Intermixing Of Layers Research Articles

A Review of Microwave-Assisted Synthesis-Based Approaches to Reduce Pd-Content in Catalysts

This review article focuses on the latest advances in the synthesis of inorganic nano-catalysts using microwave heating, which has progressed significantly since its initial implementation in the mid-1980s. Over the years, nanoparticles (NPs), which inherently offer better surface accessibility for heterogeneous catalysis, have been synthesized using a wide array of heating methods. Microwave heating is one such method and employs a unique heating mechanism that can have several benefits for catalysis. When compared to conventional form of heating which relies on inter-layer mixing via convection, microwave heating operates through the chemical polarity in the target chemicals leading to an “inside-out” mode of heating. This heating mechanism is more targeted and therefore results in rapid synthesis of catalytically active NPs. Platinum group metals (PGM) have classically been the focus of nano-catalysis; however, recent efforts have also applied non-PGM group metals with the goals of lower costs, and ideally, improved catalytic reactivity and durability. This is especially of interest with respect to Pd because of its current historically high cost. Investigations into these new materials have primarily focused on new/improved synthetic methods and catalytic compositions, but it is important to note that these approaches must also be economic and scalable to attain practical relevance. With this overarching goal in mind, this review summarizes notable recent findings with a focus on Pd-dilution and microwave heating in a chronological fashion.

Reversible control of magnetism in FeRh thin films

The multilayer of approximate structure MgO(100)/[nFe51Rh49(63 Å)/57Fe51Rh49(46 Å)]10 deposited at 200 °C is primarily of paramagnetic A1 phase and is fully converted to the magnetic B2 phase by annealing at 300 °C for 60 min. Subsequent irradiation by 120 keV Ne+ ions turns the thin film completely to the paramagnetic A1 phase. Repeated annealing at 300 °C for 60 min results in 100% magnetic B2 phase, i.e. a process that appears to be reversible at least twice. The A1 → B2 transformation takes place without any plane-perpendicular diffusion while Ne+ irradiation results in significant interlayer mixing.

An idealised approach of geometry and topology to the diffusion of cations in honeycomb layered oxide frameworks

Honeycomb layered oxides are a novel class of nanostructured materials comprising alkali or coinage metal atoms intercalated into transition metal slabs. The intricate honeycomb architecture and layered framework endows this family of oxides with a tessellation of features such as exquisite electrochemistry, unique topology and fascinating electromagnetic phenomena. Despite having innumerable functionalities, these materials remain highly underutilised as their underlying atomistic mechanisms are vastly unexplored. Therefore, in a bid to provide a more in-depth perspective, we propose an idealised diffusion model of the charged alkali cations (such as lithium, sodium or potassium) in the two-dimensional (2D) honeycomb layers within the multi-layered crystal of honeycomb layered oxide frameworks. This model not only explains the correlation between the excitation of cationic vacancies (by applied electromagnetic fields) and the Gaussian curvature deformation of the 2D surface, but also takes into consideration, the quantum properties of the cations and their inter-layer mixing through quantum tunnelling. Through this work, we offer a novel theoretical framework for the study of multi-layered materials with 2D cationic diffusion currents, as well as providing pedagogical insights into the role of topological phase transitions in these materials in relation to Brownian motion and quantum geometry.

A process control and interlayer heating approach to reuse polyamide 12 powders and create parts with improved mechanical properties in selective laser sintering

Abstract Capable of building high-quality, complex parts directly from digital models, selective laser sintering (SLS) additive manufacture (AM) is a core method of agile manufacturing. Polyamide 12 is the most commonly and successfully used polymer powders to date in SLS due to the conforming thermal behaviors of this thermoplastic polymer. State of the art technology produces a substantial amount of un-sintered powders after the manufacturing process. Failure to recycle and reuse these aged powders not only leads to economic losses but also is environmentally unfriendly. This is particularly problematic for powders close to the heat-affected zones that go through severe thermal degradations during the laser sintering processes. Limited procedures exist for systematically reusing such extremely aged powders. This work proposes a new process control method to maximize reusability of aged and extremely aged polyamide 12 powders. Building on a previously untapped interlayer heating, preprocessing, and mixing of powder materials, we show how reclaimed polyamide 12 powders can be consistently reprinted into functional samples, with mechanical properties even superior to current industrial norms. In particular, the proposed method can yield printed samples with 18.04 % higher tensile strength and 55.29 % larger elongation at break using as much as 30 % of extremely aged powders compared to the benchmark sample.

