Browsing by Subject "Optical microscopy"

Now showing 1 - 11 of 11

Open Access
Acoustic microscopy with mechanical scanning—A review
(IEEE, 1979-08) Quate, C. F.; Atalar, Abdullah; Wickramasinghe, H. K.
Acoustic waves in liquids are known to have wavelengths comparable to that of visible light if the frequency is in the gigahertz range. The phenomena of Brillouin scattering in liquids is based on such waves. In helium near 2 K acoustic waves with a wavelength of 2000 Å were studied some ten years ago at UCLA. It follows from these observations that an imaging system based on acoustic radiation with a resolving power competitive with the optical microscope is within reach if an ideal lens free from aberrations could be found. Such a lens, which was so elusive at the beginning, is now a simple device and it is the basic component in the acoustic microscope that forms the basis for this review. In this article we will establish the characteristic properties of this new instrument. We will review some of the simple properties of acoustic waves and show how a single spherical surface formed at a solid liquid interface can serve as this ideal lens free from aberrations and capable of producing diffraction limited beams. When this is incorporated into a mechanical scanning system and excited with acoustic frequencies in the microwave range images can be recorded with acoustic wavelengths equal to the wavelength of visible light. We will present images that show the elastic properties of specimens selected from the fields of material science, integrated circuits, and cell biology. The information content in these images will often exceed that of the optical micrographs. In the reflection mode we illuminate the smooth surface of a crystalline material with a highly convergent acoustic beam. The reflected field is perturbed in a unique way that is determined by the elastic properties of the reflecting surface and it shows up in the phase of the reflected acoustic field. There is a distinct and characteristic response at the output when the spacing between the object and the lens is varied. This behavior in the acoustic ieflection microscope provides a rather simple and direct means for monitoring the elastic parameters of a solid surface. It is easy to distinguish between different materials, to determine the layer thickness, and to display variations in the elastic constants on a microscopic scale. These features lead us to believe there is a promising future for the field of acoustic microscopy.
Open Access
The effect of cucurbit[n]uril on the solubility, morphology, and the photophysical properties of nonionic conjugated polymers in an aqueous medium
(2010) Tuncel, D.; Artar, M.; Hanay, S. B.
The effects of cucurbit[n]uril on the dissolution and the photophysical properties of nonionic conjugated polymers in water are described. For this purpose, a fluorine-based polymer, namely, poly[9,9-bis{6(N,N-dimethylamino) hexyl}fluorene-co-2,5-thienylene (PFT) was synthesized and characterized by spectroscopic techniques including 1D and 2D NMR, UV-vis, fluorescent spectroscopy, and matrix-assisted laser desorption mass spectrometry (MALDI-MS). For the first time, it was demonstrated that a nonionic conjugated polymer can be made soluble in water through an inclusion complex formation with CB8. The structure of the complex was elucidated by NMR experiments including 1H and selective 1D-NOESY. This complex emits green and is highly fluorescent with fluorescent quantum yield of 35%. In contrast, CB6 or water-soluble CB7 although they are chemically identical to CB8 do not have any effect on the dissolution and photophysical properties of PFT. By preparing a protonated version of PFT, the optical properties of PFT in methanol, protonated PFT and PFT@CB8 in water have been studied and compared. It was also observed that the morphology of the polymer PFT was affected by the presence of CB8. Thus CB8-assisted self-assembly of polymer chains leads to vesicles formation; these structures were characterized by DLS, AFM, SEM, and TEM fluorescent optical microscopy.
Open Access
High resolution dielectric characterization of single cells and microparticles using integrated microfluidic microwave sensors
(Institute of Electrical and Electronics Engineers, 2023-03-01) Seçme, Arda; Tefek, Uzay; Sarı, Burak; Pisheh, Hadi Sedaghat; Uslu, H. Dilara; Akbulut, Özge; Küçükoğlu, Berk; Erdogan, R. Tufan; Alhmoud, Hashim; Şahin, Özgür; Hanay, M. Selim
Microwave sensors can probe intrinsic material properties of analytes in a microfluidic channel at physiologically relevant ion concentrations. While microwave sensors have been used to detect single cells and microparticles in earlier studies, the synergistic use and comparative analysis of microwave sensors with optical microscopy for material classification and size tracking applications have been scarcely investigated so far. Here we combined microwave and optical sensing to differentiate microscale objects based on their dielectric properties. We designed and fabricated two types of planar sensor: a Coplanar Waveguide Resonator (CPW) and a Split-Ring Resonator (SRR). Both sensors possessed sensing electrodes with a narrow gap to detect single cells passing through a microfluidic channel integrated on the same chip. We also show that standalone microwave sensors can track the relative changes in cellular size in real-time. In sensing single 20-micron diameter polystyrene particles, Signal-to-Noise ratio values of approximately 100 for CPW and 70 for SRR sensors were obtained. These findings demonstrate that microwave sensing technology can serve as a complementary technique for single-cell biophysical experiments and microscale pollutant screening.
