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Effects of 9-cyanoanthracene and anthracene adsorption on the photoluminescence of porous silicon
Journal
of
Photo$emistry Photobiology A:Chemistry
ELSEVIER
Journal of Photochemistry and Photobiology A: Chemistry 112 ( 1998) 59-6 I
Effects of 9-cyanoanthracene and anthracene adsorption on the photoluminescence of porous silicon Feng Yin a, Xue Ping Li a, Xu Rui Xiao a-*, Bao Wen Zhang a, Yi Cao ‘, Jing Rong Chen ‘, Guo Hua Li b, He Xiang Han b, Zao Pin Wang b ‘National
Laboratoy.for
’ Institure Superlattices
qf Photographic and
Chemisq, Chinese Academy ofSciences. Beijing 100101, Chinu Microstructures Instirute c$Semiconductors, Chinese Academy of Sciences,
Beijing
100083,
China
Abstract The photoluminescence of porous silicon can be modified sensitively by surface adsorption of different kinds of molecules. A quite different effects of 9-cyanoanthracene and anthracene adsorption on the photoluminescence of porous silicon were observed. The adsorption of 9cyanoanthracene induced the photoluminescence enhancement, while anthracene adsorption resulted in photoluminescent quenching. An explanation of the interaction of adsorbates with surface defect sites of porous silicon was suggested anddiscussed. 0 1998 Elsevier Science S.A. Keyordst
Chemical adsorption; Porous silicon; Photoluminescence
1. Introduction
Since Canham [ I ] discovered the room temperaturevisible photoluminescencefrom porous silicon (F’S), it has causedconsiderableinterestboth theoretically and for potential applicationssuchasoptoelectronic devices,optical information storage materials, solar energy conversion and chemical sensors[ 2,3]. Owing to the photoluminescenceof PS being strongly sensitive to molecular adsorption, the effects of surface adsorption on photoluminescenceof PS have attracted much attention in the surfacechemical studies. Recentreports showedthat the photoluminescenceof PScan be quenched by a series of adsorbates,including organic solvents, amines, aromatic compounds, metal salts and hydroxide ions etc. [ 4-91. But little work hasbeen directed at photoluminescenceenhancementby adsorbatesuntil now. In this letter, we report photoluminescenceenhancementof PSby the adsorptionof 9-cyanoanthracene(9-CA) which is comparedwith the adsorptionof anthracene(An) which led to quenchingof the photoluminescence.This study may provide a great dealof insight into surfacechemistry of PSwhich has technological potential in chemical sensorapplications and better understandingof photoluminescencemechanism. * Corresponding author. 1010.6030/98/$19.00 0 1998 Elsevier Science S.A. All rights reserved PUSlOlO-6030(97)00252-9
2. Experimental details
The PS sampleswere preparedby anodic etching of p-Si (Bdoped, ( 100)) 1.Oclt cm) at a current density of 30 mA/cm2 for 10 min in a I :I solution of HF (40 wt.%): ethanol followed by chemical oxidation in HNO, solution [ IO]. After HNO, oxidized the PS sampleswere rinsed sequentially in deionized water and ethanol, then dried in a stream of dry nitrogen, and separatedinto two partsfor adsorptionof 9-CA and An. The photoluminescencemeasurementswere performed usinga microscope(BH-2) with a 488.0 nm line Ar’ laseras excitation source.A double-grating monochrometer (JY-HPD-2), a photomultiplier (GaAs cathode) and a photo-counter system were usedfor collecting and detecting the fluorescent light. The samples with and without adsorbatesfixed in a measuringtube were excited at the samepoint, monitoring with the microscope.Adsorption of 9-CA or An moleculeswere carried out by immersingthe PS samplesin 5 ml of 5 X 10e3 mol/l acetonesolutionsof 9-CA or An for 5 min, then were dried in the air. The adsorption spectraof acetone solutions that were used to wash the adsorbedPS sampleswere measuredby HITACHI 557 UV-visible spectrometer. Fourier transform infrared (FTIR) spectra were taken by Nicolet Magna IR 750 spectrometers.All the measurementswere performed at room temperature.
