DSpace at VNU: Ab initio study of the polymerisation of cyclopentasilane

This article was downloaded by: [Northwestern University] On: 24 December 2014, At: 07:46 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Molecular Physics: An International Journal at the Interface Between Chemistry and Physics Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tmph20 Ab initio study of the polymerisation of cyclopentasilane a Ayumu Sugiyama , Tatsuya Shimoda a b & Dam Hieu Chi a b c a Japan Advanced Institute of Science and Technology , 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan b ERATO, Shimoda Nano-Liquid Process Project , Japan Science and Technology Agency , 2-5-3-Asahidai, Nomi, Ishikawa 923-1211, Japan c Vietnam National University , 144 Xuan Thuy, Cau Giay, Hanoi, Vietnam Published online: 07 Jul 2010 To cite this article: Ayumu Sugiyama , Tatsuya Shimoda & Dam Hieu Chi (2010) Ab initio study of the polymerisation of cyclopentasilane, Molecular Physics: An International Journal at the Interface Between Chemistry and Physics, 108:12, 1649-1653, DOI: 10.1080/00268976.2010.489517 To link to this article: http://dx.doi.org/10.1080/00268976.2010.489517 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content This article may be used for research, teaching, and private study purposes Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions Molecular Physics Vol 108, No 12, 20 June 2010, 1649–1653 RESEARCH ARTICLE Ab initio study of the polymerisation of cyclopentasilane Ayumu Sugiyamaa, Tatsuya Shimodaab and Dam Hieu Chiabc* a Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan; ERATO, Shimoda Nano-Liquid Process Project, Japan Science and Technology Agency, 2-5-3-Asahidai, Nomi, Ishikawa 923-1211, Japan; cVietnam National University, 144 Xuan Thuy, Cau Giay, Hanoi, Vietnam b Downloaded by [Northwestern University] at 07:46 24 December 2014 (Received 25 January 2010; final version received 16 April 2010) The molecular structures and vibration modes of cyclopentasilane (Si5H10) have been examined by employing ab initio and density-functional methods Three different structures of Si5H10 with different symmetries are analysed, and the results show that the envelope (Cs) and the twist (C2) forms have similar energies and that the planar form (D5h) is about 50 meV less stable than the Cs and C2 forms The excited-state potential energy surface of Si5H10 is performed using the CIS electronic energy calculation The ring-open reaction of Si5H10 is investigated in detail by using the first-principles molecular-dynamics simulation for screening the reaction pathways The formation of Si–H–Si is found to play an important role in the ring-open reaction Keywords: ab initio calculation; cyclopentasilane; polymerisation Introduction The production of silicon electronic devices using conventional vacuum processes and vapour phase deposition requires complex manufacturing processes, which involve the use of a number of materials and high cost Therefore, the use of a solution process for the fabrication of electronic devices has received considerable attention for a wide range of applications, with a view to reducing processing costs [1–7] In particular, the ability to fabricate semiconductor devices employing a printing technique involves the use of silicon materials in the liquid phase which could significantly decrease the complexity of the required equipment, reduce the cost involved, produce large-scale electronic circuits, and open up new applications that are prohibitively expensive when current techniques are used [8] Recent research in this area intensively focused on organic semiconductors which are cost-effective and compatible with flexible substrates Owing to these advantages, studies investigating the feasibility of using a variety of organic semiconductors in electronic devices have been attracting much attention The mobilities of organic semiconductors are comparable to those of amorphous silicon; however, improving the reliability of the former is still a challenging problem Several classes of materials are being explored as a possible substitute for silicon, given the complex and expensive manufacturing processes required to fabricate devices *Corresponding author Email: dam@jaist.ac.jp ISSN 0026–8976 print/ISSN 1362–3028 online ß 2010 Taylor & Francis DOI: 10.1080/00268976.2010.489517 http://www.informaworld.com from the latter The situation might change drastically if high-quality silicon films could be prepared by a solution process Among liquid materials, cyclopentasilane is extremely useful for the fabrication of devices