Highly controllable fabrication of fiber probe for photon scanning tunneling microscope

A selective chemical etching was used to fabricate fiber probes for the photon scanning tunneling microscope (PSTM). The cladding diameter of the fiber probe was controlled by varying the first-step etching time. The cone angle of the fiber probe tip was controlled by varying the doping ratio of the fiber and the composition of the etching solution. A cladding diameter of 8 μm and a tip diameter of about 3 nm were fabricated. The smallest cone angle was 14°.     

Wide angle near-field optical probes by reverse tube etching

We present a simple modification of the tube etching process for the fabrication of fiber probes for near-field optical microscopy. It increases the taper angle of the probe by a factor of two. The novelty is that the fiber is immersed in hydrofluoric acid and chemically etched in an upside-down geometry. The tip formation occurs inside the micrometer tube cavity formed by the polymeric jacket. By applying this approach, called reverse tube etching, to multimode fibers with 200/250 microm core/cladding diameter, we have fabricated tapered regions featuring high surface smoothness and average cone angles of approximately 30 degrees . A simple model based on the crucial role of the gravity in removing the etching products, explains the tip formation process.     

Imaging tip formation in single-mode optical fibres

The formation of probe tips is a crucial step in all forms of scanning probe microscopy (SPM). In this work single-mode optical fibres are chemically etched in a variable temperature bath of etchant solution (HF acid buffered with ammonium fluoride) to produce tips for optical SPM. Tip evolution is monitored by prematurely truncating the etching process and imaging the tip end-structure using atomic force microscopy (AFM). In the case of a visible regime single-mode fibre the AFM images show a remarkable ring structure in the central cladding region and a tip structure in the core with a central depression; this serves to demonstrate the efficacy of chemical etching for converting compositional variation to three-dimensional topography. In the case of a standard, single-mode optical communications fibre the (projected) tip cone angle is assessed from AFM images in the early stages of tip formation. Values of the cone angle thus determined, for different etch conditions, are compared to those predicted by a model in which the independently determined core and cladding etch rates, and core diameter are the sole determinants of the final tip geometry. The model was devised in the context of etching multi-mode fibres and is shown to be valid here for single-mode fibres within the range of experimental accuracy and etch conditions examined.     

The art of electrochemical etching for preparing tungsten probes with controllable tip profile and characteristic parameters

Using custom made experimental apparatus, the art of electrochemical etching was systematically studied for fabricating micro/nano tungsten probes with controllable tip profiles of exponential, conical, multidiameter, and calabashlike shapes. The characteristic parameters of probe including length, aspect ratio, and tip apex radius could also be well defined. By combining of static and dynamic etching, the conical-shape probe with length up to several millimeters, controllable tip apex radius, and cone angle could be fabricated. In addition, by continuously lifting the tungsten wire up during the electrochemical etching with different speeds and distances, the multidiameter shape probe could be fabricated. Finally by controlling the anodic flow, the multiple "neck-in" could be realized creating a calabashlike probe. The aspect ratio of probes depends on (i) the effective contact time between the surrounding electrolyte and the wire, (ii) the neck-in position of immersed tungsten wire. Under the optimized etching parameters, tungsten probes with a controllable aspect ratio from 20:1 to 450:1, apex radius less than 20 nm, and cone angle smaller than 3° could be achieved. The technique is well suited for the tungsten probe fabrication with a stabilized stylus contour, ultra-sharp apex radius, and high production reproducibility. The art for preparing microprobes will facilitate the application of such microprobes in diverse fields such as dip-pen nanolithography, scanning probe microscopy, micromachining, and biological cellular studies.     

