Irradiation-mediated tailoring of carbon nanotubes

The ever-increasing demand for faster computers in various areas, ranging from entertaining electronics to computational science, is pushing the semiconductor industry towards its limits on decreasing the sizes of electronic devices based on conventional materials. According to the famous law by Gordon E. Moore, a co-founder of the world s largest semiconductor company Intel, the transistor sizes should decrease to the atomic level during the next few decades to maintain the present rate of increase in the computational power. As leakage currents become a problem for traditional silicon-based devices already at sizes in the nanometer scale, an approach other than further miniaturization is needed to accomplish the needs of the future electronics. A relatively recently proposed possibility for further progress in electronics is to replace silicon with carbon, another element from the same group in the periodic table. Carbon is an especially interesting material for nanometer-sized devices because it forms naturally different nanostructures. Furthermore, some of these structures have unique properties. The most widely suggested allotrope of carbon to be used for electronics is a tubular molecule having an atomic structure resembling that of graphite. These carbon nanotubes are popular both among scientists and in industry because of a wide list of exciting properties. For example, carbon nanotubes are electronically unique and have uncommonly high strength versus mass ratio, which have resulted in a multitude of proposed applications in several fields. In fact, due to some remaining difficulties regarding large-scale production of nanotube-based electronic devices, fields other than electronics have been faster to develop profitable nanotube applications. In this thesis, the possibility of using low-energy ion irradiation to ease the route towards nanotube applications is studied through atomistic simulations on different levels of theory. Specifically, molecular dynamic simulations with analytical interaction models are used to follow the irradiation process of nanotubes to introduce different impurity atoms into these structures, in order to gain control on their electronic character. Ion irradiation is shown to be a very efficient method to replace carbon atoms with boron or nitrogen impurities in single-walled nanotubes. Furthermore, potassium irradiation of multi-walled and fullerene-filled nanotubes is demonstrated to result in small potassium clusters in the hollow parts of these structures. Molecular dynamic simulations are further used to give an example on using irradiation to improve contacts between a nanotube and a silicon substrate. Methods based on the density-functional theory are used to gain insight on the defect structures inevitably created during the irradiation. Finally, a new simulation code utilizing the kinetic Monte Carlo method is introduced to follow the time evolution of irradiation-induced defects on carbon nanotubes on macroscopic time scales. Overall, the molecular dynamic simulations presented in this thesis show that ion irradiation is a promisingmethod for tailoring the nanotube properties in a controlled manner. The calculations made with density-functional-theory based methods indicate that it is energetically favorable for even relatively large defects to transform to keep the atomic configuration as close to the pristine nanotube as possible. The kinetic Monte Carlo studies reveal that elevated temperatures during the processing enhance the self-healing of nanotubes significantly, ensuring low defect concentrations after the treatment with energetic ions. Thereby, nanotubes can retain their desired properties also after the irradiation. Throughout the thesis, atomistic simulations combining different levels of theory are demonstrated to be an important tool for determining the optimal conditions for irradiation experiments, because the atomic-scale processes at short time scales are extremely difficult to study by any other means.

Irradiation of silicon particle detectors with MeV-protons

Silicon particle detectors are used in several applications and will clearly require better hardness against particle radiation in the future large scale experiments than can be provided today. To achieve this goal, more irradiation studies with defect generating bombarding particles are needed. Protons can be considered as important bombarding species, although neutrons and electrons are perhaps the most widely used particles in such irradiation studies. Protons provide unique possibilities, as their defect production rates are clearly higher than those of neutrons and electrons, and, their damage creation in silicon is most similar to the that of pions. This thesis explores the development and testing of an irradiation facility that provides the cooling of the detector and on-line electrical characterisation, such as current-voltage (IV) and capacitance-voltage (CV) measurements. This irradiation facility, which employs a 5-MV tandem accelerator, appears to function well, but some disadvantageous limitations are related to MeV-proton irradiation of silicon particle detectors. Typically, detectors are in non-operational mode during irradiation (i.e., without the applied bias voltage). However, in real experiments the detectors are biased; the ionising proton generates electron-hole pairs, and a rise in rate of proton flux may cause the detector to breakdown. This limits the proton flux for the irradiation of biased detectors. In this work, it is shown that, if detectors are irradiated and kept operational, the electric field decreases the introduction rate of negative space-charges and current-related damage. The effects of various particles with different energies are scaled to each others by the non-ionising energy loss (NIEL) hypothesis. The type of defects induced by irradiation depends on the energy used, and this thesis also discusses the minimum proton energy required at which the NIEL-scaling is valid.