60
F. Yin et al. /Journal
of Photochrmistry
and
Photobiology
A: Chemist:
I12
(1998)
5941
3. Results and discussion
G-0 The photoluminescencespectra of PS with and without adsorptionof 9-CA are shownin Fig. 1a. From this figure we can seethat the adsorptionof 9-CA resultedin an increaseof the photoluminescenceintensity to 120% of the initial value and a red shift of the PL peak wavelength. The photoluminescencereverted to original intensity and wavelength when 9-CA adsorbedsamplewasrinsedwith pure solvent (acetone solution). This result was reproducible and can be repeated with other PS samples.Fig. 1b showsthe photoluminescence quenchingby adsorptionof An which led to a decreaseof the PL intensity to 75% of the initial value and returning to the origin, after rinsing with acetonesolution. The adsorptionof both 9-CA andAn on the singlecrystal silicon (c-Si) surface without induction of PL responsewere also shownin Fig. la and b. In order to demonstrate the 9-CA and An molecules adsorbingon the PS samplesurface, the absorption spectra of rinsing acetonesolution were measured.In thesespectra, the strong peaksin the 350-410 nm and 330-380 nm regions correspondingto the characteristicabsorptionpeaksof 9-CA and An respectively were observed.Fig. 2 showsa comparison of the absorptionspectrabetweenthe rinsing solution of 9-CA adsorbedsampleand acetonesolution contained9-CA. As observedfrom Fig. 2 there is no absorptionat wavelength longer than 420 nm, so 9-CA cannot be excited by PL excitation wavelength (488 nm) to produce a light emission longer than 500 nm. Therefore, the enhancementof PL intensity in 9-CA adsorbed sampleis not attributed to the light emissionof 9-CA itself. In the caseof An, the PL intensity decreasedoes not stem from the competitive absorption of An in the excited light (488 nm), since An cannot absorb light at wavelength longer than 400 nm. The distinct effects of chemical adsorption on the photoluminescenceof PS between anthracene and cyano substituted anthraceneare attributed to the interaction of adsorbateswith the PSsurface, imp1ying that the photoluminescenceof PS can be modified sensitively by surface adsorption of different kinds of molecules. For understanding the photoluminescenceenhancement and quenching mechanism,the influencesof adsorbed9-CA and An on FTIR spectraof PS were studied. The resultsare illustrated in Fig. 3. As seenfrom Fig. 3, no obvious changes are observed in the FTIR spectraof PS before and after surface adsorption of 9-CA and An, especially in the HSi (Si,,O, -,) (a _<3) layer absorptionbandsbetween2000 and 2300cm- ’ [ 111.This meansthat the HSi ( Si,,03 -<,) (a I 3) layer of PS surface is unaffected by surfaceadsorptionof 9CA and An. From the combination of resultsfrom FTIR and absorption spectra,it was confirmed that the PL changesby 9-CA and An adsorption were not causedby the formation of new compounds. The quite different influencesof adsorbatesstudiedon the photoluminescenceof PS can be interpreted asfollows. The structural difference between9-CA and An is in the existence
Wavelength
I nm (b)
Wavelength
I nm
Fig. 1.Thephotoluminescent spectra of PSmodified byorganic molecules 9-CA(a) andAn (b), - blank,-. adsorbed, ... washed,- 9-CAorAn onc-Si.
ticd-. .8. 9. es3. I.
I.
I.
I.
a,
300 350 400 450 500 550 Wavelength I nm Fig.2.Absorption spectra of 9-CA( I ) in rinsingacetone solution,(2) in pureacetone solution. of a stronger electron-withdrawing cyano substituenton the anthracenering of 9-CA molecule. Therefore, 9-CA, known asan electron acceptor can interact with surfacedefect sites of PS which acted as nonradiative recombination centersto composethe charge-transfercomplex like an exciplex, causing the decreaseof nonradiative recombination centers and the enhancementof the photoluminescenceintensity of PS. Contrary to 9-CA adsorption, An can act as electron donor and electronscan transfer from An to PS surface resulting in a quenching of photoluminescenceof PS by recombination with the photogeneratedholesat the PS surface.
