We report on detailed microscopy studies of graphene and few-layer-graphene produced by mechanical exfoliation on various semi-conducting substrates. We demonstrate the possibility to prepare and analyze graphene on (001)-GaAs, manganese p-doped (001)-GaAs and InGaAs substrates. The morphology of graphene on these substrates was investigated by scanning electron and atomic force microscopy and compared to layers on silicon oxide. It was found that graphene sheets strongly follow the texture of the sustaining substrates independent on doping, polarity or roughness. Furthermore resist residues exist on top of graphene after a lithographic step. The obtained results provide the opportunity to research the graphene-substrate interactions.
We delineate a general theoretical framework to determine the substrate-regulated graphene morphology through energy minimization. We then apply such a framework to study the graphene morphology on a substrate with periodic surface grooves. Depending on the substrate surface roughness and the graphene-substrate interfacial bonding energy, the equilibrium morphology of graphene ranges from 1) closely conforming to the substrate, to 2) remaining flat on the substrate. Interestingly, in certain cases, the graphene morphology snaps between the above two limiting states. Our quantitative results en…
We perform in-situ two-cycle thermal cycling and annealing studies for a transferred CVD-grown monolayer MoS2 on a SiO2/Si substrate, using spatially resolved micro-Raman and PL spectroscopy. After the thermal cycling and being annealed at 305 deg C twice, the film morphology and film-substrate bonding are significantly modified, which together with the removal of polymer residues cause major changes in the strain and doping distribution over the film, and thus the optical properties. Before annealing, the strain associated with ripples in the transferred film dominates the spatial distributio…
Understanding the adhesion between graphene and other materials is crucial for achieving more reliable graphene-based applications in electronic devices and nanocomposites. The ultra-thin profile of graphene, however, poses significant challenge to direct measurement of its adhesion property using conventional approaches. We show that there is a strong correlation between the morphology of graphene on a compliant substrate with patterned surface and the graphene-substrate adhesion. We establish an analytic model to quantitatively determine such a strong correlation. Results show that, dependin…
The graphene morphology regulated by nanowires patterned in parallel on a substrate surface is quantitatively determined using energy minimization. The regulated graphene morphology is shown to be governed by the nanowire diameter, the nanowire spacing and the interfacial bonding energies between the graphene and the underlying nanowires and substrate. We demonstrate two representative regulated graphene morphologies and determine critical values of the nanowire spacing, nanowire diameter and interfacial bonding energies at which graphene switches between the two representative morphologies. I…
Thin films of gold were deposited on single crystalline CaF2 substrates of (100) and (111) orientation by thermal evaporation. The resulting film structure was analyzed by means of atomic force microscopy in dependence of substrate temperature and deposition thickness. A marked substrate dependency was found. On CaF2 (100), extended and flat plateaus with diameters of several hundreds of nanometers form in a network-like arrangement for deposition thicknesses between 30 and 45 nm. On CaF2 (111), closed films of small average roughness develop at film thicknesses between 70 and 90 nm. These fil…
We report measurements of the electronic structure and surface morphology of exfoliated graphene on an insulating substrate using angle-resolved photoemission and low energy electron diffraction. Our results show that although exfoliated graphene is microscopically corrugated, the valence band retains a massless fermionic dispersion, with a Fermi velocity of ~10^6 m/s. We observe a close relationship between the morphology and electronic structure, which suggests that controlling the interaction between graphene and the supporting substrate is essential for graphene device applications.
