Bridging the gap between conventional and video-speed scanning probe microscopes

A major disadvantage of scanning probe microscopy is the slow speed of image acquisition, typically less than one image per minute. This paper describes three techniques that can be used to increase the speed of a conventional scanning probe microscope by greater than one hundred times. This is achieved by the combination of high-speed vertical positioning, sinusoidal scanning, and high-speed image acquisition. These techniques are simple, low-cost, and can be applied to many conventional microscopes without significant modification. Experimental results demonstrate an increased scan rate from 1 to 200 Hz. This reduces the acquisition time for a 200×200 resolution image from 3 min to 1 s.     

In situ fabrication and regeneration of microtips for scanning tunnelling microscopy

Progress in STM, in particular for the interpretation of the tunnel signals of corrugated surfaces, is related to the possibility of sharpening and regenerating in situ reproducible tips for use as the probe. We proposed two techniques for the production of tips with controlled geometry at the atomic level. These two techniques are based on the production of tips with equilibrium profiles obtained under heat treatments in vacuum and in the presence of an electric field. Based on the pseudo-stationary profile principle, the microtips can be sharpened in situ and in a reproducible manner, either from initial cylindrical (111)-W wire, or from breakdown tips; in both cases without the need for heavy control devices (like FIM for example).     

Intercomparison of scanning probe microscopes

Comparison measurements on reference standards are reported in which 13 partners with different instruments took part. A set of prototype standards which had been produced and calibrated within a European project were used for the measurements. Here, results of measurements on a 240 nm step height standard and a two-dimensional lateral standard with a nominal pitch of 1 μm are reported.     

Rigid design of fast scanning probe microscopes using finite element analysis

To improve the performance of atomic force microscopes regarding speed and noise sensitivity, it is important to consider the mechanical rigidity of the actuator (scanner), and the overall mechanical structure. Using finite element analysis in the design process, it was possible to increase the first resonance frequency from 950 Hz for the whole system to 23.4 kHz for the whole system. This constitutes a factor of 25 in resonance frequency and a factor of 625 in stiffness and, hence, noise immunity.     

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.     

The height regulation of a near-field scanning optical microscope probe tip

A nonoptical detection of the optical fibre tip has been developed. By detecting the output signal from a tiny piezoelectric detector attached to the vibrating fibre tip, the distance between the fibre tip and the sample has been successfully controlled. The frequency responses of the system composed of tip, the dither and the detector have been studied. The difference between the shear-force detection and the tapping-mode detection is discussed. It is found that the shear force exerted on the tip reduces the vibration amplitude with an unvaried resonance frequency. However, in the tapping mode, the resonance frequency varies with the tip–sample distance as the force is exerted on the fibre tip only within a half period. This requires better adjustments for the tapping-mode detection.     

Limits of topographic measurement by the scanning tunnelling and atomic force microscopes

Parameters describing the topographic character of a surface (height, surface wavelength, slope and curvature) can be derived from equivalent sinusoidal profiles. The response of a surface-measuring instrument may be modelled in terms of instrument parameters such as stylus radius, and scanning range and resolution. The performance of the instrument may then be mapped as a zone in amplitude-wavelength (AW) space to show the sinusoidal profiles it is capable of measuring. In a first-order analysis the STM and AFM are considered as equivalent to contact-stylus instruments with a notional stylus radius equal to the tip radius plus the gap. Comparisons between different instruments and types of instrument are readily made by mapping in AW space. The error arising from convolution of the sinusoidal profile with that of the finite tip may be quantified and plotted as contours in AW space.     

