Hello

my name is Prem Prabhakaran.

I am an asst. professor at the Department of Advanced Materials and Chemical Engineering, Hannam University, Daejeon, South Korea. This is my blog about laser direct writing. I have been active in this field of research for the past ten years. First as a graduate student and now as a professor. The history of direct laser writing goes back almost three decades[1]. 

It has become more common and accessible in the past decade because of commercially available laser direct writing lithography machines from Nanoscibe, Microlight Technologies (formerly associated with TEEM photonics), Laser Zentrum Hannover etc. The rise of 3D printing has also pushed this technology more into the public eye. Past five years have seen rapid developments in hardware and materials related to this technology.

[1] Spangenberg, Arnaud, Nelly Hobeika, Fabrice Stehlin, Jean-Pierre Malval, Fernand Wieder, Prem Prabhakaran, Patrice Baldeck, and Olivier Soppera. “Recent advances in two-photon stereolithography.” In Updates in Advanced Lithography. InTech, 2013.

“This technology is reaching the point of take-off where the combination of materials and techniques developed over the past many years can be applied for mass market applications. This blog is my attempt to keep track of this rapidly growing field of research. I will attempt to introduce it to the wider public as well as try to look at various issues facing it in its current form. Beyond everything this blog is an attempt to learn more about this field of technology. I will try my best to provide the most useful information from most relavant sources. 

Research Experience

Hannam University
Position
  • Professor (Assistant)
Université de Technologie de Troyes
Position
  • PostDoc Position
Description
  • Nanomateriaux 3D (Nanomaterials for 3D lithography): Development and formulation of fast, previewable cationic photoresists for two-photon lithography.
March 2013 – March 2014
Université de Technologie de Troyes
Position
  • PostDoc Position
University Joseph Fourier – Grenoble 1
Position
  • PostDoc Position
Description
  • Development of two-photon sensitized photo acid generators (PAG) and their application ( projet 2PAGmicroFab, ANR)

Publications

We have functionalized core-shell CdSe/ZnS quantum dots (QDs) with a photosensitive monolayer, rendering them solution processable and photopatternable. Upon exposure to ultraviolet radiation, films composed of this material were found to polymerize, forming interconnected arrays of QDs. The photoluminescence properties of the nanocrystal films increased with photocuring. The material was found to be suitable for spin casting and was used as the active layer in a green electroluminescent device. The electroluminescence efficiency of devices containing a photocured active layer was found to be largely enhanced when compared to devices containing nonphotocured active layers. The material also showed excellent adhesion to both organic and inorganic substrates because of the unique combination of a siloxane and a photopatternable layer as ligands. The pristine functionalized nanocrystals could easily be used for two-dimensional patterning on organic and inorganic substrates. The photopatternable quantum dots were uniformly dispersed into a photopolymerizable resin to fabricate QD embedded three-dimensional microstructures.
 

One-, two-, and three-dimensional microstructures with dispersed silver nanoparticles are fabricated by a combination of photopatterning and thermal treatment from a silver salt containing photosensitive epoxy resin. Ultraviolet photo-irradiation and subsequent thermal treatment are combined to control the rate of silver salt reduction, the size and the arrangement of nanoparticles, as well as the reticulation of the epoxy resin. This approach allows the creation of high resolution 1-, 2-, and 3D patterns containing silver nanoparticles, with a homogeneous distribution of nanoparticles regardless of the irradiated area.

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Two-photon stereolithography based on photopolymerization provides the ability to fabricate real three-dimensional (3D) microstructures beyond the resolution of focal size. In this paper, our recent research focusing on improvement of spatial resolution in two-photon stereolithography is reviewed. The influence of system and fabrication conditions in relation to the spatial resolution is discussed. For small and low aspect ratio voxels, a minimum power and minimum exposure time (MPMT) scheme is introduced. During the two-photon process, an ascending technique, wherein the truncation amount of volumetric pixels is controlled, can be applied to improve the resolution of two-dimensional patterns. 3D Microfabrication with less than 100 nm resolution can be realized by using the radical quenching effect. After the two-photon process, the resolution of fabricated patterns can be refined to 60 nm by post-processing of plasma ashing.
 

