117 research outputs found

    3-D mapping of tellurium inclusions in CdZnTe crystals by means of improved optical microscopy

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    CdZnTe crystals are employed for the preparation of room temperature operating X-ray detectors. High resistivity is usually reached by contemporarily doping with group III or group VII elements and using tellurium deviated charge. This latter condition is responsible for the presence in crystals of a large number of tellurium inclusions. These can be incorporated at the growing interface or can form during cooling as a result of the retrograde behavior of the liquidus curve. Unfortunately, inclusions severely limit the performances of CdZnTe-based detectors, in particular in the case of imaging devices. This is why, monitoring tellurium inclusion density has become very important: i) for assessing the material quality ii) for studying the formation mechanisms of inclusions during growth iii) for checking the effectiveness of post-growth thermal treatments to reduce inclusion concentration. Tellurium inclusions are typically revealed by transmission optical microscopy in the near infrared. However, determination of the concentration of inclusions is complicated by the fact that at high magnification, the depth of field is much less then the sample thickness, so that in a single photograph only few inclusions appear really sharp. In order to overcome this problem, it is possible to take a set of photographs at different focal planes and, by means of specific software, reconstruct all inclusions on a single focal plane. This technique, also provided with some commercial microscopes, suffers two main problems: i) if one inclusion is present beneath a second one, only one is detected ii) any information about the depth in the sample of each inclusion is lost. For this reason, we have developed an instrument for the 3D mapping of the inclusions. The system is mounted on a standard optical microscope with automatic vertical movement. Pictures are taken at different focal planes. Images are then elaborated by dedicated software that ascribes each inclusion to the proper focal plane. As a result, all the inclusions are counted and precisely localized in 3D. By using the different objective lenses of the microscope is possible to tune the desired compromise between resolution and width of the monitored area. However, at high magnification it is possible to map inclusions down to 1 micron diameter. The system can be practically installed on any optical microscope that can operate in transmission mode

    L’omosessualità femminile in Italia: donne e coming out tra famiglia, amici e lavoro

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    This article focuses on the coming out of lesbian women in Italy. I analyse the impact of the coming out on their life courses and specifically within the family, the group of friends and work colleagues. A meta analysis of survey data (691 observations) was conducted. Some key factors that influence the likelihood of the coming out of women within the family, the group of friends and the colleagues were identified. The negative or positive impact of such factors on the likelihood of the coming out were identified through the use of logistic regressions. In general, a younger age, being resident in the North of Italy and in a city rather than in the south and in a small town, having a higher qualification and not being catholic are factors that have a positive impact on the likelihood of the coming out, that is they help women in their coming out process.Keywords: lesbian, coming out, logistic regression, identity.Parole chiave: lesbiche, coming out, regressione logistica, identità

    Characterization of tellurum inclusions in CdZnTe ingots grown by vertical bridgam technique

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    CdZnTe (CZT) crystals are employed for the preparation of room temperature operating X-ray detectors [1]. The functioning of the devices without refrigeration is made possible by growing high resistivity (>1010 Ohm.cm) ingots. This is usually reached by contemporarily doping with group III or group VII elements and using tellurium deviated charge. This second condition is responsible for the presence in crystals of a large number of tellurium inclusions. These can be incorporated at the growing interface or can form during cooling as a result of the retrograde behavior of the liquidus curve [2]. Unfortunately, inclusions severely limit the performances of CZT-based detectors, in particular in the case of imaging devices. In fact because of the role of diffusion of the electrons drifting from the cathode to the anode, tellurium inclusions act as traps for the charge carriers. Consequently the detector response close to the inclusions is deteriorated [3]. Hence, monitoring tellurium inclusion density is very important for assessing the material quality, selecting the best region in CZT wafer and for studying the formation mechanisms of inclusions during growth. Tellurium inclusions presence can be revealed by means of optical transmission microscopy in the near-infrared, in fact tellurium inclusions are opaque to the IR, while the CZT matrix is transparent. We developed an instrument for 3D mapping of inclusions mounted on a standard optical microscope with automatic vertical movement. Pictures are taken at different focal planes. Images are then elaborated by a dedicated software that ascribes each inclusion to the proper focal plane. As a result, all inclusions are counted and precisely localized in 3D. Using different objective lenses of the microscope it is possible to choose the optimal compromise between resolution and extent of the monitored area. However, at high magnification it is possible to map inclusions down to 1 micron diameter. The spatial position information of tellurium inclusion obtained by 3D IR mapping was used to select a single inclusion in the sample and then acquire photoluminescence (PL) map in the selected region. The inclusion was placed very close to the surface (few microns) by etching the sample. A correlation was set between the PL spectra emission and the presence of tellurium inclusion. [1] Knoll GF (2000) Radiation Detection and Measurements. Wiley [2] Rudolph P (1995), J. Cryst. Growth 147:297-304. [3] Carini GA (2006), Appl. Phys. Lett. 88:143515-143526. [4] Zambelli N (2011), J. Cryst. Growth 318:1167-1170

