Nanocrystals selfpurification mechanisms explained by energetics

first_imgIn an example of doped nanocrystals, this charge density plot shows magnesium impurities in cadmium-selenium nanocrystals at two different gap levels: (a) resonant and (b) hybrid. Image credit: Gustavo Dalpian and James Chelikowsky. On the macroscale, doping led to the transistor. On the nanoscale, scientists believe that doping could lead to an assortment of technologies, including solar cells, electroluminescent devices and electronic devices. Doping, which means adding impurities containing electrons, can enable electric conductance in a controlled way. But the miniscule size of semiconductor nanocrystals – also described as one-dimensional “quantum dots” – means that scientists must explore new methods for doping. Because nanocrystals have very little interior volume and are virtually all surface, scientists in the past believed that inner impurities can easily migrate the short distance to the surface and be ejected. “People used to believe that nanocrystals had fewer defects due to their limited size,” explains Gustavo Dalpian, coauthor with James Chelikowsky of a recent publication in Physical Review Letters on the energetics of doping. “People believed that defects could be annealed away from the nanocrystal in an easy way due to its limited size. After a few jumps, the impurity will be out of the nanocrystal.”In 2005, scientists (Erwin et al.) proposed that the difficulties in doping nanocrystals could be explained by the crystals’ surface topology and how easily impurities could bind to the surface. For these reasons, these scientists determined that the smaller the size of a nanocrystal, the less binding energy, and the more difficult doping becomes.Dalpian and Chelikowsky, from the University of Texas, have shown that understanding doping in semiconductor nanocrystals requires an understanding of both kinetic and thermodynamic/energetic properties. By explaining nanocrystals’ tendency toward self-purification in terms of the energy needed to form impurities in nanocrystals, the scientists hope to find new ways to increase the dopability of these materials.“Annealing was basically a kinetic argument,” Dalpian said to PhysOrg.com. “[Erwin et al.] show that, changing their solution to an anion-rich (negatively-charged) environment, they could put more impurities into the nanocrystals. Their argument was that there is a shape change in their nanocrystal that increases the binding energy of the impurity into the surface. We show that the difficulty of nanocrystal doping can also be explained through energetic arguments: when you change the solution to an anion-rich environment, the formation energy of the defects is decreased. Explore further ‘Nanocrystal doping’ enhances semiconductor nanocrystals Citation: Nanocrystals’ ‘self-purification’ mechanisms explained by energetics (2006, June 21) retrieved 18 August 2019 from https://phys.org/news/2006-06-nanocrystals-self-purification-mechanisms-energetics.htmllast_img read more

Will carbon nanotubes replace indium tin oxide

first_img Explore further This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. (PhysOrg.com) — Up until now, George Grüner tells PhysOrg.com, most of the studies regarding the properties – and uses – of carbon nanotubes have been restricted to the visible spectral range. “We, however, were interested in the properties in infrared range, in the window of the electromagnetic spectrum that is gaining increased prominence.” Carbon nanotubes made into conductive, flexible ‘stained glass’last_img read more

