Optical Resolution Limit Research Articles

Improved Image Resolution for Wafer Inspection Tool Using Sub-200-nm Wavelength Light Optical System

In order to extend bright field imaging systems to the 65 nm design rule and beyond, we evaluated inspection imaging characteristics with deep UV (DUV) light with a sub-200 nm wavelength, which is the shortest wavelength in practical use, by reflectivity simulations and with experiments using a pilot proof of concept (POC) tool. The results have confirmed that DUV light has enough reflectivity to enable the inspection of defects in principal semiconductor materials. Furthermore, DUV light shows up to 7 times greater image contrast than UV light (365 nm) for test pattern whose spatial frequency is near the resolution limit of UV optics. When pixel size is reduced, light contrast produced by DUV light is further enhanced to such an extent that it is up to 12 times greater than that produced by UV light. Our evaluation has also confirmed that contrast depends not only on resolving power, but also on coat thickness and reflectivity. Based on optical considerations and current UV inspection technology, it can be concluded that our DUV optical inspection system has the possibility of being used in the design rule of half-pitch 65 nm (hp65 nm) and beyond.

Superresolution optical system by common-path interferometry

We present a new approach to obtain superresolved images in digital holography by means of synthetic aperture generation using common-path interferometry and off-axis illumination in optical imaging systems. The paper includes two parts. First, we present a simple approach to double the resolution of an optical system using tilted illumination onto the object and an optical element in the image plane to produce the holographic recording. Then we present a novel approach consisting of attaching a diffraction grating in parallel together with the object in the input plane and using off-axis illumination provided by a Vertical Cavity Surface Emitting Lasers (VCSEL) array to allow us achieving a major improvement in the optical resolution limit with an extremely low penalty in the complexity of the resulting system. Experimental investigation based on commercial microscope objectives is presented.

A scalable optical detection scheme for matter wave interferometry

Imaging of surface adsorbed molecules is investigated as a novel detection method for matter wave interferometry with fluorescent particles. Mechanically magnified fluorescence imaging turns out to be an excellent tool for recording quantum interference patterns. It has a good sensitivity and yields patterns of high visibility. The spatial resolution of this technique is only determined by the Talbot gratings and can exceed the optical resolution limit by an order of magnitude. A unique advantage of this approach is its scalability: for certain classes of nano-sized objects, the detection sensitivity will even increase significantly with increasing size of the particle.

Beyond nanosizing: an approach to shape analysis of fluorescent nanostructures by SMI-microscopy

Using spatially modulated illumination (SMI) light microscopy it is possible to measure the sizes of fluorescent structures that have an extension far below the conventional optical resolution limit (“subresolution size”). Presently, the sizes are determined as the object extension along the optical axis of the SMI microscope. For this, however, “a priori” assumptions on the fluorochrome distribution (“shape”) within the examined fluorescent structure have to be made. Usually it is assumed that the fluorochrome follows a Gauss-distribution or a spherical distribution. In this report we overcome the necessity to make an assumption on the shape of the fluorochrome distribution. We introduce two new experimentally obtained parameters which allow the determination of a shape measure to describe the spatial distribution of the fluorescent dye. This becomes possible by independent measurements with different excitation wavelengths. As an example, we present shape parameter measurements on individual fluorescent microspheres with a nominal geometrical diameter (“size”) of 190 nm. In the case investigated, the experimental shape correlated well with a homogeneous fluorochrome distribution (“spherical shape”) but not with a variety of other “shapes”.

Signal Enhancement of Super Resolution Enhanced Near-Field Structure Disc by Silver Nano-Particles

We propose a carrier-to-noise ratio (CNR) increment method for a super resolution enhanced near-field structure (super-RENS) with silver nanoparticles. The silver nanoparticles were fabricated by the RF magnetron sputtering method. The mean diameters of the particles under as-deposited and 600°C annealed conditions were evaluated as 5 nm and 15 nm, respectively. The light absorption peak of the silver nanoparticles was adjusted to a laser wavelength of 405 nm for an optical disc system. The silver nanoparticles showed a higher absorption characteristic when they were annealed at above 500°C. In the case of a recording mark size of 50 nm, the CNR enhancement of the super-RENS with the silver nanoparticles was evaluated as 11 dB. This method using the silver nanoparticles provided a higher CNR increment in recording marks below the optical resolution limit.

