Photoacid Generator Research Articles

Study of Self-Patterned Zinc Tin Oxide Thin-Film Transistors Prepared from Photocurable Precursor Solution with Photoacid Generator

Solution-processed zinc tin oxide (ZTO) thin-film transistors (TFTs) have great potential uses in next-generation wearable and flexible electronic products. Zinc and tin precursor materials are naturally abundant and have low fabrication costs. To integrate a single ZTO TFT into logic circuits including inverters, NAND, and NOR gates will require the development of a facile patterning process to replace conventional and complicated photolithography techniques which are usually time-consuming and toxic. In this study, self-patterned ZTO thin films were prepared using a photo-patternable precursor solution including a photoacid generator, (4-methylthiophenyl)methyl phenyl sulfonium triflate. Solution-processed ZTO precursor films fabricated with the photoacid generator were successfully micropatterned by UV exposure, and transitioned to a semiconducting ZTO thin film by heat treatment. The UV-irradiated precursor films became insoluble in developing solvent as the generated proton from the photoacid generator affected the metal-containing ligand and changed the solubility of the metal oxide precursors. The resulting ZTO thin films were utilized as the active layers of n-type TFTs, which exhibited a typical n-type transfer, and output characteristics with appropriate threshold voltage, on/off current ratio, and field-effect mobility. We believe that our work provides a convenient solution-based route to the fabrication of metal-oxide semiconductor patterns.

Spatiotemporal Control of Supramolecular Polymerization and Gelation of Metal-Organic Polyhedra.

In coordination-based supramolecular materials such as metallogels, simultaneous temporal and spatial control of their assembly remains challenging. Here, we demonstrate that the combination of light with acids as stimuli allows for the spatiotemporal control over the architectures, mechanical properties, and shape of porous soft materials based on metal-organic polyhedra (MOPs). First, we show that the formation of a colloidal gel network from a preformed kinetically trapped MOP solution can be triggered upon addition of trifluoroacetic acid (TFA) and that acid concentration determines the reaction kinetics. As determined by time-resolved dynamic light scattering, UV-vis absorption, and 1H NMR spectroscopies and rheology measurements, the consequences of the increase in acid concentration are (i) an increase in the cross-linking between MOPs; (ii) a growth in the size of the colloidal particles forming the gel network; (iii) an increase in the density of the colloidal network; and (iv) a decrease in the ductility and stiffness of the resulting gel. We then demonstrate that irradiation of a dispersed photoacid generator, pyranine, allows the spatiotemporal control of the gel formation by locally triggering the self-assembly process. Using this methodology, we show that the gel can be patterned into a desired shape. Such precise positioning of the assembled structures, combined with the stable and permanent porosity of MOPs, could allow their integration into devices for applications such as sensing, separation, catalysis, or drug release.

Catalyst-Free Spontaneous Polymerization with 100% Atom Economy: Facile Synthesis of Photoresponsive Polysulfonates with Multifunctionalities.

Photoresponsive polymers have attracted extensive attention due to their tunable functionalities and advanced applications; thus, it is significant to develop facile in situ synthesis strategies, extend polymers family, and establish various applications for photoresponsive polymers. Herein, we develop a catalyst-free spontaneous polymerization of dihaloalkynes and disulfonic acids without photosensitive monomers for the in situ synthesis of photoresponsive polysulfonates at room temperature in air with 100% atom economy in high yields. The resulting polysulfonates could undergo visible photodegradation with strong photoacid generation, leading to various applications including dual-emissive or 3D photopatterning, and practical broad-spectrum antibacterial activity. The halogen-rich polysulfonates also exhibit a high and photoswitched refractive index and could undergo efficient postfunctionalizations to further expand the variety and functionality of photoresponsive heteroatom-containing polyesters.

Target and Nontarget Analysis of Per- and Polyfluoralkyl Substances in Wastewater from Electronics Fabrication Facilities.

