Sequential Layer Deposition Research Articles

Lamination of >21% Efficient Perovskite Solar Cells with Independent Process Control of Transport Layers and Interfaces.

Transport layer and interface optimization is critical for improving the performance and stability of perovskite solar cells (PSCs) but is restricted by the conventional fabrication approach of sequential layer deposition. While the bottom transport layer is processed with minimum constraints, the narrow thermal and chemical stability window of the halide perovskite (HP) layer severely restricts the choice of top transport layer and its processing conditions. To overcome these limitations, we demonstrate lamination of HPs─where two transport layer-perovskite half-stacks are independently processed and diffusion-bonded at the HP-HP interface─as an alternative fabrication strategy that enables self-encapsulated solar cells. Power conversion efficiencies (PCE) of >21% are realized using cells that incorporate a novel transport layer combination along with dual-interface passivation via self-assembled monolayers, both of which are uniquely enabled by the lamination approach. This is the highest reported PCE for any laminated PSC encapsulated between glass substrates. We further show that this approach expands the processing window beyond traditional fabrication processes and is adaptable for different transport layer compositions. The laminated PSCs retained >75% of their initial PCE after 1000 h of 1-sun illumination at 40 °C in air using an all-inorganic transport layer configuration without additional encapsulation. Furthermore, a laminated 1 cm2 device maintained a Voc of 1.16 V. The scalable lamination strategy in this study enables the implementation of new transport layers and interfacial engineering approaches for improving performance and stability.

Direct ink writing of viscous inks in variable gravity regimes using parabolic flights

Additive manufacturing (AM) has significant utility for off-planet fabrication where dedicated infrastructure is severely limited, weight reduction and in situ resource utilization is desirable, and demands for complex systems are high. Direct ink writing (DIW) is a useful AM technique since it enables the deposition of a broad set of materials and the co-printing of multiple materials simultaneously. This allows for the fabrication of complex functional devices and systems in addition to structural objects. To evaluate this technique for space applications, this study characterized DIW in low gravity environments. Parabolic flights were used to simulate Martian, Lunar, and Micro gravity, and the effects that these 3 gravity regimes have on two critical print performance parameters, drooping and slumping, was evaluated using viscous paste inks deposited with an auger-driven extrusion head. In the drooping case, bridging structures were printed across gaps without support material, and the deformation was monitored. In the slumping case, a wall was printed through sequential layer deposition, and the vertical displacement of each layer under reduced gravity was explored. As expected, we found that a reduction in apparent gravity led to a decrease in the droop of a printed line, and as apparent gravitational acceleration is decreased its impact on the magnitude of drooping becomes less significant. For wall structures printed in simulated Lunar or Martian gravity regimes, the total structure height was found to be similar to that of a structure printed under Earth's gravitational conditions. In contrast, for prints performed in microgravity, it was found that slumping was significantly reduced and structure height was larger. These results provide experimental data to enable the design and optimization of appropriate structures and tool paths for printing objects using DIW for off-planet manufacturing.

Physical vapor deposition of Yb-doped Cs2AgSbBr6 films

Ytterbium-doped halide double perovskites of the form Cs2AgBX6 (B = Bi, Sb, In and X = Cl, Br) are being explored as potential lead-free UV/blue to near-infrared (NIR) downconversion materials. Of the various B and X combinations, Cs2AgSbBr6 has only recently been synthesized and never yet deposited as a film using vapor deposition. Here, we report the deposition of undoped and Yb-doped Cs2AgSbBr6 thin films via thermal evaporation from CsBr, AgBr, SbBr3, and YbBr3. Film composition control is difficult due to the high volatility of SbBr3. We explored various strategies, including co-evaporation and sequential deposition of layers, followed by postdeposition annealing. The formation of Cs2AgSbBr6 was confirmed with x-ray diffraction and optical absorption, although impurity phases such as Cs2AgBr3 were often present because the films easily became Sb-deficient due to volatile SbBr3 leaving the film. NIR photoluminescence quantum yields of up to 12% were achieved with this material for the first time. The optical properties and reported bandgap transitions are critically reviewed and assessed in light of new optical absorption data from thin films. The Cs2AgSbBr6 film has an indirect bandgap at 1.95 ± 0.05 eV followed by a direct transition at 2.5 ± 0.05 eV.