    Luminescence Properties of CZT Crystals in the Presence of Tellurium Inclusions

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    CZT is a widespread material for the realization of room temperature radiation detectors. The presence of defects and in particular secondary phases, like Te inclusions, represents nowadays a limit in the realization of high resolution devices. For the development of CZT detectors, in particular for high-flux applications, is very important to understand the role of deep levels, the influence of Te inclusions on the device performance and their correlations between Te inclusions and deep levels. Using a IR microscope recently developed at IMEM, it is possible to identify the 3D position of each inclusion in the bulk and reconstruct a 3D plot describing the spacial position of every inclusion. This permits to select a sigle inclusion in the sample, to place the inclusion very close to the surface (few microns) by etching the sample and hence to study the selected inclusion. In this way it is possible to perform photoluminescence and cathodoluminescence mapping in the inclusion region and investigate the behavior of the crystal-inclusion interface. The correlation between the deep level emission acquired at the micro-scale and the presence of tellurium inclusion is discussed

    Characterization of CZT crystals grown by the Boron Oxide Encapsulated Vertical Bridgman technique for the preparation of X-ray imaging detectors"

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    CdZnTe crystals are employed for the preparation of X- and Gamma- ray detectors. However, the large-scale production of these detectors is limited by the low yield of material with the required material properties, i. e. high resistivity, high carrier mobility lifetime product, and low inclusion density. In this frame, a new technique for the growth of CZT crystals has been developed based on a modification of the vertical Bridgman technique consisting in the encapsulation of the molten charge by a layer of boron oxide [1]. The authors have found that due to a chemical interaction with the quartz ampoule [2], a boron oxide layer fully encapsulates the crystal during growth preventing the direct contact of the crystal and the crucible walls. As a consequence, 2-inches CZT crystals characterized by large single grains and extremely low dislocations density have been grown. More recently, x-ray detectors with spectroscopic characteristics and good mobility lifetime product have been obtained using these crystals [3]. In this work we present an extensive characterization of these crystals with different techniques, ranging from energy dispersion x-ray analysis, photoluminescence mapping, contactless resistivity mapping, and infrared transmission. As a result, it is determined the interface shape and the zinc concentration distribution, that is related to the fluido-dynamic properties of the melt during growth. Moreover, the good homogeneity of resistivity is demonstrated. Finally, the typical inclusion density of these crystals is studied, hence the possibility to use them for the preparation of imaging and high flux x-ray detectors

    Interface shape control and tellurium inclusion concentration distribution in CdZnTe crystals grown by vertical Bridgman for X-ray detector applications

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    In spite of the efforts devoted to the task, many problems connected with the growth of CdZnTe (Zn>0) crystals are still unresolved, in particular tellurium inclusion density control, large single crystalline yield, seeding, and interface shape control. Moreover, also the electrical properties of the crystals (high resistivity and mobility-lifetime product) must be taken into account if detector performances have to be improved. In this work, the authors report on the growth and characterization of several CdZnTe crystals (Zn=10%) by vertical Bridgman, with and without the use of boron oxide as encapsulant. Different techniques were used to characterize the crystals: i) PL mapping for determining interface shape and to study the nucleation ii) a novel IR mapping apparatus to obtain fully 3D reconstruction of the inclusion distribution iii) X-ray detector characterization by means of nuclear sources to study the transport properties of the material (with mobility-lifetime product for electrons up to 6x10-3 cm2/V)

