18th IEEE International Conference on Micro Electro Mechanical Systems, 2005. MEMS 2005., 2005
The success of future molecule -driven actuators most likely lies in the development of artificia... more The success of future molecule -driven actuators most likely lies in the development of artificial molecular motors because of their ability to provide large forces from low voltage inputs while also featuring bistable actuation characteristics and molecular design flexibility. With these advantages in mind, we have developed a mechanical device utilizing the force produced from the relative movement of artificial molecular motors -rotaxanes -in conjunction with a hybrid top-down/bottom-up fabrication approach. This process has produced insight into the promise but also the limitations of molecule-driven actuators which inspires redirected efforts for an eventually optimized new class of multiscale mechanical, optical, and medical devices.
Acid-base switchable supramolecular dendronized polyacetylenes (DPAs) with increasing steric bulk... more Acid-base switchable supramolecular dendronized polyacetylenes (DPAs) with increasing steric bulk on going from generation one [G1] to three [G3], were constructed using multiple self-assembly processes between Fréchet-type [G1]-[G3]-dendritic dialkylammonium salts and a dibenzo[24]crown-8-containing polymer. The formation of the supramolecular systems is acid-base switchable to either an ON (rodlike dendronized polymers) or an OFF (flexible polymers) state. Thus, by controlling the superstructures of the supramolecular polymers with the [G1]-[G3] dendrons, it is possible to induce conformational changes within the polymer backbones. The supramolecular dendronized polymers, as well as their threading-dethreading properties, were characterized by (1)H NMR and UV absorption spectroscopies, gel permeation chromatography (GPC) and light scattering (LS). Independent measures of molecular weight (GPC, LS) indicate that DPAs behave as increasingly rigid macromolecules with each generation in solution. Molecular dynamics simulations of each DPA suggest that the lengths of the polymer backbones increase accordingly. Atomic force microscopy of the [G3]-dendronized polystyrene (DPS), as well as the DPAs, reveal surface morphologies indicative of aggregated superstructures.
Continuous development of atomic force microscopy and its applications is not always supported by... more Continuous development of atomic force microscopy and its applications is not always supported by a rigorous theoretical treatment of the related phenomena. A proper understanding of the behavior of microscopic probes and their response to tip-sample force interactions are crucial for a microscope control, optimization of experimental procedures and rational data analysis in the frameworks of quantitative models. Several issues of the probe dynamics and instrument functionality are addressed with a rigorous theoretical analysis of the thermal tune method, which is presented in this paper. It covers theoretical derivation of the method, development of stable convergent algorithms, different averaging techniques, and implementation with high-speed acquisition or a heterodyne technique for low speed acquisition. The developed thermal tune procedure allows for precise determination of the probe resonant frequency, quality factor and spring constant. It was verified practically with AFM probes operating in different environments. It is also shown that this method is applicable for measurements of the microscope functional parameters such as optical deflection noise and inverse optical sensitivity.
