Thick SiO2 layer produced by anodisation

A method for oxidising porous silicon to obtain thick SiO2 as the cladding layer of silicon-based silica waveguides is presented. The experimental results of oxidation are given. The following conclusions are drawn: the oxidation rate of porous silicon is several orders higher than that of bulk silicon, the appropriate temperature variation rate during oxidation combined with proper porosity can prevent SiO2 on silicon substrates from cracking. and a 25 mu M thick silicon dioxide layer has been obtained.

The influence of substrate nucleation on HVPE-grown GaN thick films - art. no. 684105

Thick GaN films were grown on sapphire in a home-made vertical HVPE reactor. Effect of nucleation treatments on the properties of GaN films was investigated, including the nitridation of sapphire, low temperature GaN buffer and MOCVD-template. Various material characterization techniques, including AFM, SEM, XRD, CL and PL have been used to assess these GaN epitaxial films. It was found that the surface of sapphire after high temperature nitridation was flat and showed high density nucleation centers. In addition, smooth Ga-polarity surface of epitaxial layer can be obtained on the nitridation sapphire placed in air for several days due to polarity inversion. This may be caused by the atoms re-arrangement because of oxidation. The roughness of N-polarity film was caused by the huge inverted taper domains, which can penetrate up to the surface. The low temperature GaN buffer gown at 650 degrees C is favorable for subsequent epitaxial film, which had narrow FWHM of 307 arcsec. The epitaxial growth on MOCVD-template directly came into quasi-2D growth mode due to enough nucleation centers, and high quality GaN films were acquired with the values of the FWHM of 141 arcsec for (002) reflections. After etching in boiled KOH, that the total etch-pit density was only 5 x 106 cm(-2) illustrated high quality of the thick film on template. The photoluminescence spectrum of GaN film on the MOCVD-template showed the narrowest line-width of the band edge emission in comparison with other two growth modes.

The improvement of thick oxidized porous silicon layer growth process - art. no. 60290S

Oxidizing thick porous silicon layer into silicon dioxide is a timesaving and low-cost process for producing thick silicon dioxide layer used in silicon-based optical waveguide devices. The solution of H2O2 is proposed to post-treat thick porous silicon (PS) films. The prepared PS layer as the cathode is applied about 10 mA/cm(2) current in mixture of ethanol, HF, and H2O2 solutions, in order to improve the stability and the smoothness of the surface. With the low-temperature dry-O-2 pre-oxidizations and high-temperature wet O-2 oxidizations process, a high-quality SiO2 30 mu m thickness layer that fit for the optical waveguide device was prepared. The SEM images show significant improved smoothness on the surface of oxidized PS thick films, the SiO2 film has a stable and uniformity reflex index that measured by the prism coupler, the uniformity of the reflex index in different place of the wafer is about 0.0003.

Molecular beam epitaxial growth of GaN on 3c-SiC/Si(111) substrates using a thick AIN buffer layer

Hexagonal GaN films (similar to 3 mu m) were grown on 3c-SiC/Si(111) and carbonized Si(111) substrates using a thick AlN buffer Cracks are observed on the surface of the GaN film grown on the carbonized Si(111), while no cracks are visible on the 3c-SiC/Si(111). XRD exhibits polycrystalline nature of the GaN film grown on the carbonized Si(111) due to poorer crystalline quality of this substrate. Raman spectra reveal that all GaN layers are under tensile stress, and the GaN layer grown on 3c-SiC/Si(111) shows a very low stress value of sigma(xx) = 0.65 Gpa. In low-temperature Photoluminescence spectra the remarkable donor-acceptor-pair recombination and yellow band can be attributed to the incorporation of Si impurities from the decomposition of SiC.

LO-PHONON-ASSISTED TUNNELING IN ASYMMETRIC DOUBLE-WELL STRUCTURES WITH THICK BARRIERS

Nonresonant electron tunneling between asymmetric double quantum wells in AlxGa1-xAs/GaAs systems has been investigated by using steady-state and time-resolved photoluminescence spectra. Experimental evidence of LO-phonon-assisted tunneling through thick barriers has been obtained by enhancing excitation power densities or applying electric fields perpendicular to the well plane. LO-phonon-assisted tunneling times have also been estimated from the variation of the decay time of the narrow-well photoluminescence with applied electric fields. Our findings suggest that LO phonons in the barriers play an important role in the tunneling transfer.

