Co-reporter:Jia-Wei Yan, Zhong-Qun Tian, Bing-Wei Mao
Current Opinion in Electrochemistry 2017 Volume 4, Issue 1(Volume 4, Issue 1) pp:
Publication Date(Web):1 August 2017
DOI:10.1016/j.coelec.2017.09.008
•Recent advancements on the structure of electric double layer at electrode–ionic liquid interfaces are briefly reviewed.•Techniques with high spatial, time and energy resolutions have been combined to deeply understand the complex interfaces in ionic liquids.•Studies on the structure of electric double layer are reviewed with a particular emphasis on systematic potential-dependent measurements across the potential of zero charge.Electrochemical interfaces in ionic liquids (ILs) are structurally anisotropic with multi-scaled and multi-natured interactions between electrode and IL as well as among ions of IL. Combined short-ranged and long-ranged surface techniques with high spatial, time and energy resolutions need to be employed to precisely characterize the lateral structure and vertical arrangement of IL at the interface. We briefly review recent advancements on the understanding of the molecular structure of electric double layer (EDL) at electrode–IL interfaces, with emphasis laid on the necessity of detailed and systematic potential-dependent measurements across and at close to the potential of zero charge (PZC). Future directions of fundamental investigations on EDL are briefly discussed.
Co-reporter:Mian-Gang Li, Li Chen, Yun-Xin Zhong, Zhao-Bin Chen, Jia-Wei Yan, Bing-Wei Mao
Electrochimica Acta 2016 Volume 197() pp:282-289
Publication Date(Web):10 April 2016
DOI:10.1016/j.electacta.2015.12.227
The electrochemical interface between Ag(111) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI) has been investigated by in-situ scanning probe microscopy (SPM) and electrochemical impedance spectroscopy (EIS). In-situ scanning tunneling microscopy (STM) characterization has revealed that there is neither surface reconstruction nor strong adsorption of EMITFSI on Ag(111) surface so that EIS investigation can be fulfilled under well-defined surface condition and in the absence of pseudo capacitive process. In-situ atom force microscopy (AFM) force curve measurements further disclose that there exists five layered structures near and normal to the surface, among them three layered structures being charged and forming the electric double layer (EDL) of the interface. An electric equivalent circuit is proposed, which comprises two serial parallel branches involving the innermost layered structure and the next two layered structures in the EDL, respectively. The inner layer circuit is given by a constant phase element (CPE) in parallel to a resistor, while the outer layer circuit is given by a capacity in parallel with a resistor-Warburg element branch. Slow response is observed for the inner layer, which is attributed to the hindrance of reorientation and/or redistribution of ions in the more ordered and robust inner layer region. The inner layer capacitance and outer layer capacitance have opposing potential dependence, and the resultant double layer capacitance shows weak potential dependence.
Co-reporter:Liang Chen, Jia-Rui Wang, Li-Qiang Xie, Chao Zhan, Zhi Qiu, Jian-Zhang Zhou, Jia-Wei Yan, Bing-Wei Mao, Zhong-Qun Tian
Electrochemistry Communications 2016 Volume 68() pp:40-44
Publication Date(Web):July 2016
DOI:10.1016/j.elecom.2016.04.013
•We explore the influence of TiO2 compact layer on the hysteresis effect in perovskite solar cells.•Different morphology and thickness of compact layers by ALD and Spin-Coating methods are acquired.•Interfacial capacitance and recombination resistance are separated from AC impedance spectroscopy.•Small interfacial capacitance and large recombination resistance are responssible for reduced hysteresis effect.Organic–inorganic hybrid perovskite solar cells have attracted great attention due to their high power conversion efficiency and low cost. However, an anomalous hysteresis effect exists in the perovskite solar cells, especially with TiO2 as the n-type electron extraction layer. In this communication, we prepare two kinds of TiO2 compact layers using Atomic Layer Deposition (ALD) and Spin-Coating (SC) methods and compare their influences on the hysteresis effect. By efficiency comparison and AC impedance spectroscopy study, we find that the thickness and morphology of compact layer have a significant influence on the hysteresis effect. Compared to the SC approach, the ALD prepared compact layer is ultra-thin with uniform morphology and shows small interfacial capacitance and large recombination resistance, meaning reduced interfacial charge accumulation and accelerated electron transport, which would relieve the hysteresis effect.
Co-reporter:Li-Qiang Xie, Tai-Yang Zhang, Liang Chen, Nanjie Guo, Yu Wang, Guo-Kun Liu, Jia-Rui Wang, Jian-Zhang Zhou, Jia-Wei Yan, Yi-Xin Zhao, Bing-Wei Mao and Zhong-Qun Tian
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 27) pp:18112-18118
Publication Date(Web):09 Jun 2016
DOI:10.1039/C6CP01723A
Organolead halide perovskites exhibit superior photoelectric properties, which have given rise to the perovskite-based solar cells whose power conversion efficiency has rapidly reached above 20% in the past few years. However, perovskite-based solar cells have also encountered problems such as current–voltage hysteresis and degradation under practical working conditions. Yet investigations into the intrinsic chemical nature of the perovskite material and its role on the performance of the solar cells are relatively rare. In this work, Raman spectroscopy is employed together with CASTEP calculations to investigate the organic–inorganic interactions in CH3NH3PbI3 and CH3NH3PbBr3−xClx perovskite single crystals with comparison to those having ammonic acid as the cations. For Raman measurements of CH3NH3PbI3, a low energy line of 1030 nm is used to avoid excitation of strong photoluminescence of CH3NH3PbI3. Raman spectra covering a wide range of wavenumbers are obtained, and the restricted rotation modes of CH3–NH3+ embedded in CH3NH3PbBr3 (325 cm−1) are overwhelmingly stronger over the other vibrational bands of the cations. However, the band intensity diminishes dramatically in CH3NH3PbBr3−xClx and most of the bands shift towards high frequency, indicating the interaction with the halides. The details of such an interaction are further revealed by inspecting the band shift of the restricted rotation mode as well as the C–N, NH3+ and CH3 stretching of the CH3NH3+ as a function of Cl composition and length of the cationic ammonic acids. The results show that the CH3NH3+ interacts with the PbX3− octahedral framework via the NH3+ end through N+–H⋯X hydrogen bonding whose strength can be tuned by the composition of halides but is insensitive to the size of the organic cations. Moreover, an increase of the Cl content strengthens the hydrogen bonding and thus blueshifts the C–N stretching bands. This is due to the fact that Cl is more electronegative than Br and an increase of the Cl content decreases the lattice constant of the perovskite. The findings of the present work are valuable in understanding the role of cations and halides in the performance of MAPbX3-based perovskite solar cells.