Phonon Bridge Effect in Superlattices of Thermoelectric TiNiSn/HfNiSn With Controlled Interface Intermixing.

The implementation of thermal barriers in thermoelectric materials improves their power conversion rates effectively. For this purpose, material boundaries are utilized and manipulated to affect phonon transmissivity. Specifically, interface intermixing and topography represents a useful but complex parameter for thermal transport modification. This study investigates epitaxial thin film multilayers, so called superlattices (SL), of TiNiSn/HfNiSn, both with pristine and purposefully deteriorated interfaces. High-resolution transmission electron microscopy and X-ray diffractometry are used to characterize their structural properties in detail. A differential 3-method probes their thermal resistivity. The thermal resistivity reaches a maximum for an intermediate interface quality and decreases again for higher boundary layer intermixing. For boundaries with the lowest interface quality, the interface thermal resistance is reduced by 23% compared to a pristine SL. While an uptake of diffuse scattering likely explains the initial deterioration of thermal transport, we propose a phonon bridge interpretation for the lowered thermal resistivity of the interfaces beyond a critical intermixing. In this picture, the locally reduced acoustic contrast of the less defined boundary acts as a mediator that promotes phonon transition.

Realizing large out-of-plane magnetic anisotropy in L10-FeNi films grown by nitrogen-surfactant epitaxy on Cu(001)

Rare-metal free ferromagnetic material $L{1}_{0}$ FeNi with large uniaxial magnetic anisotropy has attracted much attention for broad use of magnetic materials in various applications. While single-crystal films of $L{1}_{0}$ FeNi can be made by layer-by-layer epitaxial growth, magnitude of the uniaxial anisotropy has been lower than expected because of the imperfection of the crystal atomic structure. Here, a nitrogen (N) -surfactant epitaxial growth below 150 K is employed for overcoming interlayer mixing of the atoms at the interface. Ordered $L{1}_{0}$ FeNi films are successfully prepared on the Cu(001) substrate precovered by a ${\mathrm{Ni}}_{2}\mathrm{N}$ monolayer. The role of the N surfactant and the absence of the intermixing among Fe and Ni during the deposition and annealing processes were investigated by scanning tunneling microscopy and x-ray photoemission spectroscopy. Element-specific magnetic properties were in situ studied by soft-x-ray magnetic circular dichroism (XMCD). The observed Fe hysteresis curve and XMCD of the nitrogen-covered Ni/Fe/Ni trilayer indicate an out-of-plane magnetocrystalline anisotropy large enough for dominating the film shape anisotropy. The N-surfactant epitaxy provides a useful method for fabricating well-ordered magnetic materials without rare metals.

Role of Microstructure and Interfaces in Governing the Mechanical Properties of Nanocomposites Manufactured in the Solid State

Considerable efforts have been made to manufacture composite materials with low density and to enhance the specific strength of metals and alloys by adding boron carbide particles. One of the major factors in enhancing the mechanical properties of these composites is the interfacial characteristics of the metal/ceramic interface, particularly the strength of the bonding between the metal/ceramic interface. Here we investigate the microstructure and interfacial characteristics of the boron carbide-nickel (B4C-Ni) and silicon carbide-boron carbide (SiC-B4C) composites processed in the solid state at relatively high pressure, using transmission electron microscopy. The sintered boron carbide and nickel powders showed improved hardness and modulus, which is attributed to the formation of nickel boride (Ni4B3) at the nickel-boron carbide interface. Using fine-probe energy dispersive spectroscopy and high-angle annular dark field imaging, we observed a Si-rich intermixing layer for the silicon carbide-boron carbide interface, which could enhance the strength of the interface. The density functional theory calculations show that the decohesion energy of silicon carbide-boron carbide (without intermixing) is smallest at the interface as compared with the bulk silicon carbide and boron carbide, and that the structure would fail along the interface.