 

Quantum dots and their chemical adaptation for various photonic applications are presented in this review. The use of quantum dots as photoactive components in many applications requires their combination with other materials playing specific roles for separation and transport of charge carriers. Achieving good interfaces between electronically matched component materials is key to improved performance in photodetectors, photovoltaics, electroluminescence application, etc. (C)2012 Optical Society of America.
The accessibility of ultrashort high-repetition rate lasers has led to the study of many nonlinear optical (NLO) phenomena and their applications in photonics. Organic and polymeric materials have attracted enormous interest as materials from nonlinear optics because of their tailorability and easy processability. In this chapter we deal with the design and structure–property relationships in materials for second- and third-order NLO effects. The phenomena that are explored include Pockel’s effect, optical Kerr effect, and two-photon absorption (TPA). The factors contributing to the design of highly active NLO materials are discussed with examples to demonstrate various approaches.
 
Charge-transfer (CT) states play a critical role in harvesting non-emissive triplets realized by triplet-to-singlet conversion through spin mixing to generate thermally activated delayed fluorescence (TADF) by providing a spin-orbital coupling (SOC) and small energy difference (∆EST). This paper discusses the spin mixing directly identified by magneto-photoluminescence (magneto-PL) for intramolecular and intermolecular CT states based on a synthesized donor-acceptor-donor (D-A-D) type molecule DMTD-Cz. The PL spectra indicate that this D-A-D molecule shows intramolecular CT states-only in solutions but both intramolecular and intermolecular CT states in solid-state thin films, allowing to separately identify the spin mixing occurring in intramolecular and intermolecular CT states by using magneto-PL measurements. We found that intramolecular and intermolecular CT states exhibit negligible and appreciable magneto-PL signals up to 900 mT at room temperature, respectively. Simultaneously, the intramolecular and intermolecular CT states are shown negligible and appreciable delayed fluorescence, respectively, in thin films. These results provide the direct observation that the SOC generates trivial and vital spin mixing within intramolecular and intermolecular CT states. This indicates that the triplets in intermolecular CT states can be harvested by using spin mixing mechanism while the triplets in intramolecular CT states should be harvested by using spin conserving mechanism through localized triplet excitons towards developing efficient organic light-emitting materials.
 
Covid19Kerala.info-Data is a consolidated multi-source open dataset of metadata from the COVID-19 outbreak in the Indian state of Kerala. It is created and maintained by volunteers of ‘Collective for Open Data Distribution-Keralam’ (CODD-K), a nonprofit consortium of individuals formed for the distribution and longevity of open-datasets. Covid19Kerala.info-Data covers a set of correlated temporal and spatial metadata of SARS-CoV-2 infections and prevention measures in Kerala. Static releases of this dataset snapshots are manually produced from a live database maintained as a set of publicly accessible Google sheets. This dataset is made available under the Open Data Commons Attribution License v1.0 (ODC-BY 1.0).
 
 
India, the second most populated country in the world, reported its first COVID-19 case in the state of Kerala with a travel history from Wuhan. Subsequently, a surge of cases was observed in the state mainly through the individuals who traveled from Europe and the Middle East to Kerala, thus initiating an outbreak. Since public awareness through dissemination of reliable information plays a significant role in controlling the spread of the disease, the Department of Health Services, Government of Kerala initially released daily updates through daily textual bulletins. However, this unstructured data requires refinement and enrichment for upstream applications, such as visualization, and/or analysis. Here we reported a citizen science initiative that leveraged publicly available and crowd-verified data on COVID-19 outbreak in Kerala from the government bulletins, supplemented with the information from media outlets to generate reusable datasets. This data was further used to provide real-time analysis, and daily updates of COVID-19 cases in Kerala, through a user-friendly bilingual dashboard (https://covid19kerala.info/) for non-specialists. We ensured longevity and reusability of the dataset by depositing it in a public repository, aligning with open source principles for future analytical efforts. Finally, to show the scope of the sourced data, we also provided a snapshot of outbreak trends and demographic characteristics of the individuals affected with COVID-19 in Kerala during the first 99 days of the outbreak.
 