Co-reporter:Run-Wen Yan
The Journal of Physical Chemistry C 2016 Volume 120(Issue 22) pp:11820-11830
Publication Date(Web):May 17, 2016
DOI:10.1021/acs.jpcc.6b03116
Co-reporter:Li-Qiang Xie, Ding Ding, Meng Zhang, Shu Chen, Zhi Qiu, Jia-Wei Yan, Zhi-Lin Yang, Ming-Shu Chen, Bing-Wei Mao, and Zhong-Qun Tian
The Journal of Physical Chemistry C 2016 Volume 120(Issue 39) pp:22500-22507
Publication Date(Web):September 8, 2016
DOI:10.1021/acs.jpcc.6b07763
Adsorption of dye molecules on semiconductor surfaces dictates the interaction at and thus the electron transfer across the interface, which is a crucial issue in dye-sensitized solar cells (DSSCs). However, despite that surface enhanced Raman spectroscopy (SERS) has been employed to study the interface, information obtained so far is gathered from surfaces of irregularly arranged nanoparticles, which places complexities for precise attribution of adsorption configuration of dye molecules. Herein, we employ single crystalline rutile TiO2(110) for Raman spectroscopic investigation of TiO2–dye interfaces under electrochemical control by utilizing the enhancement of Au@SiO2 core–shell nanoparticles. FD-TD simulation is performed to evaluate the localized electromagnetic field (EM) created by the core–shell nanoparticles while Mott–Schottky measurements are used to determine the band structure of the semiconductor electrode. Comparative investigations are carried out on nanoporous P25 TiO2 electrodes. The potential-dependent Raman shift of ν(N═C═S) suggests that the binding of the SCN group of N719 to the TiO2 surface is the intrinsic nature of the TiO2–N719 interaction, after removing the possible bonding complexity by surface roughness. Nevertheless, hydrogen bonding between COOH and the TiO2 appears to be more favorable on the atomic flat rutile TiO2(110) surface than on the surface of nanoporous P25 nanoparticle as revealed by the stronger Raman shift of ν(C═O) (COOH) on the former. Electrochemical SERS (EC-SERS) results show that photoinduced charge transfer (PICT) occurs for both the P25 and rutile(110) TiO2 surfaces, and the potential to achieve PICT resonance depends on the band structure of the semiconductor. Our work demonstrates that EC-SERS can be applied to study the single crystalline semiconductor–molecule interfaces using core–shell based surface plasmonic resonance (SPR) enhancement strategy, which would promote fundamental investigations on interfaces of photovoltaic and photocatalytic systems.
Co-reporter:Ji-Jun Li; Mei-Lin Bai; Zhao-Bin Chen; Xiao-Shun Zhou; Zhan Shi; Meng Zhang; Song-Yuan Ding; Shi-Min Hou; Walther Schwarzacher; Richard J. Nichols
Journal of the American Chemical Society 2015 Volume 137(Issue 18) pp:5923-5929
Publication Date(Web):April 20, 2015
DOI:10.1021/ja512483y
We report an electrochemically assisted jump-to-contact scanning tunneling microscopy (STM) break junction approach to create reproducible and well-defined single-molecule spintronic junctions. The STM break junction is equipped with an external magnetic field either parallel or perpendicular to the electron transport direction. The conductance of Fe-terephthalic acid (TPA)-Fe single-molecule junctions is measured and a giant single-molecule tunneling anisotropic magnetoresistance (T-AMR) up to 53% is observed at room temperature. Theoretical calculations based on first-principles quantum simulations show that the observed AMR of Fe-TPA-Fe junctions originates from electronic coupling at the TPA–Fe interfaces modified by the magnetic orientation of the Fe electrodes with respect to the direction of current flow. The present study highlights new opportunities for obtaining detailed understanding of mechanisms of charge and spin transport in molecular junctions and the role of interfaces in determining the MR of single-molecule junctions.
Co-reporter:Xiaoyan Hu, Chunlei Chen, Jiawei Yan, Bingwei Mao
Journal of Power Sources 2015 Volume 293() pp:187-195
Publication Date(Web):20 October 2015
DOI:10.1016/j.jpowsour.2015.05.078
•In-situ STM is employed to understand compatibility between ILs and graphite.•The decomposition of FSI forms film which suppresses the intercalation of Py13.•The decomposition of TFSI etches the surface which makes the intercalation easier.•The addition of Li salt suppresses the intercalation and exfoliation, especially in Py13FSI.•The surface processes are different on HOPG and Au(111) electrodes.We report electrochemical and in-situ scanning tunneling microscopy (STM) studies of surface processes on graphite and Au(111) electrodes in N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (Py13FSI) and N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (Py13TFSI) ionic liquids in the absence and presence of LiTFSI salt. In both of neat ionic liquids, the intercalation of cations and exfoliation of HOPG layers occur during cathodic excursion. However, the surface decomposition of FSI anions can form an effective protection film on the surface, which suppresses the intercalation and exfoliation processes, while the surface decomposition of TFSI anions mainly causes etching of the surface, which makes the intercalation and exfoliation easier to proceed. The addition of Li salt can promote the formation of the protective film, especially in Py13FSI, and thus significantly suppress the intercalation and exfoliation processes. The discrepancies between these two ionic liquids are caused by the different anion interactions with graphite. Additionally, comparisons of the behaviors on HOPG and on Au(111) confirm that the surface processes are crucially dependent on the nature of the electrode. Trace amounts of oxygen and water can cause the formation of a film-like structure on Au(111), but show no apparent influence on HOPG.
Co-reporter:Xiaoyan Hu;Chunlei Chen;Shuai Tang;Weiwei Wang;Jiawei Yan
Science Bulletin 2015 Volume 60( Issue 9) pp:877-883
Publication Date(Web):2015 May
DOI:10.1007/s11434-015-0746-7
We report an in situ scanning tunneling microscopic study of surface morphology changes in Au(111) electrode in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI) ionic liquid containing LiTFSI salt. The surface processes can be divided into three stages: In the first stage, a reduction wave of dissolved oxygen in the ionic liquid appears at approximately 2.0 V and a network structure covers the surface afterward; in the second stage at around 1.5 V, reduction of trace water is initiated and a surface film containing lithium hydroxide is formed; in the third stage, as potential is further decreased to 0.85 V, decomposition of the EMITFSI ionic liquid occurs, which is accompanied by lithium underpotential deposition and Au–Li alloying. In this stage, the surface experiences significant morphological changes with formation of many clusters on the surface, and eventually becomes electronically less conductive. This unique surface film is understood to be the initial stage formation of a solid electrolyte interphase on gold, which may be a common feature in ionic liquids in the presence of lithium salt.