Influence of ZnTe separation layer thickness on optical properties in CdTe/ZnTe double quantum dots on Si substrates

We investigate the influence of the ZnTe separation layer thickness on the photoluminescence (PL) dynamics of CdTe/ZnTe double quantum dots (DQDs) on Si substrates. The results clarify that the DQD's structure effectively improves the limit of the carrier collection and the thermal stability of the corresponding single-layer QDs. The unusual temperature-dependent PL is explained using the single model for thermal redistribution of carrier states. This model indicates that the main nonradiative process at high temperatures is caused by scattering via multiphonons with longitudinal optical phonon energy of about 19–21.3 meV. The confinement-induced mixing and electron-carrier coupling effects cause blue-shift and enhanced PL intensity. We propose that the separation layer controls carrier dynamics in optoelectronic devices by modulating the thermal escape and e-h pairs in the intermixing layers.

120 MeV Ag ion irradiation induced intermixing, grain fragmentation in HfO2/GaOx thin films and consequent effects on the electrical properties of HfO2/GaOx/Si-based MOS capacitors

On p-type Silicon (100) substrates GaOx (150 nm) and HfO2 (30 nm) thin films have been synthesized using the RF magnetron sputtering method. After 120 MeV Ag SHI irradiation, ion-induced inter-diffusion/inter-mixing of Hf and Ga elements has been observed which leads to the development of inter-mixing of layers at the interfaces. As deposited films have randomly oriented large, inhomogeneous and non-uniform grains with an average size of 34.5 nm, while at the highest fluence, the formation of homogeneous and uniform individual spherical grains with an average size of 13.8 nm has been observed. Furthermore, HfO2/GaOx/Si-based MOS capacitors have been fabricated and the consequent effects on the electrical properties of these devices have been discussed in detail.

Interfacial CO2-mediated nanoscale oil transport: from impediment to enhancement.

CO2-based enhanced oil recovery is widely practiced. The current understanding of its mechanisms largely focuses on bulk phenomena such as achieving miscibility or reducing oil density and viscosity. Using molecular dynamics simulations, we show that CO2 adsorption on calcite surfaces impedes decane transport at moderate adsorption density but enhances decane transport when CO2 adsorption approaches surface saturation. These effects change the decane permeability through 8 nm-wide pores by up to 30% and become negligible only in pores wider than several tens of nanometers. The strongly nonlinear, non-monotonic dependence of decane permeability on CO2 adsorption is traced to CO2's modulation of interfacial structure of long-chain hydrocarbons, and thus the slippage between interfacial hydrocarbon layers and between interfacial CO2 and hydrocarbon layers. These results highlight a new and critical role of CO2-induced interfacial effects in influencing oil recovery from unconventional reservoirs, whose porosity is dominated by nanopores.

Improving the efficiency of perovskite light emitting diode using polyvinylpyrrolidone as an interlayer

A few nanometer-thick polyvinylpyrrolidone (PVP) interlayer between PEDOT:PSS anode and active layer was introduced in a perovskite light-emitting diode (PeLED) in conjunction with nanocrystal pinning (NCP) process. The device with the PVP interlayer exhibited dramatic improvements in performance resulting in current efficiency of 20.89 cd A-1, external quantum efficiency (EQE) of 5.4%, the luminance of 39,023 cd m−2, and FWHM of 18 nm, despite the fact that some degree of intermixing of the layers was expected because identical solvent was used for all three layers (PEDOT:PSS, PVP, and perovskite). The interface between PVP and perovskite layer was investigated by using x-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) sputter depth profiling with Ar gas cluster ion beam. Although obtaining a clear interface in XPS depth profile data was not possible because of partial interlayer mixing and the thinness of the PVP layer, an obvious difference across the interface was extracted in the UPS data. The observed energy level diagram was consistent with the characteristic of hole-only device (HOD) in which charge injection from PEDOT:PSS anode to the perovskite layer was suppressed due to the PVP layer.