 
Metal halide perovskite quantum dots attract significant research interest in recent years due to their exceptional optical properties, such as tunable emission wavelength, strong quantum confinement and suppressed non-radiative recombination via surface passivation. However, the presence of dark states with low emission rate in perovskite quantum dots due to the strong spin-orbital coupling (SOC) and Rashba effects may suppress light emission efficiency. Strategies of reducing bright-to-dark exciton conversion through spin-orbital coupling (SOC) has been rarely addressed. In this work, we fabricated CsPbBr1I2 quantum dots with controlled size and uniformity by using different capping ligands. The orbit-orbit interactions between photogenerated excitons in CsPbBr1I2 quantum dots are studied based on photoexcitation polarization dependent photoluminescence. Decreasing orbit-orbit interaction in CsPbBr1I2 quantum dots can result in an improved photoluminescence quantum efficiency, which implies that less populated dark excitons with indirect recombination are generated through weak spin flipping. The PL lifetime results confirm that the improved light emission efficiency by changing organic ligand is mainly induced by tuning Rashba effects in quantum dots rather than trap passivation. These findings provide new insight on tuning Rashba effects in perovskite quantum dots towards enhanced light emission efficiency via surface modification.
 
 

Publications

Metal halide perovskite quantum dots attract significant research interest in recent years due to their exceptional optical properties, such as tunable emission wavelength, strong quantum confinement and suppressed non-radiative recombination via surface passivation. However, the presence of dark states with low emission rate in perovskite quantum dots due to the strong spin-orbital coupling (SOC) and Rashba effects may suppress light emission efficiency. Strategies of reducing bright-to-dark exciton conversion through spin-orbital coupling (SOC) has been rarely addressed. In this work, we fabricated CsPbBr1I2 quantum dots with controlled size and uniformity by using different capping ligands. The orbit-orbit interactions between photogenerated excitons in CsPbBr1I2 quantum dots are studied based on photoexcitation polarization dependent photoluminescence. Decreasing orbit-orbit interaction in CsPbBr1I2 quantum dots can result in an improved photoluminescence quantum efficiency, which implies that less populated dark excitons with indirect recombination are generated through weak spin flipping. The PL lifetime results confirm that the improved light emission efficiency by changing organic ligand is mainly induced by tuning Rashba effects in quantum dots rather than trap passivation. These findings provide new insight on tuning Rashba effects in perovskite quantum dots towards enhanced light emission efficiency via surface modification.

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Fabrication of composite microstructures comprising more than one type of material has been a fundamental challenge in nanotechnology. In this study, we report a method that can be used for the direct fabrication of complex three-dimensional (3D) polymer/metal hybrid microstructures. The patterning of materials (a polymer and a metal coatable polymer) in selected regions was achieved by a two-photon stereolithography process using a dual-stage scanning process. A precise alignment process was perfected to achieve the coincidence of polymeric and metal-coated polymer components of the microstructure. Selective metallization of the metal coatable polymer microstructure was performed through silver deposition by means of electroless plating. The 3D microcoil was demonstrated and electrically characterized. Read More

 

Two-photon absorption, a third-order phenomenon of nonlinear optics, has received considerable attention from both academic and industrial communities. Extensive studies on organic two-photon absorbents have led to meaningful correlations between structures and the development of efficient two-photon absorption material based on two-photon properties has been accelerated. This short review article focuses on two major areas, two-photon absorption chromophores and 3D microfabrication employing two-photon photopolymerization techniques: (i) design and control of two-photon absorption performances with respect to their molecular geometry and (ii) achievement of various 3D micro-mechanical and photonic systems fabricated by two-photon stereolithography.

