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Atomic force microscopy (AFM) tip-based nanofabrication is a feasible method to create nanofeatures on a variety of materials. Surface/subsurface integrity is important for qualifying surface performances. However, while machining on crystalline materials, subsurface amorphous layers are inevitably produced because of the large stress in the contact area between the sharp tip and the workpiece surface, which would reduce the mechanical performance of the surface. In this work, multi-pass reciprocating cutting (MPRC) was implemented to reduce the subsurface amorphous layer (SAL) of a single crystal silicon. The mechanism was studied by experiments and molecular dynamic simulation. Results showed the thickness of the amorphous layer can be greatly decreased to a low value and the tip wear can be reduced as well by the MPRC method. On this basis, by optimizing the machining parameters of the MPRC method, nanogrooves with varied depths but few subsurface amorphous phases were successfully fabricated. [Display omitted] • A method of multi-pass reciprocating cutting (MPRC) to fabricate nanostructures was proposed. • Nanostructures with reduced subsurface amorphous layer (SAL) was fabricated. • The tip wear was reduced by the MPRC due to its relatively low normal force. [ABSTRACT FROM AUTHOR]

As a promising micro/nanofabrication method, electrical-assisted nanomachining has obtained substantial attention due to its high material removal rate and attainable superior surface quality. In this study, a rectangular wave electrical signal was applied for nanomachining by a customized tungsten tip. Owing to the coupling effect between the electric field and mechanical force, the cutting depth of the machined grooves can be expanded. In electrical-assisted groove processing, a depth of 270 nm and an aspect ratio of 0.6 on the copper sample can be achieved. The influence of operation parameters including applied voltage, frequency, duty ratio, normal force and cutting speed on the machining performance was investigated in terms of the groove depth, width, aspect ratio, and surface roughness. The potential machining mechanisms should be a combination of electric field force, nanoscale electric discharge, electric contact thermal effects, possible annealing behavior, and scraping and plowing actions induced by mechanical forces. Highlights: Customized tungsten probes are fabricated by electrochemical etching as the machining tools for electrical-assisted tip-based nanomanufacturing. Electrical-assisted machining is implemented by applying a rectangular wave electrical signal during scratching. The effects of the operation parameters including voltage, duty ratio, and frequency on the machining performance are studied in detail. Experiments reveal the potential mechanisms underlying electrical-assisted machining is a combination of the electric field force, nanoscale electric discharge, electric contact thermal effects, possible annealing behavior, and scraping and plowing actions induced by mechanical forces. [ABSTRACT FROM AUTHOR]

Nanostructures are widely used in various industries. Nanoscratching is an important technique for fabricating nanostructures. The cutting depth in nanoscratching is a crucial parameter that is closely related to the normal force, material properties, and tip geometry. Current prediction models are only suitable for some specific processing conditions. To extend the scope of application of prediction model, a comprehensive model is proposed. In the developed model, the indenter tip is divided into three parts: a spherical crown, transition part, and pyramid base. Accordingly, a comprehensive contact model considering elastic recovery is developed in the edge-forward, face-forward and side-forward directions based on the indenter tip geometry. The computational results indicate that face-forward nanoscratching with a conventional cube-corner indenter has the smallest contact area compared to edge-forward and side-forward nanoscratching. It is noted that the established model can reduce the prediction error by more than 10% compared with the current models when the cutting depth is lower than the tip radius. The influence of the indenter geometry is analysed based on this model. The geometric shape of the indenter has a significant influence on the contact area, and the face angle of the pyramid is the key factor. The proposed model is validated by numerous nanoscratching experiments. [Display omitted] • A comprehensive cutting depth prediction model is developed by considering the effect of elastic recovery. • Transition part from spherical crown and pyramid base is contained in this model. • Machined surface is formed in the combination of elastic recovery, mechanochemical effect, and mechanical cutting effect. [ABSTRACT FROM AUTHOR]

In this paper, the combination of an advanced nanopositioning technique and a tip-based system, which can be used as an atomic force microscope (AFM) and especially for field emission scanning probe lithography (FESPL) is presented. This is possible through the use of active microcantilevers that allow easy switching between measurement and write modes. The combination of nanopositioning and nanomeasuring machines and tip-based systems overcomes the usual limitations of AFM technology and makes it possible to perform high-precision surface scanning and nanofabrication on wafer sizes up to 4 in. We specifically discuss the potential of nanofabrication via FESPL in combination with the nanofabrication machine (NFM-100). Results are presented, where nanofabrication is demonstrated in form of a spiral path over a total length of 1 mm and the potential of this technique in terms of accuracy is discussed. Furthermore, ten lines were written with a pitch of 100 nm and a linewidth below 40 nm was achieved, which is in principle possible over the entire range of motion.

