迄今為止，金屬表面電漿技術因其獨特的光學現象和各種應用而受到了廣泛的關注。目前較為常用的金屬表面電漿材料是：金和銀，在可見及近紅外光譜區域具有良好的電漿子共振性能；鋁和銅，具CMOS製程兼容性，亦有相關的電漿子應用研究。然而，上述金屬的熱穩定性和化學穩定性，因其熔點不高，導致在高溫以及高功率應用受限。氮化鈦其熔點為~3000 oC，具耐高溫、金色金屬光澤、並具高導電率；其帶間吸收於~450 nm相對金的~520 nm更短波長，因此可應用於可見光和近紅外光譜區域的電漿子共振元件，並且於~6 K具有超導的特性。基於上述優勢，氮化鈦過去已成功應用於Si-CMOS的製程所需的阻擋層，以及作為電晶的閘極金屬、氮化物發光二極體的n型電極，因此與現有的半導體技術製程相兼容。
藉由超高真空條件的電漿輔助分子束磊晶(PA-MBE)技術，成長氮化鈦(111)薄膜於c面藍寶石基板上。透過調控氮電漿通量與生長溫度，優化氮化鈦薄膜的化學劑量TiNx (x≤1)來控制其光學性質。通過反射高能電子繞射(RHEED)，可即時了解磊晶情況，並觀察不同氮電漿通量成長對氮化鈦薄膜表面形貌。此外，利用橢圓偏光技術並藉由Drude-Lorentz模型擬合TiNx之介電常數。對於，晶體結構上的分析，高解析X射線繞射(HRXRD)掃描結果顯示，其半高寬約~200 arcsec；而穿透式電子顯微鏡(TEM)亦可獲得單晶繞射圖，並可得高倍率原子解析影像。同時，採用XPS縱向分析，驗證無氧元素存在於氮化鈦薄膜，更加證實了超高真空條件對高純度的氮化鈦磊晶的重要性。利用優化之氮化鈦薄膜成長條件，成長不同厚度的單晶氮化鈦薄膜，分別是4 nm、6 nm、8 nm、20 nm及30 nm。利用電子束微影(EBL)及感應電漿耦合蝕刻(ICP etching)製程，製作不同週期之光柵，調控其表面電漿共振峰值，成功獲得1-4 μm頻率選擇面。此項成果，可應用於熱光伏電之熱吸收器或熱發射器、近紅外－中紅外光感元件設計，以及生物感測應用等。

Metal surface plasmonic has received extensive attention due to its unique optical phenomena and various applications. Au and Ag as surface plasmon materials are commonly used in the visible/NIR spectra due to good resonance performance. Al and Cu are also studied for plasmonic applications due to CMOS compatibility. However, these metals have a limitation of high temperature/power applications due to thermal and chemical instability caused by their low melting point. The advantages of titanium nitride (TiN) are high-temperature resistance (mp ~3000 oC), golden metallic color, and high conductivity. Its interband absorption is at ~450 nm shorter than gold (~520 nm). Therefore, it can be applied to the visible/NIR spectral regions plasmon devices. Besides, it has superconducting behavior at ~6 K. Based on these advantages, TiN has been successfully applied in several fields, such as blocking layer of Si-CMOS process, gate metal of transistors, and n-type electrode of nitride-LEDs, exhibiting superior compatible with existing semiconductor process.
Epitaxial TiN (111) thin films are grown on c-sapphire by ultra-high vacuum PA-MBE technique. The stoichiometric TiN as well its optical properties are optimized by adjusting the N2 plasma flux and growth temperature. In-situ RHEED patterns offer the real-time epitaxy situation and indicate TiN surface topological changed under different N2 plasma flux. Drude-Lorentz model is utilized to define the permittivity of TiNx via ellipsometry spectra. HRXRD rocking curves show FWHM are ~200 arcsec; high resolution atomic images and selected area diffraction are demonstrated epitaxial and high-quality single crystal properties by TEM. XPS depth-profile illustrates oxygen-free results to indicate importance of ultra-high vacuum growth conditions. The different thicknesses ultrathin TiN film under optimized growth conditions are presented from 4 nm to 30 nm. The tunable frequency selective surface (1-4 μm) have been achieved by varying surface plasmon resonance via EBL and ICP etching to provide different periods grating nanostructures. This achievement could be applied for thermal photovoltaics emitter/absorber, NIR/MIR photodetector, and biosensor.