Detection of motional heterogeneities in lipid bilayer membranes by dual probe fluorescence correlation spectroscopy

We report the detection of heterogeneities in the diffusion of lipid molecules for the three-component mixture dipalmitoyl-PC/dilauroyl-PC/cholesterol, a chemically simple lipid model for the mammalian plasma membrane outer leaflet. Two-color fluorescence correlation spectroscopy (FCS) was performed on giant unilamellar vesicles (GUVs) using fluorescent probes that have differential lipid phase partition behavior—DiO-C18:2 favors disordered fluid lipid phases, whereas DiI-C20:0 prefers spatially ordered lipid phases. Simultaneously-obtained fluorescence autocorrelation functions from the same excitation volume for each dye showed that, depending on the lipid composition of this ternary mixture, the two dyes exhibited different lateral mobilities in regions of the phase diagram with previously proposed submicroscopic two-phase coexistence. In one-phase regions, both dyes reported identical diffusion coefficients. Two-color FCS thus may be detecting local membrane heterogeneities at size scales below the optical resolution limit, either due to short-range order in a single phase or due to submicroscopic phase separation.

Nanotechnology: A new approach in pharmaceutics

Nanotechnology has changed our lives dramatically and influenced every sector of the research, engineering and also business community. Nanotechnology is a rapidly growing science of producing and utilizing nano-sized particles, that measure in nanometer. In other words, nanotechnology is the art of characterizing, manipulating and organizing matter systemically, at the nanometer scale, which has created a revolution in science, engineering, technology, drug delivery and therapeutics. The size of typical accessible structures is in the sub-micrometer range, being within the limits of optical resolution and barely visible with a light microscope. This scale is about 1/1000 smaller than structures that could be resolved by the naked eye, but still 1000 times larger than an atom. Recent developments are addressing the size range below these dimensions and because a typical structure size is in the nanometer range, the methods and techniques are defined as nanotechnology. There is an argue that nanotechnology in pharmaceutics is simply a new version of colloid science, but nanotechnology is clearly not a miniaturized version of the well colloidal drug delivery systems, such as microemulsions, emulsions and liposomes. Rather, nano-sized systems could be designed into a more sophisticated system associated with its physical dimension of less than 100 nm. Nanotechnology, as a novel technology, offers opportunities for the production of new generation of sophisticated drug delivery systems. There are now a wide range of nano-systems, not only nanoparticles and nanocapsules but lipid complexes, polymeric micelles, etc. In this regard, professor Florence believes that nanotechnology of course is much more than the nanoparticles themselves and it is indeed the growth of technologies based on such small-scale systems. He also mentions that what makes nanotechnology a new and exciting subject is the ability not only to manipulate nanoparticles and nanosystems, but also the new techniques available to measure and indeed visualize materials in the nanometer size range. Particles produced through nanotechnology are small and since the particle size is crucial, the maintenance of particle size is therefore of great importance. For instance, nano-sized particles possess very high surface to volume ratios and therefore, this property causes an interaction between the surface and mucus layer to occur. On the other hand, due to the huge surface area, surface properties of particles play an important role in protecting the active agents from degradation.

Thermoelectric PbTe thin film for superresolution optical data storage

To find its practical use in ultrahigh density optical data storage, superresolution (SR) technique needs a material that can render a high SR capability at no cost of durability against repeated readout and write. Thermoelectric materials appear to be promising candidates due to their capability of yielding phase-change-free thermo-optic changes. A feasibility study was carried out with PbTe for its large thermoelectric coefficient and high stability over a wide temperature range as a crystalline single phase. Under exposure to pulsed red light, the material was found to display positive, yet completely reversible changes of optical transmittance regardless of laser power, fulfilling basic requirements for SR readout and write. The material was also shown to have a high endurance against repeated static laser heating of up to 106–107 cycles tested. A read only memory disk with a PbTe SR layer led to the carrier to noise ratio value of 47dB at 3.5mW for 0.25μm pit; below the optical resolution limit (∼0.27μm) of the tester.