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In this topical review of two-photon stereolithography (TPS), we discuss novel materials and demonstrate applications of this technology. Two-photon-initiated chemical processes are used to fabricate arbitrary three-dimensional structures in TPS. In the first part of this article, the development of novel photoactive materials to fabricate pure inorganic or organic-inorganic hybrid microstructures is discussed. The second part discusses the fabrication of functional microstructures for highly specific applications to demonstrate the importance of TPS in different fields of science.

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Routine TPL studies of functional microstructures often demand strict conditions of resolution, form, and stability. This results in a tradeoff between resolution and mechanical stability in finely featured structures. Herein, the authors demonstrate a method to improve the mechanical stability of structures fabricated from a urethane acrylate photoresist, that is, prone to mechanical failure. In this work the authors show that the unique characteristics of two‐photon‐induced polymerization (TPP) can be exploited to form tightly polymerized voxels (voxels, or volume pixels, are the building blocks of a microstructure). This approach leads to stable microstructures without a sizeable trade‐off in terms of resolution. This is achieved by adding a co‐sensitizer and radical quencher pair to the photoresists sensitized with a two‐photon absorbing dye. The co‐sensitizer leads to high degrees of polymerization, while the radical quencher limits polymerization at the periphery of the voxel. The formation of tightly polymerized voxels has been validated experimentally from line dimensions of the structure and their degree of polymerization. The authors have tested the sensitizer‐radical quencher combination in another photoresist and demonstrated the adaptability of this concept to tune different photopolymer systems.

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Lead trihalide perovskite nanomaterials are widely studied due to their remarkable optoelectronic properties. Despite their outstanding and demonstrated potential, these materials have been kept from practical application due to their crippling instability in ambient conditions. From electron microscopy studies of this series of quantum dots (QDs) we demonstrate that the onset of degradation in optical properties coincides with the appearance of nano black spots (NBSs) on the QDs. Elemental mapping using electron microscopy revealed the NBSs to be areas with higher concentration of lead. We have looked at the possible mechanisms to explain NBSs and found that they may arise due to two very different pathways. The first one is due to crystal growth initiated by excess reactants and the second is due to chemical degradation of the QD surface. Further we have invoked the well known geometrical stability criterion for perovskites, Goldschmidt’s tolerance factor to predict the appearance of NBSs and the onset of optical instability of CsPbBr3−xIx QDs. This correlation can be used as a criterion to aid the selection of more optically stable perovskite QDs for practical applications.

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Surface functionalized multiwall carbon nanotube (MWCNT) reinforced teflon fibrils (MWCNT@Teflon) were successfully tested as an – oil – absorbent that can be used as a potential oil recovery material at the time of oil spill accidents in water. We found that oleic acid functionalization of MWCNTs was important for their adhesion onto teflon fibrils and at the same time prevented the MWCNT leaching into oil/water interface. The fibrils had displayed superior mechanical and thermal stability and provided a new insight to oil spill clean-up applications with easy recovery of absorbed oil by simple squeezing. Recycling of exhausted MWCNT@Teflon fibrils after oil recovery applications was conducted by pyrolysis under inert atmosphere in presence of magnetic clay. The magnetic clay absorbed the pyrolysis products, resulting in a heterostructured magnetic clay carbon composite (MCC) which was found super paramagnetic and chemically stable in all pH. The MCC was found capable of adsorbing textile dye from water ultra-fast with in a maximum contact time of 2 min and magnetically separable after adsorption experiments.

