Garfinkel David A, Tang Nan, Pakeltis Grace, Emery Reece, Ivanov Ilia N, Gilbert Dustin A, Rack Philip D
Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States.
Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States.
ACS Appl Mater Interfaces. 2022 Apr 6;14(13):15047-15058. doi: 10.1021/acsami.2c02028. Epub 2022 Mar 25.
The chemical composition and morphology of AuCo thin films and nanoparticles are controlled via a combination of cosputtering, pulsed laser-induced dewetting (PLiD), and annealing, leading to tunable magnetic and optical properties. Regardless of chemical composition, the as-deposited thin films and as-PLiD nanoparticles are found to possess a face-centered cubic (FCC) AuCo solid-solution crystal structure. Annealing results in large phase-separated grains of Au and Co in both the thin films and nanostructures for all chemical compositions. The magnetic and optical properties are characterized via vibrating sample magnetometry (VSM), ellipsometry, optical transmission spectroscopy, and electron energy loss spectroscopy (EELS). Despite the exceptionally high magnetic anisotropy inherent to Co, the presence of sufficient Au (72 atom %) in the AuCo solid solution results in superparamagnetic thin films. Among the as-PLiD nanoparticle samples, an increased Co composition leads to a departure from traditional ferromagnetism in favor of wasp-waisted hysteresis caused by magnetic vortices. Phase separation resulting from annealing leads to ferromagnetism for all compositions in both the thin films and nanoparticles. The optical properties of AuCo nanostructures are also largely influenced by the chemical morphology, where the AuCo intermixed solid solution has significantly damped plasmonic performance relative to pure Au and comparable to pure Co. Phase separation greatly enhances the quality factor, optical absorption, and electron energy loss spectroscopy (EELS) signatures. The enhancement of the localized surface plasmon resonances (LSPRs) scales with the reduction in Co composition, despite EELS evidence that excitation of the Co portions of a nanoparticle can provide a similar, and in some instances enhanced, LSPR resonance compared to Au. This behavior, however, is seemingly limited to the LSPR dipole mode, while higher-order modes are greatly damped by a Co aloof position. This observed magneto-plasmonic functionality and tunability could be applicable in biomedicine, namely, cancer therapeutics.
通过共溅射、脉冲激光诱导去湿（PLiD）和退火相结合的方法，可控制金钴（AuCo）薄膜和纳米颗粒的化学成分及形态，从而实现对其磁性能和光学性能的调控。无论化学成分如何，所沉积的薄膜和经PLiD处理后的纳米颗粒均具有面心立方（FCC）结构的AuCo固溶体晶体结构。对于所有化学成分，退火都会导致薄膜和纳米结构中出现金和钴的大尺寸相分离晶粒。通过振动样品磁强计（VSM）、椭偏仪、光透射光谱和电子能量损失谱（EELS）对磁性能和光学性能进行了表征。尽管钴本身具有极高的磁各向异性，但AuCo固溶体中足够的金（72原子%）的存在导致了超顺磁性薄膜的形成。在经PLiD处理的纳米颗粒样品中，钴成分的增加导致偏离传统铁磁性，转而呈现由磁涡旋引起的蜂腰形磁滞回线。退火导致的相分离使得薄膜和纳米颗粒中所有成分都呈现出铁磁性。AuCo纳米结构的光学性能也在很大程度上受到化学形态的影响，其中AuCo混合固溶体相对于纯金具有显著衰减的等离子体性能，与纯钴相当。相分离极大地提高了品质因数、光吸收和电子能量损失谱（EELS）特征。尽管EELS证据表明，与金相比，纳米颗粒中钴部分的激发可以提供相似的，在某些情况下甚至增强的局域表面等离子体共振（LSPR）共振，但局域表面等离子体共振（LSPRs）的增强与钴成分减少成正比。然而，这种行为似乎仅限于LSPR偶极模式，而高阶模式则因钴的远离位置而受到极大衰减。这种观察到的磁等离子体功能和可调性可应用于生物医学领域，即癌症治疗。
