Shaping Perpendicular Magnetic Anisotropy of Co2MnGa Heusler Alloy Using Ion Irradiation for Magnetic Sensor Applications.

Magnetic sensors are key elements in many industrial, security, military, and biomedical applications. Heusler alloys are promising materials for magnetic sensor applications due to their high spin polarization and tunable magnetic properties. The dynamic field range of magnetic sensors is strongly related to the perpendicular magnetic anisotropy (PMA). By tuning the PMA, it is possible to modify the sensing direction, sensitivity and even the accuracy of the magnetic sensors. Here, we report the tuning of PMA in a Co2MnGa Heusler alloy film via argon (Ar) ion irradiation. MgO/Co2MnGa/Pd films with an initial PMA were irradiated with 30 keV 40Ar+ ions with fluences (ions·cm-2) between 1 × 1013 and 1 × 1015 Ar·cm-2, which corresponds to displacement per atom values between 0.17 and 17, estimated from Monte-Carlo-based simulations. The magneto optical and magnetization results showed that the effective anisotropy energy (Keff) decreased from ~153 kJ·m-3 for the un-irradiated film to ~14 kJ·m-3 for the 1 × 1014 Ar·cm-2 irradiated film. The reduced Keff and PMA are attributed to ion-irradiation-induced interface intermixing that decreased the interfacial anisotropy. These results demonstrate that ion irradiation is a promising technique for shaping the PMA of Co2MnGa Heusler alloy for magnetic sensor applications.

High Coercivity and Magnetization in WSe2 by Codoping Co and Nb.

Introducing ferromagnetism in transition metal dichalcogenides has attracted lots of attention due to the possible applications in spintronics devices. Generally, single magnetic element doping is used to introduce magnetism. However, mostly, weak ferromagnetism is observed. In this work, codoping of two kinds of transition metals (Nb and Co) into WSe2 is used to study its magnetic properties. In detail, single crystal WSe2 is codoped with 4 at% Co and various concentrations of Nb by employing the physical ion implantation method. Raman, X-ray diffraction and X-ray photoelectron spectroscopy results reveal the effective substitutional doping of implanted elements (Co and Nb). Magnetic measurements illustrate that both un-doped and 4 at% Co doped WSe2 show weak ferromagnetism whereas magnetization is strongly enhanced when Co and Nb are codoped into WSe2 . The magnetization is comparable with a ferromagnet, which may be attributed to Co, Nb doping and defects. In addition, a large coercivity of ≈1.2 kOe is observed in the 1 at% Nb-4 at% Co codoped WSe2 sample, which may be ascribed to the combined effect of doping-induced stress, defect-dictated pinning and anisotropy of NbSe bond owing to the charge transfer between Nb and Se ions.

Low Voltage High-Energy α-Particle Detectors by GaN-on-GaN Schottky Diodes with Record-High Charge Collection Efficiency.

A low voltage (-20 V) operating high-energy (5.48 MeV) α-particle detector with a high charge collection efficiency (CCE) of approximately 65% was observed from the compensated (7.7 × 1014 /cm3) metalorganic vapor phase epitaxy (MOVPE) grown 15 µm thick drift layer gallium nitride (GaN) Schottky diodes on free-standing n+-GaN substrate. The observed CCE was 30% higher than the bulk GaN (400 µm)-based Schottky barrier diodes (SBD) at -20 V. This is the first report of α-particle detection at 5.48 MeV with a high CCE at -20 V operation. In addition, the detectors also exhibited a three-times smaller variation in CCE (0.12 %/V) with a change in bias conditions from -120 V to -20 V. The dramatic reduction in CCE variation with voltage and improved CCE was a result of the reduced charge carrier density (CCD) due to the compensation by Mg in the grown drift layer (DL), which resulted in the increased depletion width (DW) of the fabricated GaN SBDs. The SBDs also reached a CCE of approximately 96.7% at -300 V.

Enhanced Power Factor and Increased Conductivity of Aluminum Doped Zinc Oxide Thin Films for Thermoelectric Applications.

We report the structural, electrical and thermopower properties of un-doped and Al doped zinc oxide (ZnO) thin films. Al doping was carried out using 25 keV Al+ implantation with 0.1, 1 and 2% Al into ZnO. X-ray diffraction measurements showed that the lattice parameters were larger than the bulk values, which is consistent with the incorporation of Al atoms at interstitials. Al doping increased the electrical conductivity from 100 (Ωcm)-1 in the un-doped ZnO film to 598 (Ωcm)-1 in the 2% Al doped ZnO film. Electron doping by Al resulted in an increase in the carrier concentration and it had an advantageous effect on the mobility where it was highest for 2% doping. The absolute value of the Seebeck coefficient systematically increased for un-doped, 1% and 2% Al doped ZnO films where the room temperature values were -50.8, -60.9 and -66.3 µV/K, respectively. The power factor increased significantly from 2.58 × 10-5 W/mK2 in un-doped ZnO film to 2.63 × 10-4 W/mK2 in 2% Al doped ZnO film. Our results suggest that the ion beam method is a suitable technique to enhance the thermoelectric properties of ZnO.

A novel radial anode layer ion source for inner wall pipe coating and materials modification--hydrogenated diamond-like carbon coatings from butane gas.

We report a new ion source development for inner wall pipe coating and materials modification. The ion source deposits coatings simultaneously in a 360° radial geometry and can be used to coat inner walls of pipelines by simply moving the ion source in the pipe. Rotating parts are not required, making the source ideal for rough environments and minimizing maintenance and replacements of parts. First results are reported for diamond-like carbon (DLC) coatings on Si and stainless steel substrates deposited using a novel 360° ion source design. The ion source operates with permanent magnets and uses a single power supply for the anode voltage and ion acceleration up to 10 kV. Butane (C4H10) gas is used to coat the inner wall of pipes with smooth and homogeneous DLC coatings with thicknesses up to 5 µm in a short time using a deposition rate of 70 ± 10 nm min(-1). Rutherford backscattering spectrometry results showed that DLC coatings contain hydrogen up to 30 ± 3% indicating deposition of hydrogenated DLC (a-C:H) coatings. Coatings with good adhesion are achieved when using a multiple energy implantation regime. Raman spectroscopy results suggest slightly larger disordered DLC layers when using low ion energy, indicating higher sp(3) bonds in DLC coatings. The results show that commercially interesting coatings can be achieved in short time.