Oriented assembly of Ni-clusters embedded in semi-insulating NiO epitaxial films

Abstract

(111) NiO epitaxial layers embedded with crystallographically oriented Ni-clusters are grown on c-sapphire substrates using pulsed laser deposition technique. It has been found that certain growth and post-growth cooling conditions can be adjusted to vary the size, shape and density of these clusters. (111) Ni epitaxial layer can also be deposited on c-sapphire substrate by this technique when no oxygen is supplied into the chamber during growth. Structural and magnetic properties of the clusters are examined by a variety of techniques including atomic probe tomography and superconducting quantum interference device magnetometry. All cluster embedded films are found to exhibit ferromagnetic behaviour even at room temperature. Magnetic characteristics of these films depend strongly on the density, size and shape of the clusters. It has also been observed that electrical conductivity of these samples enhances by several orders of magnitude when the cluster density crosses the percolation threshold. While, strong ferromagnetic behaviour is maintained even in highly resistive samples. Therefore, the material system has a potential to serve as an efficient spin-injector, the missing link for the realization of semiconductor based spintronics.

Annealing-dependent changes in the structural and electrical properties of NiO epitaxial films

“…Similar results are seen in sample S-2, where surface roughness is reduced to 0.24 nm upon annealing at 900 • C compared to 0.33 nm before annealing. existence of nm-size Ni clusters embedded in the NiO base for samples grown with identical conditions [31]. Note that, in sample S-3 as well, a Ni-cluster-related peak is found in the XRD scans and the feature is observed to diminish above 300 • C.…”

“…NiO epitaxial films were grown on c-sapphire substrates using a PLD technique, where the NiO pellet was ablated by an excimer KrF laser of a wavelength of 248 nm and a pulse width of 25 ns. Details of the growth process and the characterization of the samples can be found elsewhere [30,31]. Two types of samples were investigated here.…”

“…It has also been shown that (111) NiO epitaxial layers embedded with crystallographically oriented Ni clusters can be grown under oxygen-deficient conditions. Moreover, the size, shape, and density of the clusters can be varied by adjusting the oxygen flow during the time of growth or post-growth cooling [31]. The resistivity of these layers can be modified by several orders of magnitude by varying the size and density of the clusters.…”

Polynitrogen clusters interaction with water: experimental and theoretical perspectives

“…One common way for generating clusters is to bombard of substrates with laser pulses, electrons and so on [14][15][16][17][18][19][20], which have also been employed to produce nitrogen clusters [21][22][23][24][25][26][27][28][29][30][31][32]. For example, the nitrogen discharges have been used to generate the linear centrosymmetric ground state of the N 4…”

Study of lithium incorporation in (111) NiO epitaxial layers grown on c-sapphire substrates using the pulsed laser deposition technique

“…The p-type conduction in the film can be ascribed to the nickel vacancies (V Ni ) [17][18][19][20]. It is noteworthy that NiO epitaxial films with high crystalline quality have been reported by different growth techniques such as pulsed laser deposition [8,21,22], mist chemical vapor deposition [23], RF magnetron sputtering [24] and molecular beam epitaxy [5] on various substrates, such as sapphire, cubic yttria-stabilized zirconia and MgO. In fact, films with improved crystallinity do not show p-type conductivity, rather these are found to be highly resistive.…”