AFM Research Papers - Academia.edu (original) (raw)

We investigated the mechanism of enzyme immobilization on silanized surfaces through coupling agents (cross-linkers) in order to understand the role of these molecules on interfacial processes and their eff ect on catalytic activity. To... more

We investigated the mechanism of enzyme immobilization on silanized surfaces through coupling agents (cross-linkers) in order to understand the role of these molecules on interfacial processes and their eff ect on catalytic activity. To this end, we used a model multimeric enzyme (G6PDH) and several cross-linking molecules with diff erent chemical properties, including the nature of the end-group (-NCO, -NCS, -CHO), the connecting chain (aliphatic vs aromatic), and geometrical constraints (meta vs paradisubstituted aromatics). There did not seem to be radical diff erences in the mechanism of enzyme adsorption according to the linker used as judged from QCM-D, except that in the case of DIC (1,4-phenylene diisocyanate) the adsorption occurred more rapidly. In contrast, the nature of the cross-linker exerted a strong infl uence on the amount of enzyme immobilized as estimated from XPS, and more unexpectedly on the stability of the underlying silane layer. DIC, PDC (1,4-phenylene diisothiocyanate), or GA (glutaraldehyde) allowed successful enzyme immobilization. When the geometry of the linker was changed from 1,4-phenylene diisothiocyanate to 1,3-phenylene diisothiocyanate (MDC), the silane layer was subjected to degradation, upon enzyme adsorption, and the amount of immobilized molecules was signifi cantly lowered. TE (terephtalaldehyde) and direct enzyme deposition without cross-linker were similar to MDC. The organization of immobilized enzymes also depended on the immobilization procedure, as diff erent degrees of aggregation were observed by AFM. A correlation between the size of the aggregates and the catalytic properties of the enzyme was established, suggesting that aggregation may enhance the thermostability of the multimeric enzyme, probably through a compaction of the 3D structure.

The aim of this work is to produce and investigate silver polymer nanocomposites formed by electron beam evaporation on PMMA-PET structure. It is demonstrated that the surface plasmon resonance (SPR) absorption peak of nanostructured... more

The aim of this work is to produce and investigate silver polymer nanocomposites formed by electron beam evaporation on PMMA-PET structure. It is demonstrated that the surface plasmon resonance (SPR) absorption peak of nanostructured silver is near 425 nm and shifts to the longer waves (up to 600 nm) and corresponding band broadening with increase of silver film thickness. The different ultrathin silver-polymer nanocomposites color filters as a result of plasmon resonance shifting in the UV-VIS wavelength region were produced. The developed method provided a simple and practical solution to create silver nanostructures in polymer matrix. Keywords: polymethylmethacrylate (PMMA), polyethylene terephthalate (PET), silver, nanocomposites, plasmonic optic, AFM.

This paper reports on the wettability and aging behaviors of the silicon wafers that had been cleaned using a piranha (3:1 mixture of sulfuric acid (H 2 SO 4 , 96%) and hydrogen peroxide (H 2 O 2 , 30%), 120 1C), SC1 (1:1:5 mixture of NH... more

This paper reports on the wettability and aging behaviors of the silicon wafers that had been cleaned using a piranha (3:1 mixture of sulfuric acid (H 2 SO 4 , 96%) and hydrogen peroxide (H 2 O 2 , 30%), 120 1C), SC1 (1:1:5 mixture of NH 4 OH, H 2 O 2 and H 2 O, at 80 1C) or HF solution (6 parts of 40% NH 4 F and 1 part of 49% HF, at room temperature) solution, and treated with gaseous plasma. The silicon wafers cleaned using the piranha or SC1 solution were hydrophilic, and the water contact angles on the surfaces would increase along with aging time, until they reached the saturated points of around 701. The contact angle increase rate of these wafers in a vacuum was much faster than that in the open air, because of loss of water, which was physically adsorbed on the wafer surfaces. The silicon wafers cleaned with the HF solution were hydrophobic. Their contact angle decreased in the atmosphere, while it increased in the vacuum up to 951. Gold thin films deposited on the hydrophilic wafers were smoother than that deposited on the hydrophobic wafers, because the numerous oxygen groups formed on the hydrophilic surfaces would react with gold adatoms in the sputtering process to form a continuous thin film at the nucleation stage. The argon, nitrogen, oxygen gas plasma treatments could change the silicon wafer surfaces from hydrophobic to hydrophilic by creating a thin (around 2.5 nm) silicon dioxide film, which could be utilized to improve the roughness and adhesion of the gold thin film.

