Biological tissue is a very complex, yet important material to describe and analyze. Its properties are affected by chemical processes too numerous to easily understand and describe. By simplifying and grouping some aspects together we are able to create a model for simulating behavior of a photon inside of a biological sample. Using the Monte Carlo method an algorithm for calculating photon propagation through the tissue based on several optical parameters, like absorption and scattering coefficients, refractive indices and optical anisotropy, can be created. Based on some of the results of the simulation a comparative measurement on a muscle sample was performed to prove the usefulness of such model and to describe changes in the tissue sample based on the aforementioned optical parameters in both real life and the simulation.
The search for alternative sources of renewable energy, including novel photovoltaics structures, is one of the principal tasks of 21th century development. In the field of photovoltaics there are three generations of solar cells of different structures going from monocrystalline silicon through thin-films to hybrid and organic cells, moreover using nanostructure details. Due to the diversity of these structures, their complex study requires the multiscale interpretations which common core includes an integrated approach bridging not only the length scales from macroscale to the atomistic, but also multispectral investigation under different working temperatures. The multiscale study is generally applied to theoretical aspects, but is also applied to experimental characterization. We investigate multiscale aspects of electrical, optical and thermal properties of solar cells under illumination and in dark conditions when an external bias is applied. We present the results of a research of the micron and sub-micron defects in a crystalline solar cell structure utilizing scanning probe microscopy and electric noise measurement.
The colors of some living organisms assosiated with the surface structure. Irridesence butterfly wings is an example of such coloration. Optical effects such as interference, diffraction, polarization are responsible for physical colors appearance. Alongside with amazing beauty this structure represent interest for design of optical devices. Here we report the results of morphology investigation by atomic force microscopy. The difference in surface structure of black and blue wings areas is clearly observed. It explains the angle dependence of the wing blue color, since these micrometer and sub-micrometer quasiperiodical structures could control the light propagation, absorption and reflection.
In this work, the etch rate of silicon carbide and aluminum oxide were studied as a function of the angle etching material and flow of plasma. Al2O3 and SiC are important materials in the design of optical and electronic devices and the topography of the wafers has a large influence on the device quality. Argon was applied for the dry etching of Al2O3 and SiC wafers. The wafer slope for highest obtained etch is defined. Atomic force microscopy was used to good morphology control of etched wafers. Statistical and correlation analysis was applied to estimate the surface perfection. Interferometry allowed to control etching rate.
Metal and semiconductor nanoparticles have excellent optical and electrochemical properties that strongly depend on their size and shape. Local biosensors are advanced devices, whose basic working principle is to analyze spectra of noble metal nanoparticles. Here a model of a local biosensor is described. It takes into account the interaction of the particle with a glass prism and the viewing angle of lens. The results for the layered particle made of a polystyrene latex core with a golden outer shell and for nanorods are presented. The influence of the metal shell thickness, particle diameter and the nanoscale rod form on the location of dissipation spectrum maximum is analyzed.
This paper describes optical scattering properties of muscle t issue, special traits, and the difficulties its composition causes. The pH of tissue and angle of the myofibrils relative to the incident light used as a probe changes the results of measurements. Distribution of colagen, as well as other substances that can be found in muscle tissue, also affect the outcome of any attempt to examine the sample via the means of optical analysis. Measurement results and scattering models are compared in effectiveness of characterization of the non-linear optical system that is muscle tissue for both medical use and food quality control, depending on the properties and composition of the tested sample.
The objective of the study is to characterize the dependence of the optical properties of solid solutions of silicon
carbide and aluminum nitride on composition. Even small differences in composition provide manipulation of band gap
features over a wide range. Data for this paper were collected by X-ray diffraction, photoluminescence and absorption
spectroscopy. The evolution of the observed optical properties as a result of compositional changes were studied. X-ray
studies confirm the presence of a(SiC)1-x(AlN)x solid solution. Investigation of absorption spectra shows the optical
band gap of the sample with composition (SiC)0,88(AlN)0,12 is 3.5eV, and 4.24 eV for the (SiC)0,36(AlN)0,64 solid
solution. The photoluminescence spectra demonstrate the strong dependence of the spectra on composition x. The
experimental results are in agreement with theory. These data demonstrate the optimization of optical properties for
particular optoelectronic applications by varying the (SiC)1-х(AlN)х composition.
