Radiation Detectors for Area (Ambient) Monitoring
K. N. Govinda Rajan in Radiation Safety in Radiation Oncology, 2017
Materials are classified as conductors, semiconductors, and insulators based on their band structure. When atoms come together and form a crystal or a solid, the energy levels of the individual atoms merge into a band of energy levels due to their mutual interactions. The gap between the discrete atomic energy levels become the band gap where electrons cannot stay since there are no energy levels available. The filled energy levels become filled bands of the solid and the partially filled levels become partially filled bands. The empty excited states of the atom become conduction bands. In materials like Al, Ag, or Ag, the valence and conduction bands overlap and so the electrons can easily move into the conduction band. That is the reason they are known as conductors. In materials like NaI, CsI, ZnS, there is a wide band gap and even at high temperatures electrons cannot gain sufficient energy to reach the conduction band. These materials are non-conductors and are known as insulators. Between these types of materials falls the semiconductor. A semiconductor is a material that has a small band gap between the valence band and conduction bands which can be less than couple of eV. These are materials like Si or Ge, the most well-known group 4 elements. Figure 7.30 illustrates the band structure of these three categories of materials.
Design and Manufacturing of CNT-Based Nanodevices for Optical Sensing Applications
Iniewski Krzysztof in Integrated Microsystems, 2017
Carbon nanotube (CNT) has some unique properties that are superior to some conventional semiconducting materials. We have developed a spectrum infrared (IR) sensor using a CNT which is capable to sense IR from near IR (NIR) middle-wave IR (MWIR) radiation in room temperature environment. This chapter gives an idea to design and fabricate CNT-based IR sensors. In addition, we have developed a series of processes to manufacture the devices. The process starts with the microfluidic-based delivery and separation of the nanomaterials. A precision assembly can be achieved by the atomic force microscopy-based nanorobotic system. It is capable of manipulating the nanomaterial at the desired position efficiently. The band gap of the semiconducting material is an important property for many applications, such as optical detectors and solar cells. We have developed an electrical breakdown control method to adjust the band structure of a CNT; this process has provided a steady and high-yield on-chip band gap engineering approach in batch electronics fabrication. Therefore, the spectral response of the devices can be adjusted. Finally, thermal annealing process and packaging process have been developed to maintain stability and reliability of nanodevices. The integration of the above technologies has provided an effective and efficient nanomanufacturing process for fabrication of nanosensors and electronic devices.
Radiation Detection and Measurement
Shaheen A. Dewji, Nolan E. Hertel in Advanced Radiation Protection Dosimetry, 2019
When a TLD is irradiated, the deposited energy can provide electrons that are in the valence band with enough energy to transition to the conduction band. This transition leaves behind a positive charge in the valence band known as a hole. The electron transitioning to the conduction band may lose some energy and drop into an energy level in the band gap that is present because of the added dopants of Mg and Ti. This energy level is known as an electron trap. A corresponding energy level near the valence band is known as a hole trap. Either electron traps or hole traps may be luminescence centers. When an electron or hole recombines at such a center, luminescence is produced. Heating of the TLD provides energy to trapped electrons causing them to enter the conduction band. As the temperature of the TLD is increased, electrons or holes recombine at a luminescence center, visible light is emitted as a function of time, and the resulting signal, detected by a photomultiplier, is known as a glow curve. It can be shown that the peak height, or the area under the glow curve, is proportional to dose. The application of heat for emptying traps is a relatively inefficient process. The probability of an electron migrating from a trap can be given as a function of time by an equation that is similar to the Arrhenius equation governing chemical reactions (Galwey and Brown 2002):