EMC 2008 14th European Microscopy Congress 1–5 September 2008, Aachen, Germany, 2008
Kelvin Force Microscopy (KFM) is a very powerful tool for mapping of surface charges, surface pot... more Kelvin Force Microscopy (KFM) is a very powerful tool for mapping of surface charges, surface potentials, and doping profiles. [1] This technique is implemented in amplitude modulation and frequency modulation Atomic Force Microscopy (AFM) modes. [2] In many applications surface electric properties are measured with two-pass technique in which a “spill over” of topographic response to the probe motion is
A simple and effective means of increasing the morphological detail in AFM phase micrographs of m... more A simple and effective means of increasing the morphological detail in AFM phase micrographs of microphase separated block copolymer films is presented. Effective AFM phase imaging of microphase separated systems hinges upon the existence of appropriate contrast mechanisms such as differences in elasticity between the microphase separated domains. For some systems, AFM phase imaging at room temperature results in low contrast images due to a paucity of differential mechanical behavior between the microphase domains, e.g. at room temperature both species are glassy. Through the use of a heating apparatus custom-designed for AFM, an elastic contrast mechanism can be created in some systems by raising the specimen to a temperature between the glass transitions of the constituent polymer species. This serves to preferentially soften one species with respect to the other, thus enhancing the phase contrast mechanism, which results in micrographs with superior detail. This simple technique is demonstrated using films of a series of polystyrene-b-poly(n-alkyl methacrylate) diblock copolymers and both commercial and custom-built heating stages. By choosing appropriate measurement temperatures, AFM phase contrast could be greatly enhanced, or indeed created, when compared to room temperature images of these specimens. For these materials, contrast enhancement required that the sample be heated roughly 201C above the glass transition of the lower-T g species. r
Two series of segmented polyurethanes having soft segment concentration of 50 and 70 wt%, and dif... more Two series of segmented polyurethanes having soft segment concentration of 50 and 70 wt%, and different concentrations of nanometerdiameter silica were prepared and tested. Atomic force microscopy revealed a strong effect of nanoparticles on the large-scale spherulitic morphology of the hard domains. Addition of silica suppresses fibril formation in spherulites. Filler particles were evenly distributed in the hard and soft phase. Nano-silica affected the melting point of the hard phase only at loadings .30 wt% silica. A single melting peak was observed at higher filler loadings. There is no clear effect of the filler on the glass transition of soft segments. Wide-angle X-ray diffraction showed decreasing crystallinity of the hard domains with increasing filler concentration in samples with 70 wt% soft segment. Ultra smallangle X-ray scattering confirms the existence of nanometer phase-separated domains in the unfilled sample. These domains are disrupted in the presence of nano-silica. The picture that emerges is that nano-silica suppresses short-scale phase separation of the hard and soft segments. Undoubtedly, the formation of fibrils on larger scales is related to short-scale segment segregation, so when the latter is suppressed by the presence of silica, fibril growth is also impeded. q
The results of scanning tunneling microscopy (STM) studies of different conductive organic charge... more The results of scanning tunneling microscopy (STM) studies of different conductive organic charge transfer systems are reviewed. Among the examined compounds are complexes of TCNQ with various donors, related polymeric systems, organic superconductors. Well-resolved STM images were registrated on monocrystal surfaces at large (hundreds of nm) and atomic scales. Interpretation of the atomic scale images and the perspectives of STM applications are discussed.
Tapping-mode atomic force microscopy (AFM), in which the vibrating tip periodically approaches, i... more Tapping-mode atomic force microscopy (AFM), in which the vibrating tip periodically approaches, interacts and retracts from the sample surface, is the most common AFM imaging method. The tip experiences attractive and repulsive forces that depend on the chemical and mechanical properties of the sample, yet conventional AFM tips are limited in their ability to resolve these time-varying forces. We have created a specially designed cantilever tip that allows these interaction forces to be measured with good (sub-microsecond) temporal resolution and material properties to be determined and mapped in detail with nanoscale spatial resolution. Mechanical measurements based on these force waveforms are provided at a rate of 4 kHz. The forces and contact areas encountered in these measurements are orders of magnitude smaller than conventional indentation and AFM-based indentation techniques that typically provide data rates around 1 Hz. We use this tool to quantify and map nanomechanical changes in a binary polymer blend in the vicinity of its glass transition.
appreciable separation between T g and T x . Therefore, even partial densification requires very ... more appreciable separation between T g and T x . Therefore, even partial densification requires very high pressures (more than 500 MPa) to activate dislocation-controlled, crystalline plasticity. In contrast, we have found that suitable kinetic windows do exist in the CaO-Al 2 O 3 , La 2 O 3 -TiO 2 and BaO-TiO 2 systems, which allowed us to perform bulk consolidation of rapidly quenched glass beads in a similar fashion to that for Al 2 O 3 -REO. On the basis of these results we believe that, as for bulk metallic glasses, the present glassforming and consolidation approach is applicable to a large variety of ionic compositions and will open the door to many new bulk oxide glasses and nanocrystalline ceramics.
