Angstrom Level Research Articles

Lattice-defective metal-organic framework membranes from filling mesoporous colloidal networks for monovalent ion separation

Ionic separations are critical to various chemical, environmental, and energy-related industries, but precise discrimination of monovalent ions with similar properties is extremely difficult. Nanoporous metal-organic framework (MOF) membranes attract intensive attention for ionic separations. However, precise adjusting transport nanochannels of frameworks and simplifying formation mechanisms of membranes remain extremely challenging. In this study, we report controllable construction of lattice-defective MOF membranes for sharp ion sieving, through filling mesoporous MOF colloidal layers by confined interior growth. By utilizing highly processable mesoporous colloidal networks to provide abundant nucleation sites, decelerate precursor diffusions, and serve as membrane-forming hosts, interior MOF growth can be confined in the mesopores of hosts, thereby eliminating any avoid spaces and constructing pinhole-free membranes in a scalable route. Moreover, through creating linker-missing lattice defects in frameworks, the microporous pathways can be accurately expanded at angstrom level, consequently, selectively improving the accessibilities for specific monovalent cations but maintaining the large resistances for others. Importantly, the prepared 150-nm MOF membranes exhibit good long-term stability and superb ion-sieving performance, especially for monovalent cations, with mixture selectivities as high as 7.5 for K+/Li+ and 51 for K+/Mg2+ during concentration-driven separations, which outperform most membranes. This study provides an alternative methodology to construct high-performance ion-sieving polycrystalline membranes.

Angstrom-Level Tuning in Confined Space of Metal-Organic Framework for Ultra-High Resolution in Gas Chromatographic Separation.

Optimizing the balance between thermodynamic interaction and kinetic diffusion is pivotal to obtaining high-performance gas chromatographic stationary phases. Here, three aluminum-based metal-organic frameworks featuring fym topology were chosen to achieve such balance by refined controlling the thermodynamic interactions toward analytes at angstrom level in a confined space. The CAU-10-H with the middle-sized channels (5.4 Å) provided weak interactions with xylenes because of the benzene ring around the channel, leading to the fastest diffusion. While the MIL-160 provided stronger interactions toward the analytes due to the abundance of O-heterocyclic sites of 2,5-furandicarboxylic acid ligands, resulting in slightly higher diffusion barriers. Thereby, although MIL-160 had a larger channel (5.9 Å) than CAU-10-H, the xylenes still diffused more slowly in MIL-160 than in CAU-10-H. The CAU-10-NH2 with the channel of 4.7 Å provided overstrong thermodynamic interactions and significant stereospecific blockade to the analytes because of the NH2 sites in the confined channels. These factors collectively contributed to achieving the lowest diffusion kinetics. The confined interactions were also proved by molecular dynamics simulation. Furthermore, the application indicated that MIL-160 exhibited the highest separation ability as a GC stationary phase among all reported materials. This strategy offers an approach for developing high-performance MOF stationary phases.

Fabrication of surface nanoscale axial photonics structures with electric arc discharge

The fabrication of surface nanoscale axial photonics (SNAP) microresonators, utilizing the approach of electric arc discharge (EAD), is accomplished, achieving a precision at the angstrom level. This paper thoroughly investigates the effects that discharge intensity and discharge duration have on SNAP microresonators, respectively, through the manipulation of relevant discharge parameters. The results indicate that, within a specified range of discharge intensity, a linear relationship is observed between the effective radius variation (ERV) and the discharge intensity, characterized by a slope of 0.325 nm/intensity unit. As the discharge duration is extended, the ERV gradually increases, eventually reaching a saturation value, which is inherently determined by the discharge intensity. Additionally, as the discharge intensity (or time) continues to increase, a “convex–concave–convex” shape is observed on the fiber, providing a method for fabricating bat microresonators. These discoveries derived from our study contribute toward providing a strong foundation for the progressive enhancement and refinement of EAD-based SNAP fabrication techniques.