ÖZET Bu araştırma atom altı parçacıkların görüntülenmesinde kullanılan teknolojilerden olan AFM(Atomik force microscope) ve SEM(Scanning electron microscope) incelenmiştir. Bu inceleme mikroskopların nasıl çalıştığı, çalışma sırasında... more

ÖZET Bu araştırma atom altı parçacıkların görüntülenmesinde kullanılan teknolojilerden olan AFM(Atomik force microscope) ve SEM(Scanning electron microscope) incelenmiştir. Bu inceleme mikroskopların nasıl çalıştığı, çalışma sırasında kullanılan materyaller ve çalışma sonunda ne gibi bilgiler verdikleri yönündedir. Her bir mikroskobun kendine göre avantaj ve dezavantajları irdelenip çalışma içerisinde paylaşılmıştır. Mikroskopların kullanım alanları ve hangi araştırmalarda tercih edildikleri bu çalışmada yer almaktadır. Mikroskopların çalışma aksamları ve özelliklerin incelenmiştir. Aynı zamanda mikroskoplar kendi aralarında karşılaştırılmıştır. Mikroskoplar hakkındaki teorik bilgiyi giriş bölümünde, uygulama alanları ve karşılaştırmaları ise AFM&SEM ve SONUÇ bölümünde bulabilirsiniz.

Keywords: Genetically modified organism (GMO) Soybean Polycarbonate (PC) microdevice Surface hydrophilic/hydrophobic modification Flow-through polymerase chain reaction (PCR) 35S promoter bar gene a b s t r a c t In this study, a... more

Keywords: Genetically modified organism (GMO) Soybean Polycarbonate (PC) microdevice Surface hydrophilic/hydrophobic modification Flow-through polymerase chain reaction (PCR) 35S promoter bar gene a b s t r a c t In this study, a polycarbonate (PC) microdevice functioning as a reactor for the polymerase chain reaction (PCR) was fabricated for rapid identification of genetically modified organisms (GMOs). The PC micro-device was fabricated by first modifying its surface with an amine-functionalized alkoxysilane, namely bis[3-(trimethoxysilyl)propyl]amine (bis-TPA), to obtain a hydrophilic surface. Coating of bis-TPA on PC was realized by forming a urethane linkage between the amine terminals of the bis-TPA with the car-bonate backbone of PC by aminolysis. This surface enabled the thermal bonding of two PC substrates at a relatively low temperature and atmospheric pressure, thereby maintaining the structure of the micro-channel in high resolution. Next, the surface of the microchannel was further treated with a fluorosilane, namely tridecafluoro-(1,1,2,2-tetrahydrooctyl)-triethoxysilane (FTES), to obtain a hydrophobic surface inside the microchannel. This modification was realized by the hydrolysis and subsequent condensation of the alkoxy terminals of both bis-TPA and FTES to form a robust siloxane (SieOeSi) bond. The hy-drophobic microchannel improved the PCR performance by stabilizing the fluid flow, particularly under heated conditions, when the flow-through PCR was conducted on a microdevice. Using the microdevice, the 35S promoter sequences and bar gene, which are commonly used for the identification of GMOs, were successfully amplified, resulting in the detection of 234 and 504 bp gene fragments for the 35S promoter sequences and 261 bp gene fragment for the bar gene from the genomic DNA extracted from the leaves of GM soybean. This process took approximately 30e35 min, which was approximately 3-fold faster than when using a conventional thermal cycler.