[1] R.W.Wood, On a remarkable case of uneven distribution of light in a diffraction grating spectrum, Proc. Phys. Soc. London. 18 (1901) 269–275. https://doi.org/10.1088/1478-7814/18/1/325.
[2] U.Fano, The theory of anomalous diffraction gratings and of quasi-stationary waves on metallic surfaces (Sommerfeld’s waves), J. Opt. Soc. Am. 31 (1941) 213. https://doi.org/10.1364/josa.31.000213.
[3] R. H. RITCHIE, Plasma losses by fast electrons in thin films, Phys. Rev. 106 (1956) 8. https://journals.aps.org/pr/pdf/10.1103/PhysRev.106.874%0Ahttps://link.aps.org/doi/10.1103/PhysRev.106.874%0Apapers3://publication/doi/10.1103/PhysRev.106.874.
[4] A.Otto, Excitation of nonradiative surface plasma waves in silver by the method of frustrated total reflection, Zeitschrift Für Phys. 216 (1968) 398–410. https://doi.org/10.1007/BF01391532.
[5] E.Kretschmann, H.Raether, Radiative decay of non radiative surface plasmons excited by light, Zeitschrift Für Naturforsch. A. 23 (1968) 2135–2136. https://doi.org/10.1515/zna-1968-1247.
[6] Z.M.Abd El-Fattah, V.Mkhitaryan, J.Brede, L.Fernández, C.Li, Q.Guo, A.Ghosh, A.R.Echarri, D.Naveh, F.Xia, J.E.Ortega, F.J.García De Abajo, Plasmonics in atomically thin crystalline silver films, ACS Nano. 13 (2019) 7771–7779. https://doi.org/10.1021/acsnano.9b01651.
[7] F.H.L.Koppens, D.E.Chang, F.J.García De Abajo, Graphene plasmonics: A platform for strong light-matter interactions, Nano Lett. 11 (2011) 3370–3377. https://doi.org/10.1021/nl201771h.
[8] M.Liu, X.Yin, E.Ulin-Avila, B.Geng, T.Zentgraf, L.Ju, F.Wang, X.Zhang, A graphene-based broadband optical modulator, Nature. 474 (2011) 64–67. https://doi.org/10.1038/nature10067.
[9] A.Manjavacas, F.J.García de Abajo, Tunable plasmons in atomically thin gold nanodisks, Nat. Commun. 5 (2014) 3548. https://doi.org/10.1038/ncomms4548.
[10] R.Yu, V.Pruneri, F.J.Garciá De Abajo, Active modulation of visible light with graphene-loaded ultrathin metal plasmonic antennas, Sci. Rep. 6 (2016) 1–7. https://doi.org/10.1038/srep32144.
[11] R.A.Maniyara, D.Rodrigo, R.Yu, J.Canet-Ferrer, D.S.Ghosh, R.Yongsunthon, D.E.Baker, A.Rezikyan, F.J.García de Abajo, V.Pruneri, Tunable plasmons in ultrathin metal films, Nat. Photonics. 13 (2019) 328–333. https://doi.org/10.1038/s41566-019-0366-x.
[12] G.Kästle, H.G.Boyen, B.Koslowski, A.Plettl, F.Weigl, P.Ziemann, Growth of thin, flat, epitaxial (111) oriented gold films on c-cut sapphire, Surf. Sci. 498 (2002) 168–174. https://doi.org/10.1016/S0039-6028(01)01685-5.
[13] C.Jeppesen, N.A.Mortensen, A.Kristensen, The effect of Ti and ITO adhesion layers on gold split-ring resonators, Appl. Phys. Lett. 97 (2010) 2012–2015. https://doi.org/10.1063/1.3532096.
[14] B.Lahiri, R.Dylewicz, R.M.DeLa Rue, N.P.Johnson, Impact of titanium adhesion layers on the response of arrays of metallic split-ring resonators (SRRs), Opt. Express. 18 (2010) 11202. https://doi.org/10.1364/oe.18.011202.
