Control of Multi-Fluorination Number and Position in D-π-A Type Polymers and Their Impact on High-Voltage Organic Photovoltaics.

Exploring the structure-performance relationship of high-voltage organic solar cells (OSCs) is significant for pushing material design and promoting photovoltaic performance. Herein, we chose a D-π-A type polymer composed of 4,8-bis(thiophene-2-yl)-benzo[1,2-b:4,5-b']dithiophene (BDT-T) and benzotriazole (BTA) units as the benchmark to investigate the effect of the fluorination number and position of the polymers on the device performance of the high-voltage OSCs, with a benzotriazole-based small molecule (BTA3) as the acceptor. F00, F20, and F40 are the polymers with progressively increasing F atoms on the D units, while F02, F22, and F42 are the polymers with further attachment of F atoms to the BTA units based on the above three polymers. Fluorination positively affects the molecular planarity, dipole moment, and molecular aggregations. Our results show that VOC increases with the number of fluorine atoms, and fluorination on the D units has a greater effect on VOC than on the A unit. F42 with six fluorine atom substitutions achieves the highest VOC (1.23 V). When four F atoms are located on the D units, the short-circuit current (JSC) and fill factor (FF) plummet, and before that, they remain almost constant. The drop in JSC and FF in F40- and F42-based devices may be attributed to inefficient charge transfer and severe charge recombination. The F22:BTA3 system achieves the highest power conversion efficiency of 9.5% with a VOC of 1.20 V due to the excellent balance between the photovoltaic parameters. Our study provides insights for the future application of fluorination strategies in molecular design for high-voltage organic photovoltaics.

The Development of Quinoxaline-Based Electron Acceptors for High Performance Organic Solar Cells.

In the recent advances of organic solar cells (OSCs), quinoxaline (Qx)-based nonfullerene acceptors (QxNFAs) have attracted lots of attention and enabled the recorded power conversion efficiency approaching 20%. As an excellent electron-withdrawing unit, Qx possesses advantages of many modifiable sites, wide absorption range, low reorganization energy, and so on. To develop promising QxNFAs to further enhance the photovoltaic performance of OSCs, it is necessary to systematically summarize the QxNFAs reported so far. In this review, all the focused QxNFAs are classified into five categories as following: SM-Qx, YQx, fused-YQx, giant-YQx, and polymer-Qx according to the molecular skeletons. The molecular design concepts, relationships between the molecular structure and optoelectronic properties, intrinsic mechanisms of device performance are discussed in detail. At the end, the advantages of this kind of materials are summed up, the molecular develop direction is prospected, the challenges faced by QxNFAs are given, and constructive solutions to the existing problems are advised. Overall, this review presents unique viewpoints to conquer the challenge of QxNFAs and thus boost OSCs development further toward commercial applications.

Effect of Number and Position of Chlorine Atoms on the Photovoltaic Performance of Asymmetric Nonfullerene Acceptors.

It has been well proved that the introduction of halogen can effectively modify the optoelectronic properties of classic symmetric nonfullerene acceptors (NFAs). However, the relevant studies for asymmetric NFAs are limited, especially the effect of halogen substitution number and position on the photovoltaic performance is not clear. In this work, four asymmetric NFAs with A-D-A1-A2 structure are developed by tuning the number and position of chlorine atoms on the 1,1-dicyanomethylene-3-indanone end groups, namely, A303, A304, A305, and A306. The related NFAs show progressively deeper energy levels and red-shifted absorption spectra as the degree of chlorination increases. The PM6:A306-constructed organic solar cells (OSCs) give a champion power conversion efficiency (PCE) of 13.03%. This is mainly ascribed to the most efficient exciton dissociation and collection, suppressed charge recombination, and optimal morphology. Moreover, by alternating the substitution position, the PM6:A305-based device yielded a higher PCE of 12.53% than that of PM6:A304 (12.05%). This work offers fresh insights into establishing excellent asymmetric NFAs for OSCs.

Tell me your position: Distantly supervised biomedical entity relation extraction using entity position marker.

