Surface Morphology Of Substrate Research Articles

Criteria for the growth of large-area adlayer-free monolayer graphene films by chemical vapor deposition

Homogeneity is important to material applications for good performance of individual devices, for making AB-stacked bilayer graphene in a layer-by-layer stacking order, and from the point of view of industrial production. Among many properties to be controlled, for the case of graphene, the thickness (or layer number) uniformity is the prerequisite. Chemical vapor deposition (CVD) of C precursors on Cu substrates is the most popular method to produce large-area graphene films. To date, precise control on the number of graphene layers as well as the uniformity over a large area is still very challenging. In this work, with a further understanding of the factors affecting adlayer growth, the synthesis of large-area adlayer-free monolayer graphene (MLG) films was achieved up to tens of squared centimeters in area by just using untreated Cu foil and a normal CVD process. We found that keeping equal C precursor concentration on the two sides of the Cu substrate is a criterion in addition to other factors such as the ratio of H:C and the substrate surface morphology for the growth of adlayer-free MLG. This finding is not only of great significance for the industrial production of large-area adlayer-free MLG films but also instructive for the synthesis of homogeneous few-layer graphene.

Adhesion strength of titanium particles to alumina substrates: A combined cold spray and LIPIT study

The cold spray process and laser-induced projectile impact test (LIPIT) are used to deposit Ti powder particles on sintered polycrystalline Al2O3. Whereas LIPIT allows real-time observations of single particle impact and measurement of particle impact velocity, cold spray rapidly and simultaneously deposits particles with a wide range of deposition velocities and sizes. By use of these two techniques, the effect of particle velocity and substrate morphology on adhesion strength of single splats is investigated. The critical velocity for deposition is identified to be approximately 580 m/s for the Ti/Al2O3 system when using LIPIT and particles of 10 μm. Above the critical velocity, flattening ratio (FR) is also evaluated and observed to be linearly dependent on the particle impact velocity. Splat adhesion testing is performed on LIPIT-deposited as well as on cold spray-deposited powder particles to measure adhesion strength. This analysis shows that adhesion strength is highly affected by local substrate surface morphology, where particles bond more weakly to relatively smooth portions of the substrate. Therefore, mechanical bonding plays a significant role in adhesion. Also, adhesion strength decreases with an increase in FR and therefore velocity. This decrease can be associated with fracture of the ceramic substrate and rebound forces.

Effect of Atmospheric Pressure Plasma Treatment on Adhesive Bonding of Carbon Fiber Reinforced Polymer.

To improve the strength of the adhesive-bonded carbon fiber reinforced polymer (CFRP) joints, atmospheric pressure plasma treatment (APPT) was used to treat a CFRP substrate surface. This study investigated the effects of nozzle distance (i.e., the distance between plasma nozzle and CFRP substrate) and nozzle speed (i.e., the moving speed of plasma nozzle relative to CFRP substrate) of APPT on the lap-shear strength of adhesive-bonded CFRP joints. Results show that the lap-shear strength of plasma-treated CFRP joints increased to a peak value and then decreased as the nozzle distance increased, and the nozzle distance associated with the peaked joint strength depends on the applied nozzle speed. The lap-shear strength of plasma-treated adhesive-bonded CFRP joints reaches up to 31.6 MPa, compared to 8.6 MPa of the as-received adhesive-bonded CFRP joints. The surface morphology of plasma-treated CFRP substrates was investigated by scanning electron microscope observation, and the mechanism associated with the improved joint strength after applying APPT was revealed through surface chemistry analysis. It is found that APPT not only effectively removed the content of Si element and –CH3 (i.e., the main compositions of release agent) from the as-received CFRP substrate surface, but also generated many polar groups (i.e., –NH2, –OH, –COOH, etc.), which has a positive effect on increasing the wettability and interfacial bonding strength of CFRP substrates and consequently results in a significant improvement of lap-shear strength of plasma-treated CFRP joints. In addition, the result of differential scanning calorimetry (DSC) test shows that the surface temperature of CFRP substrate should not exceed 175.3 °C during APPT. In this study, an empirical model governing temperature, nozzle distance and nozzle speed was established to guide the selection of atmospheric pressure plasma treatment process parameters in industrial manufacture.