The goals of this study were to improve our understanding of the types of per- and polyfluoroalkyl substances (PFASs) that occur in wastewater from electronics fabrication facilities (fabs) and to assess the relative concentrations of PFAS species. We collected wastewater samples from three fabs in the United States, analyzed the samples by means of high-resolution mass spectrometry, and implemented complementary target and nontarget analyses. Twelve of 25 target PFASs were quantified in at least one sample, and five perfluorocarboxylates and perfluorobutane sulfonate (PFBS) were quantified in all samples. PFBS was quantified at the highest concentration among the samples (8040 ng L-1) and we expect that its presence is related to the use of photoacid generators during photolithography. The sum concentrations of the target PFASs in the diluted discharge samples from each fab were 623, 394, and 376 ng L-1. Nontarget analysis revealed the presence of 41 homologous series of PFASs comprising 133 homologues. We proposed structures for 15 homologous series of nontarget PFASs, six of which are reported here for the first time. Using an approach for semiquantification of nontarget PFASs, we estimated that the sum concentrations of target and nontarget PFASs in the diluted discharge samples from each fab were 1490, 78 700, and 2170 ng L-1. Our findings are essential for developing alternative photolithography chemicals or informing the implementation of advanced wastewater treatment technologies at fabs.

The improved photosensitivity of photosensitive polyimides containing o‐nitrobenzyl ether groups induced by the addition of photoacid generator

AbstractIn this article, photosensitive polyimides (PSPIs) with photosensitive groups, o‐nitrobenzyl ether groups (Nb), were successfully synthesized based on 2,2′‐dihydroxy benzophenone‐3,3′,4,4′‐tetracarboxylic dianhydride and on diamine containing ethylene glycol chains (ODA). Also, a series of polyimide (PI), ODA‐1‐PI, ODA‐3‐PI, and ODA‐5‐PI with a number of ethylene glycol chains of 1, 3, and 5 were prepared to investigate the relationship between structure and solubility. Interestingly, ODA‐5‐PI, which possesses a large number of ethylene glycols, exhibited the most excellent solubility. Therefore, due to the good solubility of ODA‐5‐PI in organic solvents and alkaline solutions, a PSPI, poly(1,4‐phenyleneoxy‐3,6,9,12,15‐pentaoxaoctane‐1,4‐phenylene‐2,2′‐di[2‐nitrobenzyloxy]benzophenone‐3,3′,4,4′‐tetracarboxdiimide), named ODA‐5‐PSPI, was synthesized by linking Nb, which is a photosensitive group. Aiming at producing positive tone patterns, the synthesized ODA‐5‐PSPI was exposed to UV irradiation and then to a post‐exposure bake. Afterward, it was developed using a 2.38 wt% tetramethylammonium hydroxide solution. Furthermore, a photoacid generator (PAG) was additionally incorporated for a micropatterning process. Notably, in the presence of the PAG, the photocleavage of ODA‐5‐PSPI occurred not only by the intramolecular rearrangement of Nb but also by its hydrolysis reaction. As a result, due to the synergistic effect of photocleavage, the micropatterning of ODA‐5‐PSPI with PAG could be clearly obtained with less energy (2.0 J/cm2) compared with that without PAG (3.6 J/cm2). Therefore, through the addition of PAG, the photosensitivity was improved by 45%.

Bioconcentration potential and microbial toxicity of onium cations in photoacid generators.

Despite the widespread utilization of onium salts as photoacid generators (PAGs) in semiconductor photolithography, their environmental, health, and safety (EHS) properties remain poorly understood. The present work reports the bioconcentration potential of five representative onium species (four sulfonium and one iodonium compound) by determining the octanol-water partition coefficient (POW) and lipid membrane affinity coefficient (KMA); microbial toxicity was evaluated using the bioluminescent bacterium Aliivibrio fischeri (Microtox bioassay). Four of the oniums exhibited varying degrees of hydrophobic (lipophilic) partitioning (log POW: 0.08-4.12; KMA: 1.70-5.62). A strong positive linear correlation was observed between log POW and KMA (KMA = log POW + 1.76, R2 = 0.99). The bioconcentration factors (log BCF) estimated from POW and KMA for the four oniums ranged from 0.13 to 3.67Lkg-1. Bis-(4-tert-butyl phenyl)-iodonium and triphenylsulfonium had 50% inhibitory concentrations (IC50) of 4.8 and 84.6μM, whereas the IC50 values of the other three oniums were not determined because these values were higher than their aqueous solubility. Given the increased regulatory scrutiny regarding the use and potential health impacts from onium PAGs, this study fulfills critical knowledge gaps concerning the EHS properties of PAG oniums, enabling more comprehensive evaluation of their environmental impacts and potential risk management strategies.

