Multilayer Growth Research Articles

Diffusion and nucleation in multilayer growth of PTCDI-C8 studied with in situ X-ray growth oscillations and real-time small angle X-ray scattering.

We study nucleation and multilayer growth of the perylene derivative PTCDI-C8 and find a persistent layer-by-layer growth, transformation of island shapes, and an enhancement of molecular diffusivity in upper monolayers (MLs). These findings result from the evaluation of the ML-dependent island densities, obtained by in situ real-time grazing incidence small angle X-ray scattering measurements and simultaneous X-ray growth oscillations. Complementary ex situ atomic force microscopy snapshots of different growth stages agree quantitatively with both X-ray techniques. The rate and temperature-dependent island density is analyzed using different mean-field nucleation models. Both a diffusion limited aggregation and an attachment limited aggregation model yield in the first two MLs the same critical nucleus size i, similar surface diffusion attempt frequencies in the 1019-1020 s-1 range, and a decrease of the diffusion barrier Ed in the 2nd ML by 140 meV.

Layer-by-layer self-assembly of bisdendrons: An unprecedented route to multilayer thin films

We present an unprecedented route to fabricate multilayer thin films by single component layer-by-layer molecular self-assembly. Tailored water-soluble phosphorus bisdendrons were obtained via core to core assembling of two dendrons bearing anionic groups at one end and quaternizable amino groups at the other end. Adsorption of a 1st bisdendron monolayer on a charged substrate followed by sequential quaternization/deposition of a 2nd layer leads to a stepwise growth of multilayers. By this way, homogeneous multilayer thin films were successfully constructed as confirmed by spectroscopic and microscopic analysis.

Relationship between heating atmosphere and copper foil impurities during graphene growth via low pressure chemical vapor deposition

Low-pressure chemical vapor deposition synthesis of graphene films on two different Cu foils, with different surface oxygen and carbon contents, was performed by controlling H2 and/or Ar flow rates during heating. The influences of heating atmosphere on the final impurity level, quality of the synthesized graphene films and thickness uniformity were investigated depending on Cu foil impurities. Heating of carbon-rich, but oxygen-poor Cu foil in H2 environment resulted in covering the foil surface by residual carbon which then acted as active sites for multilayer graphene growth. Ar-only flow was required during heating to promote high quality graphene growth on this foil. On carbon-poor, but oxygen-rich Cu foil high quality graphene growth was promoted when the heating was carried out under Ar/H2 environment. Almost no carbon residues were observed on this foil even under H2 only flow during heating. The heating atmosphere affected not only graphene growth, but also the type and amount of impurities formed on the surface. H2 and Ar/H2 heating resulted in the formation of spherical nanometer-sized impurities, while irregular-shaped, large (a few μm) SiO2 impurities were observed when Ar alone was used during heating. Quality of the grown films was tested by Quantum Hall Effect measurements.

3D polarization texture of a symmetric 4-fold flux closure domain in strained ferroelectric PbTiO3 films

Abstract

Electrodeposited Iron(III) Oxide (α-Fe<sub>2</sub>O<sub>3</sub>) Thermoelectric Thin Films

α-Fe2O3 thermoelectric thin films were electrodeposited onto copper substrates using chloride-based electrolytes by means of potentiostatic electrodeposition. The influence of several electrodeposition parameters on the surface morphology, elemental composition and electrical conductivity of the deposited films was studied and analyzed. The deposits formed porous, wire-like morphology, with the smallest width measured to be ~60 nm. The wires tend to aggregate to form clusters, in addition to multi-layered growth of the wires. Between the parameters studied, electrolyte concentration and deposition time parameters have higher influences on the electrical conductivity of the deposited films, with the increment up to two fold higher. Deposition potential parameter offered the lowest capability to improve on the electrical conductivity in addition to the non-uniform distribution of the measured electrical conductivities. The tunable electrical conductivity is favorable for improving the performance of α-Fe2O3 films for thermoelectric applications.

Fabrication and Characterization of Cross-Linked Organic Thin Films with Nonlinear Mass Densities.

