Jining Sun

Fabrication of periodic nanostructures by single-point diamond turning with focused ion beam built tool tips

Periodic nanostructures have been widely used on emerging nano-products such as plasmonic solar cell and nano-optics. However, lack of cost-effective fabrication techniques has become the bottleneck for commercialization of these nano-products. In this work, we develop a scale up approach to fabricate high-precision nanostructures in large area. In this method, a nano-scale single crystal diamond (SCD) tool is produced by focused ion beam (FIB) machining. The nano SCD tool is then further applied to cut periodic nanostructures using single-point diamond turning (SPDT). A divergence compensation method and surface topography generation model forms a deterministic FIB fabrication approach. It has been used to generate four periods of the required periodic nano-grating structures (with a minimal dimension of 150 nm) on a normal SCD tool tip and achieves 10 nm form accuracy. The contribution of the beam tail effect has also been evaluated by using the surface topography simulation method. The fabricated diamond tool is then applied to obtain nano-grating on an electroless nickel substrate in a total area of 5 × 2 mm2 through SPDT. The whole SPDT machine process only takes 2 min (with a material removal rate up to 1.8 × 104 μm3 s−1). Due to the elastic recovery that occurred upon the workpiece material, the practical cutting width is 13 nm smaller than the tool tip. The machining trial shows it is very promising to apply this scale up nanofabrication approach for commercialization of nano-products which possess period nanostructures.

A predictive divergence compensation approach for the fabrication of three-dimensional microstructures using focused ion beam machining

In this paper, the major factors which cause fabrication divergence in the focused ion beam (FIB) milling process are discussed. A divergence compensation approach is outlined which calculates the corrected dwell time in order to allow for the divergence caused by the FIB milling process; this is due to overlap effects and the angular-dependent sputter yield. A multi-pass scanning method is used to reduce the fabrication divergence precipitated by atom redeposition. Microstructures, such as parabolic, hemispherical and sinusoidal shapes and a nano hemispherical structure have been produced during the FIB milling experiments using conventional bitmap milling and proposed divergence compensation approaches. A flat top/bottom surface is obtained in convex/concave structures when using the conventional bitmap FIB milling approach. Further research shows that the reasons for this phenomenon are mainly related to both the aspect ratio of the structures and the existence of an oxide layer on the substrate surface. The flat top/bottom phenomenon can be removed by using the combination of a novel divergence compensation approach and the removal of the oxide layer from the substrate surface prior to FIB machining. The experimental results show that the surface form accuracy has been greatly improved by using this method and the overlap effect can be suppressed by carefully choosing the normalized pixel spacing.

Fabricating optical fibre-top cantilevers for temperature sensing

In this paper, we propose techniques to fabricate micro-cantilevers onto the end of standard single mode optical fibres using a combination of picosecond laser machining and focused ion beam milling techniques and demonstrate their use as temperature sensors. Using this approach the cantilever can be pre-aligned with the core of the fibre during fabrication, therefore offering a stable and straightforward means of optically addressing the cantilever. The cantilever is designed to measure deflection over a range of 10 µm using a simple readout technique. A phase recovery algorithm is employed to reduce the interrogation error to around 2–3 nm. Finally, a temperature cycling experiment demonstrates that the cantilever could be used as a temperature sensor from room temperature to 500 °C with an average rms temperature error from 20 °C to 500 °C of ~±1.4 °C.

Laser assisted micro grinding of high strength materials

This paper aims to develop a laser assisted grinding process capable of manufacturing micro features in high strength materials. A diode laser with wavelength 808 nm was set on a precision grinding machine. Micro grooves were fabricated on high strength materials including silicon nitride and aluminium oxide by using the laser assisted grinding process, i.e. laser pre-heat workpiece flowed by micro grinding. The experimental results showed that the laser assisted grinding process resulted in deeper grooves due to thermal expansion of workpiece materials caused by laser heating. However, the machined surface roughness was more consistently better than that obtained using solo grinding process and applying coolant. No subsurface damage was observed in the SEM images of cross sections of the machined workpieces when laser assisted grinding process was used.