Investigation on the pore structure-performance relationship of porous carbon adsorbents for SF6/N2 separation via fine pore modulation

The capture and recovery of SF6 as electron specialty gas from SF6/N2 by adsorptive separation have obvious advantages such as the mitigation of greenhouse effect and resource utilization of waste gas. The comprehensive understanding of pore structure-performance relationship of porous materials is beneficial for guiding the design of highly-efficient adsorbents for separating SF6/N2, but is presently limited. In this work, a series of citric acid (CA) and KOH with different molar ratios are designed to synthesize carbon adsorbents denoted as CAK via a one-step carbonization-activation method and probed for the adsorptive separation of SF6/N2. Characterization results reveal that the micropores in carbon adsorbents are finely tuned from 0.73 to 0.88 nm at an angstrom level through increasing the KOH/CA molar ratios in precursors, and the significant mesopores are formed in CAK4. Static adsorption results indicate that the SF6 adsorptive capacity at low pressure of 10 kPa increases and then decreases with the increasing contents of KOH, and the highest value is obtained in CAK2, while the diffusion rates illustrated from the adsorption kinetics continuously increase. By correlating the pore structures with adsorption capacity of adsorbents, the critical role of micropores with size ≤ 0.9 nm in determining the SF6 capacity at 10 kPa and mesopores in enhancing the mass transfer is quantitatively confirmed. The dynamic breakthrough results of CAKx carbon adsorbents for SF6/N2 separation are well explained with these understandings, which are important for guiding the design of porous adsorbents with high-performance for SF6 capture and recovery.

ADVANCES IN ULTRAPRECISION DIAMOND TURNING: TECHNIQUES, APPLICATIONS, AND FUTURE TRENDS

Advances in ultraprecision diamond turning have revolutionized manufacturing processes across various industries, offering unparalleled precision and surface quality in the fabrication of optical components, microfluidic devices, and advanced mechanical parts. This review delves into the techniques, applications, and future trends in ultraprecision diamond turning, highlighting recent advancements and potential trajectories. Techniques in ultraprecision diamond turning have evolved significantly, driven by innovations in machine design, tooling materials, and control systems. Diamond turning machines equipped with ultra-stiff structures, high-speed spindles, and advanced feedback mechanisms enable sub-nanometer level accuracy and surface finishes down to Angstrom levels. Additionally, advancements in single-point diamond turning (SPDT), fast tool servo (FTS), and deterministic microgrinding (DMG) techniques further enhance the versatility and precision of the process. Applications of ultraprecision diamond turning span a wide range of industries, including aerospace, automotive, biomedical, and telecommunications. In optics manufacturing, diamond turning facilitates the production of aspheric lenses, freeform optics, and diffractive optical elements with unprecedented accuracy, contributing to the development of high-performance imaging systems and laser applications. Moreover, in the biomedical field, diamond-turned microfluidic devices enable precise control over fluid flow and particle manipulation, empowering advancements in drug delivery systems and lab-on-a-chip technologies. Future trends in ultraprecision diamond turning are poised to address challenges related to scalability, multi-material processing, and in-situ metrology. Integration of adaptive control algorithms and machine learning techniques promises enhanced process stability and predictive maintenance, optimizing productivity and reducing downtime. Furthermore, the development of hybrid manufacturing approaches, combining diamond turning with additive manufacturing or laser processing, offers novel avenues for fabricating complex, multi-functional components with improved efficiency and cost-effectiveness. The ongoing advancements in ultraprecision diamond turning techniques, coupled with diverse applications across industries, underscore its pivotal role in advancing manufacturing capabilities. Anticipated future trends hold promise for further expanding the scope and impact of this technology, driving innovation and pushing the boundaries of precision engineering.
 Keywords: Ultraprecision, Diamond, Turning, Technique, Review.

