Interfacial Alignment Research Articles

Determine the Complete Configuration of Single-Walled Carbon Nanotubes by One Photograph of Transmission Electron Microscopy.

Developing a convenient method to determine the complete structure of single-walled carbon nanotubes (SWNTs) is important to achieve the fully controlled growth of this nanomaterial. However, approaches that can identify handedness at the atomic level with simple equipment, operation, and data analysis are still lacking. Here, the SWNTs/graphene (Gr) vertical heterostructures are artificially constructed with aligned interfaces to realize the lattice interpretation of SWNT upper and lower walls separately by only one transmission electron microscopy image, thus transforming the 3D handedness information to projected 2D space. Gr displays prominent out-of-plane deformation at the interface, promoting the energetic advantage for the aligned interface construction. The interfacial alignment between the SWNT and Gr shows no obvious dependence on either the helical angle or diameter of SWNTs. The half-wrapping of SWNTs by deformed Gr also triggers diversified alterations in electronic structures based on theoretical calculations. 27 specimens with SWNTs prepared by two disparate methods are examined, implying equal handedness distribution in the randomly aligned SWNTs grown on quartz and potential handedness enrichment in horizontal SWNT arrays grown on a-sapphire. This work provides a simple strategy for chiral discrimination and lays a characterization foundation for handedness-selective growth of nanomaterials.

A comparative study of interfacial thermal conductance between metal and semiconductor

To understand and control thermal conductance of interface between metal and semiconductor has now become a crucial task for the thermal design and management of nano-electronic and micro-electronic devices. The interfacial alignments and electronic characteristics of the interfaces between metal and semiconductor are studied using a first-principles calculation based on hybrid density functional theory. The thermal conductance of interfaces between metal and semiconductor were calculated and analyzed using diffuse mismatch model, acoustic mismatch model and nonequilibrium molecular dynamics methods. Especially, according to nonequilibrium molecular dynamics, the values of thermal conductance were obtained to be 32.55 MW m−2 K−1 and 341.87 MW m−2 K−1 at C–Cu and Si–Cu interfaces, respectively. These results of theoretical simulation calculations are basically consistent with the current experimental data, which indicates that phonon–phonon interaction play a more important role than electron–phonon interaction during heat transport. It may be effective way to improve the interfacial thermal conductance through enhancing the interface coupling strength at the metal–semiconductor interface because the strong interfacial scattering plays a role in suppressing in the weaker interface coupling heterostructure, leading to the lower thermal conductance of interfaces. This could provide a beneficial reference for the design of the Schottky diode and thermal management at the interfaces between metal and semiconductor.

Effects of thin metal contacts on few-layer van der Waals ferrielectric CuInP2S6

Out-of-plane polarized ferroelectric materials in a capacitive structure provide a key component for several technological applications. Furthermore, two-dimensional materials are expected to aid in the quest for both ultrathin and flexible electronics. Of the various two-dimensional ferroelectrics with out-of-plane polarization, CuInP2S6 is special in that the Cu atoms are highly mobile and it has been shown to possess both low- and high-polarization states. Using density-functional-theory calculations, we explore the stabilization of the ferroelectric state for several prototypical metal contacts (Gr, Ni, Cu, Au, and Ag). In all cases, we find that the ferroelectric state can be stabilized at fewer layers than in the freestanding case. For all of the considered conventional metal contacts, we also find the existence of a quasi-ferroelectric state that stabilizes a polar phase for thicknesses greater than two layers of CIPS. In the cases of Au and Ag, interfacial alignment and strain can be used to stabilize ferroelectricity at the bilayer limit. Furthermore, we find that the strength of the interaction between the contact and CuInP2S6 also leads to stabilization of the high-polarization state when ferroelectricity is stabilized. Lastly, energy-barrier calculations show that the system is still switchable in the presence of contact doping from the metal contacts.

Preferred Interfacial Alignment in the Pd@HKUST1 System and the Role of the MOF to Affect Charge Transfer to Pd Nanoparticles

Preferred Interfacial Alignment in the Pd@HKUST1 System and the Role of the MOF to Affect Charge Transfer to Pd Nanoparticles

Magnetization and antiferromagnetic coupling of the interface between a 20 nm Y3Fe5O12 film and Gd3Ga5O12 substrate

We present evidence for and characterization of a $\ensuremath{\approx}4\text{\ensuremath{-}}\mathrm{nm}$-thick ${({\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Gd}}_{x})}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ layer with $x\ensuremath{\ge}0.4$ formed at the interface between a gadolinium gallium garnet (GGG) substrate and a sputtered ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ (YIG) epitaxial film with nominal thickness of 20 nm. Temperature-dependent polarized neutron reflectometry (PNR) and superconducting quantum interference device (SQUID) magnetometry show antiferromagnetic alignment of this interfacial layer with the bulk of the YIG film at low $T$ that persists to at least 3 tesla. These experiments also show that this interfacial alignment switches from antiparallel to parallel between 100 and 200 K in small applied magnetic fields. Simple modeling suggests correlation of this crossover with the ferrimagnetic compensation point of the mixed garnet that forms this interfacial layer.

