Tunable luminescence of nanoporous silicon via electrochemical etching parameters

Optik 127 (2016) 3513–3516 Contents lists available at ScienceDirect Optik journal homepage: www.elsevier.de/ijleo Tunable luminescence of nanoporous silicon via electrochemical etching parameters Vuong-Hung Pham a,∗ , Nguyen Thi Ha Hanh b , Phuong Dinh Tam a a b Advanced Institute for Science and Technology (AIST), Hanoi University of Science and Technology (HUST), No 01, Dai Co Viet Road, Hanoi, Viet Nam School of Chemical Engineering, Hanoi University of Science and Technology (HUST), No 01, Dai Co Viet Road, Hanoi, Viet Nam a r t i c l e i n f o Article history: Received 22 October 2015 Accepted January 2016 Keywords: Nanoporous Si Electrolyte Electrochemical etching Luminescence Etching a b s t r a c t This paper reports the surface state induces a variation in light emission of nanoporous Si as a function of electrolyte condition, anode–cathode distance and aging in common chemical reagents to achieve strong and stable luminescence of Si semiconductor The electrochemical derived nano Si was observed to have a nanoporous structure with the pore of about 20 nm in the thickness of 50 ␮m The luminescence of nanoporous Si was showed enhancing in the sample with the HF/ethanol of 1:1 and the anode–cathode distance of about cm As etched specimen, the luminescence of the nanoporous Si was centered at 800 nm; however blue-shift when they were immersed in green chemical reagents These results suggest that the potential application of electrochemical etching followed by green chemical treatment to tunable luminescence, which was potential application in nanoporous Si based devices and nanomedicine © 2016 Elsevier GmbH All rights reserved Introduction Nano silicon has received a great deal attention in recent years due its ability exhibit to interesting physical properties not observed in bulk silicon [1,2] Among the various nanostructure, nanoporous silicon is particularly fascinating because of its light emission at room temperature, compatible with electronic devices, large specific capacity for drug loading, as well as excellent biocompatibility [3,4] Until now, the scientific applications of electrochemical derived nanoporous Si have been investigated for use as optoelectronic [5,6], solar cell [7,8], gas sensor [9], biosensor [10,11], nano carrier [12,13], and substrates for cellular growth [14] Although, light emission from electrochemical etching derived nanoporous Si has been well documented, but, it is still important to control the surface states and microstructure of nanoporous Si for further improving the luminescence and long term stability of the specimens [15,16], which would be strongly dependent on the electrochemical etching parameters and chemical treatments Recently, highly nanoporous Si has been synthesized successfully in our laboratory by electrochemical etching method [17] In that research, we have investigated the effect of electrochemical etching voltages to the microstructure and luminescence of the nanoporous Si To expand this research, we herein report the effect ∗ Corresponding author Tel.: +84 36230435; fax: +84 43 6230 293 E-mail address: vuong.phamhung@hust.edu.vn (V.-H Pham) http://dx.doi.org/10.1016/j.ijleo.2016.01.009 0030-4026/© 2016 Elsevier GmbH All rights reserved of electrolyte concentration, anode–cathode distance and chemical treatment to the luminescence of nanoporous Si To the best of our knowledge, this is the first time study the effect of anode–cathode distance to the luminescence of nanoporous Si, which would build up more scientific information about nanoporous Si field for designing strong and stable light emission in optoelectronic and nanomedicine The microstructure of the nanoporous Si was characterized by field emission scanning electron microscopy (FE-SEM) The crystal structure and chemical bonding of the specimen was characterized by infrared spectroscopy The luminescence was also determined by photoluminescence spectrometer Experimental procedure A p type 0 silicon wafer (Si) with a resistivity of 0.5–2 cm was used as a substrate Before electrochemical etching, the silicon wafer was dipped into a HF solution of 48% concentration