Nano-wear of the diamond AFM probing tip under scratching of silicon, studied by AFM

In order to improve such a widely used microtribological testing procedure as surface scratching by an AFM diamond tip, an experimental study has been carried out using single-crystalline silicon as the tested material. Wear of the AFM diamond tip under scratching was observed by a decrease in the scratch depth with increasing wear cycles and by the direct imaging of the diamond tip shape using a Si₃N₄ AFM tip. It was shown that the current widely used experimental method, which assumes the diamond tip to be non-wearable, introduces uncontrollable error into the obtained values for the tested material's wear rate. The harder the tested material, the larger may be the tip wear, and, therefore, the bigger may be its effect on the obtained wear rate values. The specific wear rates for the diamond tip and a silicon wafer were estimated to be 1.4 × 10^-9 and 4.5 × 10^-4 mm³/(N m), respectively.     

掩模偏转方向对硅尖形状的影响

为制备高纵横比的纳米硅尖,研究了掩模的偏转方向对硅尖形状的影响.设计了硅尖制备的工艺流程,采用KOH溶液湿法各向异性腐蚀(100)单晶硅的方法制备硅尖,根据实验结果和{411}晶面模型,分析了硅尖侧壁的组成晶面,讨论了掩模偏转方向对硅尖形状的影响,得到了制备高纵横比纳米硅尖的工艺参数.实验结果表明:当腐蚀溶液浓度和温度一定时,正方形掩模的方向并不影响快腐蚀晶面的类型,利用正方形掩模的偏转,可以制备出八面体和四面体的硅尖.当正方形掩模边缘沿〈110〉晶向时,在78 ℃、浓度为40%的KOH溶液中腐蚀硅尖,经980 ℃干氧氧化3 h进行削尖,可制备出纵横比＞2的八面体纳米硅尖阵列,硅尖侧壁由与(100)面夹角为76.37°的{411}晶面组成.     

光笔式视觉测量系统中的测头中心自标定

考虑光笔式视觉测量系统的测量精度与测头中心位置的准确性相关,本文提出一种基于系统测量模型的测头中心自标定方法.该方法利用每幅光笔图像上的控制点信息,根据位置不变原理建立目标优化函数;利用非线性方程组最小二乘解的广义逆法对目标函数进行优化求解,获得测头中心在光笔坐标系下的位置.最后,借助参考标准锥完成标定,并结合平均思想改善收敛稳定性和速度来实验验证本方法的实用性.实验结果显示,测头中心坐标x、y、z轴的稳定性可分别达到0.033 mm,0.030 mm和0.043 mm,且具有满意的收敛速度.另外,对测量工件圆孔直径与参考值进行比较表明:测头中心标定后,系统的测量精度可满足中等精度的工业测量要求.     

Arrangement and stability of atoms at the apex of a scanning tip

A field ion microscope was used to examine the stability of the atomic arrangement at tip apexes. Although a single W atom at the top layer of a [111]-orientated tip apex protrudes from the underneath layer by only 0·91 Å, the present study suggests that the (111)-orientated W tip is the most desirable tip for scanning tunnelling microscopes because a large activation energy for surface diffusion on the (111) plane immobilizes the apex atom while the tip scans over a specimen surface and the tip apex can be resharpened by simply heating the tip.     

Note: In situ cleavage of crystallographic oriented tips for scanning probe microscopy

We report an in situ method of preparing tips for scanning probe microscopy (SPM). Oriented single-crystal nickel oxide (NiO) rods were diced, using a wafer saw, to prepare artificial breaking points. Two geometries, a single rod and a two-sided cut rod were fabricated. The cleavable tips were mounted to a force sensor based on a quartz tuning fork and cleaved using the coarse approach of the SPM. Atomically resolved force microscopy images of NiO (001) were taken with these NiO tips.     

Simulation-aided design and fabrication of nanoprobes for scanning probe microscopy

We proposed and demonstrated a flexible and effective method to design and fabricate scanning probes for atomic force microscopy applications. Computer simulations were adopted to evaluate design specifications and desired performance of atomic force microscope (AFM) probes; the fabrication processes were guided by feedback from simulation results. Through design-simulation-fabrication iterations, tipless cantilevers and tapping mode probes were successfully made with errors as low as 2% in designed resonant frequencies. For tapping mode probes, the probe tip apex achieved a 10 nm radius of curvature without additional sharpening steps; tilt-compensated probes were also fabricated for better scanning performance. This method provides AFM users improved probe quality and practical guidelines for customized probes, which can support the development of novel scanning probe microscopy (SPM) applications.     