Complex Monolayer Growth Dynamics of a Highly Symmetric Molecule: NTCDA on Ag(111)

The growth dynamics of the highly symmetric planar organic molecule NTCDA (1,4,5,6-naphthalene tetracarboxylic acid dianhydride) on Ag(111) is rather complex, already in the monolayer regime. This dynamics was investigated in situ with high lateral resolution using the aberration-corrected spectro-microscope SMART. Although the molecular structure of NTCDA is very similar to that of the slightly larger molecule PTCDA, the growth behavior of these two molecules is very different. Several differences of the static geometric, electronic, and vibrational structure have been described previously by several authors, but some dynamic properties hardly accessible by other techniques could be observed in the present real time experiments using the SMART. For instance, it is found by direct observation that after decoration of steps and step bunches and depending on substrate temperature and surface morphology, a two-dimensional lattice gas of diffusing NTCDA molecules is formed. This increases in density upon continuous deposition of molecules before islands nucleate which subsequently grow in size while the density of the lattice gas first remains constant and then is reduced. Furthermore, in a certain temperature and coverage range some macroscopic islands (of micrometer size) abruptly change their shape and position on the time scale of few seconds. These “jumping 2-dim droplets” are observable for adsorption as well as for desorption. Moreover, previously observed 2-dimensional phase transitions can now be followed in real time, yielding further insight into an interesting but complex adsorption system.

Optimization of silver nanowire formation on laser processed PEN: Surface properties and antibacterial effects

Combination of polymers with their excellent workability and long-term stability with inorganic nanomaterials exhibiting unique physic-chemical properties opens the way for preparation of nanocomposites with wide range of potential applications in electronic, environmental, medical and biomedical industry. Despite of testing of various metal nanostructures in biomedicine, the best results, particularly antibacterial effects, have been achieved with the silver-based ones. Silver nanowire arrays on the surface of polyethylene naphthalate (PEN), first modified by KrF excimer laser irradiation and then silver coated, were prepared. The laser fluence and angle of incidence of laser beam, were changed to achieve required sample surface morphology, which was controlled by AFM, SEM and FIB-SEM techniques. The surface properties of the samples in different phases of their preparation were characterized by XPS and UV–Vis. The influence of the surface morphology of the samples on their antibacterial effect was investigated by drop plate method using Gram-negative bacteria E. coli and Gram-positive S. epidermidis. The release of Ag ions into working medium was controlled by ICP-MS. The surface morphology of polymeric substrate was found to have a great influence on the resulting antibacterial effect of such silver/polymer composites.

Detection and plasma assisted degradation of dye on reusable gold coated tungsten nanofuzz array surface-enhanced Raman scattering substrate

A novel gold coated tungsten nanofuzz array (TNFA) substrate has been prepared by irradiating polycrystalline tungsten using radio frequency plasma, followed by gold sputter coating. The surface morphology of the tungsten can be modified by tuning the irradiation parameters. The surface-enhanced Raman scattering (SERS) effect of the as prepared substrates has been tested using different molecule probes, namely, Rhodamine B (RHB), brilliant blue (X-BR) and reactive brilliant red (X-3B). Results show that the TNFA substrate exhibit the highest dye detection sensitivity (as low as <10 ppb) and excellent repeatability. A simple room temperature atmospheric pressure plasma treatment can be used to clean the substrate for re-use purpose through complete oxidization/degradation of the dye species. Systematic study reveals that the SERS enhancement effect is strongly dependent on the substrate surface morphologies and the laser excitation wavelength used. In addition, the SERS activity achieved by our novel substrate can be applied to a variety of dye molecules, demonstrating its potential to be generalized for a wider range of applications.

Magnetron deposition of yttria-stabilised zirconia electrolyte for solid oxide fuel cells

The aim of the article is to review the latest achievements in the field of magnetron deposition of thinfilm yttria-stabilised zirconia (YSZ) electrolyte for solid oxide fuel cells (SOFC). The main attention is paid to the use of magnetron sputtering for formation of YSZ electrolyte up to 10 μm thick on the anode substrates of intermediate-temperature SOFCs operating at a temperature of (600 - 800)°C . The influence of the types of power sources and such deposition parameters as substrate temperature, substrate bias voltage, post-annealing treatment, etc., as well as the morphology of the anode substrate surface on the microstructure and properties of the deposited electrolyte is analyzed. It is shown that the magnetron sputtering method, despite its relatively high cost and complexity, is applicable to large area SOFC cells and is competitive compared to traditional methods of electrolyte formation, such as tape casting, tape calendering, electrophoretic deposition and screen printing.

