Iron Nitride Thin Films Research Articles

Analysis of active screen low temperature plasma-assisted deposition of iron nitride thin films on silicon (100) substrate

Thin film technology has gained significant attention in the industry due to its superior properties in comparison to bulk materials. Specifically, iron nitride-based thin films are a fascinating area of research in semiconductor technologies. The crystal structure and optical properties of these films are highly dependent on the growth method, deposition technique, gas flow, pressure, and several other factors. In this work, we prepared polycrystalline thin films of iron nitride on silicon (100) substrates by using the active screen low temperature plasma-assisted method. These films are deposited under the varying atmosphere of nitrogen and hydrogen in four proportions: 80% N2 + 15% H2; 60% N2 + 35% H2; 40% N2 + 55% H2; and 20% N2 + 75% H2, along with 5% argon to investigate its influence on the structural, morphological, and optical properties. The structural properties are determined by x-ray diffraction and revealed a mixture of ζ-Fe2N, ε-Fe3N, and γ′-Fe4N phases. Surface morphology is analyzed by scanning electron microscopy, which confirms the formation of a thin layer on the substrate. In addition, UV–Vis spectrophotometry is used to assess the optical response and bandgap energy of the samples. The result of UV–Vis optical diffuse reflectance spectra shows a decrease in the bandgap from 3.17 to 3.06 eV of substrate. For the S4 sample, we obtained a pure Fe4N phase, showing a significant decrease in the energy bandgap.

Iron Nitride Thin Films: Growth, Structure, and Properties.

The current state-of-the-art in the growth, structure, and physicochemical properties of iron nitride thin films is presented. First, different iron nitride phases are introduced based on their crystallographic structure and the Fe–N phase diagram. Second, preparation methods for thin iron nitride films are described. Next, the structure, electronic, and magnetic properties of the films are discussed. Finally, potential applications of iron nitride films, as well as the challenges to be faced in the field, are highlighted. This Review constitutes a starting point for anyone who would like to conduct research on these fascinating materials, the scientific and technological potential of which has not been fully explored to date.

Phase characterization of iron-nitride formed by reactive pulsed magnetron sputtering

The phases formed in iron nitride thin films grown on Si wafers by magnetron sputtering with pulsed power supply were investigated. X-ray diffraction and conversion electron Mössbauer spectroscopy showed that in addition to the expected temperature dependence, there was an influence of film thickness on phase composition. All films of several thickness deposited at room temperature were composed of a mixture of mononitrides, namely γ″-FeN, γ‴-FeN, and a third phase compatible with a hexagonal wurtzite-type FeN. Thin films (20 nm) deposited at higher temperatures showed increasing amounts of ε-Fe2.1N, becoming single phase above 400 °C, and staying single ε-phase up to 500 °C. Thicker films (200 nm) showed the presence of ε-Fe2.1N already at 100 °C, became single-phase ε-Fe2.1N at 300 °C, and single phase γ′-Fe4N at 500 °C.

A review of iron nitride based thin films development

Thin film technology has taken a lot of area in the industry due to their properties which is better than their parents bulk materials. One of the interesting thin films that has yet to be fully explored is iron nitride based thin films has been attracting attention for the past few years especially in the semiconductor technology. Crystal structure and magnetic properties on the film which depend greatly on the growth method, deposition technique, gas flow, pressure and many more. Suitable parameters allow the presence of required iron nitride based thin films stoichiometry. In semiconductor application, magnetization properties play an important role of developing iron nitride thin films. This will give rise to the formation of strong magnetic moment thus increasing the corrosion resistance of the thin film. However, the difficulties of growing a pure phase of these iron nitrides thin films makes it more interesting to study and recent researches have shown findings that open the possibilities in enhancing properties of this iron nitride based thin films.

