This PDF file contains the front matter associated with SPIE Proceedings Volume 11675, including the Title Page, Copyright information, and Table of Contents.

Welcome and Introduction to SPIE Photonics West LASE conference 11675: Synthesis and Photonics of Nanoscale Materials XVIII

The high-speed photodetector represented by uni-traveling-carrier photodiode is developing towards a higher bandwidth design. The high-bandwidth design will be constrained by the reduced responsivity of the device. Plasmonic photodetectors, due to their ability to confine light at the surface of the metal, can perform light-matter interaction with absorbing materials on a deep subwavelength scale, which providing a new design direction for higher speed photodetectors. We report a high-speed photodetector design that combines uni-traveling-carrier photodiode and plasmonic resonance to achieve a two-fold improvement in device responsivity. The results reveal that plasmonic uni-traveling-carrier photodiode is a potential choice for high-speed photodetector design.

Non-linear manipulation of light at the nanoscale is increasingly important for quantum optics and photonics. Plasmonic media provide one important workbench for the manipulation of these nonlinearities.1 The design of plasmonic structures typically involves time-consuming, iterative, computer simulations, nanofabrication and characterization with large suites of independent tools. Hence, in-situ fabrication and characterization along with real time design optimization is an appealing option for the development of hybrid quantum nanophotonic devices. Here, we will describe emerging capabilities for in situ electron beam induced deposition (EBID) and cathodoluminescence (CL) microscopy in an environmental SEM. We outline our work writing and characterizing nanoplasmonic structures that exhibit well-defined field localization and multiple tunable resonances over a broad spectrum as part of the development of new high-efficiency nanophotonic nonlinear media. Developing deter- ministic high-quality single photon emitters is an equally important direction for photonic quantum information processing. Due to the sub-nanometer footprint of such emitters, optical methods are often insufficient for local characterization. We describe our efforts to create, manipulate and characterize color centers in 2D and bulk materials such as hBN. We discuss e-beam induced effects for localized defect creation and EBID based control of color centers to allow emission tuning. Cathodoluminescence lifetime and autocorrelation measurements are utilized for sub-diffraction-limited in-situ assessment of the single photon emission properties.

We have succeeded in coating an aluminum oxide thin film of inorganic-organic hybrid on the inner wall of the cell of an optically pumped atomic magnetometer using spin polarization of alkali metal atoms by a unique room temperature molecular layer deposition method. The relaxation time of polarized spin was investigated by using the pump probe method, and it was revealed that the relaxation time of spin polarization can be significantly improved and the relaxation prevention effect can be remarkably exhibited as compared with the case without coating.

An infrared ultrafast laser (=1026 nm, ~160 fs) was used to synthesize nanodiamonds (ND) directly from an intense plasma in liquid ethanol (sans target) through the process of laser filamentation. The ethanol solution was characterized by its UV-VIS absorbance and optical emission spectra; and the nanodiamond particles by Raman spectroscopy and transmission electron microscopy (TEM) analysis. The absorbance spectra showed a single strong peak in the UV while the visible emission spectra displayed two lines above a background continuum. Raman spectroscopy showed the existence of D and G peaks that confirmed the presence of nanodiamonds. TEM analysis showed the nanodiamond particles had a narrow 2-5 nm size range with no aggregation and had visible lattice fringes of 2.06 Å corresponding to the diamond (111) phase. Electron energy loss spectroscopy (EELS) also confirmed the existence of nanodiamonds by revealing a 35 eV edge in the low loss region and a sharp onset of the carbon K-edge at 290 eV.

Further geometrical confinement of the Two-dimensional (2D) materials in lateral dimensions toward zero-dimensional (0D) structures can form 2D nanoparticles and quantum dots with new properties. Here, we report the formation of quantum dots-like gallium selenide (GaSe) nanoparticles ensembles in a nonequilibrium gas-phase synthesis method. We show that by condensing the laser-generated plume in an argon background gas, metastable nanoparticles can form in the gas phase via the plume condensation process. The deposition of nanoparticles onto the substrates results in the formation of nanoparticle ensembles, which are then post-processed to crystallize or sinter the nanoparticles. The effects of background gas pressures and crystallization/sintering temperatures on the properties of the generated nanoparticles are systematically studied. This method offers a clean and fast route toward the formation of various 2D nanoparticles for potential optoelectronic and photonic applications.