Using nanomaterials to enhance the additive manufacturing of polymeric resins

Additive manufacturing (AM) technologies, also called 3D printing, have dramatically developed over the past decade to allow new capabilities in materials processing with printed resolution comparable to that of traditional manufacturing techniques. Sequential layer deposition can lead to the creation of complex parts with minimized material waste, high manufacturing throughput, and increased prototyping ability, while also meeting the demand for mid- and low-volume production. The AM of polymer nanocomposites is a growing area of research because nanomaterial additives can enhance the mechanical, electrical, and other properties for end-use applications. However, the use of nanomaterial inclusions can also enhance the AM processes themselves. Here, we discuss works where nanomaterials are employed as local heaters for fused deposition modeling, as viscosifiers for direct ink writing, and as photothermal sensitizers for selective laser sintering and vat polymerization. We also note the disconnect between the researched AM capabilities and current industrial manufacturing; nanomaterials can bridge the technological gap and lead to new common practices in industrial manufacturing spaces.

The Effect of Printing Temperature on Bonding Quality and Tensile Properties of Fused Deposition Modelling 3d-Printed Parts

FDM 3D-printing, is an additive manufacturing technology that is being increasingly adapted in the engineering industry due to its ability to produce complex design at lower costs as the materials are thermoplastic based. Due to the nature of its sequential layer deposition, the bonding quality is highly dependent on the temperature development during printing. In this paper, an experimental investigation was conducted to study the effect of printing temperature on bonding quality with regards to dimensional accuracy and tensile behaviour of the fabricated parts. The test specimens were fabricated using PLA material at different printing temperature ranging from 180°C-240°C at intervals of 10°C. Uniaxial tensile test according to ASTM D638-14 standard was conducted at a strain rate of 1 mm/min and was repeated five times for each variable. Results show that specimens fabricated at higher printing temperature have better tensile properties. The ultimate tensile strength recorded for specimens fabricated at T=240°C and T=180°C were 36.97 MPa and 17.47 MPa respectively. Fracture surfaces were analysed and related with the tensile results to deduce the failure mechanism. The dimensions of the sample at printed different printing temperatures were measured using digital callipers and compared with the designed specification. Specimens printed at T=240°C had the worst dimensional accuracy, with a percentage difference of 10% although it yielded the highest tensile strength. The optimum printing temperature that yielded the best tensile behaviour while maintaining its dimensional accuracy was when T=220°C.

Laminated Monolithic Perovskite/Silicon Tandem Photovoltaics

AbstractPerovskite/silicon tandem photovoltaics have attracted enormous attention in science and technology over recent years. In order to improve the performance and stability of the technology, new materials and processes need to be investigated. However, the established sequential layer deposition methods severely limit the choice of materials and accessible device architectures. In response, a novel lamination process that increases the degree of freedom in processing the top perovskite solar cell (PSC) is proposed. The very first prototypes of laminated monolithic perovskite/silicon tandem solar cells with stable power output efficiencies of up to 20.0% are presented. Moreover, laminated single‐junction PSCs are on par with standard sequential layer deposition processed devices in the same architecture. The numerous advantages of the lamination process are highlighted, in particular the opportunities to engineer the perovskite morphology, which leads to a reduction of non‐radiative recombination losses and and an enhancement in open‐circuit voltage (Voc). Laminated PSCs exhibit improved stability by retaining their initial efficiency after 1‐year aging and show good thermal stability under prolonged illumination at 80 °C. This lamination approach enables the research of new architectures for perovskite‐based photovoltaics and paves a new route for processing monolithic tandem solar cells even with a scalable lamination process.