Thermal analysis on crystal phase synthesis of iron nitride film and its magnetic properties

The phase transition law of Fe-N system is very important for efficiently synthesizing single-phase <i>γ</i>'-Fe<sub>4</sub>N thin films. The <i>γ</i>"-FeN thin films are deposited on silicon wafers via DC reactive magnetron sputtering; some of them are stripped from the silicon wafers and measured by using the synchronous thermal analysis (TG-DSC) for studying the phase transition law of Fe-N system. The results of TG-DSC show that at a heating rate of 10 ℃/min, the Fe-N system has five phase transitions in a temperature range between room temperature (RT) and 800 ℃, i.e. I (330−415 ℃): <i>γ</i>''-FeN→ξ-Fe<sub>2</sub>N with an endothermic value of 133.8 J/g; II (415−490 ℃): ξ-Fe<sub>2</sub>N→ε-Fe<sub>3</sub>N with no obvious latent heat of phase change; III (510−562 ℃): ε-Fe<sub>3</sub>N→<i>γ</i>'-Fe<sub>4</sub>N with an exotherm value of 29.3 J/g; IV (590−636 ℃): <i>γ</i>'-Fe<sub>4</sub>N→<i>γ</i>-Fe with an exotherm value of 42.6 J/g; V (636−690 ℃): <i>γ</i>-Fe→α-Fe with an endothermic value of 14.4 J/g. According to the phase transition law of Fe-N system, the crystal phase of iron nitride thin film is effectively regulated by vacuum annealing. The x-ray diffraction pattern (XRD) results show that the iron nitride thin film obtained by direct-sputtering in pure N<sub>2</sub> is a single-phase <i>γ</i>"-FeN film, and it becomes a single-phase ξ-Fe<sub>2</sub>N film after being annealed at 350 ℃ for 2 h, a single-phase ε-Fe<sub>3</sub>N film after being annealed at 380 ℃ for 2 h, and a single-phase <i>γ</i>'-Fe<sub>4</sub>N film after being annealed at 430 ℃ for 7 h. The annealing temperature for the phase transition of Fe-N thin film is generally lower than that predicted by the TG-DSC experimental results, because it is affected by the annealing time too, that is, prolonging the annealing time at a lower temperature is also effective for regulating the crystal phase of Fe-N thin film. The magnetic properties of the Fe-N thin film are also studied via vibrating sample magnetometer (VSM) at room temperature. The <i>γ</i>'-Fe<sub>4</sub>N polycrystalline thin film shows an easy-magnetized hysteresis loop for the isotropic in-plane one, but a hard-magnetized hysteresis loop with a large demagnetizing field for the out-of-plane one, which belongs to the typical magnetic shape anisotropy. However, their saturation magnetizations are really the same (about 950 emu/cm<sup>3</sup>) both in the plane and out of the plane.

Controllable synthesis of γ′-Fe4N via prolonged high vacuum magnetic annealing of deposited Fe–N thin films

Abstract In order to develop a fast and low-cost method for preparing γ′-Fe4N thin films for spintronic applications, the iron nitride (Fe–N) thin films were deposited through reactive sputtering in pure nitrogen, followed by high vacuum magnetic annealing process. The X-ray diffraction pattern (XRD) results revealed that the N content of the Fe–N thin films were decreasing continuously with the increase of annealing temperatures and times, so as to affect their crystal phase compositions, thus a single phase of γ″-FeN, ξ-Fe2N and γ′-Fe4N can be controllable prepared through annealing process. The phase transition characteristics for Fe–N to γ′-Fe4N were studied carefully. It was found that the sample (Fe1.8N) with a mixed crystal phase of γ″-FeN and ξ-Fe2N can be totally changed into a single phase of γ′-Fe4N by annealing it at 430 °C for 3 h, and the annealing temperatures can also be as low as 375 °C but for a prolonged time to 24 h. The stoichiometric matter of the as-prepared Fe–N thin films was confirmed by the XPS analysis. The vibrating sample magnetometer (VSM) results indicated that the magnetic properties of the Fe–N thin films are mainly depending on their crystal phase compositions. The saturation magnetization (Ms) of γ′-Fe4N films depends on various factors, and it was to about 1080 emu/cm3 for the γ′-Fe4N/MgO/Si.