Photoinitiated functionalization of minerals fillers for dental composites

"Organosilanes bearing alkoxysilane are widely used in sol-gel process. In this process, the hydrolysis reaction is usually carried out in aqueous or hydroalcoholic solutions and the condensation reaction requires high temperatures. The hydrolysis of the alkoxysilanes in the presence of water is fast and can be considered as complete. The obtained silanols can then condensate into oligomers by a much slower reaction that depends on temperature. Our objective is to devise a simple synthesis way for grafting such coupling agent onto the mineral fillers surface without using solvent and heating. Mineral fillers are used as reinforcement in dental composites based on Bis-GMA/TEGDMA. The way developed in this work involves a photoinitiated sol-gel process. It consists in using a photoacid generator to activate the hydrolysis and condensation reactions under atmospheric humidity. Mineral oxides usually used in dental materials were chosen as inorganic filler: the zirconia (ZrO2) which is a radiopacifiant agent and the alumina (Al2O3) which allows improving the mechanical properties of the composite. A kinetic study of the self-condensation of the 3-MPS used as coupling agent in the presence of Irgacure 250 ® as photoacid generator was carried out and the operating conditions (irradiation intensity and time) of the functionalization reaction were optimized. Grafted fillers were characterized by FTIR spectroscopy and thermogravimetic analysis. FTIR and TGA analyses of the particles after treatment allow confirming the grafting. Compared to the conventional way, the photoinitiated process proves to be faster, easier, less expensive in energy, and much more efficient in terms of 3-MPS grafted quantity. "

Visible-Light Sensitive Reworkable Resins for Dental Application

A reworkable resin, which is degradable after use, was developed for application as a dental resin. A dimethacrylate monomer containing a ketal linkage in the molecule was used as a reworkable monomer. The reworkable monomer was successfully cured by blue light irradiation (470-nm light) using the camphorquinone/amine photoinitiating system. The cured reworkable resins were degraded in the presence of a UV- and violet-light sensitive photoacid generator by prolonged irradiation at room temperature. The degradation was due to the acid-catalyzed decomposition of the ketal linkages in the cured reworkable monomers. The preliminary result suggested the possibility of application of the reworkable monomer as dental resins.

Novel imino- and aryl-sulfonate based photoacid generators for the cationic ring-opening polymerization of ε-caprolactone

The use of photoacid generators for the ring opening polymerization of cyclic esters is investigated.

Dielectric Response Spectroscopy as Means to Investigate Interfacial Effects for Ultra-Thin Film Polymer-Based High NA EUV Lithography.

Extreme ultra-violet lithography (EUVL) is the leading-edge technology to produce advanced nanoelectronics. The further development of EUVL is heavily based on implementing the so-called high numerical aperture (NA) EUVL, which will enable even smaller pitches up to 8 nm half pitch (HP). In anticipation of this high NA technology, it is crucial to assess the readiness of the current resist materials for the high NA regime to comply with the demanding requirements of resolution, line-edge roughness, and sensitivity (RLS). The achievable tighter pitches require lower film thicknesses for both resist and underlying transfer layers. A concern that is tied to the thinning down is the potential change in resist properties and behavior due to the interaction with the underlayer. To increase the fundamental understanding of ultra-thin films for high NA EUVL, a method to investigate the interplay of reduced film thickness and different patterning-relevant underlayers is developed by looking at the glass transition temperature (Tg) of polymer-based resists. To minimize the ambiguity of the results due to resist additives (i.e., photoacid generator (PAG) and quencher), it was opted to move forward with polymer-only samples, the main component of the resist, at this stage of the investigation. By using dielectric response spectroscopy, the results obtained show that changing the protection group of the polymer, as well as altering the polymer film thickness impacts the dynamics of the polymer mobility, which can be assessed through the Tg of the system. Unexpectedly, changing the underlayer did not result in a clear change in the polymer mobility at the tested film thicknesses.

Regulating Mitochondrial pH with Light and Implications for Chemoresistance.

