Ni/(0001)InSe 2D Nanosystem on Cleaved Surface of InSe Layered Semiconductor Crystal Intercalated by Nickel

The nanoscale self-assembling systems obtained by intercalation of 3d-elements (e.g., Ni) into a matrix of InSe semiconductor layered crystal are interesting in terms of creating materials with paramagnetic properties for use in spintronic devices. The metal nanostructures in the interlayer gaps become surface ones after cleavage, and thus could be studied by low electron energy diffraction (LEED) and scanning tunneling microscopy / spectroscopy (STM/STS) methods and X-ray photoelectron spectroscopy (XPS).<br/>Nickel intercalated InSe crystals have been grown by the Bridgman method from the pre-synthesized components. Synthesis was carried out by a special procedure to prevent the formation of nickel selenides. Further thermo treatment of grown crystals in evacuated quartz ampoules, that was carried out for 60 h at 870 K, led to Ni intercalation. LEED data were analyzed using the SPECS SAFIRE Diffraction Image Acquisition and Processing System. The STM/STS data were acquired using the Omicron NanoTechnology STM/AFM System.<br/>The clear LEED spots of InSe hexagonal structure are observed for InSe (Ni). The calculated values of the two-dimensional (0001) InSe (Ni) lattice constants <b><i>a</i></b> = <b><i>b</i></b> = 4.0 Å, correspond to the ones for bulk InSe crystal. Therefore, it was confirmed that Ni was introduced in the interlayer gap. The additional LEED spots corresponding to metallic Ni phase are determined at high (~ 190-200 eV) primary electron beam energies.<br/>STM suggests the unreconstructed structure of (0001) surface covered by intercalate, which is similar for pure InSe. However, some clusters are observed on the surface in the form of local blurring of hexagonal structure. 2d FFT filtering of these clusters revealed the structure with 3.5 Å period which is characteristic for metallic nickel. The analysis of density of states by STS confirms the "metallic nature" of local areas on the (0001) InSe surface. XPS elemental and phase analysis of Ni/(0001) InSe nanosystem shows nickel quantity on the (0001)InSe surface less than 4%.