Structural and Optical Performance of GaN Thick Film Grown by HVPE

Thick GaN films were grown on GaN/sapphire template in a vertical HVPE reactor. Various material characterization techniques,including AFM, SEM, XRD, RBS/Channeling, CL, PL, and XPS, were used to characterize these GaN epitaxial films. It was found that stepped/terraced structures appeared on the film surface,which were indicative of a nearly step-flow mode of growth for the HVPE GaN despite the high growth rate. A few hexagonal pits appeared on the surface, which have strong light emission. After being etched in molten KOH, the wavy steps disappeared and hexagonal pits with {1010} facets appeared on the surface. An EPD of only 8 ×10~6cm~(-2) shows that the GaN film has few dislocations. Both XRD and RBS channeling indicate the high quality of the GaN thick films. Sharp band-edge emission with a full width at half maximum（FWHM）of 67meV was observed, while the yellow and infrared emissions were also found. These emissions are likely caused by native defects and C and O impurities.

Effect of Annealing on Structural and Magnetic Properties of a Thick (Ga,Mn)As Layer

We investigate effects of annealing on magnetic properties of a thick (Ga,Mn)As layer, and find a dramatic increase of the Curie temperature from 65 to 115 K by postgrowth annealing for a 500-nm (Ga,Mn)As layer. Auger electron spectroscopy measurements suggest that the increase of the Curie temperature is mainly due to diffusion of Mn interstitial to the free surface. The double-crystal x-ray diffraction patterns show that the lattice constant of (Ga,Mn)As decreases with increasing annealing temperature. As a result, the annealing induced reduction of the lattice constant is mainly attributed to removal of Mn interstitial.

The fabrication of thick SiO2 layer by anodization

Silicon-based silica waveguide (SiO2/Si) devices have huge applications in optical telecommunication. SiO2 up to 25-mu m thick is necessary for some passive SiO2/Si waveguide devices. Oxidizing porous silicon to obtain thick SiO2 as cladding layer is presented. The experimental results of porous layer and oxidized porous layer formation were given. The relationship between cracking of SiO2 and temperature varying rate was given experimentally. Such conclusions are drawn: oxidation rate of porous silicon is several orders faster than that of bulk silicon; appropriate temperature variation rate during oxidation can prevent SiO2 on silicon substrates from cracking, and 25 mu m thick silicon dioxide layer has been obtained. (C) 2000 Elsevier Science B.V. All rights reserved.

Cosmological equations and thermodynamics on apparent horizon in thick braneworld

We derive the generalized Friedmann equation governing the cosmological evolution inside the thick brane model in the presence of two curvature correction terms: a four-dimensional scalar curvature from induced gravity on the brane, and a five-dimensional Gauss-Bonnet curvature term. We find two effective four-dimensional reductions of the generalized Friedmann equation in some limits and demonstrate that the reductions but not the generalized Friedmann equation can be rewritten as the first law of equilibrium thermodynamics on the apparent horizon of thick braneworld.

Single-crystal-like organic heterojunction with 40 nm thick charge accumulation layers

Single-crystal-like organic heterojunction films of copper phthalocyanine (CuPc) and copper-hexadecafluoro-phthalocyanine (F16CuPc) were fabricated by weak-epitaxy-growth method. The intrinsic properties of organic heterojunction were revealed through threshold voltage shift of field-effect transistors and measurement of single-crystal-like diodes. At both sides of the heterojunction interface 40 nm thick charge accumulation layers formed, which showed that the long carriers' diffusion length is due to the high crystallinity and low density of deep bulk traps of single-crystal-like films.

Mossbauer spectra of Fe-57 in a thick film of YBa2(Cu0.97Fe0.03)(3)O7-x irradiated by a large dose of gamma-rays

Mossbauer spectra of Fe-57 in a thick film YBa2(Cu0.97Fe0.03)(3)O7-x irradiated by a large dose of gamma-rays from Co-60 have been measured. The variation of the relative intensities of some subspectra of Fe-57 in the. Mossbauer spectra of the thick film YBa2(Cu0.97Fe0.03)(3)O7-x after irradiation can be observed. This variation indicates that the change of the coordination environment around some Fe atoms in the lattice occurs due to irradiation. The relative intensity of subspectrum D1(Fe) at the Cu(1) site decreases and that of subspectrum D4(Fe) at the Cu(1) site increases. This may be because of the possible oxygen atom hopping between the coordination environments of D1(Fe) and D4(Fe) in the lattice caused by irradiation. The effect of irradiation on the coordination environment around the Fe atom at the Cu(2) site is not appreciable. (C) 1997 Elsevier Science B.V.