虹吸动态腐蚀大锥角光纤探针制备

基于虹吸原理和动态大锥角化学腐蚀方法进行改进融合,成功制备出理想的高光传输效率和高分辨力的光纤探针。针尖尺寸在80nm~300nm,锥角可以控制在32~°45°内。并通过SPSS(statistical product and serv ice so lutions)数据分析软件从数理统计方面客观分析了该方法与静态化学腐蚀方法的显著差异。     

Note: Fabrication of tapered fibre tip using mechanical polishing method

Tapered fibre tips fabricated using mechanical polishing method is studied. The fibre tips are formed by sequential polishing flat-ended single mode fibres with decreasing aluminium oxide polishing film grit size. Based on the proposed technique, tapered fibre tips with cone angle ranging from 30° to 130° are fabricated by controlling the polishing angle. Besides the variety of cone angle, considerable smoothness of the fibre tip surface may assist in good metal coating and hence a well-defined aperture can be obtained. In addition, this paper presents a two-step hybrid fabrication method combining the proposed polishing method with chemical etching method to increase the possible fibre tip cone angles achievable by chemical etching method.     

使用自激振荡法提高原子力光子扫描隧道组合显微镜的扫描速度

介绍了采用频率偏移控制样品/探针间距的原子力光子扫描隧道组合显微镜(AF/PSTM)。制备了尖端直径100nm,锥角为60～90°的锐利大锥角探针用于轻敲自激振荡模式的AF/PSTM,该探针固定在压电陶瓷片上置于一个正反馈回路中激励探针振荡。使用锁相器解调自激振荡探针的频率,调整Z方向压电陶瓷的运动使得锁相器检测到的值维持恒定来跟踪样品的起伏。对外加激励模式和自激振荡模式进行了对比。理论分析表明,自激振荡方法减小了探针响应时间;测试试验显示,采用自激振荡模式AF/PSTM的带宽为50Hz,比外加振荡模式快一个数量级。采用改进后的仪器对光栅样品以1Hz的速度进行了扫描,扫描结果显示,采用自激振荡的方式得到的形貌和光学图像比外加激励模式更清晰,不仅响应时间更快,通过提高Q值还可以提高分辨率而不会增加系统进入稳态的时间。     

Dynamic etching method for fabricating a variety of tip shapes in the optical fibre probe of a scanning near-field optical microscope

A novel etching method for an optical fibre probe of a scanning near-field optical microscope (SNOM) was developed to fabricate a variety of tip shapes through dynamic movement during etching. By moving the fibre in two-phase fluids of HF solution and organic solvent, the taper length and angle can be varied according to the movement of the position of the meniscus on the optical fibre. This method produces both long (sharp angle) and short (wide angle) tapered tips compared to tips made with stationary etching processes. A bent-type probe for a SNOM/AFM was fabricated by applying this technique and its throughput efficiency was examined. A wide-angle probe with a 50 degrees angle at the tip showed a throughput efficiency of 3.3 x 10(-4) at a resolution of 100 nm.     

Dynamic etching method for fabricating a variety of tip shapes in the optical fibre probe of a scanning near-field optical microscope

A novel etching method for an optical fibre probe of a scanning near-field optical microscope (SNOM) was developed to fabricate a variety of tip shapes through dynamic movement during etching. By moving the fibre in two-phase fluids of HF solution and organic solvent, the taper length and angle can be varied according to the movement of the position of the meniscus on the optical fibre. This method produces both long (sharp angle) and short (wide angle) tapered tips compared to tips made with stationary etching processes. A bent-type probe for a SNOM/AFM was fabricated by applying this technique and its throughput efficiency was examined. A wide-angle probe with a 50° angle at the tip showed a throughput efficiency of 3.3 × 10⁻⁴ at a resolution of 100 nm.     