Study of side burr formation in steady-state nano-polishing of Si-wafer using molecular dynamics simulation

With advancements in the semiconductor industry, it is required to have angstrom level surface finish on silicon wafers which is achieved by nano-polishing. However, side burr is formed due to material pile-up from material removal due to abrasive which becomes detrimental to achieving the high surface finish. This study employs molecular dynamics simulations to explore the mechanism underlying side burr formation during nano-polishing of mono-crystalline silicon (Si)-wafer. The study utilizes a diamond nano-abrasive grit to scratch the surface of the Si-wafer and investigates the formation of pile-ups during the steady-state process. It was observed that increasing the depth of cut by four times led to a 6.3-fold increase in the number of amorphous atoms, indicating greater bond breakage in the direction of scratching. As a result, the cutting force exceeds the thrust force at larger depths of the cut. The correlation between the side burr height and the depth of cut is also studied. Results show that the side burr height ratio increases with the depth of cut, indicating a higher sensitivity of side burr height to the depth of cut. The study suggests that to achieve a ductile mode of material removal and minimize the height of the side burr during nano-polishing of Si-wafers, it is crucial to maintain the depth of cut at or below half (≤0.5) of the abrasive radius and ensure an average friction coefficient below 0.6. The outcome of this study can be useful for the actual manufacturing of miniaturized sensors, actuators, and microsystems for microelectromechanical system devices where a high surface finish is crucial.

Biomimetic construction of smart nanochannels in covalent organic framework membranes for efficient ion separation

Smart nanochannels can regulate ion transport behavior by external stimulus and display precise ion selectivity in biological membrane systems, but constructing artificial membranes with responsive and tunable channel remains a severe challenge. Herein, smart covalent organic framework (COF) membranes decorated with photo-responsive azobenzene derivatives (COF-Azo) were fabricated by a biomimetic nanochannel modulation (BNM) strategy, endowing membranes with charged and switchable sub-nanochannels. Under different wavelength of light, the smart COF-Azo membranes simultaneously exhibited outstanding mono/monovalent and mono/divalent ion selectivity (K+/Li+ ideal selectivity of 17.9 and Li+/Mg2+ ideal selectivity of 24.9) via closing and opening channels. The conversion of effective pore size at angstrom level is realized by photoisomerization of azobenzene. After several photoswitch cycles, the smart membranes still maintained K+/Li+ selectivity of 6.1 and Li+/Mg2+ selectivity of 20.7 in mixed salt solution, exhibiting great potentials in lithium extraction. This work may blaze a trail in constructing photo-responsive nanochannel membranes for energy-efficient ion separation.

Experimental Investigation of Laser Damage Limit for ZPG Infrared Single Crystal Using Deep Magnetorheological Polishing of Working Surfaces

Zinc germanium phosphide (ZGP) crystals have garnered significant attention for their nonlinear properties, making them good candidates for powerful mid-IR optical parametric oscillators and second-harmonic generators. A ZnGeP2 single crystal was treated by deep magnetorheological processing (MRP) until an Angstrom level of roughness. The studies presented in this article are devoted to the experimental evaluation of the influence of deep removal (up to 150 μm) from the surface of a ZnGeP2 single crystal by magnetorheological polishing on the parameters of optical breakdown. It was shown that the dependence of the ZnGeP2 laser-induced damage threshold on MRP depth is a smooth monotonically decreasing logarithmic function. The obtained logarithmic dependence indicates the thermal nature of optical breakdown and the dependence of the ZnGeP2 laser-induced damage threshold on the concentration of surface absorbing defects.