Graphene monolayers supported on oxide substrates have been demonstrated with superior charge mobility and thermal transport for potential device applications. Morphological corrugation can strongly influence the transport properties of the supported graphene. In this paper, we theoretically analyze the morphological stability of a graphene monolayer on an oxide substrate, subject to van der Waals interactions and in-plane mismatch strains. First, we define the equilibrium separation and the interfacial adhesion energy as the two key parameters that characterize the van der Waals interaction b…
Layered van der Waals (vdW) materials grown by physical vapor deposition techniques are generally assumed to have a weak interaction with the substrate during growth. This leads to films with relatively small domains that are usually triangular and a terraced morphology. In this paper, we demonstrate that Bi2Se3, a prototypical vdW material, will form a nano-column morphology when grown on GaAs(001) substrates. This morphology is explained by a relatively strong film/substrate interaction, long adatom diffusion lengths, and a high reactive selenium flux. This discovery paves the way toward gro…
Growth of Co film on SiO2 substrates with the surface roughness of 0.5 nm and 1.6 nm has been studied in situ using the magneto-optical Kerr effect (MOKE) and four probe resistivity measurements. In-situ measurements jointly suggest the Volmer-Weber growth process and proceed via a nonmagnetic, superparamagnetic and ferromagnetic phase formation on both substrates. Islands are found to coalesce at film thicknesses of 0.6 nm and at 1.5 nm with continuous film formation around film thicknesses of 1.5 nm and 3.0 nm for smooth and rough substrates, respectively. Ferromagnetic long-range ordering i…
Morphology of polymer electrolytes membranes (PEM), e.g., Nafion, inside PEM fuel cell catalyst layers has significant impact on the electrochemical activity and transport phenomena that determine cell performance. In those regions, Nafion can be found as an ultra-thin film, coating the catalyst and the catalyst support surfaces. The impact of the hydrophilic/hydrophobic character of these surfaces on the structural formation of the films has not been sufficiently explored yet. Here, we report about Molecular Dynamics simulation investigation of the substrate effects on the ionomer ultra-thin …
We determine the graphene morphology regulated by substrates with herringbone and checkerboard surface corrugations. As the graphene/substrate interfacial bonding energy and the substrate surface roughness vary, the graphene morphology snaps between two distinct states: 1) closely conforming to the substrate and 2) remaining nearly flat on the substrate. Such a snapthrough instability of graphene can potentially lead to desirable electronic properties to enable graphene-based devices.
Using a CO$_2$ laser to directly heat the crystals from the back side, SrTiO$_3$ substrates may be thermally prepared in situ for epitaxy without the need for ex-situ etching and annealing. We find that the formation of large terraces with straight steps at 900-1100 °C is independent from the formation of the ideal surface reconstruction for epitaxy, which requires temperatures in excess of 1200 °C to complete. The process may be universal, at least for perovskite oxide surfaces, as it also works, at different temperatures, for LaAlO$_3$ and NdGaO$_3$, two other widely used oxide substrate mat…
Carbon is one of the most investigated materials and shows chaotic behavior in terms of evolving structure. Synthesizing carbon materials largely depend on the deposition technique, process parameters, condition of substrate surface and ratios of the gaseous chemistry. A variety of techniques have been employed to depositing carbon films from various gaseous mixtures to different substrate materials. In this study, carbon thin and thick films are discussed for different techniques known as hot filament chemical vapor deposition and microwave plasma chemical vapor deposition where their synthes…
Organic-inorganic metal halide perovskites have recently attracted increasing attention as highly efficient light harvesting materials for photovoltaic applications. However, the precise control of crystallization and morphology of organometallic perovskites deposited from solution, considered crucial for enhancing the final photovoltaic performance, remains challenging. In this context, here, we report on growing microcrystalline deposits of CH3NH3PbI3 (MAPbI3), by one-step solution casting on cylinde-shaped quartz substrates (rods). We show that the substrate curvature has a strong influence…