Proc. SPIE. 9450, Photonics, Devices, and Systems VI
KEYWORDS: Wafer-level optics, Photovoltaics, Solar cells, Silicon, Interference (communication), Optical testing, Near field scanning optical microscopy, Silicon solar cells, Semiconducting wafers, Signal detection
We report on detection and localization of imperfections in silicon solar cell bulk and surface with sub-micrometer
resolution. To obtain this resolution, a family of imaging techniques including SNOM, SEM and AFM is often separately
used for this purpose. In this paper we combine several of these proximal methods together, because each of them brings
complimentary information about the imperfection. First, we note that SNOM images often contain distortions due to the
interaction of the probe tip and sample. Therefore, we look for the possibility to circumvent this weakness and obtain
more realistic images. In our experiments, we take advantage of the fact that defects or imperfections in silicon solar cell
structures under reverse-bias voltage exhibit microscale low light emitting spots, and we apply an improved SNOM
measurement to localize these spots. As a result, this system allows a localization and measurement of low light emission
on microscale. Consequently, the size and shape of imperfections can also be determined.
Proc. SPIE. 9450, Photonics, Devices, and Systems VI
KEYWORDS: Solar cells, Photomultipliers, Crystals, Electroluminescence, Atomic force microscopy, Scanning electron microscopy, Near field scanning optical microscopy, Silicon solar cells, Scanning probe microscopy, Photomicroscopy
The paper deals with the successive localization and imaging of solar cell defects, going from macroscale to microscale.
For the purpose of localization, the light emission from reversed bias samples is used. After rough macroscopic
localization, microscopic localization by scanning probe microscopy combined with a photomultiplier (shadow mapping)
is performed. The type of microscopic defects are discernable from their current-voltage plot or from noise
measurements. Two specific defects, both of the avalanche type, with different voltage threshold, are presented in this
paper. Current voltage plots and radiant flux versus voltage characteristics for two temperatures, topography, shadow
map and corresponding SEM micrographs are shown for both samples.
At present there are known many of diagnostic methods of detection large crystal lattice defects of silicon solar cells. This paper deals about results of new potential in to use one of characteristics luminescence radiation for detection defects of solar cells. So polarization spectroscopy of defect in solar cells may be used to fitting characterization of silicon solar cells. And this can lead to understand the electrical properties of defects in silicon solar cells and study of really formation defects. We used extending existing electroluminescence technology about polarization spectroscopy to yield the polarization of luminescence radiation by defect in solar cells. Radiation emitted by the solar cell has a wave character that can interact with the silicon structures or hypothetically thin reflectance layer of solar cells. In our research we can observed the linear partially polarization luminescence light on poly-silicon crack defect. Spectral response of using CCD camera is approximately 300 to 1100 nm. Sinusoid dependence of luminescence intensity on the angle of linear polarization analyzer rotation shown this fact. The degree of polarization depends on the material, in this case the character of defect. Polarized light can be obtained in various ways. This fact opens up for potential next new questions in this widely course of study diagnostics defects silicon solar cells.
Monocrystalline silicon wafer is up-to-date most used material for the fabrication of solar cells. The recent investigation shows that the quality of cells is often degraded by structural defects emerging during processing steps. Hence the paper gives first an overview of solar cell efficiency investigation on macroscale. Then a detection and microscale localization of tiny local defects in solar cell structures which evidently affect electrical and photoelectrical properties of the cells is targeted. The local defects can be classified as microfractures, precipitates and other material structure inhomogeneities. Detection and localization of the defects in the structure and the assigning of particular defects to corresponding degradation of photoelectrical parameters are key points for solar cell lifetime and efficiency improvement. Although the breakdown can be evident in current-voltage plot, the localization of defects on the sample has to be provided by microscopic investigations as well as by defects light emission measurement under electrical bias conditions. The experimental results obtained from samples where the defects were microscopically repaired by focused ion beam are presented. Electrical and photoelectrical properties of sample before and after milling processing are also discussed.
Different ultrasonic, electromagnetic, electrical and optical methods are used for meat ageing detection. Muscles are turbid anisotropic media, they exhibit changes in electrical and optical properties according to the direction of the electrical and optical fields in the sample. The work assesses the feasibility of impedance measurements for meat ageing detection and their comparison with optical measurement of scattered light. The pork chop slices were used for their relative homogeneity. An investigation was carried out for the detection of the ageing of unpacked slices exposed directly to the air, and other packed in polyethylene bags. The electrical method is a promising method due to the possibility of getting much information and realizing cheap and fast enough measurement systems. The optical method allows measure the rotation of polarization plane in the range of 95 degrees within considered period. Nevertheless, further work has to be provided to determine closer relationships between optical scattering characteristics, electrical anisotropy in ageing-related tissue structural properties.
