A scanning tunneling microscopy study of the electronic and spin states of bis(phthalocyaninato)terbium(III) (TbPc2) molecules on Ag(111)
A scanning tunneling microscopy study of the electronic and spin states of bis(phthalocyaninato)terbium(III) (TbPc2) molecules on Ag(111)
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DOI：
10.1039/c6dt01967f
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发表时间：
2016-01-01
影响因子：
4
通讯作者：
Yamashita, Masahiro
中科院分区：
文献类型：
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作者：
Ara, Ferdous;Qi, Zhi Kun;Yamashita, Masahiro
利用低温扫描隧道显微镜（STM）研究了单分子磁性酞菁铽（TbPc 2）分子薄膜。为了研究分子-衬底相互作用对吸附分子的电子和自旋性质的影响，我们通过在Au（111）和Ag（111）之间切换衬底来调节分子-衬底耦合，其中后者提供比前者更强的与分子的相互作用。尽管与Au（111）相比，Ag（111）表面的化学反应性增强，但形成了组织良好的伪正方形膜。此外，一个棋盘式的对比度变化被确定，这是很好地解释了两种类型的分子的存在，其旋转角之间的顶部和底部Pc是θ = 45度（亮分子）和θ = 30度（暗分子）。然而，预期的更强的分子-基底相互作用表现为有趣的dI/dV映射图像，揭示了态密度（DOS）的空间分布。我们确定的对比度反转的dI/dV映射为θ = 45度和θ = 30度的分子在V = 0.7 eV和1.1 eV的样品电压。结合密度泛函理论（DFT）计算，我们将这种变化归因于电子态的移动，由于顶部和底部Pc之间的相互角的旋转。对于自旋行为，我们先前观察到吸附在Au（111）表面上的TbPc 2分子的Kondo共振。在Ag（111）表面上，几乎没有观察到近藤共振，这是由于电荷从基底转移到分子中而湮灭π自由基自旋的结果。相反，我们观察到的近藤峰的分子上的第二层，其中的自旋恢复由于减少与基板的耦合。此外，当施加垂直于表面的2 T的磁场时，第二层分子在费米能级处显示出急剧下降。我们把这归因于自旋翻转引起的非弹性隧穿特性。在TbPc 2/Au（111）系统中没有观察到这种特征，这表明TbPc 2分子和Ag（111）之间由于第一层的存在而产生的去耦在隧穿光谱中产生了非弹性特征。
In this article, we investigate a single molecule magnet bis(phthalocyaninato)terbium(III) (TbPc2) molecule film by using low temperature STM. In order to investigate the effect of molecule-substrate interaction on the electronic and spin properties of the adsorbed molecule, we tune the molecule-substrate coupling by switching the substrate between Au(111) and Ag(111), the latter of which provides stronger interaction with the molecule than the former. Despite the enhanced chemical reactivity of the Ag(111) surface compared with Au(111), a well-organized pseudo-square film is formed. In addition, a checker-board type contrast variation is identified, which is well explained by the existence of two types of molecules whose rotational angle between the top and bottom Pc is theta = 45 degrees (bright molecule) and theta = 30 degrees (dark molecule). The expected stronger molecule-substrate interaction, however, appears as an intriguing dI/dV mapping image which reveals the spatial distribution of the density of states (DOS). We identify the contrast reversal in the dI/dV mapping for the molecules of theta = 45 degrees and theta = 30 degrees at the sample voltages of V = 0.7 eV and 1.1 eV. Combined with the density functional theory (DFT) calculation, we attribute this change to the shift of an electronic state due to the rotation of the mutual angle between the top and bottom Pc. For the spin behavior, we previously observed a Kondo resonance for the TbPc2 molecule adsorbed on the Au(111) surface. On the Ag(111) surface, the Kondo resonance is hardly observed, which is due to the annihilation of the pi radical spin by the charge transfer from the substrate to the molecule. Instead we observe a Kondo peak for the molecule on the second layer, for which the spin recovers due to the reduction of the coupling with the substrate. In addition, when a magnetic field of 2 T normal to the surface is applied, the second layer molecule shows a sharp dip at the Fermi level. We attribute this to the inelastic tunneling feature caused by the spin flipping. This feature is not observed for the TbPc2/Au(111) system, suggesting that the decoupling between the TbPc2 molecule and Ag(111) by the presence of the first layer produces an inelastic feature in the tunneling spectra.