On the porosification of LTCC substrates with sodium hydroxide

Outstanding material properties of low temperature co-fired ceramics (LTCC) make them the technology of choice when targeting the realization of robust, highly integrated substrates or packaging solutions for micromachined devices. However, the relatively high permittivity limits their utilization in high-frequency applications, as in addition defined areas with reduced permittivity in one single LTCC layer would be most beneficial. The wet-chemical porosification method under alkaline conditions is a novel and most advantageous approach which can be applied for permittivity reduction through locally embedding air into the LTCC surface in its as-fired state with low impact on the surface characteristics. The resulting porosity of the LTCC substrates after the etching process is strongly affected by the LTCC tape composition as well as the etch parameters. Since the chemical composition of the tape is desired to be unaltered, optimizing the etching parameters, namely etchant concentration, etching time, and bath temperature is a reasonable procedure which allows tailoring the porosification process for the LTCC tapes in their as-fired state.In this work the etching behavior and surface morphology of the LTCC substrates have been studied, both qualitatively and quantitatively, and detailed gravimetric and roughness measurements, as well as porosification depth investigations, were carried out. The conducted analyses suggest a dominating reaction-controlled mechanism for the etching process. In addition to generating a tailored porosity in the surface-near region, overall thickness reduction of the LTCC through the overall dissolution of the LTCC surface under a defined etching condition was also possible. The experimental results were finally fitted into a nonlinear polynomial model for providing an experimental basis in order to identify the most crucial parameters to achieve a tailored porosity.

Unveiling the Direct Correlation between the CVD-Grown Graphene and the Growth Template

Chemical vapor deposition (CVD) is known to produce continuous, large-area graphene sheet with decent physical properties. In the CVD process, catalytic metal substrates are typically used as the growth template, and copper has been adopted as the representative material platform due to its low carbon solubility and resulting monolayer graphene growth capability. For the widespread industrial applications of graphene, achieving the high-quality is essential. Several factors affect the qualities of CVD-grown graphene, such as pressure, temperature, carbon precursors, or growth template. In this work, we provide detailed analysis on the direct relation between the metallic growth substrate (copper) and overall properties of the resulting CVD-grown graphene. The surface morphology of copper substrate was modulated via simple chemical treatments, and its effect on physical, optical, and electrical properties of graphene was analyzed. Based on these results, we propose a simple synthesis route to produce high-quality, continuous, monolayer graphene sheet, which can facilitate the commercialization of CVD graphene into reality.

In situ non-catalyst synthesis of multiwall carbon nanotubes and nanofibers on commercial stainless steel cylinder

Herein, we report the in situ synthesis of multi wall carbon nanotubes (MWCNTs) in addition to nanofibers on the surface of an acid etched commercial stainless cylinder in a catalytic chemical vapor deposition reactor using ethanol as a carbon source. The MWCNTs and nanofibers mixture was characterized via SEM, EDS, TEM and XRD techniques. SEM imaging showed randomly oriented thick carbon nanotubes (CNTs) of different shapes and sizes accompanied by carboneous material. EDX analysis showed carbon content of ≈ 97%. The TEM images showed thick (MWCNTs) in the range of 20–70 nm with ≈ 0.4 nm distance between the concentric tubes forming the walls. Furthermore, the SEM and TEM reflections exhibited carbon nano-fibers of about 300 nm diameters. The XRD confirmed the characteristic peaks of the graphite at 2Ө value of 26° and 43°. The structure of the nanotubes was correlated to the surface morphology of the steel substrate. The simultaneous formation of CNTs and nanofiber on stainless steel without a catalyst was successfully accomplished. The growth of nanotubes and nanofibers almost takes the same approaches with the difference in the size of nanoparticles and its orientation was detrimental in the type of product. Smaller nanopraticles entering longitudinally are observed inside the nanotubes, whereas transversely oriented large nanoparticles are observed in case of nanofibers. An excellent perceptive of nanotubes and nanofibers growth on metal surface is perhaps an excellent approach to explore the mass production of such carbon nanostructures, control conditions and surface in quest to tailor well-designed structures. These results give a clue to the possibility of using commercial stainless steel as a substrate and catalyst for versatile route preparation of multi-wall CNTs.

Surface morphology of amorphous SiO2 substrates bombarded with 1.0 MeV Si+ ions

Surface pattern formation on amorphous SiO2 substrates by implantation of 1.0 MeV Si+ ions at a current of 1.3 µA at 70° angle is reported. Surface micrometer sized ripples perpendicular to the ion beam direction are formed, observed by scanning electron microscopy and atomic force microscopy. The morphological features are more or less similar for different fluences. The formation of surface ripples at this energy is discussed in terms of ion stopping mechanisms and patterns obtained within the low- and medium-energy ranges.