Dimethylamine Exchanging of a New Hole Transport Material for Highly efficient CsPbI2Br solar cells

All inorganic α-CsPbI2Br films with a large open circuit voltage (V OC) and excellent thermal stability are promising for highly stable and efficient perovskite solar cells (PSCs). However, its device performance is limited by a low short circuit current density (J SC) and low V OC, which is strongly related to the energy misalignment and defects recombination at the perovskite/transport layer interfaces. In this work, we develop two Ni based polymers: bis (dithiobenzil) nickel (II) (BDTB) and bis(4-dimethylaminodithiobenzil) nickel (II) (BDMA), and use them as the hole transport layer for α-CsPbI2Br PSCs. As compared to BDTB based reference device (PCE ~3.2%), BDMA based device demonstrate a simultaneous increase on V OC, J SC and fill factor (FF), resulting in a remarkable power conversion efficiency (PCE) of 13.32 %. We attribute the improved device performance to a better interfacial alignment, the reduced defect recombination and improved charge extraction. Moreover, the BDMA based devices also exhibit an improved shelf-life stability than BDTB control device, which sustain over 80 % of PCE after 50 days in ambient air.

Director alignment at the nematic-isotropic interface: elastic anisotropy and active anchoring.

Activity in nematics drives interfacial flows that lead to preferential alignment that is tangential or planar for extensile systems (pushers) and perpendicular or homeotropic for contractile ones (pullers). This alignment is known as active anchoring and has been reported for a number of systems and described using active nematic hydrodynamic theories. The latter are based on the one-elastic constant approximation, i.e. they assume elastic isotropy of the underlying passive nematic. Real nematics, however, have different elastic constants, which lead to interfacial anchoring. In this paper, we consider elastic anisotropy in multiphase and multicomponent hydrodynamic models of active nematics and investigate the competition between the interfacial alignment driven by the elastic anisotropy of the passive nematic and the active anchoring. We start by considering systems with translational invariance to analyse the alignment at flat interfaces and, then, consider two-dimensional systems and active nematic droplets. We investigate the competition of the two types of anchoring over a wide range of the other parameters that characterize the system. The results of the simulations reveal that the active anchoring dominates except at very low activities, when the interfaces are static. In addition, we found that the elastic anisotropy does not affect the dynamics but changes the active length that becomes anisotropic. This article is part of the theme issue 'Progress in mesoscale methods for fluid dynamics simulation'.

ELECTRONIC AND OPTICAL MODIFICATION OF ORGANIC-HYBRID PEROVSKITES

Renewed interest has brought significant attention to tune coherently the electronic and optical properties of hybrid organic–inorganic perovskites (HOIPs) in recent years. Tailoring the intimate structure–property relationship is a primary target toward the advancement of light-harvesting technologies. These constructive progresses are expected to promote staggering endeavors within the solar cells community that needs to be revisited. Several considerations and strategies are introduced mainly to illustrate the importance of structural stability, interfacial alignment, and photo-generated carriers extraction across the perovskite heterostructures. Here, we review recent strides of such vast compelling diversity in order to shed some light on the interplay of the interfacial chemistry, photophysics, and light-emitting properties of HOIPs via molecular engineering or doping approach. In addition, we outline several fundamental knowledge processes across the role of charge transfer, charge carrier extraction, passivation agent, bandgap, and emission tunability at two-dimensional (2D) level of HOIPs/molecule heterointerfaces. An extensive range of the relevant work is illustrated to embrace new research directions for employing organic molecules as targeted active layer in perovskite-based devices. Ultimately, we address important insights related to the physical phenomena at the active molecules/perovskites interfaces that deserve careful considerations. This review specifically outlines a comprehensive overview of surface-based interactions that fundamentally challenges the delicate balance between organic materials and perovskites, which promotes bright future of desired practical applications.