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This paper reports photoexcitation-enhanced magnetization in γFe2O3-Graphene (0D-2D) van der Waals heterostructure based on the experimental studies of steady-state pump-probe measurements in magnetic field. It is observed that applying a magnetic field on the γ-Fe2O3/graphene material suspended in an organic solvent can cause a light scattering on the probe beam in the absence of pump beam, leading to a magnetic field effect of light scattering. This result shows that the magnetization on the γ-Fe2O3 nanoparticles can lead to a partial orientation of Fe2O3-graphene heterostructure components suspended in liquid. This effect of magnetic field on light scattering is caused by the dynamic magnetization of the superparamagnetic-semiconducting hybrid material. Interestingly, applying the pump beam functioning as photoexcitation can lead to an enhancement on the scattering of probe beam, increasing magnetic field effect of light scattering. The increased magnetic field effect of light scattering indicates that the photoexcitation from the pump beam applied to the hybrid enhances the magnetization on the γ-Fe2O3 nanoparticles through the d-pi electron coupling between γ-Fe2O3 and graphene in the hybrid material. This d-pi electron coupling can be a practical method to develop photoexcitation-controllable magnetization through excited states based on chemically linked magnetic-semiconducting hybrid design. 

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Nano-stereolithography, also known as two-photon direct writing is widely used for fabrication of the three-dimensional microstructure with submicron resolution. Heirarchical three-dimensional meshed microstructures are crucial for microelectromechanical systems (MEMS), photonics and biotechnological applications. Routine study for various applications using such structures requires fabrication of many sets of structures. Conventionally such meshed microstructures are constructed through layer-by-layer accumulation with discrete point-to-point laser scanning. This technique is time consuming, leading to long fabrication times placing constraints on practical applications as well as optimization of structures. In this work we propose continuous longitudinal laser scanning method as an effective means for direct writing of hierarchical three-dimensional meshed microstructures. The advantages of continuously longitudinal laser scanning method are explored for its time economy and fabrication effectiveness; a fabrication window is suggested to determine the fabrication parameter easily according to laser power and structural design.

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Photopatternable nanoparticles can be easily dispersed into polymeric matrices and used to fabricate optoelectronic devices for display, sensing and quantum information processing applications. Here we report the first instance of a cadmium-free photopatternable quantum dot. A ligand containing dithiolane group at one end and an ene-functionalization at the other end were synthesized for this purpose. The myristic acid ligands on as synthesized red indium zinc phosphide-zinc sulfide (In(Zn)P/ZnS) quantum dots were easily replaced by the newly developed ligand by a simple sonication procedure. The functionalized quantum dots could be easily incorporated into a commercially available photoresist. The quantum dot doped photoresist was used to fabricate three-dimensional quantum dot doped hierarchical microstructures by two-photon lithography. Confocal imaging microscopy was used to verify the uniform incorporation of the nanoparticles in the hybrid microstructure.

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We report the exfoliation of graphite and simultaneous N doping of graphene by two methods; by supercritical ammonia treatment and by liquid phase exfoliation with NH4OH. While the supercritical ammonia allowed N doping at a level of 6.4 at.% in 2 h, the liquid phase exfoliation with NH4OH allowed N doping at a level of 2.7at.% in 6 h. The N doped graphene obtained via supercritical ammonia route were few layers (<5), showed large lateral flake size (~8µm), low defect density (ID/IG<0.6) in spite of their high level of N doping. This work is the first demonstration of supercritical ammonia, as an exfoliation agent and N doping precursor for graphene. Notably, the N doped graphene showed electrocatalytic activity towards oxygen reduction reaction with high durability and good methanol tolerance compared to commercial Pt/C catalyst.