Co-reporter:Xueqin Zhao;Yishun Huang;Chaoyong James Yang;Bingwei Mao
Science China Chemistry 2015 Volume 58( Issue 12) pp:1858-1865
Publication Date(Web):2015 December
DOI:10.1007/s11426-015-5465-z
Nucleic acid sensing analysis has been widely applied to the fields of food quality control, environmental monitoring, and medical diagnosis. A key step in developing effective DNA-based electrochemical biosensors is to obtain a biorecognition layer on the biosensor, which can be influenced by many factors. Hence, we constructed a series of HJ24 layers on highly oriented pyrolytic graphite to investigate the relation between the configuration of the adsorbed probe HJ24 and the redox property using atomic force microscopy and voltammetry. We used HJ24 for its diagnostic value as it specifically recognizes the SH2 domain-containing phosphatase, a critical contributor in many important signaling pathways. The results demonstrated that increasing K ions induced G-quartet oxidation peak occurrence/increase ([K+]⩽400 mmol/L), and also resulted in the formation of more compact single strand sheets ([K+]⩽300 mmol/L). Moreover, transitions of molecule configurations and redox currents of G-quartets were observed at low concentration [K+]=12 mmol/L, which may indicate the appearance of new configurations under this condition. Besides, by analyzing atomic force microscopy (AFM) images, it was found that the different adsorbed configurations are correlated with the HJ24 concentration, the basal configuration, and the linker group on the HJ24 sequence. This information may be useful for understanding the adsorption process of HJ24 as well as for the further development of practical applications for HJ24 films on DNA electrochemical sensors, and may ultimately help improve the diagnosis and treatment of patients with SHP2-related diseases.
Co-reporter:Qi-Qi Zuo
The Journal of Physical Chemistry C 2015 Volume 119(Issue 32) pp:18396-18403
Publication Date(Web):July 24, 2015
DOI:10.1021/acs.jpcc.5b05318
In this paper, we present a nanoparticle-enhanced Raman spectroscopic study of TiO2–N719 (bis(tetrabutylammonium) [cis-di(thiocyanato)-bis (2,2′-bipyridyl-4′-carboxylate-4-carboxylic acid)-ruthenium(II)])) interface by employing Ag2@TiO2 dimeric core–shell nanoparticles, where the TiO2 shell serves as an active semiconductor surface. The Ag2@TiO2 nanoparticles are synthesized by connecting two Ag nanoparticles with thiol-modified complementary DNAs, followed by coating a 2 nm thin layer of TiO2 on the Ag2 dimeric nanoparticles. The Ag2@TiO2 dimeric core–shell nanoparticles show a red-shift of plasmon resonance frequency compared with Ag@TiO2 core–shell nanoparticles, and provide significant SERS enhancement over the Ag@TiO2 nanoparticles, which allows for the investigation of SERS of TiO2–N719 interface under off-resonance conditions using low energy 785 nm laser excitation. Fine potential dependent Raman measurements show that thiocyano and carboxyl groups of the N719 molecule can adsorb on the TiO2 shell competitively: Along with negative potential excursion, the thiocyano is replaced by carboxyl, which is accompanied by a conformationsl change of the molecule involving an orientation change of the bipyridine ring. Furthermore, the potential of maximum intensity of the inter-ring vibration band shifts toward a more positive value with laser excitation wavelengths from 638 to 785 nm, which verifies the photon-driven charge transfer mechanism from the HOMO of N719 to the conduction bands of TiO2. Three-dimensional finite-difference time-domain (3D-FDTD) simulations are performed to evaluate the electromagnetic (EM) enhancement from the Ag2@TiO2 dimeric core–shell nanoparticles. The present work demonstrates that the Ag2@TiO2 dimeric core–shell structures provide significant plasmon resonance, which can be used for Raman investigations of interfaces formed with the semiconductor shell layers of the nanoparticles.
Co-reporter:Yun-Xin Zhong ; Jia-Wei Yan ; Mian-Gang Li ; Xiao Zhang ; Ding-Wen He
Journal of the American Chemical Society 2014 Volume 136(Issue 42) pp:14682-14685
Publication Date(Web):October 7, 2014
DOI:10.1021/ja508222m
We report enhanced force detection selectivity based on Coulombic interactions through AFM tip modification for probing fine structures of the electric double layer (EDL) in ionic liquids. When AFM tips anchored with alkylthiol molecular layers having end groups with different charge states (e.g., −CH3, −COO–, and −NH3+) are employed, Coulombic interactions between the tip and a specified layering structure are intensified or diminished depending on the polarities of the tip and the layering species. Systematic potential-dependent measurements of force curves with careful inspection of layered features and thickness analysis allows the fine structure of the EDL at the Au(111)–OMIPF6 interface to be resolved at the subionic level. The enhanced force detection selectivity provides a basis for thoroughly understanding the EDL in ionic liquids.
Co-reporter:Meng Zhang, Li-Juan Yu, Yi-Fan Huang, Jia-Wei Yan, Guo-Kun Liu, De-Yin Wu, Zhong-Qun Tian and Bing-Wei Mao
Chemical Communications 2014 vol. 50(Issue 94) pp:14740-14743
Publication Date(Web):06 Oct 2014
DOI:10.1039/C4CC06269H
We employ, for the first time, a shell-isolated nanoparticle-enhancement strategy to extend Raman spectroscopy studies to single crystal electrode surfaces in ionic liquids, and combine density functional theory (DFT) calculations to elucidate the structural details of the imidazolium-based ionic liquid–Au single crystal electrode interfaces.
Co-reporter:Zhao-Bin Chen, Zheng-Lian Peng, Jing-Hong Liang, Xiao-Shun Zhou, De-Yin Wu, C. Amatore, Bing-Wei Mao
Electrochemistry Communications 2014 Volume 47() pp:41-44
Publication Date(Web):October 2014
DOI:10.1016/j.elecom.2014.07.022
•Conductance of Au atomic contact (AC) is studied under interfacial charge transfer.•Conductance of Au AC changes from quantization to random distribution•Transient oxidation and structural relaxation of Au AC are proposed.This paper presents a work on hitherto unreported conductance alteration of gold atomic contact by electrochemical reduction of redox species at the contact. The interfacial charge transfer current due to reduction of Ru(NH3)63 + at Au atomic contacts can cause paradigm change of electron transport through the contacts: Conductance quantization is altered to random distribution with substantially reduced length of conductance plateau on the conductance traces. Transient oxidation of the Au atomic contact upon reduction of Ru(NH3)63 +, which relaxes atomic contact structures and hence the conductance, is proposed together with DFT calculation. The observations in the present work also disclose possible mechanistic information that might be generalized to electrochemical reduction at atomic scale.