Fabrication of polyimide microfluidic devices by laser ablation based additive manufacturing

Polyimide microfluidic devices (MFDs) have been attached enormous significance because of its excellent organic-solvent inertness, biocompatibility, and thermal stability. In this paper, a novel fabrication method based on the thought of additive manufacturing, which is adding materials layer by layer from bottom to top, was used to construct a multilayer polyimide MFD. The MFD has sophisticated three-dimensional (3D) microchannels with adjustable cross-sectional geometries and high bonding strength, which leads to good reagent mixing performance, large surface-to-volume ratio, and great durability. Starting from a single polyimide film, ultraviolet (UV) laser was utilized to ablate microchannels on the film. Due to the studies over the influence of UV laser on the channel width, the microchannel edge shape is under control, varying from trapezoid to rectangle. From monolayer to multilayer MFDs, thermal bonding with fluorinated ethylene propylene (FEP) nanoparticle dispersion as the adhesive was adopted to stack polyimide films tightly with precise alignment. In this way, microchannels can be connected vertically between layers to form 3D structures. Besides, a homogeneous adhesive interlayer and polyimide-FEP mixing regime were formed, which can provide high bonding strength. Results of computational fluid dynamics simulation of 3D microchannel structures and organic synthesis experiment revealed that our device has great reagent mixing efficiency and promising application prospects in diverse research fields, especially organic chemical and biological studies.

Effect of the annealing atmosphere on the layer interdiffusion in Pd/Ti/Pd multilayer stacks deposited on pure Ti and Ti-alloy substrates

Pd(50 nm)/Ti(25 nm)/Pd(50 nm) multilayer stack has been deposited on Ti and Ti6Al4V substrates; we have studied the intermixing of layers upon annealing at the hydrogenation temperature of 550 °C, under vacuum, H/Ar gas mixture and pure hydrogen atmospheres. Scanning electron microscopy (SEM) micrographs indicated surface roughening in samples annealed under vacuum and H/Ar gas mixture while those annealed under pure H2 remained relatively smoother. Rutherford backscattering spectrometry (RBS) revealed intermixing of layers as evidenced by the diffusion of Pd toward the bulk, while XRD indicated the formation of PdTi2 phase in the samples annealed under vacuum and H/Ar gas mixture atmosphere. In-situ, real-time RBS showed that the annealing under pure H2 preserves the integrity of the Pd catalyst. No indication of the PdTi2 formation in the pure H2 annealed samples was observed; instead only the TiH2 phase appeared, indicating the absorption of H into the system.