Halloysite nanoclay doped ceramic membrane fabrication and evaluation of textile wastewater treatment performance

In this study, halloysite nanoclay-doped ultrafiltration and tight-ultrafiltration ceramic membranes were fabricated by sequential layer deposition using relatively low temperatures. The produced membranes were structurally characterized by contact angle tests and a scanning electron microscope. The pure water flux and bovine serum albumin removal were also examined, in order to determine the performance of the membranes. Finally, 3 different real wastewater treatability tests were carried out and the change in membrane performance was observed by using hot textile wastewater. In the coated membranes, the pure water flux decreased from 2000 L/(m2.h) to 100 L/(m2.h) for the ultrafiltration membrane and from about 370 L/(m2.h) to 23 L/(m2.h) for the tight-ultrafiltration membrane. In the bovine serum albumin removal efficiency test, approximately 30 % removal was obtained for the ultrafiltration membrane and 100 % for the tight-ultrafiltration membrane. In real wastewater filtration tests performed with the tight- ultrafiltration membrane, the average removal efficiency of approximately 40 % and above 44 % was obtained for chemical oxygen demand and total organic carbon and color removal, respectively. Finally, in the hot water test, it was observed that the permeate flux increased approximately 3 times, but there was no significant decrease in the treatment efficiency.

A Rational Ternary Design of P3HT/Insulating Polymers–CNTs/P3HT for the Enhanced Thermoelectric Performances

ABSTRACT This work shows the design and development of ternary layer thermoelectric composites based on semiconducting polymer P3HT, insulating polymers, and carbon nanotubes. The ternary layer composite film is prepared by a straightforward drop‒cast deposition. The design consists of sandwiching an insulating polymer‒CNTs layer between two layers of a semiconducting polymer P3HT. A systematic investigation is employed by optimizing various features including the type of insulating polymers and CNTs (SWNT vs. MWNT), and doping. The electrical conductivity of the doped ternary composites is improved up to 265 S cm−1, with minimal loss in the Seebeck coefficient, leading to power factors (PF) up to ~30 μW m−1 K−2, however electrical conductivity of single‒layer doped P3HT is only 39.1 S cm−1 with a PF of 7.6 μW m−1 K−2 at room temperature. The enhancement in the TE properties can be ascribed to the formation of more efficient charge transport between the layers due to the rearrangement of the polymer chains and the generation of more junctions at the interface during the sequential layer deposition. The results also reveal that this method gives n‒type materials from intrinsically p‒type P3HT, and it switches to p‒type after doping.

Effect of Metallic Nanocoatings Deposited on Silicon Oxide on Wetting by Filler Melts II. Effect from the Annealing of Nanocoatings Deposited on SiO2 on their Structure and Interaction with the Oxide

The sessile drop method using capillary melt cleaning was employed in the experiment to study the effect of metallic nanocoatings (single Ti, Nb, and Mo coatings and binary Ti–Cu, Nb–Cu, and Mo–Cu coatings with a copper layer of constant thickness) on the wetting of silicon oxide by Pb–15 wt.% In melt in 1 ∙ 10–3 Pa vacuum at 500°C after their annealing at 900°C. The metallic coatings were applied by electron beam evaporation in vacuum. The binary coatings were produced by sequential deposition of layers. The dependences of contact angle on coating thickness show that the ‘threshold’ thickness is determined by the annealing temperature of the coating or, in other words, its structure. The threshold coating thickness for different metals depends on their chemical affinity to oxygen. When freshly applied and annealed single Mo, Nb, and Ti coatings are wetted, their threshold thickness increases from 70 to 80 nm for the titanium coating, from 63 to 70 nm for the niobium coating, and from 50 to 60 nm for the molybdenum coating. The structure of Cu, Ni, Mo, Cr, Nb, and Ti coatings annealed at 600, 900, and 1200°C was studied. The initial (freshly deposited) metallic coatings showed high integrity. The coatings became dispersed after annealing and their integrity decreased with increasing temperature. The dispersed metallic coatings formed ‘islands’ of various shapes, round shape being predominant, depending on the chemical affinity of the coating metal to oxygen. The so-called ‘solid’ wetting was observed. The shape of the islands is determined by equilibrium between the metal–substrate attraction forces (interaction, adhesion) and the very strong surface tension of the metal (at such a small coating thickness). To use metallic coatings for brazing quartz with aluminum alloys, coatings of adhesive metals (Mo, Cr, Nb, Ti) should be annealed at temperatures of 900–1000°C with a holding time of 10 min. The coating thickness should be within the threshold range.