Chemoresistance is one of the major challenges for cancer treatment, more recently ascribed to defective mitochondrial outer membrane permeabilization (MOMP), significantly diminishing chemotherapeutic agent-induced apoptosis. A boron-dipyrromethene (BODIPY) chromophore-based triarylsulfonium photoacid generator (BD-PAG) was used to target mitochondria with the aim to regulate mitochondrial pH and further depolarize the mitochondrial membrane. Cell viability assays demonstrated the relative biocompatibility of BD-PAG in the dark while live cell imaging suggested high accumulation in mitochondria. Specific assays indicated that BD-PAG is capable of regulating mitochondrial pH with significant effects on mitochondrial membrane depolarization. Therapeutic tests using chlorambucil in combination with BD-PAG revealed a new strategy in chemoresistance suppression.

Light-Triggered Rheological Changes in a System of Cationic Wormlike Micelles Formulated with a Photoacid Generator.

“Smart” fluids displaying large changes in their rheological properties in response to external stimuli have been of great interest in recent years. For example, “smart” wormlike micelles (WLMs) that respond to pH can be readily formulated by combining a cationic surfactant such as cetyltrimethylammonium bromide (CTAB) with an aromatic compound such as 1,2-dihydroxybenzene (DHB). Here, we show that a pH-responsive aqueous formulation as mentioned above can be simultaneously made responsive to ultraviolet (UV) light by incorporating a photoacid generator (PAG) into the system. A commercially available PAG, diphenyliodonium-2-carboxylate, is used here. Upon exposure to UV light, this PAG irreversibly photolyzes into iodobenzene (IB) and benzoic acid (BA), with the formation of BA, leading to a drop in pH. WLMs formed by mixtures of CTAB, DHB, and the PAG are systematically characterized before and after UV irradiation. As the PAG photolyzes, an increase in the viscosity of WLMs occurs by a factor of 1000. We show that the ratio of the zero-shear viscosity η0 (after UV/before UV) depends on the initial pH of the sample. The UV-induced increase in η0 can be attributed to the growth of WLMs in solution, which in turn is influenced by both the ionization state of DHB and the presence of IB and BA.

Regression analysis of photodecomposable quencher concentration effects on chemical gradient in chemically amplified extreme ultraviolet resist processes

Chemically amplified resists have been used in the state-of-the-art extreme ultraviolet (EUV) lithography. A basic additive has been added to the resist formula as a quencher to control acid diffusion. In this study, the effects of photodecomposable quencher (PDQ) concentration on the chemical gradient (an indicator of line edge roughness) in chemically amplified EUV resist processes were investigated. The chemical gradient was calculated on the basis of the sensitization and reaction mechanisms for different half-pitches, sensitivities, photoacid generator (PAG) concentrations, PDQ concentrations, and effective reaction radii for deprotection. The obtained 130 000 data were analyzed by least squares, lasso, ridge, and elastic net regressions. Regarding the contribution to the chemical gradient, PDQ concentration was apparently symmetric to PAG concentration. Optimum PDQ concentrations were well predicted (accuracy of approximately 10%) within the examined variable ranges even with 495 training data using the fitted parameters obtained by lasso, ridge, and elastic net regressions.

Impact of inorganic nanoparticles on optical properties of low refractive index waveguiding polymers

The objective of this work is to improve the optical properties of low refractive index polymers used for waveguide by introduction of inorganic nanoparticles. Copolymers of fluorinated monomers and glycidyl methacrylate are used. Introduction of SiO2 nanoparticles into polymer matrix is performed by direct mixing; copolymerization with SiO2 nanoparticles modified by monomer, and in situ sol-gel formation of SiO2 during photochemical cross-linking and annealing catalyzed by photoacid generator. It is demonstrated that nanoparticles are able to decrease thermo-optic coefficient. It is also possible to fabricate waveguiding layers by direct introduction of nanoparticles without compromising of optical propagation losses.

Multi-acrylate-based UV-curable dismantlable adhesives

Herein, a dismantlable, photo-curable adhesive is reported. The adhesive is composed of a multi-acrylate oligomer with a tertiary ester, a photo radical initiator, a photo acid generator, and a phosphate-substituted acrylate as an adhesion promoter. Photo-exposure to the adhesive sandwiched between two glass slides induces crosslinking and causes the slides to bond to each other. Post-exposure baking promotes the acid-catalyzed decomposition of the hardened adhesive, which results in significantly decreased adhesion strength. An alkaline developer can easily remove the residual adhesive on the debonded glass plates, thus recovering glass transparency. Photo-bonding and debonding mechanisms were elucidated by spectroscopic analyses. By using the dismantlable adhesive, a small glass plate attached to a glass slide can be successfully transferred to another glass slide.