Researchers devise a means to obtain abnormal grain growth in metal using

first_img More information: Abnormal Grain Growth Induced by Cyclic Heat Treatment, Science 27 September 2013: Vol. 341 no. 6153 pp. 1500-1502 DOI: 10.1126/science.1238017ABSTRACTIn polycrystalline materials, grain growth occurs at elevated temperatures to reduce the total area of grain boundaries with high energy. The grain growth rate usually slows down with annealing time, making it hard to obtain grains larger than a millimeter in size. We report a crystal growth method that employs only a cyclic heat treatment to obtain a single crystal of more than several centimeters in a copper-based shape-memory alloy. This abnormal grain growth phenomenon results from the formation of a subgrain structure introduced through phase transformation. These findings provide a method of fabricating a single-crystal or large-grain structure important for shape-memory properties, magnetic properties, and creep properties, among others. Explore further This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. It’s the fineness of the grind Journal information: Science Citation: Researchers devise a means to obtain abnormal grain growth in metal using cyclic heat treatment (2013, September 27) retrieved 18 August 2019 from https://phys.org/news/2013-09-abnormal-grain-growth-metal-cyclic.htmlcenter_img (Phys.org) —A team of researchers from Tohoku University and Kyoto University in Japan has found a way to cause abnormal grain growth in metal crystals using cyclic heat treatment. In their paper published in the journal Science, the team describes how they came up with the approach, how well it works and how it might be used in future applications. © 2013 Phys.org In the never ending struggle to develop more kinds of metals that are suitable for a larger variety of purposes, scientists have studied the very nature of metals to better learn how it is they perform the way they do under different circumstances. Creating them one way, for example, results in a highly bendable but relatively weak metal—creating them another way can produce just the opposite. As part of the research involving metals, scientists have discovered that metals hold their shape in ways that are very similar to ceramics—it’s all based on crystal formation and how the crystals bind to one another.With metals, crystals bond together where they interface, known in the trade as the Grain Boundary (GB). Treating the metal can cause changes to the boundary which in turn impacts the properties of the finished product. Unfortunately, working with metals is still oftentimes more art than science—how grain boundaries form and impact interactions between crystals is still not wholly understood. What is known is that applying heat can cause the GB to stretch, causing longer grain formation—the result is a metal that can better endure multiple bends. Unfortunately, adding heat can only go so far, which is why researchers continue to look for ways to change the GB to add more desirable properties to metals.In this new effort, the researchers tried a cycling method—applying heat, allowing for cooling, then reapplying for as many times as appears to be beneficial. They applied the heat cycling to a copper based shape-memory alloy (metal that has been developed to revert automatically back to its original shape under certain specified conditions). Doing so they found, resulted in what metallurgists call Abnormal Grain Growth (AGG) which is where some of the crystals grow to different sizes than their neighbors. When it occurs in beneficial ways, as it did in the researchers experiment, it can result in the development of much longer grains, which translate to more robust metals.The researchers believe their technique might be used to create alloys with longer service lives and also may serve as the jumping off point for a whole new line of research, dedicated to better understanding the relationship between grain size as it relates to GB and the way it is changed with heat. The microstructure of a Cu-Al-Mn alloy with simple isothermal heat treatment and cyclic heat treatment. Credit: Science 27 September 2013: Vol. 341 no. 6153 pp. 1500-1502 DOI: 10.1126/science.1238017last_img read more

Using magnets to control chemical reactions that target release of medicines inside

first_img(Phys.org)—A team of researchers with the University of Georgia in Athens has developed a technique for controlling chemical reactions that release drugs inside the body. In their paper published in the journal Nature Catalysis, the group describes coating chemicals to prevent a reaction from occurring until the application of a magnetic field that releases a desired drug. In some medical applications, it is better for a medical treatment if a chemical can be applied directly to a certain part of the body and nowhere else. Chemicals meant to treat tumors are the prime example—chemotherapy drugs act on every cell they contact, causing a host of negative side effects. In this new effort, the group took a novel approach to solving this problem, using a magnet to force coated chemicals together, prompting a drug releasing reaction.To provide a means for controlling when chemicals come into contact inside the body, the researchers created tiny packets by first coating iron oxide nanoparticles with silica and then coating them further with two types of polymers, which, when combined, form a brush-like structure. Each of the packets was then loaded with either an enzyme or a substrate meant to react with the enzyme, and, of course, the drug to be released. In practice, the packets would be released into the body of a patient, where they would make their way to the whole body, behaving harmlessly, as the brushes prevent them from reacting whenever they meet. When the packets made their way to a site where a reaction was wanted, the researcher applied a magnet that forced them close together—close enough that they could react, releasing the drug. The other packets not involved in the reaction would slowly be flushed out of the body naturally, without causing harm.The researchers tested their packets in vitro using a real chemotherapy drug and cancer cells. They report it worked just as they had envisioned. More testing is required, of course, to ensure the technique is safe, but if all goes well, it could eventually be used to treat a wide variety of cancers. Multi stimuli-responsive nanocapsules selectively deliver drugs to exactly where they are needed Journal information: Nature Catalysis Explore further E- and S-type superparamagnetic nanoparticles carrying the enzyme and the substrate. a,b, Cryo-transmission electron microscopy (cryo-TEM) image (a) and schematic (b) explaining the concept of the magnetic-field-triggered biocatalysis. The particle superparamagnetic core is made of Fe3O4 nanoparticles enveloped by silica. The silica envelope is labelled with covalently bound fluorescent dyes (red for E-particles and green for S-particles). In the magnetic field, due to dipole–dipole interactions, the particles are brought into contact, so that the brush-like double-layer shells merge and intertwine, enabling interactions between the enzyme and substrate. The inner layers of the brush-shell are made of polyacrylic acid (PAA), which carries conjugated molecules of enzymes and substrates and provides the acidic environment for hydrolytic reactions. The external shell of poly(ethylene glycol methyl ether acrylate) polymer (PPEGMA) secures a barrier function to block ‘unauthorized’ or premature reactions of the enzyme and the substrate. The biocatalytic reaction is localized within the biocatalytic nanocompartment, which is generated in the magnetic field. The reaction is monitored by detecting the released cargo molecules. Credit: (c) Nature Catalysis (2017). DOI: 10.1038/s41929-017-0003-3last_img read more