This paper develops and characterizes a three-dimensional (3-D) nanofabrication process using ultrasonic vibration assisted nanomachining based on an atomic force microscope (AFM). The superiorities of height control over force control in the process are explained and are demonstrated by the fabrication results. Three factors impacting actual feature depths are investigated, including the ultrasonic z-vibrational amplitude, the assigned base feature depth, and the machining speed. 3-D nanostructures with continuous height variations were successfully fabricated on polymethyl methacrylate (PMMA) films with the feature height manipulated through controlling the absolute height of the cantilever tip in AFM. By selecting machining parameters based on characterizations, feature dimensions can be controlled as desired values within small variances. The capability of transferring 3-D nanostructures from PMMA films to silicon substrates is further explored in this paper. After selecting recipes of the reactive ion etching process, 3-D nanostructures are successfully transferred to silicon substrates with controllable selectivity. The reported ultrasonic vibration assisted nanomachining process in height control provides a robust approach of fabricating 3-D nanostructures. [ABSTRACT FROM AUTHOR]

Tip-based nanofabrication (TBN) is a family of emerging nanofabrication techniques that use a nanometer scale tip to fabricate nanostructures. In this review, we first introduce the history of the TBN and the technology development. We then briefly review various TBN techniques that use different physical or chemical mechanisms to fabricate features and discuss some of the state-of-the-art techniques. Subsequently, we focus on those TBN methods that have demonstrated potential to scale up the manufacturing throughput. Finally, we discuss several research directions that are essential for making TBN a scalable nano-manufacturing technology. [ABSTRACT FROM AUTHOR]

As one of the tip-based nanoscale machining methods, AFM-based nanolithography has been proved to be capable of fabricating nanostructures and devices on a wide range of materials by means of mechanical force, bias voltage, chemical reaction, etc. In this paper, we have compared the influences of the bias voltage effect and the force effect during the nanoscale AFM electric lithography on the metallic copper film surface respectively through the bias voltage dominating scheme and the contact force dominating scheme. The geometric sizes of the line structures and the area patterns fabricated under the two schemes with different parameter settings were compared to obtain the machining characteristics and mechanisms of the two distinct effects separately. The ratios of debris amount to the total material removal amount under the two schemes were quantitatively evaluated. Furthermore, both the arbitrary line structure with high aspect ratio and the area pattern with small surface roughness were fabricated under the appropriate scheme and parameter settings. This study is of great help to effectively achieve the desired nanoscale patterns by AFM electric lithography for their promising applications in the fabrication of various MEMS or NEMS devices. SCANNING 38:412-420, 2016. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of ultrasonic tip–sample vibration in regulating the fabricated feature depth and reducing machining force in ultrasonic vibration-assisted nanomachining with an atomic force microscope (AFM). Nanopatterns on aluminum and polymethyl methacrylate (PMMA) substrates are fabricated by the ultrasonic vibration-assisted nanomachining approach. It is demonstrated that using a small set-point force and the same vibration amplitude for machining PMMA and aluminum, nearly the same feature depth is achieved. The fabrication depth is mainly controlled by the amplitude of the tip–sample z-vibration, and is insensitive to sample materials. A theoretical analysis of the sample contact stiffness and dynamic stiffness of the cantilever is used to explain the observed material-insensitive depth regulation by ultrasonic tip–sample vibration. The ultrasonic vibration also effectively reduces the normal force and friction during nanomachining. On both PMMA and aluminum samples, experimental results demonstrate significant reduction in set-point force and lateral friction force in ultrasonic vibration-assisted nanomachining compared with nanomachining without ultrasonic z-vibration. Smaller tip wear is observed in ultrasonic vibration-assisted nanomachining for the fabrication of PMMA samples. [ABSTRACT FROM PUBLISHER]

Abstract: Sequential and parallel local oxidation nanolithographies have been applied to pattern pentacene samples by creating a variety of nanostructures. The sequential local oxidation process is performed with an atomic force microscope and requires the application of a sequence of voltage pulses of 36V for 1ms. The parallel local oxidation process is performed by using a conductive and patterned stamp. Then, a voltage pulse is applied between the stamp and the pentacene surface. Patterns formed by arrays of parallel lines covering 1mm2 regions and with a periodicity of less than 1μm have been generated in a few seconds. We also show that the patterns can be used as templates for the deposition of antibodies. [Copyright &y& Elsevier]

• The experimental investigation of effects of key vibration parameters including vibration mode, frequency, and amplitude in vibration-assisted tip-based nanofabrication (VTBN) is presented. • The experiments are conducted with a self-developed 3D ultrasonic VTBN system, which mainly consists of a tip displacement detection system, a 3-DOF nano-positioner, and a 3D ultrasonic vibration platform. • To analyze the specific effects, the experiments are elaborately designed with the general factorial method. • The experiments results show that the effects of three parameters are all significant factors of the responses of single scratch in VTBN process. • The maximum error for the depth and the width of the established model is less than 8%, which validates the effectiveness of this method. [Display omitted] The experimental investigation of the effects of key vibration parameters including vibration mode, frequency, and amplitude on vibration-assisted tip-based nanofabrication (VTBN) is presented in this paper. To analyze the detailed effects, the experiments were specifically designed with the general factorial method. The experiments are conducted with a self-developed 3D ultrasonic VTBN system, which integrates a 3-DOF tip-based nanofabrication system and a 3D ultrasonic vibration platform. According to the experimental results, three parameters are all significant factors of the responses of single scratch. On the whole, the fabricated grooves with 2D vibration in x − y plane have the largest depth and widest width. Moreover, the vibrations with 1D vibration in x-axis and 2D vibration in x − y plane add to the width controllability of single scratch by tuning the amplitude of the component in the x -axis. The vibration amplitude has an almost linear relationship between the responses and the factors. Finally, to verify the accuracy and effectiveness of the established model, a validation test is conducted. The results show that the maximum error for the depth and the width between the model and the result is less than 8%, which validates the effectiveness of the method. [ABSTRACT FROM AUTHOR]