The grumpy stump - ultrasound and stump appendicitis

BACKGROUND: Stump appendicitis, the inflammation of an incompletely removed appendix, is a rare clinical presentation. Sonography can be useful in the diagnosis of the condition; by either directly visualising the inflamed stump, or by identifying signs of peri-caecal inflammation that can raise suspicion of the condition. SUMMARY OF WORK: A potential case of stump appendicitis was identified. This prompted a review of literature focused on the incidence of stump appendicitis, utility of ultrasound to identify an inflamed appendiceal stump, and surgical techniques used in appendectomy. SUMMARY OF RESULTS: Stump appendicitis is rare, with as few as 61 cases identified in literature during the last 60 years1. Of the two common techniques of appendectomy, which are ligation and invagination, the former can sometimes leave a residual stump that acts as a potential lumen for the pathophysiological process of appendicitis to recur. Established sonographic criteria for appendicitis also apply to the residual stump. Sonographic secondary signs that suggest the presence of acute appendicitis2 have also been demonstrated in cases of stump appendicitis3, even in the absence of an identifiable stump. DISCUSSION AND CONCLUSIONS: Appendicitis is usually dismissed in patients with a history of appendectomy. Though uncommon, sonographers should be aware of stump appendicitis in post-appendectomy patients that present with right iliac fossa pain from months to decades later. REFERENCE(S) 1. Subramanian A, Liang MK. A 60-year literature review of stump appendicitis: The need for a critical view. Am J Surg; 2012;203(4):503–7. 2. Reddan T, Corness J, Mengersen K, Harden F. Ultrasound of paediatric appendicitis and its secondary sonographic signs: providing a more meaningful finding. J Med Radiat Sci. 2015;DOI: 10.1002/jmrs.154 3. Martínez Chamorro E, Merina Castilla A, Muñoz Fraile B, Koren Fernández L, Borruel Nacenta S. Stump appendicitis: Preoperative imaging findings in four cases. Abdom Imaging. 2013;38(6):1214–9.

Contrast-enhanced ultrasound of abdominal organs in cats

The primary aim of this thesis was the evaluation of the perfusion of normal organs in cats using contrast-enhanced ultrasound (CEUS), to serve as a reference for later clinical studies. Little is known of the use of CEUS in cats, especially regarding its safety and the effects of anesthesia on the procedure, thus, secondary aims here were to validate the quantitative analyzing method, to investigate the biological effects of CEUS on feline kidneys, and to assess the effect of anesthesia on splenic perfusion in cats undergoing CEUS. -- The studies were conducted on healthy, young, purpose-bred cats. CEUS of the liver, left kidney, spleen, pancreas, small intestine, and mesenteric lymph nodes was performed to characterize the normal perfusion of these organs on ten anesthetized, male cats. To validate the quantification method, the effects of placement and size of the region of interest (ROI) on perfusion parameters were investigated using CEUS: Three separate sets of ROIs were placed in the kidney cortex, varying in location, size, or depth. The biological effects of CEUS on feline kidneys were estimated by measuring urinary enzymatic activities, analyzing urinary specific gravity, pH, protein, creatinine, albumin, and sediment, and measuring plasma urea and creatinine concentrations before and after CEUS. Finally, the impact of anesthesia on contrast enhancement of the spleen was investigated by imaging cats with CEUS first awake and later under anesthesia on separate days. -- Typical perfusion patterns were found for each of the studied organs. The liver had a gradual and more heterogeneous perfusion pattern due to its dual blood flow and close proximity to the diaphragm. An obvious and statistically significant difference emerged in the perfusion between the kidney cortex and medulla. Enhancement in the spleen was very heterogeneous at the beginning of imaging, indicating focal dissimilarities in perfusion. No significant differences emerged in the perfusion parameters between the pancreas, small intestine, and mesenteric lymph nodes. -- The ROI placement and size were found to have an influence on the quantitative measurements of CEUS. Increasing the depth or the size of the ROI decreased the peak intensity value significantly, suggesting that where and how the ROI is placed does matter in quantitative analyses. --- A significant increase occurred in the urinary N-acetyl-β-D-glucosaminidase (NAG) to creatinine ratio after CEUS. No changes were noted in the serum biochemistry profile after CEUS, with the exception of a small decrease in blood urea concentration. The magnitude of the rise in the NAG/creatinine ratio was, however, less than the circadian variation reported earlier in healthy cats. Thus, the changes observed in the laboratory values after CEUS of the left kidney did not indicate any detrimental effects in kidneys. Heterogeneity of the spleen was observed to be less and time of first contrast appearance earlier in nonanesthetized cats than in anesthetized ones, suggesting that anesthesia increases heterogeneity of the feline spleen in CEUS. ---- In conclusion, the results suggest that CEUS can be used also in feline veterinary patients as an additional diagnostics aid. The perfusion patterns found in the imaged organs were typical and similar to those seen earlier in other species, with the exception of the heterogeneous perfusion pattern in the cat spleen. Differences in the perfusion between organs corresponded with physiology. Based on the results, estimation of focal perfusion defects of the spleen in cats should be performed with caution and after the disappearance of the initial heterogeneity, especially in anesthetized or sedated cats. Finally, these results indicate that CEUS can be used safely to analyze kidney perfusion also in cats. Future clinical studies are needed to evaluate the full potential of CEUS in feline medicine as a tool for diagnosing lesions in various organ systems.

