Epitaxy and Roughness Study of Glancing Angle Deposited Nanoarrays. Hamid Alouach and G. J. Mankey

Transcription

1 Epitaxy and Roughness Study of Glancing Angle Deposited Nanoarrays Hamid Alouach and G. J. Mankey

2 Introduction Objective: Approach: Characterization: Fabrication of nanoscale magnetic wires for spin transport studies. Use glancing angle deposition (GLAD) technique to fabricate wires. SEM, AFM, X-Ray diffraction, and Magnetometry.

3 Substrate GLAD Film GLAD Growth Mechanism α Φ Azimuthal Rotation Film Shadowed Regions Deposition Angle Growth Flux (R) Incident Flux Growth Angle: β Tan(β) = (½) Tan(α ) Nieuwenhuizen et al.,philips Tech. Rev. 27, 87 (1966) β = α- asin[1/2(1-cos(α)] Tait et al. Thin solid Films 226, 196 (1993) Normal to the substrate β Substrate Wire orientation α Deposition angle

4 Effect of the Azimuthal Rotation on the Wire Orientation Φ= 3*10 3(s 1) Normal to the substrate Φ=0 Inclined structure α = 75 º Rotating the substrate during deposition produces pillars normal to the substrate since the shadowed regions follow the substrate rotation.

5 The Three Motorized Angle-Movements of the X Pert-MRD Cradle Wire β θ z θ θ Wire Ψ, Φ = 0º ; 2θ = 43.36º ψ y X-Ray Detector Φ X-Ray Source x

6 Demonstration of the [111](1-10) FCC Configuration on Cu nanowire arrays Intensity (CpS) (111)-Nanowires (111)-Bottom layer Ψ (deg) (111)-Nanowires Polar scan of the Cu (111) peak signal in the deposition plane (1-10). Ψ= 59 º : Wire orientation. Ψ= 32 º : Texture orientation. The reduction in the intensity of the Cu (11-1) signal compared to (111) signal is due to the defocusing error.

7 Intensity (CpS) Cu(111)-Crystal Orientation in Nanowire Arrays deposited with Azimuthal Rotation Φ=90 Φ=45 Φ= Ψ (deg) Intensity (CpS) Intensity (CpS) Ψ = 0 Ψ = 35.3 Cu (111) Cu (200) Cu (220) Θ The polar scans at different azimuthal orientations (left) reveal a cone-like distribution of the Cu(111) signal; the 2Θ scans show a strong Cu(220) texturing along the wire direction normal to the substrate.

8 Texture and Cu[111] orientation in relation to the wire orientation and the deposition angle Normal to the substrate 35.3 Cu[220] Cu[111] Wire orientation Cu[111] β 32 Cu[111] Wire orientation Deposition angle Deposition angle With Azimuthal Rotation Substrate Without Azimuthal Rotation

9 Conclusion I!The [111](1-10) configuration of Fcc materials of nanowire arrays deposited using glancing angle deposition.!in samples deposited without azimuthal rotation, the texture lies between the wire direction and the normal to the substrate.!in samples deposited with azimuthal rotation, the [111] low energy orientation of copper is evenly distributed in a cone around the wire geometrical orientation. The Scherrer analysis suggests that the wires have a crystallographic mosaic structure.

10 Objective: Approach: Characterization: Refinement Fabrication of epitaxial nanoarrays as a seed layer for subsequent growth of single crystal magnetic nanowires for spin transport studies. Glancing angle deposition of Cu on Si(110) to fabricate nanoscale arrays. AFM, X-Ray diffraction.

11 Sample Preparation U.V. radiation Hydrofluoric acid diluted to 5% Si(110) The Si(110) substrates were exposed to 255 nm ultraviolet radiation for 1day; degreased and etched in a 5% HF-deionized water solution prior to insertion through a load lock into the high vacuum chamber. Within 5 min, the sample was at a pressure of better than 5* 10-7 torr.

12 Epitaxial Growth of Cu(111) Films on Si(110) Intensity (a. u.) Cu(111) Si(220) Cu(222) ω (deg.) The rocking curve of Cu(111)/Si(110) 2θ (deg.) XRD pattern of Cu(111)/Si(110) using the θ-2θ mode. The film is deposited using e-beam evaporation. Intensity (a. u.) FWHM=1

13 Intensity (cps) Twinned Epitaxial Growth of Copper on H-Terminated Si(110) (220) (200) (111) Φ (deg.) XRD pattern of Cu(111), (200) and (220) on Si(110) using the Φ-mode. [002] [100] [220] [111] (110) plane [010] n*λ = 2d*sin(Θ) d (200) = d (002)

14 Epitaxial Orientation Relationship of Cu/Si Si[110] Si[001] // Cu[110] projection of a twinned cubic crystal Cu[110] Si[001] Cu[110] Si (d 100 =a =5.43Å) Cu (a=3.61å d 110 =a 2 =5.12Å) Atomic arrangement at the Cu-Si interface The lattice mismatch at the Si/Cu interface is about 5.7% ===> The Cu film will have a high amount of stress.

15 Crystallographic Texture of GLAD Cu(111) Films on Si(110) Intensity (a. u.) Si(220) Cu(111) Cu(222) θ (deg.) XRD pattern of a 75 -GLAD film using the θ-2θ mode. Films thicker than 300 nm exhibited additional texture peaks.

16 Intensity (a. u.) Texture Evolution Vs. Thickness nm 2000 nm Si θ Thick. (nm)int. (111/200) Int. (111/220) Int. (111/311) Literature NA NA NA

17 6.0 nm Topography and Surface Roughness α = 0û α = 25û 10.0 nm 0.5µm x 0.5µm 0.0 nm 0.0 nm 16.0 nm 40.0 nm α = 45û α = 75û 0.0 nm 0.0 nm

18 Conclusion II!Epitaxial copper nanoarrays of Copper were fabricated on hydrogen terminated Si(110) substrates.!thick films have texture resembling that of nanoarrys deposited on amorphous substrates.!the Copper nonoarrays will serve as a conductive seed layer for the growth magnetic nanowires, such as permalloy or Cobalt, using glancing angle deposition.