(Invited) Plasma-Enhanced Atomic Layer Etching for Metals and Dielectric Materials

The critical dimensions of semiconductor devices are continuously shrinking with 3D device structure and are approaching to nanometer scale. The demand for dimension control in angstrom level is drastically increasing also in etching processes. Atomic layer etching (ALE) processes are being actively studied and developed for various semiconductor, dielectric materials as well as metals. In this talk, various plasma-enhanced ALE (PEALE) processes will be discussed for isotropic and anisotropic patterning of metals and dielectric materials such as molibdenum, ruthenium, cobalt, titanium nitride, tantalum nitride, halfnium oxide, zirconium oxides.[1-7] Typical ALE processes consist of surface modification step and removal step. For the surface modification, various fluorination, chlorination and oxidation schemes are applied through fluorocarbon deposition, halogenation, oxidation with radicals generated plasmas. For the removal or etching step, various schemes were applied including ion-bomardment, heating, ligand volatilization, ligand exchange, and halogenation. The surface characteristics and requirements of plasma-enhanced ALE will be also discussed.1) K. Koh, Y. Kim, C.-K. Kim, H. Chae, J. Vac. Sci. Technol. A, 36(1), 10B106 (2017)2) Y. Cho, Y. Kim, S. Kim, H. Chae, J. Vac. Sci. Technol. A, 38(2), 022604 (2020)3) Y. Kim, S. Lee, Y. Cho, S. Kim, H. Chae, J. Vac. Sci. Technol. A, 38(2), 022606 (2020)4) D. Shim, J. Kim, Y. Kim, H. Chae, J. Vac. Sci. Technol. B., 40(2) 022208 (2022)5) Y. Lee, Y. Kim, J. Son, H. Chae, J. Vac. Sci. Technol. A., 40(2) 022602 (2022)6) J. Kim, D. Shim, Y. Kim, H. Chae, J. Vac. Sci. Technol. A., 40(3) 032603 (2022)7) Y. Kim, S. Chae, H. Ha, H. Lee, S. Lee, H. Chae, Appl. Surf. Sci. 619, 156751 (2023)

Angstrom surface on copper induced by novel green chemical mechanical polishing using ceria and silica composite abrasives

Toxic and corrosive slurries are widely employed in traditional chemical mechanical polishing (CMP), leading to the pollution to the environment. Consequently, it is a challenge to acquire angstrom surface using green CMP. To solve this challenge, a novel green CMP was developed for copper (Cu), including only four ingredients. Ceria and silica are used as composite abrasives. Tartaric acid was applied to adjust the pH value of the developed green slurry to 6.5. After CMP, surface roughness Ra is 0.1 nm measured by atomic force microscopy and surface profilometer respectively, with measurement areas of 5 × 5 μm2 and 50 × 50 μm2, correspondingly. So far, this is the lowest surface roughness reported in such a large measurement area. Transmission electron microscopy confirms that the thickness of damaged layer after CMP varies from 0.4 to 2 nm. CMP mechanism is elucidated by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Firstly, the Cu surface was oxidized by hydrogen peroxide, then solved via hydrogen ions, and finally chelated with hydroxyl groups of tartaric acid. These findings provide a novel approach and new insights to achieve angstrom level surface, for the potential use in high-performance devices of Cu.

Microproteins-Discovery, structure, and function.

Advances in proteogenomic technologies have revealed hundreds to thousands of translated small open reading frames (sORFs) that encode microproteins in genomes across evolutionary space. While many microproteins have now been shown to play critical roles in biology and human disease, a majority of recently identified microproteins have little or no experimental evidence regarding their functionality. Computational tools have some limitations for analysis of short, poorly conserved microprotein sequences, so additional approaches are needed to determine the role of each member of this recently discovered polypeptide class. A currently underexplored avenue in the study of microproteins is structure prediction and determination, which delivers a depth of functional information. In this review, we provide a brief overview of microprotein discovery methods, then examine examples of microprotein structures (and, conversely, intrinsic disorder) that have been experimentally determined using crystallography, cryo-electron microscopy, and NMR, which provide insight into their molecular functions and mechanisms. Additionally, we discuss examples of predicted microprotein structures that have provided insight or context regarding their function. Analysis of microprotein structure at the angstrom level, and confirmation of predicted structures, therefore, has potential to identify translated microproteins that are of biological importance and to provide molecular mechanism for their in vivo roles.