AFM salah satu metoda karakterisasi dari keluarga SPM (Scanning Probe Microscopy) bekerja pada bagian permukaan bahan dengan melibatkan interaksi antara probe dan permukaan bahan melalui proses fisis tertentu. Interaksi ini kemudian dapat... more

AFM salah satu metoda karakterisasi dari keluarga SPM (Scanning Probe Microscopy) bekerja pada bagian permukaan bahan dengan melibatkan interaksi antara probe dan permukaan bahan melalui proses fisis tertentu. Interaksi ini kemudian dapat men-generate citra permukaan bahan pada skala mikroskopik, sehingga susunan partikel pada permukaan bahan dapat terlihat dengan jelas. Berbeda dengan microscopy lainnya, metoda karakterisasi ini hanya melibatkan gaya yang terjadi antara tip dan sampel. Gaya yang terjadi bisa berupa gaya tarikan atau dorongan. Setiap gaya akan mengakibatkan pembengkokan tertentu pada bagian cantilever dimana akan terdeteksi oleh berkas laser dan kemudian ditangkap oleh detektor yang kemudian akan dicitrakan menjadi sebuah image yang bernilai.

Nanotechnology, which deals with features as small as a 1 billionth of a meter, began to enter into mainstream physical sciences and engineering some 20 years ago. Recent applications of nanoscience include the use of nanoscale materials... more

Nanotechnology, which deals with features as small as a 1 billionth of a meter, began to enter into mainstream physical sciences and engineering some 20 years ago. Recent applications of nanoscience include the use of nanoscale materials in electronics, catalysis, and biomedical research. Among these applications, strong interest has been shown to biological processes such as blood coagulation control and multimodal bioimaging, which has brought about a new and exciting research field called nanobiotechnology. Biotechnology, which itself also dates back ∼30 years, involves the manipulation of macroscopic biological systems such as cells and mice in order to understand why and how molecular level mechanisms affect specific biological functions, e.g., the role of APP (amyloid precursor protein) in Alzheimer’s disease (AD). This review aims (1) to introduce key concepts and materials from nanotechnology to a non-physical sciences community; (2) to introduce several state-of-the-art examples of current nanotechnology that were either constructed for use in biological systems or that can, in time, be utilized for biomedical research; (3) to provide recent excerpts in nanotoxicology and multifunctional nanoparticle systems (MFNPSs); and (4) to propose areas in neuroscience that may benefit from research at the interface of neurobiologically important systems and nanostructured materials.

A systematic approach is required in order to determine the frictional characteristics of a contacting pair in the presence of a tribofilm. Despite the clear benefits in functionality and in reducing wear, the generation of ZDDP-based... more

A systematic approach is required in order to determine the frictional characteristics of a contacting pair in the presence of a tribofilm. Despite the clear benefits in functionality and in reducing wear, the generation of ZDDP-based tribofilms often lead to increased frictional losses. Such an increase is also observed in the tribometric tests reported here, as well as in open literature. This paper investigates the underlying mechanics for the rise in friction using an integrated methodology, based upon Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS). The use of an analytical contact mechanics model demonstrates that the pressure coefficient of boundary shear strength, measured using lateral force microscopy, provides an explanation for the observed increase in measured friction at micro-scale.

The effect of surface roughness and shape factor on behavior of particles in flotation has been investigated. Surface roughness of various degrees was applied on spherical glass beads of -150 +106 µm by means of acid etching. The same... more

The effect of surface roughness and shape factor on behavior of particles in flotation has been investigated. Surface roughness of various degrees was applied on spherical glass beads of -150 +106 µm by means of acid etching. The same procedure was also performed on ground glass beads of the same size interval with different shape factors. The effect of these variations on surface morphology of particles was investigated in terms of flotation recovery, contact angle, and bubble-particle attachment. An Atomic Force Microscope (AFM) was used for surface roughness characterizations and a correction methodology on roughness measurements of spherical particles is proposed. A digital image analyzer was used for shape factor characterizations. It is shown that increase in surface roughness improves the flotation recovery, contact angle, and bubble attachment. Shape factor, however, was found to be more predominant in flotation and bubble attachment. This is attributed to the effect of sharp edges of ground particles which triggers the film rupture process and shortens the attachment time.