Established techniques for global gene expression profiling, such as microarrays, face fundamenta... more Established techniques for global gene expression profiling, such as microarrays, face fundamental sensitivity constraints. Due to greatly increasing interest in examining minute samples from micro-dissected tissues, including single cells, unorthodox approaches, including molecular nanotechnologies, are being explored in this application. Here, we examine the use of single molecule, ordered restriction mapping, combined with AFM, to measure gene transcription levels from very low abundance samples. We frame the problem mathematically, using coding theory, and present an analysis of the critical error sources that may serve as a guide to designing future studies. We follow with experiments detailing the construction of high density, single molecule, ordered restriction maps from plasmids and from cDNA molecules, using two different enzymes, a result not previously reported. We discuss these results in the context of our calculations.
Self-organization of individual dendronized poly (phenylacetylene)(PPA) macromolecules on highly ... more Self-organization of individual dendronized poly (phenylacetylene)(PPA) macromolecules on highly oriented pyrolytic graphite (HOPG) is revealed by atomic force microscopy (AFM). The dendronized PPA is composed of amphiphilic, self-assembling dendrons. Individual ...
Scanning force microscopy has been used to reveal the surface topology of the smectic B phase of ... more Scanning force microscopy has been used to reveal the surface topology of the smectic B phase of (styreneisoprene) diblock copolymers that have semifluorinated (SF) alkane mesogens attached as three-arm monodendrons to the isoprene backbone. On the largest length scales, the block copolymers microphase separate into well-known diblock copolymer microstructures and evidence of these can been seen in the surface topology. However, there are periodic surface structures, so-called domes (with periodicities of about 18.5 nm), that arise solely from the arrangement of the SF mesogens at the polymer surface. These domes are intrinsically independent of the much larger morphology of the block copolymer. Very long range (ca. micrometers) ordering of the domes is possible for lamellar block copolymer microstructures if the surfaces are prepared by very slow cooling from the isotropic to the smectic B phase. We infer that the domes arise because of spontaneous surface curvature resulting from mesogen crowding within the monodendrons.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2009
The uncertainty of the shape of the tip is a significant source of error in atomic force microsco... more The uncertainty of the shape of the tip is a significant source of error in atomic force microscopy (AFM) based quantitative nanomechanical measurements. Using transmission electron microscopy, scanning electron microscopy, or tip reconstruction images, it is possible to ...
Acid-base switchable supramolecular dendronized polyacetylenes (DPAs) with increasing steric bulk... more Acid-base switchable supramolecular dendronized polyacetylenes (DPAs) with increasing steric bulk on going from generation one [G1] to three [G3], were constructed using multiple self-assembly processes between Fréchet-type [G1]-[G3]-dendritic dialkylammonium salts and a dibenzo[24]crown-8-containing polymer. The formation of the supramolecular systems is acid-base switchable to either an ON (rodlike dendronized polymers) or an OFF (flexible polymers) state. Thus, by controlling the superstructures of the supramolecular polymers with the [G1]-[G3] dendrons, it is possible to induce conformational changes within the polymer backbones. The supramolecular dendronized polymers, as well as their threading-dethreading properties, were characterized by (1)H NMR and UV absorption spectroscopies, gel permeation chromatography (GPC) and light scattering (LS). Independent measures of molecular weight (GPC, LS) indicate that DPAs behave as increasingly rigid macromolecules with each generation in solution. Molecular dynamics simulations of each DPA suggest that the lengths of the polymer backbones increase accordingly. Atomic force microscopy of the [G3]-dendronized polystyrene (DPS), as well as the DPAs, reveal surface morphologies indicative of aggregated superstructures.