Rapid growth of nanotubes and nanorods of wurtzite ZnO through microwave-irradiation of a metalorganic complex of zinc and a surfactant in solution

Large quantities of single-crystalline ZnO nanorods and nanotubes have been prepared by the microwave, irradiation of a metalorganic complex of zinc, in the presence of a surfactant. The method is simple, fast, and inexpensive (as it uses a domestic microwave oven), and yields pure nanostructures of the hexagonal wurtzite phase of ZnO in min, and requires no conventional templating. The ZnO nanotubes formed have a hollow core with inner diameter varying from 140-160 nm and a wall of thickness, 40-50 nm. The length of nanorods and nanotubes varies in the narrow range of 500-600 nm. These nanostructures have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The ZnO nanorods and nanotubes are found by SAED to be single-crystalline. The growth process of ZnO nanorods and nanotubes has been investigated by varying the surfactant concentration and microwave irradiation time. Based on the various results obtained, a tentative and plausible mechanism for the formation of ZnO nanostructures is proposed.

Elastic property estimation using Ultrasound Assisted Optical Elastography through Remote Palpation - A simulation study - art. no. 61640Q

We propose an effective elastography technique in which an acoustic radiation force is used for remote palpation to generate localized tissue displacements, which are directly correlated to localized variations of tissue stiffness and are measured using a light probe in the same direction of ultrasound propagation. The experimental geometry has provision to input light beam along the ultrasound propagation direction, and hence it can be prealigned to ensure proper interception of the focal region by the light beam. Tissue-mimicking phantoms with homogeneous and isotropic mechanical properties of normal and malignant breast tissue are considered for the study. Each phantom is insonified by a focusing ultrasound transducer (1 MHz). The focal volume of the transducer and the ultrasound radiation force in the region are estimated through solving acoustic wave propagation through medium assuming average acoustic properties. The forward elastography problem is solved for the region of insonification assuming the Lame's parameters and Poisson's ratio, under Dirichlet boundary conditions which gives a distribution of displacement vectors. The direction of displacement, though presented spatial variation, is predominantly towards the ultrasound propagation direction. Using Monte Carlo (MC) simulation we have traced the photons through the phantom and collected the photons arriving at the detector on the boundary of the object in the direction of ultrasound. The intensity correlations are then computed from detected photons. The intensity correlation function computed through MC simulation showed a modulation whose strength is found to be proportional to the amplitude of displacement and inversely related to the storage (elastic) modulus. It is observed that when the storage modulus in the focal region is increased the computed displacement magnitude, as indicated by the depth of modulation in the intensity autocorrelation, decreased and the trend is approximately exponential.

Effect of √-irradiation on the structure and dynamics of domains in triglycine selenate

A comparative study of the switching properties of pure and √-irradiated TGSe crystals has been carried out to see the effect of irradiation on the structure and dynamics of domains. The switching behaviour of √-irradiated TGSe has been found to be qualitatively similar to that of unirradiated crystal and this has been interpreted in terms of structural inhibition caused by the formation of radiolysis products as well as the difference between the domain structures of the unirradiated and irradiated samples. Confirmation of this has been obtained by studying the domain patterns using the etch method.

Assessment of ultrasound modulation of near infrared light on the quantification of scattering coefficient