Uno strumento che operi a livello macroscopico con tecniche analoghe a quelle usate nell'indagine a livello microscopico. Potrebbe sembrare inutile produrre con questa tecnica l'immagine di un oggetto che già si vede bene ad occhio nudo;... more

Uno strumento che operi a livello macroscopico con tecniche analoghe a quelle usate nell'indagine a livello microscopico. Potrebbe sembrare inutile produrre con questa tecnica l'immagine di un oggetto che già si vede bene ad occhio nudo; dal punto di vista didattico, invece, è proprio la possibilità che si offre allo stu-dente di confrontare l'immagine "naturale" con quella ricostruita, e di poter seguire il processo di ricostruzione passo passo che ci sembra possa aiu-tare lo studente a comprendere la natura diversa delle due immagini.
Lo strumento descritto in questo articolo, e che abbiamo battezzato "macroscopio", deriva direttamente dalla tecnologia dei profilometri a stilo. Diversamente però dai normali profilometri, che lavorano in una sola dimensione e forniscono cioè il profilo del campione in esame lungo una linea, questo strumento esegue la scansione di una superficie, con una operazione di spostamento del sensore lungo una serie di linee parallele, analoga a quella utilizzata per acquisire immagini a matri-ci di punti.

The influence of polyethylene terephthalate (PET) substrate surface roughness on the structure and optical properties of coated ZnO thin-film have been studied using scanning probe microscope (SPM), scanning electron microscopy (SEM) and... more

The influence of polyethylene terephthalate (PET) substrate surface roughness on the structure and optical properties of coated ZnO thin-film have been studied using scanning probe microscope (SPM), scanning electron microscopy (SEM) and UV-vis spectrophotometer. The PET substrate was chemically treated using alkaline hydrolysis by sodium hydroxide aqueous solution to stimulate the surface roughness. The surface roughness of PET substrate has been measured as a function of treatment time, temperature and concentration of NaOH using SPM. As a result, the surface roughness increases with the treatment time, treatment temperature and treatment concentration. The ZnO thin-film was then spin-coated on a series of chemically treated PET substrates. In addition, the morphology of the coated ZnO thin film on chemically treated PET was also investigated. The SEM results show that the morphology of the coated ZnO thin-film have fiber-like streaks. Besides, UV-vis measurement was performed to investigate the absorbance and transmittance of ZnO thin-film. The optical band gap obtained was in the range of 3.24-3.36 eV. In conclusion, pre-treatment of PET surface is essential to produce desired ZnO thin-film on this particular substrate which would pave the way for the integration of future devices.

Tribofilms are activated using precision sliding strip microscale tribometry with a base and a fully formulated lubricant with a ZDDP anti-wear additive. The employed tribometry uses combined pressure, shear and temperature activation.... more

Tribofilms are activated using precision sliding strip microscale tribometry with a base and a fully formulated lubricant with a ZDDP anti-wear additive. The employed tribometry uses combined pressure, shear and temperature activation. The chemical compositions of the formed tribofilms are ascertained through use of Photo-electron X-ray Spectroscopy (XPS). Nanoscale frictional measurements of the tribofilms are reported using fluid cell lateral force microscopy (LFM). The measured coefficient of interfacial boundary shear strength is used with analytical contact mechanics to relate the in-situ conditions to the activation energy components of the Eyring potential cage model. The paper shows that combined LFM and the Eyring model can explain the variations in the frictional characteristics of formed tribofilms.