Self-Assembled Fluid Phase Floating Membranes with Tunable Water Interlayers.

We present a reliable method for the fabrication of fluid phase, unsaturated lipid bilayers by self-assembly onto charged Self-Assembled Monolayer (SAM) surfaces with tunable membrane to surface aqueous interlayers. Initially, the formation of water interlayers between membranes and charged surfaces was characterized using a comparative series of bilayers deposited onto charged, self-assembled monolayers by sequential layer deposition. Using neutron reflectometry, a bilayer to surface water interlayer of ∼8 Å was found between the zwitterionic phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) membrane and an anionic carboxyl terminated grafted SAM with the formation of this layer attributed to bilayer repulsion by hydration water on the SAM surface. Furthermore, we found we could significantly reduce the technical complexity of sample fabrication through self-assembly of planar membranes onto the SAM coated surfaces. Vesicle fusion onto carboxyl-terminated monolayers yielded high coverage (>95%) bilayers of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) which floated on a 7-11 Å solution interlayer between the membrane and the surface. The surface to membrane distance was then tuned via the addition of 200 mM NaCl to the bulk solution immersing a POPC floating membrane, which caused the water interlayer to swell reversibly to ∼33 Å. This study reveals that biomimetic membrane models can be readily self-assembled from solution onto functionalized surfaces without the use of polymer supports or tethers. Once assembled, surface to membrane distance can be tailored to the experimental requirements using physiological concentrations of electrolytes. These planar bilayers only very weakly interact with the substrate and are ideally suited for use as biomimetic models for accurate in vitro biochemical and biophysical studies, as well as for technological applications, such as biosensors.

Investigation of Ni@CoO core-shell nanoparticle films synthesized by sequential layer deposition

Films of Ni@CoO core-shell nanoparticles (NP Ni core size d≈11nm) have been grown on Si/SiOx and lacey carbon supports, by a sequential layer deposition method: a first layer of CoO was evaporated on the substrate, followed by the deposition of a layer of pre-formed, mass-selected Ni NPs, and finally an overlayer of CoO was added. The Ni NPs were formed by a magnetron gas aggregation source, and mass selected with a quadrupole mass filter. The morphology of the films was investigated with Scanning Electron Microscopy and Scanning Transmission Electron Microscopy. The Ni NP cores have a shape compatible with McKay icosahedron, caused by multitwinning occurring during their growth in the source, and the Ni NP layer shows the typical random paving growth mode. After the deposition of the CoO overlayer, CoO islands are observed, gradually extending and tending to merge with each other, with the formation of shells that enclose the Ni NP cores. In situ X-ray Photoelectron Spectroscopy showed that a few Ni atomic layers localized at the core-shell interface are oxidized, hinting at the possibility of creating an intermediate NiO shell between Ni and CoO, depending on the deposition conditions. Finally, X-ray Magnetic Circular Dichroism at the Ni L2,3 absorption edge showed the presence of magnetization at room temperature even at remanence, revealing the possibility of magnetic stabilization of the NP film.

Tunability of exchange bias in Ni@NiO core-shell nanoparticles obtained by sequential layer deposition

Films of magnetic Ni@NiO core–shell nanoparticles (NPs, core diameter d ≅ 12 nm, nominal shell thickness variable between 0 and 6.5 nm) obtained with sequential layer deposition were investigated, to gain insight into the relationships between shell thickness/morphology, core–shell interface, and magnetic properties. Different values of NiO shell thickness ts could be obtained while keeping the Ni core size fixed, at variance with conventional oxidation procedures where the oxide shell is grown at the expense of the core. Chemical composition, morphology of the as-produced samples and structural features of the Ni/NiO interface were investigated with x-ray photoelectron spectroscopy and microscopy (scanning electron microscopy, transmission electron microscopy) techniques, and related with results from magnetic measurements obtained with a superconducting quantum interference device. The effect of the shell thickness on the magnetic properties could be studied. The exchange bias (EB) field Hbias is small and almost constant for ts up to 1.6 nm; then it rapidly grows, with no sign of saturation. This behavior is clearly related to the morphology of the top NiO layer, and is mostly due to the thickness dependence of the NiO anisotropy constant. The ability to tune the EB effect by varying the thickness of the last NiO layer represents a step towards the rational design and synthesis of core–shell NPs with desired magnetic properties.