Mechanical Mechanism of Ion and Water Molecular Transport through Angstrom-Scale Graphene Derivatives Channels: From Atomic Model to Solid-Liquid Interaction.

Ion and water transport at the Angstrom/Nano scale has always been one of the focuses of experimental and theoretical research. In particular, the surface properties of the angstrom channel and the solid-liquid interface interaction will play a decisive role in ion and water transport when the channel size is small to molecular or angstrom level. In this paper, the chemical structure and theoretical model of graphene oxide (GO) are reviewed. Moreover, the mechanical mechanism of water molecules and ions transport through the angstrom channel of GO are discussed, including the mechanism of intermolecular force at a solid/liquid/ion interface, the charge asymmetry effect and the dehydration effect. Angstrom channels, which are precisely constructed by two-dimensional (2D) materials such as GO, provide a new platform and idea for angstrom-scale transport. It provides an important reference for the understanding and cognition of fluid transport mechanism at angstrom-scale and its application in filtration, screening, seawater desalination, gas separation and so on.

Rational Strategy for Space-Confined Atomic Layer Deposition

Atomic layer deposition (ALD) offers excellent controllability of spatial uniformity, film thickness at the Angstrom level, and film composition even for high-aspect-ratio nanostructured surfaces, which are rarely attainable by other conventional deposition methodologies. Although ALD has been successfully applied to various substrates under open-top circumstances, the applicability of ALD to confined spaces has been limited because of the inherent difficulty of supplying precursors into confined spaces. Here, we propose a rational methodology to apply ALD growths to confined spaces (meter-long microtubes with an aspect ratio of up to 10 000). The ALD system, which can generate differential pressures to confined spaces, was newly developed. By using this ALD system, it is possible to deposit TiOx layers onto the inner surface of capillary tubes with a length of 1000 mm and an inner diameter of 100 μm with spatial deposition uniformity. Furthermore, we show the superior thermal and chemical robustness of TiOx-coated capillary microtubes for molecular separations when compared to conventional molecule-coated capillary microtubes. Thus, the present rational strategy of space-confined ALD offers a useful approach to design the chemical and physical properties of the inner surfaces of various confined spaces.

Angstrom‐Level Ionic Sieve 2D‐MOF Membrane for High Power Aqueous Zinc Anode

AbstractAqueous Zn‐ion energy‐storage deviceswith metal Zn as anodes, including batteries and capacitors (ZIBs and ZICs), is largely hindered by dendritic growth and low coulombic efficiency since the side reactions between Zn anodes and electrolyte, originating fromthat targeted and efficient isolation of H2O and SO42− is extremely challenging. Herein, inspired by density functional theory (DFT) that the 2D angstrom level metal‐organic framework(2D‐MOF) is highly selective for the passage of ions, simultaneously excluding the SO42− and H2O but allowing Zn2+ selective conduction. Moreover, 2D‐MOF exhibits better mechanical strength compared with 3D‐MOF, which is more conducive to inhibit dendrite growth. Impressively, benefiting from the 2D‐MOFlayer, symmetric Zn cells survived up to 2000 h at 4 mA cm−2,near 20‐times that of bare Zn anodes. Coupling it with cathode for ZICs and ZIBs, excellent electrochemical performances are presented. Importantly, symmetric Na cells with 2D‐MOF as ionic sieve membrane also deliver small polarization and outstanding performance, indicating that this study provides an efficient strategy to develop long‐life metal anode.

Tracking down fluorophores to the angstrom level by MINSTED.