Graphene is intrinsically non-flat and corrugates randomly. Since the corrugating physics of atomically-thin graphene is strongly tied to its electronics properties, randomly corrugating morphology of graphene poses significant challenge to its application in nanoelectronic devices for which precise (digital) control is the key. Recent studies revealed that the morphology of substrate-supported graphene is regulated by the graphene-substrate interaction, thus is distinct from the random intrinsic morphology of freestanding graphene. The regulated extrinsic morphology of graphene sheds light on…
Herein, an effort has given to sheds light on the effects of plasma process parameters on the growth of vertical graphene nanosheets (VGNs) by plasma enhanced chemical vapor deposition (PECVD. The parameters include substrate temperature, microwave power and distance between plasma sources to substrate. The significant influence of these variable parameters is observed on the morphology, growth rate and crystallinity. Thus these parameters are found to be deciding factors, which determine the surface reaction and growth kinetics that governed the final structure and controlled morphology of VG…
We study the effect of the presence of a regular substrate pattern on the irreversible adsorption of nanosized and colloid particles. Deposition of disks of radius $r_0$ is considered, with the allowed regions for their center attachment at the planar surface consisting of square cells arranged in a square lattice pattern. We study the jammed state properties of a generalized version of the random sequential adsorption model for different values of the cell size, $a$, and cell-cell separation, $b$. The model shows a surprisingly rich behavior in the space of the two dimensionless parameters $α…
Ice accumulation hinders the performance of, and poses safety threats for infrastructure both on the ground and in the air. Previously, rationally designed superhydrophobic surfaces have demonstrated some potential as a passive means to mitigate ice accretion; however, further studies on material solutions that reduce impalement and contact time for impacting supercooled droplets and can also repel droplets that freeze during surface contact are urgently needed. Here we demonstrate the collaborative effect of substrate flexibility and surface nanotexture on enhancing both icephobicity and the …
Vertical graphene nanosheets (VGNs) are the material of choice for next-generation electronic device applications. The growing demand for flexible devices in electronic industry brings in restriction on growth temperature of the material of interest. However, VGNs with better structural quality is usually achieved at high growth temperatures. The difficulty associated with the direct growth on flexible substrates can overcome by adopting an effective strategy of transferring the well grown VGNs onto arbitrary flexible substrates through soft chemistry route. Hence, we demonstrated a simple, in…
Smooth interfaces and surfaces are beneficial for most (opto)electronic devices based on thin films and their heterostructures. For example, smoother interfaces in (010) beta-Ga2O3/(AlxGa1-x)2O3 heterostructures, whose roughness is ruled by that of the Ga2O3 layer, can enable higher mobility 2DEGs by reducing interface roughness scattering. To this end we experimentally prove that a substrate offcut along the [001] direction allows to obtain smooth beta-Ga2O3 layers in (010)-homoepitaxy under metal-rich conditions. Applying In-mediated metal-exchange catalysis (MEXCAT) in molecular beam epitax…
Two-dimensional simulations are used to explore topological transitions that occur during the formation of films grown from grains that are seeded on substrates. This is done for a relatively large range of the initial value $Φ_s$ of the grain surface fraction $Φ$. The morphology of porous films is captured at the transition when grains connect to form a one-component network using newly developed raster-free algorithms that combine computational geometry and network theory. Further insight on the morphology of porous films and their suspended counterparts is obtained by studying the pore surf…
We investigate the morphology of quasi-free-standing monolayer graphene (QFMLG) formed at several temperatures by hydrogen intercalation and discuss its relationship with transport properties. Features corresponding to incomplete hydrogen intercalation at the graphene-substrate interface are observed by scanning tunneling microscopy on QFMLG formed at 600 and 800°C. They contribute to carrier scattering as charged impurities. Voids in the SiC substrate and wrinkling of graphene appear at 1000°C, and they decrease the carrier mobility significantly.