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We report the synthesis and biological studies of a fluorescence dye with an oligoethylene glycol substituted (OEG) perylene centered dye N, N’-(2,6-diisopropylphenyl)-1-[oligo(ethylene glycol)methyl ether]- 1,6,7,12-trichloroperylene-3,4:9,10-tetracarboxdiimide (PDI-OEG). The activity of the dye is juxtaposed with a precursor molecule without the OEG substitution. The OEG substitution contributes to the increased biocompatibility of PDI-OEG. Cell viability studies lead to the survival of more than 80% of the PDI-OEG cultured cells endorsing its biocompatibility. Fluorescence imaging studies were carried out using multiple cell lines. Ex-vivo studies involving nude mice were used to establish liver and lung specific organ targeting of PDI-OEG. This fluorophore is an excellent example of a stable and biocompatible red emitting small molecule for bioimaging.
This paper reports the synthesis and characterization of a 2,5-bis(phenylacrylonitrile)thiophene based two-photon dye, designed to show enhancement in fluorescence quantum yield in nanoaggregated form. Strong solvatochromism has been observed and explained by the favoritism of locally excited (LE) or internal charge transfer (ICT) state depending on the solvent polarity. Aqueous dispersions of nanoparticles have been prepared and investigated regarding their optical properties which were correlated to the LE and ICT state and the molecular structure of the aggregates

In this contribution we present an overview of two-photon sensitized bioimaging in the perspective of the materials. This review is primarily meant to be used by a chemist to gain an overview of the scope and challenges of this rapidly growing field of science. We look at the spectrum of two-photon active organic, organic-inorganic hybrid materials that have been studied for this application. Two-photon imaging is being used extensively in the study of cancerous cells. In this context we have also looked at different strategies of material design for targeting cancer cells.

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In this paper, the surface modification of CdSe- and CdZnS-based quantum dots (QDs) with a functional silica shell is reported. Functionalized silica shells are prepared by two routes: either by ligand exchange and a modified Stöber process or by a miniemulsion process with amphiphilic poly(oxyethylene) nonylphenylether also know as Igepal CO-520 (IG) as oligomeric amphiphile and modified silica precursors. The polymerizable groups on the functionalized silica shell allow covalent bonding to a polymer matrix and prevent demixing during polymerization and crosslinking. This allows the homogeneous incorporation of QDs in a crosslinked polymer matrix. This paper furthermore demonstrates that the resulting QDs, which are i) shielded with a proper silica shell and ii) functionalized with crosslinkable groups, can be used in two-photon-initiated polymerization processes in combination with different photoresists to obtain highly luminescent 3D structures. The resulting luminescent structures are attractive candidates for photonics and metamaterials research.

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Hybrid materials composed of colloidal semiconductor quantum dots and π-conjugated organic molecules and polymers have attracted continuous interest in recent years, because they may find applications in bio-sensing, photodetection, and photovoltaics. Fundamental processes occurring in these nanohybrids are light absorption and emission as well as energy and/or charge transfer between the components. For future applications it is mandatory to understand, control, and optimize the wide parameter space with respect to chemical assembly and the desired photophysical properties. Accordingly, different approaches to tackle this issue are described here. Simple organic dye molecules (Dye)/quantum dot (QD) conjugates are studied with stationary and time-resolved spectroscopy to address the dynamics of energy and ultra-fast charge transfer. Micellar as well as lamellar nanostructures derived from diblock copolymers are employed to fine-tune the energy transfer efficiency of QD donor/dye acceptor couples. Finally, the transport of charges through organic components coupled to the quantum dot surface is discussed with an emphasis on functional devices. 

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We have functionalized core-shell CdSe/ZnS quantum dots (QDs) with a photosensitive monolayer, rendering them solution processable and photopatternable. Upon exposure to ultraviolet radiation, films composed of this material were found to polymerize, forming interconnected arrays of QDs. The photoluminescence properties of the nanocrystal films increased with photocuring. The material was found to be suitable for spin casting and was used as the active layer in a green electroluminescent device. The electroluminescence efficiency of devices containing a photocured active layer was found to be largely enhanced when compared to devices containing nonphotocured active layers. The material also showed excellent adhesion to both organic and inorganic substrates because of the unique combination of a siloxane and a photopatternable layer as ligands. The pristine functionalized nanocrystals could easily be used for two-dimensional patterning on organic and inorganic substrates. The photopatternable quantum dots were uniformly dispersed into a photopolymerizable resin to fabricate QD embedded three-dimensional microstructures.
 