A significant amount of textual data has been produced in the biomedical area recently as a result of the advancement of biomedical technologies. Large-scale biomedical data can be automatically obtained with the help of distant supervision. However, the noisy data brought by distant supervision methods makes relation extraction tasks more difficult. Previous work has focused more on how to restore mislabeled relationships, but little attention has been paid to the importance of labeled entity locations for relationship extraction tasks. In this paper, we present a "four-stage" model based on BioBERT and Multi-Instance Learning by using entity position markers. Firstly, the sentence is marked with position. Secondly, BioBERT, a biomedical pre-trained language model, is used in the final sentence feature vector representation not only with the global position marker but also with the start and end marker of both the head and tail entity. Thirdly, the aggregation of sentence vectors in the bag is used as the vector feature of the bag by three aggregation methods, and the performance of different sentence feature vectors combined with different bag encoding methods is discussed. At last, relation classification is performed at the bag level. According to experimental results, the presented model significantly outperforms all baseline models and contributes to noise reduction. In addition, different bag encoding methods need to match corresponding sentence encoding representation to achieve the best performance.

Tricyclic or Pentacyclic D Units: Design of D-π-A-Type Copolymers for High VOC Organic Photovoltaic Cells.

Although there are several electron-donating (D) units, only the classic benzo[1,2-b:4,5-b']dithiophenes (BDT) unit was utilized to develop D-π-A-type copolymers for high-voltage organic photovoltaic (OPV) cells. Hence, in this work, we chose two tricyclic D units, BDT and benzo[1,2-b:4,5-b']difurans (BDF), together with one pentacyclic ring, dithieno[2,3-d;2',3'-d']benzo[1,2-b;4,5-b']dithiophenes (DTBDT), to comprehensively study the effect of different D units on the optoelectronic properties and photovoltaic performance. By copolymerized with the benzo[1,2,3]triazole (BTA) electron-accepting unit, the final copolymers J52-Cl, F11, and PE52 were combined with a nonfullerene acceptor (NFA) F-BTA3 according to the "Same-A-Strategy." As we preconceived, all the three single-junction OPV cells can obtain high open-circuit voltage (VOC) over 1.10 V. Although the tricyclic D unit of BDF exhibits a slightly lower VOC of 1.12 V because of its mildly larger energy loss of 0.698 eV, its higher carrier mobilities and exciton dissociation efficiency strikingly boost the short-circuit current (JSC) and fill factor, which contribute to a comparable PCE of 10.04% with J52-Cl (10.10%). However, the DTBDT-based polymer PE52 shows the worst performance with a PCE of 6.78% and a VOC of 1.14 V, owing to the higher bimolecular recombination and disordered molecular stacking. Our results indicate that tricyclic D units should be a better choice for constructing D-π-A-type polymers for high-voltage photovoltaic materials than the pentacyclic analogues.

Fabrication of High VOC Organic Solar Cells with a Non-Halogenated Solvent and the Effect of Substituted Groups for "Same-A-Strategy" Material Combinations.

We report a class of high-voltage organic solar cells (OSCs) processed by the environmentally friendly solvent tetrahydrofuran (THF), where four benzotriazole (BTA)-based p-type polymers (PE31, PE32, PE33, and J52-Cl) and a BTA-based small molecule BTA5 are applied as p-type and n-type materials, respectively, according to "Same-A-Strategy" (SAS). The single-junction OSCs based on all four material blends exhibit a high open-circuit voltage (VOC) above 1.10 V. We systematically study the impact of the three different substituents (-OCH3, -F, -Cl) on the BTA unit of the polymer donors. Interestingly, PE31 containing the unsubstituted BTA unit shows the efficient hole transfer and more balanced charge mobilities, thus leading to the highest power conversion efficiency (PCE) of 10.08% with a VOC of 1.11 V and a JSC of 13.68 mA cm-2. Due to the upshifted highest electron-occupied molecular orbital (HOMO) level and the weak crystallinity of the methoxy-substituted polymer PE32, the resulting device shows the lowest PCE of 7.40% with a slightly decreased VOC of 1.10 V. In addition, after the chlorination and fluorination, the HOMO levels of the donor materials PE33 and J52-Cl are gradually downshifted, contributing to increased VOC values of 1.16 and 1.21 V, respectively. Our results prove that an unsubstituted p-type polymer can also afford high voltage and promising performance via non-halogenated solvent processing, which is of great significance for simplifying the synthesis steps and realizing the commercialization of OSCs.

Early Diagnosis of Brain Injury in Premature Infants Based on Amplitude-Integrated EEG Scoring System.