Optimizing layer-by-layer deposition of interpolymer complexes on solid substrates using Biacore

The layer-by-layer deposition of polymers onto surfaces allows the fabrication of multilayered materials for a wide range of applications, from drug delivery to biosensors. This work describes the analysis of complex formation between poly(acrylic acid) and methylcellulose in aqueous solutions using Biacore, a surface plasmon resonance analytical technique, traditionally used to examine biological interactions. This technique characterized the layer-by-layer deposition of these polymers on the surface of a Biacore sensor chip. The results were subsequently used to optimize the experimental conditions for sequential layer deposition on glass slides. The role of the solution pH and poly(acrylic acid) molecular weight on the formation of interpolymer multilayered coatings was researched, and showed that the optimal deposition of the polymer complexes was achieved at pHs ≤2.5 with a poly(acrylic acid) molecular weight of 450 kDa.

The effect of the sputtering gas (Ar, Xe) on FePt clusters formation: structural and magnetic properties

It will be reported about the effect of the sputtering gases, Ar and Xe, on FePt clusters formation by magnetron sputtering deposition at high working pressures. All layers, with bulk equivalent thicknesses between 3 to 5 nm, were realized at RT by a sequential layer by layer deposition or a co-deposition of Fe and Pt. After rapid thermal annealing at 500 °C, the highest L10 fraction was found using Xe as sputtering gas: Xe decreases the transformation activation energy and therefore, reduces the critical thickness necessary to obtain the high anistropic ferromagnetic phase. Ar assisted growths lead to FePt clusters in the L10 phase only if the sequential layer deposition is used, whereas for Xe no differences in the deposition techniques were observed.

Rapid structural and chemical characterization of ternary phase diagrams using synchrotron radiation

A technique based on synchrotron radiation was developed that allows for rapid structural and chemical characterization of ternary alloys over a wide range of composition. The technique was applied to isothermal sections of the Cr–Fe–Ni system grown on Al2O3(0001) sapphire substrates by sequential deposition of layers of graded.thickness followed by annealing to interdiffuse the elements. A film spanning the Cr–Fe–Ni ternary system was measured in 4 h at a resolution of 2 at.% by rastering the sample under a focused beam of synchrotron radiation while simultaneously measuring the diffraction pattern with a charge-coupled device detector to determine crystallographic phases, texture, and lattice parameters and also measuring the x-ray fluorescence with an energy-dispersive detector to determine elemental composition. Maps of phase composition and lattice parameter as a function of composition for several annealing treatments were found to be consistent with equilibrium values. The technique will be useful in combinatorial materials design.

Novel Composite Coatings With 3D Coating Architectures for Tribological Applications Fabricated Using Semiconductor Patterning Processes

ABSTRACTComposite coatings consisting of hard compounds and soft solid lubricant phases have been actively investigated as tribological coatings for reducing friction while improving wear resistance. In most cases structural modifications in these coatings have been achieved by either natural phase separation or sequential layer deposition. In this study, we explore the concept of creating a three-dimensional structure in a tribological composite coating by using well-established semiconductor patterning methods. Using photolithography, we have patterned the substrate surface with a regular array of micron-size islands. The substrate was then coated with various metal and carbide coatings, including Cr and TiC, using sputter deposition. The substrates were sonicated in a solvent to remove the photoresist islands leaving an array of holes. MoS2 was then deposited onto the substrates. A pin-on-disk friction and wear test was conducted on a TiC/MoS2 sample to examine the effects of these islands on wear morphology. The results showed that the MoS2-filled holes can act as lubricant reservoirs, and the areas of the sample coated with TiC/MoS2 provided better wear protection than areas coated with only MoS2.