Open Access
Lyotropic liquid-crystalline phase of oligo(ethylene oxide) surfactant/transition metal salt and the synthesis of mesostructured cadmium sulfide
(American Chemical Society, 2003) Dag, Ö.; Alayoǧlu, S.; Tura, C.; Çelik, Ö.
Lyotropic liquid-crystalline (LLC), transition metal salt: oligo(ethylene oxide) nonionic surfactant (CnH2n+1(CH2CH2O)mOH, denoted as CnEOm), systems have been studied by means of diffraction, microscopy, and spectroscopy to elucidate the structural, thermal, and templating properties. In the system, the lyotropic salts of transition metal aqua complexes, such as chlorides and sulfates, are insoluble and do not form a LC phase in CnEOm-type nonionic surfactants. However, the transition metal aqua complexes of nitrates and perchlorates are soluble and form 2D and 3D hexagonal and cubic mesophases. These phases are stable in a very broad range of salt:surfactant mole ratios (1.0 and 3.6). The nitrate salts form a hexagonal mesophase. However, in high nitrate salt concentrations (above 3.2 salt:surfactant mole ratio), the salt crystals are either insoluble or the salt:surfactant mixtures are in a cubic mesophase. The structure and thermal properties of the new system are determined by the solubility of the transition metal salts, the concentration of the salt, and the surfactant type. The LC [Cd(H2O)4](NO3)2: C12EO10 mesophase has been reacted with H2S gas to produce solid mesostructured CdS (meso-CdS). The meso-CdS particles are spherical in morphology and are made up of hierarchical organization of 2-4-nm CdS particles. The salt:surfactant LLC systems and the solid meso-CdS have been investigated using polarized optical microscopy, X-ray diffraction, Fourier transform infrared, Fourier transform Raman, and UV-vis absorption spectroscopy, scanning electron microscopy, and transmission electron microscopy.
Open Access
Nanoengineering hybrid supramolecular multilayered biomaterials using polysaccharides and self-assembling peptide amphiphiles
(Wiley-VCH Verlag, 2017) Borges, J.; Sousa, M. P.; Cinar, G.; Caridade, S. G.; Güler, Mustafa O.; Mano, J. F.
Developing complex supramolecular biomaterials through highly dynamic and reversible noncovalent interactions has attracted great attention from the scientific community aiming key biomedical and biotechnological applications, including tissue engineering, regenerative medicine, or drug delivery. In this study, the authors report the fabrication of hybrid supramolecular multilayered biomaterials, comprising high-molecular-weight biopolymers and oppositely charged low-molecular-weight peptide amphiphiles (PAs), through combination of self-assembly and electrostatically driven layer-by-layer (LbL) assembly approach. Alginate, an anionic polysaccharide, is used to trigger the self-assembling capability of positively charged PA and formation of 1D nanofiber networks. The LbL technology is further used to fabricate supramolecular multilayered biomaterials by repeating the alternate deposition of both molecules. The fabrication process is monitored by quartz crystal microbalance, revealing that both materials can be successfully combined to conceive stable supramolecular systems. The morphological properties of the systems are studied by advanced microscopy techniques, revealing the nanostructured dimensions and 1D nanofibrous network of the assembly formed by the two molecules. Enhanced C2C12 cell adhesion, proliferation, and differentiation are observed on nanostructures having PA as outermost layer. Such supramolecular biomaterials demonstrate to be innovative matrices for cell culture and hold great potential to be used in the near future as promising biomimetic supramolecular nanoplatforms for practical applications.
Open Access
An optical microcantilever with integrated grating coupler
(IEEE, 2009-06) Olcum, Selim; Karademir, Ertuğrul; Taş. Vahdettin; Akça, İmran; Kocabaş, Aşkın; Atalar, Abdullah; Aydınlı, Aydınlı
In this paper, we have fabricated an optical cantilever with an integrated grating coupler. We have used an inexpensive and repeatable method for integrating the grating to the silicon cantilever with a microfabrication compatible process. The sensitivity of the method can be further increased by integrating the detection circuitry onto the cantilever substrate. We believe that this is a promising method for sensing applications which provide a simple yet sensitive measurement technique using microcantilevers.
Open Access
Probing nanoscale domains of J-Aggregates deposited on a mica surface
(American Chemical Society, 2004) Özçelik, S.; Demir, M. M.; Birkan, B.
