OPTIMIZING DEPOSITION REGIMES TO FABRICATE VANADIUM DIOXIDE FILM FOR ACTIVE METASURFACES Текст научной статьи по специальности «Физика»

i l St. Petersburg Polytechnic University Journal. Physics and Mathematics. 2022 Vol. 15, No. 3.3 Научно-технические ведомости СПбГПУ. Физико-математические науки. 15 (3.3) 2022

Conference materials

UDC 538.911, 538.953

DOI: https://doi.org/10.18721/JPM.153.358

Optimizing deposition regimes to fabricate vanadium dioxide film for active metasurfaces

M. E. Kutepov ,e, I. K. Domaratskiy 2, S. S. Zhukov 2, E. M. Kaidashev \ I. V. Lisnevskaya ,, K. G. Abdulvakhidov ,, V.E. Kaydashev 1

1 Southern Federal University, Rostov-on-Don, Russia;

2 Moscow Institute of Physics and Technology (MIPT), Dolgoprudny, Russia H kutepov.max@yandex.ru

Abstract: Several deposition protocols to obtain epitaxial VO2 films from metallic vanadium and VO2 targets are compared. Films obtained from VO2 target showed much smoother and droplet free surface compared to those prepared from V target. The samples prepared from oxide target in average showed larger middle IR reflection of 55—67% in conducting state compared to ~ 56% for samples obtained from metal V target.

Keywords: vanadium dioxide, metal-to-isolator transition, pulsed laser deposition

Funding: This study was funded by SFU project No. 07/2020-06-MM, RSF project No. 21-79-00209 and RSF project No. 22-29-01037.

Citation: Kutepov M. E., Domaratskiy I. K., Zhukov S. S., Kaidashev E. M., Lisnevskaya I. V., Abdulvakhidov K. G., Kaydashev V. E., Optimizing deposition regimes to fabricate vanadium dioxide film for active metasurfaces. St. Petersburg State Polytechnical University Journal. Physics and Mathematics, 15 (3.3) (2022) 295-299. DOI: https://doi. org/10.18721/JPM.153.358

This is an open access article under the CC BY-NC 4.0 license (https://creativecommons. org/licenses/by-nc/4.0/)

Материалы конференции

УДК 538.911, 538.953

DOI: https://doi.org/10.18721/JPM.153.358

Оптимизация режимов осаждения пленки диоксида ванадия для активных метаповерхностей

М. Е. Кутепов ,н, И. К. Домарацкий 2, С. С. Жуков 2, Е. М. Кайдашев ,, И. В. Лисневская ,, К. Г. Абдулвахидов ,, В. Е. Кайдашев 1

1 Южный федеральный университет, Ростов-на-Дону, Россия; 2 Московский физико-технический институт, Долгопрудный, Россия н kutepov.max@yandex.ru

Аннотация. Проведено сравнение нескольких протоколов напыления эпитаксиальных пленок VO2 из мишени металлического ванадия и VO2. В отличии от пленок изготовленных из металлической мишени пленки из оксидной мишени показали поверхность свободную от капель. Образцы, синтезированные из оксидной мишени, в среднем показали большее среднее ИК-отражение 55-67% в проводящем состоянии по сравнению с ~ 56% для образцов, полученных из металлической ванадиевой мишени.

Ключевые слова: диоксид ванадия, переход металл-изолятор, импульсное лазерное напыление

Финансирование: Работа выполнен в рамках гранта ЮФУ № 07/2020-06-MM, гранта РНФ № 21-79-00209, гранта РНФ № 22-29-01037.

Ссылка при цитировании: Кутепов М. Е., Домарацкий И. К., Жуков С. С., Кайдашев Е. М., Лисневская И. В., Абдулвахидов К. Г., Кайдашев В. Е. Оптимизация

© Kutepov M. E., Domaratskiy I. K., Zhukov S. S., Kaidashev E. M., Lisnevskaya I. V., Abdulvakhidov K. G., Kaydashev V.

E., 2022. Published by Peter the Great St.Petersburg Polytechnic University.