    Crystal Defects and Charge Collection in CZT X-Ray and Gamma Detectors

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    CdZnTe (CZT) is very promising material for room-temperature x-ray detectors proposed for medical, environmental and astrophysics applications. CZT can potentially provide high resistivity, low leakage current and high charge-collection efficiency. However, commercial CZT material is affected by crystal defects limiting the use of CZT in the large-scale production of x-ray and gamma detectors. In this work we have tested several CZT samples grown at IMEM-CNR Institute, in order to understand the roles of defects on the charge transport. Different optical and electrical techniques were used and the results will be reported. Te inclusions were studied with an IR microscope and accurate measurement of the electron mu-tau product u were conducted using an alpha particle source. We also studied the effect caused by grain boundaries and dislocations, which were identified using White beam X-ray Diffraction Topography. The homogeneity of the device response and the uniformity of the electric field were examined in the National Synchrotron Light Source using a 25-KeV highly collimated X-ray beam and raster scanning the device. A strong correlation between the extended defects and the detector response was found

    Hodgkin's disease as unusual presentation of post-transplant lymphoproliferative disorder after autologous hematopoietic cell transplantation for malignant glioma

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    BACKGROUND: Post-transplant lymphoproliferative disorder (PTLD) is a complication of solid organ and allogeneic hematopoietic stem cell transplantation (HSCT); following autologous HSCT only rare cases of PTLD have been reported. Here, a case of Hodgkin's disease (HD), as unusual presentation of PTLD after autologous HSCT for malignant glioma is described. CASE PRESENTATION: 60-years old man affected by cerebral anaplastic astrocytoma underwent subtotal neurosurgical excision and subsequent high-dose chemotherapy followed by autologous HSCT. During the post HSCT course, cranial irradiation and corticosteroids were administered as completion of therapeutic program. At day +105 after HSCT, the patient developed HD, nodular sclerosis type, with polymorphic HD-like skin infiltration. CONCLUSION: The clinical and pathological findings were consistent with the diagnosis of PTLD

    Exploring the feasibility and acceptability of a sleep wearable headband among a community sample of chronic pain individuals: An at-home observational study

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    Background: Chronic pain conditions affect up to one third of the adult population in the United Kingdom. Sleep problems are prevalent and negatively impact quality of life. Lack of standardised tools for routine screening and assessment of sleep changes have been a barrier for sleep management. Novel sleep wearables offer an exciting and accessible way to measure sleep but have not been tested outside of the consumer-led landscape and are not commonly used in research and clinical settings. // Aims: The study aimed to explore the feasibility and acceptability of a sleep monitoring headband (Dreem 2) utilising EEG technology and accompanying smartphone application among a cohort of adults with chronic pain. // Results: Twenty-one adults (81% women) completed a one-week home sleep study using a sleep headband and accompanying app. Ninety per cent of participants met the pre-defined requirement of two-night's sleep recording. All participants recorded one night of sleep data via the sleep headband. The majority (76%) of participants were satisfied with the sleep study, and 86% of participants were willing to wear the headband longer than the 2-night minimum requirement. Finally, 76% reported the headband as ‘somewhat’ or ‘extremely’ comfortable whist awake; 57% rated the headband as comfortable during sleep. // Conclusion: The Dreem 2 headband appears to be a feasible and acceptable means of collecting sleep measurements among individuals with chronic pain, despite common sleep disturbances. These devices may have utility for screening, assessment and monitoring in research and practice. Further research is needed to provide guidelines and training for integration

    Electroless Ink-Jet Printing on CdZnTe

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    CdZnTe is one of the most exploited materials for the realization of room temperature X- and gamma- ray detectors. However the final cost of the devices remains a limiting factor for large-scale applications. A strong effort was done in the last years for decreasing the cost of both crystals and device fabrication processes. Because of the important role played by the metal-CZT interface on the functioning of the final device, a special attention should be payed to the technology employed in the realization of metal contacts. A novel, reproducible and low-cost method for metal deposition on CZT surface has been developed combining two different technologies: ink-jet printing and electroless deposition. With this technique it is possible to avoid the photolithography process and still obtain complex contact patterns with a good spatial resolution and high reproducibility. The current-voltage characteristics of the obtained contacts are also reported, demonstrating good electrical properties
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