Topical delivery of growth factors and metal/metal oxide nanoparticles to infected wounds by polymeric nanoparticles: an overview
Published in Expert Review of Anti-infective Therapy, 2020
Mehran Alavi, Mahendra Rai
To sum up, several factors should be considered for the application of GFs as a remedy for chronic wounds. In this context, finding carriers with properties of suitable biocompatibility, biodegradability, and controlled release of growth factors is important. Wound type and wound-healing phase are other determinant factors in selection of appropriate GFs for capsulation. Moreover, in infected wounds such as DFU, removal of pathogenic microorganisms particularly bacteria and fungi can be a complicated issue. In this review, we have compared wound healing and antimicrobial capacities of encapsulated MNPs/MONPs with growth factors in micro- and nanocarrier systems. In the case of bacterial infection, the release of metal ion forms MNPs particularly AgNPs followed by ROS production can form a pit in cell wall and damage biological macromolecules involving enzymes and nucleic acids. The major drawback in using AgNPs is higher cytotoxicity of these NPs against human cells. ZnO and TiO2NPs as two common MONPs have more antibacterial activities under a specific wavelength of light irradiation. This ability is associated to the amount of band gap energy
Green synthesis of zinc oxide nanoparticles using different plant extracts and their antibacterial activity against Xanthomonas oryzae pv. oryzae
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2019
Solabomi Olaitan Ogunyemi, Yasmine Abdallah, Muchen Zhang, Hatem Fouad, Xianxian Hong, Ezzeldin Ibrahim, Md. Mahidul Islam Masum, Afsana Hossain, Jianchu Mo, Bin Li
The synthesis of zinc oxide by chamomile flower (Matricaria chamomilla L.), olive leaves (Olea europaea), and red tomato fruit (Lycopersicon esculentum M.) gave an end product of pale white and light brown precipitate respectively (Figure 1). The precipitates were freeze-dried to yield zinc oxide nanopowder which was used for further characterization. The UV – vis spectra of zinc oxide nanoparticles showed a strong absorption band at 384, 380, and 386 nm for chamomile flower (Matricaria chamomilla L.), olive leaves (Olea europaea), and red tomato fruit (Lycopersicon esculentum M.) respectively (Figure 2). The synthesized zinc oxide nanoparticles confirmed in this study by the UV – vis absorption spectra at the wavelength range of 380 to 386 nm which is the characteristic wavelength range of zinc oxide nanoparticles is consistent with the studies of [45]. The synthesized zinc oxide nanoparticles exhibited surface plasmon resonance (SPR) peak at 320 nm which is a blue shift. The band gap energy of SPR was calculated using the formula E = hc/λ, where “h” is the Plank’s constant, “c” is the velocity of light and “λ” the wavelength. The band gap was found to be 3.88 eV as earlier reported [46].
Health hazards of nanoparticles: understanding the toxicity mechanism of nanosized ZnO in cosmetic products
Published in Drug and Chemical Toxicology, 2019
Vimala Devi Subramaniam, Suhanya Veronica Prasad, Antara Banerjee, Madhumala Gopinath, Ramachandran Murugesan, Francesco Marotta, Xiao-Feng Sun, Surajit Pathak
The physicochemical aspects of TiO2 and ZnO nanoparticles elevate their potency in these products. The particle size of metal oxide nanoparticles influences the structural characteristics, namely the lattice symmetry and cell parameters, whereas their bulk counterparts are normally robust and stable systems with precise crystallographic structures. The decrease in size of an oxide particle alters the magnitude of band gap by increasing the conductivity and chemical reactivity. Theoretical studies of oxides in their bulk state have shown wide band gaps and low reactivity (Rodriguez 2002). The key factors involved in toxicity evaluation of such metal oxide nanoparticles include size, surface characteristics, dissolution, and exposure routes. There is a growing concern about the safety aspects of these nanostructured metal oxides, where various scientific studies regarding genotoxicity and cytotoxicity have been reported (Yin et al. 2012, Ivask et al. 2015). Some of the eminent leading brands in cosmetics continue to extensively manufacture tons of products containing nanoscale ingredients despite the alarming rise of toxicity reports of these nanomaterials (Raj et al. 2012, Melo et al. 2015).
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