Angstrom Level Research Articles

Integration of polarization-multiplexing and phase-shifting in nanometric two dimensional self-mixing measurement.

Integration of phase manipulation and polarization multiplexing was introduced to self-mixing interferometry (SMI) for high-sensitive measurement. Light polarizations were used to increase measuring path number and predict manifold merits for potential applications. Laser source was studied as a microwave-photonic resonator optically-injected by double reflected lights on a two-feedback-factor analytical model. Independent external paths exploited magnesium-oxide doped lithium niobate crystals at perpendicular polarizations to transfer interferometric phases into amplitudes of harmonics. Theoretical resolutions reached angstrom level. By integrating two techniques, this SMI outperformed the conventional single-path SMIs by simultaneous dual-targets measurement on single laser tube with high sensitivity and low speckle noise. In experimental demonstration, by nonlinear filtering method, a custom-made phase-resolved algorithm real-time figured out instantaneous two-dimensional displacements with nanometer resolution. Experimental comparisons to lock-in technique and a commercial Ploytec-5000 laser Doppler velocity meter validated this two-path SMI in micron range without optical cross-talk. Moreover, accuracy subjected to slewing rates of crystals could be flexibly adjusted.

A quantum spin-probe molecular microscope.

Imaging the atomic structure of a single biomolecule is an important challenge in the physical biosciences. Whilst existing techniques all rely on averaging over large ensembles of molecules, the single-molecule realm remains unsolved. Here we present a protocol for 3D magnetic resonance imaging of a single molecule using a quantum spin probe acting simultaneously as the magnetic resonance sensor and source of magnetic field gradient. Signals corresponding to specific regions of the molecule's nuclear spin density are encoded on the quantum state of the probe, which is used to produce a 3D image of the molecular structure. Quantum simulations of the protocol applied to the rapamycin molecule (C51H79NO13) show that the hydrogen and carbon substructure can be imaged at the angstrom level using current spin-probe technology. With prospects for scaling to large molecules and/or fast dynamic conformation mapping using spin labels, this method provides a realistic pathway for single-molecule microscopy.

A New Approach to Tuning Carbon Ultramicropore Size at Sub‐Angstrom Level for Maximizing Specific Capacitance and CO2 Uptake

Ultramicroporous carbon materials with uniform pore size accurately adjusted to the dimension of electrolyte ions or CO2 molecule are highly desirable for maximizing specific capacitance and CO2 uptake. However, efficient ways to fine‐tuning ultramicropore size at angstrom level are scarce. A completely new approach to precisely tuning carbon ultramicropore size at sub‐angstrom level is proposed herein. Due to the varying activating strength and size of the alkali ions, the ultramicropore size can be finely tuned in the range of 0.60–0.76 nm as the activation ion varies from Li+ to Cs+. The carbons prepared by direct pyrolysis of alkali salts of carboxylic phenolic resins yield ultrahigh capacitances of up to 223 F g‐1 (205 F cm‐3) in ionic liquid electrolyte, and superior CO2 uptake of 5.20 mmol g‐1 at 1.0 bar and 25 °C. Such outstanding performance of the finely tuned carbons lies in its adjustable pore size perfectly adapted to the electrolyte ions and CO2 molecule. This work paves the way for a new route to finely tuning ultramicropore size at the sub‐angstrom level in carbon materials.

Nanoparticle-Polymer Surface Adsorption Relevant to CMP Applications

Chemical Mechanical Polishing (CMP) has emerged as a critical technology for the planarization of precision optical components, data storage media, and integrated circuit semiconductor devices. This process is a delicate balance between chemical surface modification and mechanical removal utilizing a nanoparticle dispersion (slurry) to remove defects/irregularities with the goal to attain angstrom level uniformity. As technology continues to advance, next generation nanoparticle dispersions and CMP slurries will increase in complexity to meet stringent performance demands, making it necessary to develop polymeric media that reduce overall surface defectivity and increase planarization efficiency. To uncover dynamics amongst the slurry additives, abrasives, polymeric interfaces, and the CMP substrate the molecular level interactions at the nanoparticle-polymer interface need to be explored. This work set out to explore these interaction mechanisms by using a modified electrochemical quartz crystal nanobalance (EQCN) technique. This modified technique utilizes thin film deposition to place a polymer on the electrode and then by applying the Sauerbrey equation it is possible to gain insight about the surface adsorption at the nanoparticle-polymer interface. The synergistic interaction of the slurry chemistry and the polymeric substrate is further explored to determine the role of surface reactions that alter the polymeric medium’s surface energy and subsequently alter the nanoparticle binding mechanisms.

