Browsing by Subject "Ion beams"

Now showing 1 - 7 of 7

Open Access
50 nm Hall Sensors for Room Temperature Scanning Hall Probe Microscopy
(Institute of Physics Publishing, 2004) Sandhu, A.; Kurosawa, K.; Dede, M.; Oral, A.
Bismuth nano-Hall sensors with dimensions ∼50nm × 50 nm were fabricated using a combination of optical lithography and focused ion beam milling. The Hall coefficient, series resistance and optimum magnetic field sensitivity of the sensors were 4 × 10-4 Ω/G, 9.1kΩ and 0.8G/√Hz, respectively. A 50nm nano-Bi Hall sensor was installed into a room temperature scanning Hall probe microscope and successfully used for directly imaging ferromagnetic domains of low coercivity garnet thin films.
Open Access
Analysis of electrical characteristics and magnetic field dependences of YBCO step edge and bicrystal grain boundary junctions for rf-SQUID applications
(Institute of Physics, 2004) Fardmanesh, M.; Schubert, J.; Akram, R.; Bick, M.; Banzet, M.; Zander, W.; Zhang, Y.; Krause, H-J.
The dc characteristics and magnetic field dependences of Y-Ba-Cu-O bicrystal grain boundary junctions (BGBJs) and step edge junctions (SEJs) were investigated for fabrication of rf-SQUIDs. Test junctions with up to 8 μm widths as well as the junctions of the two types of junction-based rf-SQUID were studied. The SEJs typically showed lower Jc and higher ρN as compared to the BGBJs, resulting in close IcRN products. All the BGBJs showed classical field dependent Ic following their junction width, resembling Fraunhofer patterns. The field sensitivity of the BGBJs' Uc led to low yield submicron BGBJ rf-SQUIDs partially impaired by the Earth's magnetic field. Two major behaviours of low and high field dependences of Ic were observed for the SEJs. Only the low field-sensitive SEJs resulted in micron size junction rf-SQUIDs not impaired by the Earth's magnetic field. The low field-sensitive SEJs led to low I/f noise magnetically stable rf-SQUIDs appropriate for applications in unshielded environments at 77 K.
Open Access
Bismuth nano-Hall probes fabricated by focused ion beam milling for direct magnetic imaging by room temperature scanning Hall probe microscopy
(The Institution of Engineering and Technology (IET), 2001) Sandhu, A.; Masuda, H.; Kurosawa, K.; Oral, A.; Bending, S. J.
Bismuth nano-Hall probes fabricated by using focused ion beam (FIB) milling were studied. The nano-Hall probes were used for direct magnetic imaging of domain structures in low coercivity garnets and demagnetized strontium ferrite permanent magnets. The analysis was performed using room temperature scanning Hall probe microscopy and it was found that the Bi nano-probes could overcome limitations due to surface depletion and large series resistances.
Open Access
Dependence of the substrate structure and the film growth at the junction of YBCO SEJ rf-SQUIDs on the IBE process and effects on the SQUID's characteristics
(Elsevier, 2002) Fardmanesh, Mehdi; Schubert, J.; Akram, Rizwan; Banzet, M.; Zander, W.; Zhang, Y.; Schilling, M.; Krause, H-J.
Step edge junction (SEJ) rf-SQUIDs were made of 200 nm thick YBCO films on LaAlO3(100) substrates using pulsed laser deposition technique. The steps on the substrates were developed using a combination of stationary and rotating angled argon ion beams with different beam energies and intensities. While sharp clean steps with heights up to 300 nm were obtained on the substrates using the combinatorial ion beam etching (IBE) process, very shallow ramp-type surfaces were found developing on the bottom of the trench, close to the steps. The ramp-type surfaces were found to be a source of hole-type defects in the films grown at the step edges. High quality films could be obtained on the flat regions away from the steps. Higher defect densities in the films close to the SEJs resulted in devices with higher 1/f noise and wider spread of the junction parameters. The 1/f noise of such devices increased with decreasing temperature. High quality films on sharp clean steps with flat substrate surfaces, developed using optimized combinatorial IBE process, resulted in higher yield of low 1/f noise SQUIDs. The Ic of the junctions and hence the working temperature of the SQUID could also be controlled by the junction width and the step height.
Open Access
Effects of thickness on the metal-insulator transition in free-standing vanadium dioxide nanocrystals
(American Chemical Society, 2017) Fadlelmula, M. M.; Sürmeli, E. C.; Ramezani, M.; Kasırga, T. S.
Controlling solid state phase transitions via external stimuli offers rich physics along with possibilities of unparalleled applications in electronics and optics. The well-known metal-insulator transition (MIT) in vanadium dioxide (VO2) is one instance of such phase transitions emerging from strong electronic correlations. Inducing the MIT using electric field has been investigated extensively for the applications in electrical and ultrafast optical switching. However, as the Thomas-Fermi screening length is very short, for considerable alteration in the material’s properties with electric field induced MIT, crystals below 10 nm are needed. So far, the only way to achieve thin crystals of VO2 has been via epitaxial growth techniques. Yet, stress due to lattice mismatch as well as interdiffusion with the substrate complicate the studies. Here, we show that free-standing vapor-phase grown crystals of VO2 can be milled down to the desired thickness using argon ion-beam milling without compromising their electronic and structural properties. Among our results, we show that even below 4 nm thickness the MIT persists and the transition temperature is lowered in two-terminal devices as the crystal gets thinner. The findings in this Letter can be applied to similar strongly correlated materials to study quantum confinement effects.
Open Access
In-situ focused ion beam implantation for the fabrication of a hot electron transistor oscillator structure
(1996) Kaya I.I.; Dellow, M.W.; Bending, S.J.; Linfield, E.H.; Rose P.D.; Ritchie, D.A.; Jones G.A.C.
Recent advances using in situ focused ion beam implantation during an MBE growth interruption have been exploited to fabricate planar GaAs hot electron structures without the need for shallow ohmic contacts. This novel fabrication route shows a very high yield and has been used to demonstrate a prototype high-frequency oscillator structure based on electron multiplication in the base layer. Existing devices show transfer factors in excess of unity as well as reversal of the base current at high injection levels, which are the prerequisites for oscillator action. Future improvements in device design are discussed.
Open Access
Room temperature scanning Hall probe microscopy using GaAs/AlGaAs and Bi micro-hall probes
(Elsevier Science B.V., 2002) Sandhu, A.; Masuda, H.; Oral, A.; Yamada, A.; Konagai, M.
A room temperature scanning Hall probe microscope system utilizing GaAs/AlGaAs and bismuth micro-Hall probes was used for magnetic imaging of ferromagnetic domain structures on the surfaces of crystalline thin film garnets and permanent magnets. The Bi micro-Hall probes had dimensions ranging between 0.25 and 2.8μm2 and were fabricated using a combination of optical lithography and focused ion beam milling. The use of bismuth was found to overcome surface depletion effects associated with semiconducting micro-Hall probes. Our experiments demonstrated that Bi is a practical choice of material for fabricating sub-micron sized Hall sensors.