Analyzing and discussing the relationship between brain injury in preterm infants and related risk factors can provide evidence for perinatal prevention and early intervention of brain injury in preterm infants, thereby improving the quality of life of preterm infants. This paper selects term preterm infants diagnosed with preterm infant asphyxia in the NICU of a university's First Affiliated Hospital from January 2018 to February 2019 as the research object. In addition, healthy term infants born at the same time in the obstetric department of this hospital are selected as the control group. Both groups of premature infants were monitored for brain function within 6 hours after birth. The aEEG results range from background activity (continuous normal voltage, discontinuous normal voltage, burst suppression, continuous low voltage, and plateau) and sleep-wake cycle (no sleep-wake cycle, immature, and mature sleep-wake cycle) to epileptic activity (single seizures, recurrent seizures, and status epilepticus), three aspects to judge. Statistical analysis uses SPSS 17.0 software. Amplitude-integrated EEG is a simplified form of continuous EEG recording. The trace of the trace represents the voltage change signal of the entire EEG background activity, which can reflect the EEG amplitude, frequency, burst-inhibition, and other pieces of information. aEEG can reflect the degree of HIE lesions in premature infants and the long-term prognosis. It is easy to operate and effective in diagnosis and can be continuously monitored. It is worthy of clinical popularization. There is a good correlation between the expression of EEG and biomarkers. Combining multiple methods can diagnose HIE earlier and evaluate the prognosis.

Gradual Fluorination on the Phenyl Side Chains for Benzodithiophene-Based Linear Polymers to Improve the Photovoltaic Performance.

To study the impact of introducing fluorine atoms onto the conjugated phenyl side chains of benzo[1,2-b:4,5-b']dithiophene (BDT)-based copolymers, three novel donor-π-acceptor (D-π-A) alternative polymers PE40, PE42, and PE44 were designed and synthesized. The phenyl-substituted-BDT, thieno[3,2-b]thiophene, and benzo[d][1,2,3]triazole (BTA) served as the donor, π-bridge, and acceptor units, respectively, to enable linear polymer backbones. When introducing two or four fluorine atoms into the phenyl side units of PE40, the polymers PE42 and PE44 demonstrate a gradual decrease of energy levels and an increase of crystallinity in the pristine and blend films. It was noted that the increase in fluorine atoms gradually improved the performance parameters of polymer solar cells (PSCs) with Y6 as the acceptor. The PE40:Y6 device yielded a power conversion efficiency (PCE) of up to 7.07% with a short-circuit (JSC) of 21.36 mA cm-2, an open-circuVOC) of 0.65 V, and a fill factor (FF) of 0.51, and PE42:Y6 exhibited a better PCE of 10.11% (JSC = 23.25 mA cm-2, VOC = 0.74 V, and FF = 0.59), while PE44:Y6 exhibited the best PCE of 13.62% (JSC = 25.29 mA cm-2, VOC = 0.82 V, and FF = 0.66). The suitable energy offsets between the donor and the acceptor, high and balanced charge-carrier mobility, and the optimal morphology of the blend film contributed to the high performance of PE44:Y6 combination. Our results demonstrate that introducing more fluorine atoms onto the phenyl side units of BDT is a prospective approach to break the trade-offs between VOC, JSC, and FF, and finally improve the performance of PSCs.

The prevalence of spinal muscular atrophy carrier in China: Evidences from epidemiological surveys.

INTRODUCTION: Spinal muscular atrophy (SMA) was the second most fatal autosomal recessive hereditary disease in clinic. There had been no detailed study to characterize the prevalence of SMA carrier among people in China. So, we conducted a systematic review and meta-analysis to obtain a reliable estimation of the prevalence of SMA carrier to characterize its epidemiology for the first time. METHODS: We systematically searched for articles in kinds of important electronic databases, including PubMed, Embase, Wanfang Database and China National Knowledge Infrastructure (CNKI) to identify all relevant literatures about carrier rates of SMA in China. The prevalence was performed by forest plot choosing random effect models. The publication bias was evaluated by means of funnel plots and Egger test. The sensitivity analysis was carried out by the method of omitting any literature at a time. Combined with the results of subgroup analysis, the source of heterogeneity was also discussed absolutely. RESULTS: A total of 10 studies published between 2005 and 2016 were included in our analysis at last. The sample size ranged from 264 to 107,611 in included studies. The random effect models of meta-analysis showed that the overall carrier rate of SMA was 2.0% (95% confidence interval [CI], 1.7%-2.3%) in a heterogeneous set of studies (I = 64%). There was a gradual rise trend observed in the SMA carrier rate during the study period. The funnel plots and Egger test (Coef = 0.02, t = -0.45, P = .667 > .05) showed no obvious potential risk of publication bias. CONCLUSION: The overall carrying rate of SMA was high as 2.0% and may be on a slow upward trend. So it was recommended that the countries should take active and effective measures to roll out routine prenatal screening and health genetic counseling for SMA as early as possible. What is more, further studies also need to be conducted to explore the etiology and epidemic factors of SMA to better control the risk of this common birth defect.