Thin Film Morphological Characteristics of a Perfluorinated Anion Exchange Membrane

Perfluorinated anion exchange membranes are promising materials for alkaline fuel cell applications. Our previous work indicates they have high conductivity of >100 mS/cm at 80ᵒC and 95%RH.(1) They have also displayed good fuel cell performance of 1W/cm2.(2) We have also performed transmission small- and wide-angle X-ray scattering (SAXS/WAXS) of the bulk membrane to understand the bulk morphology.(3) Properties of Perfluorinated sulfonic acid (PFSA) ionomers as thin films have been thoroughly investigated in the past.(4) However, there is no literature about thin film characterization of perfluorinated anion exchange polymer and hence there is a lack of understanding about the interfacial properties. Here, we have studied the structure of these materials using Grazing-incidence small-angle x-ray scattering (GISAXS). Polymer solutions of different concentrations were used to spin-cast the thin films onto silicon substrates with native oxide layer and also coated with silver and Platinum.. Ellipsometry was used to obtain a calibration curve of thin film thickness vs. concentration of the polymer solution (wt%). From GISAXS, we can conclude that the polymer chains align horizontally parallel to the plain silicon as well as silver substrate. This alignment becomes significant at higher film thicknesses. Understanding the interfacial alignments of polymer on potential catalyst surfaces will help us better design them for optimal fuel cell performance or other electro-chemical applications.

Energy Level Tuning at the MAPbI3 Perovskite/Contact Interface Using Chemical Treatment

Metal halide perovskites are rivaling established materials for thin film photovoltaics. Being able to tune interfacial alignment of energy levels may allow a further boost to the efficiency of per...

Understanding Interfacial Alignment in Solution Coated Conjugated Polymer Thin Films.

Domain alignment in conjugated polymer thin films can significantly enhance charge carrier mobility. However, the alignment mechanism during meniscus-guided solution coating remains unclear. Furthermore, interfacial alignment has been rarely studied despite its direct relevance and critical importance to charge transport. In this study, we uncover a significantly higher degree of alignment at the top interface of solution coated thin films, using a donor-acceptor conjugated polymer, poly(diketopyrrolopyrrole-co-thiophene-co-thieno[3,2-b]thiophene-co-thiophene) (DPP2T-TT), as the model system. At the molecular level, we observe in-plane π-π stacking anisotropy of up to 4.8 near the top interface with the polymer backbone aligned parallel to the coating direction. The bulk of the film is only weakly aligned with the backbone oriented transverse to coating. At the mesoscale, we observe a well-defined fibril-like morphology at the top interface with the fibril long axis pointing toward the coating direction. Significantly smaller fibrils with poor orientational order are found on the bottom interface, weakly aligned orthogonal to the fibrils on the top interface. The high degree of alignment at the top interface leads to a charge transport anisotropy of up to 5.4 compared to an anisotropy close to 1 on the bottom interface. We attribute the formation of distinct interfacial morphology to the skin-layer formation associated with high Peclet number, which promotes crystallization on the top interface while suppressing it in the bulk. We further infer that the interfacial fibril alignment is driven by the extensional flow on the top interface arisen from increasing solvent evaporation rate closer to the meniscus front.

Molecular Alignment and Electronic Structure of N,N'-Dibutyl-3,4,9,10-perylene-tetracarboxylic-diimide Molecules on MoS2 Surfaces.

The molecular orientation of organic semiconductors on a solid surface could be an indispensable factor to determine the electrical performance of organic-based devices. Despite its fundamental prominence, a clear description of the emergent two-dimensional layered material-organic interface is not fully understood yet. In this study, we reveal the molecular alignment and electronic structure of thermally deposited N,N'-dibutyl-3,4,9,10-perylene-dicarboximide (PTCDI-C4) molecules on natural molybdenum disulfide (MoS2) using near-edge X-ray absorption fine structure spectroscopy (NEXAFS). The average tilt angle determination reveals that the anisotropy in the π* symmetry transition of the carbon K-edge (284-288 eV range) is present at the sub-monolayer regime. Supported by ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), and resonant photoemission spectroscopy (RPES) measurements, we find that our spectroscopic measurements indicate a weak charge transfer established at the PTCDI-C4/MoS2 interface. Sterical hindrance due to the C4 alkyl chain caused tilting of the molecular plane at the initial thin film deposition. Our result shows a tunable interfacial alignment of organic molecules on transition metal dichalcogenide surfaces effectively enhancing the electronic properties of hybrid organic-inorganic heterostructure devices.