One-, two-, and three-dimensional microstructures with dispersed silver nanoparticles are fabricated by a combination of photopatterning and thermal treatment from a silver salt containing photosensitive epoxy resin. Ultraviolet photo-irradiation and subsequent thermal treatment are combined to control the rate of silver salt reduction, the size and the arrangement of nanoparticles, as well as the reticulation of the epoxy resin. This approach allows the creation of high resolution 1-, 2-, and 3D patterns containing silver nanoparticles, with a homogeneous distribution of nanoparticles regardless of the irradiated area.

Read more

Two-photon stereolithography based on photopolymerization provides the ability to fabricate real three-dimensional (3D) microstructures beyond the resolution of focal size. In this paper, our recent research focusing on improvement of spatial resolution in two-photon stereolithography is reviewed. The influence of system and fabrication conditions in relation to the spatial resolution is discussed. For small and low aspect ratio voxels, a minimum power and minimum exposure time (MPMT) scheme is introduced. During the two-photon process, an ascending technique, wherein the truncation amount of volumetric pixels is controlled, can be applied to improve the resolution of two-dimensional patterns. 3D Microfabrication with less than 100 nm resolution can be realized by using the radical quenching effect. After the two-photon process, the resolution of fabricated patterns can be refined to 60 nm by post-processing of plasma ashing.
 

 

Quantum dots and their chemical adaptation for various photonic applications are presented in this review. The use of quantum dots as photoactive components in many applications requires their combination with other materials playing specific roles for separation and transport of charge carriers. Achieving good interfaces between electronically matched component materials is key to improved performance in photodetectors, photovoltaics, electroluminescence application, etc. (C)2012 Optical Society of America.
The accessibility of ultrashort high-repetition rate lasers has led to the study of many nonlinear optical (NLO) phenomena and their applications in photonics. Organic and polymeric materials have attracted enormous interest as materials from nonlinear optics because of their tailorability and easy processability. In this chapter we deal with the design and structure–property relationships in materials for second- and third-order NLO effects. The phenomena that are explored include Pockel’s effect, optical Kerr effect, and two-photon absorption (TPA). The factors contributing to the design of highly active NLO materials are discussed with examples to demonstrate various approaches.
 
Charge-transfer (CT) states play a critical role in harvesting non-emissive triplets realized by triplet-to-singlet conversion through spin mixing to generate thermally activated delayed fluorescence (TADF) by providing a spin-orbital coupling (SOC) and small energy difference (∆EST). This paper discusses the spin mixing directly identified by magneto-photoluminescence (magneto-PL) for intramolecular and intermolecular CT states based on a synthesized donor-acceptor-donor (D-A-D) type molecule DMTD-Cz. The PL spectra indicate that this D-A-D molecule shows intramolecular CT states-only in solutions but both intramolecular and intermolecular CT states in solid-state thin films, allowing to separately identify the spin mixing occurring in intramolecular and intermolecular CT states by using magneto-PL measurements. We found that intramolecular and intermolecular CT states exhibit negligible and appreciable magneto-PL signals up to 900 mT at room temperature, respectively. Simultaneously, the intramolecular and intermolecular CT states are shown negligible and appreciable delayed fluorescence, respectively, in thin films. These results provide the direct observation that the SOC generates trivial and vital spin mixing within intramolecular and intermolecular CT states. This indicates that the triplets in intermolecular CT states can be harvested by using spin mixing mechanism while the triplets in intramolecular CT states should be harvested by using spin conserving mechanism through localized triplet excitons towards developing efficient organic light-emitting materials.
 
