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1. Contact Angle Dynamics during the Evaporation of Water from Hydrophilic and Hydrophobic Graphene Surfaces

   Chakraborty, Partha P.; Das, Suprem R.; Derby, Melanie M. (September 2018, http://mnf2018.me.gatech.edu/abstracts.php)

   For this experimental study on evaporation of water from graphene, two graphene samples with different thickness and microstructure were used. Figure 1 shows the representative optical and scanning electron microscope (SEM) images of the two samples. Sample 1, shown in Figure 1a-b, is a 3 to 4 atomic layer of continuous graphene sheet grown on copper substrate via chemical vapor deposition (CVD) and was subsequently transferred to a quartz substrate using a wet chemical method reported previously [5]. The graphene thickness is at 1.2 nm to 1.4 nm, as measured by Atomic Force Microscopy. Sample 2, shown in Figure 1c-d, represents an inkjet-printed reduced graphene oxide on silicon and subsequently treated with a direct pulsed laser writing (DPLW) process for surface 3D-nanostructuring. The layer thickness is between 6 µm and 7 µm. 

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2. Anisotropic Etching of InGaN Thin Films with Photoelectrochemical Etching to Form Quantum Dots

   https://doi.org/10.3390/ma16051890  

   Wei, Xiongliang; Al Muyeed, Syed Ahmed; Xue, Haotian; Wierer, Jonathan J. (March 2023, Materials)

   Traditional methods for synthesizing InGaN quantum dots (QDs), such as the Stranski-Krastanov growth, often result in QD ensembles with low density and non-uniform size distribution. To overcome these challenges, forming QDs using photoelectrochemical (PEC) etching with coherent light has been developed. Anisotropic etching of InGaN thin films is demonstrated here with PEC etching. InGaN films are etched in dilute H2SO4 and exposed to a pulsed 445 nm laser with a 100 mW/cm2 average power density. Two potentials (0.4 V or 0.9 V) measured with respect to an AgCl|Ag reference electrode are applied during PEC etching, resulting in different QDs. Atomic force microscope images show that while the QD density and sizes are similar for both applied potentials, the heights are more uniform and match the initial InGaN thickness at the lower applied potential. Schrodinger-Poisson simulations show that polarization-induced fields in the thin InGaN layer prevent positively charged carriers (holes) from arriving at the c-plane surface. These fields are mitigated in the less polar planes resulting in high etch selectivity for the different planes. The higher applied potential overcomes the polarization fields and breaks the anisotropic etching. 

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3. Sub-picosecond timing jitter between optically synchronized femtosecond and picosecond laser systems

   https://doi.org/10.1088/1361-6501/acc41b  

   Jiang, Zhenfei; Strycker, Benjamin; Hand, Lucian; Adamonis, Jonas; Yi, Zhenhuan; Sokolov, Alexei; Scully, Marlan (March 2023, Measurement Science and Technology)

   Abstract Synchronized optical pulses are widely used. We report here characterization and measurement of synchronized femtosecond and picosecond pulses from a Ti:Sapphire laser (nominally 800 nm) and a Nd:YAG laser (1064 nm), respectively. Synchronization is achieved by utilizing soliton self-frequency shift in a photonic-crystal fiber that allows the 800 nm femtosecond oscillator to seed the third-harmonic generation (355 nm) of picosecond regenerative amplifier. The relative timing jitter between the amplified femtosecond and the third-harmonic generation of picosecond pulses is (710 ± 160) fs, which is only (1.17 ± 0.26)% of the picosecond pulse duration. This work paves way for applications in stimulated Raman scattering spectroscopy and amplification. 

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4. Nanoimprint Lithography for Next-Generation Carbon Nanotube-Based Devices

   https://doi.org/10.3390/nano14121011  

   Fialkova, Svitlana; Yarmolenko, Sergey; Krishnaswamy, Arvind; Sankar, Jagannathan; Shanov, Vesselin; Schulz, Mark J; Desai, Salil (June 2024, Nanomaterials)

   This research reports the development of 3D carbon nanostructures that can provide unique capabilities for manufacturing carbon nanotube (CNT) electronic components, electrochemical probes, biosensors, and tissue scaffolds. The shaped CNT arrays were grown on patterned catalytic substrate by chemical vapor deposition (CVD) method. The new fabrication process for catalyst patterning based on combination of nanoimprint lithography (NIL), magnetron sputtering, and reactive etching techniques was studied. The optimal process parameters for each technique were evaluated. The catalyst was made by deposition of Fe and Co nanoparticles over an alumina support layer on a Si/SiO2 substrate. The metal particles were deposited using direct current (DC) magnetron sputtering technique, with a particle ranging from 6 nm to 12 nm and density from 70 to 1000 particles/micron. The Alumina layer was deposited by radio frequency (RF) and reactive pulsed DC sputtering, and the effect of sputtering parameters on surface roughness was studied. The pattern was developed by thermal NIL using Si master-molds with PMMA and NRX1025 polymers as thermal resists. Catalyst patterns of lines, dots, and holes ranging from 70 nm to 500 nm were produced and characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Vertically aligned CNTs were successfully grown on patterned catalyst and their quality was evaluated by SEM and micro-Raman. The results confirm that the new fabrication process has the ability to control the size and shape of CNT arrays with superior quality. 

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5. Modeling for Chemical-Etching Enhanced Pulsed Laser Ablation

   https://doi.org/10.1115/MSEC2019-2844  

   Zhang, Xing; Mao, Bo; Histed, Rebecca; Liao, Yiliang (November 2019, Proceedings of the ASME 2019 14th International Manufacturing Science and Engineering Conference)

   Pulsed laser ablation (PLA) under active liquid confinement, also known as chemical etching enhanced pulsed laser ablation (CE-PLA), has emerged as a novel laser processing methodology, which breaks the current major limitation in underwater PLA caused by the breakdown plasma and effectively improves the efficiencies of underwater PLA-based processes, such as laser-assisted nano-/micro-machining and laser shock processing. Despite of experimental efforts, little attention has been paid on CE-PLA process modeling. In this study, an extended two-temperature model is proposed to predict the temporal/spatial evolution of the electron-lattice temperature and the ablation rate in the CE-PLA process. The model is developed with considerations on the temperature-dependent electronic thermal properties and optical properties of the target material. The ablation rate is formulated by incorporating the mutual promotion between ablation and etching processes. The simulation results are validated by the experimental data of CE-PLA of zinc under the liquid confinement of hydrogen peroxide. 

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