[15] P.R.West, S.Ishii, G.V.Naik, N.K.Emani, V.M.Shalaev, A.Boltasseva, Searching for better plasmonic materials, Laser Photonics Rev. 4 (2010) 795–808. https://doi.org/10.1002/lpor.200900055.
[16] D.Gu, C.Zhang, Y.-K.Wu, L.J.Guo, Ultra-smooth and thermally-stable ag-based thin films with sub-nanometer roughness by Al doping, ACS Nano. 8 (2014) 10343–10351.
[17] C.W.Cheng, Y.J.Liao, C.Y.Liu, B.H.Wu, S.S.Raja, C.Y.Wang, X.Li, C.K.Shih, L.J.Chen, S.Gwo, Epitaxial aluminum-on-sapphire films as a plasmonic material platform for ultraviolet and full visible spectral regions, ACS Photonics. 5 (2018) 2624–2630. https://doi.org/10.1021/acsphotonics.7b01366.
[18] Seok Ho Song, Dispersion relation of SPPs on thin metal films,. http://optics.hanyang.ac.kr/~shsong/11-Dispersion relation of SPPs on thin metal films.pdf.
[19] U.Guler, A.Boltasseva, V.M.Shalaev, Refractory plasmonics, Science. 344 (2014) 263–264. https://doi.org/10.1126/science.1252722.
[20] A.Boltasseva, H.A.Atwater, Low-loss plasmonic metamaterials, Science. 331 (2011) 290–291. https://doi.org/10.1126/science.1198258.
[21] A.Boltasseva, V.M.Shalaev, All that glitters need not be gold, Science. 347 (2015) 1308–1310. https://doi.org/10.1126/science.aaa8282.
[22] G.Y.Yang, H.Peng, H.B.Guo, S.K.Gong, Deposition of TiN/TiAlN multilayers by plasma-activated EB-PVD: tailored microstructure by jumping beam technology, Rare Met. 36 (2017) 651–658. https://doi.org/10.1007/s12598-016-0824-2.
[23] G.C.Lain, F.Cemin, C.M.Menezes, C.Aguzzoli, I.J.R.Baumvol, S.S.Tomiello, C.A.Figueroa, Bias influence on titanium interlayer for titanium nitride films, Surf. Eng. 32 (2016) 279–283. https://doi.org/10.1179/1743294415Y.0000000097.
[24] A.Mumtaz, W.H.Class, Color of titanium nitride prepared by reactive dc magnetron sputtering, J. Vac. Sci. Technol. 20 (1981) 345–348. https://doi.org/10.1116/1.571461.
[25] D.Steinmüller-Nethl, R.Kovacs, E.Gornik, P.Rödhammer, Excitation of surface plasmons on titanium nitride films: Determination of the dielectric function, Thin Solid Films. 237 (1994) 277–281. https://doi.org/10.1016/0040-6090(94)90273-9.
[26] A.P.Hibbins, J.R.Sambles, C.R.Lawrence, Surface plasmon-polariton study of the optical dielectric function of titanium nitride, J. Mod. Opt. 45 (1998) 2051–2062. https://doi.org/10.1080/09500349808231742.
[27] G.V.Naik, J.L.Schroeder, X.Ni, A.V.Kildishev, T.D.Sands, A.Boltasseva, Titanium nitride as a plasmonic material for visible and near-infrared wavelengths, Opt. Mater. Express. 2 (2012) 478. https://doi.org/10.1364/OME.2.000478.
[28] H.Reddy, U.Guler, Z.Kudyshev, A.V.Kildishev, V.M.Shalaev, A.Boltasseva, Temperature-dependent optical properties of plasmonic titanium nitride thin films, ACS Photonics. 4 (2017) 1413–1420. https://doi.org/10.1021/acsphotonics.7b00127.
[29] D.Shah, H.Reddy, N.Kinsey, V.M.Shalaev, A.Boltasseva, Optical properties of plasmonic ultrathin TiN films, Adv. Opt. Mater. 5 (2017) 1–5. https://doi.org/10.1002/adom.201700065.