Prevention of Metal Contamination in Sub 50 Nm SC1 Cleaning Process

The RCA cleaning process is a standard wet cleaning process for removal of contaminants from silicon wafer surface. As well known, the SC1 cleaning solution which consists of a mixture of NH4OH (ammonium hydroxide), H2O2 (hydrogen peroxide) and H2O is an efficient particle removal. Cleaning mechanism of SC1 cleaning solution on particles removal from silicon surface is slightly surface etching and lift off the particles from the Si surface by electrostatic repulsive force between particles and surface. SC1 cleaning process may etch a few angstrom (Å) level of silicon surface. However, metal contaminant which has a high redox potential is critical when bare silicon is exposed. Metal deposition on Si surface is induced by the oxidation reduction reaction between metal ion and Si surface. Metal ion can take electrons from Si surface and are reduced to become metal. Si surface beneath the metal particles is oxidized to become SiO2 and is etched away by OH- in SC1 solution. The metal pit is a form of localized etching that leads to the creation of small hole under the metal. Thus, the etching has a crucial effect on the formation of defects and removal of particles. The etch rate of Si increased with NH4OH concentration whereas it decreased with H2O2 concentration. This indicates that metal pitting increased with NH4OH concentration while H2O2 inhibits it. However, particle removal efficiency (PRE) decreased in high H2O2concentration. Particle removal is affected by etch rate and pH of cleaning solution. For high pH value in the SC1 solution, particles take on a strongly negative charge. The particles are repelled from a Si surface. This electrostatic interaction prevents recontamination by particles to Si surface. Therefore, it is important to optimize SC-1 cleaning process in Si surface cleaning process. In this study, we investigated the relationship between PRE, surface etch rate and removal of metal contaminant with various concentrations of SC1 cleaning solution. The thermally oxidized 200 mm p-type Si (100) wafers were used. To identify relationship between etch rate and formation of defect, etch depth was measured for various composition of SC-1 solution by using atomic force microscopy. The Cu ions were used as a source of metal pitting to making Cu precipitate on Si surface. Si wafers were contaminated with Cu ions and particles by dipping method. Cu precipitate and particles on Si surface were counted using atomic force microscopy and a dark field optical microscope to confirm cleaning efficiency of SC1 solution. Etching of Si wafer surface in SC1 solution was evaluated as a function of composition of SC1 solution. It was shown that Cu precipitates decreased with H2O2 concentration in SC1 solution. But PRE also decreased. It was suggested that H2O2 reduced the formation of Cu precipitates and PRE was dependent of NH4OH concentration. This study proposes cleaning process to minimize Cu precipitates with a high PRE in the optimized SC1 solution. Figure 1

Chirality of Single-Handed Twisted Titania Tubular Nanoribbons Prepared Through Sol-gel Transcription.

Single-handed twisted titania tubular nanoribbons were prepared through sol-gel transcription using a pair of enantiomers. Handedness was controlled by that of the template. The obtained samples were characterized using field-emission electron microscopy, transmission electron microscopy, diffuse reflectance circular dichroism (DRCD), and X-ray diffraction. The DRCD spectra indicated that the titania nanotubes exhibit optical activity. Although the tubular structure was destroyed after being calcined at 700 °C for 2.0 h, DRCD signals were still identified. However, the DRCD signals disappeared after being calcined at 1000 °C for 2.0 h. The optical activity of titania was proposed to be due to chiral defects. Previous results showed that straight titania tubes could be used as asymmetric autocatalysts, indicating that titania exhibit chirality at the angstrom level. Herein, it was found that they also exhibit DRCD signals, indicating that there are no obvious relationships between morphology at the nano level and chirality at the angstrom level. The nanotube chirality should originate from the chiral defects on the nanotube inner surface. The Fourier transform infrared spectra indicated that the chirality of the titania was transferred from the gelators through the hydrogen bonding between N-H and Ti-OH.

Microsecond protein folding events revealed by time-resolved fluorescence resonance energy transfer in a microfluidic mixer.

