Introduction

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Nonlinear optical response of materials can provide powerful fingerprints of physicochemical properties, including crystallography, interfacial state, and carrier dynamics. Former LTL PhD student and postdoctoral fellow Yoonsoo Rho showed efficient second harmonic generation (SHG) nanoscopy for ZnO NWs using a SHG-active plasmonic nanotip. The experimental results combined with EM modeling and theoretical analysis suggest quantum mechanical nonlinear energy transfer between the tip and the sample. In terms of an application, this method could probe nanoscale corrosion of ZnO NW. Professor Seokjae Yoo of Inha U. in Korea developed the framework for the analysis of the experimental results. The work was done in collaboration with Dr. Daniel Durham and Professor Andy Minor of UCB MSE and supported by Laser Prismatics LLC under a DOE STTR/SBIR Phase II grant. The paper was published in Nano Letters, 
https://pubs.acs.org/doi/pdf/10.1021/acs.nanolett.2c04748.

​Atomic layer etching  (ALEt) has attracted significant interest due to the ever-shrinking critical feature size in electronic devices. PhD student Matthew Eliceiri with former LTL PhD student and postdoctoral fellow Yoonsoo Rho and undergraduate research assistant Jacky Li demonstrated laser driven ALEt of silicon. They used i) a nanosecond pulsed UV laser to dissociate chlorine inducing surface chlorination, ii) a picosecond laser to locally remove the chlorinated layer and iii) a continuous wave (CW) laser to anneal and recrystallize the material. This process yielded digital and spatially selective material removal at the sub-nm level. The research was performed at the LACVD facility at the UCB Nanolab and published in the Journal of Vacuum Science and Technology A,  https://doi.org/10.1116/6.0002399.
Postdoctoral fellow Jingang Li and PhD student Rundi Yang demonstrated a new type of optical nanoscopy that can measure electron dynamics in semiconductors, a task that has become more challenging as demand grows for ever-smaller and faster integrated circuits. The method integrates near-field scanning optical microscopy and pump-probe optics to enable high resolution at both spatial and temporal scales. Yoonsoo Rho, a former LTL PhD student and postdoctoral fellow contributed his expertise to the development of the optical nanoscopy. Matthew Eliceiri of LTL, Penhong Ci and Prof. Junqiao Wu of MSE, and Hee K. Park of Laser Prismatics were also co-authors in the Nano Letters paper, https://pubs.acs.org/doi/full/10.1021/acs.nanolett.2c04790.
PhD student Matthew Eliceiri used a spatially-resolved transient plasma absorption probe in conjunction with normal and  side imaging to interrogate the ablation mechanisms of Al upon nanosecond laser excitation. The experimental results were compared with numerical simulations done at JHU-APL (Mark Anthony, Xun Zhu and Iyer Kaushik). Darren Luke of AFRL collaborated on the research. The work was published in Applied Physics A, https://doi.org/10.1007/s00339-022-06217-1
The figure shows surface snapshots juxtaposed with numerical plasma simulations.
PhD students Timon Meier and Brian Blankenship, in collaboration with Haris Sheikh (PhD student in Prof. Phil Marcus group) and former LTL PhD student Zacharias Vangelatos demonstrated the realization of Cauchy symmetric structures. To accomplish this, they used finite element analysis, Bayesian optimization, 3D multi-photon fabrication and mechanical testing. Undergraduate researcher Nai Chen Zhao helped in the numerical simulations and CAD modeling. The work was published in the International Journal of Mechanical Sciences.
https://doi.org/10.1016/j.ijmecsci.2022.107741
Former PhD student and post-doctoral fellow Yoonsoo Rho demonstrated atomic layer precision thinning of MoTe2 while maintaining the high crystallinity of thinned material. The functionality of the thinned material was confirmed by Raman, SHG and electrical performance characterization.
https://doi.org/10.1002/admi.202200634
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Former PhD student and Post-doctoral fellow Yoonsoo Rho demonstrated that a two-laser beam assisted chlorination process can enable highly doped and rewritable patterns in graphene. chemical doping of various 2D materials. The method cannot only achieve doping to control the density and polarity of the charge carriers, but also allows alloying to tune the bandgap of 2D materials. Our method offers unprecedented flexibility in the tuning of the electronic properties and shape of 2D materials using site-selective doping, alloying and patterning, allowing the formation of laterally modulated electrical landscapes in 2D materials.The work was done in collaboration with Prof. Alex Zettl's and Junqiao Wu's groups. Kyunghoon Lee of UCB Physics contributed on the device fabrication and characterization. The work and an accompanying research briefing appeared in Nature Electronics
DOI: 10.1038/s41928-022-00801-2.

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About

The Laser Thermal Lab is directed by Prof. Costas P Grigoropoulos of the Mechanical Engineering Department, UC Berkeley. Current research interests are focused on laser materials interactions, nanomanufacturing and the fundamental study of microscale and nanoscale transport phenomena.
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Learn more about LTL

Some Recent Publications

For a full list go to the Publications/Journals

Eliceiri M, Grigoropoulos CP, 2022, "Optical trapping and positioning of Silicon nanowires via photonic nozzling" Nano Letters, 22, 3777-3783, https://pubs.acs.org/doi/full/10.1021/acs.nanolett.2c00834.
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Park M, Balkey MM, Mao X, Grigoropoulos CP, Zorba V, 2021, “Spatio-temporal ablation dynamics and plasma chemistry of aluminum induced by temporally modulated ytterbium fiber laser,” Applied Physics Letters, 119, 224103, https://doi.org/10.1063/5.0076527.
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Vangelatos Z, Sheikh HM, Marcus, PS, Grigoropoulos C, Lopez V, Flamourakis G, Farsari M, 2021, "Strength through defects: A novel Bayesian approach for the optimization of architected materials", Science Advances, 7, eabk2218, https://www.science.org/doi/epdf/10.1126/sciadv.abk2218​
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Park M, Jeun J, Han G, Grigoropoulos CP, 2020, “Time-resolved emission and scattering imaging of plume dynamics and nanoparticle ejection in femtosecond laser ablation of silver thin films,” Applied Physics Letters, 116, 234105, https://doi.org/10.1063/5.0009227 (Featured Article).

Wang L, Eliceiri M, Deng Y, Rho Y, Shou W, Pan H, Yao J, Grigoropoulos CP, 2020, “Fast reversible phase change silicon for visible active photonics,” Advanced Functional Materials, 1910784, https://doi.org/10.1002/adfm.201910784  

Rho Y, Pei J, Wang L, Su Z, Eliceiri M, Grigoropoulos CP, 2019, “Site-selective atomic Layer precision thinning of MoS2 via laser-assisted anisotropic chemical etching,” Applied Materials and Interfaces, 11, 39385-39393, https://doi.org/10.1021/acsami.9b14306

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