Cobalt Nitride Thin Films Research Articles

Wireless magneto-ionics: voltage control of magnetism by bipolar electrochemistry

Modulation of magnetic properties through voltage-driven ion motion and redox processes, i.e., magneto-ionics, is a unique approach to control magnetism with electric field for low-power memory and spintronic applications. So far, magneto-ionics has been achieved through direct electrical connections to the actuated material. Here we evidence that an alternative way to reach such control exists in a wireless manner. Induced polarization in the conducting material immersed in the electrolyte, without direct wire contact, promotes wireless bipolar electrochemistry, an alternative pathway to achieve voltage-driven control of magnetism based on the same electrochemical processes involved in direct-contact magneto-ionics. A significant tunability of magnetization is accomplished for cobalt nitride thin films, including transitions between paramagnetic and ferromagnetic states. Such effects can be either volatile or non-volatile depending on the electrochemical cell configuration. These results represent a fundamental breakthrough that may inspire future device designs for applications in bioelectronics, catalysis, neuromorphic computing, or wireless communications.

Time-resolved in-situ investigation of Co-nitride thin film growth by grazing incidence X-ray absorption spectroscopy

The growth of cobalt nitride thin films prepared by reactive sputtering on float glass substrates was in-situ investigated using surface sensitive, grazing incidence X-ray absorption fine structure spectroscopy. Time-resolved measurements employing a quick-scanning monochromator allow to follow the growth on time-scales of a few seconds per spectrum, so that the film growth could be studied in detail. A quantitative modeling of the obtained data clearly show that a zinc blende type CoN is formed already during the initial stages of film growth, and the formation of small crystalline clusters finally lead to a 3D-growth of polycrystalline CoN-films.

Structural, electronic, and magnetic properties of Co4N thin films deposited using HiPIMS

We studied the growth behavior, structural, electronic, and magnetic properties of cobalt nitride (Co-N) thin films deposited using direct current (dc) and high power impulse magnetron sputtering (HiPIMS) processes. The N2 partial gas flow (RN2) was varied in close intervals to achieve the optimum conditions for the growth of the tetra cobalt nitride (Co4N) phase. We found that Co-N films grown using the HiPIMS process adopt (111) orientation as compared to the growth taking place along the (100) direction in the dcMS process. It was observed that HiPIMS grown Co-N films were superior in terms of crystallite size and uniform surface morphology. The local structure of films was investigated using x-ray absorption fine structure (XAFS) measurements. We found that the high energy of adatoms in the HiPIMS technique assisted in the more excellent stabilization of fcc-Co and the novel Co4N phase relative to the dcMS process. Magnetic properties of Co-N thin films were studied using magneto-optical Kerr effect, vibrating sample magnetometry and polarized neutron reflectivity. It was found that though the saturation magnetization remains almost similar in films grown by dcMS or HiPIMS processes, they differ in terms of their magnetic anisotropy. Such variation can be understood in terms of differences in the growth mechanisms in dcMS and HiPIMS processes affecting the resulting Co4N phase’s local structure.

Structural and magnetic properties of Co-N thin films deposited using magnetron sputtering at 523 K

In this work, we studied cobalt nitride (Co-N) thin films deposited using a dc magnetron sputtering method at a substrate temperature (Ts) of 523 K. We find that independent of the reactive gas flow (RN2) used during sputtering, the phases of Co-N formed at this temperature seems to be identical having N at.% ∼ 5. This is contrary to Co-N phases formed at lower Ts. For example at Ts∼ 300 K, an evolution of Co-N phases starting from Co(N) → Co4N → Co3 N → CoN can be seen as RN2 increases gradually to 100%, whereas when Ts increases to 523 K, the phase formed is fcc Co along with a minuscule Co4N phase for RN2 ≥ 25%. We used x-ray diffraction (XRD) to probe long range ordering, x-ray absorption spectroscopy (XAS) at Co absorption edge for the local structure, Magneto-optical Kerr effect (MOKE) and polarized neutron reflectivity (PNR) to measure the magnetization of samples. Quantification of N at.% was done using secondary ion mass spectroscopy (SIMS). Measurements suggest that the magnetic moment of Co-N samples deposited at 523 K is slightly higher than the bulk Co moment and does not get affected with the RN2 used for reactive sputtering. Our results provide an important insight about the phase formation of Co-N thin films which is discussed in this work.

Initial nitride formation during plasma-nitridation of cobalt surfaces

Nitridation of metal surfaces is of central importance in microelectronics and spintronics due to the excellent mechanical, thermal, and electrical properties of refractory nitrides. Here, we examine the chemical and structural modification of cobalt surfaces upon nitrogen plasma treatment, using in situ spectroscopic methods, as a method for synthesis of cobalt nitride thin films. We find that nitrogen is incorporated below the surface and forms an ultrathin film of CoN at temperatures as low as 50 °C. In addition, we observe the incorporation of oxygen and NO+ within the surface region. The nitrided cobalt surfaces are fully passivated by N, O, and NO+. These results provide a route for incorporation of cobalt nitride into a wide range applications.