We investigate localized defects of silicon solar cells. These imperfections represent real problem because of solar cell long-term degradation and decreasing conversion efficiency. To solve this issue, this paper does systematic research about optical investigation of local defect spots and correlation with rectangular microplasma fluctuation. Sensitive CCD camera has been used for mapping of surface photon emission. The operation point of the samples has been set to reverse bias mode and the different electric field intensity was applied. It turns out, that some solar cells exhibit an imperfection in the bulk and close to the edges. Nevertheless, we confine ourselves to bulk defects of potential barrier. We managed to get interesting information using combination of optical investigations and electrical noise measurement in the time and spectral domain. It will be revealed that a direct correlation between noise and photon emission exists and the results related to several defect spots are presented in this paper in detail.
The real-time nondestructive inspection of biological tissues begins to be one of important tools which could contribute
to better human life not only in medical diagnosis but also in everyday mankind activities. A biological tissue is
considered as a turbid medium in which light is scattered. Although single or multiple scattering in tissue multiple
randomizes polarization states of incident light, linear, circular and elliptical polarization states in the medium are
considered, and there are circumstances when appreciable degree of polarization can be observed in diffusive scattering.
Our work shows that with a sufficient degree of sensitivity is possible to detect structural changes due to the aging of
processed meat by using Mueller matrix polarimeter. Moreover, it demonstrated that the degree of polarization of the
backscattered light is sensitive to the optical properties of specimen material and to its thickness.
Light emission inspection technique are generally used for the localization of defects. In this paper, the emission comes from reverse biased mono-crystalline solar cells. Firstly, it is demonstrated that light emission of reverse biased solar cells is observable with our system. Experimental data of light emission from cracks, bulk defects, and borders of the cell are presented. Following these measurements, a few scratches were wittingly made on the top side of the solar cell sample and light emission was measured again for the same reverse voltage value. A method for distinguishing micro-crack and scratches from recombination centers is also presented. This method is based on detecting light emission intensity while varying the sample temperature, holding the reverse bias level fixed. The light emission data are then correlated with laser beam induced current maps. It is found that there is a different light emission temperature behavior in the case of bulk recombination defects and artificial damage defects. Finally, the scratched areas are inspected as sites of local structure damage.
In this study the optical properties of SiC/(SiC)1-x(AlN)x heterostructures were investigated. The photoluminescence
spectrum of (SiC)1-x(AlN)x samples at different temperatures and also the dependence of photoluminescence on
wavelength of exciting light were studied. Absorption factor is defined using measured values of transmitting efficiency.
The results of study of morphology and composition of obtained samples confirm growth regularity in single-crystal
phase. It was observed that n-SiC/p-(SiC)1-x(AlN)x begins to shine at reverse voltage that a little exceed the voltage of
The propagation of laser light in biological tissues is of growing importance in many medical and food applications. This
problem is seriously studied in live science. The biological tissues consist of cells which dimensions are bigger than
wavelength of visible light and display large compositional variations, inhomogeneities, and anisotropic structures.
Therefore a Mie scattering of transmitted or backscattered light occurs and different polarization states arise.
The changes of polarization state due to the multiple scattering of light in the biological cellular tissues also allow
measure the freshness of processed victuals. The transmitted and backscattered laser light exhibits multiple scattering on
the thin slice of sample. The phenomenon is different if the cellular tissues are living or dead.
In the case of meat, there are temporal and dynamic changes not only as a result of chemical process, but also geometric
deformations due to the water evaporation from intracellular and extracellular sites. The polarization measurement shows
the changes in polarization orientation due to the muscle orientation and meat aging.
Two types of measurements were provided: a) Measurement of polarized light reflected and twice transmitted forward
and backward through the biological tissue samples - meat slice attached on sample holder mirror. b) Measurement of
polarized light transmitted through the biological tissue sample. The relationship between polarization changes and meat
freshness, and a dynamic temporal behavior of polarization states in the aged meat is reported.