Corrosion, optical and magnetic properties of flexible iron nitride nano thin films deposited on polymer substrate

Iron nitride thin films of different compositions and thicknesses were deposited on flexible polymer substrate in Ar/N2 atmosphere by reactive magnetron sputtering under varying nitrogen flow rates. The nano structured films were characterized by X-ray diffraction, UV–visible spectrophotometer, electrochemical impedance (EIS), atomic force (AFM) and transmission electron microscopies. The dependence of their functional properties on coating and growth conditions was studied in detail. It was found that the thin films show a uniform permeability in the frequency range of 200MHz to 1Ghz and can be used in this range without appreciable changes. Decrease of nitrogen flow rate resulted in the smoother surfaces which in turn increase transmittance quality and corrosion resistance. Functional properties are dependent of nature, relative concentration of the iron nitride phases and film thickness. Surface integrity is excellent for180 nm thick sample because the films appear to be very dense and free from open pores. By keeping sputtering power stable at 110W, nitrogen flow rate of 10 sccm was ideal to develop the ferromagnetic γʹFe4N phase at room temperature.

Influence of nitrogen flow rates on iron nitride thin films prepared by DC reactive magnetron sputtering

Iron nitride (FeN) thin films were deposited on silicon wafer substrates by dc reactive magnetron sputtering techniques. The FeN thin films were prepared at the fixed substrate temperature 200°C under different nitrogen flow rates. The crystal structures, physical morphologies, and surface roughness of the prepared FeN thin films were characterized by the grazing-incident X-ray diffraction (GIXRD), field-emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM), respectively. From the results, the GIXRD patterns indicated the change in the film orientations from ξ-Fe2N to γ”-FeN along with the increased nitrogen flow rates. In addition, the FE-SEM micrographs demonstrated the decrease of the FeN film thickness. The effects of the nitrogen flow rates towards the crystallinity, the physical morphology, and surface roughness of the thin films were investigated and discussed.

Perpendicular Magnetic Anisotropy in Fe–N Thin Films: Threshold Field for Irreversible Magnetic Stripe Domain Rotation

The magnetic properties of an iron nitride thin film obtained by ion implantation have been investigated. N[Formula: see text] ions were implanted in a pristine iron layer epitaxially grown on ZnSe/GaAs(001). X-ray diffraction measurements revealed the formation of body-centered tetragonal N-martensite whose [Formula: see text]-axis is perpendicular to the thin film plane and [Formula: see text]-parameter is close to that of [Formula: see text]-Fe8N. Magnetic measurements disclosed a weak perpendicular magnetic anisotropy (PMA) whose energy density [Formula: see text] was assessed to about 105[Formula: see text]J/m3. A sharp decline of the in-plane magnetocrystalline anisotropy (MCA) was also observed, in comparison with the body-centered cubic iron. The origin of the PMA is attributed to the MCA of N-martensite and/or stress-induced anisotropy. As a result of the PMA, weak magnetic stripe domains with a period of about 130[Formula: see text]nm aligned along the last saturating magnetic field direction were observed at remanence by magnetic force microscopy. The application of an increasing in-plane magnetic field transverse to the stripes [Formula: see text] highlighted a threshold value ([Formula: see text][Formula: see text]T) above which these magnetic domains irreversibly rotated. Interestingly, below this threshold, the stripes do not rotate, leading to a zero remanent magnetization along the direction of the applied field. The interest of this system for magnetization dynamics is discussed.

Effect of Al doping on phase formation and thermal stability of iron nitride thin films

In the present work, we systematically studied the effect of Al doping on the phase formation of iron nitride (Fe–N) thin films. Fe–N thin films with different concentration of Al (Al = 0, 2, 3, 6, and 12 at.%) were deposited using dc magnetron sputtering by varying the nitrogen partial pressure between 0 and 100%. The structural and magnetic properties of the films were studied using x-ray diffraction and polarized neutron reflectivity. It was observed that at the lowest doping level (2 at.% of Al), nitrogen rich non-magnetic Fe–N phase gets formed at a lower nitrogen partial pressure as compared to the un-doped sample. Interestingly, we observed that as Al doping is increased beyond 3 at.%, nitrogen rich non-magnetic Fe–N phase appears at higher nitrogen partial pressure as compared to un-doped sample. The thermal stability of films were also investigated. Un-doped Fe–N films deposited at 10% nitrogen partial pressure possess poor thermal stability. Doping of Al at 2 at.% improves it marginally, whereas, for 3, 6 and 12 at.% Al doping, it shows significant improvement. The obtained results have been explained in terms of thermodynamics of Fe–N and Al–N.