режимов осаждения пленки диоксида ванадия для активных метаповерхностей // Научно-технические ведомости СПбГПУ. Физико-математические науки. 2022. Т. 15. № 3.3. C. 295-299. DOI: https://doi.org/10.18721/JPM.153.358

Статья открытого доступа, распространяемая по лицензии CC BY-NC 4.0 (https:// creativecommons.org/licenses/by-nc/4.0/)

Introduction

THz/middle IR imaging techniques for biology and medicine as well as sixth generation (6G) of mobile communication systems urgently need new tools to in-situ manipulate a front of a plane wave in sub-THz range of 0.1-1 THz and middle IR range of 10-60 THz. By exploiting "static" metasurfaces made of metallic antenna array one may already fabricate a great variety of devices to filter mid-IR/THz waves, modulate its intensity or manipulate a wavefront, i.e. focus radiation [1], obtain beam steering to a given angle [2], alter polarization [1, 3], filter wavelength [4] or achieve ultrafast modulation [5]. Due to use of metallic elements the functions of these devices are pre-defined by their design. VO2-based metasurfaces whose mid-IR/THz transmission/reflection are dynamically altered due to isolator-to-metal transition (IMT) do offer a great flexibility in programming device characteristics by local heating [6], electric current [7], mechanical stress [8] or laser light exposure [9]. Some progress in this direction has already been achieved recently [10, 11]. However, to obtain an advanced performance of a metasurface several characteristics of VO2 film should be engineered in proper manner. These properties of VO2 film should be simultaneously optimized, namely, isolator-to-metal state resistance alteration ratio, abruptness of a resistance versus temperature characteristics, lower phase transition temperature and reduced photo- and/or electrically induced switching times. Earlier we obtained VO2 films from metallic V target. However large amount of droplets is observed on the surface of the VO2 film deposited by pulsed laser deposition from metallic vanadium target. Poor surface smoothness still makes it challenging to manufacture devices by e-beam lithography.

In this report we optimized PLD protocols to obtain VO2 films on c-Al2O3 substrates with droplet free surface as well as high crystallinity, abrupt and narrow electrical hysteresis loop and large dynamic range of middle IR reflection alteration. Characteristics of samples obtained by ablation V and VO2 targets in different regimes are compared.

Experimental

VO2 films were prepared by pulsed laser deposition method. KrF laser beam (248 nm, 15ns, 10 Hz) was focused on the surface of rotating VO2 or metallic vanadium target to give a fluence of 2 J/cm2. The c-Al2O3 substrate was positioned at 5 cm from the target. The substrate temperature was maintained at 550 °C. The films were deposited in oxygen ambient for 4000 laser pulses. Samples in the first series were deposited by ablating a vanadium oxide target using the same laser fluence of 2 J/cm2 and varied oxygen pressure in the range of 1.5* 10-2 — 5*10-2 mbar. Another series of samples was deposited from metallic V target at substrate temperature of T = 650 °C oxygen pressure of 6*10-2 mbar and laser fluence of 2.3 J/cm2

Results and discussion

VO2 films obtained from VO2 target showed much smoother surface in contrast to those prepared by ablating metallic target whose surface suffers from droplets condensed in plasma plume.

X-ray diffraction patterns for both series of samples reveal characteristic reflexes of monocline VO2 lattice with VO2 (002) || c-Al2O3 (006) as shown in Fig. 2 a, b. FWHM of (020) and (040) reflexes are 0.17° and 0.19° for samples prepared from VO2 target and 0.18° and 0.20° correspondingly for samples obtained from metallic one. The XRD spectra for series of samples prepared from VO2 target reveal several additional reflexes (not assigned yet) evidencing the presence of some extra phases. In contrast the XRD spectra of samples prepared from metallic vanadium target showed much better crystalline homogeneity without any structural impurities as shown in Fig. 2, b.

© Кутепов М. Е., Домарацкий И. К., Жуков С. С., Кайдашев Е. М., Лисневская И. В., Абдулвахидов К. Г., Кайдашев В. Е., 2022. Издатель: Санкт-Петербургский политехнический университет Петра Великого.

Fig.1 Morphology of VO2 film prepared from vanadium dioxide (a) and metallic vanadium (b) target.

Field of view 100x134 ^m

a)

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150

VOJc-A\zOJ

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30 35 40 45 75 80 86 90

20, (feg

30 35 40 45 50 55 60 65 70 75 30 35 90 95 20 deg

Fig. 2 XRD spectra of VO2/ c-Al2O3 films prepared from oxide VO2 (a) and metallic V (b) targets

Resistance versus temperature related MIT hysteresis loops are varied for VO2 samples deposited form oxide target at different oxygen pressure as shown in Fig. 3, a. The temparature of phase transition, resistance change ratio and hysteresis loop width may be slihgtly tuned by choosing oxygen pressure during the deposition. In particular the curve with narrowest hysteresis of 4.5 °C and maximal isolator-to-metallic phase resistance change ratio of 2.4*103 was recordered for films deposited at 4*10-2 mbar as shown in Fig. 3, b. Note, that R(T) curve for VO2 film prepared from metallic target shows even narrower loop width of 3.3 °C.