In situ,atomic scale observation of electrode topography and reactions

The topographical changes occurring on a Au(111) electrode during simple electrochemical reactions have been followed with an STM capable of operating in situ, i.e. in the electrochemical environment, and of yielding atomic scale resolution. Changes in the surface structure induced by adsorption and desorption of Cl^? ions could be observed and the effects of subjecting the sample to an oxidation-reduction cycle could be monitored.     

A role of a tip geometry on STM images

Scanning tunnelling microscopes operable in both ultrahigh vacuum (UHV) and aqueous conditions are described with emphasis on a tip geometry. An atomically resolved STM image was obtained for the Si(111)-Mo√3 surface in UHV condition and changes of a diffraction grating surface in aqueous condition due to an electrochemical reaction were monitored.     

Fabrication of hierarchical micro/nanostructures via scanning probe lithography and wet chemical etching

In this study, we propose a simple and effective method for fabricating hierarchical silicon structures via the combination of scanning probe lithography (SPL) and wet chemical etching. Here, silicon oxide structures were protruded from a 100-oriented silicon surface, followed by the passivation of silicon nitride by AFM tip-induced local oxidation. Based on the two-dimensional (2D) silicon oxide patterns, three-dimensional (3D) microstructures with high aspect ratios were formed by wet etching with HF and KOH. A variety of combinations of SPL and the etching process allowed us to fabricate diverse silicon-based structures such as deep-etched microstructures and multi-terraced nanostructures.     

切点约束和探针针尖半径补偿的金刚石刀具刃口钝圆半径求解方法

本文对金刚石刀具刃口钝圆半径求解方法展开研究,以有效提升金刚石刀具刃口锋利度的测量精度。文中分析了原子力显微镜(AFM)扫描探针几何形貌对金刚石刀具刃口锋利度测量结果的影响,并提出了基于切点约束和AFM探针针尖半径补偿的刀具刃口钝圆半径求解方法;讨论了消噪滤波、测量角度误差以及切点分离方法对测量结果的影响;在高精度测量平台上完成了金刚石刀具刃口锋利度测量,并将被测量的刀具用于飞切加工KDP晶体。结果表明:提出的刃口钝圆半径求解方法能够准确求解金刚石刀具的刃口锋利度,测量结果能很好地描述金刚石刀具的刃口锋利程度,可以为金刚石超精密切削加工的选刀和用刀提供有效指导。     

Image contrast of dielectric specimens in transmission mode near-field scanning optical microscopy: imaging properties and tip artefacts

Near-field scanning optical microscopy (NSOM) is a scanned probe technique utilizing a subwavelength-sized light source for high-resolution imaging of surfaces. Although NSOM has the potential to exploit and extend the experimental utility of the modern light microscope, the interpretation of image contrast is not straightforward. In near-field microscopy the illumination intensity of the source (probe) is not a constant value, rather it is a function of the probe–sample electronic environment. A number of dielectric specimens have been studied by NSOM to elucidate the contrast role of specimen type, topography and crystallinity; a summary of metallic specimen observations is presented for comparative purposes. Near-field image contrast is found to be a result of lateral changes in optical density and edge scattering for specimens with little sample topography. For surfaces with considerable topography the contributions of topographic (Z) axis contrast to lateral (X,Y) changes in optical density have been characterized. Selected near-field probes have also been shown to exhibit a variety of unusual contrast artefacts. Thorough study of polarization contrast, optical edge (scattering) contrast, as well as molecular orientation in crystalline specimens, can be used to distinguish lateral contrast from topographic components. In a few cases Fourier filtering can be successfully applied to separate the topographic and lateral contrast components.     

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%.