Bengal BJP targeting 22 Lok Sabha seats ahead of 2019 polls

first_imgKolkata: The state BJP is targeting 22 Lok Sabha seats where election will be held in 2019. The 22 seats cover 154 Assembly constituencies and every Assembly segment will be placed under a state leader. This was decided at a meeting held between state president Dilip Ghosh and national president Amit Shah.Though BJP has finished the race in three-tier Panchayat election as a distant second, the party’s leaders at both national and local levels have expressed satisfaction over the performance of the party in Purulia and Junglemahal. Also Read – Heavy rain hits traffic, flightsIt has been decided that special drives will be conducted in these two districts. Various NGOs, without holding any party flag, will go to these districts to distribute books and clothes to the students.It has been learnt that RSS workers are secretly running schools in Jhargram and they have brainwashed not only the students but their parents as well and convinced them that the projects taken up by the state government to develop the district are actually Central government projects.Some local CPI-M cadres have also joined them to disturb peace in Belpahari, Binpur and Lalgarh, where peace has been restored by the efforts of Chief Minister Mamata Banerjee.last_img read more

Members of two Purulia families join Trinamool

first_imgKolkata: The members of two families from Purulia whose houses were visited by BJP national president Amit Shah on Thursday, joined Trinamool Congress on Friday.Sishubala Rajghar and her son Sanjay and Astami Rajghar and her son Puchu, came to the Trinamool office in Kolkata and joined the party.Dr Santanu Sen, Trinamool Congress Rajya Sabha MP, said that the families from Labda village are not associated with BJP in any way. On Thursday, Shah, along with other BJP leaders, went to their house and spent some time there. Also Read – Speeding Jaguar crashes into Merc, 2 B’deshi bystanders killed”They got frightened after Shah and his team left and without wasting any time, they left for Kolkata. As they saw Abhishek Banerjee, the party’s Youth Congress president in a meeting, they came to Kolkata and took shelter in the party office,” said Sen.Sen said the persons are apolitical and over the past eight years, they have seen major changes taking place in the area, following the initiative taken by Mamata Banerjee.”The roads have improved and people are getting power and drinking water. People had been deprived of basic amenities in the past 34 years under the CPI-M rule. Children are going to school,” he maintained.Local people said the families had shifted to BJP recently. Their relatives still support BJP. On Thursday, some BJP leaders, along with Shah, visited their houses and stayed there for five minutes.Trinamool leaders alleged that BJP had brainwashed the poor people by making false promises and during the Panchayat election, they spent money to win four Gram Panchayats and Panchayat Samitys in Purulia.last_img read more

Mamata to inaugurate Rath Yatra festival today

first_imgKolkata: Chief Minister Mamata Banerjee will inaugurate the Rath Yatra festival organised by ISKCON on Saturday morning.There will be different functions at the temple premises. She will be inaugurating the Rath Yatra and at around 1 pm, it will start moving ahead from Hungerford Street and pass through AJC Bose Road, Sarat Bose Road, Hazra Road, SPM Road, ATM Road, Chowringhee, Exide Crossing, Jawaharlal Nehru Road, Outram Road to reach Brigade Parade Ground. Also Read – Speeding Jaguar crashes into Merc, 2 B’deshi bystanders killedThousands of people will be turning up to take part in the Rath Yatra. People from different walks of life will start pouring into the city from Saturday morning itself to attend the biggest Rath Yatra festival in Kolkata. The police have also made an elaborate arrangement to avoid any untoward incident during the Rath Yatra festival on Saturday. Steps have also been taken to ensure that no traffic congestion happens when the Rath passes through the important thoroughfares. The top brass of the Kolkata Police have held a meeting in this connection and chalked out a plan to divert vehicles through other roads. Additional policemen will be on-duty for the security of the devotees who will take part in the Rath Yatra. Policemen in plainclothes and women cops will also be deployed. Also Read – Naihati: 10 councillors return to TMC from BJPThe chariot will be staying at Brigade Parade Ground till July 13 and people can visit to offer prayers to Lord Jagannath, Balaram and Subhadra. There will also be a fair at the ground on the eve of Rath Yatra. It is on July 22 noon that the festival of Ulta Rath Yatra will start. The Rath will be brought back to the temple through Outram Road near Park Street Metro, Jawaharlal Nehru Road, Dorina Crossing, S N Banerjee Road, Moulali Crossing, CIT Road, Suhrawardy Avenue, Park Circus 7 Point Crossing, Shakespeare Sarani and Hungerford Street. The Rath Yatra will be celebrated across the state on Saturday with great pomp and show where lakhs of devotees will gather at Mahesh in Hooghly.last_img read more