Tip-based Nanofabrication Research Articles

AFM tip-based fabrication of silicon nanostructures with reduced subsurface amorphous layers

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.

Investigations on tip-based large area nanofabrication and nanometrology using a planar nanopositioning machine (NFM-100)

This paper explores large area application of tip-based nanofabrication by field emission scanning probe lithography and showcases the simultaneous possibility of atomic force microscopy on macroscopic scales. This is made possible by the combination of tip-based technology and a planar nanopositioning and nanomeasuring machine. Using long range atomic force microscopy measurement of regular grating structures, the performance of the machine is thoroughly characterized over the full 100 mm range of motion of the positioning machine, which was confirmed by repeated measurements. After initially focussing on achieving the minimum line width of < 40 nm in microscopic areas, a grating with a pitch of 1 μm is additionally fabricated over a total length of 10 mm, whereby the dimensions and deviations are also considered.

Tip-based nanofabrication below 40 nm combined with a nanopositioning machine with a movement range of Ø100 mm

Tip-based nanofabrication below 40 nm combined with a nanopositioning machine with a movement range of Ø100 mm

Modeling and experimental study of machining outcomes when conducting nanoscratching using dual-tip probe on single-crystal copper

Atomic force microscopy (AFM) tip-based nanomachining technique has been proved as a powerful method to fabricate nanostructures. The nanomachining approach proposed in this study offers a new concept to improve the width resolution and processing efficiency of AFM tip-based nanofabrication techniques. The method uses a dual-tip probe and single-crystal copper is used as the sample material. A depth prediction model is developed for the nanoscratching process using the dual-tip probe. The results obtained by nanoscratching tests show that symmetrical three-dimensional (3D) nanostructures composed of two large pile-ups and one small hump can be machined. The model predicts the machined nanostructure depth accurately when the machined depth reaches approximately 40 nm; the blunt tip and the inclined inner wall of the dual-tip gap may be the main reasons for the inaccurate predictions at smaller machined depths. Moreover, molecular dynamics (MD) simulation is also used to investigate the scratching process with the dual-tip probe. The simulation results obtained agree well with the experimental results.

Experimental investigation of the effects of vibration parameters on ultrasonic vibration-assisted tip-based nanofabrication

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.

Towards understanding the machining mechanism of the atomic force microscopy tip-based nanomilling process

Atomic force microscopy (AFM) tip-based nanofabrication is as a powerful method to machine nanostructures. However, the traditional AFM scratching process suffers from low processing efficiency and a low rate of material removal. Thus, an AFM tip-based nanomilling method was previously proposed to improve the machining efficiency and material removal rate; however, the machining mechanism of the nanomilling process, especially on hard-brittle silicon crystals, is not well understood. In this study, we used an AFM tip-based nanomilling approach to machine nanochannels on single-crystal silicon to investigate the machining mechanism (i.e., the material removal state, undeformed chip thickness, the brittle-to-ductile transition, and subsurface damage). For the first time, we established a theoretical model for tip-based nanomilling with a constant normal load to predict the machined depth. Nanochannels fabricated with a wide range of feed directions, crystal orientations, and tip trajectories were obtained, which provided a reference for machining high-quality nanochannels and an in-depth understanding of the nanomilling of single-crystal silicon. The experimental results demonstrated that we could machine a nanochannel without pile-ups by selecting a specific trajectory with a feed smaller than 4 nm in the 0° direction, a normal load no greater than 120 μN, and a crystal orientation at rotation angles of 135°, 157.5°, or 180°. Moreover, transmission electron microscope analysis of the subsurface of the nanochannel revealed a large number of dislocations, stacking faults, and a layer of amorphous silicon. Our findings are of great significance for obtaining high-quality nanochannels with a predicable machined depth and understanding the nanomilling mechanism of hard-brittle materials.

Design of a novel 3D ultrasonic vibration platform with tunable characteristics

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.

Design of a novel 3D tip-based nanofabrication system with high precision depth control capability

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.