• The design, modeling, and experimental validation of a novel 3D ultrasonic vibration platform with tunable characteristics is presented. • Multiple vibration modes including 1D (linear) and 2D (in-plane or out-of-plane) vibrations can be achieved. • Both the vibration amplitude and frequency can be set to an arbitrary value within a wide range according to the fabrication requirement. • A novel flexure hinge, named T-shaped spatial flexure hinge is used to realize both in-plane and out-of-plane motions with a compact structure. • The maximum amplitude and frequency can reach around 50 nm and 20 kHz, i.e. ultrasonic frequency, respectively. Vibration-assisted tip-based nanofabrication techniques have advantages including increased material removal rate, reduced tip wear, and better material adaptability over traditional tip-based mechanical plowing. However, the influences of different vibration parameters on the machining efficiency are unclear, and how to select appropriate cutting parameters to guarantee the machined surface quality need further investigations. This paper introduces the design, modeling, and experimental validation of a novel 3D ultrasonic vibration platform with tunable characteristics. Moreover, multiple vibration modes including 1D (linear) and 2D (in-plane or out-of-plane) vibrations can be achieved. A novel flexure hinge, named T-shaped spatial flexure hinge is used to realize both in-plane and out-of-plane motions with a compact structure. Static modeling and dynamic modeling are conducted to guide the design process, and finite element analysis is utilized to verify the established model. Afterwards, a prototype is fabricated, and a number of experiments are implemented to validate the characteristics of the developed vibration platform. The experimental results show that different vibration modes can be achieved, and both the vibration amplitude and frequency can be set to an arbitrary value within a wide range according to the fabrication requirement. The maximum amplitude and frequency can reach around 50 nm and 20 kHz, i.e. ultrasonic frequency, respectively. [ABSTRACT FROM AUTHOR]

• A novel 3D tip-based nanofabrication system with high precision depth control capability is presented. • A new depth control method, namely tip displacement-based closed-loop (DC) depth control method is proposed to decrease the complexity and the high uncertainty. • To evaluate and investigate the effectiveness of the proposed machining system and the DC method, a series of patterns were fabricated. • The experimental results demonstrate that the system has advantages of distinguished depth control capability, high machining accuracy, and excellent repeatability. The design, analysis, and experimental investigation of a novel 3D tip-based nanofabrication system with high precision depth control capability is presented in this paper. Based on this system, a new depth control method, namely tip displacement-based closed-loop (DC) depth control methodology is proposed to improve the depth control capability. As the force-depth prediction with the commonly-used depth control method, i.e. the normal force-based closed-loop (FC) method, may depend on the machining speed, the machining direction, and the material properties, etc. Compared with the FC method, the DC method decreases the complexity and the high uncertainty. The tip feed system utilizes a non-contact force, i.e. the electromagnetic force, to adjust the tip displacement. Therefore, the tip support mechanism can be used to accomplish the tip-sample contact detection. Additionally, an active compensation method is proposed to eliminate the tilt angle between the sample surface and the horizontal plane. Otherwise the machining depth will change gradually, i.e. getting deeper or lower. Furthermore, a series of patterns have been fabricated on silicon sample surface with the proposed system and method. The maximum machining depth of a single scan reaches 300 nm, which is much larger than that of an atomic force microscope (AFM)-based nanofabrication system. The experimental results demonstrate that the system has advantages of distinguished depth control capability, high machining accuracy, and excellent repeatability, which diminishes the influence of above-mentioned factors on the machining depth. Also, the method has the potential of machining arbitrary 2D/3D patterns with well-controlled depth and high accuracy. [ABSTRACT FROM AUTHOR]

As one of the tip-based top-down nanoscale machining methods, atomic force microscopy (AFM) electric lithography is capable of directly generating flexible nanostructures on conductive or semi-conductive sample surfaces. In this work, distinct fabrication mechanisms and mechanism transition from local anodic oxidation (LAO) to electrical breakdown (BD) in the AFM nanoscale electric lithography of the highly oriented pyrolytic graphite sample surface was studied. We provide direct evidence of the transition process mechanism through the detected current-voltage (I-V) curve. Characteristics of the fabrication results under the LAO, transition, and BD regions involving the oxide growth rate or material removal rate and AFM probe wear are analyzed in detail. These factors are of great significance for improving the machining controllability and expanding its potential applications.

Alignment of perpendicularly oriented lamellar block copolymer domains using an AFM tip is demonstrated. The AFM tip orients the domains through local shearing, resulting in domain alignment parallel to tip travel. AFM tips can also deposit block copolymer nanostructures on heated substrates with a variety of experimentally observed domain alignments., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)