Degradation of the type II collagen network early in the degeneration of cartilage

Type II collagen has been characterized as being present in joint tissues subjected to compression rather than tension. The purposes of this study were to investigate the distribution and ultrastructural changes in the type II collagen fibrillar network in the early stage of degeneration of cartilages. Softened cartilage which represents the early stage of degeneration was obtained from the tibial surfaces of a cow. Normal control cartilage was obtained from the femoral condyles in the same joint. Nomarski light microscopy and transmission electron microscopy (TEM) were performed respectively for structural and ultrastructural studies. Confocal light micrscopy was applied for imaging the staining of collagen type II in normal and softened matrices by immunohistochemical studies. The results demonstrated that in normal cartilage the extracellular matrix was characterized by a fine ”ground-glass-like” amorphous texture. This reflects the fact that individual fibril elements in their repeatedly interconnecting configuration present a fineness of structure that is beyond the limits of optical resolution. The normal matrix observed by TEM was shown to have a pseudo-randam fibrillar architecture. The extracellular matrix in the softened cartilage was characterized by a distinct fibrous texture strongly aligned in the radial direction. This optically resolved structural feature of the softened matrix reflects a tendency for individual collagen flbrils to aggregate into relatively large fibrillar bundles strongly aligned in the radial direction as observed under TEM. The type II collagen-labeled images obtained from the normal matrix exhibited a fine texture. By contrast, staining of the softened matrix exhibited a relatively coarse granularity with a distinctly radial texture in the deeper zones. It was concluded that the degeneration of cartilage begins with degeneration of the extracellular matrix, and the decrease in collagen fibrillar interactions is mainly caused by the loss of cross-linking in type II collagen. This is the first report to correlate ultrastructural changes of the fibrillar network with confocal imaging of the type II collagen distribution in the process of cartilage degeneration.

More than 20 GB Capacity Rewritable Disk with the Same Physical Parameters as that of Digital Versatile Disc, Using a New Recording Method and Domain Wall Displacement Detection

We have developed a new light intensity modulation recording method called domain tail erasing method. This new recording method enables high-density recording far beyond the optical resolution limit with a medium combining the layer structure of domain wall displacement detection (DWDD) with that of light intensity modulation direct overwrite (LIMDOW). A recording performance nearly identical to that using magnetic field modulation (MFM) was confirmed with this method, using conventional optics with a wavelength of 660 nm and NA of 0.60.

High-Density Magneto-Optical Recording with DWDD and DTE

ABSTRACTWe have developed a new light intensity modulation recording method called Domain Tail Erasing (DTE). This new recording method enables high-density recording far beyond the optical resolution limit with a medium combining the layer structure of Domain Wall Displacement Detection (DWDD) with that of Light Intensity Modulation Direct Overwrite (LIMDOW). Recording performance nearly identical to that with Magnetic Field Modulation (MFM) was confirmed with this method, using conventional optics with a wavelength of 660 nm and an NA of 0.60. However, the DTE method still requires a bias magnet, which remains a disadvantage in cases in which a thinner drive apparatus is required.We have therefore also made the bias magnets unnecessary by introducing a device to generate a magnetic field as a magnetic film included inside the medium.

193 nm Resist Line Collapse Study by Modifying the Resist Polymer and Process Conditions with Utilizing FIRM Process

Device design rules are continuously shrinking toward the optical resolution limit of k1 factors below 0.3. The requirements for 193 nm photoresist below 90 nm node manufacturing are quite challenging. Using a DI water rinse after development gives a significant amount of line collapse when the aspect ratio is over 3. To avoid line collapse, Tokyo Electron co-developed a special rinse solution for the FIRM process with Clariant Japan K.K. Utilizing FIRM process, 90 nm dense line collapse was measured by CD SEM using focus-exposure matrices. Line collapse in experimental 193 nm positive tone resists was studied by varying monomer ratios of the polymer and process conditions. The surface properties of the resist were also studied to investigate the interaction with the rinse solution in the de-protected region. However, a high surfactant concentration in the DI water rinse can lead to swelling of the resist pattern profile. It is important to co-optimize the resist component and the adequate surfactant concentration in the rinse solution to minimize line collapse and pattern deformation. Both δP and σmax were calculated along the FEM to investigate line collapse dependence on the resist hydrophobicity.

