Design of metal-cladded near-field fiber probes with a dispersive body-of-revolution finite-difference time-domain method

A dispersive body-of-revolution finite-difference time-domain method is developed to simulate metal-cladded near-field scanning optical microscope (NSOM) probes. Two types of NSOM probe (aperture and plasmon NSOM probes) are analyzed and designed with this fast method. The influence of the metal-cladding thickness and the excitation mode on the performance of the NSOM probes is studied. We introduce a new scheme of illumination-mode NSOM by employing the plasmon NSOM probe with the TM01 mode excitation. Such a NSOM probe is designed, and we demonstrate its advantages over the conventional aperture NSOM probe by scanning across a metallic object.     

Plasmonic nearfield scanning probe with high transmission

Nearfield scanning optical microscopy (NSOM) offers a practical means of optical imaging, optical sensing, and nanolithography at a resolution below the diffraction limit of the light. However, its applications are limited due to the strong attenuation of the light transmitted through the subwavelength aperture. To solve this problem, we report the development of plasmonic nearfield scanning optical microscope with an efficient nearfield focusing. By exciting surface plasmons, plasmonic NSOM probes are capable of confining light into a 100 nm spot. We show by nearfield lithography experiments that the intensity at the near field is at least one order stronger than the intensity obtained from the conventional NSOM probes under the same illumination condition. Such a high efficiency can enable plasmonic NSOM as a practical tool for nearfield lithography, data storage, cellular visualization, and many other applications requiring efficient transmission with high resolution.     

Near-field optical apertured tip and modified structures for local field enhancement

We present experimental measurements and simulation of the spatial distribution of near-field light at the aperture of a Si micromachined near-field scanning optical microscopy (NSOM) probe. A miniature aperture at the apex of a SiO(2) tip on a Si cantilever was fabricated with the low temperature oxidation and selective etching technique. An optical transmission efficiency (optical throughput) of the fabricated probe was determined to be approximately 10(-2) when the aperture size was approximately 100 nm, which is several orders of magnitude higher than that for conventional optical fibers. A three-dimensional finite difference time domain (FDTD) simulation shows that the near-field light is well confined within the aperture area with a throughput of 1% for a 100-nm aperture, which is in good agreement with the measurement. The spatial distribution of the near-field light at an aperture of 300-nm diameter shows a full width at half-maximum of 250 nm with a sharp peak that is nearly 60 nm wide. The 2.4% throughput for a 300-nm aperture was estimated based on the measured spatial distribution of the near-field light that is almost the same as the experimental result. We also present the initial results of the fabrication of high throughput coaxial and surface plasmon enhancement NSOM probes.     

Convenient near-field optical measurement and analysis of polystyrene spheres

The modification of a commercial tapping mode atomic force microscope (AFM) into a transmission mode near-field scanning optical microscope (NSOM) is presented and polystyrene spheres in the diameter of 100 nm are used in this experiment. The detection of near-field signals is based on photodiodes with lock-in technique, and resolutions of topography and near-field signals obtained are about 10 and 20 nm, respectively. Furthermore, it is discovered that the computer-simulated near-field energy distribution profile, obtained by scanning over polystyrene spheres under illumination mode, falls within 5% range as compared with experimental values. The near-field absorption coefficient can be determined by this way. This will be a useful theoretical model to analyze the near-field transmission effect from others.     

Nanometer scale polarimetry studies using a near-field scanning optical microscope

We describe a new technique that incorporates polarization modulation into near-field scanning optical microscopy (NSOM) for nanometer scale polarimetry studies. By using this technique, we can quantitatively measure the optical anisotropy of materials with both the high sensitivity of dynamic polarimetry and the high spatial resolution of NSOM. The magnitude and relative orientation of linear birefringence or linear dichroism are obtained simultaneously. To demonstrate the sensitivity and resolution of the microscope, we map out stress-induced birefringence associated with submicrometer defects at the fusion boundaries of SrTiO3 bicrystals. Features as small as 150 nm were imaged with a retardance sensitivity of approximately 3 x 10(-3) rad.     

Extraordinary optical transmission brightens near-field fiber probe

Near-field scanning optical microscopy (NSOM) offers high optical resolution beyond the diffraction limit for various applications in imaging, sensing, and lithography; however, for many applications the very low brightness of NSOM aperture probes is a major constraint. Here, we report a novel NSOM aperture probe that gives a 100× higher throughput and 40× increased damage threshold than conventional near-field aperture probes. These brighter probes facilitate near-field imaging of single molecules with apertures as small as 45 nm in diameter. We achieve this improvement by nanostructuring the probe and by employing a novel variant of extraordinary optical transmission, relying solely on a single aperture and a coupled waveguide. Comprehensive electromagnetic simulations show good agreement with the measured transmission spectra. Due to their significantly increased throughput and damage threshold, these resonant configuration probes provide an important step forward for near-field applications.     