J-aggregates of 1,1′,3,3′-tetraethyl-5,5′,6,6′- tetrachlorobenzimidazolocarbocyanine (TTBC) were deposited on a mica surface and probed by atomic force microscopy operated at tapping mode in air. Optical spectra showed that J-aggregates were formed in aqueous solutions. Atomic force microscopy images revealed that J-aggregates deposited on mica surfaces mainly present single domains with a mean height of 2.00 ± 0.25 nm and an average diameter of 100 ± 20 nm. Quantitative analysis of the morphology of images indicated that the single domain of J-aggregates exhibits very uniform height and diameter distributions with polydispersity indices of 1.02 and 1.04, respectively. Based on the results, we propose a two-dimensional nanostructure in which TTBC J-aggregates could be arranged in a monolayer.
Open Access
Room temperature sub-micron magnetic imaging by scanning hall probe microscopy
(Japan Society of Applied Physics, 2001) Sandhu, A.; Masuda, H.; Oral, A.; Bending, S. J.
An ultra-high sensitive room temperature scanning Hall probe microscope (RT-SHPM) system incorporating a GaAs/A1GaAs micro-Hall probe was used for the direct magnetic imaging of localized magnetic field fluctuations in very close proximity to the surface of ferromagnetic materials. The active area, Hall coefficient and field sensitivity of the Hall probe were 0.8 μm×0.8 μm, 0.3 Ω/G and 0.04 G/√Hz, respectively. The use of a semiconducting Hall probe sensor enabled measurements in the presence of externally applied magnetic fields. Samples studied included magnetic recording media, demagnetized strontium ferrite permanent magnets, and low coercivity perpendicular garnet thin films. The RT-SHPM offers a simple means for quantitatively monitoring sub-micron magnetic domain structures at room temperature.
Open Access
Spectroscopic investigation of nitrate-metal and metal-surfactant interactions in the solid AgNO3/C12EO10 and liquid-crystalline [M(H2O)n](NO3)2/C12EO10 systems
(American Chemical Society, 2003) Dag, Ö.; Samarskaya, O.; Tura, C.; Günay, A.; Çelik, Ö.
Interactions of the nitrate ions in various metal nitrate salts with CnH2n-1(CH2CH2O)mOH (CnEOm)-type nonionic surfactants have been investigated both in the solid and in the liquid-crystalline (LC) systems. In the ternary system, the mixture of salt/water/CnEOm has a mesophase up to a certain concentration of salt, and the nitrate ions in this phase are usually in a free-ion form. However, upon the evaporation of the water phase, the nitrate ion interacts with the metal center and coordinates as either a bidentate or unidentate ligand. It is this interaction that makes the AgNO3 ternary system undergo a phase separation by releasing solid Ag(CnEOm)xNO3 complex crystals. In contrast, the salt/surfactant systems maintain their stable LC phases for months. Note also that the salt/surfactant systems consist of transition-metal aqua complexes in which the coordinated water molecules play a significant role in the self-assembly and organization of the nonionic surfactant molecules into an LC mesophase. Throughout this work, Fourier transform infrared spectroscopy has been extensively used to investigate the interactions of the nitrate ions with a metal center and the metal ions with the surfactant molecules. Polarized optical microscopy and X-ray diffraction techniques have been applied to investigate the nature of the crystalline and LC phases.
Open Access
Surface-state emission enhancement in white-luminophor CdS nanocrystals using localized plasmon coupling
(IEEE, 2008-11) Özel, Tuncay; Soğancı, İbrahim Murat; Nizamoğlu, Sedat; Huyal, İlkem Özge; Mutlugün, Evren; Sapra, S.; Gaponik, N.; Eychmüller, A.; Demir, Hilmi Volkan
To make surface-state emission stronger than band-edge emission for the first time, we proposed and demonstrated plasmon coupling of the surface-state emission from the traps in these CdS nano-luminophors using localized plasmons.
Open Access
Visualization of one-dimensional diffusion and spontaneous segregation of hydrogen in single crystals of VO2
(Institute of Physics Publishing, 2016-07) Kasirga, T. S.; Coy, J. M.; Park, J. H.; Cobden, D. H.
Hydrogen intercalation in solids is common, complicated, and very difficult to monitor. In a new approach to the problem, we have studied the profile of hydrogen diffusion in single-crystal nanobeams and plates of VO2, exploiting the fact that hydrogen doping in this material leads to visible darkening near room temperature connected with the metal-insulator transition at 65 ï¿½C. We observe hydrogen diffusion along the rutile c-axis but not perpendicular to it, making this a highly one-dimensional diffusion system. We obtain an activated diffusion coefficient ∼ 0.01 e-0.6eV/kBT cm2s-1, applicable in metallic phase. In addition, we observe dramatic supercooling of the hydrogen-induced metallic phase and spontaneous segregation of the hydrogen into stripes implying that the diffusion process is highly nonlinear, even in the absence of defects. Similar complications may occur in hydrogen motion in other materials but are not revealed by conventional measurement techniques.