillar Array

Nanocrystallites Au particles are deposited on a well-aligned silicon nanoporous pillar array （Si-NPA） surface through immersion plating to form an Au/Si-NPA composite system. It is found that a large number of Au nanoparticles are accumulated on the bottom of Si pillars to form a regular network structure. By studying the field emission properties of such an Au/Si-NPA composite system, we find that the Au/Si-NPA exhibits good field emission properties, with staring field about 2 V/μm and emission current density 67μA/cm^2 at 7.59 V/μm. The enhanced field emission can be deduced from the unique morphology and structure of Au/Si-NPA.     

GaN Selective Epitaxy in Sub-Micron Windows with Different Depths Formed by Ion Beam Nanolithography

Physics of the Solid State - A significant difference in the growth mechanism of spatially closed structures of gallium nitride during selective growth in submicron windows with and without...     

铂修饰的{001}面暴露的二氧化钛纳米片阵列的制备和光催化性能

采用有机溶剂热法在FTO衬底上制备{001}面暴露的单晶锐钛矿相TiO₂纳米片阵列,通过FESEM和XRD研究样品的形貌和晶体结构. 与水热法制备的纳米片阵列相比,有机溶剂热法制备的样品取向性更好. 采用光沉积方法在纳米片阵列上沉积Pt,所得到的Pt纳米颗粒粒径更为均匀,并且更容易沉积在{001}面上. 所负载的Pt 纳米颗粒增强了TiO₂纳米片的光吸收性能,同时大大减弱了光致发光强度. 在光催化性能测试中,具有最优负载量的样品催化性能提高了一倍. 与传统的Pt负载相比,{001}面的最优负载量显得相当小,这可能源于高活性{001}面的原子结构.     

A new fabrication technique for photonic crystals: Nanolithography combined with alternating-layer deposition

We propose two photonic crystal structures that can be created by combining nanolithography with alternating-layer deposition. Photonic band calculations suggest that a drilled alternating-layer photonic crystal combining two-dimensional (2D) alternating multilayers and an array of vertically drilled holes may achieve a full photonic bandgap. In addition, a 3D/2D/3D cross-dimensional photonic crystal, which sandwiches a 2D photonic crystal slab between three-dimensional (3D) alternating-layer photonic crystals, should provide better vertical confinement of light than a conventional index guiding slab. Fabrication techniques based on existing technologies (electron beam lithography, bias sputtering, and low-pressure ECR etching) require very few process steps. Our preliminary fabrication suggests that, by refining these technologies, we will be able to realize photonic crystals.