Direct Optical Patterning of Quantum Dot Light-Emitting Diodes via In Situ Ligand Exchange.

Precise patterning of quantum dot (QD) layers is an important prerequisite for fabricating QD light-emitting diode (QLED) displays and other optoelectronic devices. However, conventional patterning methods cannot simultaneously meet the stringent requirements of resolution, throughput, and uniformity of the pattern profile while maintaining a high photoluminescence quantum yield (PLQY) of the patterned QD layers. Here, a specially designed nanocrystal ink is introduced, "photopatternable emissive nanocrystals" (PENs), which satisfies these requirements. Photoacid generators in the PEN inks allow photoresist-free, high-resolution optical patterning of QDs through photochemical reactions and in situ ligand exchange in QD films. Various fluorescence and electroluminescence patterns with a feature size down to ≈1.5 µm are demonstrated using red, green, and blue PEN inks. The patterned QD films maintain ≈75% of original PLQY and the electroluminescence characteristics of the patterned QLEDs are comparable to thopse of non-patterned control devices. The patterning mechanism is elucidated by in-depth investigation of the photochemical transformations of the photoacid generators and changes in the optical properties of the QDs at each patterning step. This advanced patterning method provides a new way for additive manufacturing of integrated optoelectronic devices using colloidal QDs.

Photoinitiated Transformation of Nanocrystal Superlattice Polymorphs Assembled at a Fluid Interface

AbstractDirecting the assembly of nanoscale building blocks into programmable superstructures is of broad scientific and technological interest. Advances in nanocrystal self‐assembly at fluid interfaces are combined with digital light processing to demonstrate that how the extent and spatial region of superlattice structure transformation can be controlled. It is shown that the addition of a photoacid generator to the fluid subphase provides new experimental degrees of freedom to modulate the dynamic equilibrium of ligands bound to the colloidal nanocrystal surface. Within the photoexposed regions, the nanocrystal ligand coverage is reduced which impacts the interactions between proximate nanocrystals and drives the transformation from a sixfold to a fourfold symmetric superlattice. Structural analysis is presented from transmission electron microscopy and chemical analysis is presented from infrared spectroscopy to establish the relationship between superlattice structure and ligand coverage. Beyond new insights understanding of and control over deprotection of colloidal nanocrystals at fluid interfaces, the processing method described in this work presents new opportunities to create nanocrystal assemblies with spatially programmable structures.

Highly Ordered Nanocellular Polymeric Foams Generated by UV-Induced Chemical Foaming.

Nanocellular polymer foams have shown significant potential for industrial applications because of their superior thermal, mechanical, and optical properties. Some of these properties may be further improved by enhancing the ordering of cell structures. However, it is challenging for conventional foaming methods to control both the cell size and ordering at the nanoscale. Here, we show an innovative method to produce highly ordered nanocellular polymer foams by incorporating the self-assembly of an asymmetric diblock copolymer with the UV-induced chemical foaming technique. The minor domains are designed to generate a gaseous compound from the partial cleavage of the functional group. It is demonstrated that the gas-producing reaction can be accelerated at a temperature low enough to prevent melting of the whole self-assembled template, by mixing a small amount of photoacid generator into the copolymer, followed by UV irradiation. The result is the production of polymer foams with the nanoscale cells highly aligned to the self-assembled domains.

Activating Acid-Sensing Ion Channels with Photoacid Generators.

Acid-sensing ion channels (ASICs), present in both central and peripheral neurons, respond to changes in extracellular protons. They play important roles in many symptoms and diseases, such as pain, ischemic stroke and neurodegenerative diseases. Herein, we report a novel approach to activate ASICs with the precision of light using organic photoacid generators (PAGs), which are molecules that release H+ upon light illumination, and have been recently used in biomedical studies. The PAGs showed low toxicity in dark conditions. Under LED light illumination, ASICs activation and consequent calcium ion influx was monitored and analysed by fluorescence microscopy, and showed a strong light-dependent response. This approach allows the activation of ASICs with the precision of light, and may be valuable to help better elucidate the molecular mechanism of ASICs and unveil their roles in physiology, pathophysiology, and behaviour.

Influence of material and process parameters in the dry-development of positive-tone, polyaldehyde photoresist

Abstract