for 10 to remove the native oxide layer on the wafer The dipped Si wafer was then electrochemically etched with an electrolyte solution containing various ratios of HF and ethanol, anode–cathode distance in order to control the luminescence The sample was exposed to the electrolyte solution was approximately cm2 A platinum grid was used as a counter electrode The electrochemical etching system was operated under fixed voltages of 10 V at 25 ◦ C in a conventional Teflon bath To investigate the effect of chemical treatment on the light emission of specimens, the as etched specimen was also immersed in various green chemical solution 3514 V.-H Pham et al / Optik 127 (2016) 3513–3516 such as distil water, ethanol, and H2 O2 The microstructure of the nanoporous Si was determined by field emission scanning electron microscopy (JEOL, JSM-7600F, JEOL Techniques, Tokyo, Japan) To investigate the chemical bonding of the nanoporous Si, infrared absorption spectra (IR) were recorded in the wave number range from 4000 to 500 cm−1 with a Perkin-Elmer Spectrum BX spectrometer using KBr pellets Room temperature photoluminescence (PL) tests were performed under excitation wavelength of 276 nm NANO LOG spectrofluorometer (Horiba, USA) equipped with 450 W Xe arc lamp and double excitation monochromators was used The PL spectra were recorded automatically during the measurements Results and discussion 3.1 Microstructure characterization The microstructure of the nanoporous Si was examined by SEM, as shown in Fig 1(A) and (B) The nanoporous Si showed a relatively clear nanoporous layer formation with a thickness of ∼50 ␮m (Fig 1(A) In addition, there was good adhesion between the nanoporous layer Si and the Si substrate, which was attributed to the use of electrochemical etching Si wafer to create the nanoporous Si layer on the same substrate materials The surface of the nanoporous Si showed a homogenously tiny pore of ∼20 nm without noticeable cracks (Fig 1(B)) Fig FT-IR spectra of nanoporous Si with variation of HF/ethanol electrolyte concentration (A) concentrate (B) HF/EtOH 1:1, and (C) HF/EtOH 1:2 3.2 FT-IR analysis Fig 2(A)–(C) shows the typical FTIR spectra of the nanoporous Si processed with the variation of electrolyte concentration The peak situated at 2090 cm−1 and 906 cm−1 was attributed, respectively, to the stretching mode of the SiH and the scissor mode of SiH2 [18,19] The peak at 1080 cm−1 was corresponded to Si O Si symmetric stretching mode and was introduced during the electrochemical etching process [20] The most intense and broad absorption band around 3400 cm− is attributed to Fig Photoluminescence spectra of nanoporous Si prepared by electrochemical etching in different electrolyte concentrations stretching of the O H bond in SiOH groups and adsorbed water [21] The SiH stretching mode is centered on 624 cm−1 [22,23] The absorption band around 1630 cm−1 is due to C O bond, probably because of the surface contamination [22] The intensities of hydride stretching mode, SiH2 scissor mode and Si O Si vibration peak increase on the sample with HF/ethanol of 1:1 These results indicate that the nanoporous Si processed at variation of electrolyte concentration induce a significant change in surface state of the nanoporous Si 3.3 Effect of electrolyte concentration Fig SEM images showing (A) cross-section and (B) surface morphology of the nanoporous Si Fig shows the emission spectra of nanoporous Si with different HF/ethanol ratio monitored at 276 nm All the nanoporous Si showed strong visible luminescence However, it should be noted that the PL spectra of the nanoporous Si film etched with HF without addition of ethanol showed a signal peak at ∼700 nm As the HF/ethanol ratio of 1:1 and 1:2, the PL signal shifted to longer wavelengths of ∼800 nm and 850, respectively and also its intensity increased significantly It is well documented that the ethanol play important role in the controlling the surface tension or the viscosity of the electrolyte of HF/ethanol mixture in the electrochemical etching, resulting in enhancing the probability of the pore formation and functionalized surface state; that is, the specimens have a variation in luminescence [24] The observed a higher luminescent emission of nanoporous Si with HF/ethanol of 1:1 is related to the V.