Characterization of Ga-Mn Decagonal Quasicrystals in GaAs
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Characterization of Ga-Mn decagonal quasicrystals in GaAs
K. Sun and N. D. Browning Department of Physics (M/C273), University of Illinois at Chicago, 845 W. Taylor St. Chicago IL 60607-7059 ABSTRACT Ga-Mn decagonal quasicrystals (DQC), as well as a Ga-Mn approximant and a normal crystal in GaAs are investigated by electron energy-loss spectroscopy (EELS) and energy dispersive Xray spectroscopy (EDS) combined with Z-contrast imaging. Plasmon peak positions (Ep), fullwidth-half-maxima (FWHM) and Mn L3/L2 ratios of these three phases are derived from their low-loss spectra and core-loss spectra respectively. Mn, Ga and As distributions in ion implanted GaAs layers are characterized by EDS at line-scan mode. These results show that the Ga-Mn DQC has higher Ep and FWHMs than those of its normal crystal counterpart, as well as all other reported QCs. The much larger L3/L2 intensity ratio of the Ga-Mn DQC over that of the Al-Mn icosahedral quasicrystals (IQC) may suggest Mn atoms in the Ga-Mn DQC have much larger local magnetic moments. INTRODUCTION Quasicrystals are unique in their atomic structures compared with normal crystals because they have forbidden symmetries. This suggests they may have special electronic, optical and magnetic properties, which are much different from their normal crystal counterparts. In order to measure such unique properties from different quasicrystal systems, different techniques have been tried. Among these, spectroscopic techniques, such as SQUID magnetometer [1], photoemission [2] and tunneling spectroscopy [3], etc have offered many interesting results. However, most of these experimental techniques measure properties over a macroscopic specimen, which by nature is microscopically inhomogeneous. Electron energy-loss spectroscopy in the electron microscope can be used for characterizing materials at high spatial resolution and gives microscopic optical, electronic and magnetic data from the band-gap, low-loss and core-loss ranges [4,5]. Nevertheless, there are few reports of EELS studies on QCs. It was firstly used for characterizing IQC-Al6Mn [6], in which low-loss spectra from IQC, amorphous, normal crystal Al6Mn and Al were collected and compared. Later, several papers concerning low-loss spectra collected from different IQC and DQC phases were published. These QCs are IQC -Al80Mn20 and -Al74Mn20Si6 [7], IQC -PdUSi and -AlCuV [8], IQC -AlPd and -AlPdMn [9], IQC-AlCuRu, DQC -AlNiCo and -AlNiRh [10], and IQC -AlFeCu, -AlPdMn and -AlPdRe [11]. All the low-loss spectra displayed an intense peak around 16-19 eV. It was suggested to be a free electron like plasmon excitation by sonic [7,10], but others thought it should be anomalously damped or even absent in quasicrystals [6,9]. There has only been one paper, which mentioned the collection of core-loss (Mn L2,3) spectra from the IQC-Al86Mn14 [12]. It showed the Mn L3/L2 intensity ratio of the Al-Mn IQC is a little bit larger than that of a normal Al-Mn crystal. They discussed that this may be due to the Mn atoms in the IQC have high spin
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