Freeze-fracture electron microscopy of lipid membranes on colloidal polyelectrolyte multilayer coated supports.

Lipid membranes were assembled on polyelectrolyte (PE)-coated colloidal particles. The assembly was studied by means of confocal microscopy, flow cytometry, scanning force microscopy, and freeze-fracture electron microscopy. A homogeneous lipid coverage was established within the limits of optical resolution. Flow cytometry showed that the lipid coverage was uniform. Freeze-fracture electron microscopy revealed that the lipid was adsorbed as a bilayer, which closely followed the surface profile of the polyelectrolyte support. Additional adsorption of polyelectrolyte layers on top of the lipid bilayer introduced inhomogeneities as evident from jumps in the fracture plane. Characteristic lipid multilayers have not been seen with freeze-fracture electron microscopy.

Fluorescence Correlation Spectroscopy: Molecular Complexing in Solution and in Living Cells

FCS is an important technique for biophysicists, biochemists, and cell biologists. FCS represents an example of how one can make use of the microscope and electronics to extract information beyond the resolution limit of classical optics. It can be used to study single-molecules both in solution and in living cells and can be used to monitor a wide variety of macromolecular interactions. When used as an in vitro technique, FCS measurements are easy to conduct and can be made on simplified instrumentation. When used in vivo on living cells, many additional factors must be considered when evaluating experimental data. Despite these concerns, FCS represents a new approach that has broad applicability for the determination of molecular stoichiometry both in vivo and in vitro for a variety of membrane and soluble receptor systems.

Subwavelength size determination by spatially modulated illumination virtual microscopy

A new approach for determining the sizes of individual, small fluorescent objects with diameters considerably below the optical resolution limit is described in which spatially modulated illumination (SMI) microscopy and 360-647-nm excitation wavelengths are used. The results of SMI virtual microscopy computer simulations indicate that, in this wavelength range, reliable measurements of sizes as small as approximately 20 nm are feasible if the low numbers of fluorescence photons that are usually detected from such small objects are taken into account. This method is based on the well-known fact that the modulation of the diffraction image in a SMI microscope is disturbed by the size of the object. Using appropriately calculated calibration functions, one can use this disturbance of the modulation to determine the size of the original object.

Spatial coding of position and orientation in primary visual cortex.

We examined the spatial distribution of population activity in primary visual cortex (V1) of tree shrews with optical imaging and electrophysiology. A line stimulus, thinner than the average V1 receptive field, evoked a broad strip of neural activity of nearly constant size for all stimulus locations tested within the central 10 degrees of visual space. Stimuli in adjacent positions activated highly overlapping populations of neurons; nevertheless, small changes in stimulus position produced orderly changes in the location of the peak of the population response. Statistically significant shifts in the population response were found for stimulus displacements an order of magnitude smaller than receptive field width, down to the limit of optical imaging resolution. Based on the pattern of population activity, we conclude that the map of visual space in V1 is orderly at a fine scale and has uniform coverage of position and orientation without local relationships in the mapping of these features.