-H Pham et al / Optik 127 (2016) 3513–3516 3515 for one day PL peak position of the aged porous Si film in H2 O2 exhibited significantly blue shift compared to the other chemical reagents treatments and its intensity reduced significantly It is well accepted that the tunable PL peak from porous Si after immersion in different chemical reagent are clearly related to surface passivation of porous Si [25,26] More specifically, in the as-etched Si film, the Si H bonding is replaced by Si O Si and Si OH bond and the oxidation of the surface chemistry after chemical treatments could cause a reduction in cored size of the nanoporous Si and consequently the blue shift of the PL spectrum Conclusions Fig Photoluminescence spectra of nanoporous Si prepared by electrochemical etching in different anode–cathode distance We herein demonstrated the luminescence of nanoporous Si could be tailored effectively by different electrolyte concentration, anode–cathode distance as well as chemical surface treatments in common passivation reagents In particular, the FT-IR spectra of the nanoporous Si were controlled by electrolyte concentration The photoluminescence of the nanoporous Si with HF/ethanol electrolyte of 1:1 and anode–cathode of cm were displayed strongest light emission Furthermore, the light emission center of nanoporous Si could be controlled when they were treated in different green chemical treatments These findings suggest that the present method is very useful to tailoring the luminescence, which was potential application in Si based devices and medicine Acknowledgment This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 103.99-2013.05 References Fig Photoluminescence spectra variation of nanoporous Si treated in different reagents intense SiH and SiH2 bond on the surface state of nanoporous Si, which can be confirmed by IR results 3.4 Effect of anode–cathode distance Fig shows the emission spectra of nanoporous Si prepared by electrochemical etching in different anode–cathode distance monitored at 276 nm Similar to affect of nanoporous Si with different electrolyte concentration, the luminescence of nanoporous Si also showed strong visible emission peaks appeared at about 800 nm It can be seen that intensity of the PL increased by decreasing anode–cathode distance in the electrochemical etching process Further experiments are underway to elucidate the exact luminescence mechanism in tunable luminescence in nanoporous Si prepared by electrochemical etching in different anode–cathode distance 3.5 Effect of green chemical treatments The photoluminescence of the nanoporous Si treatments with various aging reagents were further characterized by surface passivation in common reagents, as shown in Fig The as-etched Si showed PL signal peak at about 800 nm Under the chemical aging condition, PL signal gradually shift to shorter wavelength and its intensity decreased More specifically, PL peak shift from 800 nm to 760 nm after prolonging in immersed distil water time, while it was shift back to 700 nm after immersion of porous Si film in ethanol [1] M Khorasaninejad, N Abedzadeh, J Walia, S Patchett, S.S Saini, Color matrix refractive index sensors using coupled vertical silicon, Nano Lett 12 (2012) 4228–4232 [2] E.G Barbagiovanni, D.J Lockwood, P.J Simpson, Quantum confinement in Si and Ge nanostructures: theory and experiment, Appl Phys Rev (2014) 011302–11347 [3] J.H Park, L Gu, G Von Maltzahn, E Ruoslahti, S.N Bhatia, Biodegradable luminescent porous silicon nanoparticles for in vivo applications, Nat Mater (2009) 331–336 [4] M.A Shahbazi, M Hamidi, E.M Mäkilä, H Zhang, P.V Almeida, M Kaasalainen, J.J Salonen, J.T Hirvonen, The mechanisms of surface chemistry effects of mesoporous silicon nanoparticles on immunotoxicity and biocompatibility, Biomaterials 34 (2013) 7776–7789 [5] P.M Fauchet, L Tsybeskov, S.P Duttagupta, K.D Hirschman, Stable photoluminescence and electroluminescence from porous silicon, Thin Solid Films 297 (1997) 254–260 [6] C.X Thang, V.H Pham, Luminescence from micro-/nano-scale anodic aluminium oxide containing electrochemical derived nanoporous silicon, Mater