[30] C.M.Zgrabik, E.L.Hu, Optimization of sputtered titanium nitride as a tunable metal for plasmonic applications, Opt. Mater. Express. 5 (2015) 2786. https://doi.org/10.1364/ome.5.002786.
[31] D.Steinmüller-Nethl, R.Kovacs, E.Gornik, P.Rödhammer, Excitation of surface plasmons on titanium nitride films: determination of the dielectric function, Thin Solid Films. 237 (1994) 277–281. https://doi.org/10.1016/0040-6090(94)90273-9.
[32] G.V.Naik, J.L.Schroeder, X.Ni, A.V.Kildishev, T.D.Sands, A.Boltasseva, Titanium nitride as a plasmonic material for visible and near-infrared wavelengths, Opt. Mater. Express. 2 (2012) 478. https://doi.org/10.1364/OME.2.000478.
[33] D.Shah, H.Reddy, N.Kinsey, V.M.Shalaev, A.Boltasseva, Optical Properties of Plasmonic Ultrathin TiN Films, Adv. Opt. Mater. 5 (2017) 1–5. https://doi.org/10.1002/adom.201700065.
[34] R.P.Sugavaneshwar, S.Ishii, T.D.Dao, A.Ohi, T.Nabatame, T.Nagao, Fabrication of highly metallic TiN films by pulsed laser deposition method for plasmonic applications, ACS Photonics. 5 (2018) 814–819. https://doi.org/10.1021/acsphotonics.7b00942.
[35] A.Moatti, J.Narayan, High-quality TiN/AlN thin film heterostructures on c-sapphire, Acta Mater. 145 (2018) 134–141. https://doi.org/10.1016/j.actamat.2017.11.044.
[36] D.Fomra, R.Secondo, K.Ding, V.Avrutin, N.Izyumskaya, Ü.Özgür, N.Kinsey, Plasmonic titanium nitride via atomic layer deposition: A low-temperature route, J. Appl. Phys. 127 (2020). https://doi.org/10.1063/1.5130889.
[37] K.Hansen, M.Cardona, A.Dutta, C.Yang, Plasma enhanced atomic layer deposition of plasmonic TiN ultrathin films using TDMATi and NH3, Materials (Basel). 13 (2020). https://doi.org/10.3390/ma13051058.
[38] H.A.Smith, S.Elhamri, K.G.Eyink, L.Grazulis, M.J.Hill, T.C.Back, A.M.Urbas, B.M.Howe, A.N.Reed, Epitaxial titanium nitride on sapphire: Effects of substrate temperature on microstructure and optical properties, J. Vac. Sci. Technol. A. 36 (2018) 03E107. https://doi.org/10.1116/1.5022068.
[39] W.P.Guo, R.Mishra, C.W.Cheng, B.H.Wu, L.J.Chen, M.T.Lin, S.Gwo, Titanium nitride epitaxial films as a plasmonic material platform: Alternative to gold, ACS Photonics. 6 (2019) 1848–1854. https://doi.org/10.1021/acsphotonics.9b00617.
[40] K.C.Maurya, V.M.Shalaev, A.Boltasseva, B.Saha, Reduced optical losses in refractory plasmonic titanium nitride thin films deposited with molecular beam epitaxy, Opt. Mater. Express. 10 (2020) 2679. https://doi.org/10.1364/ome.405259.
[41] R.Mishra, C.-W.Chang, A.Dubey, Z.-Y.Chiao, T.-J.Yen, H.W.Howard Lee, Y.-J.Lu, S.Gwo, Optimized titanium nitride epitaxial film for refractory plasmonics and solar energy harvesting, J. Phys. Chem. C. 2021 (2021). https://doi.org/10.1021/acs.jpcc.1c03053.
[42] R.Mishra, C.-W.Chang, A.Dubey, Z.-Y.Chiao, T.-J.Yen, H.W.Howard Lee, Y.-J.Lu, S.Gwo, Optimized Titanium Nitride Epitaxial Film for Refractory Plasmonics and Solar Energy Harvesting, J. Phys. Chem. C. 2021 (2021). https://doi.org/10.1021/acs.jpcc.1c03053.
