Micro/Nano-Functional Structures: Design, Manufacturing, Characterization and Applications

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "D:Materials and Processing".

Deadline for manuscript submissions: closed (30 January 2023) | Viewed by 10755

Special Issue Editor


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Guest Editor
Centre of Micro/Nano Manufacturing Technology (MNMT-Dublin), School of Mechanical and Materials Engineering, University College Dublin, Dublin 4, Ireland
Interests: micro/nano-manufacturing; design and manufacturing of functional structures; design and manufacturing of medical devices and bio-implants

Special Issue Information

Dear Colleagues,

Micro- and nano-scale functional structures have contributed extraordinary performance to diversified applications and attracted an increasing research focus in recent decades. A wide range of such functional structures, either working as the independent component or an integral part of the device, have come into our daily lives and offered people improved, or even totally new, services. One example is the nanopore, a simple tiny hole with nanoscale dimensions, which contributed significant advancements in DNA/RNA sequencing, energy conversion and storage, water desalination, etc. At the micro-, nano- or multi-scale, the functionality of these structures highly depends on the achievable manufacturing accuracy. Lithography-based technology forms the manufacturing basis of micro-electromechanical systems (MEMS) mainly for semiconductors, while micro/nano-manufacturing technologies have created more possibilities for metals, polymers and ceramics. The application, design and manufacturing of micro/nano-scale functional structures are facing unprecedented challenges due to the increasing complexity of architecture and decreasing dimension tolerance, which also poses a limitation for characterization.

Accordingly, this Special Issue seeks to showcase research papers and review articles that focus on novel methodological developments in micro- and nano-scale functional structure design, manufacturing, characterization and application. While manufacturing is advancing towards Atomic and Close-to-atomic Scale Manufacturing (ACSM), submissions based on the latest research findings related to ACSM are also welcome.

We look forward to your contributions!

Dr. Jufan Zhang
Guest Editor

Manuscript Submission Information

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Keywords

  • functional structures
  • micro/nano structures
  • micro/nano manufacturing
  • ultra-precision manufacturing
  • surface engineering

Published Papers (5 papers)

