QUARTZ SENSOR ARRAY WITH MESOPOROUS SILICA FILMS AS FUNCTIONAL MATERIALS ALAGAPPAN PALANIAPPAN B Eng., Master of Science in Mechatronics A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF MECHANICAL ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2006 Acknowledgements I wish to express my deep gratitude to Associate Professor Tay Eng Hock, Francis, Faculty of Engineering, National University of Singapore (NUS) and Dr Su Xiaodi, Research Scientist, Institute for Materials Research and Engineering (IMRE) for their zeal and encouragement in bringing out this thesis successfully I am grateful to Dr Zhang Jian, Research Scientist, IMRE, for providing valuable suggestions for this study I am also thankful to Dr Li Xu, Research Scientist, and other research staffs working in IMRE for their valuable discussions and suggestions Finally, I would like to thank NUS and IMRE for providing an opportunity for me to pursue my research work in their prestigious institutions and also for their financial support and technical assistance I would be happy to welcome constructive criticisms and suggestions from the readers of this thesis for further improvement of this study Contents Summary List of Tables List of Figures List of Abbreviations 11 Chapter Introduction 12 Chapter Literature Review 15 Chapter Quartz sensors 18 3.1 Quartz Crystal Microbalance 18 3.2 QCM equivalent circuit/Network analyzer 20 Chapter Mesoporous silica film 23 4.1 Sol-gel technique 23 4.2 Silica film deposition 25 4.3 Calcination 25 4.4 Argon plasma calcination 26 4.5 Organic template removal 27 4.6 Surfactant removal 36 4.7 Mechanical properties of the silica film 40 Chapter Preparation and characterization of silica hybrids 5.1 Preparation and characterization of β-CD – Silica hybrid on QCM 42 43 5.1.1 Cyclodextrin (CD) 43 5.1.2 β-CD-Silica hybrid preparation 43 5.1.3 Alkenylation of β-CD 45 5.1.4 Characterization of alkenyl-b-CD functionalized silica matrix 46 5.2 Preparation and characterization of PPh3 modified silica matrix 50 5.2.1 Preparation of PPh3 - silica hybrid on QCM 50 5.2.2 Characterization of PPh3 - silica hybrid 51 Chapter QCM gas sensor 53 6.1 Introduction 53 6.2 Sensor response to benzene vapor 54 6.3 Sensor response to ethanol vapor 57 6.4 Frequency response summary and sensitivity enhancement 58 Chapter QCM array sensors 61 7.1 QCM array fabrication 62 7.2 QCM array frequency interference 64 7.3 QCM array gas sensors 65 7.3.1 Two-channel QCA 65 7.3.2 Four-channel QCA 72 Chapter Concluding remarks 78 Publications related to this work 80 References 82 Appendices 89 Abstracts of publications related to this work 89 Summary This thesis outlines the use of plasma calcined mesoporous silica films to form hybrids for gas sensing applications by entrapping sensitive receptor molecules in its porous network Quartz Crystal Microbalance (QCM) is used as the sensing platform on which mesoporous silica films are deposited using sol-gel technique Argon plasma calcination, a low temperature process, is employed to gel the sol instead of conventional thermal calcination Polymers and surfactants are used as templates for generating the mesoporous structure upon removal by plasma calcination Field Emission Scanning Electron Microscopy, Energy Dispersive X-ray Analysis, Fourier Transform Infra Red Spectroscopy, Small Angle X-ray Scattering, Nuclear Magnetic Resonance, Time of Flight Secondary Ion Mass Spectroscopy, nano-indentation and nitrogen adsorption analysis are used to characterize the obtained films QCM coated with silica hybrid films is tested as a gas sensor for selectively capturing target analytes The higher surface area of the mesoporous silica film ensures the accommodation of more receptor molecules and subsequently more target analytes that enhance the QCM response and thereby the sensitivity QCM Arrays (Quartz Crystal Array: QCA), fabricated using standard photolithography techniques, are coated with different sensing