Gan Wang

Gan Wang will defend his PhD thesis on 20 January 2025.

Gan Wang will defend his PhD thesis on 20 January 2025. The defense will take place in PJ, Institutionen för fysik, Origovägen 6b, Göteborg, at 10:00.

Title: Microfabrication technique applications: from passive particle manipulation to active microswimmers, micromachines, and fluidic control

Abstract: Overcoming Brownian motion at the micro- and nanoscale to achieve precise control of objects is crucial for fields such as materials science and biology. Significant progress has been made in trapping and manipulating micro- and nanoscale objects, either by generating gradients through external physical fields or by engineering systems that can harvest energy from their environment for autonomous motion. These techniques rely on the precise application of forces, such as optical and electromagnetic forces, and have found extensive applications across various scientific disciplines. Recent advances in micro- and nanofabrication technologies have greatly enhanced the generation and regulation of these forces, offering new possibilities for manipulating micro- and nanoscale objects.

This thesis applies traditional micro- and nanofabrication techniques, typically used in semiconductor manufacturing, to construct micro- and nanostructures for manipulating forces, primarily critical Casimir forces and optical forces, to achieve precise control over microscale object movement.

I first show the fabrication of periodic micropatterns on a substrate, followed by chemical functionalization to impart hydrophilic and hydrophobic properties. Near the critical temperature of a binary liquid, attractive and repulsive critical Casimir forces are generated between the micropatterns and microparticles. These forces allow the stable trapping of the microparticles on the substrate and the manipulation of their configuration and movement.
Then, my research transitions from passive control to active motion by fabricating metasurfaces capable of modulating optical fields and embedding them within micro-particles (microswimmers). This enables light-momentum exchange under planar laser illumination, resulting in autonomous movement of the microswimmers. By varying the metasurface design as well as the intensity and polarization of the light, complex behaviors can emerge within these microswimmers. Subsequently, My research focused on using these microfabrication techniques to build micromotors integrated on a chip surface. These micromotors couple with other objects through gear structures, creating miniature machines that can execute functional tasks. Finally, by altering the configuration of these machines and the distances between them, I acheived precise, multifunctional control over fluid dynamics, facilitating the transport of micro- and nanoscale objects.

Insights gained from this research suggest innovative manufacturing approaches for scalable manipulation of particles, more intelligent microrobots, and powerful miniaturized on-chip machines, with applications across various fields.

Thesis: https://hdl.handle.net/2077/84048

Supervisor: Giovanni Volpe
Examiner: Dag Hanstorp
Opponent: Peer Fischer
Committee: Heiner Linke, Anna Maciolek, Hao Zeng
Alternate board member: Francesco Ferranti

Microscopic Geared Mechanisms on ArXiv

Schematic and brightfield image (inset) of the movement of 16μm diameter micromotor under the illumination of linearly polarized 1064nm laser. *(Image by G. Wang. Schematic by A. Ciarlo)*

Microscopic Geared Mechanisms
Gan Wang, Marcel Rey, Antonio Ciarlo, Mohanmmad Mahdi Shanei, Kunli Xiong, Giuseppe Pesce, Mikael Käll and Giovanni Volpe
arXiv: 2409.17284

The miniaturization of mechanical machines is critical for advancing nanotechnology and reducing device footprints. Traditional efforts to downsize gears and micromotors have faced limitations at around 0.1 mm for over thirty years due to the complexities of constructing drives and coupling systems at such scales. Here, we present an alternative approach utilizing optical metasurfaces to locally drive microscopic machines, which can then be fabricated using standard lithography techniques and seamlessly integrated on the chip, achieving sizes down to tens of micrometers with movements precise to the sub-micrometer scale. As a proof of principle, we demonstrate the construction of microscopic gear trains powered by a single driving gear with a metasurface activated by a plane light wave. Additionally, we develop a versatile pinion and rack micromachine capable of transducing rotational motion, performing periodic motion, and controlling microscopic mirrors for light deflection. Our on-chip fabrication process allows for straightforward parallelization and integration. Using light as a widely available and easily controllable energy source, these miniaturized metamachines offer precise control and movement, unlocking new possibilities for micro- and nanoscale systems.