扫描近场光学显微镜光纤探针的制作与分析

描述了制作扫描近场光学显微镜光纤探针的两种简便有效的方法－－带保护层的化学腐蚀法和光纤熔接机拉锥法,从实验中比较、分析了两种制作方法的优缺点,实验表明这两种方法均能制作出针尖直径为５０ｎｍ左右的光纤探针。     

Nonlinear chemical imaging microscopy: near-field third harmonic generation imaging of human red blood cells

Third harmonic generation (THG) imaging using a near-field scanning optical microscope (NSOM) is demonstrated for the first time. A femtosecond, tunable near-infrared laser was used to generate both nonresonant and resonantly enhanced third harmonic radiation in human red blood cells. We show that resonantly enhanced THG is a chemically specific bulk probe in NSOM imaging by tuning the excitation source onto and off of resonance with the Soret transition of oxyhemoglobin. Additionally, we provide evidence that tightly focused, nonresonant, far-field THG imaging experiments do not produce contrast that is truly surface specific.     

Fluorescence lifetime imaging with near-field scanning optical microscopy

Near-field scanning optical microscopy (NSOM) is a high-resolution scanning probe technique capable of obtaining simultaneous optical and topographic images with spatial resolution of tens of nanometers. We have integrated time-correlated single-photon counting and NSOM to obtain images of fluorescence lifetimes with high spatial resolution. The technique can be used to measure either full fluorescence lifetime decays at individual spots with a spatial resolution of <100 nm or NSOM fluorescence images using fluorescence lifetime as a contrast mechanism. For imaging, a pulsed Ti:sapphire laser was used for sample excitation and fluorescent photons were time correlated and sorted into two time delay bins. The intensity in these bins can be used to estimate the fluorescence lifetime at each pixel in the image. The technique is demonstrated on thin films of poly(9,9'-dioctylfluorene) (PDOF). The fluorescence of PDOF is the results of both inter- and intrapolymer emitting species that can be easily distinguished in the time domain. Fluorescence lifetime imaging with near-field scanning optical microscopy demonstrates how photochemical degradation of the polymer leads to a quenching of short-delay intrachain emission and an increase in the long-delay photons associated with interpolymer emitting species. The images also show how intra- and interpolymer species are uniformly distributed in the films.     

Fluorescent nanoscale detection of biotin-streptavidin interaction using near-field scanning optical microscopy

We describe a nanoscale strategy for detecting biotin-streptavidin binding using near-field scanning optical microscopy (NSOM) that exploits the fluorescence properties of single polydiacetylene (PDA) liposomes. NSOM is more useful to observe nanomaterials having optical properties with the help of topological information. We synthesized amine-terminated 10,12-pentacosadiynoic acid (PCDA) monomer (PCDA-NH(2)) and used this derivatized monomer to prepare PCDA liposomes. PCDA-NH(2) liposomes were immobilized on an aldehyde-functionalized glass surface followed by photopolymerization by using a 254?nm light source. To measure the biotin-streptavidin binding, we conjugated photoactivatable biotin to immobilized PCDA-NH(2) liposomes by UV irradiation (365?nm) and subsequently allowed them to interact with streptavidin. We analyzed the fluorescence using a fluorescence scanner and observed single liposomes using NSOM. The average height and NSOM signal observed in a single liposome after binding were ～31.3 to 8.5 ± 0.5?nm and 0.37 to 0.16 ± 0.6?kHz, respectively. This approach, which has the advantage of not requiring a fluorescent label, could prove highly beneficial for single molecule detection technology.     

Noninvasive scanned probe potentiometry for integrated circuitdiagnostics

This paper describes a simple noncontact scanned probe microscope for the static potential measurement of operating integrated circuits. The instrument extracts the local potential on the integrated circuit by nulling the electrostatic force between a small cantilever probe and the circuit test point. The force is detected by monitoring the mechanical deflection of the probe with an optical fiber interferometer. The constructed instrument has demonstrated a millivolt accuracy with a spatial resolution of less than 3 μm. Measurements can be made directly in air on circuits both with and without a top insulating passivation layer. The nulling technique allows absolute potential measurements to be performed without complex calibration requirements     

Three-dimensional imaging with optical tweezers

We demonstrate a three-dimensional scanning probe microscope in which the extremely soft spring of an optical tweezers trap is used. Feedback control of the instrument based on backscattered light levels allows three-dimensional imaging of microscopic samples in an aqueous environment. Preliminary results with a 2-mum-diameter spherical probe indicate that features of approximately 200 nm can be resolved, with a sensitivity of 5 nm in the height measurement. The theoretical resolution is limited by the probe dimensions.     