18th IEEE International Conference on Micro Electro Mechanical Systems, 2005. MEMS 2005., 2005
The success of future molecule -driven actuators most likely lies in the development of artificia... more The success of future molecule -driven actuators most likely lies in the development of artificial molecular motors because of their ability to provide large forces from low voltage inputs while also featuring bistable actuation characteristics and molecular design flexibility. With these advantages in mind, we have developed a mechanical device utilizing the force produced from the relative movement of artificial molecular motors -rotaxanes -in conjunction with a hybrid top-down/bottom-up fabrication approach. This process has produced insight into the promise but also the limitations of molecule-driven actuators which inspires redirected efforts for an eventually optimized new class of multiscale mechanical, optical, and medical devices.
Acid-base switchable supramolecular dendronized polyacetylenes (DPAs) with increasing steric bulk... more Acid-base switchable supramolecular dendronized polyacetylenes (DPAs) with increasing steric bulk on going from generation one [G1] to three [G3], were constructed using multiple self-assembly processes between Fréchet-type [G1]-[G3]-dendritic dialkylammonium salts and a dibenzo[24]crown-8-containing polymer. The formation of the supramolecular systems is acid-base switchable to either an ON (rodlike dendronized polymers) or an OFF (flexible polymers) state. Thus, by controlling the superstructures of the supramolecular polymers with the [G1]-[G3] dendrons, it is possible to induce conformational changes within the polymer backbones. The supramolecular dendronized polymers, as well as their threading-dethreading properties, were characterized by (1)H NMR and UV absorption spectroscopies, gel permeation chromatography (GPC) and light scattering (LS). Independent measures of molecular weight (GPC, LS) indicate that DPAs behave as increasingly rigid macromolecules with each generation in solution. Molecular dynamics simulations of each DPA suggest that the lengths of the polymer backbones increase accordingly. Atomic force microscopy of the [G3]-dendronized polystyrene (DPS), as well as the DPAs, reveal surface morphologies indicative of aggregated superstructures.
Continuous development of atomic force microscopy and its applications is not always supported by... more Continuous development of atomic force microscopy and its applications is not always supported by a rigorous theoretical treatment of the related phenomena. A proper understanding of the behavior of microscopic probes and their response to tip-sample force interactions are crucial for a microscope control, optimization of experimental procedures and rational data analysis in the frameworks of quantitative models. Several issues of the probe dynamics and instrument functionality are addressed with a rigorous theoretical analysis of the thermal tune method, which is presented in this paper. It covers theoretical derivation of the method, development of stable convergent algorithms, different averaging techniques, and implementation with high-speed acquisition or a heterodyne technique for low speed acquisition. The developed thermal tune procedure allows for precise determination of the probe resonant frequency, quality factor and spring constant. It was verified practically with AFM probes operating in different environments. It is also shown that this method is applicable for measurements of the microscope functional parameters such as optical deflection noise and inverse optical sensitivity.