F. Yin et al. /Journal
of Photochemistry
and
Photohiologv
A: Chemistry
112 (1998)
5941
61
the enhancement and quenching of photoluminescence. Further studies on other adsorbates are underway with a view to clarifying the origin of these effects.
Acknowledgements We thank the National Natural Science Foundation of China and Laboratory of Photochemistry of Chinese Academy of Sciences for financial support.
Wavenumbem / cm“
References (11
L.T. Canham,
Appl. Phys. Lett. 57 ( 1990) 1046. Appl. Phys. Lett. 60 ( 1992) 347. I31 J.P. Zheng, K.L. Jiao, W.P. Shen, W.A. Anderson. H.S. Kwok, Appl. Phys. Lett. 61 ( 1992) 459. 141 J.M. Lauerhaas. C.M. Credo, J.L. Heinrich, M.J. Sailor, J. Am. Chem. sot. I I4 (1992) 1911. [51 J.M. Lauerhaas, M.J. Sailor, Science 261 ( 1993) 1567. 161J.K.M. Chun, A.B. Bocarsly, T.R. Cottrell, J.B. Benziger, J.C. Yee, J. Am. Chem. Sot. 1 I5 ( 1993) 3024. 171 J.L. Coffer, S.C. Lilley, R.A. Martin, L.A. Files-Sesler, J. Appl. Phys. 74 (1993) 2094. 181 D.L. Fisher, J. Harper, M.J. Sailor, J. Am. Chem. Sot. 117 (1995) 7846. [91 M.C. Ko, G.J. Meyer, Chem. Mater. 7 (1995) 12. I101 F. Yin, X.P. Li, Z.Z. Zheng, T.F. Chen. X.R. Xiao, Chin. Chem. Lett. 7 (1996) 1037. I111 D.V. Tsu. G. Lucovsky, B.N. Davidson. Phys. Rev. B40 ( 1989) 1795.
PI N. Koshida, H. Koyama,
Wavenumbers / cm“ Fig. 3. FTIR spectra of PS modified by organic molecules An(b) ( I ) before adsorption, (2) after adsorption.
9-CA(a)
and
4. Conclusion Aspect of the surface reactivity of HN03 oxidized porous silicon was revealed by the effect of surface adsorption on
of
Photo$emistry Photobiology A:Chemistry
ELSEVIER
Journal of Photochemistry and Photobiology A: Chemistry 112 ( 1998) 59-6 I
Effects of 9-cyanoanthracene and anthracene adsorption on the photoluminescence of porous silicon Feng Yin a, Xue Ping Li a, Xu Rui Xiao a-*, Bao Wen Zhang a, Yi Cao ‘, Jing Rong Chen ‘, Guo Hua Li b, He Xiang Han b, Zao Pin Wang b ‘National
Laboratoy.for
’ Institure Superlattices
qf Photographic and
Chemisq, Chinese Academy ofSciences. Beijing 100101, Chinu Microstructures Instirute c$Semiconductors, Chinese Academy of Sciences,
Beijing
100083,
China
Abstract The photoluminescence of porous silicon can be modified sensitively by surface adsorption of different kinds of molecules. A quite different effects of 9-cyanoanthracene and anthracene adsorption on the photoluminescence of porous silicon were observed. The adsorption of 9cyanoanthracene induced the photoluminescence enhancement, while anthracene adsorption resulted in photoluminescent quenching. An explanation of the interaction of adsorbates with surface defect sites of porous silicon was suggested anddiscussed. 0 1998 Elsevier Science S.A. Keyordst
Chemical adsorption; Porous silicon; Photoluminescence
1. Introduction
Since Canham [ I ] discovered the room temperaturevisible photoluminescencefrom porous silicon (F’S), it has causedconsiderableinterestboth theoretically and for potential applicationssuchasoptoelectronic devices,optical information storage materials, solar energy conversion and chemical sensors[ 2,3]. Owing to the photoluminescenceof PS being strongly sensitive to molecular adsorption, the effects of surface adsorption on photoluminescenceof PS have attracted much attention in the surfacechemical studies. Recentreports showedthat the photoluminescenceof PScan be quenched by a series of adsorbates,including organic solvents, amines, aromatic compounds, metal salts and hydroxide ions etc. [ 4-91. But little work hasbeen directed at photoluminescenceenhancementby adsorbatesuntil now. In this letter, we report photoluminescenceenhancementof PSby the adsorptionof 9-cyanoanthracene(9-CA) which is comparedwith the adsorptionof anthracene(An) which led to quenchingof the photoluminescence.This study may provide a great dealof insight into surfacechemistry of PSwhich has technological potential in chemical sensorapplications and better understandingof photoluminescencemechanism. * Corresponding author. 1010.6030/98/$19.00 0 1998 Elsevier Science S.A. All rights reserved PUSlOlO-6030(97)00252-9
2. Experimental details