Presentation by G. Wang at ECIS, Copenhagen, 5 September 2024

Light-driven metamachines
Gan Wang, Marcel Rey, Antonio Ciarlo, Mohanmmad Mahdi Shanei, Kunli Xiong, Giuseppe Pesce, Mikael Käll and Giovanni Volpe
Date: 5 September 2024
Time: 15:45-16:00

The incorporation of Moore’s law into integrated circuits has spurred opportunities for downsizing traditional mechanical components. Despite advancements in single on-chip motors using electrical, optical, and magnetic drives under ~100 μm, creating complex machines with multiple units remains challenging. Here, we developed a ~10 μm on-chip micromotor using a method compatible with complementary metal oxide semiconductors (CMOS) process. The meta-surface is embedded with the motor to control the incident laser beam direction, enabling momentum exchange with light for movement. The rotation direction and speed are adjustable through the meta-surface, along with the intensity and polarization of applied light. By combining these motors and controlling the configuration, we create complex machines with a size similar to traditional machines below 50um, such as the rotary motion mode of multiple gear coupled gear trains, and the linear motion mode combined with rack and pinion, and combine the micro metal The mirror is introduced into the machine to realize the self-controlled scanning function of the laser in a fixed area.

Presentation by G. Wang at SPIE-MNM, San Diego, 19 August 2024

Light-driven metamachines
Gan Wang, Marcel Rey, Antonio Ciarlo, Mohanmmad Mahdi Shanei, Kunli Xiong, Giuseppe Pesce, Mikael Käll and Giovanni Volpe
Date: 19 August 2024
Time: 16:25-16:40 (PDT)

Nanoalignment by Critical Casimir Torques featured in the Editors’ Highlights of Nature Communications

Artist rendition of a disk-shaped microparticle trapped above a circular uncoated pattern within a thin gold layer coated on a glass surface. *(Image by the Authors of the manuscript.)*

Our article, entitled Nanoalignment by Critical Casimir Torques, has been selected as a featured article by the editor at Nature Communications. This recognition highlights the significance of our research within the field of applied physics and mathematics.

The editors have included our work in their Editors’ Highlights webpage, which showcases the 50 best papers recently published in this area. You can view the feature on the Editors’ Highlights page (https://www.nature.com/ncomms/editorshighlights) as well as on the journal homepage (https://www.nature.com/ncomms/).

Screenshot from the Editors’ Highlights page of Nature Communications, dated 2 July 2024.

Poster by G. Wang at DINAMO 2023, Svolvær, 13 June 2023

Light-driven micromachines. *(Image by G. Wang.)*

Nanophotonic encoding of light-driven micromachines
Gan Wang, Marcel Rey, Mahdi Shanei, Kunli Xiong, Einstom Engay, Mikael Käll, and Giovanni Volpe
Date: 13 June 2023
Time: 21:00 (CEST）

On-chip micromotors hold significant application potential in various fields, including cells, microfluidic manipulation, and the micro integration of machines. .The driving mechanism plays a crucial role in the design of micromotors. Currently, various methods such as static electricity, light, magnetism, chemical energy, and mechanical conduction are utilized for this purpose. Optics, in particular, offers distinct advantages including precise control, addressability, non-contact operation, and compatibility with diverse liquid environments. However, existing optically actuated on-chip motors necessitate high energy input, resulting in phototoxicity concerns and hindrances to large-scale manipulation. Furthermore, achieving precise control over speed and direction remains challenging, along with difficulties in establishing coupling among multiple devices.

Presentation by G. Wang at ISMC 2022, Poznan, 20 September 2022

Recognize and selectively trap chiral particles by critical Casimir force. *(Image by G. Wang.)*

Nanopositioning and nanoalignment of microparticles on patterned surfaces
Gan Wang, Piotr Nowakowski, Nima Farahmand, Benjamin Midtvedt, Falko Schmidt, Mikael Käll, Svyatoslav Kondrat, Sigfried Dietrich and Giovanni Volpe
Date: 20 September 2022
Time: 14:10 (CEST）

Direct manipulation of objects in a solution can provide opportunities to investigate material properties and construct microscopic devices. However, currently available methods, such as optical tweezers and thermal tweezers, have several limitations especially to control the orientation and alignment of particles near surfaces. Here, we experimentally demonstrate that by exploiting the critical Casimir effect, emerging in the presence of a critical binary liquid, microparticles (diameter d≈2µm) can be trapped with nanometer precision. We investigated the motion of SiO2 microscopic disks above nanopatterned surfaces coated with a thin gold film immersed inside a critical mixture. By adjusting the adsorption preference of the gold film to one of the two components of the mixture liquid, we can finely tune the balance between the critical Casimir repulsion and attraction generated between different regions of the substrate and the disk. In this way, we can control the configuration of the disk and make it perform some complex motion. Furthermore, we show how this approach can be used to align particles with patterns, e.g., to sort asymmetric particles with respect to their chirality. We foresee this method can be extended to control the movement of small objects of various materials, thereby severing as a platform to study microscale physical and chemical phenomena.