Study of magnetic iron nitride thin films deposited by high power impulse magnetron sputtering

In this work, we studied phase formation, structural and magnetic properties of iron-nitride (Fe-N) thin films deposited using high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (dc-MS) techniques. The nitrogen partial pressure during deposition was systematically varied both in HiPIMS and dc-MS processes. Resulting Fe-N films were characterized for their microstructure, magnetic properties and nitrogen concentration. We found that HiPIMS deposited Fe-N thin films show improved soft magnetic properties and likely to possess globular nanocrystalline microstructure. In addition, it was found that the nitrogen reactivity with Fe get suppressed in HiPIMS discharge as compared to that in dc-MS plasma. Obtained results can be understood in terms of distinct plasma properties of HiPIMS discharge.

Magnetic properties of iron nitride films prepared by oblique sputtering under different nitrogen gas flow ratios (N2/N2+Ar)

Iron nitride thin films were prepared on Si (100) substrates by oblique radio-frequency reactive magnetron oblique sputtering. Structures, phases and magnetic properties were investigated as a function of nitrogen gas flow ratio FN(FN=FN2/(FN2+FAr)×100%). When FN is in the range of 2–7%, the iron nitride films show amorphous or nano-crystalline structures, which exhibit good soft magnetic properties. With 3%≤FN≤6%, films show in-plane uniaxial magnetic anisotropy. Both intrinsic damping factor αin and extrinsic damping factor αex of the iron nitride films increase with increasing FN. The film deposited under FN=6% with the resonance frequency fr=3.3GHz and full width at half-maximum Δf=3.6GHz has great potential for high-frequency electromagnetic shielding applications.

X-ray photoelectron spectroscopic investigation on Fe geometrical sites of iron nitride thin films

A partially ordered Fe16N2 thin film, which exhibits a higher saturation magnetization than a bcc-Fe thin film, was grown on a Au(001) texture on a GaAs(001) substrate for studies of crystalline structure, electronic structure, and magnetic properties. Fe 2p3/2 and 2p1/2 X-ray photoelectron spectroscopies (XPS) reveal the electronic hybridization between the Fe atoms and the adjacent N atoms, whereas a multipeak analysis suggests the charge-transfer-induced electronic rearrangement of electronic configuration in Fe(8h) and Fe(4e) geometrical sites. These results are consistent with the previous model and help explain the saturation magnetization enhancement in the α-FeN system.

Growth of iron nitride thin films by molecular beam epitaxy

Iron nitride films were grown by atomic-nitrogen-assisted molecular beam epitaxy. ZnS-type FeN (γ″-FeN) was synthesized with low Fe evaporation rates (≤ 0.2Å/s) at low growth temperatures below 210°C whereas γ′-Fe4N was synthesized with high Fe evaporation rates (≥1.0Å/s) at 130–415°C. Our results indicate that the stabilization of ZnS-type FeN requires not only the fulfillment of thermodynamic constraints but also the control of a delicate balance of kinetically driven competition. The use of lattice-matched GaN(0001) substrates enables the growth of epitaxial films of ZnS-type FeN.

Correlation between iron self-diffusion and thermal stability in doped iron nitride thin films

Nanocrystalline Fe-X-N thin films (with doping X = 0, 3.1 at. % Al, 1.6 at. % Zr), were deposited using reactive ion beam sputtering. Magnetization study reveals that the deposited films exhibit a perpendicular magnetic anisotropy. Thermal stability of the films was investigated systematically and it was observed that the structural and the magnetic stability gets significantly enhanced with Al doping, whereas Zr doping has only a marginal effect. Fe self-diffusion, obtained using polarized neutron reflectivity, shows a suppression with both additives. A correlation between the thermal stability and the diffusion process gives a direct evidence that the enhancement in the thermal stability is primarily diffusion controlled. A combined picture of diffusion, structural, and magnetic stability has been drawn to understand the obtained results.