The PS sampleswere preparedby anodic etching of p-Si (Bdoped, ( 100)) 1.Oclt cm) at a current density of 30 mA/cm2 for 10 min in a I :I solution of HF (40 wt.%): ethanol followed by chemical oxidation in HNO, solution [ IO]. After HNO, oxidized the PS sampleswere rinsed sequentially in deionized water and ethanol, then dried in a stream of dry nitrogen, and separatedinto two partsfor adsorptionof 9-CA and An. The photoluminescencemeasurementswere performed usinga microscope(BH-2) with a 488.0 nm line Ar’ laseras excitation source.A double-grating monochrometer (JY-HPD-2), a photomultiplier (GaAs cathode) and a photo-counter system were usedfor collecting and detecting the fluorescent light. The samples with and without adsorbatesfixed in a measuringtube were excited at the samepoint, monitoring with the microscope.Adsorption of 9-CA or An moleculeswere carried out by immersingthe PS samplesin 5 ml of 5 X 10e3 mol/l acetonesolutionsof 9-CA or An for 5 min, then were dried in the air. The adsorption spectraof acetone solutions that were used to wash the adsorbedPS sampleswere measuredby HITACHI 557 UV-visible spectrometer. Fourier transform infrared (FTIR) spectra were taken by Nicolet Magna IR 750 spectrometers.All the measurementswere performed at room temperature.
60
F. Yin et al. /Journal
of Photochrmistry
and
Photobiology
A: Chemist:
I12
(1998)
5941
3. Results and discussion
G-0 The photoluminescencespectra of PS with and without adsorptionof 9-CA are shownin Fig. 1a. From this figure we can seethat the adsorptionof 9-CA resultedin an increaseof the photoluminescenceintensity to 120% of the initial value and a red shift of the PL peak wavelength. The photoluminescencereverted to original intensity and wavelength when 9-CA adsorbedsamplewasrinsedwith pure solvent (acetone solution). This result was reproducible and can be repeated with other PS samples.Fig. 1b showsthe photoluminescence quenchingby adsorptionof An which led to a decreaseof the PL intensity to 75% of the initial value and returning to the origin, after rinsing with acetonesolution. The adsorptionof both 9-CA andAn on the singlecrystal silicon (c-Si) surface without induction of PL responsewere also shownin Fig. la and b. In order to demonstrate the 9-CA and An molecules adsorbingon the PS samplesurface, the absorption spectra of rinsing acetonesolution were measured.In thesespectra, the strong peaksin the 350-410 nm and 330-380 nm regions correspondingto the characteristicabsorptionpeaksof 9-CA and An respectively were observed.Fig. 2 showsa comparison of the absorptionspectrabetweenthe rinsing solution of 9-CA adsorbedsampleand acetonesolution contained9-CA. As observedfrom Fig. 2 there is no absorptionat wavelength longer than 420 nm, so 9-CA cannot be excited by PL excitation wavelength (488 nm) to produce a light emission longer than 500 nm. Therefore, the enhancementof PL intensity in 9-CA adsorbed sampleis not attributed to the light emissionof 9-CA itself. In the caseof An, the PL intensity decreasedoes not stem from the competitive absorption of An in the excited light (488 nm), since An cannot absorb light at wavelength longer than 400 nm. The distinct effects of chemical adsorption on the photoluminescenceof PS between anthracene and cyano substituted anthraceneare attributed to the interaction of adsorbateswith the PSsurface, imp1ying that the photoluminescenceof PS can be modified sensitively by surface adsorption of different kinds of molecules. For understanding the photoluminescenceenhancement and quenching mechanism,the influencesof adsorbed9-CA and An on FTIR spectraof PS were studied. The resultsare illustrated in Fig. 3. As seenfrom Fig. 3, no obvious changes are observed in the FTIR spectraof PS before and after surface adsorption of 9-CA and An, especially in the HSi (Si,,O, -,) (a _<3) layer absorptionbandsbetween2000 and 2300cm- ’ [ 111.This meansthat the HSi ( Si,,03 -<,) (a I 3) layer of PS surface is unaffected by surfaceadsorptionof 9CA and An. From the combination of resultsfrom FTIR and absorption spectra,it was confirmed that the PL changesby 9-CA and An adsorption were not causedby the formation of new compounds. The quite different influencesof adsorbatesstudiedon the photoluminescenceof PS can be interpreted asfollows. The structural difference between9-CA and An is in the existence
Wavelength
I nm (b)
Wavelength
I nm
Fig. 1.Thephotoluminescent spectra of PSmodified byorganic molecules 9-CA(a) andAn (b), - blank,-. adsorbed, ... washed,- 9-CAorAn onc-Si.