Study of Si Nanowire Surface Cleaning

The Gate-All-Around (GAA) architecture constructed of vertically stacked horizontal Silicon Nano-Wires (Si NWs) are a promising candidate to replace FinFET for device scaling at sub 5-nm technology nodes. In this paper, Si NWs’ release, which is the sacrificial film etching of SiGe 25% (Silicon0.75 Germanium0.25) selective to Si, will be presented. It is known that the boundary layer between Si and SiGe 25% in the multistack is very sharp, since Ge diffusion depth into Si is generally limited up to 1nm. However, the thermal annealing process is known to cause intermixing of SiGe/Si at the boundary layer with an intermixing depth ranging from 1 to 2 nm [1]. In other words, there is a possibility of Ge residue remaining at the Si NWs’ surface after the selective etch of the sacrificial SiGe 25% film using a formulated chemistry [2]. The presence of impurities on the Si NWs channel surface is expected to cause an increase in leakage current causing a degradation in device performance. Therefore, the motivation in this study is to investigate the Ge residue in Si NWs after SiGe:Si selective etching and means of removal them from the Si NWs’ surface. To investigate the surface clean, blanket wafers of 50-nm SiGe 25% on Si were prepared by epitaxial growth. The SiGe 25% layer was then removed using the formulated chemical. These wafers were analyzed by dynamic SIMS and confirmed the diffusion of Ge into Si, which indicates the need of a subsequent surface clean to remaining Ge. At first, various commodity chemicals like HF, HCl and HPM (a mixture of HCl/H2O2/H2O) followed by DIW rinse were evaluated; however, none of these reduced the level of diffused Ge. Similarly, there was no further Ge reduction even with additional process time with the formulated chemical. Finally, APM (a mixture of NH4OH/H2O2/H2O) followed by DIW rinse was investigated, and the Ge concentration on the Si surface was reduced. The H2O2 oxidized Ge to Ge (OH)2, which subsequently dissolved in H2O [3][4]. Furthermore, the H2O2 oxidized the Si surface to SiO2, which was etched by NH4OH. As a result, it is proposed that the intermixing layer of SiGe/Si of Si surface was etched with concomitant reduction of the Ge concentration on the Si surface [5]. The intermixing layer of SiGe/Si has a much lower Ge concentration than SiGe 25%. Therefore, the chemicals that are effective for Si etching should also be effective for removing the intermixing layer of SiGe/Si [6][7]. The result of etching the intermixing layer of SiGe/Si with these chemicals will be presented. In addition, the surface roughness compared to before post process was improved, which is also beneficial for enhancing device performance. Furthermore, the impact of the thermal budget during the annealing process on the removal performance of Ge residue and the difference of intermixing depth of SiGe/Si will be shown. Finally, the most efficient post cleaning for Si NWs will be proposed. In summary, the Ge residue remaining at the Si NWs channel surface, which could not be removed by the formulated chemistry, will be efficiently removed by etching this intermixing layer. It will be shown that an optimized clean after the Si NWs’ release can be effective in removing Ge residue from this Si channel surface. [1] H. Mertens et al., ECS Transactions, 77 (5) 19-30 (2017) [2] K. Komori et al., UCPSS.1662-9787, 282,107-112(2018) [3] K. Komori et al., ECS Transactions, 80(2) 141-146 (2017) [4] N. Cerniglia et al., J. Electrochem. Soc, 109(6) 508-125(1962) [5] G. K. Celler et al., Electrochemical and Solid-State Letters, 3 (1) 47-49 (2000) [6] J. Phys. Chem. C, 118, 4, 2044-2051(2014) [7] O. Tabata et al., Sensors and Actuators A, 34(1) 51-57(1992)

Comparing Different Cross-Section Cutting Methods for SEM Analysis of Membrane-Electrodes Assemblies

The observation of membrane-electrodes assemblies (MEAs) in cross-section is a basic tool for their morphological characterization, and the study of changes occurring in the different layers by operation in a fuel cell. But the preparation of a well-defined and representative cross-section plane in the MEAs is difficult due to a layered structure with very different mechanical properties among the layers, including a Nafion membrane, two catalyst layers, and two gas diffusion layers. For this reason, the preparation of samples for cross-sectional observation requires appropriate cutting techniques able to leave a cross-sectional plane showing the morphology of each layer with minor changes, ie. avoiding uneven surfaces, mixing of layers, porosity and morphology alterations, and/or delamination. It is possible that no single method may accomplish with all requirements, so different cross sectioning procedures must be used to have a complete characterization. With this aim, different preparation methods for cross-section analysis of MEAs have been tested in order to make a comparative analysis, showing advantages and disadvantages for each of the methods. The preparation procedures analyzed are cutting with sharp-edge, laser-cutting, embedded-mechanical polishing, and focused ion beam (FIB). Results are shown in the figure. Cutting with a sharp edge (Fig. a) is a quick and easy method that may provide good cross-sectional observation and morphology preservation if an appropriate tool is used and careful handling. However, the probability for a successful preparation is not high due to frequent intermixing of layers, delamination, and uneven surface. Laser-cutting with a CO2 laser (Fig. b)) occurs by burning and vaporization of the material, leaving a plane with a clear damage at a micrometric scale. Especially Nafion membranes and carbon clothes showed severe alteration of the phases in the cutting plane, so this method cannot be used for a micrometric study of the morphology of the layers. Mechanical polishing of an embedded MEA a resin (Fig.c) provides, on the other hand, better preserved layers and more reproducible results; the morphology of powder layers, like the catalyst layer and microporous layer, may be altered because of the rearrangement of particles during the polishing process. Better preservation of multilayered samples can be obtained with the FIB technique (Fig.d), although the observation profile cannot be extended beyond a few millimeters. The FIB cross-cutting technique, that may be combined with a cross section polishing with argon gas, appears to better preserve the morphology of the layers and in a reproducible way. Acknowledgements. This work was supported by the Ministerio de Economía y Competitividad of Spain, and Fondo Europeo de Desarrollo Regional (FEDER), Project E-LIG-E, ENE2015-70417-P (MINECO/FEDER). Figure 1