The preparation of urea (bonded) cross-linked multilayer thin films by sequential deposition of bifunctional and tetrafunctional molecular building blocks is demonstrated. Multilayer growth as a function of deposition cycles was inspected using UV-vis absorption spectroscopy. From infrared results, three characteristic infrared bands of amide I, amide II, and asymmetric νa(N-C-N) stretching confirmed the formation of polyurea networks by alternate dipping into solutions of amine and isocyanate functionality monomers. The deconvoluted component of the C 1s and N 1s spectra obtained by X-ray photoelectron spectroscopy shows clear evidence of stable polyurea networks. The enhancement of structural periodicity with film growth was demonstrated by grazing-incidence small-angle X-ray scattering measurements. The thin film near the substrate surface seems to have an amorphous structure. However, molecular ordering improves in the surface normal direction of the substrate with a certain number of deposited layers. Constant mass density was not observed with deposition cycles. The mass density increased up to 16% within deposited layers from proximate layers to those extending away from the substrate surface. This difference in the packing density might derive from the different degrees of cross-linking among layers proximate to the substrate surface and extending away from the substrate surface.

Thermal decomposition and chemical vapor deposition: a comparative study of multi-layer growth of graphene on SiC(000-1)

ABSTRACTThis work presents a comparison of the structural, chemical and electronic properties of multi-layer graphene grown on SiC(000-1) by using two different growth approaches: thermal decomposition and chemical vapor deposition (CVD). The topography of the samples was investigated by using atomic force microscopy (AFM), and scanning electron microscopy (SEM) was performed to examine the sample on a large scale. Raman spectroscopy was used to assess the crystallinity and electronic behavior of the multi-layer graphene and to estimate its thickness in a non-invasive way. While the crystallinity of the samples obtained with the two different approaches is comparable, our results indicate that the CVD method allows for a better thickness control of the grown graphene.

Extreme Ultraviolet Multilayer Defect Compensation in Computational Lithography.

For the extreme ultraviolet (EUV) lithography, multilayer (ML) defects such as bump and pit defects can disrupt the phase of reflected field and degrade aerial images on wafer. In this paper, a defect printability and repair simulator (DPRS) is introduced to predict and repair the effect of ML defects in EUV aerial images. DPRS is composed of multilayer growth by using Gaussian function and Stearns's method, mask simulation by using a scattering matrix (S-matrix) analysis method, and projection simulation by using Köhler's illumination. For bump and pit ML defects, the combining the modified absorber and the layer-by-layer ML peeling is better than other methods. This study can be helpful in understanding EUV defect and also give insight into the EUV defect compensation for the device volume production.

Identifying Enclosed Chemical Reaction and Dynamics at the Molecular Level Using Shell-Isolated Miniaturized Plasmonic Liquid Marble.

Current microscale tracking of chemical kinetics is limited to destructive ex situ methods. Here we utilize Ag nanocube-based plasmonic liquid marble (PLM) microreactor for in situ molecular-level identification of reaction dynamics. We exploit the ultrasensitive surface-enhanced Raman scattering (SERS) capability imparted by the plasmonic shell to unravel the mechanism and kinetics of aryl-diazonium surface grafting reaction in situ, using just a 2-μL reaction droplet. This reaction is a robust approach to generate covalently functionalized metallic surfaces, yet its kinetics remain unknown to date. Experiments and simulations jointly uncover a two-step sequential grafting process. An initial Langmuir chemisorption of sulfonicbenzene diazonium (dSB) salt onto Ag surfaces forms an intermediate sulfonicbenzene monolayer (Ag-SB), followed by subsequent autocatalytic multilayer growth of Ag-SB3. Kinetic rate constants reveal 19-fold faster chemisorption than multilayer growth. Our ability to precisely decipher molecular-level reaction dynamics creates opportunities to develop more efficient processes in synthetic chemistry and nanotechnology.

Engineering the Structure and Properties of DNA-Nanoparticle Superstructures Using Polyvalent Counterions.