A method for manufacturing a probe for a combined scanning tunneling and atomic-force microscope on the basis of a quartz tuning fork with a supersharp metal tip

A method for manufacturing a probe for a combined scanning tunneling and atomic-force microscope on the basis of a quartz tuning fork with a metal tip, which is equipped with an independent conductor, is described. When the probe is manufactured, the billet for a tip has the form of a rather small (in order not to change the frequency and quality factor of the quartz tuning fork) metal cone, which is glued to the end of the beam of the quartz resonator-tuning fork together with a carbon fiber as a conductor. A spark is used to form a melted ball at the vertex of the cone. The thickness of the cone near the ball is reduced to a diameter of <0.5 μm by the electrochemical technique, and the ball is then mechanically detached. The main advantage of this method is that it allows manufacturing a high-quality-factor force detector with a single super sharp and clean tip, which is made of platinum (or platinum alloys) and tungsten, with a yield of ≥80%.     

Shape control of near-field probes using dynamic meniscus etching

Dynamic etching methods for fabricating fibre optic tips are explored and modelled. By vertically translating the fibre during etching by an HF solution under an organic protective layer, a variety of tip shapes were created. The probe taper lengths, cone angles and geometrical probe shapes were measured in order to evaluate the dynamic meniscus etching process. Fibre motion, etching rate, meniscus distortion and etching time were all found to be important variables that can be used to control the final probe shape.     

Fabrication of high-quality SNOM probes by pre-treating the fibres before chemical etching

A new method to fabricate high‐quality fibre probes for scanning near‐field optical microscopes by pre‐treating the fibre before chemical etching was proposed and implemented. In the pre‐treating process, the diameter of the fibre is reduced to a range of 7 –20 μm by etching one end of the fibre in the HF solution and a taper angle is formed simultaneously. Then the tapered part of the fibre is coated with a thick layer of plastic film and etched in the HF solution again. High‐quality probes are obtained with an apex diameter as low as ∼20 nm and a large cone angle.     

Optical Fiber Catheter with Distal End Bending Mechanism Control for Raman Biospectroscopy

Abstract

This work proposes the development of an optical catheter with bending control of the distal end. The probe consists of seven optical fibers wrapped in a resin and a biocompatible flexible teflon tube with a novel mechanical device that allows bending of the distal extremity to access a desired location of a human organ. A central fiber is used for tissue Raman excitation, five fibers are used for Raman signal collection, and the seventh for “optoclinical” treatment applications. Infrared, dispersive Raman spectra at 785 nm excitation were employed to optically characterize the proposed catheter. An excitation transmission loss of 16% was found compared to the traditional six collecting fibers catheter, both with their distal tip straight. By bending of the distal tip at different angles, with turning the intermediated section of the catheter around cylinders of different diameters (one finds a correlation between curvature angle of the tip and cylinder diameter), the transmission loss coefficient and transmission were determined for each distal tip angle. A transmission reduction of 5% was found for a 180° curvature. This optical catheter could be very useful in clinics, providing a way to control the fiber tip position and angle onto the tissue or organ.     

基于光纤布拉格光栅的化学传感器

除掉光纤布拉格光栅的包层,可以使它的布拉格波长对外界环境的折射率变化敏感。采用氢氟酸腐蚀掉光纤布拉格光栅的包层,获得了直径约为6 μm的布拉格光栅。实验研究了布拉格波长对化学溶液的浓度敏感性特征,结果表明:采用10 pm分辨率的光谱仪,丙二醇溶液在低浓度时的浓度分辨率为0.7%,在高浓度时的分辨率为0.32%;糖溶液在低浓度时的分辨率为0.55%,高浓度时为0.1%。采用商用的分辨率为1 pm的高精度波长解调系统,它们的分辨率可以提高一个数量级。     

Method of electrochemical etching of tungsten tips with controllable profiles

We demonstrate a new and simple process to fabricate tungsten tips with good control of the tip profile. In this process, we use a commercial function generator without any electronic cutoff circuit or complex mechanical setup. The tip length can be varied from 160 μm to 10 mm, corresponding to an aspect ratio of 1.6-100. The radius of curvature of the tip apex can be controlled to a size <10 nm. Surface roughness and the taper angle can be controlled independently. Through control of the etching parameters, the tip length, the radius of curvature, surface roughness, and the taper angle can be controlled to suit different requirements of various applications. The possible etching mechanisms are also discussed.     