Co-reporter:Yi-Min Wei, Jing-Hong Liang, Zhao-Bin Chen, Xiao-Shun Zhou, Bing-Wei Mao, Oscar A. Oviedo and Ezequiel P. M. Leiva
Physical Chemistry Chemical Physics 2013 vol. 15(Issue 30) pp:12459-12465
Publication Date(Web):27 Mar 2013
DOI:10.1039/C3CP50473E
This work describes jump-to-contact STM-break junction experiments leading to novel statistical distribution of last-step length associated with conductance of a single atom contact. Last-step length histograms are observed with up to five for Fe and three for Cu peaks at integral multiples close to 0.075 nm, a subatomic distance. A model is proposed in terms of gliding from a fcc hollow-site to a hcp hollow-site of adjacent atomic planes at 1/3 regular layer spacing along with tip stretching to account for the multiple subatomic step-length behavior.
Co-reporter:Jinghong Liang, Ling Liu, Yajun Gao, Yimin Wei, Zhaobin Chen, Xiaoshun Zhou, Jianwei Zhao, Bingwei Mao
Journal of Electroanalytical Chemistry 2013 Volume 688() pp:257-261
Publication Date(Web):1 January 2013
DOI:10.1016/j.jelechem.2012.07.012
In this paper, we use Ag as a probe to compare the conductance of the NCs created by STM-based jump-to-contact and crash-to-contact approaches with the results of theoretical modeling reported in the literature. It is shown that the jump-to-contact created Ag NCs have most probable conductance at 1, 2 and 3 G0, with that at 2 G0 most abundant, which is in agreement with theoretical modeling. It is thus proved that metal Ag NCs created by jump-to-contact STM-BJ bear well-defined structures.Highlights► We compare the structure of Ag NCs created via jump-to-contact and crash-to-contact STM Break junction. ► Jump-to-contact created Ag NCs at two-atom width bears integral conductance of 2 G0. ► Crash-to-contact created Ag NCs at two-atom width bears fractional conductance of 2.5 G0. ► Jump-to-contact approach creates Ag NCs with well-defined structure.
Co-reporter:Jiawei Yan, Feng Zhu, Yang Wang, Zaiwen Zhu, Bingwei Mao
Journal of Electroanalytical Chemistry 2013 Volume 688() pp:40-44
Publication Date(Web):1 January 2013
DOI:10.1016/j.jelechem.2012.07.007
A method for selective detection based on the concept of electrochemical depletion of interfering species in diffusion layer is proposed. By applying an appropriate pre-depletion pulse (PDP) to the working electrode, interfering species is oxidized and thus an interferent-depleted micro-environment is created in diffusion layer. Then a follow-up differential pulse voltammetry (DPV) is utilized for detecting target analyte. The feasibility of the method is verified by detecting dopamine in the presence of ascorbic acid. The results demonstrate that the detection limit is improved by more than an order of magnitude compared with that of the method of combining potential step with linear sweep voltammetry, owing to the ability of differential pulse voltammetry to eliminate background current. Experimental parameters affecting the dopamine detection are investigated systematically. Because only easily achievable potential control and commonly used electrode without modification are required, the proposed method is facile and thus high reproducibility is expected.Highlights► Electrochemical depletion of interfering species in diffusion layer is performed. ► Differential pulse voltammetry is used to eliminate background current. ► Only easily achievable potential control and commonly used electrode are required.
Co-reporter:Dr. Feng Liu;Kamran Khan;Jing-Hong Liang; Jia-Wei Yan; De-Yin Wu; Bing-Wei Mao;Dr. Palle Skovhus Jensen; Jingdong Zhang; Jens Ulstrup
ChemPhysChem 2013 Volume 14( Issue 5) pp:952-957
Publication Date(Web):
DOI:10.1002/cphc.201200901
Abstract
Redox reactions of solvated molecular species at gold-electrode surfaces modified by electrochemically inactive self-assembled molecular monolayers (SAMs) are found to be activated by introducing Au nanoparticles (NPs) covalently bound to the SAM to form a reactive Au–alkanedithiol–NP–molecule hybrid entity. The NP appears to relay long-range electron transfer (ET) so that the rate of the redox reaction may be as efficient as directly on a bare Au electrode, even though the ET distance is increased by several nanometers. In this study, we have employed a fast redox reaction of surface-confined 6-(ferrocenyl) hexanethiol molecules and NPs of Au, Pt and Pd to address the dependence of the rate of ET through the hybrid on the particular NP metal. Cyclic voltammograms show an increasing difference in the peak-to-peak separation for NPs in the order Au<Pt<Pd, especially when the length of the alkanedithiol increases from octanedithiol to decanedithiol. The corresponding apparent rate constants, kapp, for decanedithiol are 1170, 360 and 14 s−1 for NPs of Au, Pt and Pd, respectively, indicating that the efficiency of NP mediation of the ET clearly depends on the nature of the NP. Based on a preliminary analysis rooted in interfacial electrochemical ET theory, combined with a simplified two-step view of the NP coupling to the electrode and the molecule, this observation is referred to the density of electronic states of the NPs, reflected in a broadening of the molecular electron/NP bridge group levels and energy-gap differences between the Fermi levels of the different metals.
Co-reporter:Zhi Qiu;Meng Zhang; De-Yin Wu;Dr. Song-Yuan Ding;Qi-Qi Zuo;Dr. Yi-Fan Huang;Wei Shen;Xiao-Dong Lin; Zhong-Qun Tian; Bing-Wei Mao
ChemPhysChem 2013 Volume 14( Issue 10) pp:2217-2224
Publication Date(Web):
DOI:10.1002/cphc.201300381
Abstract
Herein, we employ Ag@TiO2 core–shell nanoparticles for surface-enhanced Raman scattering (SERS) investigations of TiO2–N719 dye interfaces. In situ electrochemical SERS investigations of the Ag@TiO2–N719 interaction are systematically carried out under a series of electrode-potential controls. By comparing the potential dependence of resonant and pre-resonant SERS spectra recorded with different laser excitations, bidentate carboxylate linkage is considered to be involved in N719 adsorption on TiO2. Meanwhile, SCN ligand shows obvious interactions with TiO2, and their role in the adsorption and orientation of N719 on TiO2 should not be underestimated. The in situ SERS spectra of Ag@TiO2 show a clear bell-shaped intensity–potential relation for the major bands of N719. A molecule-to-TiO2 charge-transfer resonance is tentatively attributed to account for such a phenomenon. Under the influence of such a charge-transfer resonance, valuable information about the N719–TiO2 interaction as well as the intramolecular deformation of N719 is obtained.
