Ultrashort-pulse laser depositiUltrashort-pulse laser depositionon

of thin filmsof thin films

Y.-M. Chena,c( 陳彥穆 ), Y.-C. Tsoua,c( 鄒昀晉 ), C.-Y. Yeha,c( 葉啟宇 ), C.-J. Chena,b,c( 陳俊嘉 ), C.-S. Wua,b,c( 吳強生 ), M.-J. Jianga,c,d( 江銘

哲 ), H.-H. Chuc( 朱旭新 ), J.-Y. Lind( 林俊元 ), J. Wanga,b,c( 汪治平 ), and S.-Y. Chena,c( 陳賜原 )

a. Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan.b. Department of Physics, National Taiwan University, Taipei 106, Taiwan.c. Department of Physics, National Central University, Jhongli 320, Taiwand. Department of Physics, National Chung Cheng University, Chia-Yi 621, Taiwan.

OutlineOutline

The features of ultrashort-pulse laser deposition (UPLD)

Gd22Fe74.6Co3.4 amorphous thin film

FeBO3 single-crystalline and polycrystalline films

Experimental setup of UPLD

The features of ultrashort pulse laser deposition (UPLD)The features of ultrashort pulse laser deposition (UPLD)

PLD is of great success in depositing chemically complex materials due to its ability to nonthermally and congruently transfer material from a multicomponent target to a substrate.

PLD is advantageous for the cases in which a lower substrate temperature is preferred, because the mobility of the atoms/ions can be provided by the momentum of the ions in the impinging plasma plume.

The problem of ejection of macroscopic particles from the target in PLD can be greatly alleviated by using ultrashort (< 1 ps) laser pulse. The remaining particles can be decomposed by using another laser beam.

The intensity of ultrashort pulse laser is high enough to ionize the target through optical-field ionization, so UPLD is adequate for all kinds of targets whether the target is transparent at the laser wavelength or not.

Experimental setupExperimental setup

ablation pulse – 2

off-axis parabolic (OAP)mirror post machining pulse

gas-jet nozzle beam splitter

substrate holder

with heater

shieldingbox

targetcarousel

ablation pulse – 1

relayed imaging system

post-machining pulsewavelength: 532 nmenergy: 1.4 Jpulse duration: 10 ns (FWHM)focal spot: 2 mm (FWHM)

ablation pulse – 1wavelength: 810 nmenergy: 230 mJpulse duration: 40 fs (FWHM)focal spot: 5~2000 μm (FWHM)

Eliminating particulates by using a post-machining pulseEliminating particulates by using a post-machining pulse

ablation pulse fluence: 3 J/cm2

post-machining pulse fluence: 3 J/cm2

substrate material: glass

Surface images (SEM)

0 μs 100 μs 500 μs300 μs200 μs

Particulates formed due to ejection of macroscopic particles or condensation in the plasma plume degrade the quality of the thin film.

The SEM images show that the surface quality of the film can be improved significantly by using a post-machining pulse with appropriate time delay to decompose the particles in the plume or heat up the cooler part of the plume.

various time delays between ablation and post-machining pulses

Ultrafast magnetic switchingUltrafast magnetic switchingRef: C. D. Stanciu et al., Phys. Rev. Lett. 99, 047601 (2007)

Staciu et al. experimentally demonstrate that the magnetization of Gd22Fe74.6Co3.4 can be reversed in a reproducible manner by a single 40-fs circularly-polarized laser pulse, without any applied magnetic field.The direction of this opto-magnetic switching is determined only by the helicity of light. This finding reveals an ultrafast and efficient pathway for writing magnetic bits at record-breaking speeds.