A Micro-Machined Optical Fiber Cantilever as a Miniaturized pH Sensor

A micro-cantilever fabricated using a combination of picosecond-laser machining and focused ion beam milling directly onto the end of a standard telecommunications optical fiber is demonstrated as a liquid pH sensor. Conventional pH meters typically require relatively large reaction volumes up to ~50 mL, which is not always convenient. The micro-scale nature of this sensor offers the potential for pH measurement on a smaller sample volume down to micro-liter. The fiber end-tip cantilever is coated with a pH sensitive layer, and the pH-induced deflection is monitored interfermetically. A detectable pH range from 4.0 to 10.0 is demonstrated for the cantilevers coated with 16-mercapto-hexadecanoic-1-acid as the functional layer, and a detectable pH range from 4.0 to 9.0 is demonstrated for the cantilevers coated with Al2O3 as the functional layer.

Single Point Diamond Turning of Single Crystal Silicon Carbide: Molecular Dynamic Simulation Study

Silicon carbide can meet the additional requirements of operation in hostile environments where conventional silicon-based electronics (limited to 623K) cannot function. However, being recent in nature, significant study is required to understand the various machining properties of silicon carbide as a work material. In this paper, a molecular dynamic (MD) simulation has been adopted, to simulate single crystal β-silicon carbide (cubic) in an ultra precision machining process known as single point diamond turning (SPDT). β-silicon carbide (cubic), similar to other materials, can also be machined in ductile regime. It was found that a high magnitude of compression in the cutting zone causes a sp3- sp2 order-disorder transition which appears to be fundamental cause of wear of diamond tool during the SPDT process.

Micro-Machined Optical Fiber Side-Cantilevers for Acceleration Measurement

We propose an accelerometer based on a micro-cantilever fabricated onto the side of a single mode optical fiber using a combination of ps-laser machining and focused ion beam (FIB) processing. FIB machining is also used to fabricate a 45° mirror onto the end of the fiber that is accurately aligned with optical fiber core. This provides a reliable means to optically address components attached to the side of the fiber, such as the cantilever. Using interferometry to accurately monitor the deflection of the side cantilever results in a device that is capable of measuring two-axis acceleration. Acceleration up to 6 g is measured with a resolution of ~0.01 g and a frequency range from dc to 500 Hz has been demonstrated. The cross-axis sensitivity is below −32 dB.

Deterministic Fabrication of Micro- and Nanostructures by Focused Ion Beam

Focused ion beam (FIB) machining is an ideal technique for both micro- and nanofabrication. This chapter describes a deterministic fabrication approach to accurately obtain micro- and nanostructures. It starts with a detailed introduction of FIB machining mechanism, followed by a surface topography simulation method and a divergence compensation method. The effectiveness of this fabrication approach has been fully demonstrated through a number of experiments which show that the surface topography of the machined material can be precisely predicted; the divergence compensation method can reduce the machining error, and the machined surface form accuracy can be dramatically improved. Combining with other techniques, some hybrid manufacturing techniques based on FIB machining are also introduced.

Highly directional emission from a quantum emitter embedded in a hemispherical cavity

We report the design of a solid-state, micron-sized hemispherical cavity that yields significantly enhanced extraction efficiency with modest Purcell enhancement from embedded quantum emitters. A simple analytical model provides a guideline for the design and optimization of the structure, while finite-difference time-domain simulations are used for full analysis of the optimum structure. Cavity modes with up to 90% extraction efficiency, a Purcell enhancement factor >2, and a quality factor of ≈50 are achieved. In addition, Gaussian-like far-field beam profiles with low divergence are exhibited for several modes. These monolithic cavities are promising for solid-state emitters buried in a high dielectric environment, such as self-assembled quantum dots and optically active defects in diamond.

Single Point Diamond Turning of Calcium Fluoride Optics

This paper aims to develop a cost-effective diamond turning process to obtain nanosmooth CaF2 optics. Diamond tool wear was also carried out through a number of cutting trials. Three CaF2 specimens (diameter of 50 mm and thickness of 5 mm, crystal orientation of (111)) were diamond turned on an ultra precision lathe (Moore Nanotech 350UPL) by a number of facing cuts. In the cutting trials feed rate varied from 1 μm/rev to 10 μm/rev. White spirit mist was used as the coolant. Cutting forces were measured by a dynamometer (Kistler BA9256). Surface roughness of the CaF2 optics and tool flank wear were measured by a white light interferometer (Zygo Newview 5000) and a scanning electron microscope (FEI Quanta 3D FEG), respectively. It was found that using a feed rate of 1 μm/rev surface roughness Ra of 2 nm could be obtained. When the ratio of the normal cutting force to the tangential cutting force was lower than 1 tool wear would initiate. In diamond turning of calcium fluoride abrasive wear was the main tool wear mechanism. Using white spirit mist as thecoolant could avoid generation of thermal type brittle fracture on the machined CaF2 surfaces.