(Invited) High Field THz Spectroscopy of Monolayer Graphene: Effect of Grain Size and Doping

Using a high terahertz electric field (E THz), up to 282 kV/cm, the optical conductivity of monolayer graphene is studied as functions of grain size and doping concentration. In order to study the effect of the grain size on the optical conductivity, the graphene with three different grain size, small (5 μm), medium (70 μm), and large grains (500 μm), are prepared by controlling surface morphology of Cu substrates. The dominant carrier scattering source in large- and small-grained graphene differs at high field, i.e., optical phonon scattering for the large grained, but defect scattering for the small grained. The enhanced optical phonon scattering in high THz field from the large-grained graphene is caused by a higher optical phonon temperature, originating from the slow relaxation of accelerated electrons. Unlike the large-grained graphene, lower electron and optical phonon temperatures are found in the small-grained graphene, resulting from the effective carrier cooling through the defects, called supercollisions. In addition, the optical conductivity of graphene monolayer shows an opposite behavior between at high and low doping concentration of the graphene. At large Fermi energy > 110 meV, the conductivity reduced with increasing THz field, resulting from the emission of optical phonons by excited electrons. However, for ≤ 110 meV, electron–phonon scattering rate is suppressed owing to the diminishing density of states near the Dirac point. Therefore, E THz continues to accelerate carriers without them losing energy to optical phonons, allowing the carriers to travel at the Fermi velocity. This leads to the enhanced optical conductivity of graphene when EF is low. The exotic carrier dynamics does not result from the massless trait, but the electron-optical phonon scattering rate that depends on Fermi-level in the graphene. Our observations provide insight into the application of graphene for high-speed electronics without degrading carrier mobility.

Influence of hydrogen intercalation on graphene/Ge(0 0 1)/Si(0 0 1) interface

Hydrogen intercalation is widely used to weaken graphene-substrate interactions and as a result enhancing graphene’s electronic properties. This paper presents the study of microstructure of hydrogen intercalated graphene grown on Ge(0 0 1)/Si(0 0 1) substrate using Low-Voltage Scanning Electron Microscopy. The findings reveal a significant change in the surface morphology of germanium substrate: faceting structure disappears almost completely, the germanium surface flattens, and steps/terraces are formed. This leads to degradation of graphene’s electronic properties, which shows the negative impact of hydrogen intercalation when graphene is grown on the germanium substrate.

Highly-efficient low cost anisotropic wet etching of silicon wafers for solar cells application

In this work, a novel aqueous etching solution was investigated for texturization of silicon substrates. Nearly 30% of incident light is reflected from the surface of crystalline silicon due to its high refractive index. Surface texturization is an efficient practice to reduce surface reflection by enhancing light trapping. Newly formulated etching solution was evaluated for optical reflection, surface morphology and hydrophilicity of silicon substrates. Amazingly, experimental results demonstrate lowest optical reflectance, improved surface morphology as well as enhanced periodicity of the resulting pyramids. A remarkably lowest surface reflectance of 9.94% was achieved. Meanwhile, addition of IPA in the solution plays a major part in improving hydrophilicity of the silicon substrates.

Influence of substrate surface morphology on wetting behavior of tracks during selective laser melting of aluminum-based alloys

AlSi12 samples were prepared by selective laser melting (SLM) under different processing conditions in order to obtain different top surface morphologies, where single tracks were produced using a fixed processing parameter to reveal the mechanism of the single track on different morphologies. The results show that the morphologies of single tracks changed with roughness of the top surface (Top Ra) of SLM parts, reflected in the variation of wetting angles on the surface processed previously as well as in dimensions of height, width, and depth at the cross-section of each single track. These changes were mainly caused by different wettability and flow behavior of the molten metal under various solidification environments of the single track during SLM. A poor solidification environment in which numerous balls existed limited an effective wetting behavior of molten metal on a previously processed surface of a SLM sample because of an increasing solid-liquid contact area, thus causing dramatical instability of the melt pool and attendant inferior processability of the single track. Meanwhile, under the action of surface tension, the molten metal had a high tendency to transfer into a pore near the single track to form an extending track or flow toward an upper region of melt to form a balling track, hence showing various morphologies of single tracks. This study proposes a theory of the solidification mechanism of single track on the non-ideal surface to provide a better understanding of the SLM processing of Al-Si alloy.