EMC 2008 14th European Microscopy Congress 1–5 September 2008, Aachen, Germany, 2008
Kelvin Force Microscopy (KFM) is a very powerful tool for mapping of surface charges, surface pot... more Kelvin Force Microscopy (KFM) is a very powerful tool for mapping of surface charges, surface potentials, and doping profiles. [1] This technique is implemented in amplitude modulation and frequency modulation Atomic Force Microscopy (AFM) modes. [2] In many applications surface electric properties are measured with two-pass technique in which a “spill over” of topographic response to the probe motion is
A simple and effective means of increasing the morphological detail in AFM phase micrographs of m... more A simple and effective means of increasing the morphological detail in AFM phase micrographs of microphase separated block copolymer films is presented. Effective AFM phase imaging of microphase separated systems hinges upon the existence of appropriate contrast mechanisms such as differences in elasticity between the microphase separated domains. For some systems, AFM phase imaging at room temperature results in low contrast images due to a paucity of differential mechanical behavior between the microphase domains, e.g. at room temperature both species are glassy. Through the use of a heating apparatus custom-designed for AFM, an elastic contrast mechanism can be created in some systems by raising the specimen to a temperature between the glass transitions of the constituent polymer species. This serves to preferentially soften one species with respect to the other, thus enhancing the phase contrast mechanism, which results in micrographs with superior detail. This simple technique is demonstrated using films of a series of polystyrene-b-poly(n-alkyl methacrylate) diblock copolymers and both commercial and custom-built heating stages. By choosing appropriate measurement temperatures, AFM phase contrast could be greatly enhanced, or indeed created, when compared to room temperature images of these specimens. For these materials, contrast enhancement required that the sample be heated roughly 201C above the glass transition of the lower-T g species. r
Two series of segmented polyurethanes having soft segment concentration of 50 and 70 wt%, and dif... more Two series of segmented polyurethanes having soft segment concentration of 50 and 70 wt%, and different concentrations of nanometerdiameter silica were prepared and tested. Atomic force microscopy revealed a strong effect of nanoparticles on the large-scale spherulitic morphology of the hard domains. Addition of silica suppresses fibril formation in spherulites. Filler particles were evenly distributed in the hard and soft phase. Nano-silica affected the melting point of the hard phase only at loadings .30 wt% silica. A single melting peak was observed at higher filler loadings. There is no clear effect of the filler on the glass transition of soft segments. Wide-angle X-ray diffraction showed decreasing crystallinity of the hard domains with increasing filler concentration in samples with 70 wt% soft segment. Ultra smallangle X-ray scattering confirms the existence of nanometer phase-separated domains in the unfilled sample. These domains are disrupted in the presence of nano-silica. The picture that emerges is that nano-silica suppresses short-scale phase separation of the hard and soft segments. Undoubtedly, the formation of fibrils on larger scales is related to short-scale segment segregation, so when the latter is suppressed by the presence of silica, fibril growth is also impeded. q
The results of scanning tunneling microscopy (STM) studies of different conductive organic charge... more The results of scanning tunneling microscopy (STM) studies of different conductive organic charge transfer systems are reviewed. Among the examined compounds are complexes of TCNQ with various donors, related polymeric systems, organic superconductors. Well-resolved STM images were registrated on monocrystal surfaces at large (hundreds of nm) and atomic scales. Interpretation of the atomic scale images and the perspectives of STM applications are discussed.
Tapping-mode atomic force microscopy (AFM), in which the vibrating tip periodically approaches, i... more Tapping-mode atomic force microscopy (AFM), in which the vibrating tip periodically approaches, interacts and retracts from the sample surface, is the most common AFM imaging method. The tip experiences attractive and repulsive forces that depend on the chemical and mechanical properties of the sample, yet conventional AFM tips are limited in their ability to resolve these time-varying forces. We have created a specially designed cantilever tip that allows these interaction forces to be measured with good (sub-microsecond) temporal resolution and material properties to be determined and mapped in detail with nanoscale spatial resolution. Mechanical measurements based on these force waveforms are provided at a rate of 4 kHz. The forces and contact areas encountered in these measurements are orders of magnitude smaller than conventional indentation and AFM-based indentation techniques that typically provide data rates around 1 Hz. We use this tool to quantify and map nanomechanical changes in a binary polymer blend in the vicinity of its glass transition.
appreciable separation between T g and T x . Therefore, even partial densification requires very ... more appreciable separation between T g and T x . Therefore, even partial densification requires very high pressures (more than 500 MPa) to activate dislocation-controlled, crystalline plasticity. In contrast, we have found that suitable kinetic windows do exist in the CaO-Al 2 O 3 , La 2 O 3 -TiO 2 and BaO-TiO 2 systems, which allowed us to perform bulk consolidation of rapidly quenched glass beads in a similar fashion to that for Al 2 O 3 -REO. On the basis of these results we believe that, as for bulk metallic glasses, the present glassforming and consolidation approach is applicable to a large variety of ionic compositions and will open the door to many new bulk oxide glasses and nanocrystalline ceramics.