by solution process because of its ability to transform to high purity silicon and its relative stability In addition, cyclopentasilane can act as a solvent to dissolve the polymer formed for application to the inkjet printing technique [9,10] However, owing to the difficulties faced in the synthesis of cyclopentasilane and the instability of the compound, very few studies on cyclopentasilane have been reported so far when compared to those on its counterpart, cyclopentane Further, most research focuses either on the geometrical structures or on the anion of cyclopentasilane [11,12] The photo- and thermo-induced ring-opening and polymerisation reactions of cyclopentasilane which are manifested in the experiment have not received any attention from any theoretical approach Further studies on the properties and polymerisation of cyclopentasilane are required to develop more efficient fabrication techniques involving liquid silicon In this paper, we report on our computational study on cyclopentasilane carried out by using ab initio and density-functional methods Different structures of Si5H10 with different symmetries are analysed, and the results show that the envelope (Cs) and twist (C2) forms have similar energies and the planar form (D5h) is 1650 A Sugiyama et al about 50 meV less stable than the Cs and twist C2 forms The ab initio study of the excited-state potential energy surface of Si5H10 is performed using the CIS electronic energy calculation for having an insight into the photo-induced polymerisation reaction Metastable structures in the ring-open reaction is investigated in detail by using the first-principles molecular-dynamics simulation for screening the reaction pathways The formation of Si–H–Si is found to be essential in the ring-open reaction of Si5H10 Downloaded by [Northwestern University] at 07:46 24 December 2014 Computational method The calculations in this study were based on the Hatree–Fock theory, Møllet–Plesset perturbation theory, and the density-functional theory (DFT), which are formulated using the cc-pVTZ basis set with the Gaussian 03 program [13] The ‘frozen core approximation’ was applied for MP2 computations For the DFT calculations, Becke’s three parameter exchange functional together with the correlation functional developed by Lee, Yang, and Parr (B3LYP), the correlation functional developed by Perdew, Burke, and Ernzerhof (PBE), and the correlation functional developed by Vosko, Wilk, and Nusair (VWN) were used as implemented in Gaussian 03 along with the cc-pVTZ basis set The geometrical structures of cyclopentasilane were optimised within the given symmetry point group Vibrational frequencies were evaluated analytically at the B3LYP/cc-pVTZ level Calculations based on the DFT using the PBE and BLYP functionals and the TNP basis set were also carried out with the Dmol3 [14,15] package for comparison The excited-state calculation is performed using the CIS/cc-pVTZ method to probe energetics of the low-lying electronic states, as implemented in Gaussian 03 The first-principles molecular-dynamics simulation based on the DFT with the BLYP functional is carried out by using the Dmol3 package for screening the reaction pathways of the ring-open reaction Results and discussion 3.1 Molecular structure and vibrational spectrum of cyclopentasilane All the stable structures of cyclopentasilane determined by our calculations, namely, planar (D5h), envelope (Cs), and twist (C2) are shown in Figure Results of our calculations at all theoretical levels employed show that the twist structure is the most stable structure for cyclopentasilane The relative energies of each structure are summarised in Table Our calculation results Figure Structures of cyclopentasilane with geometries optimised by B3LYP/cc-pVTZ: planar (D5h), envelope (Cs), and twist (C2) also confirm that the two structures of cyclopentasilane, twist (C2) and envelope (Cs), have similar energies at all the theoretical levels employed (the difference in their energies is in the order of 1.0 meV) These results are in good agreement with the results of previous theoretical studies [11,12] Only a slight distortion is needed for a transformation between the twist structures and the envelope structure The energy barrier for this structural transformation is evaluated to be less than 0.1 meV at all the theoretical levels employed Our vibrational frequency calculation for the two most stable structures by B3LYP/cc-pVTZ shows that the twist and envelope structures have the lowest vibrational frequencies, at 2.6 and 3.8 cmÀ1, respectively It is apparent that these