Synthesis and characterization of Pb (ZrxTi1−x)O3 thin films produced by an automated laser ablation deposition technique

Ferroelectric lead zirconium titanate [Pb (ZrxTi1−x)O3] (PZT) thin films have been synthesized by using an automated laser ablation deposition technique with a capability for layer-by-layer or simultaneous deposition of elemental film constituents. The technique is suitable for producing multicomponent and/or multilayered thin films with controlled stoichiometry, such as high-temperature superconductor, ferroelectric, and electro-optic thin films. PZT films were synthesized on MgO (100) by either sequential deposition of layers of ZrO2, TiO2, and PbO, produced by laser ablation of ZrO2, TiO2, and PbO targets, or by simultaneous deposition of all species from ablation of stoichiometric or PbO-rich PZT targets. Films were deposited at 200 °C and subsequently annealed at 600 °C for different periods of time. The orientation, microstructure, surface topography, and composition of the films were characterized by x-ray diffraction, transmission electron microscopy, scanning electron microscopy, and Rutherford backscattering spectrometry, respectively. As-deposited layer films consists of highly oriented (001) PbO layers, from which highly oriented (110) PZT films are produced after postdeposition annealing. On the other hand, laser ablation of bulk PZT targets yields amorphous as-deposited films, which evolve into highly oriented (100) PZT films after postdeposition annealing. Preliminary electrical characterization of the PZT films included polarization hysteresis, fatigue, conductivity (ac and dc), and capacitance versus voltage measurements. From the initial electrical measurements, it appears that the remnant polarization of the layered PZT films is similar to that of the films produced by laser ablation of bulk PZT targets.

Sputtering and Molecular Beam Epitaxy (MBE) Deposition of Magneto-Optical Materials

Materials with anisotropies giving rise to perpendicular magnetization are important for optical data storage applications. However, the microscopic origin of the anisotropies is not well understood. It is now widely recognized that understanding the origin of surface and interface anisotropies is one of the most important problems in magnetism. Ultra-high vacuum deposition techniques allow the sequential deposition of layers of several elements with great regularity, and little interdiffusion and contamination at the interfaces. The microstructure of the resultant multilayer materials can vary from amorphous, or polycrystalline with only short range order, to high quality superlattices with long range structural coherence in all three dimensions. This paper gives an introduction to rare-earth/transitionmetal and transition-metal/transition-metal multilayers and superlattices. Sputtering and Molecular Beam Epitaxy (MBE) processes used to grow these materials are then described, as are the in situ and ex situ characterization techniques used to determine their electronic and physical structure, and to measure their magnetooptic properties. Some of the magnetic and magneto-optic properties of materials produced by sputtering and MBE related to optical data storage are discussed.

Sequence Of Phase Formation In Ni/Ai Contrasted With Ni/Si

ABSTRACTWe have investigated the interactions of Al/Ni, NiAl3/Ni, and Ni2Al3/Ni thin films between 350 and 500°C. Sequential layer deposition and coevaporation were used to prepare the films which were then vacuum annealed and analyzed by Rutherford backseat tering and X-ray diffraction. Initially, NiAl3 is formed, followed by the more Ni-rich phases. All four intermetallic phases were formed.

Magneto-Optic Properties of CrTe Films Prepared by Sequential Evaporation

A study was made of the magnetic properties of CrTe films relevant to magneto-optic memory applications. Polar-Faraday rotation measurements in the visible and near infrared were taken on CrTe films prepared by sequential deposition of layers of Cr–Te–Cr on cleaved mica substrates. The Faraday rotation and absorption decreased respectively from 0.5×105°/cm at 0.55 μm to 0.4×105°/cm at 1 μm and 2×105 cm−1 at 0.5 μm to 0.6×105 cm−1 at 2.5 μm. The rotation and coercive field decreased with the magnetization and vanished at the Curie temperature (∼70°C). The polar remanence ratio was 0.2. An in-plane magnetization curve had a remanence ratio of 0.8, a saturation induction (4πMs) of 1015 G and a coercive field of 117 Oe. The measurements indicate significant advantages for CrTe films in memory applications if the epitaxial growth can be improved resulting in higher polar remanence.