Established techniques for global gene expression profiling, such as microarrays, face fundamenta... more Established techniques for global gene expression profiling, such as microarrays, face fundamental sensitivity constraints. Due to greatly increasing interest in examining minute samples from micro-dissected tissues, including single cells, unorthodox approaches, including molecular nanotechnologies, are being explored in this application. Here, we examine the use of single molecule, ordered restriction mapping, combined with AFM, to measure gene transcription levels from very low abundance samples. We frame the problem mathematically, using coding theory, and present an analysis of the critical error sources that may serve as a guide to designing future studies. We follow with experiments detailing the construction of high density, single molecule, ordered restriction maps from plasmids and from cDNA molecules, using two different enzymes, a result not previously reported. We discuss these results in the context of our calculations.
Self-organization of individual dendronized poly (phenylacetylene)(PPA) macromolecules on highly ... more Self-organization of individual dendronized poly (phenylacetylene)(PPA) macromolecules on highly oriented pyrolytic graphite (HOPG) is revealed by atomic force microscopy (AFM). The dendronized PPA is composed of amphiphilic, self-assembling dendrons. Individual ...
Scanning force microscopy has been used to reveal the surface topology of the smectic B phase of ... more Scanning force microscopy has been used to reveal the surface topology of the smectic B phase of (styreneisoprene) diblock copolymers that have semifluorinated (SF) alkane mesogens attached as three-arm monodendrons to the isoprene backbone. On the largest length scales, the block copolymers microphase separate into well-known diblock copolymer microstructures and evidence of these can been seen in the surface topology. However, there are periodic surface structures, so-called domes (with periodicities of about 18.5 nm), that arise solely from the arrangement of the SF mesogens at the polymer surface. These domes are intrinsically independent of the much larger morphology of the block copolymer. Very long range (ca. micrometers) ordering of the domes is possible for lamellar block copolymer microstructures if the surfaces are prepared by very slow cooling from the isotropic to the smectic B phase. We infer that the domes arise because of spontaneous surface curvature resulting from mesogen crowding within the monodendrons.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2009
The uncertainty of the shape of the tip is a significant source of error in atomic force microsco... more The uncertainty of the shape of the tip is a significant source of error in atomic force microscopy (AFM) based quantitative nanomechanical measurements. Using transmission electron microscopy, scanning electron microscopy, or tip reconstruction images, it is possible to ...
Acid-base switchable supramolecular dendronized polyacetylenes (DPAs) with increasing steric bulk... more Acid-base switchable supramolecular dendronized polyacetylenes (DPAs) with increasing steric bulk on going from generation one [G1] to three [G3], were constructed using multiple self-assembly processes between Fréchet-type [G1]-[G3]-dendritic dialkylammonium salts and a dibenzo[24]crown-8-containing polymer. The formation of the supramolecular systems is acid-base switchable to either an ON (rodlike dendronized polymers) or an OFF (flexible polymers) state. Thus, by controlling the superstructures of the supramolecular polymers with the [G1]-[G3] dendrons, it is possible to induce conformational changes within the polymer backbones. The supramolecular dendronized polymers, as well as their threading-dethreading properties, were characterized by (1)H NMR and UV absorption spectroscopies, gel permeation chromatography (GPC) and light scattering (LS). Independent measures of molecular weight (GPC, LS) indicate that DPAs behave as increasingly rigid macromolecules with each generation in solution. Molecular dynamics simulations of each DPA suggest that the lengths of the polymer backbones increase accordingly. Atomic force microscopy of the [G3]-dendronized polystyrene (DPS), as well as the DPAs, reveal surface morphologies indicative of aggregated superstructures.
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Papers by Sergei Magonov