Co-reporter:Yuzhuan Su ; Jiawei Yan ; Miangang Li ; Meng Zhang ;Bingwei Mao
The Journal of Physical Chemistry C 2013 Volume 117(Issue 1) pp:205-212
Publication Date(Web):December 10, 2012
DOI:10.1021/jp3079919
We have carried out differential capacitance measurements and in-situ scanning tunneling microscope (STM) characterizations to investigate the effect of the length of alkyl side chains on an electric double layer of Au(100)/imidazolium-based ionic liquids interface. In ionic liquids consisting of BMI+ cation (1-butyl-3-methylimidazolium), differential capacitance curves present an obvious bell-shaped feature. In ionic liquids with PMI+ (1-methyl-3-propylimidazolium) or OMI+ (1-methyl-3-octylimidazolium) cations, the rising of capacitance from about −0.5 V disturbs the bell-shaped feature. In-situ STM characterizations reveal the generality of surface etching and micelle-like adsorption of imidazolium cations on Au(100) at potential around the peaks of the bell-shaped feature, demonstrating that the potential of zero charge (PZC) should locate at the potential close to the peaks. Because of the longer side chain length and stronger interaction with Au(100) substrate, an extra capacitance peak appears at the potential as negative as −1.65 V in OMIPF6 and a corresponding order–disorder transformation of OMI+ cation adlayer is revealed by STM, indicating a correlation between differential capacitance curve and STM.
Co-reporter:Xiao Zhang, Yun-Xin Zhong, Jia-Wei Yan, Yu-Zhuan Su, Meng Zhang and Bing-Wei Mao
Chemical Communications 2012 vol. 48(Issue 4) pp:582-584
Publication Date(Web):22 Nov 2011
DOI:10.1039/C1CC15463J
High quality AFM force curves are presented with detailed potential dependent layering behaviors of the ionic liquid molecules, from which charged interior and neutral exterior layers are distinguished. The electric double layer is confined within the interior layers of one to two molecular size within the potential range of up to 1 V negative of the PZC.
Co-reporter:Xue-Qin Zhao, Jie Wu, Jing-Hong Liang, Jia-Wei Yan, Zhi Zhu, Chaoyong James Yang, and Bing-Wei Mao
The Journal of Physical Chemistry B 2012 Volume 116(Issue 37) pp:11397-11404
Publication Date(Web):August 28, 2012
DOI:10.1021/jp303518b
With widespread applications in biosensors, diagnostics, and therapeutics, much investigation has been made in the structure of the G-quadruplexes and mechanism of their interactions with protein targets. However, in view of AFM based single-molecule force spectroscopic (SMFS) studies of G-quadruplex systems, only bimolecular approaches have been employed. In this article, we present an improved dual-labeling approach for surface immobilization of G-quadruplex DNA apatmers for investigation of intramolecular interaction from an integral unimolecular G-quadruplex system. The melting force of HJ24 G-quadruplex aptamer in the presence of K+ has been successfully measured. It has been found that dynamic equilibrium exists between unfolding and folding structures of the HJ24 aptamer even in pure water. We also investigated the interactions between the HJ24 aptamer and its target protein (Shp2) under the same solution condition. The HJ24/Shp2 unbinding force in the absence of K+, 42.0 pN, is about 50% smaller than that in the presence of K+, 61.7 pN. The great reduction in force in the absence of K+ suggests that the stability of G-quadruplex secondary structure is important for a stable HJ24/Shp2 binding. The methodology developed and demonstrated in this work is applicable for studying the stability of secondary structures of other unimolecular G-quadruplex aptamers and their interactions with target proteins.
Co-reporter:Zheng-Lian Peng, Zhao-Bin Chen, Xiao-Yi Zhou, Yan-Yan Sun, Jing-Hong Liang, Zheng-Jiang Niu, Xiao-Shun Zhou, and Bing-Wei Mao
The Journal of Physical Chemistry C 2012 Volume 116(Issue 41) pp:21699-21705
Publication Date(Web):September 19, 2012
DOI:10.1021/jp3069046
In this work, the single molecule conductance of alkanedicarboxylic acid (HOOC–(CH2)n–COOH, n = 1–5) binding to Cu and Ag electrodes is systematically studied by using the electrochemical jump-to-contact scanning tunneling microscopy break junction approach (ECSTM-BJ). The results show that the conductance depends on molecular length and the electrode materials, which give a decay constant βN of 0.95 ± 0.02 per (−CH2) unit for Cu electrodes and 0.71 ± 0.03 for Ag electrodes. The contact conductance shows the order of Gn=0,Cu > Gn=0,Ag. These differences can be attributed to the different electronic coupling efficiencies between molecules and electrodes. The conductance of ultrashort molecular junctions is also studied using oxalic acid as the target molecule, the results revealing that the through-space mechanism (TS) should be considered when the distance between two electrodes is very short. The present work demonstrates that electrode materials play an important role on the molecular conductance, contact conductance, and also the tunneling decay constant.
Co-reporter:Zai-Wen Zhu, Yang Wang, Xuan Zhang, Chun-Feng Sun, Mian-Gang Li, Jia-Wei Yan, and Bing-Wei Mao
Langmuir 2012 Volume 28(Issue 41) pp:14739-14746
Publication Date(Web):September 18, 2012
DOI:10.1021/la303047v
We present electrochemical impedance spectroscopic (EIS) and two-chamber AFM investigations of the electrical and mechanical properties of solvent-containing nano-BLMs suspended on chip-based nanopores of diameter of 200, 400, and 700 nm. The chips containing nanoporous silicon nitride membranes are fabricated based on low-cost colloidal lithography with low aspect ratio of the nanopores. BLMs of DPhPC lipid molecules are constructed across the nanopores by the painting method. Two equivalent circuits are compared in view of their adequacy in description of the EIS performances of the nano-BLMs and more importantly the structures associated with the nano-BLMs systems. The BLM resistance and capacitance as well as their size and time dependence are studied by EIS. The breakthrough forces, elasticity in terms of apparent spring constant, and lateral tension of the solvent-containing nano-BLMs are investigated by AFM force measurements. The exact relationship of the breakthrough force of the nano-BLM as a function of pore size is revealed. Both EIS and AFM studies show increasing lifetime and mechanical stability of the nano-BLMs with decreasing pore size. Finally, the robust 200 nm diameter nanopores are used to accommodate functional BLMs containing DPhPC lipid molecules and gramicidins by using a painting method with drop of mixture solutions of DPhPC and gramicidins. EIS investigation of the functional nano-BLMs is also performed.
