Accurate measurement and adjustment method for interference fringe direction in a scanning beam interference lithography system.

To improve the exposure contrast of the scanning beam interference lithography (SBIL) system, a mathematical model of scanning exposure that includes the direction error of the measurement mirror is established. The effect of the angle between the interference fringe direction and the X-axis measurement mirror direction on the exposure contrast is analyzed. An accurate method for interference fringe direction measurement based on the heterodyne interferometry measurement method of the metrology grating and phase shift interferometry is proposed. This method combines the diffraction characteristics of the metrology grating and the phase shift algorithm to calculate the angle between the interference fringe direction and the measurement mirror direction accurately and adjust it. Experiments show that this angle reaches 0.6777 µrad, which meets high-precision grating fabrication requirements. Exposure comparison experiments performed at various angles show that a smaller angle between the interference fringe direction and the measurement mirror direction leads to better grating groove production by scanning exposure, which is consistent with the theoretical analysis. The accuracy of the theoretical analysis and the feasibility of the interference fringe direction adjustment method are verified, laying a foundation for high-quality grating fabrication by the SBIL system.

Fabrication of ultra-high aspect ratio silicon grating using an alignment method based on a scanning beam interference lithography system.

The high-aspect-ratio silicon grating (HARSG) is an important X-ray optical device that is widely used in X-ray imaging and spectrum detection systems. In this paper, we propose a high-precision alignment method based on the scanning beam interference lithography (SBIL) system to realize precise alignment between the <111> orientation on the (110) wafer plane and the grating lines direction, which is an essential step in HARSG manufacture to obtain the high-aspect-ratio grating structure. After the location of the <111> orientation through fan-shaped mask etching and reference grating fabrication, a two-step method that combines static preliminary alignment and dynamic precision alignment is used to align the reference grating lines direction with the interference field fringes of the SBIL system through the interference of the diffracted light from the reference grating near the normal direction, which can realize a minimal alignment error of 0.001°. Through the overall alignment process, HARSGs with groove densities of 500 gr/mm, 1800 gr/mm, and 3600 gr/mm were fabricated through anisotropic wet etching in KOH solution, producing ultra-high aspect ratios and etch rate ratios greater than 200.

Pd Reaction Intermediates in Suzuki-Miyaura Cross-Coupling Characterized by Mass Spectrometry.

Palladium-catalyzed Suzuki-Miyaura (SM) coupling is widely utilized in the construction of carbon-carbon bonds. In this study, nanoelectrospray ionization mass spectrometry (nanoESI-MS) is applied to simultaneously monitor precatalysts, catalytic intermediates, reagents, and products of the SM cross-coupling reaction of 3-Br-5-Ph-pyridine and phenylboronic acid. A set of Pd cluster ions related to the monoligated Pd (0) active catalyst is detected, and its deconvoluted isotopic distribution reveals contributions from two neutral molecules. One is assigned to the generally accepted Pd(0) active catalyst, seen in MS as the protonated molecule, while the other is tentatively assigned to an oxidized catalyst which was found to increase as the reaction proceeds. Oxidative stress testing of a synthetic model catalyst 1,5-cyclooctadiene Pd XPhos (COD-Pd-XPhos) performed using FeCl3 supported this assignment. The formation and conversion of the oxidative addition intermediate during the catalytic cycle was monitored to provide information on the progress of the transmetalation step.

Quantum Mechanical Modeling of Reaction Rate Acceleration in Microdroplets.

Organic reactions in microdroplets can be orders of magnitude faster than their bulk counterparts. We hypothesize that solvation energy differences between bulk and interface play a key role in the intrinsic rate constant increase and test the hypothesis with explicit solvent calculations. We demonstrate for both the protonated phenylhydrazine reagent and the hydrazone transition state (TSB) that molecular orientations which place the charge sites at the surface confer high energy. A pathway in which this high-energy form transforms into a fully solvated TSB has a lower activation energy than bulk by some 59 kJ/mol, a result that is consistent with experimental rate acceleration studies.

High-yield gram-scale organic synthesis using accelerated microdroplet/thin film reactions with solvent recycling.

A closed system has been designed to perform microdroplet/thin film reactions with solvent recycling capabilities for gram-scale chemical synthesis. Claisen-Schmidt, Schiff base, Katritzky and Suzuki coupling reactions show acceleration factors relative to bulk of 15 to 7700 times in this droplet spray system. These values are much larger than those reported previously for the same reactions in microdroplet/thin film reaction systems. The solvent recycling mode of the new system significantly improves the reaction yield, especially for reactions with smaller reaction acceleration factors. The microdroplet/thin film reaction yield improved on recycling from 33% to 86% and from 32% to 72% for the Katritzky and Suzuki coupling reactions, respectively. The Claisen-Schmidt reaction was chosen to test the capability of this system in gram scale syntheses and rates of 3.18 g per h and an isolated yield of 87% were achieved.

Accelerated reactions in field desorption mass spectrometry.

Field desorption mass spectrometry under ambient conditions is used to study solution-phase organic reactions in micro-volumes. Reagent solution is transferred onto the microdendrites of the field emitter, and reaction products are examined online by mass spectrometry. Three reactions, hydrazone formation by phenyl hydrazine and indoline-2,3-dione, the Katritzky reaction between a pyrylium salt and anisidine, and the Hantzsch synthesis of 1,4-dihydropyridine, were investigated, and reaction acceleration was observed to different extents. The increase in rate relative to the corresponding bulk reactions is attributed to solvent evaporation (simple concentration effect) and to the increase of surface-to-volume ratio (enhanced interfacial reactions). A distinguishing feature of this method of reaction acceleration, relative to that based on nano electrospray ionization, is the observation of radical cations and the formation of radical cation products. The study also breaks new ground in using field emitters at atmospheric pressure.

Photoaffinity labeling of transcription factors by DNA-templated crosslinking.

Characterization of transcription factor-DNA interaction is of high importance in elucidating the molecular mechanisms of gene transcriptions. DNA-based affinity probes were developed to capture and identify transcription factors by covalent crosslinking; however, the requirement of a crosslinker on the affinity probe remains a disadvantage, as the crosslinker itself often interferes with the protein-DNA interactions. We report a dual-probe method able to capture DNA-binding transcription factors with unmodified protein-binding sites in scenarios where conventional probes have failed. We have also shown the method's converse application in selecting specific transcription factor-binding DNA sequences from a probe library and its extension to studying proteins recognizing epigenetic marks. This study may provide a new tool for exploring DNA-binding proteins in biology.