vibrations correspond to the structural transformation between the two structures This result confirms that the structural transformation can be achieved easily The planar (D5h) structure was characterised as a second-order stationary point by using the HF, VWN, B3LYP, and MP2 theory with the cc-pVTZ basis set, and it is 60.6 meV higher in energy (by the MP2/cc-pVTZ) than the twist and envelope structures In contrast, calculation by the PBE/cc-pVTZ method characterised the planar (D5h) structure as a minimum structure having no imaginary frequency This result suggests that the electron correlation treating method can affect strongly the results obtained in studies of silicon materials The vibrational spectra of the most stable structures of cyclopentasilane are evaluated analytically at the B3LYP/cc-pVTZ level (Figure 2) The vibrational frequencies corresponding to the Si–H bond are found in the region from 2100 to 2200 cmÀ1 The vibrational frequencies corresponding to the scissoring and rocking vibrations of the H–Si–H groups are found in the region from 850 to 950 cmÀ1 and from 300 to 400 cmÀ1, respectively 1651 Molecular Physics Table Comparison of energies of the structures of CPS and the twist structure Structure HF/cc-pVTZ VWN/cc-pVTZ PBE/cc-pVTZ B3LYP/cc-pVTZ MP2/cc-pVTZ 0.03 60.79 1.02 80.85 0.01 61.20 0.03 53.65 0.03 60.58 Downloaded by [Northwestern University] at 07:46 24 December 2014 Twist (eV) Envelope (meV) Planar (meV) Figure Infrared spectra calculated by B3LYP/cc-pVTZ Red solid line indicates the infrared spectra of the twist and envelope structures, respectively The green dotted lines indicate the infrared spectrum of the intermediate structures after the formation of the Si–H–Si bridge bond The vibrational frequencies corresponding to the wagging vibrations of the H–Si–H groups are located at around 725 cmÀ1, and the breathing frequency of the pentagonal ring is found at 344.8 cmÀ1 Further, it should be noted that for the cyclopentasilane molecule, no vibrational frequency is found in the region from 1000 to 2100 cmÀ1 3.2 Ring-open reaction It is well known that the Si–Si bonding in silane compounds can be broken by the introduction of UV light of an appropriate wavelength Therefore, in our study, we carried out an ab initio calculation of the excited-state potential energy surface of Si5H10 using the CIS electronic energy calculation in order to have an insight into the photo-induced polymerisation reaction The molecular structure of cyclopentasilane at the first excited state is optimised from the twist structure The dependencies, on the variation of the geometrical structure, of the total energy at the first excited state and the ground state, and the transition rate between the two states were calculated and summarised in Figure Figure Structure dependence of the total energy at the first excited state (red) and the ground state (blue), and the transition rate (green) between the two states calculated by CIS/cc-pVTZ Our calculation results show that the excitation with the highest transition rate occurred with an UV light of about 416 nm, which agrees very well with our experiments [8] This excitation requires a structure deformation of the molecule in which a silicon atom that is not present in the single plane in the envelope structure, deviate far from the plane This structure deformation corresponds to the second lowest vibrational frequencies at 73.5 cmÀ1 A cooperative phenomenon of the photo- and thermo-induced effects is therefore expected for the polymerisation of cyclopentasilane In the next step of our study, we carried out a firstprinciples molecular-dynamics simulation based on the DFT using BLYP with the Dmol3 package for screening the reaction pathways of the ring-open reaction The simulation is performed by using an appropriate periodic supercell including 16 cyclopentasilane molecules Canonical (NVT ) ensembles are employed at several temperatures above 800C Our simulation results suggest three possible intermediate structures in the ring-open reaction, namely, SiH2–Si3H6–SiH2, SiH–Si3H6–SiH3, and Si–H–Si bridge bond structures On the basis of the results of the first-principles 1652 A Sugiyama et al Table Comparison of energies of the intermediate structures and the twist structure HF/cc-pVTZ Intermediate structure Singlet Downloaded by [Northwestern University] at 07:46 24 December 2014 non-stable SiH2–Si3H6–SiH2 SiH–Si3H6–SiH3 1.979 Si–H–Si bridge bond 1.938 VWN/cc-pVTZ PBE/cc-pVTZ B3LYP/cc-pVTZ Triplet (eV) Singlet Triplet (eV) Singlet Triplet (eV) Singlet Triplet (eV) 2.100 1.906 1.926 non-stable 