Atomic force microscope integrated with a scanning electron microscope for correlative nanofabrication and microscopy

More than 40 years after its invention, the atomic force microscopy (AFM) can be integrated with scanning electron microscope (SEM) instruments as an increasingly capable and productive characterization tool with sub-nanometer spatial resolution. The authors have designed and developed an AFM instrument capable to be integrated into any SEM or in a combination of SEM with a focused ion-beam (FIB) tool. The combination of two or more different types of techniques like SEM, energy dispersive x-ray spectroscopy, and AFM is called correlative microscopy because analytical information from the same place of the sample can be obtained and correlated. For the first time, they introduced to the SEM/FIB tool correlative nanofabrication methods like field-emission scanning probe lithography, tip-based electron beam induced deposition, and nanomachining. The combination of all these methods provides a completely new nanotechnology instrument, which should be seen as a tool for correlative nanofabrication and microscopy. Thus, it provides for the first time the capabilities of a stand-alone instrument with the capabilities of nondestructive three-dimensional tip-based metrology and nanofabrication into the combined SEM/FIB tool. In this article, the authors describe all these methods in detail and present a brief example of the results obtained. They demonstrate that the self-sensing, self-actuating cantilevers (called active cantilevers) equipped with Diamond tip are a versatile toolkit for fast imaging and emerging nanofabrication. The AFM integrated into SEM is using active cantilevers that can characterize and generate nanostructures all in situ without the need to break-vacuum or contaminate the sample.

Low power femtosecond tip-based nanofabrication with advanced control

In this paper, we propose an approach to enable the use of low power femtosecond laser in tip-based nanofabrication (TBN) without thermal damage. One major challenge in laser-assisted TBN is in maintaining precision control of the tip–surface positioning throughout the fabrication process. An advanced iterative learning control technique is exploited to overcome this challenge in achieving high-quality patterning of arbitrary shape on a metal surface. The experimental results are analyzed to understand the ablation mechanism involved. Specifically, the near-field radiation enhancement is examined via the surface-enhanced Raman scattering effect, and it was revealed the near-field enhanced plasma-mediated ablation. Moreover, silicon nitride tip is utilized to alleviate the adverse thermal damage. Experiment results including line patterns fabricated under different writing speeds and an “R” pattern are presented. The fabrication quality with regard to the line width, depth, and uniformity is characterized to demonstrate the efficacy of the proposed approach.

A Computer-Aided Design and Manufacturing Implementation of the Atomic Force Microscope Tip-Based Nanomachining Process for Two-Dimensional Patterning

This paper reports a feasibility study that demonstrates the implementation of a computer-aided design and manufacturing (CAD/CAM) approach for producing two-dimensional (2D) patterns on the nanoscale using the atomic force microscope (AFM) tip-based nanomachining process. To achieve this, simple software tools and neutral file formats were used. A G-code postprocessor was also developed to ensure that the controller of the AFM equipment utilized could interpret the G-code representation of tip path trajectories generated using the computer-aided manufacturing (CAM) software. In addition, the error between a machined pattern and its theoretical geometry was also evaluated. The analyzed pattern covered an area of 20 μm × 20 μm. The average machined error in this case was estimated to be 66 nm. This value corresponds to 15% of the average width of machined grooves. Such machining errors are most likely due to the flexible nature of AFM probe cantilevers. Overall, it is anticipated that such a CAD/CAM approach could contribute to the development of a more flexible and portable solution for a range of tip-based nanofabrication tasks, which would not be restricted to particular customised software or AFM instruments. In the case of nanomachining operations, however, further work is required first to generate trajectories, which can compensate for the observed machining errors.

Tip-Based Nanofabrication for Scalable Manufacturing

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.

