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Magnetron discharge plasma was applied for the synthesis of CN x thin layers using methane and nitrogen gas precursors. The incorporation of nitrogen in the carbon network resulted in the dramatic evolution of growth morphology: from a 'buried' porous layer observed at low nitrogen incorporation to aligned bundles of nanorods grown perpendicular to the substrate surface at maximum discharge power and nitrogen flow. The films deposited at the low discharge power and high nitrogen incorporation exhibited a mesoporous sponge-like morphology after vacuum annealing. Relevant physical mechanisms responsible for the formation of nano- and mesoshaped morphology are discussed in terms of the effects of internal mechanical stresses and plasma etching. In addition, the sensing properties of the sponge-like layer were preliminarily examined in water vapor and ammonia ambients. The CN x films showed enhanced sensitivity to ammonia and reverse electrical response to moisture in comparison with a nitrogen-free nanoporous carbon film, which were assigned to modification of the electronic properties of the nitridated surface. [ABSTRACT FROM AUTHOR]

We studied dielectrical properties of canine myocardium during acute ischemia and hypoxia using dielectrical spectroscopy method at frequency spectrum from 100 kHz to 6 GHz. This study was conducted on a group of six canines with acute ischemia and seven canines with hypoxia. Hypoxia (10% for 30 min) decreases myocardial resistance ([rho]), while the dielectrical permittivity ([epsilon]') of the myocardial tissue remains statistically unchanged. Acute ischemia for 2 hr causes significant frequency-dependent changes in both [epsilon]' and [rho] of myocardial tissue. Myocardial resistance increases, while the sign and amplitude of changes in the myocardial [epsilon]' are frequency and time dependent. These observations open up an opportunity for assessing the properties of myocardial tissue using dielectrical spectroscopy as well as noninvasively with the help of imaging methods based on electrical impedance and microwave tomography. Index Terms--Dielectric properties, hypoxia, ischemia, myocardium.

The purpose of this study was to construct a microwave tomographic system capable of conducting experiments with whole scale biological objects and to demonstrate the feasibility of microwave tomography for imaging such objects using a canine model. Experiments were conducted using a three-dimensional (3-D) microwave tomographic system with working chamber dimensions of 120 cm in diameter and 135 cm in height. The operating frequency was 0.9 GHz. The object under study was located in the central area of the tomographic chamber filled with a salt solution. Experimentally measured attenuation of the electromagnetic field through the thorax was about -- 120 dB. To obtain images, we used various two-dimensional and 3-D reconstruction schemes. Images of the canine were obtained. In spite of imperfections, the images represent a significant milestone in the development of microwave tomography for whole body imaging and demonstrate its feasibility. Index Terms--Dielectrical properties, image reconstruction, imaging, infarction, ischemia.

In this paper, a variant of the Newton method, which uses a fast solution of the direct problem and a dual mesh, is proposed. Computational and physical experiments with simple two-dimensional high-contrast phantoms are discussed, and a full-scaled image of a two-dimensional mathematical model of a human torso is obtained. Index Terms - Image reconstruction, inverse problems, iterative methods, microwave imaging, Newton method, tomography.

Microwave tomographic approach is proposed to detect and image breast cancers. Taking into account the big difference in dielectrical properties between normal and malignant tissues, we have proposed using the microwave tomographic method to image a human breast. Because of the anatomical features of the objects, this case has to be referred to the tomography with a limited angle of observation. As a result of computer experiments we have established that multiview cylindrical configurations are able to provide microwave tomograms of the breast with a small size tumor inside. Using the gradient method, we have developed a computer code to create images of the three-dimensional objects in dielectrical properties on microwave frequencies. Index Terms--Dielectric model of breast, gradient method, inverse problem, microwave tomography.

