联系我们  |  网站地图  |  English   |  移动版  |  中国科学院 |ARP
站内搜索:
首页 简介 管理部门 科研部门 支撑部门 研究队伍 科研成果 成果转化 研究生教育 党建与创新文化 科普 信息公开 办公内网
科技信息
Low-cost wearables manuf...
Researchers develop 3-D-...
硫化钴能用来制作超级电容
青岛能源所在石墨炔能源存...
二维非铅钙钛矿动力学机理...
Scientists fine-tune sys...
Amorphous diamond synthe...
化学耦合的硫化镍和碳空心...
全无机钙钛矿光电探测器动...
科研人员提出纳米催化医学...
Newly-discovered semicon...
Molecular nanoparticles ...
碳纳米点固态高效发光新方法
基于甲胺气体的钙钛矿薄膜...
新型镁电池可使储能技术更...
现在位置:首页>新闻动态>科技信息
Scientists find new method to control electronic properties of nanocrystals
2017-08-11 08:44:27 | 编辑: | 【 【打印】【关闭】

  Researchers from The Hebrew University of Jerusalem, Stony Brook University, and the U.S. Department of Energy's (DOE) Brookhaven National Laboratory have discovered new effects of an important method for modulating semiconductors. The method, which works by creating open spaces or "vacancies" in a material's structure, enables scientists to tune the electronic properties of semiconductor nanocrystals (SCNCs)—semiconductor particles that are smaller than 100 nanometers. This finding will advance the development of new technologies like smart windows, which can change opaqueness on demand.

  Scientists use a technique called "chemical doping" to control the electronic properties of semiconductors. In this process, chemical impurities—atoms from different materials—are added to a semiconductor in order to alter its electrical conductivity. Though it is possible to dope SCNCs, it is very difficult due to their tiny size. The amount of impurities added during chemical doping is so small that in order to dope a nanocrystal properly, no more than a few atoms can be added to the crystal. Nanocrystals also tend to expel impurities, further complicating the doping process.

  Seeking to control the electronic properties of SCNCs more easily, researchers studied a technique called vacancy formation. In this method, impurities are not added to the semiconductor; instead, vacancies in its structure are formed by oxidation-reduction (redox) reactions, a type of chemical reaction where electrons are transferred between two materials. During this transfer, a type of doping occurs as missing electrons, called holes, become free to move throughout the structure of the crystal, significantly altering the electrical conductivity of the SCNC.

  "We have also identified size effects in the efficiency of the vacancy formation doping reaction," said Uri Banin, a nanotechnologist from the Hebrew University of Jerusalem. "Vacancy formation is actually more efficient in larger SCNCs."

  In this study, the researchers investigated a redox reaction between copper sulfide nanocrystals (the semiconductor) and iodine, a chemical introduced in order to influence the redox reaction to occur.

(Top) The removal of copper from copper sulfide nanocrystals and the growth of copper iodine on nanocrystal facets is depicted by results from XAFS; (Bottom left) Larger nanocrystals are doped more efficiently by vacancy formation; (Right) Vacancy formation is observed by XRD. Credit: Brookhaven National Laboratory

  "If you reduce copper sulfide, you will pull out copper from the nanocrystal, generating vacancies and therefore holes," said Anatoly Frenkel, a chemist at Brookhaven National Laboratory holding a joint appointment with Stony Brook University, and the lead Brookhaven researcher on this study.

  The researchers used the x-ray powder diffraction (XPD) beamline at the National Synchrotron Light Source II (NSLS-II)—a DOE Office of Science User Facility—to study the structure of copper sulfide during the redox reaction. By shining ultra-bright x-rays onto their samples, the researchers are able to determine the amount of copper that is pulled out during the redox reaction.

  Based on their observations at NSLS-II, the team confirmed that adding more iodine to the system caused more copper to be released and more vacancies to form. This established that vacancy formation is a useful technique for tuning the electronic properties of SCNCs.

  Still, the researchers needed to find out what exactly was happening to copper when it left the nanocrystal. Understanding how copper behaves after the redox reaction is crucial for implementing this technique into smart window technology.

  "If copper uncontrollably disappears, we can't pull it back into the system," Frenkel said. "But suppose the copper that is taken out of the crystal is hovering around, ready to go back in. By using the reverse process, we can put it back into the system, and we can make a device that would be easy to switch from one state to the other. For example, you would be able to change the transparency of a window on demand, depending on the time of day or your mood."

  To understand what was happening to copper, the researchers used x-ray absorption fine structure (XAFS) spectroscopy at the Advanced Photon Source (APS)—also a DOE Office of Science User Facility—at Argonne National Laboratory. This technique allows the researchers to study the extremely small copper complexes that x-ray diffraction cannot detect. XAFS revealed that copper was combining with iodine to form copper iodine, a positive result that indicated copper could be put back into the nanocrystal and that the researchers have full control of the electronic properties.

   Explore further: Nanocage surfaces get 'makeover' in room temperature 

  More information: Orian Elimelech et al. Size Dependence of Doping by a Vacancy Formation Reaction in Copper Sulfide Nanocrystals, Angewandte Chemie International Edition (2017). DOI: 10.1002/anie.201702673   

  Journal reference: Angewandte Chemie International Edition 

版权所有 中国科学院上海硅酸盐研究所 沪ICP备05005480号
长宁园区地址:上海市长宁区定西路1295号 电话:86-21-52412990 传真:86-21-52413903 邮编:200050
嘉定园区地址:上海市嘉定区和硕路585号  电话:86-21-69906002 传真:86-21-69906700 邮编:201899