The Ellenbogen's "Matter as Software" Concept for Quantum Computer Implementation: III. Selection of X@C&lt;SUB&gt;60&lt;/SUB&gt; Molecular Building Blocks (MBBs) for Tip-Based Nanofabrication (TBN) of Trapped Neutral Atom Quantum Computing Devices

The Ellenbogen's "Matter as Software" Concept for Quantum Computer Implementation: III. Selection of X@C&lt;SUB&gt;60&lt;/SUB&gt; Molecular Building Blocks (MBBs) for Tip-Based Nanofabrication (TBN) of Trapped Neutral Atom Quantum Computing Devices

The Ellenbogen's "Matter as Software" Concept for Quantum Computer Implementation: II. Bonding Between the C&lt;SUB&gt;60&lt;/SUB&gt; and X@C&lt;SUB&gt;60&lt;/SUB&gt; Molecules as Available Molecular Building Blocks (MBBs) for Tip-Based Nanofabrication (TBN) of Quantum Computing Devices

The Ellenbogen's "Matter as Software" Concept for Quantum Computer Implementation: II. Bonding Between the C&lt;SUB&gt;60&lt;/SUB&gt; and X@C&lt;SUB&gt;60&lt;/SUB&gt; Molecules as Available Molecular Building Blocks (MBBs) for Tip-Based Nanofabrication (TBN) of Quantum Computing Devices

Flexure-based dynamic-tunable five-axis nanopositioner for parallel nanomanufacturing

With the increasing demand for devices and systems with nanometer precision in the modern manufacturing industry, tip-based nanofabrication (TBN) has become an indispensable part of manufacturing process. However, a common issue that needs to be addressed is to increase the throughput of TBN, which is sequential and inherently slow. To overcome the difficulty, in this paper we present the design and control of a flexure-based five-axis nanopositioner with dynamic-tuning capability for parallel nanomanufacturing applications. The dynamic-tuning method enables trade-offs between the range and speed of the nanopositioner so as to increase the throughput of the nanomanufacturing system. The experimental results indicate that the nanopositioner conforms with the in-plane range and resolution requirements, i.e., ±5mm/100nm in X/Y axis, while its natural frequencies in X/Y axis can be increased by two to three times at the expense of decreased stroke, i.e., elastic range. In addition, real-time dynamic-tuning experiments show active vibration cancellation techniques can be implemented on the nanopositioner and effectively eliminate the unwanted dynamics and improve the overall dynamic performance. Lastly, we performed nano-scratching experiments using an 18 tip AFM array to fabricate optical grating patterns on gold coated silicon substrates of 5×1mm2 to demonstrate the practicality of the new method. The experiment confirmed good parallelism had been achieved during the experiments, where the scratched gold lines have a consistent depth of ∼160nm.

Study of the electrode tool wear and the probe tip sharpening phenomena during the nanoscale STM electric discharge lithography of the bulk HOPG surface

Scanning tunneling microscope (STM)-based electric discharge lithography or machining is capable of fabricating nanostructures or nano-devices out of the carbon-based materials with low cost and high accuracy. As a tip-based nanofabrication method, the evolution of the STM probe tip, which functionalized as the electrode tool, is of great importance to the machining capability and performance of the STM electric discharge lithography. In this work, both the electrode tool wear (ETW) and the probe tip sharpening phenomena were investigated during the SPM electric discharge lithography of the bulk highly oriented pyrolytic graphite (HOPG) sample surface. The influence of the electrode tool wear evolution on the machining results was experimentally studied. The geometric parameters of the STM probe tip were measured from SEM imaging. Moreover, the probe tip sharpening phenomenon was specifically observed by applying the negative polarity machining. The evidences of the underlying mechanisms for the tip sharpening effect were revealed experimentally in this study, which have never been reported in the previous work. It is further proved that this effect could be utilized to the in-situ sharpening of the STM probe tip. Finally, the effective methods to improve the machining consistency and the tool lifetime were proposed.

The Ellenbogen's “Matter as Software” Concept for Quantum Computer Implementation. C&lt;SUB&gt;60&lt;/SUB&gt; and X@C&lt;SUB&gt;60&lt;/SUB&gt; Molecules as Available Molecular Building Blocks (MBBs) for Tip-Based Nanofabrication (TBN) of Quantum Computing Devices

The Ellenbogen's “Matter as Software” Concept for Quantum Computer Implementation. C&lt;SUB&gt;60&lt;/SUB&gt; and X@C&lt;SUB&gt;60&lt;/SUB&gt; Molecules as Available Molecular Building Blocks (MBBs) for Tip-Based Nanofabrication (TBN) of Quantum Computing Devices

Tip-Based Nanofabrication of Arbitrary Shapes of Graphene Nanoribbons for Device Applications.