Effects of interfacial alignments on the stability of graphene on Ru(0001) substrate

Structure and electronic properties of two-dimensional materials could be tuned by interfacial misfit or orientation angles. However, graphene grown on Ru(0001) substrate usually shows stable moiré superlattice with a periodicity of 3.0 nm indicating an aligned geometry. The reason for the absence of misaligned structure is still unknown. We have performed first-principles calculation to investigate the microstructure and morphology of graphene on Ru(0001) substrate in both aligned and misaligned geometries with rotation angles of 0°, 7.6°, and 23.4°, respectively. Our results indicate that both the graphene corrugation and moiré superlattice periodicity decrease as the rotation angle increases. Meanwhile the interaction energy between graphene and Ru(0001) substrate also becomes weakened with the rotation angle, as the decrease and discretization of intense charge transfer sites at the graphene/Ru interface, which is closely related to the interface stacking structure. Counterintuitively, the strain energy in graphene also increases anomalously with the rotation angle, which is attributed to the highly distorted local deformation of graphene due to the strong but discrete covalent bonding with Ru substrate. The simultaneous increase in both the interaction energy and strain energy in graphene/Ru(0001) heterostructure with rotation angle contributes to the preferred configuration in the aligned state.

Control of polystyrene-block-poly(methyl methacrylate) directed self-assembly by laser-induced millisecond thermal annealing

Directed self-assembly of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) during laser thermal annealing at peak temperatures of 300°C–800°C for dwells of 1–10 ms has been explored. The enhanced mobility of polymer chains at these temperatures improves registration compared with conventional thermal anneals. PS-b-PMMA films (forming 15-nm line/space standing lamellae) were cast on chemically patterned substrates with a copolymer neutral layer and annealed by laser and hot plate. Annealing by hot plate or multiple laser scans resulted in well-aligned features over micron length scales. By laser annealing multiple times, defectivity was reduced by ∼60%. However, laser annealing for only 10 ms before performing a hot plate anneal reduced defectivity by >80%. We believe that this reduction arises from improved interfacial alignment of the film to the template during laser annealing near the order–disorder transition.

Highly Ordered 1D Fullerene Crystals for Concurrent Control of Macroscopic Cellular Orientation and Differentiation toward Large-Scale Tissue Engineering.

A highly aligned 1D fullerene whisker (FW) scaffold in a centimeter area is fabricated by interfacial alignment. The resulting aligned FW scaffold enables concurrent control over cellular orientation and differentiation to muscle cells. This aligned FW scaffold is made by a facile method, and hence the substrate is a promising alternative to other cell scaffolds for tissue engineering.

Interfacial Alignment Mechanism of Forming Spherical Silica with Radially Oriented Nanopores

When cationic surfactants are added to the Stober process, spherical particles with radially oriented mesopores can be prepared by precipitation of silica from a solution of ethanol, water, and ammonia. Van Tendeloo and co-workers proposed that these particles form by epitaxial growth of cylindrical assemblies from the facets of Ia3d cubic (MCM-48) seeds. [J. Phys. Condens. Matter 2003, 15, S3037.] Here, we reexamine this hypothesis by detailed characterization of intermediate and final mesoporous silica particles formed from ethanol/water/ammonia solutions. We find that the presence of a cubic core is not required to explain the synthesis of spherical particles with radially oriented pores. Instead, we hypothesize that the radial orientation originates at the particle surface because of the preferred alignment of CTAB micelles normal to that interface. Consistent with previous studies of the Stober process, we initially observe small, irregular silica/surfactant clusters. After an induction time, these c...

FT-IR Studies of the Interfacial Alignment of the Liquid Crystal 4′-Cyano-4-biphenyl[4-(4-pentenyloxy)] benzoate Bonded to Silica

The liquid crystal, 4′-cyano-4-biphenyl[4-(4-pentenyloxy)] benzoate (CBPB) has been chemically bonded to silica and the resulting material's interfacial properties examined by Fourier transform infrared spectroscopy. The spectral features of the nitrile stretching region for the chemically anchored system were significantly less complex than those obtained from samples of silica physically coated with CBPB. Further when CBPB was physically coated onto the chemically modified surface, its interactions with the substrate were reduced significantly.

Surface technologies for liquid crystal display.

Devices for non-active matrix addressed liquid crystal displays and their substrate surface treatments are reviewed. Liquid crystal interfacial alignment with a high pretilt angle is needed for the display panels with large information contents. This is being achieved by substrate surface treatments utilizing selected polyimide coating materials and a controlled surface rubbing technique. For the further improvement of the technology, controlling both interfacial liquid crystal molecular alignment angle and its anchoring strength, is strongly required.