zhimao ni growth of mg b2 films on metallic substrates by hpcvd

Growing MgB2 Films on Metallic Substrates by HPCVD

Zhimao Ni1, Fa He1, Kexin Liu1 and Qingrong Feng2

1Institute of Heavy Ion Physics & State Key Laboratory of Nuclear Physics and Technology, Peking University, China

2School of Physics & State Key Laboratory for Artificial Structure and Mesoscopic Physics, Peking University, China

6th Workshop on Thin Films and New Ideas for SRF, Padua, Italy, October 6-8, 2014

1

Outline

IHIP, Peking University, China

§ Background

§ Growing MgB2 Films on Mo/Cu Substrates

§ Growing 2”MgB2 Films on Nb Substrates

§ Summary

2Thin Films & New Ideas for SRF 2014

Background


MgB2 shows potential for SRF application since the discovery of its

superconductivity in 2001. (High Tc, low RBCS, possible high Hc[1])

Many laboratories have involved in the research of fabricating MgB2

films for SRF application.

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Coating Research Methods Reference

LANL Cu cavity (trying) HPCVD T. Tajima, et al. SRF2013

KEK Quadrant cavity Pulse laser deposition S. Mitsunobu, et al. SRF2009

STI0.5-4” samples

2” films /Nb (RF tested)Reactive evaporation B H Moeckly, et al. SUST 19(2006)

D E Oates, et al. SRFTF 2012

Temple Univ.…

Small samples2” films /sapphire (RF

tested) 6GHz cavity (trying)

HPCVD&CVD

X X Xi, et al. SRFTF 2012M A Wolak, et al. PRST 17(2014)

RF test systems for samples : JLab, MIT, SLAC, CERN, Cornell, …

[1]. X X Xi, Supercond. Sci. Technol. 22(2009) 043001

Thin Films & New Ideas for SRF 2014

Background

IHIP, Peking University, China 4

MgB2 films research have started at PKU since 2008, cooperated

with the group of MgB2 films in school of physics.

Two kinds of HPCVD systems were developed.

￭ Quartz reactor with inductive heater

￭ Stainless steel reactor with resistive heater


Background


Early research of MgB2 films on metallic substrates for SRF at PKU.

MgB2/Cu

38.2K

MgB2/Nb

[1]. Fa He, et al. Supercond. Sci. Technol. 25 (2012) 065003

MgB2/Mo[1]

Recent works:

￭ Growing MgB2 Films on Mo/Cu Substrates

￭ Growing 2”MgB2 Films on Nb Substrates


Outline


§ Background

§ growing MgB2 Films on Mo/Cu Substrates

§ growing 2”MgB2 Films on Nb Substrates

§ Summary


Growing MgB2 Films on Mo/Cu Substrates


Mo/Cu substrates

[1]. Fen Li, et al. Supercond. Sci. Technol. 19 (2006) [2]. Fa He, et al. Supercond. Sci. Technol. 25 (2012) 065003

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MgB2/Cu[1]

MgB2/Mo[2]

￭ Mo

– Stable with Mg

– But poor ductility

￭ Cu

– High thermal conductivity

– But reacting with Mg

￭ Two step experiments:

– Sputtering Mo films on Cu substrates

– Growing MgB2 films on substrates of

Cu buffered with Mo by HPCVD.MgB2/Mo/Cu




Sputtering Mo films on Cu substrates.

（ b ）￭ Surface treatments of Cu

－ Mechanical and chemical polishing

－ Ultrasonic cleaning

－ Sputtering cleaning

Sputteringcleaning

DC Sputtering

Cathode Voltage(V) 684 213

Gas Pressure (Pa) 5 2.8

Time(min) 15 40*

(a) Without Sputtering cleaning

(b) With Sputtering cleaning

▌The photos of Mo films after ultrasonic cleaning

* The growth rate was about 6nm/min, and the film was 240nm thick..