Effects of argon thermal annealing on surface structure, microstructural and silicide formation of Silicon-Titanium-Cobalt thin film

Co-Ti system was prepared on Si (1 0 0) substrates using an electron beam evaporator equipped with thickness monitor. Co (10 nm) thin film was deposited on top of pre-deposited Ti (10 nm) film at 0.6 Å/sec deposition rate. First three samples were then argon and vacuum annealed at temperatures between 350 °C and 550 °C for three hours. Scanning electron microscopy images depicted formation of small structure attributing to rough surface as an indication of film transformation especially at 550 °C. Surface roughness increased with temperature from 350 °C to 550 °C due to the formation of nanostructures for argon annealed samples. In-situ real-time RBS revealed intermixing of layers at the interface and exchange of atoms between Co, Si and Ti layers that started below 450 °C forming silicide with stoichiometry CoSi, CoSi2 and CoSi3. Diffusion of Ti atoms through the Co layer towards the surface, allowing Co to diffuse inward to react with Si to form silicide was also observed. X-ray diffraction pattern also revealed the presence of the CoSi2 phase in addition to TiCo2 phase in the argon annealed sample at 550 °C. No indication of the silicide formation in the vacuum annealed samples. The results pointed toward a successful utilization of this approach to prepare CoSi2 at temperatures lower than the one reported in the literature, which is above 600 °C.

Investigation of the buried planar interfaces in multi-layered inverted organic solar cells using x-ray reflectivity and impedance spectroscopy

The hole and electron extracting interlayers in the organic solar cells (OSCs) play an important role in high performing devices. The present work focuses on an investigation of Zinc oxide/bulk heterojunction (ZnO/BHJ) and BHJ/MoOx (Molybdenum oxide) buried planar interfaces in inverted OSC devices using the optical contrast in various layers along with the electrical measurements. The x-ray reflectivity (XRR) analysis demonstrates the formation of additional intermixing layers at the interfaces of ZnO/BHJ and BHJ/MoOx. Our results indicate infusion of PC71BM into ZnO layer up to ~4 nm which smoothen the ZnO/BHJ interface. In contrast, thermally evaporated MoOx molecules diffuse into PTB7-Th dominant upper layers of BHJ active layer resulting in an intermixed layer at the interface of MoOx/BHJ. The high recombination resistance (~5 kΩ cm2) and electron lifetime (~70 μs), obtained from the impedance spectroscopy (IS), support such vertical segregation of PTB7-Th and PC71BM in the active layer. The OSC devices, processed in ambient condition, exhibit high power conversion efficiency of 6.4%. We consider our results have great significance to understand the structure of buried planar interfaces at interlayers and their correlation with the electrical parameters representing various interfacial mechanisms of OSCs.