Lett 146 (2015) 55–58 [7] Y Xiao, X Li, H.D Um, X Gao, Z Guo, J.H Lee, Controlled exfoliation of a heavily n-doped porous silicon double layer electrochemically etched for layer-tranfer photovoltaics, Electrochim Acta 74 (2012) 93–97 [8] J.Y Lee, W.K Han, J.H Lee, Effect of ultrasonic frequency on electrochemical Si etching in porous Si layer transfer process for thin film solar cell fabrication, Sol Energy Mater Sol Cells 95 (2011) 77–80 [9] J Kanungo, H Saha, S Basdu, Effect of porosity on the performance of surface modified porous silicon, Sens Actuators, B 147 (2010) 145–151 [10] M Simion, M Kusko, I Mihalache, A Br˘agaru, Dual detection biosensor based on porous silicon substrate, Mater Sci Eng., B 178 (2013) 1268–1274 [11] A Jane, R Dronov, A Hodges, N.H Voelcker, Porous silicon biosensor on the advance, Trends Biotechnol 27 (2009) 230–239 [12] K.L Jarvis, T.J Barnes, C.A Prestidge, Surface chemistry of porous silicon and implications for drug encapsulation and delivery applications, Adv Colloid Interface Sci 175 (2012) 25–38 [13] L Gu, L.E Ruff, Z Qin, M Corr, S.M Hedrick, M.J Sailor, Multivalent porous silicon nanoparticles enhance the immune activation potency of agonistic CD40 antibody, Adv Mater 24 (2012) 3981–3987 [14] Y.L Khung, G Barritt, N.H Voelcker, Using continuous porous silicon gradients to study the influence of surface topography on the behavior of neuroblastoma cells, Exp Cell Res 314 (2008) 789–800 3516 V.-H Pham et al / Optik 127 (2016) 3513–3516 [15] S.H Park, K.W Lee, Y.Y Kim, A technique for the fabrication of various multiparametric porous silicon samples on the substrate, Thin Solid Films 518 (2010) 2860–2863 [16] H Sato, T Yamaguchi, T Kobe, S Shoji, T Homma, Electrochemical etching process to tune the diameter of arrayed deep pores by controlling carrier collection at a semiconductor-electrolyte interface, Electrochem Commun 12 (2010) 765–768 [17] V.H Pham, P.T Huy, Strong luminescence from nanoporous Si with high degree of nanoporous structure by electrochemical etching of Si wafer, Mater Lett 142 (2015) 126–129 [18] B Hamilton, Porous silicon, Semicond Sci Technol 10 (1995) 1187–1207 [19] S Gardelis, A.G Nassiopoulou, M Mahdouani, R Bourguiga, S Jaziri, Enhancement and red shift of photoluminescence of fresh porous Si under prolonged laser irradiation or aging: role of surface vibration modes, Physica E 41 (2009) 986–989 [20] M Naddaf, H Hamadeh, Visible luminescence in photo-electrochemically etched p-type porous silicon: effect of illumination wavelength, Mater Sci Eng., C 29 (2009) 2092–2098 [21] A Borghesi, A Sassella, B Pivac, L Pavesi, Characterization of porous silicon inhomogeneities by high spatial resolution infrared spectroscopy, Solid State Commun 87 (1993) 1–4 [22] M Li, M Hu, Q Liu, S Ma, P Sun, Microstructure characterization and NO2 sensing properties of porous silicon with intermediate pore size, Appl Surf Sci 268 (2013) 188–194 [23] X.W Du, Y Jin, N.Q Zhao, Y.S Fu, S.A Kulinich, Controlling surface states and photoluminescence of porous silicon by low-energy-ion irradiation, Appl Surf Sci 254 (2008) 2479–2482 [24] H Föll, M Christophersen, J Carstensen, G Hasse, Formation and application of nanoporous silicon, Mater Sci Eng., R 39 (2002) 93–141 [25] Y Zhang, Z Yang, D Liu, E Nie, X Bai, Z Li, H Song, Y Zhou, W Li, M Gong, X Sun, Stable ultraviolet photoluminescence emission in n-type porous silicon, J Lumin 130 (2010) 1005–1010 [26] S.P Low, K.A William, L.J Caham, N.H Voelcker, Generation of reactive oxygen species from porous silicon microparticles in cell culture medium, J Biomed Mater Res., A 93 (2010) 1124–1131  ... reduction in cored size of the nanoporous Si and consequently the blue shift of the PL spectrum Conclusions Fig Photoluminescence spectra of nanoporous Si prepared by electrochemical etching in different... 3400 cm− is attributed to Fig Photoluminescence spectra of nanoporous Si prepared by electrochemical etching in different electrolyte concentrations stretching of the O H bond in SiOH groups and... FT-IR spectra of the nanoporous Si were controlled by electrolyte concentration The photoluminescence of the nanoporous Si with HF/ethanol electrolyte of 1:1 and anode–cathode of cm were displayed