Phase formation, thermal stability and magnetic moment of cobalt nitride thin films

Cobalt nitride (Co-N) thin films prepared using a reactive magnetron sputtering process are studied in this work. During the thin film deposition process, the relative nitrogen gas flow (RN2) was varied. As RN2 increases, Co(N), Co4N, Co3N and CoN phases are formed. An incremental increase in RN2, after emergence of Co4N phase at RN2 = 10%, results in a linear increase of the lattice constant (a) of Co4N. For RN2 = 30%, a maximizes and becomes comparable to its theoretical value. An expansion in a of Co4N, results in an enhancement of the magnetic moment, to the extent that it becomes even larger than pure Co. Such larger than pure metal magnetic moment for tetra-metal nitrides (M4N) have been theoretically predicted. Incorporation of N atoms in M4N configuration results in an expansion of a (relative to pure metal) and enhances the itinerary of conduction band electrons leading to larger than pure metal magnetic moment for M4N compounds. Though a higher (than pure Fe) magnetic moment for Fe4N thin films has been evidenced experimentally, higher (than pure Co) magnetic moment is evidenced in this work.

Synthesis, structural and nanomechanical properties of cobalt based thin films

Purpose – The purpose of this paper is to produce cobalt (Co)-based thin films by metalorganic chemical vapor deposition (CVD) technique and then to evaluate structural and mechanical integrity. Design/methodology/approach – Co-based thin films were produced by metalorganic CVD technique. Boronizing, carburization and nitridation of the produced Co thin films were accomplished through a post-treatment stage of thermal diffusion into as-deposited Co thin films, in order to produce cobalt boride (Co2B), cobalt carbide and cobalt nitride thin films in the surface layer of Co. The surface topography and the crystal structure of the produced thin films were evaluated through scanning electron microscopy and X-ray diffraction, respectively. The mechanical integrity of the produced thin films was evaluated through nanoindentation technique. Findings – The obtained results indicate that Co2B thin film exhibits the highest nanomechanical properties (i.e. H and E), while Co thin film has enhanced plasticity. The cobalt oxide thin film exhibits higher resistance to wear in comparison to the cobalt thin film, a fact that is confirmed by the nanoscratch analysis showing lower coefficient of friction for the oxide. Originality/value – This work is original.

Direct-liquid-evaporation chemical vapor deposition of smooth, highly conformal cobalt and cobalt nitride thin films

By a direct-liquid-evaporation chemical vapor deposition (DLE-CVD) method, we deposited smooth low-resistance cobalt (Co) and cobalt nitride (CoxN) thin films with excellent conformality at low temperatures down to 200 °C.

Phase transition behavior of reactive sputtering deposited Co–N thin films using transmission electron microscopy

Cobalt nitride thin films could be prepared by employing a direct current reactive sputtering deposition on (100) silicon substrates in mixtures of fixed Ar (4×10−1 Pa) and N2 at various partial pressures. The CoxN thin films could be tailored by appropriately controlling the partial pressure of the reactive nitrogen. With adequately increasing nitrogen to argon partial pressure, a series of sequence phase formation from α-Co, Co4N, Co3N, Co2N, and CoN could be observed. The phase transition sequence was accompanied by a substantial refinement and improvement of the films’ grain structure. Rapid thermal annealing of cobalt nitride thin films exhibited a stepwise decomposition via the dissociating of Co4N→Co3N+β-Co(N), Co3N→Co2N+β-Co(N), and Co2N→CoN+β-Co(N) with increasing the elevated temperature. Phase formation, thermal decomposition, electrical resistivity, and microstructure of reactive sputtered cobalt nitride films were discussed in this study.

Preparation of CoxN Thin Films by the Ion Reacting Deposition Method

The formation of cobalt-nitride thin films by the ion reacting deposition method was investigated. A low-energy broad-beam ion source (Kaufman type) was used for ionizing nitrogen. X-ray diffraction spectra revealed that the N-rich cobalt nitrides Co 3 N and Co 2 N were formed only at low ion current densities during deposition. The magnetic properties of the films changed suddenly with increasing Jion. H c was maximum at J ion =1.5 (mA/m2)/(A/s), above which the N-poor compound Co 4 N was formed. The nitrogen which was contained in films but was not involved in the nitriding reaction, was degassed above 250°.

イオンビーム照射を併用した窒化Ｃｏ蒸着薄膜の形成

The formation of cobalt-nitride thin films by the ion reacting deposition method was investigated. A low energy broad-beam ion source (Kaufman type) was used for ionizing nitrogen. From the X-ray diffraction spectra, it was found that the N-rich cobalt-nitrides, Co3N and Co2N, were formed only under the deposition condition of low ion current density. The magnetic properties of the films changed suddenly with increasing Jion. Hc took a maximum value at Jion=1.5 (mA/m2)/(Å/s), above which the N-poor composition, Co4N, was formed. The nitrogen, which was contained in the films but did not take part in the nitriding reaction, was degassed above 250°C

Perpendicular magnetic anisotropy of reactively sputtered cobalt nitride thin films

This paper discusses the perpendicular magnetic anisotropy of reactively sputtered cobalt nitride thin films. The perpendicular anisotropy is induced in an almost single γ phase film, and does not depend on its crystallite orientation. The films with the anisotropy exhibit a clear columnar structure. The structure changes to a granular one as temperature increases above 300°C. This change is caused by the nitrogen dissociation from the films. Finally, the actual measurements on recording characteristics are performed on CoNx films, and high density perpendicular recording is realized.

Magnetic properties of cobalt nitride thin films

Cobalt nitride (CoNx) thin films with a large perpendicular magnetic anisotropy are synthesized by reactive sputtering. The perpendicular magnetic anisotropy is induced by substrate heating during deposition, annealing after deposition, or ion bombardment during deposition.