We demonstrate the combination of the time-resolved fluorescence resonance energy transfer (tr-FRET) measurement and the ultrarapid hydrodynamic focusing microfluidic mixer. The combined technique is capable of probing the intermolecular distance change with temporal resolution at microsecond level and structural resolution at Angstrom level, and the use of two-photon excitation enables a broader exploration of FRET with spectrum from near-ultraviolet to visible wavelength. As a proof of principle, we used the coupled microfluidic laminar flow and time-resolved two-photon excitation microscopy to investigate the early folding states of Cytochrome c (cyt c) by monitoring the distance between the tryptophan (Trp-59)-heme donor-acceptor (D-A) pair. The transformation of folding states of cyt c in the early 500 μs of refolding was revealed on the microsecond time scale. For the first time, we clearly resolved the early transient state of cyt c, which is populated within the dead time of the mixer (<10 μs) and has a characteristic Trp-59-heme distance of ∼31 Å. We believe this tool can find more applications in studying the early stages of biological processes with FRET as the probe.

Molecular structure and the dynamics of the functioning of conformationally mobile systems

The state of art of research on the dynamics of biomacromolecules and complexes thereof is briefly outlined. Emphasis is placed on the work conduced over the last 30 years at Lomonosov Moscow State University and Semenov Institute of Chemical Physics RAS. The physical mechanisms of fluctuation dynamics on the angstrom and subangstrom levels in condensed matter are considered based on Mossbauer spectroscopy and molecular dynamics modeling. The results of all-atom simulations of the functioning of ion channels obtained on a “Lomonosov” supercomputer (MSU) are reported. The self-organizing dynamics of macromolecular structures is examined for model polymer structures and nanostructures. The topology of multidimensional energy surfaces for conformationally mobile systems and its influence on the dynamic properties of objects are considered. In conclusion, the dynamics of functioning of simple molecular machines based on catenanes and rotaxanes and the role of conformational mobility in ensuring their operation are discussed.

Angstrom Scale Wear of the Air-Bearing Sliders in Hard Disk Drives

We utilize thermal fly-height control (TFC) technology to perform in situ measurements of carbon overcoat wear at the angstrom level at the read–write area of magnetic recording heads. We also study the durability of the molecularly thin lubricated disk surface. Experimental findings reveal a linear relationship between the quantified carbon wear depth on the flying head versus the head–disk contact level produced by the TFC power. It is demonstrated that this method can serve as a measurement and probing technique of wear resistance for different types of lubricants. Lubricants possessing more polar hydroxyl end-groups and less mobility tend to show a superior surface stability under head–disk contacts, but raise concerns on head carbon overcoat wear.

Mechanosensing by Tropomyosin-Controlled Myosin Contractions

Control of cell growth, death or differentiation involves the integration of microenvironmental signals through cell motile processes to produce the desired cellular responses. In the case of cell-matrix interactions, the cell tests the matrix by asking several if-then questions such as is the matrix clustered, can force be generated and later what is the rigidity of the matrix. Using lipid-linked matrix ligands, we found that cells would not spread on the surface unless the liganded integrins were clustered and cells generated forces on the ligands by pulling to barriers (Yu et al., 2011. PNAS 108:20565). Upon activation of cell spreading, the flattening of the cells removed the folds in the membranes until a rise in membrane tension activated contraction to sense rigidity (Gauthier et al., 2011. PNAS 108:14467). Rigidity sensing involved local contraction units that pulled about 100 nm independent of rigidity (Ghassemi et al., 2012 PNAS 109:5325. Recently, we found that local contraction units resembled dynamic sarcomeres with alpha actinin at ends and myosin in the middle (Meacci et al., submitted). Further, generation of force involved repeated step-wise movements of myosin controlled by tropomyosin-1 (Wolfenson et al., submitted). Angstrom level measurements of fibroblasts pulling on elastomeric PDMS pillars showed that pillar displacement occurred in discrete steps of ∼1 nm. In contractile pairs, simultaneous steps of opposing pillars had a total step size of ∼2.2 nm, independent of rigidity. Changes in the stepping patterns on different rigidities indicated that the level of contractile force was critical for sensing pillar stiffness. Importantly, knockdown of tropomyosin-1 caused larger steps and increased forces that resulted in aberrant rigidity sensing. This indicates that the process of cell-matrix adhesion formation involves multiple, sequential steps with if-then decisions based upon the physical as well as biochemical properties of the matrix.