ticd-. .8. 9. es3. I.
I.
I.
I.
a,
300 350 400 450 500 550 Wavelength I nm Fig.2.Absorption spectra of 9-CA( I ) in rinsingacetone solution,(2) in pureacetone solution. of a stronger electron-withdrawing cyano substituenton the anthracenering of 9-CA molecule. Therefore, 9-CA, known asan electron acceptor can interact with surfacedefect sites of PS which acted as nonradiative recombination centersto composethe charge-transfercomplex like an exciplex, causing the decreaseof nonradiative recombination centers and the enhancementof the photoluminescenceintensity of PS. Contrary to 9-CA adsorption, An can act as electron donor and electronscan transfer from An to PS surface resulting in a quenching of photoluminescenceof PS by recombination with the photogeneratedholesat the PS surface.
F. Yin et al. /Journal
of Photochemistry
and
Photohiologv
A: Chemistry
112 (1998)
5941
61
the enhancement and quenching of photoluminescence. Further studies on other adsorbates are underway with a view to clarifying the origin of these effects.
Acknowledgements We thank the National Natural Science Foundation of China and Laboratory of Photochemistry of Chinese Academy of Sciences for financial support.
Wavenumbem / cm“
References (11
L.T. Canham,
Appl. Phys. Lett. 57 ( 1990) 1046. Appl. Phys. Lett. 60 ( 1992) 347. I31 J.P. Zheng, K.L. Jiao, W.P. Shen, W.A. Anderson. H.S. Kwok, Appl. Phys. Lett. 61 ( 1992) 459. 141 J.M. Lauerhaas. C.M. Credo, J.L. Heinrich, M.J. Sailor, J. Am. Chem. sot. I I4 (1992) 1911. [51 J.M. Lauerhaas, M.J. Sailor, Science 261 ( 1993) 1567. 161J.K.M. Chun, A.B. Bocarsly, T.R. Cottrell, J.B. Benziger, J.C. Yee, J. Am. Chem. Sot. 1 I5 ( 1993) 3024. 171 J.L. Coffer, S.C. Lilley, R.A. Martin, L.A. Files-Sesler, J. Appl. Phys. 74 (1993) 2094. 181 D.L. Fisher, J. Harper, M.J. Sailor, J. Am. Chem. Sot. 117 (1995) 7846. [91 M.C. Ko, G.J. Meyer, Chem. Mater. 7 (1995) 12. I101 F. Yin, X.P. Li, Z.Z. Zheng, T.F. Chen. X.R. Xiao, Chin. Chem. Lett. 7 (1996) 1037. I111 D.V. Tsu. G. Lucovsky, B.N. Davidson. Phys. Rev. B40 ( 1989) 1795.
PI N. Koshida, H. Koyama,
Wavenumbers / cm“ Fig. 3. FTIR spectra of PS modified by organic molecules An(b) ( I ) before adsorption, (2) after adsorption.
9-CA(a)
and
4. Conclusion Aspect of the surface reactivity of HN03 oxidized porous silicon was revealed by the effect of surface adsorption on