Manganite thin films are promising candidates for studying the strongly correlated electron systems. Understanding the growth-and morphology-driven changes in the physical properties of manganite thin films is vital for their applications in oxitronics. This work reports the morphological, structural, and electrical transport properties of nanostructured Nd0.6Sr0.4MnO3 (NSMO) thin films fabricated using the pulsed laser deposition technique. Scanning electron microscopy (SEM) imaging of the thin films revealed two prominent surface morphologies: a granular and a unique crossed-nano-rod-type mo…
We investigate the growth of the graphene buffer layer and the involved step bunching behavior of the silicon carbide substrate surface using atomic force microscopy. The formation of local buffer layer domains are identified to be the origin of undesirably high step edges in excellent agreement with the predictions of a general model of step dynamics. The applied polymer-assisted sublimation growth method demonstrates that the key principle to suppress this behavior is the uniform nucleation of the buffer layer. In this way, the silicon carbide surface is stabilized such that ultra-flat surfa…
We present a comparative study on the morphology and structural as well as magnetic properties of crystalline Fe$_3$O$_4$/NiO bilayers grown on both MgO(001) and SrTiO$_3$(001) substrates by reactive molecular beam epitaxy. These structures are investigated by means of x-ray photoelectron spectroscopy, low energy electron diffraction, x-ray reflectivity and diffraction as well as vibrating sample magnetometry. While the lattice mismatch of NiO grown on MgO(001) is only 0.8%, it is exposed to a lateral lattice mismatch of -6.9% if grown on SrTiO$_3$. In the case of Fe$_3$O$_4$, the misfit strai…
The evolution in the surface morphology of epitaxial graphene films and 6H-SiC(0001) substrates is studied by electron channeling contrast imaging. Whereas film thickness is determined by growth temperature only, increasing growth times at constant temperature affect both internal stress and film morphology. Annealing times in excess of 8-10 minutes lead to an increase in the mean square roughness of SiC step edges to which graphene films are pinned, resulting in compressively stressed films at room temperature. Shorter annealing times produce minimal changes in the morphology of the terrace e…
Here we report mid infrared (mid-IR) photothermal response of multi layer MoS2 thin film grown on crystalline (p-type silicon and c-axis oriented single crystal sapphire) and amorphous substrates (Si/SiO2 and Si/SiN) by pulsed laser deposition (PLD) technique. The photothermal response of the MoS2 films was measured as changes in the resistance of MoS2 films when irradiated with mid IR (7 to 8.2 μm) source. We show that it is possible to enhance the temperature coefficient of resistance (TCR) of the MoS2 thin film by controlling the interface through proper choice of substrate and growth condi…
Graphene layers were created on both C and Si faces of semi-insulating, on-axis, 4H- and 6H-SiC substrates. The process was performed under high vacuum (<10-4 mbar) in a commercial chemical vapor deposition SiC reactor. A method for H2 etching the on-axis sub-strates was developed to produce surface steps with heights of 0.5 nm on the Si-face and 1.0 to 1.5 nm on the C-face for each polytype. A process was developed to form graphene on the substrates immediately after H2 etching and Raman spectroscopy of these samples confirmed the formation of graphene. The morphology of the graphene is descr…
The shape dependence for the technologically important nickel oxide (NiO) nanocrystals on (001) strontium titanate substrates is investigated under the generalized Wulff-Kaichew (GWK) theorem framework. It is found that the shape of the NiO nanocrystals is primarily governed by the existence (or absence) of interfacial strain. Nanocrystals that have a fully pseudomorphic interface with the substrate (i.e. the epitaxial strain is not relaxed) form an embedded smooth ball-crown morphology with {001}, {011}, {111} and high-index {113} exposed facets with a negative Wulff point. On the other hand,…
We demonstrate the growth of graphene nanocrystals by molecular beam methods that employ a solid carbon source, and that can be used on a diverse class of large area dielectric substrates. Characterization by Raman and Near Edge X-ray Absorption Fine Structure spectroscopies reveal a sp2 hybridized hexagonal carbon lattice in the nanocrystals. Lower growth rates favor the formation of higher quality, larger size multi-layer graphene crystallites on all investigated substrates. The surface morphology is determined by the roughness of the underlying substrate and graphitic monolayer steps are ob…