Effects of Oxygen Atoms Introduced at Different Positions of Non-Fullerene Acceptors in the Performance of Organic Solar Cells with Poly(3-hexylthiophene).

With the development of large-area fabrication technologies for organic solar cells (OSCs), poly(3-hexylthiophene) (P3HT) is the best choice as a photovoltaic donor polymer because it can be easily synthesized in the scale of kilograms at low cost. However, non-fullerene acceptors (NFAs) matching with P3HT for high performance OSCs are very rare. Herein, by introducing oxygen atoms into the side chains or the fused-ring core of indaceno[1,2-b:5,6-b']dithiophene, we synthesized two new A2-A1-D-A1-A2 type NFAs, where benzotriazole (BTA) and 2-(1,1-dicyanomethylene)rhodanine were used as the bridged A1 and terminal A2, respectively. The final NFAs, named BTA43 and BTA53, show wider absorption spectra and enhanced intermolecular/intramolecular interaction in comparison with their analogue BTA3 without oxygen atoms. The photovoltaic devices based on P3HT:BTA43 and P3HT:BTA53 can achieve a high power conversion efficiency of 6.56 and 6.31%, respectively, which are obviously higher than that of BTA3 (5.64%). Our results provide a simple and effective strategy to design promising NFAs to pair with the classic photovoltaic polymer P3HT.

Exploring a Fused 2-(Thiophen-2-yl)thieno[3,2-b]thiophene (T-TT) Building Block to Construct n-Type Polymer for High-Performance All-Polymer Solar Cells.

In the field of all-polymer solar cells, exploring new electron-donating units (D) to match with electron-accepting units (A) is an important subject to promote the performance of D-A-type polymer acceptors. Herein, we developed a fused D unit 2-(thiophen-2-yl)thieno[3,2-b]thiophene (T-TT) derivated from the famous 2-(2-(thiophen-2-yl)vinyl)thiophene (TVT) unit. With classical naphthalene diimide (NDI) as A unit, the new D-A polymer PNDI-T-TT exhibits enhanced absorption coefficient, electron mobility, and miscibility with donor polymer in comparison with the analogous PNDI-TVT polymer. These advantages can be attributed to the enlarged conjugation and reduced rotamers due to the fused T-TT unit, leading to a stronger intermolecular interaction. When blending with the donor polymer PBDB-T, both NDI-based polymers can form better interpenetrating nanostructures than the corresponding blend films with the donor polymer J71. Finally, PBDB-T/PNDI-T-TT device achieves a power conversion efficiency of 6.1%, which is much higher than that of PBDB-T/PNDI-TVT device (4.24%). These results demonstrate that n-type polymer based on fused T-TT unit can ameliorate the absorption coefficient, molecular aggregation, and charge-carrier mobility and consequently achieve an improved photovoltaic performance in comparison with the classic TVT unit.

Changing the π-bridge from thiophene to thieno[3,2-b]thiophene for the D-π-A type polymer enables high performance fullerene-free organic solar cells.

For photovoltaic polymers with a D-π-A backbone, there are a great deal of D and A units, but the choice of π bridge is relatively limited and thiophene (T) is still the most effective one. Here, we utilize two D-π-A polymers, J52-FS with thiophene as the π bridge and PE2 with thieno[3,2-b]thiophene (TT) as the π bridge, to combine with a low band-gap non-fullenere Y6, respectively. The photovoltaic cells based on PE2:Y6 can realize a PCE of 13.50%, which is obviously higher than the 10.58% PCE of the J52-FS:Y6 analogue. Our work demonstrates that using TT as the π-bridge is a simple and promising approach to construct efficient photovoltaic polymers.