Fabrication of gold micro- and nanostructures by photolithographic exposure of thiol-stabilized gold nanoparticles

Exposure of thiol-stabilized gold nanoparticles supported on silicon wafers to UV light leads to oxidation of the thiol molecules and coagulation of the nanoparticles, forming densified structures that are resistant to removal by solvent exposure. Unoxidized particles may, in contrast, readily be removed leaving gold structures behind at the surface. This process provides a convenient and simple route for the fabrication of gold structures with dimensions ranging from micrometers to nanometers. The use of masks enables micrometer-scale structures to be fabricated rapidly. Exposure of nanoparticles to light from a near-field scanning optical microscope (NSOM) leads to the formation of gold nanowires. The dimensions of these nanowires depend on the method of preparation of the film: for spin-cast films, a width of 200 nm was achieved. However, this was reduced significantly, to 60 nm, for Langmuir-Schaeffer films.     

近场光镊与AFM探针复合的光阱力分析

本文针对纳米材料的纳米操作,提出了一种复合激光近场光镊与AFM探针进行纳米操作的方法,并基于动量守恒原理,采用三维时域有限差分方法建立了该方案中激光近场对纳米微粒的作用力模型,分析了各轴向光阱力的分布情况,讨论了两探针间距离、针尖材料的电导率、入射平面光场的偏振方向、入射角和波长等参数对近场光阱力的影响.结果表明:位于...     

Fabrication of silicon oxide nanotips by mechanical contact and elongation methods

We investigated the thinning process of silicon oxide tips by mechanical contact and elongation by in situ high-resolution transmission electron microscopy with functions of atomic force microscopy and scanning tunneling microscopy. The processing precision of thinning reached the atomic scale. However, the stability of the thinned tips determined their minimum size; the size of the produced tips was at least approximately 1 nm. We produced thin, long nanotips for optical fiber probes by this method. We also performed the aperture opening of optical fiber probes for scanning near-field optical microscopy. Scraping produced an aperture of approximately 15 nm.     

一种可溯源原子力探针显微镜

研制了一种基于白光干涉的可溯源原子力探针扫描显微镜,提出了一种稳健的白光干涉零级条纹定位算法,建立了一套高分辨激光干涉位移测量系统。在此基础上提出了一种探针标定方法,实现微纳表面可溯源测量。通过对台阶高度为(21.4±1.5)nm的标准光栅进行10次重复测量,其结果的平均值为21.56 nm,标准差为0.51 nm;同时对高度为150 nm的三维特征样件进行了三维测量,验证了所研制仪器测量的准确性和稳定性。     

PSTM中不同探针扫描成像的模拟分析

金属纳米粒子或薄膜在可见光的激励下产生表面增强效应。尝试在光子扫描隧道显微镜(PSTM)中应用带铝的光纤探针来提高成像的分辨率和灵敏度。采用二维时域有限差分法(FDTD)模拟计算了裸光纤、尖端镀铝颗粒光纤、孔径镀铝膜光纤和全镀铝膜光纤探针的成像。结果显示,采用带铝探针后的灵敏度均比裸光纤提高两个数量级;尖端镀铝颗粒光纤探针的分辨率最好,可优于20nm;全镀铝膜和孔径镀铝膜光纤探针的分辨率分别可达到20nm和60nm。结果可供探针制备及实验参数设置参考。     

扫描近场光学显微镜的光纤探针

扫描近场光学显微镜（ＳＮＯＭ）打破了传统光学显微镜的衍射极限分辨率,自８０年代中期出现以来在１０多年的时间内获得了迅速的发展,并在很多的领域有很广阔的应用前景。扫描探针的形状及针尖的大小是影响ＳＮＯＭ分辨率的关键因素之一。     

Integrated optical motor

A light-driven micrometer-sized mechanical motor is created by laser-light-induced two-photon photopolymerization. All necessary components of the engine are built upon a glass surface by an identical procedure and include the following: a rigid mechanical framework, a rotor freely rotating on an axis, and an integrated optical waveguide carrying the actuating light to the rotor. The resulting product is a most practical stand-alone system. The light introduced into the integrated optical waveguide input of the motor provides the driving force: neither optical tweezers or even a microscope are needed for the function. The power and efficiency of the motor are evaluated. The independent unit is expected to become an important component of more complex integrated lab-on-a-chip devices.     

Fabrication method of ultra-small gradient-index fiber probe

Fabrication method and device of ultra-small gradient-index(GRIN) fiber probe were investigated in order to explore the development of ultra-small probes for optical coherence tomography(OCT) imaging.The beamexpanding effect of no-core fiber(NCF) and the focusing properties of the GRIN fiber lens were analyzed based on the model of GRIN fiber probe consisting of single-mode fiber(SMF),NCF and GRIN fiber lens.A stereo microscope based system was developed to fabricate the GRIN fiber probe.A fiber fusion splicer and an ultrasonic cleaver were used to weld and cut the fiber respectively.A confocal microscopy was used to measure the dimensions of probe components.The results show that the sizes of probe components developed are at the level of millimeter.Therefore,the proposed experimental system meets the fabrication requirements of an ultra-small self-focusing GRIN fiber probe.This shows that this fabrication device and method can be employed in the fabrication of ultrasmall self-focusing GRIN fiber probe and applied in the study of miniaturized optical probes and OCT systems.