H2

B2H6

substrateMg

susceptor

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Growing MgB2 films on Mo/Cu by HPCVD

Gas pressure ~20 kPa

Flow rate of H2 100 sccm

B2H6(75%) 10 sccm

Temperature# ~680℃

Reacting time 3min

Mo/Cu film

（ a）

（ b）

MgB2/Mo/Cu film

#The deposition temperature should be controlled carefully!

Inductive Heater




￭ SEM images

Mo/Cu

MgB2/Mo/Cu

×2000 ×50000

×50000×2000

1μm

1μm

a b

c d

20μm

20μm




￭ XRD patterns

Mo/Cu MgB2/Mo/Cu

• XRD indicates MgCu2 still generated from the reaction between Mg and Cu.




• The transition curve was not sharp may due to the presence of MgCu2.

Future plan:

Increasing the thickness of the Mo layer Using other materials as the buffer layer

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￭ M-T


Outline


§ Background



§ Summary


Growing 2”MgB2 Films on Nb Substrates


For RF test, 2”MgB2 films on metallic substrates was fabricated.

(The size of 2” is required for SIC system at JLab, )

The structure of the HPCVD reactor with resistive heater was

modified.

susceptor

Cu posts

Resistive heater

For small samples

For large samples




Experiments (Nb substrates)

Gas pressure 5 kPa

H2 flow rate 100 sccm

B2H6 (75%) 10 sccm

Temp. of susceptor ~ 850℃

Temp. of substrate ~ 720℃

time 5 min

￭ The 2 mm thick quartz was used

to make the substrate cooler than

the susceptor.

2”




• The grains became denser.

• The size of the grains became larger

• Directions of the grains changed: c-axis, slanted ,vertical

￭ SEM images

Center area Edge area

• The distribution of Mg vapor above the substrate was not uniform.

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1 32

4 5

500nm




323nm

￭ Cross-sectional images

￭ XRD scans

517nm

Center area

Edge area




position Tc(K)

1 36

2 35.5

3 34

4 36.5

5 34

￭ R-T measurement

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• The shortage of Mg vapor may lead to the poor properties at the center area.




Design of the new Susceptor

• Heat shield —— increasing Mg vapor

• Heat transfer layer —— adjusting the temperature of the substrate by

changing the material and thickness.

Heat shield

Heat transfer layer

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We tried to increase the Mg vapor above the substrates.

Etched by Mg

MgB2




￭ XRD scans

~850nm

￭ SEM images of the MgB2 film

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Cross- sectional image

MgB2

500nm




𝑇 𝑐 (𝑜𝑛𝑠𝑒𝑡)=40.6𝐾

￭ R-T measurement

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MgB2




￭ Critical current density Jc (Calculated by Bean model)

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MgB2

Jc(10K,0T) = 4×104A/cm2

Jc(20K,0T) = 2.6×104A/cm2




￭ More 2”MgB2 films will be fabricated and prepared to be tested.

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Adjusting the temperatures of the substrates

MgB2

Etched by Mg

￭ Changing the heat transfer layer.

① ② ③ ④

4 mm thick quartz 2 mm thick quartz 2 mm thick Al2O3 2 mm thick Mo

Sample ① Sample ② Sample ③ Sample ④


Outline


§ Background



§ Summary


Summary


MgB2 films on different metallic substrates of Cu, Mo, Nb have been

fabricated with HPCVD method at Peking University.

We coated MgB2 films on Cu substrates buffered with Mo layers successfully.

— The films have polycrystalline structure, and the Tc is around 35K.

— However, the quality of this MgB2 films are still not as good as expected and further

research is ongoing.

We have grown 2”MgB2 films on Nb substrates for RF test.

— High quality MgB2 films with 0.8μm thick, clear hexagonal crystallites was obtained,

and the Tc is as high as about 40.6 K.

25Email: [email protected] & [email protected]

Future works:

— Improve the quality of MgB2 further

— Test the RF characteristics of MgB2 films at JLab

— Develop the techniques of coating cavities with MgB2 films.

Thank you for your attention!

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zhimao ni growth of mg b2 films on metallic substrates by hpcvd

Science

growing mgb2 films

background mgb2 films

sputtering mo films

peking university

srf application

china background

substrates ofmgb2mocu

metallic substrates