Co-reporter:Xiao-Shun Zhou ; Ling Liu ; Philippe Fortgang ; Anne-Sophie Lefevre ; Anna Serra-Muns ; Noureddine Raouafi ; Christian Amatore ; Bing-Wei Mao ; Emmanuel Maisonhaute ;Bernd Schöllhorn
Journal of the American Chemical Society 2011 Volume 133(Issue 19) pp:7509-7516
Publication Date(Web):April 25, 2011
DOI:10.1021/ja201042h
We measured single-molecule conductances for three different redox systems self-assembled onto gold by the STMBJ method and compared them with electrochemical heterogeneous rate constants determined by ultrafast voltammetry. It was observed that fast systems indeed give higher conductance. Monotonous dependency of conductance on potential reveals that large molecular fluctuations prevent the molecular redox levels to lie in between the Fermi levels of the electrodes in the nanogap configuration. Electronic coupling factors for both experimental approaches were therefore evaluated based on the superexchange mechanism theory. The results suggest that coupling is surprisingly on the same order of magnitude or even larger in conductance measurements whereas electron transfer occurs on larger distances than in transient electrochemistry.
Co-reporter:Yong-Chun Wang, Cong-Bin Lin, Jian-Jia Su, Ying-Ming Ru, Qiao Wu, Zhao-Bin Chen, Bing-Wei Mao, and Zhao-Wu Tian
Analytical Chemistry 2011 Volume 83(Issue 12) pp:4930
Publication Date(Web):May 11, 2011
DOI:10.1021/ac200656u
In this paper, we present an electrochemically driven large amplitude pH alteration method based on a serial electrolytic cell involving a hydrogen permeable bifacial working electrode such as Pd thin foil. The method allows solution pH to be changed periodically up to ±4∼5 units without additional alteration of concentration and/or composition of the system. Application to the acid–base driven cyclic denaturation and renaturation of 290 bp DNA fragments is successfully demonstrated with in situ real-time UV spectroscopic characterization. Electrophoretic analysis confirms that the denaturation and renaturation processes are reversible without degradation of the DNA. The serial electrolytic cell based electrochemical pH alteration method presented in this work would promote investigations of a wide variety of potential-dependent processes and techniques.
Co-reporter:Xiao-Shun Zhou, Jing-Hong Liang, Zhao-Bin Chen, Bing-Wei Mao
Electrochemistry Communications 2011 Volume 13(Issue 5) pp:407-410
Publication Date(Web):May 2011
DOI:10.1016/j.elecom.2011.02.005
In this communication, we demonstrate an approach for conductance measurement of single molecular junctions with different metallic electrodes based on STM-break junction (STM-BJ) technique with electrochemical strategy. Conductance of molecular junctions formed with succinic acid using Cu, Ag and Au as metal electrodes has been systemically studied, the values being 18.6, 13.2 and 5.6 nS for Cu, Ag and Au electrodes, respectively. The observed decrease in conductance indicates the weakening of electronic coupling efficiency at the electrode–molecule contacts in the order of Cu > Ag > Au, which should be taken into account in evaluating the molecular conductance in the junctions.Research highlights► New method to measure single molecule conductance with different metallic electrodes. ► Electrodes forming molecular junctions are in-situ created by electrochemical STM-BJ. ► Cu, Ag and Au binding to succinic acid display a conductance order of Cu > Ag > Au. ► Conductances show different electronic couplings of electrode-molecule contacts.
Co-reporter:Gang Liu;Chunfeng Sun;Di Li;Shiping Song;Bingwei Mao;Chunhai Fan;Zhongqun Tian
Advanced Materials 2010 Volume 22( Issue 19) pp:2148-2150
Publication Date(Web):
DOI:10.1002/adma.200903590
Co-reporter:Yi-Min Wei ; Yong-Chun Fu ; Jia-Wei Yan ; Chun-Feng Sun ; Zhan Shi ; Zhao-Xiong Xie ; De-Yin Wu
Journal of the American Chemical Society 2010 Volume 132(Issue 23) pp:8152-8157
Publication Date(Web):May 25, 2010
DOI:10.1021/ja1021816
Fe electrodeposition on Au(111) and Au(100) in BMIBF4 ionic liquid is found to form hitherto unreported shape-ordered nanoscale morphologies of pseudorods and pseudosquare rings, respectively, both composed of grains of 4−7 nm. The manner of growth of the square rings is a ring-on-ring structure with enlarging side length and slightly protruding four corners. The generality of the growth mechanism is verified by the formation of almost exactly the same shape-ordered Fe nanostructures on Pt, i.e., pseudorod structure on Pt(111) and pseudosquare rings Pt(100). These structures are explained within the framework of magnetostatic interactions of spontaneously magnetized grains under crystallographic constraint of the substrate surface, which result in an antiparallel arrangement in magnetization of the grains at pseudorods and magnetic flux closure at the pseudosquare rings. The closed magnetic flux further leads to magnetic field-enhanced growth at the four corners and the outer peripheries of the pseudosquare rings. The observed shape-ordering of the Fe thin film serves as a paradigm of magnetostatic coupling, in which the roles of ionic liquid as surfactant and magnetic media may not be underestimated. The present work adds a new dimension to electrodeposition in ionic liquid, by which new magnetic film structures may be expected.
Co-reporter:Yu-Zhuan Su;Yong-Chun Fu;Yi-Min Wei;Dr. Jia-Wei Yan ; Bing-Wei Mao
ChemPhysChem 2010 Volume 11( Issue 13) pp:2764-2778
Publication Date(Web):
DOI:10.1002/cphc.201000278
Abstract
The last decade has witnessed remarkable advances in interfacial electrochemistry in room-temperature ionic liquids. Although the wide electrochemical window of ionic liquids is of primary concern in this new type of solvent for electrochemistry, the unusual bulk and interfacial properties brought about by the intrinsic strong interactions in the ionic liquid system also substantially influence the structure and processes at electrode/ionic liquid interfaces. Theoretical modeling and experimental characterizations have been indispensable in reaching a microscopic understanding of electrode/ionic liquid interfaces and in elucidating the physics behind new phenomena in ionic liquids. This Minireview describes the status of some aspects of interfacial electrochemistry in ionic liquids. Emphasis is placed on high-resolution and molecular-level characterization by scanning tunneling microscopy and vibrational spectroscopies of interfacial structures, and the initial stage of metal electrodeposition with application in surface nanostructuring.