Microwave tomographic experiments have been performed on a three-dimensional (3-D) phantom and excised canine heart using a 3-D system operating at frequency of 2.4 GHz. A modified gradient reconstruction approach has been employed for the 3-D image reconstruction. To compare two-dimensional (2-D) and 3-D approaches, we also performed 2-D image reconstruction using an approach based on the Newton method. Experimental data acquired on experimental phantoms were analyzed using both 2-D and 3-D reconstruction approaches. High-quality images were reconstructed using the 3-D approach. The reconstruction procedure failed when the 2-D approach was applied to reconstruct images of the 3-D object. An image of the dielectrical properties of the excised canine heart was obtained using a 3-D reconstruction approach. Images successfully revealed a complex internal structure of the heart, including both right-hand side and left-hand side ventricles. Index Terms--Biophysical experiment, imaging, microwave tomography.

In this paper, the experimental study of spatial resolution of microwave tomography was performed. Our microwave tomographic system with operational frequencies of 0.9 and 2.36 GHz and with signal-to-noise ratio of 30 dB allowed us to achieve a spatial resolution between 7.3-9.5 mm and 6.3-7.8 mm at the former and latter frequencies, respectively. It was shown in experiments, with structurally complicated objects, that the spatial resolution of about the same distances can be expected in a practical application of microwave tomography to detect areas of myocardial ischemia and infarction. Index Terms--Microwave tomography, myocardial infarction, spatial resolution.

Initial porous silicon (por‐Si), carbonized porous silicon (por‐Si:C), and carbon‐incorporated porous silicon oxide (por‐SiO2:C) layers are studied by electron paramagnetic resonance (EPR) at T = 10–13 K. Scanning transmission electron microscopy and electron energy loss (EEL) spectroscopy show that por‐Si:C and por‐SiO2:C layers have a highly disordered structure with mixing sp2 and sp3 CC bonds. In the por‐SiO2:C layers, the peak of the oxygen bonded to carbon in the form of hydroxyl groups is found in the EEL spectrum of the C K‐edge region. Low‐intensity signals of Lorentzian lineshape are detected in the EPR spectrum of por‐Si, por‐Si:C, por‐SiO2:C layers. One of them is attributed to the Pb0 defect at the Si/SiO2 interface of nanocrystalline grain and the second to the silicon dangling bonds (SiDB) localized in nanocrystalline Si. The carbonization of por‐Si layers and subsequent oxidation of por‐Si:C gives rise to the appearance of additional EPR signals of high intensity at g = 2.0035(3) in por‐Si:C and at g = 2.0030(3) in por‐SiO2:C, which are assigned to carbon‐related defects (CRD) and carbon clusters, correspondingly. It was found that predominant defect types in por‐Si:C and por‐SiO2:C layers are CRD and carbon clusters, respectively, while the spin concentration of Pb0 interface defects and SiDB is low. [ABSTRACT FROM AUTHOR]

Radio-frequency (RF) hydrogen plasma treatment, thermal annealing in a furnace, and rapid thermal annealing of high-dose P+ ion implanted p-type Ge layers have been studied by Raman scattering spectroscopy, atomic force microscopy, secondary ion mass spectrometry, electrochemical capacitance-voltage profiling, four-point probes method, and x-ray reflectometry. It was shown that low-temperature RF plasma treatment at temperature about 200 °C resulted in full recrystallization of amorphous Ge layer implanted by P+ ions and activation of implanted impurity up to 6.5 × 1019 cm-3 with a maximum concentration at the depth of about 20 nm. Rapid thermal annealing (15 s) and thermal annealing (10 min) in nitrogen ambient required considerably higher temperatures for the recrystallization and activation processes that resulted in diffusion of implanted impurity inside the Ge bulk. It was demonstrated that RF plasma treatment from the samples with front (implanted) side resulted in considerable stronger effects of recrystallization and activation as compared with the same treatment from the back (unimplanted) side. The experiment shows that nonthermal processes play an important role in enhanced recrystallization and dopant activation during the RF plasma treatment. Mechanisms of enhanced modification of the subsurface implanted Ge layer under plasma treatment are analyzed. [ABSTRACT FROM AUTHOR]