Resolving the transient dynamics of ultrafast magnetic switchingResolving the transient dynamics of ultrafast magnetic switching

photo diode – a(Ia)

photo diode – b(Ib)

pump pulse(circular polarization)

probe pulse(linear

polarization)targetpolarizer pump-probe scheme parameters

pump pulse fluence: 5 mJ/cm2

pump pulse duration: 500 fspump pulse wavelength: 800 nmprobe pulse wavelength: 650 nmprobe pulse duration: 40 fs

Ultrafast magnetic switching of GdUltrafast magnetic switching of Gd2222FeFe74.674.6CoCo3.43.4

PLD parametersablation beam fluence: 5 J/cm2

substrate material: glasstarget material: Gd22Fe74.6Co3.4

film thickness: 27 nmcapping layer: SiO2

Magnetic thin films of Gd22Fe74.6Co3.4 are successfully produced by using UPLD. For ultrafast magnetic switching the transition time is measured to be 780 fs, which is as good as that reported by Hohlfeld et al., but with a fidelity (reliability) of 100% which is better than that reported by Hohlfeld et al. (75%).

Ref: J. Hohlfeld et al., Appl. Phys. Lett. 94, 152504 (2009)

5757FeBOFeBO33 single crystal for the experiment of storage of nuclear excitation energy single crystal for the experiment of storage of nuclear excitation energy

through magnetic switchingthrough magnetic switchingRef: Yu. V. Shvyd’ko et al., Phys. Rev. Lett. 77, 3232 (1996)

e0: incident radiation (14.4 keV)Hc = 20 G: external field for initial settingHp = 58 G: switching field perpendicular to Hc

t’: timing of turning on Hp

t’’: timing of turning off Hp

(a) unperturbed

scheme of switching the hyperfine fielddirections in FeBO3 single crystal

time spectra of the nuclear forward scattering in FeBO3

(b) perturbed

t’ = 16 nst’’ = 308 ns

(c) perturbed

t’ = 8 nst’’ = 81 ns

(d) perturbed

t’ = 8 nst’’ = 188 ns

(e) perturbed

t’ = 8 nst’’ = 390 ns

Suppression and restoration originate from drastic changes of the nuclear states and of the interference within the nuclear transitions.

(111) surface

Polycrystalline thin film of FeBOPolycrystalline thin film of FeBO33 on on glassglass

PLD parametersablation beam fluence: 10 J/cm2

substrate material: glasstarget material: FeBO3

film thickness: 400 nmsubstrate temperature: 25 ℃

The XRD of this film shows that the grown film is polycrystal of FeBO3.

Single-crystalline thin film of FeBOSingle-crystalline thin film of FeBO33 on on SiOSiO22 (111) substrate (111) substrate

PLD parametersablation beam fluence: 10 J/cm2

substrate material: SiO2 (111)target material: FeBO3

film thickness: 400 nmsubstrate temperature: 550 ℃

Simulated FeBO3 XRD spectrum

Condition for constructive diffraction (n = integer)

-h + k + l = 3n-1 + 1 +1 = 1 destructive

The XRD of this FeBO3 film shows no diffraction peak except for the strongest diffraction peak of the SiO2 substrate, which is attenuated by the FeBO3 film. The disappearance of all the polycrystalline diffraction peaks support the transition into a single-crystalline film, and the nonexistence of the (111) peak is expected from the selection rule for hexagonal system.

Single-crystalline thin film of FeBOSingle-crystalline thin film of FeBO33 onon CaCOCaCO33 (104) substrate (104) substrate

PLD parametersablation beam fluence: 10 J/cm2

substrate material: CaCO3 (104)target material: FeBO3

film thickness: 400 nmsubstrate temperature: 550 ℃

effect of lattice mismatch

The asymmetric broadening of the (104) XRD peak towards larger angle can be ascribed to the effect of lattice mismatch between the film and the substrate.

Compared to the XRD of the substrate the XRD of this sample shows an additional peak at about 33 degrees, verifying that the grown film is FeBO3 single crystal with the normal in the (104) direction.

SummarySummary

Eliminating particulates in the deposition process is attained by using a post-machining pulse with appropriate time delay.

Amorphous magnetic thin films of Gd22Fe74.6Co3.4 are successfully produced by using ultrashort-pulse laser deposition. Using these films ultrafast magnetic switching with a transition time of 780 fs and 100% fidelity is achieved.

Polycrystalline FeBO3 film and single-crystalline FeBO3 films with (104) and (111) orientations are successfully produced by using pulsed laser deposition for the first time.

Thanks for your attention!Thanks for your attention!