Frictional losses are one of the main causes of reduced energy efficiency in all machines and mechanisms. In particular, there is mounting pressure upon manufacturers of all forms of vehicle to comply with increasingly stringent... more

Frictional losses are one of the main causes of reduced energy efficiency in all machines and mechanisms. In particular, there is mounting pressure upon manufacturers of all forms of vehicle to comply with increasingly stringent legislation and directives with regard to harmful emissions. Therefore, reduction of friction has become an imperative issue. The traditional approach of dealing with surface material and lubricant formulation in isolation has been replaced by a lubricant–surface system approach. This paper presents multi-scale experimentation from nano/meso-scale lateral force microscopy of ultra-thin surface adsorbed films through to micro-scale precision sliding tribometry to investigate lubricant–surface friction optimisation within the mixed regime of lubrication, using lubricants with different organic and inorganic friction modifying species. These affect the parameters of the system, commonly used as input to models for mixed and boundary regimes of lubrication. Therefore, the precise measurement of these parameters at different physical scales is important. The study also makes use of detailed numerical predictions at micro-scale through combined solution of the average Reynolds equation as well as interaction of wetted asperities in mixed and boundary regimes of lubrication. Good agreement is found between the predictions and measurements at micro-scale tribometric interactions. Furthermore, the same trends are observed in testing across the physical scales.

Complexes of polyelectrolytes (PECs) are oppositely charged polymers assemblies held together by electrostatic interaction. As the non-covalent assembly of macromolecules/colloids in solution has been thoroughly investigated over the last... more

Complexes of polyelectrolytes (PECs) are oppositely charged polymers assemblies held together by electrostatic interaction. As the non-covalent assembly of macromolecules/colloids in solution has been thoroughly investigated over the last decade with a particular emphasis put on the morphology of the final aggregates as a function of the building blocks-chemistry, the objective of this thesis is to come to a better understanding of the influence of interaction strength between polyelectrolytes on complexes morphologies, as well as kinetics and thermodynamics of the complexation. For this study, weakly and strongly interacting systems given rise to coacervate and precipitate phases has been elected. Those systems have been studied on a wide charge ratio scale (Z[+]/[-]) to span several physical states of the PECs (soluble and colloidal PECs, dense phases). Morphologies of assemblies are assessed by microscopy (optical, fluorescence, atomic force) and scattering techniques (neutron, light). Kinetics and thermodynamics of the complexation process are studied by use of a stopped-flow mixing device and an isothermal titration calorimeter. Results gave us keys to discriminate strongly interacting systems from weakly interacting ones. In particular, the ‘strong systems’ are showed to be non-equilibrium assemblies, ie. the formulation pathway or the way these different macromolecules are coming into contact is then a key step. Another important aspect that could explain the complexation process behavior is the hydration energy of the polyelectrolytes. Calorimetry measurements have been performed for numerous polyelectrolytes and then correlated to complexes properties.

The heteroepitaxial growth of the new ternary, group-IV, semiconductor material, Si1-x-yGexCy on Si(100), has been investigated. The epitaxial quality of Si1-x-yGexCy is found to be inferior to that of Si1-xGex with similar Si/Ge... more

The heteroepitaxial growth of the new ternary, group-IV, semiconductor material, Si1-x-yGexCy on Si(100), has been investigated. The epitaxial quality of Si1-x-yGexCy is found to be inferior to that of Si1-xGex with similar Si/Ge concentration ratio, grown under identical conditions, and the quality deteriorates with increasing C fraction. Also, the surface roughness, as studied by tapping mode atomic force microscopy, increases with increasing C fraction as well as with increasing Ge fraction, suggesting a transition from Frank-van der Merve to Stranski-Krastanov type growth. We suggest that the very large mismatch between the average bond length in the Si1-x-yGexCy material, as determined by Vegard's law, and the equilibrium Si-C bond length, weakens the Si-C bonds and reduces the elastic range of the material, thus lowering the barrier for dislocation and stacking fault formation. The change in elasticity may also be responsible for the change in growth morphology, either directly by a lowered barrier for island formation or indirectly through the formation of defects. A decrease in Ge incorporation in the Si1-x-yGexCy films with increasing C incorporation suggests a repulsive Ge-C interaction. Moreover, we observe a C-rich, Ge-deficient precursor phase to SiC precipitates at a growth temperature of 560 degrees C, whereas at 450 degrees C no such phase can be observed. The temperature dependence of the precursor formation is consistent with C bulk diffusion. Infrared absorption measurements cannot be used to detect the precursor phase. Finally, the onset of epitaxial breakdown is discussed and an accurate and independent determination of the C fraction and its substitutionality is emphasized. (