Micro-Anatomical Quantitative Imaging Towards Enabling Automated Diagnosis of Thick Tissues at the Point of Care

Histopathology is the clinical standard for tissue diagnosis. However, histopathology has several limitations including that it requires tissue processing, which can take 30 minutes or more, and requires a highly trained pathologist to diagnose the tissue. Additionally, the diagnosis is qualitative, and the lack of quantitation leads to possible observer-specific diagnosis. Taken together, it is difficult to diagnose tissue at the point of care using histopathology.

Several clinical situations could benefit from more rapid and automated histological processing, which could reduce the time and the number of steps required between obtaining a fresh tissue specimen and rendering a diagnosis. For example, there is need for rapid detection of residual cancer on the surface of tumor resection specimens during excisional surgeries, which is known as intraoperative tumor margin assessment. Additionally, rapid assessment of biopsy specimens at the point-of-care could enable clinicians to confirm that a suspicious lesion is successfully sampled, thus preventing an unnecessary repeat biopsy procedure. Rapid and low cost histological processing could also be potentially useful in settings lacking the human resources and equipment necessary to perform standard histologic assessment. Lastly, automated interpretation of tissue samples could potentially reduce inter-observer error, particularly in the diagnosis of borderline lesions.

To address these needs, high quality microscopic images of the tissue must be obtained in rapid timeframes, in order for a pathologic assessment to be useful for guiding the intervention. Optical microscopy is a powerful technique to obtain high-resolution images of tissue morphology in real-time at the point of care, without the need for tissue processing. In particular, a number of groups have combined fluorescence microscopy with vital fluorescent stains to visualize micro-anatomical features of thick (i.e. unsectioned or unprocessed) tissue. However, robust methods for segmentation and quantitative analysis of heterogeneous images are essential to enable automated diagnosis. Thus, the goal of this work was to obtain high resolution imaging of tissue morphology through employing fluorescence microscopy and vital fluorescent stains and to develop a quantitative strategy to segment and quantify tissue features in heterogeneous images, such as nuclei and the surrounding stroma, which will enable automated diagnosis of thick tissues.

To achieve these goals, three specific aims were proposed. The first aim was to develop an image processing method that can differentiate nuclei from background tissue heterogeneity and enable automated diagnosis of thick tissue at the point of care. A computational technique called sparse component analysis (SCA) was adapted to isolate features of interest, such as nuclei, from the background. SCA has been used previously in the image processing community for image compression, enhancement, and restoration, but has never been applied to separate distinct tissue types in a heterogeneous image. In combination with a high resolution fluorescence microendoscope (HRME) and a contrast agent acriflavine, the utility of this technique was demonstrated through imaging preclinical sarcoma tumor margins. Acriflavine localizes to the nuclei of cells where it reversibly associates with RNA and DNA. Additionally, acriflavine shows some affinity for collagen and muscle. SCA was adapted to isolate acriflavine positive features or APFs (which correspond to RNA and DNA) from background tissue heterogeneity. The circle transform (CT) was applied to the SCA output to quantify the size and density of overlapping APFs. The sensitivity of the SCA+CT approach to variations in APF size, density and background heterogeneity was demonstrated through simulations. Specifically, SCA+CT achieved the lowest errors for higher contrast ratios and larger APF sizes. When applied to tissue images of excised sarcoma margins, SCA+CT correctly isolated APFs and showed consistently increased density in tumor and tumor + muscle images compared to images containing muscle. Next, variables were quantified from images of resected primary sarcomas and used to optimize a multivariate model. The sensitivity and specificity for differentiating positive from negative ex vivo resected tumor margins was 82% and 75%. The utility of this approach was further tested by imaging the in vivo tumor cavities from 34 mice after resection of a sarcoma with local recurrence as a bench mark. When applied prospectively to images from the tumor cavity, the sensitivity and specificity for differentiating local recurrence was 78% and 82%. The results indicate that SCA+CT can accurately delineate APFs in heterogeneous tissue, which is essential to enable automated and rapid surveillance of tissue pathology.

Two primary challenges were identified in the work in aim 1. First, while SCA can be used to isolate features, such as APFs, from heterogeneous images, its performance is limited by the contrast between APFs and the background. Second, while it is feasible to create mosaics by scanning a sarcoma tumor bed in a mouse, which is on the order of 3-7 mm in any one dimension, it is not feasible to evaluate an entire human surgical margin. Thus, improvements to the microscopic imaging system were made to (1) improve image contrast through rejecting out-of-focus background fluorescence and to (2) increase the field of view (FOV) while maintaining the sub-cellular resolution needed for delineation of nuclei. To address these challenges, a technique called structured illumination microscopy (SIM) was employed in which the entire FOV is illuminated with a defined spatial pattern rather than scanning a focal spot, such as in confocal microscopy.