In this work, we report a one-step sputtering method for direct preparation of Cu2O and CuO coatings on different substrates, i.e. glass, thin polymer films and titanium alloy. Interestingly, these coatings possessing micro- and nanostructures exhibiting controlled dual-scale roughness and the wettability investigation reveals that we can tune the wetting properties.

Photopolymerization of (meth)acrylate-based formulations has become a widespread method for industry due to the high energy efficiency and low curing times of this technology. Various products from simple coatings to more complex applications such as additive manufacturing technologies are based on this versatile method. Common industrial radical photoinitiators are generally based on aromatic ketones. Benzaldehyde is an organic compound consisting of a benzene ring with a formyl substituent. It is the simplest aromatic aldehyde and one of the most industrially useful; for instance in the preparation of various aniline dyes, perfumes, flavorings, and pharmaceutics. Parallel to this, triphenylamines are extensively used for the design of dyes used for solar energy conversion. In this work, three triphenylamine derivatives bearing formyl groups are as a new substance class of multi-photon lithography photoinitiators. The photophysical properties of the PIs were investigated by UV−Vis abs

Publisher’s Note: This conference presentation, originally published on 5 March 2021, was withdrawn on 20 May 2021 per author request.

Two-dimensional (2D) materials have been viewed as a promising candidate for future electronic, optoelectronic, and photonic applications. This, however, demands controlled synthesis and precise integration of such materials with complex patterns onto rigid and flexible substrates. Here we introduce a new laser-based approach that enables the integration of 2D materials onto the flexible and rigid substrate with desired shapes and patterns. We report direct laser crystallization and the pattering of MoS₂ and WSe₂ on PDMS and quartz substrates. A thin layer of solid-state stoichiometric amorphous 2D film is deposited onto the substrates, followed by a controlled crystallization and direct writing process using a tunable nanosecond laser (1064 nm). This novel method enables the use of emerging 2D materials in future electronics, optoelectronics, and photonics applications where intricate patterning and/or flexible substrates are required.

We utilized in situ laser-heating within a TEM to reveal how nanomaterials transform from amorphous precursors, and used electron spectroscopy to characterize the optical properties of these nanostructures in situ and in real time. The recrystallization, grain growth, phase separation, and solid state dewetting of AgNi films were investigated using stepwise laser heating. The experiments reveal a wealth of in situ information, including changes of composition and lattice constants during phase separation. To establish the true and dynamic structure–property relationship of nanostructures, we also characterized the photonic properties of the synthesized materials in situ. For example, the plasmon modes of metallic particles were mapped using electron energy gain induced by photon-plasmon-electron coupling. These in situ TEM studies of laser-induced heating are a valuable discovery tool for the rapid exploration of synthesis pathways and functional properties of nanostructures.

Exciton transport is a fundamental process of energy conversion in semiconductors. The strong interaction of light with two-dimensional (2D) semiconductors provides the opportunity to optimize exciton transport for 2D optoelectronic devices. However efficient exciton transport in atomically thin 2D semiconductors is still challenging due to various scattering sources such as defects and traps. Here we show that photoinduced processes can achieve a giant enhancement in exciton diffusivity (from 1.5 to 22.5 cm2/s in monolayer MoS2 crystals)[1] and can be revealed by in situ optical spectroscopy monitoring. The mechanism of the enhancement is revealed: the scattering of excitons is screened by trapped charges generated by a photoinduced electron-hole plasma. This understanding of how to improve and control exciton transport in 2D semiconductors opens new avenues for the development of high-performance excitonic and photovoltaic devices. [1] Y. Yu et al., Sci. Adv., 2020, eabb4823.

The vapor or gas-phase synthesis methods (e.g., CVD) are widely adopted to grow mono and few-layer two-dimensional (2D) materials. However, uncontrolled gas-phase reactions, complex flow dynamics, and limited reproducibility have made the gas phase growth of monolayer TMDCs crystals extremely challenging. Here we introduce a novel laser-assisted synthesis method for the rapid growth of various 2D materials. To produce the atomically-thin crystals, instead of using conventional multi-component precursors, this synthesis method utilizes stoichiometric powders as precursors that are laser vaporized to create the right vapor flux for the controlled growth of mono and few-layer crystals. We demonstrate a successful synthesis of four semiconducting TMDC monolayers such as MoS₂, MoSe₂, WSe₂, and WS₂ crystals. This laser vaporization process promises an efficient general synthesis solution for the accelerated growth of a variety of high-quality 2D quantum materials.