Effect of dopants on thermal stability and self-diffusion in iron-nitride thin films

We studied the effect of dopants (Al, Ti, Zr) on the thermal stability of iron nitride thin films prepared using a dc magnetron sputtering technique. Structure and magnetic characterization of deposited samples reveal that the thermal stability together with soft magnetic properties of iron nitride thin films get significantly improved with doping. To understand the observed results, detailed Fe and N self-diffusion measurements were performed. It was observed that N self-diffusion gets suppressed with Al doping whereas Ti or Zr doping results in somewhat faster N diffusion. On the other hand Fe self-diffusion seems to get suppressed with any dopant of which heat of nitride formation is significantly smaller than that of iron nitride. Importantly, it was observed that N self-diffusion plays only a trivial role, as compared to Fe self-diffusion, in affecting the thermal stability of iron nitride thin films. Based on the obtained results effect of dopants on self-diffusion process is discussed.

Magnetic Study of α" and γ"-Phases of Iron Nitride Thin Films

Magnetic Study of α" and γ"-Phases of Iron Nitride Thin Films

Effect of N<sub>2</sub> Gas Pressure Ratio and DC Bias on Formation of Iron Nitride Thin Film by RF Sputtering Method

In this paper, we investigated the effect of N2 gas pressure ratio and DC bias on the formation of iron nitride thin films deposited by RF sputtering method. As a result, the amounts of γ'-Fe4N and ε-Fe3N, which had high N2 content than that of α”-Fe16N2, increased with increasing N2 gas pressure ratio. From the result of x-ray diffraction, the Fe-N film at the N2 gas pressure ratio of 15% became the single phase of γ'-Fe4N. Therefore, we attempted the formation of α'-martensite and α”-Fe16N2 by applying DC bias voltage. It revealed that it was possible to control the N2 content and the coercive force by applying DC bias voltage. However, the formation of α”-Fe16N2 was not observed.

Growth and characterization of epitaxial iron–nitride thin films

Many of the Fe–nitride phases have been studied in much detail. Nevertheless there is still a debate on the most efficient, exact and controlled way of obtaining thin films of the desired iron nitrides phases. We present the recent state of our research focusing on the low and high nitrogen-iron phases and transformations between them due to irradiation, temperature and time exposure. Thin films of iron nitrides were deposited by Molecular Beam Epitaxy in Ultra High Vacuum conditions. We grew films of the FeN alpha (α″-Fe16N2), epsilon (ε-FexN, 2 ⩽ x ⩽ 3) and gamma (FeNy, y > 0.5) phases. By changing the parameters of growth conditions we tried to obtain the α″-phase in its possible purest form. We grew the ε-phase mainly in a nonmagnetic form. We worked also on iron mononitride FeN, which is known to exist in different phases. There is a debate on the exact crystal structure and the coexistence of these phases. On the basis of room temperature Conversion Electron Mössbauer Spectroscopy analysis accompanied with Rutherford Backscatering Spectroscopy spectra we show our results on the growth and transformations of the samples under different conditions.

Microstructure and magnetic properties of iron nitride thin films

• Iron nitride films with d ⩽ 119 nm exhibit in-plane uniaxial magnetic anisotropy. • Iron nitride films with d = 182 nm show isotropy property with coercivity of 72 Oe. • An applied magnetic field (AMF) can prevent the crystallization of the sample. • The resonance around gigahertz were observed for iron nitride films d ⩽ 119 nm. • As deposited iron nitride films have much potential for high-frequency application. A series of iron nitride thin films with thickness d ranging from 38 to 182 nm were fabricated on silicon (1 0 0) substrates by reactive rf magnetron sputtering in a N 2 –Ar atmosphere. The microstructure and magnetic properties have been investigated systematically. It was found that the resistivity of iron nitride films is up to 190 μΩ cm. Due to the in-plane applied magnetic field (50 Oe), iron nitride films with d ⩽ 119 nm are amorphous or nano-crystalline structure, while the polycrystalline γ′-Fe 4 N samples are obtained as d ⩽ 182 nm. Iron nitride films with d ⩽ 119 nm exhibit in-plane uniaxial magnetic anisotropy and excellent soft magnetic properties. However, Iron nitride films with d = 182 nm show isotropy property with coercivity of 72 Oe. Furthermore, the investigation of dynamic magnetic properties shows that the resonance frequency of the iron nitride films with d ⩽ 119 nm are in the range 1.1–2.2 GHz. As a consequence, the applied magnetic field (50 Oe) has a significant influence on the magnetic properties and microstructure of iron nitride thin films.