Thus, the second aim was to improve image contrast and increase the FOV through employing wide-field, non-contact structured illumination microscopy and optimize the segmentation algorithm for new imaging modality. Both image contrast and FOV were increased through the development of a wide-field fluorescence SIM system. Clear improvement in image contrast was seen in structured illumination images compared to uniform illumination images. Additionally, the FOV is over 13X larger than the fluorescence microendoscope used in aim 1. Initial segmentation results of SIM images revealed that SCA is unable to segment large numbers of APFs in the tumor images. Because the FOV of the SIM system is over 13X larger than the FOV of the fluorescence microendoscope, dense collections of APFs commonly seen in tumor images could no longer be sparsely represented, and the fundamental sparsity assumption associated with SCA was no longer met. Thus, an algorithm called maximally stable extremal regions (MSER) was investigated as an alternative approach for APF segmentation in SIM images. MSER was able to accurately segment large numbers of APFs in SIM images of tumor tissue. In addition to optimizing MSER for SIM image segmentation, an optimal frequency of the illumination pattern used in SIM was carefully selected because the image signal to noise ratio (SNR) is dependent on the grid frequency. A grid frequency of 31.7 mm-1 led to the highest SNR and lowest percent error associated with MSER segmentation.

Once MSER was optimized for SIM image segmentation and the optimal grid frequency was selected, a quantitative model was developed to diagnose mouse sarcoma tumor margins that were imaged ex vivo with SIM. Tumor margins were stained with acridine orange (AO) in aim 2 because AO was found to stain the sarcoma tissue more brightly than acriflavine. Both acriflavine and AO are intravital dyes, which have been shown to stain nuclei, skeletal muscle, and collagenous stroma. A tissue-type classification model was developed to differentiate localized regions (75x75 µm) of tumor from skeletal muscle and adipose tissue based on the MSER segmentation output. Specifically, a logistic regression model was used to classify each localized region. The logistic regression model yielded an output in terms of probability (0-100%) that tumor was located within each 75x75 µm region. The model performance was tested using a receiver operator characteristic (ROC) curve analysis that revealed 77% sensitivity and 81% specificity. For margin classification, the whole margin image was divided into localized regions and this tissue-type classification model was applied. In a subset of 6 margins (3 negative, 3 positive), it was shown that with a tumor probability threshold of 50%, 8% of all regions from negative margins exceeded this threshold, while over 17% of all regions exceeded the threshold in the positive margins. Thus, 8% of regions in negative margins were considered false positives. These false positive regions are likely due to the high density of APFs present in normal tissues, which clearly demonstrates a challenge in implementing this automatic algorithm based on AO staining alone.

Thus, the third aim was to improve the specificity of the diagnostic model through leveraging other sources of contrast. Modifications were made to the SIM system to enable fluorescence imaging at a variety of wavelengths. Specifically, the SIM system was modified to enabling imaging of red fluorescent protein (RFP) expressing sarcomas, which were used to delineate the location of tumor cells within each image. Initial analysis of AO stained panels confirmed that there was room for improvement in tumor detection, particularly in regards to false positive regions that were negative for RFP. One approach for improving the specificity of the diagnostic model was to investigate using a fluorophore that was more specific to staining tumor. Specifically, tetracycline was selected because it appeared to specifically stain freshly excised tumor tissue in a matter of minutes, and was non-toxic and stable in solution. Results indicated that tetracycline staining has promise for increasing the specificity of tumor detection in SIM images of a preclinical sarcoma model and further investigation is warranted.

In conclusion, this work presents the development of a combination of tools that is capable of automated segmentation and quantification of micro-anatomical images of thick tissue. When compared to the fluorescence microendoscope, wide-field multispectral fluorescence SIM imaging provided improved image contrast, a larger FOV with comparable resolution, and the ability to image a variety of fluorophores. MSER was an appropriate and rapid approach to segment dense collections of APFs from wide-field SIM images. Variables that reflect the morphology of the tissue, such as the density, size, and shape of nuclei and nucleoli, can be used to automatically diagnose SIM images. The clinical utility of SIM imaging and MSER segmentation to detect microscopic residual disease has been demonstrated by imaging excised preclinical sarcoma margins. Ultimately, this work demonstrates that fluorescence imaging of tissue micro-anatomy combined with a specialized algorithm for delineation and quantification of features is a means for rapid, non-destructive and automated detection of microscopic disease, which could improve cancer management in a variety of clinical scenarios.

Emission spectroscopy from optically thick laboratory acetylene samples at high temperature

info:eu-repo/semantics/published