High quality AlxGa1-xAs distributed Bragg reflectors (DBRs) were successfully monolithically grown on on-axis Si (100) substrates via a Ge layer formed by aspect ratio trapping (ART) technique. The GaAs/ART-Ge/Si-based DBRs have reflectivity spectra comparable to those grown on conventional bulk off-cut GaAs substrates and have smooth morphology, and good periodicity and uniformity. Anitphase domain formation is significantly reduced in GaAs on ART-Ge/Si substrates, and etch pit density of the GaAs base layer on the ART-Ge substrates ranges from 10^5 to 6 x 10^6 cm^(-2). These results paved th…
In this paper we have derived Young's, Wenzel's and Cassie-Baxter's equations using conceptual model rather than showing rigorous derivation to help the new-comers in this field. We then pointed out that if the substrate is initially hydorphilic then one can modify the surface morphology and make the substrate to become hydrophobic or superhydrophobic. But, if the substrate is initially hydrophobic then one can only make it superhydrophobic but not hydrophilic by modifying the surface morphology using the formalisms mentioned in this paper
The effects of substrate treatment, temperature and composition on the surface morphology of Ni-Cr thin films grown on MgO(001) are studied by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). A combination of acid-etching and high temperature deposition (400C) will result in smooth films and terraces (up to 30 nm wide) suitable for the study of progression of chemical reactions on the surface. Two different treatments are used to prepare the MgO substrates for deposition and they introduce characteristic differences in film surface morphology. Thin films that are grown on…
Thin TiO2 films on quartz substrates were prepared by spin coating of undoped and metal-ion-doped Sol Gel precursors. These films were characterised by Scanning Electron Microscopy, Laser Raman Microspectroscopy, Xray Diffraction and UV Vis Transmission. The photocatalytic performances of the films were assessed by the photo-degradation of methylene-blue in aqueous solution under UV irradiation. Films exhibited a high degree of orientation and a thermal stabilization of the anatase phase as a result of substrate effects. In the absence of dopants, the rutile phase formed as parallel bands in t…
Control of Cu morphology on TaN barrier and combined Ru-TaN barrier/liner substrates for nanoscale interconnects from atomistic kinetic Monte Carlo simulations
本研究利用基于 DFT 能垒的原子尺度 kMC 模拟，考察不同 Ru 掺入量、温度和分压下 TaN 及 Ru-TaN 复合阻挡层/衬垫层上的 Cu 沉积形貌，以优化纳米互连体积。
We have demonstrated that the island nucleation in the initial stage of epitaxial thin film growth can be tuned by substrate surface charge doping. This charge effect was investigated using spin density functional theory calculation in Fe-deposition on graphene substrate as an example. It was found that hole-doping can apparently increase both Fe-adatom diffusion barrier and Fe inter-adatom repulsion energy occurring at intermediate separation, whereas electron-doping can decrease Fe-adatom diffusion barrier but only slightly modify inter-adatom repulsion energy. Further kinetic Monte Carlo si…
Two-dimensional van der Waals (2D-vdW) layered hexagonal boron nitride (h-BN) has gained tremendous research interest over recent years due to its unconventional domain growth morphology, fascinating properties and application potentials as an excellent dielectric layer for 2D-based nano-electronics. However, the unidirectional domain growth of h-BN thin films directly on insulating substrates remains significantly challenging because of high-bonding anisotropicity and complex growth kinetics than the conventional thin films growth, thus resulting in the formation of randomly oriented domains …
The growth of Cr adlayers on the Mn-Ga terminated surface of Ni2MnGa(100) has been studied in this work. We show formation of islands of epitaxial Cr layer up to 4 atomic layer heights using scanning tunneling microscopy, while core-level x-ray photoelectron spectroscopy (XPS) indicates absence of any intermixing of the adlayer and the substrate. The density of states (DOS) of the thin Cr layer (2.7 ML) measured by scanning tunneling spectroscopy exhibits nice agreement with density functional theory (DFT) that establishes that it is ferromagnetic. In contrast, a thick layer of Cr that also gr…