Difluorochloromethane treated thin CdS buffer layers for improved CdTe solar cells

One of the major improvements for CdTe solar cells is the increase of the current density by enhancing the transparency of the buffer layer. CdS, with its 2.4 eV band gap, results in being opaque at low wavelength regions. For this reason, in order to gain in blue and UV light, extremely thin CdS has to be applied, if the buffer is not substituted with other materials. On the other hand, by thinning the CdS layer we create pinholes also due to the wide intermixing of CdTe and CdS layers and subsequently consumption of CdS.For this reason we have applied and compared different CdS post-deposition treatments in order to stabilize the layer and avoid excess intermixing. Treatments at temperatures above 500 °C in an argon and chlorine atmosphere on 80 nm thick CdS have led to the fabrication of more stable samples compared to untreated CdS, resulting in improved performance with a 10% increase in current density and a 5% increase in open circuit voltage and fill factor. Moreover, light transmission of the CdS treated layers from 300 to 450 nm is increased by about 10%.In this paper, a study of treated thin CdS with recrystallization treatments is presented; the layers have been analysed by means of X-ray photoelectron spectroscopy, X-ray diffraction and atomic force microscopy. Finished CdTe devices made on thin CdS are characterized in terms of current-voltage and quantum efficiency.

Revealing working mechanisms of PFN as a cathode interlayer in conventional and inverted polymer solar cells.

Energy level alignments at the PC71BM/PFN/Ag interface in conventional polymer solar cells (c-PSCs) and the ITO/PFN/PC71BM interface in inverted polymer solar cells (i-PSCs) are systematically investigated via ultraviolet photoelectron spectroscopy and by using the integer charge transfer (ICT) model. The findings demonstrate that PFN as a cathode interlayer is able to effectively reduce the electron extraction barriers from 0.72 eV to 0.38 eV for the c-PSCs and from 0.58 eV to 0.36 eV for the i-PSCs, respectively. In the c-PSCs, the final modified electron extraction barrier matches the predicted value (∼0.4 eV) using the ICT model. In the i-PSCs, there exists an intermixing layer of PFN and the active layer above PFN because some PFN is dissolved by the organic solvent in the active layer solution, resulting in a special energy level alignment at the PFN/PC71BM interface. ITO/PFN (2 nm)/PC71BM (20 nm) in the i-PSCs actually forms such an interface as ITO/PFN/PFN:PC71BM with an energy level alignment like Al/LiF/PC71BM/PFN (0.65 nm), which rationalizes a higher short circuit and fill factor in the i-PSCs than c-PSCs. Finally, a general model to simulate the intermixing layer between the organic cathode interlayer and the active layer has been proposed to describe the energy level alignment of the complicated interfaces in the i-PSCs.

Decorative black coatings on titanium surfaces based on hard bi-layered carbon coatings synthesized by carbon implantation

New approaches to synthesize decorative black coatings on metallic surfaces are of significant research and commercial interest to manufacturing industries. In this work, decorative hard black coatings were deposited on a titanium surface by carbon ion implantation at ambient temperature. A 10 keV C+ beam was implanted on a Ti substrate to a fluence of 1–1.25 × 1018 C cm−2. Rutherford backscattering spectrometry and transmission electron microscopy results show that the implantation resulted in a bi-layered coating structure with a ~50 nm amorphous carbon layer at the surface followed by a ~50 nm amorphous titanium carbide intermixing layer deposited on top of a crystalline Ti surface. Raman spectroscopy confirms the formation of carbide intermixing layer and shows that the amorphous carbon layer has 15–20% sp3 content. Nanoindentation measurements show that the surface hardness of the implanted surface has increased by 72%, from 3.7 to 6.6 GPa, upon carbon implantation. Scratch tests further demonstrate a reduction in coefficient of friction in the implanted surface by 25%, signifying an improvement in wear-resistance of the coated materials. Colorimetry measurements reveal that carbon implantation reduces the luminosity of the Ti surface from 77 to 49 and chromaticity from 4.67 to 1.36, confirming incorporation of black color on Ti surface. The results demonstrate that C implantation onto a Ti surface at high fluence results in a black coating with high surface hardness and wear-resistance that can be employed in decorative surface applications for manufacturing industries.