Magnetic dipolar coupling and collective effects for binary information codification in cost-effective logic devices

Physical limitations foreshadow the eventual end to traditional Complementary Metal Oxide Semiconductor (CMOS) scaling. Therefore, interest has turned to various materials and technologies aimed to succeed to traditional CMOS. Magnetic Quantum dot Cellular Automata (MQCA) are one of these technologies. Working MQCA arrays require very complex techniques and an excellent control on the geometry of the nanomagnets and on the quality of the magnetic thin film, thus limiting the possibility for MQCA of representing a definite solution to cost-effective, high density and low power consumption device demand. Counter-intuitively, moving towards bigger sizes and lighter technologies it is still possible to develop multi-state logic devices, as we demonstrated, whose main advantage is cost-effectiveness. Applications may be seen in low cost logic devices where integration and computational power are not the main issue, eventually using flexible substrates and taking advantage of the intrinsic mechanical toughness of systems where long range interactions do not need wirings. We realized cobalt micrometric MQCA arrays by means of Electron Beam Lithography, exploiting cost-effective processes such as lift-off and RF sputtering that usually are avoided due to their low control on array geometry and film roughness. Information relative to the magnetic configuration of MQCA elements including their eventual magnetic interactions was obtained from Magnetic Force Microscope (MFM) images, enhanced by means of a numerical procedure and presented in differential maps. We report the existence of bi-stable magnetic patterns, as detected by MFM while sampling the z-component of magnetic induction field, arising from dipolar inter-element magnetostatic coupling, able to store and propagate binary information. This is achieved despite the array quality and element magnetic state, which are low and multi-domain, respectively. We discuss in detail shape, inter-element spacing and dot profile effects on the magnetic coupling. Numerical Finite Element Method (FEM) simulations show a possible microspin arrangement producing such magnetostatic coupling.     

Photo-induced Janus effect of graphene oxide films

The effect of UV irradiation on the wettability of GO films, as well as the possibility of making a film with different properties of its surface, the Janus film, has been studied. The O/C ratio changes from 0.32 to 0.26 after 6 ​h of UV irradiation. The contact angle of water droplet wetting on an unirradiated surface is θ ​≈ ​35°. The contact angle reaches more than 95° on the irradiated surface, which means that a hydrophobic surface on a film can be obtained. The origin of amphiphilic properties of the GO film are associated with the photochemical reduction of GO.     

磁控溅射制备纳米TiO_2半导体薄膜的工艺研究与光谱分析

通过射频反应磁控溅射在玻璃基片上制备TiO2薄膜。采用X射线衍射仪和Raman光谱仪研究退火温度对薄膜晶体结构的影响;还探讨了磁控溅射氧分压对薄膜性能的影响。结果表明：磁控溅射制备的薄膜在不同温度下退火。300℃退火时薄膜没有结晶;400℃退火出现锐钛矿结构;500℃退火后薄膜锐钛矿结构更完善,（101）方向开始优先生长,是因为锐钛矿结构更完整。随着退火温度的升高晶粒长大拉曼光谱出现红移,拉曼光谱所反应的锐钛矿信息增强,500℃退火时197cm-1出现了Eg振动模式。和标准的单晶TiO2体材料相比,拉曼峰位置都略有红移是纳米量子尺寸效应造成的。氩氧比分别为9∶1、7∶3和6∶4溅射制备的薄膜通过400℃退火后的XRD衍射谱没有明显的区别,但拉曼光谱显示氩氧比为7∶3时结晶要完善些。     

Ag-TiO2和Au-TiO2复合薄膜光催化降解偶氮染料酸性大红GR的研究

以玻璃珠为载体,溶胶-凝胶法制Ag-TiO2和Au-TiO2复合薄膜,研究了水溶液中的偶氮染料酸性大红GR进行了固定相光催化氧化以及银和金的掺杂量、染料水溶液的pH值、光源、催化剂的重复使用性等因素的影响.负载型复合光催化剂Ag-TiO2和Au-TiO2的光催化活性显著提高.当Ag和Au掺杂TiO2的质量分数分别为0.4%和0.6%时,最高光解率分别提高了2.1倍和1.8倍.     

Pb(Mg_(1/3)Nb_(2/3))O_3-PbTiO_3/CoFe_2O_4复合薄膜电学、磁学性能的研究

利用射频磁控溅射技术在LaNiO_3/SiO_2/Si基底上制备了Pb(Mg_(1/3)Nb_(2/3))O_3-PbTiO_3/CoFe_2O_4和Pb(Mg_(1/3)Nb_(2/3))O_3-Pb TiO_3/Co Fe_2O_4/Pb(Mg_(1/3)Nb_(2/3))O_3-PbTiO_3两种复合薄膜.我们采取了三种退火条件对复合薄膜进行退火处理,研究两种复合薄膜的晶体结构、电学和磁学性能.通过对两种复合薄膜的结构的分析,发现两步法退火后得到复合薄膜同时存在纯钙钛矿相和尖晶石相两种结构.铁电性能测试表明,两种复合薄膜均具有较好的铁电性能,其中三层复合薄膜的剩余极化强度Pr最大可以达到14.9μC/cm2,这要归因于多层复合薄膜内部的应力-应变效应和界面耦合效应.在电场强度为80 k V/cm的漏电流密度数量级仅10-5A/cm2,其导电机制在高电场区满足Schottky机制.介频性能测试表明:复合薄膜的介频特性较差,双层复合薄膜的介电性能较好,其介电常数εr为1078,其介电损耗tgδ较大,约为0.43.此外,对复合薄膜的磁滞回线测试表明:两种复合薄膜中均存在磁学性能,且双层结构复合薄膜的铁磁性能较大,其饱和磁化强度Ms为119 emu/cm3,剩余磁化强度Mr达到31.6 emu/cm3,矫顽场Hc为1360 Oe.以上测试结果表明,铁电有序和磁有序可以存在于钙钛矿-尖晶石结构当中,通过多层复合和合适退火方式可以增强其铁电和介电性能.     

Imaging of laser-polarized solid xenon

The enhanced spin polarization produced by optical pumping of gaseous rubidium/xenon samples has made possible a number of recent experiments in nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI). Here we report MRI of laser-polarized xenon in the solid phase at low temperature. Due to the high xenon density in the solid phase and the enhanced spin polarization, it is possible to achieve high intensity and spatial resolution of the image. Signals were observed from xenon films solidified onto the glass container walls and not from an enclosed chili pepper.