The presentation will overview our on-going activities on laser ablative synthesis of novel biocompatible colloidal nanomaterials (TiN, Si, Sm2O3, Bi, Au-Fe3O4 core-shells,) and their testing in tasks of bioimaging (optical non-linear imaging) and therapies (photo-hyperthermia, nuclear therapy)

Radiation nanomedicine is an emerging field, which utilizes nanoformulations of high-Z elements and nuclear agents to improve therapeutic outcome and to reduce radiation dosage. This field lacks methods for controlled fabrication of biocompatible nanoformulations. Here, we present application of femtosecond laser ablation in liquids to fabricate stable colloidal solutions of ultrapure elemental Bi and isotope-enriched samarium oxide nanoparticles (NPs). The obtained spherical Bi and Sm oxide NPs have controllable size, while Bi NPs have remarkable absorption in the near-IR region. Exempt of any toxic by-products, laser-ablated Bi and Sm oxide NPs present a novel appealing nanoplatform for nuclear and radiotherapies.

Owing to a red-shifted absorption/scattering feature compared to conventional plasmonic metals, titanium nitride nanoparticles (TiN NPs) constitute a promising candidate for nanomedicine. However, their potential is still underexplored due to difficulties of synthesis of stable biocompatible colloids of TiN NPs. Here, we provide results of elaboration of laser-ablative synthesis of TiN NPs in liquids which can solve the problem. Laser-ablated TiN NPs have strong plasmonic peak in near-IR. We also present their first comprehensive biocompatibility assessment. The obtained results evidence high safety of laser-synthesized TiN NPs for biological systems, which promises a major advancement of phototheranostic modalities on their basis.

Silicon (Si) nanoparticles (NPs) synthesized by pulsed laser ablation in water are explored as sensitizers of photothermal therapy under a laser excitation in the window of relative tissue transparency. Based on theoretical calculations and experimental data, it is shown that the NPs can be heated up to temperatures above 42–50 °C by laser diode irradiation at 808 nm in continuous wave (CW) and quasi-continuous wave (QCW) regimes. Profiting from the laser-induced heating, a high efficiency Si-NPs as sensitizers of the hyperthermia of cells in Paramecium Caudatum model is demonstrated. The QCW regime is found to be more efficient, leading to complete cell destruction even under relatively mild laser irradiation conditions. The obtained data evidence a great potential in using laser-ablated Si-NPs as sensitizers of photohyperthermia in antibacterial or cancer therapy applications

This presentation was recorded for SPIE Photonics West LASE, 2021.

Laser-induced structuring of nanoporous glass composites is promising for numerous emerging applications in photonics, plasmonics and medicine. In these laser interactions, an interplay of photo-thermo-chemical mechanisms is commonly activated and is extremely difficult to control. The choice of optimum laser parameters to tune the resulted optical properties remains extremely challenging. In this paper, we analyze the mechanisms involved and propose a way to control over not only structures formed by laser inside a nanoporous glass composites doped by metallic ions and nanocparticles, but also their plasmonic properties. For this, both experimental and numerical approaches are combined. The transmitted laser power is used to analyze the modification process. Spectral microanalysis provides plasmonic properties. Numerical effective medium modeling connects the measured data to the estimated size, concentration, and chemical composition of the secondary phase across the initial sample.

There is a lack of a comprehensive understanding of the size reduction in femtosecond two-photon polymerization (TPP) fabricated structures. In this work, we aim to evaluate the volumetric strain distribution induced by covalent bond formation during TPP. We present a transient computational model which simulates the photochemical processes during TPP and calculates the functional group conversion at each time step. The nonuniform strain development is obtained by incorporating the shrinkage – double bond conversion correlation of bulk materials. The shrinkage induced by chemical bond formation is found to reduce the size of the final structure on the order of a few percent.

Raman spectroscopy is often considered as a powerful tool for chemical sensing and imaging and in the times of COVID-19 pandemic is frequently suggested as the way to identify the presence of viral particles in solution. In this report, we evaluate the ability of Raman spectroscopy to quantitatively assess the presence of nanoparticles in colloidal solutions.