Today photovoltaic cells are divided into two principal types: higher-efficiency but quite expensive crystalline silicon
solar cells (either monocrystalline or multicrystalline), and lower-cost thin-film solar cells, usually composed of
amorphous silicon, polycrystalline silicon, cadmium telluride, or copper indium gallium diselenide. In both cases their
operation is based on a large-area pn junction. Their efficiency is generally limited by defects and impurities, which
include grain boundaries, dislocations, and transition metals. A wide variety of defects can be formed in a silicon
crystals during and after their growth. Some of defects arise on cell surface during its life-time such as scratches. These
surface damages are origin of lower light-trapping efficiency. Many of defects do not cause cell malfunction, but
generate local microplasmas, which are conductive and hence reduce overall cell efficiency. A number of defects of
various kinds, some of them being of local character only, can not be observed with classical methods in such large-area
junctions. Therefore a use of more precise scanning probe microscopes represents a novel approach to surface
investigations with superresolving features. The paper presents results of experimental study of high resolution map of
induced photocurrent and local electroluminescence in monocrystalline silicon solar cells. Photovoltaic solar cells are
evaluated by I-V electric measurement, Far-field and Near-field Optical Beam Induced photocurrent (NOBIC), as well
as by Scanning Near-field Optical Microscope (SNOM) topography and reflection. The correlation between reflection
and transport characteristics indicates power of this diagnostic tool.
The biological tissues consist of cells which dimensions are bigger than a wavelength of visible light. Therefore a Mie
scattering of transmitted and reflected light occurs and different polarization states arise. The back-scattered polarized
laser light exhibits multiple scattering from the surface and subsurface layers of the sample. Notwithstanding this
phenomenon is different if the cellular tissues are live or dead. In the case of porcine meat, there are temporal and
dynamic changes not only as a result of chemical process, but also geometric deformations due to the water evaporation
from intracellular and extracellular sites. Although multiple scattering in tissue randomizes incident polarization states,
the shift of polarization can be clearly observed in diffusive scattering pattern due to the muscle orientation and meat
aging. Accordingly, these temporal changes due to the multiple scattering of backscattered light allow measure the
freshness of processed meat.
This paper presents the results of our experimental study of high resolution map of induced photocurrent in
monocrystalline silicon solar cells. Photovoltaic solar cells are evaluated by Near-field Optical Beam Induced
photocurrent (NOBIC), as well as by Scanning Near-field Optical Microscope (SNOM) topography and reflection. The
correlation between reflection and transport characteristic indicates possibility of this diagnostic tool. Therefore the
SNOM and NOBIC represent the coupling of very useful methods to provide a non-destructive local characterization on
silicon semiconductor solar cells.
Conventional optics is diffraction limited to about half of the effective optical wavelength. However the current trend
towards miniaturization of optical elements and devices requires methods of observation with high spatial resolutions
adapted to the micrometer and submicrometer optical regime. More specifically, the use of Scanning near-field optical
microscope (SNOM or NSOM) in various domains is overviewed. Basically an optical tip with a subwavelength
aperture at its apex scans over a surface with a spatial resolution, which is not limited by light diffraction. This
characteristic makes SNOM a valuable tool to perform various optical or spectroscopic studies on nanoobjects, such as
semiconductor quantum dots (QDs), or to address them optically. The paper reviews different methods of far-field and
near-field approach to visualize nano-size objects.
We introduce two types of optical fiber Bragg grating sensor with nanoscale spatial resolution and chemical specificity. This sensing technique holds promise for gaining deeper insight into the functionality of nanoscale structures superposed on the gold thin film or embedded in its complex environments. The techniques are based on the effect of surface plasmon resonance and surface plasmon resonance fluorescence. Properly p-polarized laser light illuminates the Bragg grating and induces a strongly enhanced field at the gold thin film. This is due to the coupling of guided mode of the optical fiber and surface plasmon mode. The laboratory prototype of sensor with linear Bragg grating is used for the measurement of smooth variances in refractive index and a sensor with oblique Bragg grating combined with the Scanning near field optical microscope is used for the measurement of analyte thickness. Here, the spatial resolution is determined by the tip size (typically on the order of 60-80 nm).
The relevance of scanning near-field scanning optical microscopy (SNOM) for optical characterization of semiconductors with quantum dots is presented. The SNOM technique and some of its properties appropriate to real-time in-situ measurements are evaluated. Several optical characterization methods -- widely used in the far-field, including reflectance, reflectance-difference spectroscopy, and carrier lifetime, are estimated for their use with SNOM. Experimental data are included for some of these methods. Numerous standard optical characterization methods can be coupled with SNOM to provide higher spatial resolution. The applicability of SNOM as a real-time in-situ probe shares some of the problems of other local probe methods, but offers enough new capabilities to assure its application.