materials and are used to analyze complex mixture of target analytes It is concluded that the sensitivity of the QCM/QCA is enhanced by depositing functionalized argon plasma calcined mesoporous films on the QCM/QCA electrodes Keywords: QCM, QCM array, mesoporous silica film, silica hybrid, plasma calcination, gas sensor List of Tables Table 4.1: Spin coating recipe 25 Table 4.2: Nano-indentation results for thermo calcined and plasma calcined silica films 40 Table 6.1: Frequency shift values of 10 MHz QCM coated with β-CD to different concentrations of benzene and ethanol vapors 60 Table 7.1: Frequency shift values of the two-channel QCA to different concentrations of benzene and ethanol vapors 70 List of Figures Figure 3.1: QCM schematic 18 Figure 3.2: Equivalent circuit of a quartz resonator 20 Figure 3.3 (a) and (b): Frequency shift Vs PS - Toluene conc 22 Figure 4.1: Procedure for silica film deposition on quartz sensor by using sol-gel technique 24 Figure 4.2: RIE schematic 27 Figure 4.3: SEM observation of the silica surface obtained using the plasma parameters of (a) 50 W, 180 s (b) 100 W, 180 s and (c) 200 W, 180 s 29 Figure 4.4: SEM image of the cross section of silica film deposited on (100) oxidized silicon substrate with the plasma parameter of 200 W and 300 s 30 Figure 4.5: TEM observation of silica gel 30 Figure 4.6: Energy dispersive X-ray Analysis spectrum of plasma calcined silica film 31 Figure 4.7: FT-IR spectra of the sol-gel silica films prepared by (A) conventional thermal calcination and argon plasma calcination for 300s at (B) 200 W (C) 100 W (D) 50 W 32 Figure 4.8: Relationship between the film thickness and the plasma processing time 33 Figure 4.9: The curve of ln [q3I(q)] vs q2 34 Figure 4.10: Pore size distribution of the plasma treated silica films 35 Figure 4.11: Nitrogen adsorption isotherm of plasma treatment silica film 36 Figure 4.12: SAXS pattern of the silica films prepared by argon plasma calcination at (b) 50 W for 180 s and (c) 100 W for 180 s The curve for the scotch tape without samples (a) is also recorded as a reference 37 Figure 4.13: N2 adsorption – desorption isotherm (inset) and corresponding BJH pore-size distribution curve of silica gel prepared by argon plasma calcination at 50 W for 180 s 38 Figure 4.14: FT-IR spectra of the sol-gel silica films prepared by (a) conventional thermal calcination and argon plasma calcination at 200 W for (b) 300 s 39 Figure 5.1: Schematic illustration of sol-gel silica film prepared on QCM through 3- MPTMS treatment of the gold electrode (step 1), thiolation of the silica film (step 2), and covalent immobilization of the alkenyl-β-CD through alkenyl-propyl thioether linkage (step 3) 45 Figure 5.2: FT-IR spectra of (A) β-CD on thiol layer (B) Thiol layer on silica film 46 Figure 5.3: NMR spectrum of the modified alkenyl-β-CD Sample was prepared in DMSO-d6 47 Figure 5.4: SIMS spectra of (A) plasma calcined silica film prepared in step 1, (B) thiol functionalized silica film prepared at step 2, and (C) alkenyl-βCD functionalized silica film prepared at step as shown in Fig 5.1 48 Figure 5.5: Depth profile of alkenyl-β-CD functionalized silica film (A) gold content, (b) carbon content, and (C) silicon content 49 Figure 5.6: FT-IR spectrum of the silica film containing PPh3 51 Figure 5.7: SIMS spectrum of the silica film containing PPh3 52 Figure 6.1: β-CD/silica-QCM response to benzene at concentrations of µL (curve B), 10 µL (curve C), 100 µL (curve D), and 500 µL (curve E) in an L chamber The reference curve (A) shows the negligible response of an uncoated QCM to 500 µL benzene at the same experimental condition 55 Figure 6.2: Comparison of sensor responses of QCM with β-CD modified silica-QCM (β-CD/silica-QCM, curve C), β-CD modified planar QCM (βCD-QCM, curve B) and non- β-CD modified silica-QCM (silica-QCM, curve A) to benzene vapor at 500 µL in an L chamber 56 Figure 6.3: Frequency response of β-CD/silica-QCM and