2.26 non-stable 3.12 3.27 3.14 non-stable non-stable non-stable 2.896 2.758 2.888 non-stable 2.052 1.682 2.802 2.677 2.683 molecular-dynamics simulation, we carefully evaluate the stability of the three intermediate structures at both singlet and triplet states by HF, VWN, PBE, and B3LYP theory with the cc-pVTZ basis set The results obtained are summarised in Table The results of our calculation show that the first intermediate structure (SiH2–Si3H6–SiH2) is unstable in the singlet state but stable in the triplet state, at all the theoretical levels employed In contrast, the other intermediate structures are found to be stable in both the singlet and triplet states, at all the theoretical levels employed except DFT/PBE It is important to note that the third intermediate structure, in which the Si–H–Si bridge bond is formed, is found to be more stable than the second intermediate structure in the singlet state These results strongly suggest that the formation of Si–H–Si plays an important role in the ring-open reaction of Si5H10 The vibrational spectra of the intermediate structure after the formation of the Si–H–Si bridge bond are also evaluated (Figure 2) Similar to the frequency region of the twist and envelope structures, the results of our calculation for the structure comprising the Si–H–Si bridge bond show the Si–H stretching vibrational frequencies at greater than 1950 cmÀ1 and H–Si–H twisting and rocking vibrational modes, at frequencies less than 950 cmÀ1 We also reveal frequencies corresponding to the Si–H–Si bridge bond as shown in Figure The results of our calculation for the intermediate structure which is surrounded by some CPS molecules shows that the frequencies of the Si–H–Si bridge bond are influenced by the presence of other CPS molecules in the surrounding environment Furthermore, the other cyclopentasilane molecules also contribute to a decrease in the difference in energies between the Si5H10 molecule and the intermediate structure comprising the Si–H–Si bridge bond Conclusion A computational study on cyclopentasilane is carried out by using ab initio and density-functional methods All the different stable structures of Si5H10 with different symmetries are analysed, and the results show that the envelope (Cs) and the twist (C2) structures have similar energies that are also the lowest The planar structure (D5h) is about 50 meV less stable than the Cs and C2 structures The calculation of the excited-state potential energy surface of Si5H10 is carried out using the CIS electronic energy calculation Our calculation results show that the first excitation of Si5H10 with the highest transition rate occurred with an UV light of about 416 nm, which agrees very well with our experiments Further, the pathways of, and the metastable structures in the ringopen reaction is investigated in detail by using the first-principles molecular-dynamics simulation The formation of Si–H–Si is found to play an important role in the ring-open reaction of Si5H10 Acknowledgements This research was partly supported by the Special Coordination Funds for Promoting Science and Technology commissioned by the MEXT, Japan, by the Special project QGTD.08.09 commissioned by the Vietnam National University, Hanoi, and by the Fundamental Research Project 103.02.111.09 commissioned by NAFOSTED, Vietnam The computations presented in this study were performed at the Center for Information Science, Japan Advanced Institute of Science and Technology References [1] T Shimoda, in SID International Symposium Digest of Technical Papers (Society for Information Display, San Jose, CA, 1999), pp 376–379 [2] S Miyashita, in 21st International Display Research Conference in Conjunction with 8th International Display Workshop (Asia Display/IDW ’01) (Society for Information Display, San Jose, 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B.01 (Gaussian, Inc., Pittsburgh, PA, 2003) [14] B Delley, Chem Phys 92, 508 (1990) [15] B Delley, Chem Phys 113, 7756 (2000)  ... into the photo-induced polymerisation reaction The molecular structure of cyclopentasilane at the first excited state is optimised from the twist structure The dependencies, on the variation of the. .. calculation show that the first intermediate structure (SiH2–Si3H6–SiH2) is unstable in the singlet state but stable in the triplet state, at all the theoretical levels employed In contrast, the other... wagging vibrations of the H–Si–H groups are located at around 725 cmÀ1, and the breathing frequency of the pentagonal ring is found at 344.8 cmÀ1 Further, it should be noted that for the cyclopentasilane