DNA assembly of nanoparticles is a powerful approach to control their properties and prototype new materials. However, the structure and properties of DNA-assembled nanoparticles are labile and sensitive to interactions with counterions, which vary with processing and application environment. Here we show that substituting polyamines in place of elemental counterions significantly enhanced the structural rigidity and plasmonic properties of DNA-assembled metal nanoparticles. These effects arose from the ability of polyamines to condense DNA and cross-link DNA-coated nanoparticles. We further used polyamine wrapped DNA nanostructures as structural templates to seed the growth of polymer multilayers via layer-by-layer assembly, and controlled the degree of DNA condensation, plasmon coupling efficiency, and material responsiveness to environmental stimuli by varying polyelectrolyte composition. These results highlight counterion engineering as a versatile strategy to tailor the properties of DNA-nanoparticle assemblies for various applications, and should be applicable to other classes of DNA nanostructures.

Multiscale Simulation and Modeling of Multilayer Heteroepitactic Growth of C60 on Pentacene.

We apply multiscale methods to describe the strained growth of multiple layers of C60 on a thin film of pentacene. We study this growth in the presence of a monolayer pentacene step to compare our simulations to recent experimental studies by Breuer and Witte of submonolayer growth in the presence of monolayer steps. The molecular-level details of this organic semiconductor interface have ramifications on the macroscale structural and electronic behavior of this system and allow us to describe several unexplained experimental observations for this system. The growth of a C60 thin film on a pentacene surface is complicated by the differing crystal habits of the two component species, leading to heteroepitactical growth. In order to probe this growth, we use three computational methods that offer different approaches to coarse-graining the system and differing degrees of computational efficiency. We present a new, efficient reaction-diffusion continuum model for 2D systems whose results compare well with mesoscale kinetic Monte Carlo (KMC) results for submonolayer growth. KMC extends our ability to simulate multiple layers but requires a library of predefined rates for event transitions. Coarse-grained molecular dynamics (CGMD) circumvents KMC's need for predefined lattices, allowing defects and grain boundaries to provide a more realistic thin film morphology. For multilayer growth, in this particularly suitable candidate for coarse-graining, CGMD is a preferable approach to KMC. Combining the results from these three methods, we show that the lattice strain induced by heteroepitactical growth promotes 3D growth and the creation of defects in the first monolayer. The CGMD results are consistent with experimental results on the same system by Conrad et al. and by Breuer and Witte in which C60 aggregates change from a 2D structure at low temperature to 3D clusters along the pentacene step edges at higher temperatures.

Magnetically controlled space charge capacitance at La1−xSrxMnO3/SrxLa1−xTiO3 interfaces

This work reports on magnetocapacitance (MC) effects in epitaxial heterostructures of nominally 15 unit cells (u.c.) LaMnO3 (LMO) and 2 u.c. SrTiO3 (STO) with an alternating layer‐repetition rate of 8: (LMO15/STO2)8. Epitaxial multilayer growth at high temperatures (900 °C) activates a selective inter‐diffusion of La3+ and Sr2+ cations across the interfaces, which gives rise to Sr p‐doping of the LMO and La n‐doping of the STO layers. MC effects at the buried La1–xSrxMnO3/SrxLa1–xTiO3 (LSMO/SLTO) interfaces are probed by frequency, temperature and magnetic field dependent AC impedance spectroscopy. The technique is shown to be appropriate to account for the separate analysis of different resistance and capacitance contributions at the buried interfaces. As a result of the La/Sr inter‐diffusion process, Schottky barriers are formed at the LSMO/SLTO interfaces, which give rise to massive MC of up to ≈ −200% in the out‐of‐plane film direction. The capacitance of the manganite‐titanate LSMO/SLTO interfaces may be coupled indirectly to the resistance of the LSMO layers, because the Schottky space‐charge layers and their capacitance can be modulated by varying the concentration of highly mobile charge carriers in the LSMO with a magnetic field.