Covid19Kerala.info-Data is a consolidated multi-source open dataset of metadata from the COVID-19 outbreak in the Indian state of Kerala. It is created and maintained by volunteers of ‘Collective for Open Data Distribution-Keralam’ (CODD-K), a nonprofit consortium of individuals formed for the distribution and longevity of open-datasets. Covid19Kerala.info-Data covers a set of correlated temporal and spatial metadata of SARS-CoV-2 infections and prevention measures in Kerala. Static releases of this dataset snapshots are manually produced from a live database maintained as a set of publicly accessible Google sheets. This dataset is made available under the Open Data Commons Attribution License v1.0 (ODC-BY 1.0).
 
 
India, the second most populated country in the world, reported its first COVID-19 case in the state of Kerala with a travel history from Wuhan. Subsequently, a surge of cases was observed in the state mainly through the individuals who traveled from Europe and the Middle East to Kerala, thus initiating an outbreak. Since public awareness through dissemination of reliable information plays a significant role in controlling the spread of the disease, the Department of Health Services, Government of Kerala initially released daily updates through daily textual bulletins. However, this unstructured data requires refinement and enrichment for upstream applications, such as visualization, and/or analysis. Here we reported a citizen science initiative that leveraged publicly available and crowd-verified data on COVID-19 outbreak in Kerala from the government bulletins, supplemented with the information from media outlets to generate reusable datasets. This data was further used to provide real-time analysis, and daily updates of COVID-19 cases in Kerala, through a user-friendly bilingual dashboard (https://covid19kerala.info/) for non-specialists. We ensured longevity and reusability of the dataset by depositing it in a public repository, aligning with open source principles for future analytical efforts. Finally, to show the scope of the sourced data, we also provided a snapshot of outbreak trends and demographic characteristics of the individuals affected with COVID-19 in Kerala during the first 99 days of the outbreak.
 
 
Metal halide perovskite quantum dots attract significant research interest in recent years due to their exceptional optical properties, such as tunable emission wavelength, strong quantum confinement and suppressed non-radiative recombination via surface passivation. However, the presence of dark states with low emission rate in perovskite quantum dots due to the strong spin-orbital coupling (SOC) and Rashba effects may suppress light emission efficiency. Strategies of reducing bright-to-dark exciton conversion through spin-orbital coupling (SOC) has been rarely addressed. In this work, we fabricated CsPbBr1I2 quantum dots with controlled size and uniformity by using different capping ligands. The orbit-orbit interactions between photogenerated excitons in CsPbBr1I2 quantum dots are studied based on photoexcitation polarization dependent photoluminescence. Decreasing orbit-orbit interaction in CsPbBr1I2 quantum dots can result in an improved photoluminescence quantum efficiency, which implies that less populated dark excitons with indirect recombination are generated through weak spin flipping. The PL lifetime results confirm that the improved light emission efficiency by changing organic ligand is mainly induced by tuning Rashba effects in quantum dots rather than trap passivation. These findings provide new insight on tuning Rashba effects in perovskite quantum dots towards enhanced light emission efficiency via surface modification.
 
 

Two-photon stereolithography based on photopolymerization provides the ability to fabricate real three-dimensional (3D) microstructures beyond the resolution of focal size. In this paper, our recent research focusing on improvement of spatial resolution in two-photon stereolithography is reviewed. The influence of system and fabrication conditions in relation to the spatial resolution is discussed. For small and low aspect ratio voxels, a minimum power and minimum exposure time (MPMT) scheme is introduced. During the two-photon process, an ascending technique, wherein the truncation amount of volumetric pixels is controlled, can be applied to improve the resolution of two-dimensional patterns. 3D Microfabrication with less than 100 nm resolution can be realized by using the radical quenching effect. After the two-photon process, the resolution of fabricated patterns can be refined to 60 nm by post-processing of plasma ashing.

Read More