uncoated QCM to 50 µL ethanol in an L chamber The inset shows the stabilization of frequency response of the QCM before introducing the target analyte in the chamber 57 Figure 6.4: Frequency response of β-CD/silica-QCM and planar β-CDQCM to benzene and ethanol vapor at different concentrations 59 Figure 7.1: QCM array fabricated on quartz blank 61 Figure 7.2: (a) QCA fabrication procedure (b) QCA fabrication process flow 62-63 Figure 7.3: Negligible frequency interference between the two QCM in the QCM array (distance between them is mm) 64 Figure 7.4 Silica hybrid film deposition procedure on the two-channel QCA 65 Figure 7.5: Frequency response of PPh3 functionalized QCA ethanol vapors 68 Figure 7.6: Frequency response of PPh3 functionalized QCA to benzene vapors 68 Figure 7.7: Frequency response of β-CD functionalized QCA to benzene vapors 69 Figure 7.8: Frequency response of β-CD functionalized QCA to ethanol vapors 69 Figure 7.9: Two-Channel QCA frequency response summary 70 Figure 7.10: QCA gas concentration evaluation 71 Figure 7.11: QCA schematic 73 Figure 7.12: Film deposition procedure on the four-channel QCA 74 Figure 7.13: Four-channel QCA frequency response to 10 µL ethanol vapors 75 Figure 7.14: Four-channel QCA frequency response to 10 µL benzene vapors 76 Figure 7.15: Four-channel QCA frequency response to a mixture of 50 µL benzene and 50 µL Ethanol vapors 77 10 Publications related to this work Journal papers Palaniappan, Al.; Su, X.D.; Tay, F E H, IEEE sensors Vol 6, Issue No.6, December 2006 [In press] Palaniappan, Al.; Su, X.D.; Tay, F E H, J Electroceramics 16 (2006) 503 Palaniappan, Al.; Li, X.; Tay, F E H., Su, X.D.; Li, J.; Sens & Act B 119 (2006) 220 Zhang, J.; Palaniappan, Al.; Su, X.D.; Tay, F E H.; App Surf Sci 245 (2005) 304 Palaniappan, Al.; Zhang, J.; Su, X.D.; Tay, F E H.; Chem Phys Lett 395 (2004) 70 Palaniappan, Al.; Zhang, J.; Su, X.D.; Tay, F E H.; Int J Comp Eng Sci (2003) 645 Conference papers and Presentations Quartz sensor array using mesoporous silica hybrids for gas sensing applications, IEEE Sensors 2005, Irvine, California, USA Palaniappan, Al.; Su, X.D.; Tay, F E H.; “Functionalized mesoporous silica films for gas sensing applications” Oral presentation, ICMAT 2005, Suntec City, Singapore 80 Palaniappan, Al.; Su, X.D.; Tay, F E H.; “Plasma calcined mesoporous silica films” Poster presentation , MRSS 04, IMRE, Singapore Zhang, J.; Palaniappan, Al.; Su, X.D.; Tay, F E H.; “Mesoporous silica thin films prepared by calcination in plasma” Poster presentation , SAB 2004, IMRE, Singapore Palaniappan, Al.; Zhang, J.; Su, X.D.; Tay, F E H.; “Electrical Impedance And Energy Dissipation Analyses of Quartz Crystal Microbalance for Polymer Coating” Poster presentation, ICMAT 2004, Suntec City, Singapore 81 References Alfonta, L.; Willner, I.; Throckmorton, D J.; Singh, A K., Analytical Chemistry 2001, 73, 5287 Sutherland, R M.; Dahne, C.; Place, J F.; Ringrose, A R., Journal of Immunological Methods 1984, 74, 253 Hieda, M.; 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Silica Films For Gas Sensing Applications Al Palaniappan, 1, 2, Xiaodi Su,* 1, Francis E H Tay, Institute of Materials Research & Engineering, Research Link, Singapore 117602 Mechanical Engineering Department, National University of University, 10 Kent Ridge Crescent Road, Singapore 119260 A four-channel Quartz Crystal Microbalance Array (QCA) coated with silica hybrid films is tested as a gas sensor to identify and quantify target analytes Plasma calcined mesoporous silica films have been used to form hybrids for gas sensing applications Silica hybrids are obtained by incorporating various receptor molecules in the porous network through physisorption and (or) chemical bonding between the silica matrix and receptor molecules FESEM, FT-IR, SIMS and nitrogen adsorption analysis are used to characterize the obtained films The frequency interference between the individual QCM in the QCA has been