Proton Mediated Conformational Changes in ACID Sensing Ion Channel1a

Acid sensing ion channels (ASIC) are cation channels, activated when there is a reduction in pH. They are involved in key functions including nociception, synaptic transmission and in the physiopathology of ischemic stroke. Previous crystal structures show a trimeric receptor, with each monomer having a large extracellular domain, shaped like a hand, with finger, palm and thumb domains which in turn connect to the transmembrane segments. Available structures indicate that there are three pairs of aspartate and glutamate residues located in the extracellular region, lining the thumb and finger domains. Previous studies have shown that mutating one or two pairs of the carboxylates leads to a shift in EC50 but not a loss in function, suggesting additional residues are involved in proton sensing. Our results from simulation studies indicate that neutralizing these two pairs alone is not sufficient to reduce the electrostatic potential. However, neutralizing all three pairs of carboxylates eliminates much of the negative electrostatic potential in this region, indicating the role of all three pairs in proton binding and gating of the ion channel. Electrophysiological studies with the triple mutant shows a loss of function, while surface biotinylation and pull down assays show expression of the receptors at the surface. To test the pH mediated structural changes and also the role of these residues in the same, we used Luminescence Resonance Energy Transfer to study the angstrom level changes that occur upon pH reduction from 8 to 6. We see that there is a cleft closure conformational change that occurs between the finger and thumb domain. This motion is lost in the triple carboxylate mutant protein, thus confirming that these residues play an important role in proton mediated conformational change in the receptor and ultimately gating of the receptor.

The Intersection of Interfacial Forces and Electrochemical Reactions

We review recent developments in experimental techniques that simultaneously combine measurements of the interaction forces or energies between two extended surfaces immersed in electrolyte solutions-primarily aqueous-with simultaneous monitoring of their (electro)chemical reactions and controlling the electrochemical surface potential of at least one of the surfaces. Combination of these complementary techniques allows for simultaneous real time monitoring of angstrom level changes in surface thickness and roughness, surface-surface interaction energies, and charge and mass transferred via electrochemical reactions, dissolution, and adsorption, and/or charging of electric double layers. These techniques employ the surface forces apparatus (SFA) combined with various "electrochemical attachments" for in situ measurements of various physical and (electro)chemical properties (e.g., cyclic voltammetry), optical imaging, and electric potentials and currents generated naturally during an interaction, as well as when electric fields (potential differences) are applied between the surfaces and/or solution-in some cases allowing for the chemical reaction equation to be unambiguously determined. We discuss how the physical interactions between two different surfaces when brought close to each other (<10 nm) can affect their chemistry, and suggest further extensions of these techniques to biological systems and simultaneous in situ spectroscopic measurements for chemical analysis.

Can Electron Tunneling Occur in a Hundred-Nanometer Thick Nafion Film and be Utilized to Image Nafion/Electrode Interfaces With An Angstrom Level Resolution?

not Available.

Formation and asymmetric catalysis of C- and 8-shaped titania tubes

Two trans-1,2-diaminocyclohexane-derived chiral cationic gelators were synthesized, each of which could self-assemble into ribbons in n-propanol. Titania tubes resembling the letter ‘C’ and the numeral ‘8’ in the nano- and micro-size range were prepared using the self-assemblies of the gelators as the templates through a sol–gel transcription approach. Field emission electron microscopy images indicated the C- and 8-shaped titania tubes were formed by the adsorption of titania nanoparticles on the edges of the organic nanoribbons. The titania tubes were found to be applicable as asymmetric catalysts. We infer that gelator chirality is imparted on the titania surface at the angstrom level.