Graphene nanoribbons (GNRs) have promising applications in future nanoelectronics, chemical sensing and electrical interconnects. Although there are quite a few GNR nanofabrication methods reported, a rapid and low-cost fabrication method that is capable of fabricating arbitrary shapes of GNRs with good-quality is still in demand for using GNRs for device applications. In this paper, we present a tip-based nanofabrication method capable of fabricating arbitrary shapes of GNRs. A heated atomic force microscope (AFM) tip deposits polymer nanowires atop a CVD-grown graphene surface. The polymer nanowires serve as an etch mask to define GNRs through one step of oxygen plasma etching similar to a photoresist in conventional photolithography. Various shapes of GNRs with either linear or curvilinear features are demonstrated. The width of the GNR is around 270 nm and is determined by the width of the depositing polymer nanowire, which we estimate can be scaled down 15 nms. We characterize our TBN-fabricated GNRs using Raman spectroscopy and I-V measurements. The measured sheet resistances of our GNRs fall within the range of 1.65 kΩ/□-1 - 2.64 kΩ/□-1, in agreement with previously reported values. Furthermore, we determined the high-field breakdown current density of GNRs to be approximately 2.94×108 A/cm2. This TBN process is seamlessly compatible with existing nanofabrication processes, and is particularly suitable for fabricating GNR based electronic devices including next generation DNA sequencing technologies and beyond silicon field effect transistors.

Nanofluidic channels of arbitrary shapes fabricated by tip-based nanofabrication

Nanofluidic channels have promising applications in biomolecule manipulation and sensing. While several different methods of fabrication have been demonstrated for nanofluidic channels, a rapid, low-cost fabrication method that can fabricate arbitrary shapes of nanofluidic channels is still in demand. Here, we report a tip-based nanofabrication (TBN) method for fabricating nanofluidic channels using a heated atomic force microscopy (AFM) tip. The heated AFM tip deposits polymer nanowires where needed to serve as etch mask to fabricate silicon molds through one step of etching. PDMS nanofluidic channels are easily fabricated through replicate molding using the silicon molds. Various shapes of nanofluidic channels with either straight or curvilinear features are demonstrated. The width of the nanofluidic channels is 500 nm, and is determined by the deposited polymer nanowire width. The height of the channel is 400 nm determined by the silicon etching time. Ion conductance measurement on one single curvy shaped nanofluidic channel exhibits the typical ion conductance saturation phenomenon as the ion concentration decreases. Moreover, fluorescence imaging of fluid flowing through a fabricated nanofluidic channel demonstrates the channel integrity. This TBN process is seamlessly compatible with existing nanofabrication processes and can be used to achieve new types of nanofluidic devices.

An investigation of heat transfer between a microcantilever and a substrate for improved thermal topography imaging

This paper reports the numerical and experimental investigation of heat transfer from a heated microcantilever to a substrate and uses the resulting insights to improve thermal topography imaging. The cantilever sensitivity, defined as change in thermal signal due to changes in the topography height, is relatively constant for feature heights in the range 100–350 nm. Since the cantilever-substrate heat transfer is governed by thermal conduction through the air, the cantilever sensitivity is nearly constant across substrates of varying thermal conductivity. Surface features with lateral size larger than 2.5 μm can induce artifacts in the cantilever signal resulting in measurement errors as large as 28%. These artifacts arise from thermal conduction from the cantilever in the lateral direction, parallel to the surface. We show how these artifacts can be removed by accounting for this lateral conduction and removing it from the thermal signal. This technique reduces the measurement error by as much as 26%, can be applied to arbitrary substrate topographies, and can be scaled to arrays of heated cantilevers. These results could lead to improvements in nanometer-scale thermal measurements including scanning thermal microscopy and tip-based nanofabrication.