eliminated by appropriate positioning of the electrodes It is concluded that the sensitivity and selectivity of the four-channel QCA could be enhanced by depositing plasma calcined mesoporous hybrids on the electrodes Keywords: Multi-channel QCM, Quartz Crystal Array, Mesoporous silica film, Gas sensor 89 Publication - Abstract Journal of Electroceramics Vol 16 (2006) 503 Functionalized mesoporous silica films for gas sensing applications Alagappan Palaniappan · Xiaodi Su · Francis E H Tay Abstract Mesoporous silica films prepared by sol gel process and argon plasma calcination have been used to form hybrids for gas sensing applications by entrapping sensitive materials in the porous network Plasma calcination, a low temperature process, is employed to gel the sol instead of conventional thermal calcination Polymers and surfactants are used as templates for generating the mesoporous structure upon removal by the plasma calcination TEM, EDX and FTIR are used to characterize the obtained films To demonstrate the gas sensing property of the functionalized silica films,10 MHz Quartz Crystal Microbalance (QCM) coated with β-cyclodextrin (β-CD) functionalized silica film is tested as a sensor for benzene vapor detection The higher surface area of the mesoporous silica films could accommodate more receptor molecules (β-CD molecules) and subsequently more target analytes that enhance the QCM response The sensitivity of the QCM is enhanced by depositing plasma calcined mesoporous sensing films on the electrodes Keywords: Gas sensor, Mesoporous silica film, QCM, Plasma calcination 90 Publication - Abstract Sensors and Actuators B, Vol 119 (2006) 220 Cyclodextrin functionalized mesoporous silica films on quartz crystal microbalance for enhanced gas sensing Al Palaniappan, 1, 2, Xu Li, 1, Francis E H Tay, 2, Xiaodi Su,* 1, Jun Li, 1 Institute of Materials Research & Engineering, Research Link, Singapore 117602 Mechanical Engineering Department, National University of University, 10 Kent Ridge Crescent Road, Singapore 119260 We have attempted to enhance the detection sensitivity of frequency domain sensors such as Quartz Crystal Microbalance (QCM) by depositing a mesoporous silica film on their flat electrode surface The mesoporous silica film is prepared using sol-gel process in combination with plasma calcination To demonstrate the effect of mesoporous silica film on the sensitivity of the QCM, β-cyclodextrin (β-CD) is trapped in the mesoporous network to detect benzene vapors To ensure a covalent immobilization, the β-CD molecules are modified through alkenylation of the hydroxyl groups and then immobilized on thiolated silica film using the anti-Markovnikov reaction A Field Emission Scanning Electron Microscopy (FESEM) and nitrogen adsorption analysis are used to characterize the mesoporous structure of the silica film NMR and a Time-ofFlight Secondary Ion Mass Spectroscopy SIMS (ToFSIMS) are used to confirm the alkenylation of β-CD and the presence of β-CD in the silica network, respectively The sensitivity of the QCM to benzene vapor is enhanced by the introduction of the mesoporous sensing film on the electrodes Keywords: Mesoporous silica, QCM, β-Cyclodextrin, Gas sensor 91 Publication - Abstract Applied Surface Sciences, Vol 245 (2005) 304 Mesoporous silica thin films prepared by argon plasma treatment of sol–gel-derived precursor Jian Zhang, *1, Al Palaniappan, 1, 2, Xiaodi Su, Francis E H Tay, Institute of Materials Research & Engineering, Research Link, Singapore 117602 Mechanical Engineering Department, National University of University, 10 Kent Ridge Crescent Road, Singapore 119260 Argon plasma is used to generate the mesoporous silica thin films from sol–gel-derived precursor Poly (ethylene glycol) (PEG, MW = 400) is employed as the template, i.e., the pore-directing agent as well as the binder The influence of the plasma parameters (plasma power and processing time) on the mesoscopic properties of silica