Nanofiber Near-Field Light–Matter Interactions for Enhanced Detection of Molecular Level Displacements and Dynamics

We experimentally demonstrate that plasmonic nanoparticles embedded in the evanescent field of subwavelength optical waveguides (WGs) are highly sensitive to distances normal to the propagation of light, showing an ~10× increase in spatial resolution compared to the optical field decay of the WG. The scattering cross-section of the Au nanoparticle is increased by the plasmon-dielectric coupling interaction when the nanoparticle is placed near the dielectric surface of the WG, and the decay of the scattering signal is enhanced, showing angstrom level distance sensitivity within 10 nm from the WG. Numerical studies with the finite-difference time-domain (FDTD) method correlate well with the experimental results. To demonstrate real-time monitoring of a single molecule stretching in the evanescent field, we linked individual single-stranded DNA molecules between the WG and plasmonic nanoparticles and pushed on the nanoparticles with fluidic forces. The simple design and ease of obtaining optical feedback on molecular displacements makes our approach ideal for new in situ force sensing devices, imaging technologies, and high-throughput molecular analysis.

Development of Alkaline Solvent Stripper for Wafer Level Package

In this paper, the advantage and limitation of different alkali photoresist stripper is reviewed. Different from traditional dry film stripper, tetramethyl ammonium hydroxide is adopted to replace potassium hydoxide as an etchant to prevent precipitation. In details, the substrate protection, such as Al, Cu, Ag and Sn, is studied, and angstrom level etch rate is received with the carefully-designed inhibitor system; Secondly, the effective photoresist removal performance is acheived with the components balance; In the end, the cleaning mechanism and capability of this novel photoresist removal stripper are disclosed.

Chirality of the 1,4-phenylene–silica nanoribbons at the nano and angstrom levels

We reported the preparation of chiral 1,4-phenylene–silicas, using a sol–gel transcription approach, by self-assembly using low-molecular-weight gelators as templates. The silicas exhibited chirality at both the nano and angstrom levels. However, the relation between the chirality at the nano level and that at the angstrom levels has not been well studied. In this study, chiral 1,4-phenylene–silica nanoribbons were prepared by the self-assemblies of three chiral cationic gelators derived from amino acids as templates. These samples were characterized using field-emission scanning electron microscopy, transmission electron microscopy, x-ray diffraction, and circular dichroism. The results indicated that the handedness of the nanoribbons and the stacking of the aromatic rings were controllable. Although the nanoribbons exhibited left-handedness at the nano level, the stacking of the aromatic rings could exhibit left- or right-handedness. The handedness of the nanoribbons at the nano level was controlled by the organic self-assembly of the gelator. However, the stacking of the aromatic rings seemed to be controlled by the gelator itself.

Nanopore DNA sequencing inches closer to commercial debut

Developers of a promising single-molecule detection technique hope to accomplish in hours what took the Human Genome Project several years.

P53 Mdm2 Inhibitors

The protein-protein interaction (PPI) between p53 and its negative regulator MDM2 comprises one of the most important and intensely studied PPI's involved in preventing the initiation of cancer. The interaction between p53 and MDM2 is conformation-based and is tightly regulated on multiple levels. Due to the Angstrom level structural insight there is a reasonable understanding of the structural requirements needed for a molecule to bind to MDM2 and successfully inhibit the p53/MDM2 interaction. The current review summarizes the binding characteristics of the different disclosed small molecules for inhibition of MDM2 with a co-crystal structure. Synthetic access to these compounds as well as their derivatives are described in detail.

High-efficiency x-ray gratings with asymmetric-cut multilayers

We present the fabrication and analysis of efficient and highly dispersive gratings for the x-ray and extreme ultraviolet (EUV) regime. We show that an asymmetric-cut multilayer structure can act as a near-perfect blazed grating. The precision and high line density are achieved by layer deposition of materials, which can be controlled to the angstrom level. We demonstrate this in the EUV regime with two structures made by cutting and polishing magnetron-sputtered multilayer mirrors of over 2000 bilayers thick, each with a period of 6.88 nm. These were cut at angles of 2.9° and 7.8° to the surface. Within the 3% bandwidth rocking curve of the multilayer, the angular dispersion of the diffracted wave was in agreement with the grating equation for elements with 7250 and 19,700 line pairs/mm, respectively. The dependence of the measured efficiency was in excellent agreement with a formulation of dynamical diffraction theory for multilayered structures. At a wavelength of 13.2 nm, the efficiency of the first-order diffraction was over 95% of the reflectivity of the uncut multilayer. We predict that such structures should also be effective at shorter x-ray wavelengths. Both the Laue (transmitting) and Bragg (reflecting) geometries are incorporated in our formalism, which is applied to the analysis of multilayer Laue lenses and focusing and dispersing Bragg optics.