Tracking Invisible Transformations of Physisorbed Monolayers: LDI-TOF and MALDI-TOF Mass Spectrometry as Complements to STM Imaging

Polymerization of Physisorbed Molecular Monolayers via Overhanging Alkynyl Chains: Characterization of Polymerization Kinetics and Monolayer Durability

Monolayers self-assembled by triphenyleneethynylene (TPE) compounds bearing two terminal alkynyl chains were polymerized by Glaser-Hay (G-H) alkyne coupling at the acetonitrile-HOPG interface. The alkynyl chains extend into the solution due to the monolayer's dense-packed morphology. Reacting substructures that have no morphology-determining roles is a potential strategy for preserving monolayer morphology throughout polymerization. Monolayer G-H reaction kinetics and polymerized monolayer durability were characterized by using mass spectrometry and fluorescence. Fourier transform ion cyclotron resonance (FTICR) mass spectrometry (MS) and time-of-flight (TOF) MS were used to identify TPE-oligomers in the monolayer and to track the monolayer populations of TPE-monomer, -dimer, and -trimer as a function of G-H reaction duration. Comparison of the observed kinetics to a Monte Carlo simulation provided evidence of step-growth polymerization. The durability of polymerized monolayers depended strongly on the length of the alkynyl chains linked by G-H reaction. Polymerized T6y monolayers (O(CH2)3C≡CH alkynyl chains) desorbed minimally during 16-h immersion in 90 °C o-dichlorobenzene (oDCB), whereas polymerized T8y (O(CH2)5C≡CH alkynyl chains) and polymerized T11y (O(CH2)8C≡CH alkynyl chains), desorbed 33 and 60%, respectively, of their TPE units after 4 h in 90 °C oDCB. All the polymerized monolayers are much more durable than unpolymerized monolayers, which desorb quantitatively from HOPG when rinsed with 25 μL of oDCB. Polymerized T6y monolayer is a highly durable anchor that may be adapted to build multilayer structures "permanently" attached to the HOPG surface. The alkynyl chain length dependence may be useful for tuning polymerized TPE monolayer durability for specific applications.

Recent Applications of Langmuir-Blodgett Technique in Battery Research

The Langmuir-Blodgett (LB) technique, in which monolayers are commonly transferred from a liquid/gas interface to a solid surface, allows convenient fabrication of highly ordered thin films with molecular-level precision. This method is widely applicable to substances ranging from organic molecules to nanomaterials. Therefore, LB methods have provided a critical toolbox for researchers to engineer nanoarchitectures. The LB fabrication process is also compatible with numerous substrate materials over large areas, which is advantageous for practical application. Despite its wide applicability, the LB strategy has not been extensively employed in battery studies. The versatility of LB film, along with the accumulated knowledge associated with this technique, makes it a promising platform for promoting battery chemistry evolution. This Review summarizes recent advances of LB methods for high-performance battery development, including preparation of electrode materials, fabrication of functional layers, and battery diagnosis and thus illustrates the high utility of LB approaches in battery research.

Recent Applications of Molecular Structures at Silicon Anode Interfaces

Silicon (Si) is a promising anode material to realize many-fold higher anode capacity in next-generation lithium-ion batteries (LIBs). Si electrochemistry has strong dependence on the property of the Si interface, and therefore, Si surface engineering has attracted considerable research interest to address the challenges of Si electrodes such as dramatic volume changes and the high reactivity of Si surface. Molecular nanostructures, including metal–organic frameworks (MOFs), covalent–organic frameworks (COFs) and monolayers, have been employed in recent years to decorate or functionalize Si anode surfaces to improve their electrochemical performance. These materials have the advantages of facile preparation, nanoscale controllability and structural diversity, and thus could be utilized as versatile platforms for Si surface modification. This review aims to summarize the recent applications of MOFs, COFs and monolayers for Si anode development. The functionalities and common design strategies of these molecular structures are demonstrated.

Time-of-flight mass spectrometers based on a wedge-shaped electrostatic mirror with a two-dimensional field

RATIONALE

For most of the last two decades, a considerable effort has been made towards improving time-of-flight mass spectrometry (TOF MS), which has become an irreplaceable instrumental platform for the purposes of performing analytical measurements in life sciences, such as molecular biology, proteomics, medicine, etc. This can primarily be attributed to the ability of TOF MS to rapidly detect and identify nearly any targeted chemical trace with both high precision and accuracy. However, multi-span TOF MS experiments are limited due to aberrations arising from multiple reflection; our proposed scheme will minimize these aberrations.

METHODS

The inhomogeneous accelerating field is generated without using meshes by changing the potentials on the electrodes of the mirror. The ions are extracted from the ion source by short impulse activation of the accelerating electric field. Since the ions are extracted from various points of the source, even ions with identical masses acquire different velocities during acceleration.

RESULTS

We have shown that the "rear" ions of the packet catch up with the "front" ions, and packets of ions with identical masses are compressed in the direction of their movement. It is concluded that, by placing the detector in a plane with the greatest compression of ion packets, an enhanced performance of a time-of-flight mass spectrometer is achieved.

CONCLUSIONS

We have shown that effective spatial-temporal focusing allows a small mass spectrometer to achieve high resolution and sensitivity. We also propose and numerically evaluate a new platform for designing multi-stage and multi-reflective time-of-flight analyzers with wedge-shaped mirrors. We applied the simulation results to the modernization of old equipment and showed that by simply replacing the electrostatic mirror with an optimized one, a significant increase in the analyzing power can be achieved.

Reactive two-component monolayers template bottom-up assembly of nanoparticle arrays on HOPG

Two triphenyleneethynylene derivatives, 1OH and 2, self-assemble a patterned monolayer (ML) at the solution-graphite (HOPG) interface. The four molecule unit cell of the ML, (1OH1OH22), spans 19 nm and contains adjacent columns of 1OH molecules spaced by 4.7 nm. Following ML assembly, a disulfide is appended to the alcohol group on each 1OH molecule and used to capture 2.0 nm gold nanoparticles (AuNP). The patterned monolayer directs bottom-up assembly of a 5 nm/19 nm double pitch AuNP pattern.

Template-Assisted Proximity for Oligomerization of Fullerenes

Demonstrated herein is an unprecedented porous template-assisted reaction at the solid-liquid interface involving bond formation, which is typically collision-driven and occurs in the solution and gas phases. The template is a TMA (trimesic acid) monolayer with two-dimensional pores that host fullerenes, which otherwise exhibit an insignificant affinity to an undecorated graphite substrate. The confinement of C₈₄ units in the TMA pores formulates a proximity that is ideal for bond formation. The oligomerization of C₈₄ is triggered by an electric pulse via a scanning tunneling microscope tip. The spacing between C₈₄ moieties becomes 1.4 nm, which is larger than the edge-to-edge diameter of 1.1-1.2 nm of C₈₄ due to the formation of intermolecular single bonds. In addition, the characteristic mass-to-charge ratios of dimers and trimers are observed by mass spectrometry. The experimental findings shed light on the active role of spatially tailored templates in facilitating the chemical activity of guest molecules.

Zipping and unzipping monolayers: switchable monolayer oligomerization and adhesion via thiol–disulfide interconversion

Triphenyleneethynylene (TPE) monolayers at the solution–HOPG interface are oligomerized by the oxidation of pendant thioethers to form disulfide cross-links. Subsequent disulfide reduction unzips oligomers to form monomeric TPE monolayer with pendant thiols.