Hexagonal boron nitride (h-BN) is a layered two-dimensional material with properties that make it promising as a dielectric in various applications. We report the growth of h-BN films on Ni foils from elemental B and N using molecular beam epitaxy. The presence of crystalline h-BN over the entire substrate is confirmed by Raman spectroscopy. Atomic force microscopy is used to examine the morphology and continuity of the synthesized films. A scanning electron microscopy study of films obtained using shorter depositions offers insight into the nucleation and growth behavior of h-BN on the Ni sub…
Changing the morphology of the growing surface and the nature of residual impurities in (Ge,Mn) layers - by using different substrates - dramatically changes the morphology of the ferromagnetic Mn-rich inclusions and the magnetotransport properties. We obtained p-type layers with nanocolumns, either parallel or entangled, and n-type layers with spherical clusters. Holes exhibit an anomalous Hall effect, and electrons exhibit a tunneling magnetoresistance, both with a clear dependence on the magnetization of the Mn-rich inclusions; holes exhibit orbital MR, and electrons show only the normal Ha…
A clean, flat and orientation-identified graphene on a substrate is in high demand for graphene electronics. In this study, the hetero-epitaxial graphene growth on Cu(111)/mica(001) by chemical vapor deposition is investigated to check the applicability for the top-gate insulator research on graphene as well as the graphene channel research by transferring graphene on SiO2/Si substrates. After adjusting the graphene-growth condition, the surface roughness of the graphene/Cu/mica substrate and the average smooth area are ~0.34 nm and ~100 um2, respectively. The orientation of graphene in the gr…
The deposition of one silicon monolayer on the silver (111) substrate in the temperature range 150-300$^\circ$C, gives rise to a mix of (4$\times$4), ($2\sqrt{3}\times 2\sqrt{3}$)R30$^\circ$ and ($\sqrt{13}\times\sqrt{13}$)R13.9$^\circ$ superstructures which strongly depends on the substrate temperature. We deduced from a detailed analysis of the LEED patterns and the STM images that all these superstructures are given by a quasi identical silicon single layer with a honeycomb structure (i.e. a silicene-like layer) with different rotations relatively to the silver substrate. The STM images mor…
In this paper, we report the growth of NaxCoO2 thin films by pulsed-laser deposition (PLD). It is shown that the concentration of sodium is very sensitive to the substrate temperature and the target-substrate distance due to the evaporation of sodium during the deposition. alpha prime-phase Na0.75CoO2 and gamma- phase Na0.71CoO2 thin films can be obtained with different conditions. Correspondingly, the surface morphology of the films changes from flake-like to particle-like. The temperature dependence of resistivity for the films prepared with the optimal condition shows metallic behavior, con…
Pulsed laser deposition from a Nd:YAG laser was employed in production of hundreds of nanometer thick quasicrystalline Ti-Zr-Ni films on glass substrate. The influence of deposition temperature Ts on the structure, morphology and microstructure of the films across their thickness was investigated. The morphology and microstructure features were evaluated by X-ray diffraction and transmission electron microscopy techniques. The low deposition temperatures were found to produce films with nanometer sized grains embedded in an amorphous matrix. The grains exhibit quasicrystalline order. The highe…
The effects of growth rate (G_r), deposition temperature (T_d), film thickness (t_F), and substrate induced strain (epsilon) on morphological, crystallographic and magnetic characteristics of equiatomic CoPt epitaxial films synthesized with PLD are investigated. The (001) substrates of MgO, STO and LAO provide different degree of epitaxial strain for growth of the disordered face centered cubic (fcc) and ordered face centered tetragonal (L1_0) phases of CoPt. The films deposited at T_d~600 ^0C on all three substrates are fcc with in-plane magnetization and a narrow hysteresis loop of width~200…
We report on the impact of growth conditions on surface hillock density of N-polar GaN grown on nominally on-axis (0001) sapphire substrate by metal organic chemical vapor deposition (MOCVD). Large reduction in hillock density was achieved by implementation of an optimized high temperature AlN nucleation layer and use of indium surfactant in GaN overgrowth. A reduction by more than a factor of five in hillock density from 1000 to 170 hillocks/cm$^{-2}$ was achieved as a result. Crystal quality and surface morphology of the resultant GaN films were characterized by high resolution x-ray diffrac…