Bilayer Adsorption of Porphyrin Molecules Substituted with Carboxylic Acid atop the NN4A Network Revealed by STM and DFT.

Bottom-up technology is a bridge connecting a two-dimensional (2D) monolayer structure with a three-dimensional (3D) bulk structure. From 2D to 3D, it helps us to understand the driving force of an organization process to control the molecular arrangement in the 3D phase. Here, we aimed at the fabrication of multilayer nanostructures on solid substrates. Bis(3,5-diacidic)diazobenzene (NN4A) was chosen as one molecule because of its photosensitive azo group and carboxylic group possessing hydrogen bonding effect, while porphyrin molecules composed of different numbers and positions of carboxylic acid groups were used as the other component. It was found that the porphyrin molecules could adopt different adsorption configurations because of the influence of carboxylic groups, leading to different subsequent coassemblies on the solid surface. The NN4A/porphyrin systems underwent structural transformation when NN4A molecules were adsorbed on the highly oriented pyrolytic graphite surface with predeposited porphyrin. This work displayed an efficient method on the construction of multilayer nanostructures in the molecular surface engineering and provided a new way to construct 3D structures based on the molecular design.

Planar Benzofuran Inside-Fused Perylenediimide Dimers for High VOC Fullerene-Free Organic Solar Cells.

Bulk heterojunction organic solar cells based on perylenediimide (PDI) derivatives as electron acceptors have afforded high power conversion efficiency (PCE) but still lagged behind fullerene-based analogues. Design of novel molecular structures by adjusting the PDI ring and/or connection mode remains the breakthrough point to improve the photovoltaic performance. After introducing benzofuran at the inside bay positions and being linked with a single bond and a fluorene unit, mandatory planar PDI dimers were achieved and named FDI2 and F-FDI2. Both acceptors show high-lying LUMO energy levels and realize high VOC beyond 1.0 V when using the classic polymer of PBDB-T as an electron donor. However, FDI2 and F-FDI2 gave totally different photovoltaic performance with PCEs of 0.15 and 6.33%, respectively. The central fluorene linkage increased the miscibility of materials and ensured a much higher short-circuit current because of the formation of suitable phase separation. Our results demonstrated that utilizing the mandatory planar skeleton of PDI dimers is a simple and effective strategy to achieve high-performance nonfullerene electron acceptors, and the modulation of central conjugated units is also vital.

Introducing Fluorine and Sulfur Atoms into Quinoxaline-Based p-type Polymers To Gradually Improve the Performance of Fullerene-Free Organic Solar Cells.

Three quinoxaline-based "D-π-A" conjugated polymers, named as PE61, PE62, and PE63, are utilized to investigate the effect of introducing fluorine and sulfur atoms into the thiophene side chains on the photovoltaic performance when paired with a nonfullerene Y6. The open-circuit voltage (VOC) and power conversion efficiency (PCE) can be improved from 0.66 V and 8.61% for PE61:Y6 to 0.78 V and 12.02% for PE62:Y6, and then to 0.83 V and 13.10% for PE63:Y6, respectively. The results provide a simple and effective strategy to fine-tune the optoelectronic properties and thus improve the photovoltaic performance.

Unravelling the Self-Assembly of Diketopyrrolopyrrole-Based Photovoltaic Molecules.

The nanostructure of bulk heterojunction in an organic solar cell dominating the electron transport process plays an important role in improving the device efficiency. However, there is still a great need for further understanding the local nanostructures from the viewpoint of molecular design because of the complex alignment in the solid film. In this work, four kinds of photovoltaic materials containing a diketopyrrolopyrrole (DPP) unit combined with other different building blocks were selected and their self-assembled structures on a solid surface were studied by scanning tunneling microscopy technique in combination with theory calculations. The results reveal these DPP-based photovoltaic molecules self-assembled into different nanostructures, which strongly depend on the chemical structure, in particular the backbones and alkyl side chains. The planarities of backbones are affected both by molecule-substrate interaction and steric hindrance induced by the substituted thiophene or benzo[ b]thiophene units on DPP and porphyrin building blocks. The substituted branched alkyl side chains are out of the plane, which are influenced by the alignments of molecular backbones. In addition, the solution concentration also shows a large effect on the self-assembled nanostructures. This systematic research on the self-assembled structures of DPP-based semiconductors on a surface would provide guidance for designing materials and controlling the morphology of a donor/acceptor heterojunction system.