The ability to localize a fluorophore down to its physical size is a unique feature of state of the art nanoscopy methods like MINFLUX and MINSTED. MINSTED achieves this localization precision with minimal number of detected photons by stimulated emission depletion (STED) and detection-driven repositioning of the central minimum of the STED donut towards the fluorophore position. STED, as one of the key principles of MINSTED, makes use of a dedicated light pattern to inhibit the fluorophore's ability to fluoresce. The intensity needed is proportional to the stimulated emission cross-section of the fluorophore at the laser wavelength. This wavelength is a compromise between cross-section and direct excitation of the fluorophore. Conventional STED imaging cannot benefit much from shifting the STED wavelength closer to the emission maximum, as peripheral fluorophores are excited by the STED laser. By contrast, MINSTED, operating on singularized emitters, can make use of STED light at shorter wavelength to localize emitters down to the angstrom level. Using switchable fluorophores, this allows imaging of both reference DNA origami samples and biological specimens, with localization precisions smaller than the physical size of the fluorophore. Such high localization precisions pave the way for new insights into biological systems, as the instrument is not the resolution-limiting factor anymore.

Smart Covalent Organic Frameworks with Intrapore Azobenzene Groups for Light-Gated Ion Transport

Constructing gated ion transport channels is of profound significance for a variety of applications but remains challenging. Covalent organic frameworks (COFs), as a new class of reticular materials, have demonstrated superiority in controllable transport and precise separation of fine species including ions. Herein, we engineer a light-responsive COF featuring intrapore azobenzene groups for highly efficient and adjustable transport of multivalent ions. Such azobenzene-tagged channels afford a customizable configuration that is precisely switchable at an angstrom level without compromising crystallinity. The membrane-shaped COFs exhibit an exceptional discrimination capability between monovalent and multivalent ions, rendering a K+/Al3+ selectivity of above 6000. Particularly, the azobenzene-decorated ordered nanochannels empower reversible, remote-controlled ion transport, implementing the tailor-made recycling of ionic adjuvants used for antibiotic production. This study reports the design and synthesis of a stimulus-responsive COF and demonstrates the efficient separation of ions by light-gated nanochannels of the smart COF.

Utilization of an α,β-Unsaturated Carboxylic Acid to Employ an “over Cutting” Mechanism for Defect Mitigation during Cu Post-Chemical Mechanical Planarization (p-CMP) Cleaning

As features on integrated circuits (IC) continue to shrink, the implementation of chemical mechanical planarization (CMP) is a critical processing step to reduce surface topography in an effort to continue to extend Moore’s law. Specifically, Cu CMP utilizes complex slurry formulations containing an abrasive nanoparticle (SiO2) and additives (i.e., corrosion inhibitors, oxidizers, and complexing agents) to achieve angstrom level uniformity. However, one drawback to this process is the generation of detrimental surface defects that result from residual contamination (i.e., organic residues, abrasive particles, pad remnants, etc.) that are reliant on post-CMP (p-CMP) cleaning methods. Current Cu p-CMP cleaning methods implement the use of an industry standard polymer brush coupled with cleaning chemistries to remove residual contamination. It has been well established that shear and compressive forces coupled with surface active cleaning chemistries have proven to be efficient albeit with the potential for secondary defect induction (i.e., pitting, etching, scratching). Additionally, current cleaning formulations rely on additives that promote aggressive redox conditions to remove residues through an undercutting mechanism, which leads to the propagation of the aforementioned defect modes. This work focuses on the investigation of “soft” cleaning chemistries via the implementation of a structurally unique additive to create a synergy at the liquid-brush-wafer interface. More specifically, the implementation of an -unsaturated carboxylic acid (i.e., itaconic acid) has shown the capability of chemically activating an organic residue mosaic (i.e., BTA/nanoparticle) resulting in effective removal through an “overcutting” mechanism to significantly alter mechanical processing conditions. Through the implementation of corrosion studies utilizing a rotating disk electrode, the addition of itaconic acid has shown a reduction in icorr value and a shift in the passivation characteristics of the system. Open circuit potential (OCP) vs. time measurements indicates that the recovery of the passivation film is more effective in the itaconic acid formulation. A time resolved contact angle technique showed that itaconic acid had a significantly faster diffusion rate on a Cu surface coated with an exaggerated residue film indicating an enhanced surface adsorption. Furthermore, there is clear evidence that under brush conditions the presence of itaconic acid significantly enhances the removal of organic residues at the surface of a Cu substrate without the expense of effective nanoparticle removal.