Pentacene on Au(1 1 1), Ag(1 1 1) and Cu(1 1 1): From physisorption to chemisorption

We measured the electronic and the molecular surface structure of pentacene deposited on the (1 1 1)-surfaces of coinage metals by means of ultraviolet photoelectron spectroscopy (UPS) and low-energy electron diffraction (LEED). Pentacene is almost flat-lying in monolayers on all three substrates and highly ordered on Au(1 1 1) and on Cu(1 1 1). On Ag(1 1 1), however, weak chemisorption leads to almost disordered monolayers, both, at room temperature and at 78 K. On Cu(1 1 1) pentacene is strongly chemisorbed and the lowest unoccupied molecular orbital becomes observable in UPS by a charge transfer from the substrate. On Ag(1 1 1) and Cu(1 1 1) multilayers adopt a tilted orientation and a high degree of crystallinity. On Au(1 1 1), most likely, also in multilayers the molecular short and long axes are parallel to the substrate, leading to a distinctively different electronic structure than on Ag(1 1 1) and Cu(1 1 1). Overall, it could be demonstrated that the substrate not only determines the geometric and electronic characteristics of molecular monolayer films but also plays a crucial role for multilayer film growth.

3D solid supported inter-polyelectrolyte complexes obtained by the alternate deposition of poly(diallyldimethylammonium chloride) and poly(sodium 4-styrenesulfonate).

This work addresses the formation and the internal morphology of polyelectrolyte layers obtained by the layer-by-layer method. A multimodal characterization showed the absence of stratification of the films formed by the alternate deposition of poly(diallyldimethylammonium chloride) and poly(sodium 4-styrenesulfonate). Indeed the final organization might be regarded as three-dimensional solid-supported inter-polyelectrolyte films. The growth mechanism of the multilayers, followed using a quartz crystal microbalance, evidences two different growth trends, which show a dependency on the ionic strength due to its influence onto the polymer conformation. The hydration state does not modify the multilayer growth, but it contributes to the total adsorbed mass of the film. The water associated with the polyelectrolyte films leads to their swelling and plastification. The use of X-ray photoelectron spectroscopy has allowed for deeper insights on the internal structure and composition of the polyelectrolyte multilayers.

Few-Layer Silicon Films on the Ag(111) Surface

Growth by molecular beam epitaxy (MBE) of Si on Ag(111) results in a two-dimensional film with (√3 × √3) surface structure at near monolayer (ML) coverage. The same (√3 × √3) pattern persists for coverages of Si up to several MLs. The atomic structure of the resulting Si film has posed an intriguing question. One possible scenario is that Ag acts as a surfactant to foster the low-temperature growth of metastable silicene multilayers, which would be an analogue of graphite and a new state of Si. Yet another possibility is the formation of diamond-structured Si. In our experiment, we use low-temperature scanning tunneling microscopy (LT-STM) to observe the chemical response of the film surface exposed to an atomic deuterium (D) beam. We find D displaces the Ag surfactant adatoms, resulting in a D-terminated (1 × 1) surface. The displaced Ag atoms migrate on the surface to form Ag(111) crystallites. The same reactions have been observed for a Si(111) bulk single-crystal surface decorated by Ag. The results c...

Sputtered tungsten–silver and tungsten–aluminium thin films for non-volatile magnetic memories applications

We report on the structural and electrical characterization of sputter-deposited W–Ag and W–Al alloy thin films which are of interest for non-volatile magnetoresistive random-access memory (MRAM) applications. Films with Ag doping between 5 and 27wt.% and Al doping between 5 and 31wt.% were studied, before and after annealing at 250°. The desired for MRAMs highly resistive β-W phase is obtained after annealing of the 5wt.% Ag-doped film and its resistivity is 112.5±4.3μΩ·cm, lower than the one of annealed pure W films (133.9±4.9μΩ·cm). This W–Ag alloy provides an underlayer for MRAM multilayer growth, improved compared to pure W films.

Comment on "Formation of polyelectrolyte multilayers: ionic strengths and growth regimes" by K. Tang and A. M. Besseling, Soft Matter, 2016, 12, 1032.