Atomic force microscopy analysis of alkali textured silicon substrates for solar cell applications

In this paper, the surface morphology of textured silicon substrates is explored. Prior to the surface morphology analysis, textured silicon substrates were obtained by KOH anisotropic texturing of polished silicon wafers. This was achieved by investigating of the dependence surface texturing on the process parameters; etchant concentration, etching time and temperature. The surface morphology of the textured silicon samples was obtained using atomic force microscopy that was operated in the tapping mode. The resulting atomic force microscopy (AFM) images were analyzed using the Nanoscope and Gwyddion software packages. The AFM analysis revealed more surface details such as the depth, roughness, section, and step height analysis. The analysis was limited to a length scale of a few micrometers, which carefully reveals the number of individualities of the initial stages of pyramid growth. The average roughness was found to be 593nm for an optimally textured silicon wafer. The implications of the study are then discussed for potential light trapping application in silicon solar cells.

Morphology Evaluation of Microelectronic Packaging Substrates Using Shadow Moiré Technique

The surface quality and long-term reliability of packaging substrates in microelectronic packaging processes have become subjects of increasing concern as circuit board component density increases while the pitches of these components decrease. As a result, packaging substrate morphology inspection is becoming more crucial than ever before. This paper presents a noncontact measurement technology based on a shadow moire technique to evaluate the surface quality and morphology of microelectronic packaging substrates. Fringe pattern images of packaging substrates are acquired through the noncontact measurement technology, and the resulting images are then analyzed using the phase-shifting technique to determine the morphology and surface quality (specifically, the flatness) of the microelectronic packaging substrates. A full-field morphology measurement system with adjustable sensitivity and measurement range was developed. The measurement system was tested using three typical types of microelectronic packaging substrate, a coin and a step made from two standard gauge blocks. The measurement system proved to be both feasible and effective by the test results.

Investigation of osteogenic responses of Fe-incorporated micro/nano-hierarchical structures on titanium surfaces.

Effective and fast osseointegration is important for the survival of titanium-based orthopaedic implants. Previous studies confirmed that topographic features combined with inorganic ions showed positive effects on the biological functions of osteoblastic cells. In this study, we report an approach for fabricating Fe-incorporated micro-nano hierarchical structures on titanium substrates, which was realized by dual acid etching and subsequent hydrothermal treatment. The surface morphology, surface chemistry and wettability of the titanium substrates were characterized using scanning electron microscopy, X-ray photoelectron spectroscopy and contact angle measurements, respectively. The Fe-incorporated micro-nano hierarchical titanium substrates were probed to be biocompatible and positively improved protein adsorption, cell proliferation and cell differentiation of osteoblasts in vitro. Furthermore, the Fe-incorporated titanium substrates significantly enhanced the expressions of osteogenic genes (such as Runx2, Col I, OPN, and OCN), which were attributed to the synergistic effects of micro-nano structures and Fe ions. More importantly, the Fe-incorporated titanium implants with micro-nano hierarchical structures promoted new bone formation in vivo. This study provides an alternative for the development of orthopaedic implants with improved osseointegration for potential clinical applications.

A Study on the Role of Additives in Non-Cyanide Baths for the Fabrication of Anisotropic Metallic Nanostructures

In this study, bath solutions have been prepared for synthesis of gold nanostructures. The role of different additives in bath formulations and their effects on gold nanostructures has been investigated. Synthesis of gold nanostructures through electroless deposition is widely performed using cyanide baths. Here, two non-cyanide gold solutions (bath A and B) are prepared in house and a commercial cyanide gold plating solution (bath C) is used. The 2-Mercaptobenzothiazole that may act as a stabilizing agent is added in Bath A. The Na L-Ascorbate that is a reducing agent is added in bath B. The zeta potential analysis was carried out that exhibited bath B as the most stable formulation. A variety of metallic substrates like silver, copper and nickel have been studied. The surface morphology of metallic substrates was characterized using SEM technique. Anisotropic gold nanostructures of different shapes like star, spherical, dendrite, polyhedral were achieved using non-cyanide baths.

Impact of short duration, high-flow H2 annealing on graphene synthesis and surface morphology with high spatial resolution assessment of coverage

Treatment of graphene growth substrates with H2 has long been known to impact the quality of deposited graphene. However, the parameters for hydrogen treatment that are considered the optimum – very long anneals under low hydrogen concentrations – are often undesirable for practical reasons. In this paper we optimize anneal parameters for fast anneals of <1 h, via investigation of both substrate surface modification and graphene growth quality using a number of traditional and novel experimental techniques. Our results indicate a dual effect of H2 annealing on the surface morphology of the copper substrate, and consequent graphene growth quality, whereby H2 passivates and smoothens the Cu surface, causing it to become morphologically more favorable for graphene growth, but may in large quantities make the surface less chemically favorable, limiting the quality of grown graphene. Moreover, we use a novel method based on Atomic Force Microscopy (AFM) for higher spatial resolution analysis of the homogeneity of graphene using maps of the Hamaker coefficient.