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Research

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12 pages, 2308 KiB  
Article
Connection of ssDNA to Silicon Substrate Based on a Mechano–Chemical Method
by Liqiu Shi, Feng Yu, Mingming Ding, Zhouming Hang, Yan Feng, Aifang Yan and Hongji Dong
Micromachines 2023, 14(6), 1134; https://doi.org/10.3390/mi14061134 - 28 May 2023
Viewed by 1084
Abstract
A novel fabrication process to connect single-stranded DNA (ssDNA)to a silicon substrate based on a mechano–chemical method is proposed. In this method, the single crystal silicon substrate was mechanically scribed in a diazonium solution of benzoic acid using a diamond tip which formed [...] Read more.
A novel fabrication process to connect single-stranded DNA (ssDNA)to a silicon substrate based on a mechano–chemical method is proposed. In this method, the single crystal silicon substrate was mechanically scribed in a diazonium solution of benzoic acid using a diamond tip which formed silicon free radicals. These combined covalently with organic molecules of diazonium benzoic acid contained in the solution to form self-assembled films (SAMs). The SAMs were characterized and analyzed by AFM, X-ray photoelectron spectroscopy and infrared spectroscopy. The results showed that the self-assembled films were covalently connected to the silicon substrate by Si–C. In this way, a nano-level benzoic acid coupling layer was self-assembled on the scribed area of the silicon substrate. The ssDNA was further covalently connected to the silicon surface by the coupling layer. Fluorescence microscopy showed that ssDNA had been connected, and the influence of ssDNA concentration on the fixation effect was studied. The fluorescence brightness gradually increased with the gradual increase in ssDNA concentration from 5 μmol/L to 15 μmol/L, indicating that the fixed amount of ssDNA increased. However, when the concentration of ssDNA increased from 15 μmol/L to 20 μmol/L, the detected fluorescence brightness decreased, indicating that the hybridization amount decreased. The reason may be related to the spatial arrangement of DNA and the electrostatic repulsion between DNA molecules. It was also found that ssDNA junctions on the silicon surface were not very uniform, which was related to many factors, such as the inhomogeneity of the self-assembled coupling layer, the multi-step experimental operation and the pH value of the fixation solution. Full article
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23 pages, 13178 KiB  
Article
Method for Keyhole-Free High-Aspect-Ratio Trench Refill by LPCVD
by Henk-Willem Veltkamp, Yves L. Janssens, Meint J. de Boer, Yiyuan Zhao, Remco J. Wiegerink, Niels R. Tas and Joost C. Lötters
Micromachines 2022, 13(11), 1908; https://doi.org/10.3390/mi13111908 - 4 Nov 2022
Cited by 1 | Viewed by 2857
Abstract
In micro-machined micro-electromechanical systems (MEMS), refilled high-aspect-ratio trench structures are used for different applications. However, these trenches often show keyholes, which have an impact on the performance of the devices. In this paper, explanations are given on keyhole formation, and a method is [...] Read more.
In micro-machined micro-electromechanical systems (MEMS), refilled high-aspect-ratio trench structures are used for different applications. However, these trenches often show keyholes, which have an impact on the performance of the devices. In this paper, explanations are given on keyhole formation, and a method is presented for etching positively-tapered high-aspect ratio trenches with an optimised trench entrance to prevent keyhole formation. The trench etch is performed by a two-step Bosch-based process, in which the cycle time, platen power, and process pressure during the etch step of the Bosch cycle are studied to adjust the dimensions of the scallops and their location in the trench sidewall, which control the taper of the trench sidewall. It is demonstrated that the amount of chemical flux, being adjusted by the cycle time of the etch step in the Bosch cycle, relates the scallop height to the sidewall profile angle. The required positive tapering of 88° to 89° for a keyhole-free structure after a trench refill by low-pressure chemical vapour deposition is achieved by lowering the time of the etch step. Full article
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8 pages, 3530 KiB  
Communication
The Reflectance Characteristics of an Inverse Moth-Eye Structure in a Silicon Substrate Depending on SF6/O2 Plasma Etching Conditions
by Jong-Chang Woo and Doo-Seung Um
Micromachines 2022, 13(10), 1556; https://doi.org/10.3390/mi13101556 - 20 Sep 2022
Cited by 2 | Viewed by 1655
Abstract
The global RE100 campaign is attracting attention worldwide due to climate change caused by global warming, increasingly highlighting the efficiency of renewable energy. Texturing of photovoltaic devices increases the devices’ efficiency by reducing light reflectance at their surfaces. This study introduces the change [...] Read more.
The global RE100 campaign is attracting attention worldwide due to climate change caused by global warming, increasingly highlighting the efficiency of renewable energy. Texturing of photovoltaic devices increases the devices’ efficiency by reducing light reflectance at their surfaces. This study introduces the change in light reflectance following the process conditions of plasma etching as a texturing process to increase the efficiency of photovoltaic cells. Isotropic etching was induced through plasma using SF6 gas, and the etch profile was modulated by adding O2 gas to reduce light reflectance. A high etch rate produces high surface roughness, which results in low surface reflectance properties. The inverse moth-eye structure was implemented using a square PR pattern arranged diagonally and showed the minimum reflectance in visible light at a tip spacing of 1 μm. This study can be applied to the development of higher-efficiency optical devices. Full article
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13 pages, 6718 KiB  
Article
Material Removal Mechanism in Photocatalytic−Assisted Jet Electrochemical Machining of SiCp/Al
by Feng Wang, Jing Zhou, Siyi Wu, Xiaoming Kang, Lin Gu and Wansheng Zhao
Micromachines 2022, 13(9), 1482; https://doi.org/10.3390/mi13091482 - 6 Sep 2022
Cited by 2 | Viewed by 1784
Abstract
Silicon carbide particle reinforced aluminum matrix (SiCp/Al) composites are increasingly used in high−end industries because of their superior comprehensive material properties. However, their advanced properties also create severe challenges for traditional processing technologies. A new hybrid machining method named photocatalytic−assisted jet [...] Read more.
Silicon carbide particle reinforced aluminum matrix (SiCp/Al) composites are increasingly used in high−end industries because of their superior comprehensive material properties. However, their advanced properties also create severe challenges for traditional processing technologies. A new hybrid machining method named photocatalytic−assisted jet electrochemical machining (PAJECM) is proposed to improve the machining capability by synchronously removing the metal aluminum matrix and the SiC particles. Comparative experiments were carried out on whether photocatalysis was added. The results show that after photocatalytic−assisted jet electrochemical machining, the height of SiC particles’ extrusion on the surface is significantly reduced. Compared with jet electrochemical machining (JECM) without photocatalysis at the same processing voltage, the surface roughness value is reduced, and the processing quality is improved. In PAJECM, the aluminum matrix is removed by electrochemical anodic dissolution, while the SiC particles generate a SiO2 reaction layer through photocatalysis, and the TiO2 abrasive flow’s mechanical action repeatedly removes the reaction layer. The electrochemical polarization curves and energy diffraction spectroscopy elemental analysis confirmed the material removal mechanism of PAJECM. Based on analyzing the phenomenon of material removal in detail, a qualitative model of the PAJECM material removal mechanism is established. This study provides valuable insights into the material removal mechanism in photocatalytic and jet electrochemical machining composite processes. Full article
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Review

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20 pages, 2857 KiB  
Review
Developing Meso and Microholes by Spark-Erosion Based Drilling Processes: A Critical Review
by Sujeet Kumar Chaubey and Kapil Gupta
Micromachines 2022, 13(6), 885; https://doi.org/10.3390/mi13060885 - 31 May 2022
Cited by 4 | Viewed by 2631
Abstract
The increased demand for miniature components has drawn the attention of researchers, engineers, and industry users to manufacture precision micro and mesoholes on foils, sheets, and plates made from a variety of engineering materials. These days, micro-drilling is extensively being adopted as a [...] Read more.
The increased demand for miniature components has drawn the attention of researchers, engineers, and industry users to manufacture precision micro and mesoholes on foils, sheets, and plates made from a variety of engineering materials. These days, micro-drilling is extensively being adopted as a fundamental operation in all kinds of smart manufacturing industries to make different types of microholes, such as through holes, blind holes, and taper holes on micro-parts and components. Drilled holes with a diameter of less than 1 mm are referred to as microholes, while drilled holes whose diameter ranges between 1 and 10 mm are known as mesoholes. Meso and microholes are commonly referred to as fine-holes. Modern or advanced drilling processes are mostly used to drill microholes from a variety of materials. This paper presents an extensive review of the previous research conducted on the drilling of fine holes (meso and micro size) by spark- erosion-based processes along with highlighting work and tool electrode materials, specifications of drilled holes, types of microholes (through or blind holes), process parameters, performance measures, and key findings. The paper aims to facilitate researchers and scholars by highlighting the capabilities of spark erosion machining, drilling, and its variants to fabricate miniature holes. The paper ends with a conclusion and future research directions to encourage further work in this area. Full article
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