Tang and Besseling recently published a study on the growth of polyelectrolyte multilayers formed by poly(diallyl-dimethylammonium chloride), PDADMAC, and the sodium salt of poly(4-styrenesulfonate), PSSNa. They described the different growth regimes appearing in the (PDADMAC + PSS)n multilayers within a scenario in which the appearance of interdiffusion of the polyelectrolyte chains within the multilayer architecture plays a central role in the transition between the different regimes. However, this account contrasts, without an apparent explanation, with previous experimental evidence reported in the literature.

Regulation of the growth, morphology, mechanical properties and biocompatibility of natural polysaccharide-based multilayers by Hofmeister anions.

Herein the optimization of the physicochemical properties and surface biocompatibility of polyelectrolyte multilayers of the natural, biocompatible and biodegradable, linear polysaccharides hyaluronan and chitosan by Hofmeister anions was systematically investigated. We demonstrated that there is an interconnection between the bulk and surface properties of HA/Chi multilayers both varying in accordance with the arrangement of the anions in the Hofmeister series. Kosmotropic anions increased the hydration, thickness, micro- and macro-roughness, and hydrophilicity and improved the biocompatibility of the films by reduction (2 orders of magnitude) of the films stiffness and complete anti-thrombogenicity.

Proteomic Profiling of In-Vitro Bone-Conditioned Skbr3 Breast Cancer Cells

A major complication of advanced breast cancer is the frequent formation of bone metastases. To our knowledge, however, the information on the phenotypic properties of cancer cells able to survive and colonize the bone tissue is still fragmentary. We report here a proteomic study of breast cancer cells (SKBR3) collected after a colonization of bone fragments in a special model of co-culture, used to simulate the phenotype of breast cancer metastasizing cells. The scanning electron microscopy of the seeded cancer cells into the bone fragments, showed their peculiar traits of multilayered growth and spiny surface, typical of a very aggressive phenotype. The comparative proteomic profiling of the bone-conditioned cells (SKBR3-B1) versus the parental cell line (SKBR3-WT), performed by applying two-dimensional electrophoresis (2D-IPG) and mass spectrometry (Maldi / TOF) revealed the existence of an interesting differential proteomic profiling. Within this pattern, an increase of several members of the S100 protein family, not described before in relation to bone metastasis from breast cancer, was observed in the SKBR3-B1. Other up-regulated proteins belong to protein classes involved mainly in cytoskeleton dynamics, chaperone / folding, negative regulation of apoptosis and cell metabolism. These results suggest that, rather than individual proteins, a coordinated network of strategic proteins is able to determine or drive the invasive and metastatic phenotype of breast cancer cells, namely: proteins primarily strategic for the cell penetration and homing into the bone, and proteins coming into play to satisfy the modified metabolic needs of the cells. We believe that the present study represents an innovative approach of co-culture with fresh human bone fragments, and that it may contribute greatly to improve the knowledge of the molecular mechanisms underlying the propensity of breast cancer cells to colonize, survive and proliferate into the bone microenvironment.

Optofluidic Modulation of Self-Associated Nanostructural Units Forming Planar Bragg Microcavities.

Bragg microcavities (BMs) formed by the successive stacking of nanocolumnar porous SiO2 and TiO2 layers with slanted, zigzag, chiral, and vertical configurations are prepared by physical vapor deposition at oblique angles while azimuthally varying the substrate orientation during the multilayer growth. The slanted and zigzag BMs act as wavelength-selective optical retarders when they are illuminated with linearly polarized light, while no polarization dependence is observed for the chiral and vertical cavities. This distinct optical behavior is attributed to a self-nanostructuration mechanism involving a fence-bundling association of nanocolumns as observed by focused ion beam scanning electron microscopy in the slanted and zigzag microcavities. The outstanding retarder response of the optically active BMs can be effectively modulated by dynamic infiltration of nano- and mesopores with liquids of different refraction indices acting as a switch of the polarization behavior. The unprecedented polarization and tunable optofluidic properties of these nanostructured photonic systems have been successfully simulated with a simple model that assumes a certain birefringence for the individual stacked layers and accounts for the light interference phenomena developed in the BMs. The possibilities of this type of self-arranged nanostructured and optically active BMs for liquid sensing and monitoring applications are discussed.