Proc. SPIE. 5036, Photonics, Devices, and Systems II
KEYWORDS: Semiconductors, Quantum wells, Gallium arsenide, Optical testing, Near field scanning optical microscopy, Near field, Scanning probe microscopy, Molecular beam epitaxy, Near field optics, Absorption
Photocurrent (PC) spectroscopic techniques have demonstrated to be helpful experimental method to investigate the local properties of bulk semiconductors, microstructures, surfaces and interfaces. We have measured locally induced PC of semiconductor quantum structures using a technique of reflection Scanning Near-field Optical Microscope (r-SNOM) in combination with Ti:Sapphire laser and tuning dye laser and with He-Ne laser. The r-SNOM employs an uncoated and/or Au-metalized single-mode fiber tip both in illumination and collection mode. Taking opportunity of the high lateral resolution of the microscope and combining it with fast micro-PL, it is possible to locate e.g. defects in a multiple quantum well grown by molecular beam epitaxy. Near-field characteristics of measured quantities are also discussed.
Submicron spatial resolution photoluminescence is used to assess radiative efficiency and spatial uniformity of GaAlAs/GaAs heterojunctions. Room temperature photo-luminescence of multiple GaAlAs wells with GaAs barriers was measured as a function of a facet of device perpendicular to the layer structure. The scanning near-field optical microscope is applied for the diagnostics of the defects in semiconductor devices for instance in a multiple quantum well grown by molecular beam epitaxy. Our high resolution studies reveal that the radiative recombination for the GaAlAs quantum well is approx. 50 times more efficient than for the underlying GaAs film. The comparison of the Far-field and Near-field characteristics of measured quantities are also given.
Photoluminescence (PL), photoreflectance (PR) and photocurrent (PC) spectroscopic techniques have demonstrated to be helpful experimental methods to investigate the properties of bulk semiconductors, microstructures, surfaces and interfaces. We present near-field local PL, PR and PC spectroscopic study of semiconductor quantum structures using a technique of reflection Scanning Near-field Optical Microscope (SNOM) in combination with Nitrogen laser and tuning dye laser and with He-Ne laser. Reflection Scanning Near-field Optical Microscope (SNOM) employs an uncoated and/or Au-metallized single-mode fiber tip both as nanosource and a nanoprobe. In the illumination-collection hybrid mode, the first one serves to excite the semiconductor sample and the second one to investigate characteristics of the structure and to pick up the PL and PR intensity reflected from the sample. In the illumination mode, the nanosource illuminates locally the semiconductor structure, and excites the photoelectrons in the PC spectroscopy. This near-field device is applied for the diagnostics of the defects in semiconductor devices. Take opportunity of the high lateral resolution of the microscope and combine it with fast micro-PL, PR responses, it is possible to locate for instance defects in a multiple quantum well grown by molecular beam epitaxy. Near-field characteristics of measured quantities are also discussed.
An experimental method for the measurement of the profile of the laser beam focused by a high NA lens is presented. A homemade PZT driven stage is used to scan a near-field optical microscope probe through the beam profile. The probe position is detected via strain gauges which were calibrated by laser interferometer and the intensity collected by the probe is measured by photomultiplier. The stage positioning accuracy +/- 50 nm enables the measurement of the intensity distributions within submicron-sized beam spots. As an example, intensity profiles of a TEM00 laser beam focused by a water immersion objective are presented.
In the paper some basic optical near field theoretical approaches will be explained as well as the principles of microscope set-ups. Application items as nanoscale topography with lateral superresolution, local spectroscopy of semiconductors, local fluorescence of dielectric films and achieving of higher data density of the recording medium will be also presented.
Proc. SPIE. 3098, Optical Inspection and Micromeasurements II
KEYWORDS: Microscopes, Polarization, Reflection, Atomic force microscopy, Semiconductor lasers, Near field scanning optical microscopy, Near field, Objectives, Scanning tunneling microscopy, Near field optics
The 1/f noise is a general phenomenon on physical systems. In this paper low-frequency noise of silicon crystal have been analyzed. Noise spectra can not be explained completely by a homogeneous band model of semiconductor. Therefore, we have developed a new tool, so called 'tunnel noise spectroscopy' permitting to localize a noise sources on the surface. Some applications of scanning tunnel microscopy and of reflection scanning near-field optical microscopy in the investigation of 1/f noise of the semiconductor surface coated by a thin gold film are also presented.
For overcoming the classical limits of resolution in optical microscopy it is necessary to detect the diffracted signal from the small details of an object in the near field. These light waves interact with the object details and then can be used for determining the object topology. The solution consists of frustrating the evanescent field by means of optical fiber probes. In this present communication a new super-resolution scanning near-field optical microscope using a diode laser ((lambda) equals 1.3 micrometers ) and optical fibers is demonstrated to measure the samples with submicron structure in a noncontact manner. A reproducible method manufacturing of the fiber probes is proposed. First, results dealing with the characterization of the device are reported.