Ultra-Sensitive Microscopy of Lipid Microdomains in Living Cells Using Two Photon Excitation

The view of the plasma membrane of biological cells was dramatically changed due to the discovery of lipid microdomains. Initially found as structurally distinct areas characterized by a specific protein content, the concept of lipid microdomains was rapidly taken over as a new scheme for explaining membrane targeted cellular processes. Despite its impact on the current image of cell function, there is still a lack of knowledge on the structural origin, size, distribution and mobility of such domains. We addressed these questions through high-resolution imaging of microdomains enriched in flourescence labeled lipids with a two-photon microscope. Our findings showed that domains are of heterogeneous size close to the optical resolution limit, and are dispersed randomly over the cell surface. For studying the functional role of microdomains, we investigated the interplay of lipids and certain membrane proteins utilizing simultaneous two color imaging. While in some cases we observed colocalization between lipids and proteins, on occasion proteins were confined to domains which were clearly separated from lipid domains. This is in perfect agreement with biochemical studies showing structurally distinct sets of domains confining different types of proteins. For maintaining functional flexibility of the cell, microdomains are expected to be linked to the cytoskeleton. We studied the mobility of individual microdomains using repeated imaging of the same area of the cell surface at a rate of one image per 10s. Interestingly, most domains were almost immobile within the plasma membrane. On occasion, however, domains were transported actively over distances up to several micrometers, which is strong evidence for interactions between domains and the cytoskeleton. These results for the first time demonstrate that ultra-sensitive optical microscopy is perfectly suited to resolve the dynamical processes of the organization of the plasma membrane, which allows for much deeper insights into the details of cell response.

Observation of Translational Diffusion of Single Terrylenediimide Molecules in a Mesostructured Molecular Sieve

The translational motion of single terrylenediimide (TDI) dye molecules incorporated into the organic part of a surfactant−silica mesostructure of a monolithic M41S host was observed by confocal microscopy. Only isotropic motion was found indicating that the channel-like motion lies below the optical resolution limit of the experiment. An effective diffusion constant was evaluated to be D = 3.72 × 10-2 μm2 s-1. In contrast, for the TDI molecules diffusing in the pure lyotropic hexagonal phase of the same surfactant in water, a one-dimensional anisotropic diffusion with a diffusion constant of D = 2.07 μm2 s-1 was measured. The decrease in D and the occurrence of isotropic diffusion on the length scale of the optical experiment on going from the lyotropic phase to the mesostructured host are attributed to an increase in viscosity and tortuosity due to the formation of the silica walls around the template micelles in the synthesis of the M41S material. Apart from the mobile fraction, which shows normal diffusion, a stationary fraction of ∼10% of TDI molecules is observed; however, no intermediate cases were detected.

Orogenic Displacement in Mixed β-Lactoglobulin/β-Casein Films at the Air/Water Interface

The adsorption of mixed β-casein/β-lactoglobulin films to the air/water interface and the subsequent displacement by the nonionic surfactant Tween 20 was studied. A combination of fluorescent labeling of the protein and Langmuir−Blodgett deposition was used to study the mixed protein layer. The adsorption was also monitored using two surface rheological techniques, shear and dilatation. Fluorescent labeling was able to show that to within the limits of optical resolution the two proteins were well mixed at the interface. We also show that the film remained well mixed after 3 days. Surface rheological data from the two techniques used was self-consistent and showed that during the initial stages of development, the films were dominated by the adsorption of the β-casein. Both fluorescence microscopy and atomic force microscopy were used to follow the displacement of the mixed film by surfactant. Results on films displaced by the nonionic surfactant Tween 20 showed that β-casein was preferentially displaced ...

Enhancement of Reflection-Enhanced Backscatter Confocal Microscopy

Tremendous advances have been made in the last twenty years in extending the usefulness of the light microscope in visualizing living biological specimens, and it is now possible to visualize most thin tissues in an unstained state at – or near – the limit of optical resolution. in general, however, these techniques have been used successfully on biological specimens in the transmitted light mode; unstained biological specimens generally do not have sufficient albedo or sufficient difference in refractive index from their surroundings to be efficiently visualized in epi-illumination. A number of applications, including studies of the growth of bacteria on metallic substrates, and studies of the studies of the formation of interfaces between living neurons and silicon chips, would benefit from being able to resolve living, unstained biological specimens growing on opaque substratesWe found that by imaging biological specimens on a reflective substrate in the reflection mode of the confocal microscope, we could get images that resemble transmission mode differential interference contrast images.