Surface Separation and in Situ Structural Regulation of Photosensitive Oligomer in a Flexible Template.

Surface-selective adsorption and separation are very important for the application of surface functional materials. In this study, a photosensitive diazo-macrocycle has been synthesized by the solvent method with a very low yield, which can adsorb onto the substrate surface modified with a template molecule. By using this flexible template on the graphite surface, a simple separation strategy for the macrocyclic molecule with specific shape and size from reaction mixtures was developed. Additionally, one of the two azo units in this trapped photosensitive macrocycle could convert from trans to cis conformation under UV irradiation due to the steric effect. Our results provide a new way to construct functional nanodevices using a surface flexible template as the separation and regulation medium.

Self-assemblies of TTF derivatives programmed by alkyl chains and functional groups.

Tetrathiafulvalenes (TTFs) are a class of important functional materials whose intermolecular interaction, which will contribute to constructing a supramolecular structure, still needs further understanding. In this study, the self-assembly behavior and structure of a series of TTFs bearing different alkyl chains and substituents were investigated by scanning tunneling microscopy (STM) in combination with density functional theory (DFT) calculations. Contrary to previous reports, herein, a series of benzoic acid-functionalized TTFs (CnTTFCOOH) and pyridine-functionalized TTFs (CnTTFN) with different lengths of alkyl chains have been substituted on the sulfur atom, where n is equal to 8, 10, 14, or 16. Due to the weak intra- and intermolecular interactions, CnTTFN (n = 8 and 10) molecules cannot be observed during STM scanning. For other cases, various self-assembled monolayers with different nanostructures were observed depending on different substituents. The results reveal that the alkyl chains and functional groups on the TTF skeleton synergistically affect the molecular self-assembly process, which results from the synergism of van der Waals, hydrogen bonding, and SS interactions. These results not only help to explain the relationship between structures and properties, but also help to design better molecular structures for various fields.

Determination of glycated albumin using boronic acid-derived agarose beads on paper-based devices.

Self-monitoring of glycated albumin (GA), a useful glycemic marker, is an established method for preventing diabetes complications. Here, the paper-based lateral flow assay devices were developed for the sensitive detection of GA and the total human serum albumin (tHSA) in self-monitoring diabetes patients. Boronic acid-derived agarose beads were packed into a hole on a lateral flow channel. These well-coordinated agarose beads were used to capture GA through specific cis-diol interactions and to enhance the colorimetric signals by concentrating the target molecules. The devices exhibited large dynamic ranges (from 10 µg/ml to 10 mg/ml for GA and from 10 mg/ml to 50 mg/ml for tHSA) and low detection limits (7.1 µg/ml for GA and 4.7 mg/ml for tHSA), which cover the range of GA concentration in healthy plasma, which is 0.21-1.65 mg/ml (0.6%-3%). In determining the unknown GA concentrations in two commercial human plasma samples, the relative percentage difference between the values found by a standard ELISA kit and those found by our developed devices was 2.62% and 8.80%, which are within an acceptable range. The measurements of GA and tHSA were completed within 20 min for the total sample-to-answer diagnosis, fulfilling the demand for rapid analysis. Furthermore, the recovery values ranged from 99.4% to 110% in device accuracy tests. These results indicate that the developed paper-based device with boronic acid-derived agarose beads is a promising platform for GA and tHSA detection as applied to self-monitoring systems.

Two-dimensional (2D) self-assembly of oligo(phenylene-ethynylene) molecules and their triangular platinum(ii) diimine complexes studied using STM.

In this investigation, the two-dimensional (2D) self-assembly nanostructures of a series of cyclic oligo(phenylene-ethynylene) (OPE) molecules (L1, L2-6 and L2-12) at the 1-phenyloctane/highly oriented pyrolytic graphite (HOPG) interface were thoroughly studied using scanning tunneling microscopy (STM). Comparative STM studies with their triangular Pt(ii) diimine complexes (C1, C2-6 and C2-12) were also carried out. Based on careful measurements on single molecule level STM images and density functional theory (DFT) calculations, the formation mechanisms of the nanoarrays formed were revealed.