电荷有序化(CO)现象在强相关电子系统中引起了广泛的争论,主要是关于它们在高温超导中的作用。这里,在有和没有覆盖层的情况下制备的NdNiO2薄膜中的结构和电荷分布,并以CO的不存在和存在为特征。通过扫描透射电子显微镜-电子能量损失光谱(STEM-EELS)和硬X射线发射光谱(HAXPES)进行微观结构和光谱分析。封端样品显示Ni1+,平面外(o-o-p)晶格参数约为3.30µ,表明无限层结构具有良好的稳定性。Ni-2p上的批量敏感HAXPES显示出微弱的卫星特征,表明电荷转移能量大。未加盖的样品表明,薄膜顶部的o-o-p参数增加了3.65,并且该区域的价态朝向Ni2。这里,图4D-STEM展示了从部分占据的顶端氧出现的(303)取向的条纹。这些条纹形成准2D相干域,在倒数空间中被视为棒,Δqz≈0.24倒数晶格单元(r.l.u.)延伸位于Q=(±13,0,±13$\\pm\\frac{1}{3},0,\\pm\\frac{1}{3}$)和(±23,0,±23$\\pm\\frac{2}{3},0,\\pm\\frac{2}{3}$)r.l.u。与氧再嵌入相关的条纹与空穴掺杂表明,无限层镍酸盐薄膜中可能与先前报道的CO有关。
Charge ordering (CO) phenomena have been widely debated in strongly-correlated electron systems mainly regarding their role in high-temperature superconductivity. Here, the structural and charge distribution in NdNiO2 thin films prepared with and without capping layers, and characterized by the absence and presence of CO are elucidated. The microstructural and spectroscopic analysis is done by scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS) and hard X-ray photoemission spectroscopy (HAXPES). Capped samples show Ni1+ , with an out-of-plane (o-o-p) lattice parameter of around 3.30 Å indicating good stabilization of the infinite-layer structure. Bulk-sensitive HAXPES on Ni-2p shows weak satellite features indicating large charge-transfer energy. The uncapped samples evidence an increase of the o-o-p parameter up to 3.65 Å on the thin film top with a valence toward Ni2+ in this region. Here, 4D-STEM demonstrates (303)-oriented stripes which emerge from partially occupied apical oxygen. Those stripes form quasi-2D coherent domains viewed as rods in the reciprocal space with Δqz ≈ 0.24 reciprocal lattice units (r.l.u.) extension located at Q = ( ± 1 3 , 0 , ± 1 3 $\\pm \\frac{1}{3},0,\\pm \\frac{1}{3}$ ) and ( ± 2 3 , 0 , ± 2 3 $\\pm \\frac{2}{3},0,\\pm \\frac{2}{3}$ ) r.l.u. The stripes associated with oxygen re-intercalation concomitant with hole doping suggest a possible link to the previously reported CO in infinite-layer nickelate thin films.