films are investigated by scanning electron microscopy (SEM), FT-IR, low-angle X-ray scattering (SAXS), and nitrogen adsorption isotherm It is concluded that the plasma treatment is a promising way to remove organic templates and generate mesoporous thin films Compared to the conventional thermal calcination methods, the plasma treatment provides a promising low-temperature, low-cost and timesaving preparation process Keywords: Sol–gel; Silica; Mesoporous; Argon plasma; PEG template 92 Publication - Abstract Chemical Physics Letters Vol 395 (2004) 70 Preparation of mesoporous silica films using sol–gel process and argon plasma treatment Al Palaniappan, * 1, 2, Jian Zhang, 1, Xiaodi Su, Francis E H Tay, Institute of Materials Research & Engineering, Research Link, Singapore 117602 Mechanical Engineering Department, National University of University, 10 Kent Ridge Crescent Road, Singapore 119260 This Letter demonstrates the first attempt of using sol–gel technique in combination with argon plasma calcination for the preparation of mesoporous silica films CTAB is used as an organic template to generate the porous structure upon removal by the argon plasma treatment Field emission scanning electron microscope, Fourier transform infrared spectroscopy, small angle X-ray scattering, N2-sorption experiment and nanoindentation technique are used for characterization Results show that the obtained films have identical chemical structure and comparable mechanical properties with those prepared using thermal calcination The plasma parameters have distinct influences on the thickness and mesoporous property of the films 93 Publication - Abstract International Journal of Computational Engineering Science Vol (2003) 645 Electrical Impedance and Energy Dissipation Analyses of Quartz Crystal Microbalance for Polymer Coating Al Palaniappan, * 1, 2, Jian Zhang, Xiaodi Su, Francis E H Tay, Institute of Materials Research & Engineering, Research Link, Singapore 117602 Mechanical Engineering Department, National University of University, 10 Kent Ridge Crescent Road, Singapore 119260 Electrical impedance analysis and energy dissipation methods are the two main methods to evaluate the damping behavior of the quartz crystal The motional resistance of the quartz crystal, which can reflect the quality factor (Q), is monitored in the electrical impedance analysis and the dissipation factor (D), which is inversely proportional to the Q, is measured in the energy dissipation methods A comparison of the Q from electrical impedance analysis, termed as “electrical Q” and from the energy dissipation methods, termed as “mechanical Q” is presented in this work The damping behavior of MHz QCM subjected to polymer coatings are studied by both methods The resonant frequency, f, and Q before and after polymer coatings are measured using the network analyzer and a QCM-energy dissipation (QCM-D) instrument The frequency shifts from both methods are quite comparable and the changes of the dissipation factor and the Q factor are also similar Possible factors accounting for the Q change such as mass loading effect, evenness of the polymer coating, surface roughness of the crystal, are analyzed The thickness range of the coating over which the QCM can be used as a platform for bio sensing is also discussed Keywords: QCM; Dissipation factor; Quality factor 94 ... depositing functionalized argon plasma calcined mesoporous films on the QCM/QCA electrodes Keywords: QCM, QCM array, mesoporous silica film, silica hybrid, plasma calcination, gas sensor List... thesis emphasizes the incorporation of argon plasma calcined sol-gel based mesoporous silica film /silica hybrids with the QCM/QCA for enhanced gas sensing By depositing a porous film on the quartz. .. Chapter Quartz sensors Quartz based sensors, like Surface Acoustic Wave (SAW) and Bulk Acoustic Wave (BAW) sensors have gained attention over the past few decades as these frequency domain sensors