Theoretical and experimental study on plasma-induced atom-migration manufacturing (PAMM) of glass

Optical manufacturing plays an important role in various fields, such as optical lenses, telescopes, and laser optics. Generally, traditional optical manufacturing techniques are all subtractive processes based on the micro-shearing effect between the tool and surface protrusions. This paper reports a plasma-induced atom migration manufacturing (PAMM) process, which is a nonsubtractive finishing approach by which angstrom level surface roughness of fused silica has been successfully achieved. Inductively coupled plasma (ICP), which is characterized by high temperature and high radical density, is used as the tool of PAMM. After obtaining instantaneous plasma energy input on the fused silica surface, the peak site atoms migrate to the valley sites, thereby reducing the roughness. According to the energy minimization principle, this migration process continues until an ultra-smooth surface with reduced surface energy is formed. Atomic-scale molecular dynamics simulations were performed to clarify the microscopic mechanisms of PAMM, and experiments were conducted to verify its smoothing capability. The roughness of a ground silica surface was drastically reduced from Sa 391 nm to Sa 0.16 nm. This study demonstrates the feasibility of the PAMM as an alternative approach for atomic-level surface manufacturing.

Atomic surface manufacturing based on plasma-induced atom-selective etching

<p indent="0mm">Manufacturing is developing from Manufacturing I, based on empirical skills, and Manufacturing II, based on classical theory, to Manufacturing III, based on quantum theory. Although these three manufacturing paradigms appear at different historical stages, they will coexist, and Manufacturing II will still play a leading role for the foreseeable future. The core area of Manufacturing III will be atomic and close-to-atomic scale manufacturing (ACSM), covering manufacturing accuracy, feature dimensions, and the scale of material removal, migration, and addition. The manufacturing of atomic surfaces is an important area for the development of ACSM. This article will introduce a novel atomic surface fabrication technique named plasma-induced atom-selective etching (PASE). The atoms on the rough surface of a single-crystal material have different bonding states and therefore have different priorities during plasma etching. These reaction priorities can be modulated by changing the radicals, concentration, and temperature of the plasma. Hence, PASE could selectively remove the excess atoms on the single-crystal material surface and eventually achieve an atomic surface. PASE has been successfully applied to many hard and brittle materials, including Si, SiC, and Al₂O₃. Using CF₄-O₂ based plasma, a lapped surface with a surface roughness of over <sc>100 nm</sc> can be directly polished to an angstrom level (<italic>S</italic>_a&lt;<sc>0.5 nm),</sc> and the atomic surface can be achieved.

Time-Resolved Imaging of Stochastic Cascade Reactions over a Submillisecond to Second Time Range at the Angstrom Level

Many chemical reactions, such as multistep catalytic cycles, are cascade reactions in which a series of transient intermediates appear and disappear stochastically over an extended period. The mechanisms of such reactions are challenging to study, even in ultrafast pump-probe experiments. The dimerization of a van der Waals dimer of [60]fullerene producing a short carbon nanotube is a typical cascade reaction and is probably the most frequently studied in carbon materials chemistry. As many as 23 intermediates were predicted by theory, but only the first stable one has been verified experimentally. With the aid of fast electron microscopy, we obtained cinematographic recordings of individual molecules at a maximum frame rate of 1600 frames per second. Using Chambolle total variation algorithm processing and automated cross-correlation image matching analysis, we report on the identification of several metastable intermediates by their shape and size. Although the reaction events occurred stochastically, varying the lifetime of each intermediate accordingly, the average lifetime for each intermediate structure could be obtained from statistical analysis of many cinematographic images for the cascade reaction. Among the shortest-living intermediates, we detected one that lasted less than 3 ms in three independent cascade reactions. We anticipate that the rapid technological development of microscopy and image processing will soon initiate an era of cinematographic studies of chemical reactions and cinematic chemistry.