[43] H.A.Wriedt, J.L.Murray, The N-Ti (nitrogen-titanium) system, Bull. Alloy Phase Diagrams. 8 (1987) 378–388. https://doi.org/10.1007/BF02869274.
[44] V.Abalakin, Section 14: Geophysics, astronomy, and acoustics, in: W.M.Haynes, D.R.Lide, T.J.Bruno (Eds.), CRC Handb. Chem. Phys., 97th ed., Taylor & Francis Group, New York, 2017: p. 17.
[45] J.F.Shackelford, Appendix 1: Physical and chemical data for the elements, in: Introd. to Mater. Sci. Eng., Pearson Higher Education, Upper Saddle River, New Jersey, 2015: pp. A1–A3. https://doi.org/10.1017/CBO9781107415324.004.
[46] H.O.Pierson, Carbides of Group VI, in: Handb. Refract. Carbides Nitrides, Elsevier, Westwood, New Jersey, 1996: pp. 100–117. https://doi.org/10.1016/B978-081551392-6.50007-6.
[47] G.VSamsonov, Chapter VI. Mechanical properties of the elements, in: G.VSamsonov (Ed.), Handb. Physicochem. Prop. Elem., 1 st, Springer US, New York, 1968: pp. 438–443. https://doi.org/10.1007/978-1-4684-6066-7.
[48] E.J.Zeman, G.C.Schatz, An accurate electromagnetic theory study of surface enhancement factors for Ag, Au, Cu, Li, Na, Al, Ga, In, Zn, and Cd, J. Phys. Chem. 91 (1987) 634–643. https://doi.org/10.1021/j100287a028.
[49] H.Ehrenreich, H.R.Philipp, Optical properties of Ag and Cu, Phys. Rev. 128 (1962) 1622–1629.
[50] D.Gerard, S.K.Gray, Aluminium plasmonics, J. Phys. D. Appl. Phys. 48 (2015) 184001. https://doi.org/10.1088/0022-3727/48/18/184001.
[51] P.Patsalas, N.Kalfagiannis, S.Kassavetis, Optical properties and plasmonic performance of titanium nitride, Materials (Basel). 8 (2015) 3128–3154. https://doi.org/10.3390/ma8063128.
[52] M.Kumar, N.Umezawa, S.Ishii, T.Nagao, Examining the performance of refractory conductive ceramics as plasmonic materials: A theoretical approach, ACS Photonics. 3 (2016) 43–50. https://doi.org/10.1021/acsphotonics.5b00409.
[53] M.A.Herman, Molecular beam epitaxy: Fundamentals and current status, 1st Ed., Heidelberg, Germany, 1989. https://doi.org/10.1524/zkri.1990.190.3-4.315.
[54] F.LISCIO, Self-assembled magnetic nanostructures prepared by molecular beam epitaxy on low energy surfaces, University of Roma Tre, 2009.
[55] 吳靖宙,張憲彰,掃描式探針顯微鏡於生物樣本的量測與應用,科儀新知. 23 (2002) 88–99. https://doi.org/10.1201/9781420075250.
[56] N.A.Saveskul, N.A.Titova, E.M.Baeva, A.V.Semenov, A.V.Lubenchenko, S.Saha, H.Reddy, S.I.Bogdanov, E.E.Marinero, V.M.Shalaev, A.Boltasseva, V.S.Khrapai, A.I.Kardakova, G.N.Goltsman, Superconductivity behavior in epitaxial TiN films points to surface magnetic disorder, Phys. Rev. Appl. 12 (2019) 1. https://doi.org/10.1103/PhysRevApplied.12.054001.
[57] J.S.Chawla, X.Y.Zhang, D.Gall, Effective electron mean free path in TiN(001), J. Appl. Phys. 113 (2013) 1–6. https://doi.org/10.1063/1.4790136.
[58] D.Shah, A.Catellani, H.Reddy, N.Kinsey, V.Shalaev, A.Boltasseva, A.Calzolari, Controlling the plasmonic properties of ultrathin TiN films at the atomic level, ACS Photonics. 5 (2018) 2816–2824. https://doi.org/10.1021/acsphotonics.7b01553.