a) 1000, -1,5x10"3mbar

2*10"' mbar 2,5*10"!nibar 4*102 tnbar 5x10'J mbar

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50 60 70

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80 90 100

Fig.3 R(T) hysteresis loop of VO2 samples obtained from VO2 target at different oxygen pressures (a) and from metallic V target (b). Example of derivative curve d(lg(R(T))/dT of VO2 film fabricated from

metallic V target is shown in inset

The quality of electrical switching hysteresis loop readily analyzed from the derivative of lg10(R(T)) value plotted as function of film temperature. The features of electrical switching of VO2 films prepared at different oxygen pressure, namely the phase transition temperature T№ hysteresis loop width AT and film resistance in isolator and conducting states are summarized in Table 1. Abruptness of R( T) characteristics can be estimated by FWHM and minimum value of d(lg(R(T))/dT curve.

Table 1

The features of electrical switching of VO2 films prepared at different oxygen pressure

P(O2), mbar T °C PT FWHM d(lg R(T))/dT min RRr R , m min AT, °C R isolato/RmetaUic

1.5x10-2 59.5 8 - 0.31 89.7 0.042 7.1 2.1x103

2x10"2 55.5 6 - 0.37 74.8 0.042 5.8 1.8x103

4x10-2 64 6.8 - 0.42 145 0.034 4.5 4.3x103

5x10-2 59.9 5.5 - 0.41 180 0.142 5.9 1.3x103

Reflection spectra in the middle and near IR were studied using Bruker Vertex 80V FTIR spectrometer equipped with a Hyperion 2000 microscope. The spectra were recorded from a spot of ~ 40 ^m2 from the homogeneous surface free of droplets. Optical reflection spectra in the middle infrared range reveal drastic change upon film heating above the isolator-metal transition due to its conductivity alteration as shown in Fig. 4. The characteristic shape of reflection spectra is altered at the temperature of structural phase transition TTR evidencing the change of VO2 lattice symmetry as well as electronic strucure. Notably that films prepared from VO2 target show greater reflection variation as shown in Fig. 4, a compared to the ones deposited from metallic vanadium target (Fig. 4, b). In particular, VO2 temperature alteration from 30 °C to 80 °C results in mid IR reflection (at 10^m) increase of 55—67% for samples obtained at different oxygen pressure from VO2 target. Samples obtained from metal V target showed ~ 56% mid IR reflection change. Note that samples synthesised from VO2 target at oxygen pressure of 2*10-2 mbar in series shown in Fig. 4, a reveal greatest dynamic range of mid IR transmission alteration.

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b)

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eoo moo 1200 Frequency / cm-1

eoo 1000 1200

Frequency / cm '

Fig. 4 Temperature dependent middle IR reflection spectra of VO2 film prepared by ablating VO2 (a)

and metallic V target (b)

Conclusion

Several pulsed laser deposition regimes to obtain quality VO2 films are discussed. Samples obtained from VO2 target show smooth surface whereas the ones obtained by ablating metallic vanadium target reveal a lot of droplets. Both types of films reveal high electrical, structural and optical switching characteristics, however the samples obtained from VO2 target show some extra crystalline orientations/phases, which is a subject of further studies. The samples prepared from oxide target in average showed larger middle IR reflection of 55—67% in conducting state compared to ~ 56% for samples obtained from metal V target. The sample synthesized at 4*10-2 had the smallest difference of 4.5° between the hysteresis heating and cooling curves, as well as the greatest resistance change abruptness.

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THE AUTHORS

KUTEPOV Maxim E.

kutepov.max@yandex.ru ORCID: 0000-0002-3805-5416

DOMARATSKIY Ivan K.

Domaratskiy@phystech.edu ORCID: 0000-0002-8036-8301

ZHUKOV Sergey S.

zhukov.ss@mipt.ru ORCID: 0000-0001-7268-8666

LISNEVSKAYA Inna V.

liv@sfedu.ru

ABDULVAKHIDOV Kamaludin G.

kgabdulvahidov@sfedu.ru

KAYDASHEV Vladimir E.

kaydashev@gmail.com ORCID: 0000-0003-1913-591X

KAIDASHEV Evgeni M.

emkaydashev@sfedu.ru ORCID: 0000-0002-5886-6443

Received 01.09.2022. Approved after reviewing 15.09.2022. Accepted 19.09.2022.

© Peter the Great St. Petersburg Polytechnic University, 2022