Common-path optical coherence tomography with side-viewing bare fiber probe for endoscopic optical coherence tomography

All-fiber-optic common-path optical coherence tomography (OCT) using a side-viewing bare fiber probe has been demonstrated and analyzed. A bare single mode fiber tip is angle cleaved at approximately 49 degrees to enable side illumination due to total internal reflection. The bare fiber probe was inserted in an arterial tissue and a circumferential OCT scan was obtained. The research is aimed at realizing highly miniaturized monolithic probes for possible applications in miniature endoscopic OCT or intravascular OCT. The effects of the angle of the cleaved fiber on reference reflection and the sensitivity of the common-path OCT system have been studied theoretically. The angle cleaved fiber probe is also used in series with a microlens to analyze and optimize its performance in a common-path OCT system. Our research aims to explore the combined advantages of common-path OCT and extremely simplified miniature probe design and to discuss how it may greatly simplify the endoscopic OCT instrumentation eventually.     

Two-step controllable electrochemical etching of tungsten scanning probe microscopy tips

Dynamic electrochemical etching technique is optimized to produce tungsten tips with controllable shape and radius of curvature of less than 10 nm. Nascent features such as "dynamic electrochemical etching" and reverse biasing after "drop-off" are utilized, and "two-step dynamic electrochemical etching" is introduced to produce extremely sharp tips with controllable aspect ratio. Electronic current shut-off time for conventional dc "drop-off" technique is reduced to ～36 ns using high speed analog electronics. Undesirable variability in tip shape, which is innate to static dc electrochemical etching, is mitigated with novel "dynamic electrochemical etching." Overall, we present a facile and robust approach, whereby using a novel etchant level adjustment mechanism, 30° variability in cone angle and 1.5 mm controllability in cone length were achieved, while routinely producing ultra-sharp probes.     

超声技术在石英光纤腐蚀中的运用

为了获得光滑的腐蚀光纤表面并精确管理光纤的腐蚀直径,采用自行设计的超声腐蚀系统,在质量百分比浓度为12.5％的氢氟酸(HF)溶液中研究了超声功率和腐蚀温度对石英光纤包层、纤芯腐蚀速率以及腐蚀后光纤表面形貌的影响.研究表明:在HF溶液中,超声扰动有利于提高光纤的腐蚀速率,光纤腐蚀速率与腐蚀时间呈非线性关系,腐蚀表面随着腐蚀的进行越来越粗糙.基于研究结果,进一步采用质量百分比浓度为12.5％的HF溶液和25％的NH4OH溶液配制了缓冲氢氟酸(BHF)溶液,探讨了光纤腐蚀速率及表面形貌的变化,结果表明:在V(HF)∶V(NH4OH)=2的BHF溶液中,当超声功率为165 W、腐蚀温度为40℃时,可获得光滑的腐蚀光纤表面和腐蚀速率与腐蚀时间的线性关系.     

Manufacturing process of copper microgrooves utilizing a novel optical fiber-based laser-induced etching technique

A new approach for the fabrication of copper microgrooves with near triangular cross-sectional profile is introduced. For manufacturing the microgrooves, a laser-induced thermochemical etching technique based on an optical fiber as an optical waveguide and machining tool is proposed, which significantly reduced the complexity of a conventional laser etching set up. It is explained that the possible problem of fiber damage during laser etching with the proposed method can be solved by appropriately controlling the gap between the sample surface and fiber tip. The fabrication of copper microgrooves with 100 ∼ 300 μm in depth and 100 ∼ 150 μm in width is accomplished with the proposed technique. The grooves fabricated in the optimal process condition have smooth surfaces and clear edge. The angle of triangular groove is measured to be in the range of 30 ∼ 50 degree and the aspect ratio of grooves is about 1 ∼ 2. The overall etching results such as etch width, depth, and aspect ratio variation are reported in detail with respect to process variables.