Co-reporter:Dr. Jing-Hua Tian;Yang Yang;Dr. Xiao-Shun Zhou;Dr. Bernd Schöllhorn;Dr. Emmanuel Maisonhaute;Zhao-Bin Chen;Fang-Zu Yang; Yong Chen; Christian Amatore; Bing-Wei Mao; Zhong-Qun Tian
ChemPhysChem 2010 Volume 11( Issue 13) pp:2745-2755
Publication Date(Web):
DOI:10.1002/cphc.201000284
Abstract
Atomic wires (point contacts) and molecular junctions are two fundamental units in the fields of nanoelectronics and devices. This Minireview introduces our recent approaches aiming to develop versatile methods to fabricate and characterize these unique metallic and molecular structures reliably. Electrochemical methods are coupled with mechanically controllable break junction (EC-MCBJ) or scanning tunneling microscopy (STM) break junction (EC-STMBJ) methods to fabricate metallic point contacts and metal/molecule/metal junctions. With the designed electrodeposition method, the metal of interest (e.g. Au, Cu, Fe or Pd) is deposited in a controlled way on the original electrode pair, on a chip for MCBJ or on the STM tip, to make the metallic contact. Then, various metal atomic wires and molecular junctions can be fabricated and characterized systematically. Herein, we measured the quantized conductance through the construction of histograms of these metal atomic point contacts and of single molecules including benzene-1,4-dithiol (BDT), ferrocene-bisvinylphenylmethyl dithiol (Fc-VPM), 4,4′-bipyridine (BPY), 1,2-di(pyridin-4-yl)ethene (BPY-EE), and 1,2-di(pyridin-4-yl)ethane (BPY-EA). Finally, we briefly discussed the future of EC-MCBJ and EC-STM for nanoelectronics and devices, for example, for the formation of heterogeneous metal-based atomic point contacts and molecular junctions.
Co-reporter:Yong-Chun Fu ; Yu-Zhuan Su ; De-Yin Wu ; Jia-Wei Yan ; Zhao-Xiong Xie
Journal of the American Chemical Society 2009 Volume 131(Issue 41) pp:14728-14737
Publication Date(Web):September 24, 2009
DOI:10.1021/ja902373q
Neutral inorganic molecules are generally weak in surface adsorption and intermolecular interactions. Self-assembly of such types of molecule would provide valuable information about various interactions. At electrochemical interfaces, the relative strength of these interactions may be modified through control of electrode potential and electrolyte, which may lead to the discovery of new structures and new phenomena. However, studies of this nature are as yet lacking. In this work, we consider the covalent-bound semimetal compound molecules, XCl3 (X = Sb, Bi), as model systems of neutral inorganic molecules to investigate their self-assembly at electrochemical interfaces under a high ionic atmosphere. To fulfill such investigations, in situ STM and cyclic voltammetry are employed, and comparative experiments are performed on Au(111) in ionic liquids as well as aqueous solutions with high ionic strength. In the room temperature ionic liquid of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF4), potential-dependent partial charge transfer between the Au surface and XCl3 molecules creates a molecule−surface interaction and provides the driving force for adsorption of the molecules. Supramolecular aggregations of adsorbed XCl3 are promoted through chlorine-based short-range intermolecular correlation under crystallographic constraint, while repulsive Coulombic interactions created between the partially charged aggregations facilitate their long-range ordering. For SbCl3 molecules, hexagonally arranged 6- or 7-member clusters are formed at 0.08 to −0.2 V (vs Pt), which assemble into a secondary (√31 × √31)R8.9° structure. For BiCl3 molecules, both the 6-membered hexagonal and 3-membered trigonal clusters are formed in the narrow potential range −0.3 to −0.35 V, and are also arranged into an ordered secondary structure. Comparative studies were performed with SbCl3 in concentrated aqueous solutions containing 2 M HCl to simulate the strong ionic strength of the ionic liquid. Almost identical 6-/7-member clusters and long-range (√31 × √31)R8.9° structure are observed at −0.1 V, demonstrating the crucial role of strong ionic strength in such supramolecular aggregations. However, such supramolecular structures are modified and eventually destroyed as ionic strength is further increased by addition of NaClO4 up to 6 M. The destructive changes of the supramolecular structures are attributed to the alteration of ion distribution in the double layer from cation-rich to anion-rich at increasing NaClO4 concentration. This modifies and eventually breaks the balance of intermolecular and molecule−electrolyte interactions. Finally, the dynamic behavior of the SbCl3 assembly is investigated down to molecular level. It has been demonstrated that the initial stage of assembly follows a two-dimensional nucleation and growth mechanism and has a potential-dependent rate that is closely related to the surface mobility of the SbCl3 clusters. There is a probability that clusters can escape from an existing assembly domain or insert into a vacancy in such a domain while they can also relax with central or ring members in a dynamic fashion. These phenomena indirectly reflect the dynamic properties of cations from electrolytes at the interface. The rich information contained in the self-assembly behavior of SbCl3 and BiCl3 demonstrates that neutral inorganic molecules can be employed for fundamental studies of a variety of interesting issues, especially the interplay of various interfacial interactions.
Co-reporter:Yu-Zhuan Su;Yong-Chun Fu;Jia-Wei Yan Dr.;Zhao-Bin Chen Dr.
Angewandte Chemie International Edition 2009 Volume 48( Issue 28) pp:5148-5151
Publication Date(Web):
DOI:10.1002/anie.200900300
Co-reporter:Yu-Zhuan Su;Yong-Chun Fu;Jia-Wei Yan Dr.;Zhao-Bin Chen Dr.
Angewandte Chemie 2009 Volume 121( Issue 28) pp:5250-5253
Publication Date(Web):
DOI:10.1002/ange.200900300
Co-reporter:Xuan Zhang;Zaiwen Zhu;Chunfeng Sun;Feng Zhu;Zhongzi Luo
Microchimica Acta 2009 Volume 167( Issue 1-2) pp:
Publication Date(Web):2009 November
DOI:10.1007/s00604-009-0216-5
Nanoporous membranes provide a basis for constructing non-supported biomembranes, which enable biological processes such as ion and molecule transport through the biomembranes to be investigated under physiological conditions with ease of control. Preparation of such membranes usually requires expensive equipments and extensive experiences. In this paper, we provide a cheap and controllable scheme of high volume fabricating suspended nanoporous Si3N4 membranes on a Si wafer by combined colloidal lithography and standard Si fabrication technology including low cost ICP etching and anisotropic Si wet-etch. Si3N4 layers are grown on Si wafers. Polystyrene particles of 200-nm-diameter are then monodispersed on the Si3N4 layers based on electrostatic repulsions with an average density of 2%. This is followed by Cr masking, ICP etching and Si wet-etch processes to form suspended Si3N4 membranes with 200-nm-deep nanopores through the membranes. The well-aligned cylindrical nanopores have a low aspect radio of ca. 0.9, which would be beneficial to forming stable suspended lipid bilayers.