Purpose: To assess the effect of ultrasound modulation of near infrared (NIR) light on the quantification of scattering coefficient in tissue-mimicking biological phantoms.Methods: A unique method to estimate the phase of the modulated NIR light making use of only time averaged intensity measurements using a charge coupled device camera is used in this investigation. These experimental measurements from tissue-mimicking biological phantoms are used to estimate the differential pathlength, in turn leading to estimation of optical scattering coefficient. A Monte-Carlo model base numerical estimation of phase in lieu of ultrasound modulation is performed to verify the experimental results. Results: The results indicate that the ultrasound modulation of NIR light enhances the effective scattering coefficient. The observed effective scattering coefficient enhancement in tissue-mimicking viscoelastic phantoms increases with increasing ultrasound drive voltage. The same trend is noticed as the ultrasound modulation frequency approaches the natural vibration frequency of the phantom material. The contrast enhancement is less for the stiffer (larger storage modulus) tissue, mimicking tumor necrotic core, compared to the normal tissue. Conclusions: The ultrasound modulation of the insonified region leads to an increase in the effective number of scattering events experienced by NIR light, increasing the measured phase, causing the enhancement in the effective scattering coefficient. The ultrasound modulation of NIR light could provide better estimation of scattering coefficient. The observed local enhancement of the effective scattering coefficient, in the ultrasound focal region, is validated using both experimental measurements and Monte-Carlo simulations. (C) 2010 American Association of Physicists in Medicine. [DOI: 10.1118/1.3456441]

Formation of crystalline diamond from amorphous diamond-like carbon films by pulsed laser irradiation

The formation of crystalline diamond films from amorphous diamond-like carbon films by pulsed laser irradiation with a 300 μs non-Q-switched Nd:YAG laser has been established by a combined study of transmission electron microscopy, x-ray photoelectron spectroscopy, and electrical resistivity. The films have been prepared by glow discharge decomposition of a mixture of propane, n-butane, and hydrogen in a rf plasma operating at a frequency of 13.56 MHz. Prior to laser irradiation, the films have been found to be amorphous by transmission electron microscope studies. After irradiation, the electron diffraction patterns clearly point out the formation of cubic diamond structure with a lattice spacing of 3.555 Å. However, the close similarity between diamond and graphite electron diffraction patterns could sometimes be misleading regarding the formation of a diamond structure, and hence, x-ray photoelectron spectroscopic studies have been carried out to confirm the results. A chemical shift in the C 1s core level binding energies towards higher values, viz., from 286.5 to 287.8 eV after laser irradiation, and a high electrical resistivity >1013 Ω cm are consistent with the growth of diamond structure. This novel "low-temperature, low-pressure" synthesis of diamond films offers enormous potential in terms of device compatibility with other solid-state devices.

A novel two sources ultrasound modulated optical tomographic system for screening breast cancer through elasticity characterization

The study of non-invasive characterization of elastic properties of soft biological tissues has been a focus of active researches since recent years. Light is highly scattered by biological tissues and hence, sophisticated reconstruction algorithms are required to achieve good imaging depth and a reasonable resolution. Ultrasound (US), on the otherhand, is less scattered by soft tissues and it has been in use for imaging in biomedical ultrasound systems. Combination of the contrast sensitivity of light and good localization of ultrasound provides a challenging technique for characterization of thicker tissues deep inside the body non-invasively. The elasticity of the tissues is characterized by studying the response of tissues to mechanical excitation induced by an acoustic radiation force (remotely) using an optical laser. The US modulated optical signals which traverse the tissue are detected by using a CCD camera as detector array and the pixel map formed on the CCD is used to characterize the embedded inhomogeneities. The use of CCD camera improves the signal-noise-ratio (SNR) by averaging the signals from all of the CCD pixels.

Surface modifications in single crystal surfaces of YBa2Cu3O7-delta upon high energy ion irradiation

Atomic force microscopy investigations on swift heavy ion (200 MeV An) irradiated surfaces of a high T-c single crystal YBa2Cu3O7-delta are presented. Results obtained revealed an ion-induced erosion/sputtering clearly confirming our earlier observation on grain boundary dominated thin films. Apart from sputtering, notable effects were seen with many defect structures like dikes/hillocks surrounded by craters, dikes, holes, pearl like structures and ripple formation of sub-micron undulations, all in one crystal. Results are discussed in the light of co-operative phenomena of material re-distribution mechanism related to mass transfer and crater formations.

Microwave irradiation-assisted method for the deposition of adherent oxide films on semiconducting and dielectric substrates

We report a method for the deposition of thin films and thick coatings of metal oxides through the liquid medium, involving the micro waveirradiation of a solution of a metal-organic complex in a suitable dielectric solvent. The process is a combination of sol-gel and dip-coating methods, wherein coatings can be obtained on nonconducting and semiconducting substrates, within a few minutes. Thin films of nanostructured ZnO (wurtzite) have been obtained on Si(100), glass and polymer substrates, the nanostructure determined by process parameters The coatings are strongly adherent and uniform over 15 mm x 15 mm, the growth rate similar to 0.25 mu m/min Coatings of nanocrystalline Fe2O3 and Ga2O3 have also been obtained The method is scalable to larger substrates, and is promising as a low temperature technique for coating dielectric substrates, including flexible polymers. (C) 2010 Elsevier B.V. All rights reserved.