Graphene microbubbles make perfect lenses
New method generates precisely controlled graphene microbubbles with
perfectly spherical curvature for lenses

Date:
October 9, 2020
Source:
SPIE--International Society for Optics and Photonics
Summary:
Researchers are developing a method to generate precisely controlled
graphene microbubbles on a glass surface using laser pulses.



FULL STORY ==========================================================================
Tiny bubbles can solve large problems. Microbubbles -- around 1-50
micrometers in diameter -- have widespread applications. They're
used for drug delivery, membrane cleaning, biofilm control, and water treatment. They've been applied as actuators in lab-on-a-chip devices
for microfluidic mixing, ink-jet printing, and logic circuitry, and in photonics lithography and optical resonators. And they've contributed remarkably to biomedical imaging and applications like DNA trapping
and manipulation.


========================================================================== Given the broad range of applications for microbubbles, many methods for generating them have been developed, including air stream compression
to dissolve air into liquid, ultrasound to induce bubbles in water,
and laser pulses to expose substrates immersed in liquids. However,
these bubbles tend to be randomly dispersed in liquid and rather unstable.

According to Baohua Jia, professor and founding director of the Centre
for Translational Atomaterials at Swinburne University of Technology,
"For applications requiring precise bubble position and size, as well as
high stability -- for example, in photonic applications like imaging and trapping - - creation of bubbles at accurate positions with controllable volume, curvature, and stability is essential." Jia explains that,
for integration into biological or photonic platforms, it is highly
desirable to have well controlled and stable microbubbles fabricated
using a technique compatible with current processing technologies.

Balloons in graphene Jia and fellow researchers from Swinburne University
of Technology recently teamed up with researchers from National University
of Singapore, Rutgers University, University of Melbourne, and Monash University, to develop a method to generate precisely controlled graphene microbubbles on a glass surface using laser pulses. Their report is
published in the peer-reviewed, open-access journal, Advanced Photonics.

The group used graphene oxide materials, which consist of graphene
film decorated with oxygen functional groups. Gases cannot penetrate
through graphene oxide materials, so the researchers used laser to
locally irradiate the graphene oxide film to generate gases to be
encapsulated inside the film to form microbubbles -- like balloons. Han
Lin, Senior Research Fellow at Swinburne University and first author on
the paper, explains, "In this way, the positions of the microbubbles can
be well controlled by the laser, and the microbubbles can be created
and eliminated at will. In the meantime, the amount of gases can be
controlled by the irradiating area and irradiating power.

Therefore, high precision can be achieved." Such a high-quality bubble
can be used for advanced optoelectronic and micromechanical devices with
high precision requirements.

The researchers found that the high uniformity of the graphene oxide
films creates microbubbles with a perfect spherical curvature that can be
used as concave reflective lenses. As a showcase, they used the concave reflective lenses to focus light. The team reports that the lens presents
a high-quality focal spot in a very good shape and can be used as light
source for microscopic imaging.

Lin explains that the reflective lenses are also able to focus light
at different wavelengths at the same focal point without chromatic
aberration. The team demonstrates the focusing of a ultrabroadband
white light, covering visible to near-infrared range, with the same
high performance, which is particularly useful in compact microscopy
and spectroscopy.

Jia remarks that the research provides "a pathway for generating highly controlled microbubbles at will and integration of graphene microbubbles
as dynamic and high precision nanophotonic components for miniaturized lab-on-a- chip devices, along with broad potential applications in high resolution spectroscopy and medical imaging."

========================================================================== Story Source: Materials provided by SPIE--International_Society_for_Optics_and_Photonics.

Original written by Renae Keep. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Han Lin, Scott Fraser, Minghui Hong, Manish Chhowalla, Dan Li,
Baohua
Jia. Near-perfect microlenses based on graphene
microbubbles. Advanced Photonics, 2020; 2 (05) DOI:
10.1117/1.AP.2.5.055001 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201009114201.htm

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