Co-reporter:Xiao-Mi Xu, Hui-Ping Zhong, Hai-Ming Zhang, Yi-Rong Mo, Zhao-Xiong Xie, La-Sheng Long, Lan-Sun Zheng, Bing-Wei Mao
Chemical Physics Letters 2004 Volume 386(4–6) pp:254-258
Publication Date(Web):11 March 2004
DOI:10.1016/j.cplett.2004.01.071
Abstract
Silver adlayer can be formed on Au single crystal surfaces by surface-induced dissociation of Ag coordinated complex precursor [(dptap–Ag)2](NO3)2, where dptap denotes 2-(2-pyridylimino)-2H-1,2,4-thia-diazolo [2,3-a] pyridine, by immersing in the acetonitrile containing such a complex. STM study shows (4 × 4) and (√2×5√2) adlayer structures on Au(1 1 1) and Au(1 0 0), respectively, resembling the Ag UPD adlayer structures on the corresponding Au single crystal electrodes at high underpotential shifts. The formation of the Ag adlayer is confirmed by XPS study, and computational calculations suggest a mechanism of surface-induced weakening and dissociation of the (electrostatic) Ag–N bond by charge transfer from the Au surface.
Co-reporter:J.W. Yan, Z.X. Xie, Z.X. Cao, C.J. Zhou, J.Y. Kang, B.W. Mao
Chemical Physics Letters 2003 Volume 373(5–6) pp:575-579
Publication Date(Web):28 May 2003
DOI:10.1016/S0009-2614(03)00649-3
Abstract
This Letter presents a study on the oxidation of electrochemically deposited Sn monolayer on Au(1 1 1) surface and STM tip-induced reduction of as-prepared ultra thin SnO film. A threshold bias of 0.6 V (tip negative) at a low tunneling current of ∼50 pA is required to image the as-formed SnO thin film by STM, typical of a semiconductor characteristic. Increasing the tunneling current to ∼2 nA leads to the reduction of the SnO back to Sn. Based on the energy level calculation for the SnO, a mechanism involving direct electron tunneling is proposed to account for the tip-induced reduction.
Co-reporter:Meng Zhang, Li-Juan Yu, Yi-Fan Huang, Jia-Wei Yan, Guo-Kun Liu, De-Yin Wu, Zhong-Qun Tian and Bing-Wei Mao
Chemical Communications 2014 - vol. 50(Issue 94) pp:NaN14743-14743
Publication Date(Web):2014/10/06
DOI:10.1039/C4CC06269H
We employ, for the first time, a shell-isolated nanoparticle-enhancement strategy to extend Raman spectroscopy studies to single crystal electrode surfaces in ionic liquids, and combine density functional theory (DFT) calculations to elucidate the structural details of the imidazolium-based ionic liquid–Au single crystal electrode interfaces.
Co-reporter:Xiao Zhang, Yun-Xin Zhong, Jia-Wei Yan, Yu-Zhuan Su, Meng Zhang and Bing-Wei Mao
Chemical Communications 2012 - vol. 48(Issue 4) pp:NaN584-584
Publication Date(Web):2011/11/22
DOI:10.1039/C1CC15463J
High quality AFM force curves are presented with detailed potential dependent layering behaviors of the ionic liquid molecules, from which charged interior and neutral exterior layers are distinguished. The electric double layer is confined within the interior layers of one to two molecular size within the potential range of up to 1 V negative of the PZC.
Co-reporter:Yi-Min Wei, Jing-Hong Liang, Zhao-Bin Chen, Xiao-Shun Zhou, Bing-Wei Mao, Oscar A. Oviedo and Ezequiel P. M. Leiva
Physical Chemistry Chemical Physics 2013 - vol. 15(Issue 30) pp:NaN12465-12465
Publication Date(Web):2013/03/27
DOI:10.1039/C3CP50473E
This work describes jump-to-contact STM-break junction experiments leading to novel statistical distribution of last-step length associated with conductance of a single atom contact. Last-step length histograms are observed with up to five for Fe and three for Cu peaks at integral multiples close to 0.075 nm, a subatomic distance. A model is proposed in terms of gliding from a fcc hollow-site to a hcp hollow-site of adjacent atomic planes at 1/3 regular layer spacing along with tip stretching to account for the multiple subatomic step-length behavior.
Co-reporter:Li-Qiang Xie, Tai-Yang Zhang, Liang Chen, Nanjie Guo, Yu Wang, Guo-Kun Liu, Jia-Rui Wang, Jian-Zhang Zhou, Jia-Wei Yan, Yi-Xin Zhao, Bing-Wei Mao and Zhong-Qun Tian
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 27) pp:NaN18118-18118
Publication Date(Web):2016/06/09
DOI:10.1039/C6CP01723A
Organolead halide perovskites exhibit superior photoelectric properties, which have given rise to the perovskite-based solar cells whose power conversion efficiency has rapidly reached above 20% in the past few years. However, perovskite-based solar cells have also encountered problems such as current–voltage hysteresis and degradation under practical working conditions. Yet investigations into the intrinsic chemical nature of the perovskite material and its role on the performance of the solar cells are relatively rare. In this work, Raman spectroscopy is employed together with CASTEP calculations to investigate the organic–inorganic interactions in CH3NH3PbI3 and CH3NH3PbBr3−xClx perovskite single crystals with comparison to those having ammonic acid as the cations. For Raman measurements of CH3NH3PbI3, a low energy line of 1030 nm is used to avoid excitation of strong photoluminescence of CH3NH3PbI3. Raman spectra covering a wide range of wavenumbers are obtained, and the restricted rotation modes of CH3–NH3+ embedded in CH3NH3PbBr3 (325 cm−1) are overwhelmingly stronger over the other vibrational bands of the cations. However, the band intensity diminishes dramatically in CH3NH3PbBr3−xClx and most of the bands shift towards high frequency, indicating the interaction with the halides. The details of such an interaction are further revealed by inspecting the band shift of the restricted rotation mode as well as the C–N, NH3+ and CH3 stretching of the CH3NH3+ as a function of Cl composition and length of the cationic ammonic acids. The results show that the CH3NH3+ interacts with the PbX3− octahedral framework via the NH3+ end through N+–H⋯X hydrogen bonding whose strength can be tuned by the composition of halides but is insensitive to the size of the organic cations. Moreover, an increase of the Cl content strengthens the hydrogen bonding and thus blueshifts the C–N stretching bands. This is due to the fact that Cl is more electronegative than Br and an increase of the Cl content decreases the lattice constant of the perovskite. The findings of the present work are valuable in understanding the role of cations and halides in the performance of MAPbX3-based perovskite solar cells.
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