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Recently, deep-ultraviolet (DUV) light-emitting devices have attracted attention for various applications. GaN/AlN superlattices have emerged as a promising alternative for achieving high-efficiency DUV emission. To fabricate superlattices with high crystal quality and abrupt interfaces, we have utilized face-to-face-annealed sputter-deposited AlN template substrates characterized by a flat surface and low dislocation density. Furthermore, radio-frequency plasma-assisted molecular beam epitaxy with in situ reflection high-energy electron diffraction monitoring was employed for the growth process. The growth of the superlattices follows a specific sequence. Step 1: AlN growth, Step 2: conversion of Al droplets to AlN, Step 3: GaN growth, and Step 4: evaporation of Ga droplets. This study explored the impact of GaN thickness on the GaN/AlN superlattice. The GaN thickness was linearly controlled by changing the duration of Step 3. This approach allowed for the growth of a flat GaN layer up to 1 monolayer (ML) and achieved superlattices with abrupt interfaces. Single-peak cathodoluminescence (CL) emission at 240–245 nm was observed from the superlattices, with the peak shift toward longer wavelengths as the GaN thickness increased. In contrast, quantum dot-like GaN islands were generated with a thickness of over 1 ML, induced by compressive strain. Superlattices with thicker GaN exhibited broad CL emission with multiple peaks. However, the AlN barrier layer reduced the surface roughness and maintained abrupt interfaces within the superlattices. Therefore, to obtain sharp single-peak UV emission from GaN/AlN superlattices, the growth sequence should be controlled to obtain flat GaN layers without dots. [ABSTRACT FROM AUTHOR]

Achieving high material perfection in aluminum (Al) films and their associated Al/AlOx heterostructures is essential for enhancing the coherence time in superconducting quantum circuits. We grew Al films with thicknesses ranging from 3 to 30 nanometers (nm) epitaxially on sapphire substrates using molecular beam epitaxy (MBE). An integral aspect of our work involved electron-beam (e-beam) evaporation to directly deposit aluminum oxide (Al2O3) films on the freshly grown ultrathin epitaxial Al films in an ultra-high-vacuum (UHV) environment. This in situ oxide deposition is critical for preventing the oxidation of parts of the Al films, avoiding the formation of undesired native oxides, and thereby preserving the nm-thick Al films in their pristine conditions. The thicknesses of our Al films in the study were accurately determined; for example, coherence lengths of 3.0 and 20.2 nm were measured in the nominal 3.0 and 20 nm thick Al films, respectively. These Al films were epitaxially grown on sapphire substrates, showing an orientational relationship, denoted as Al (111) ⟨ 2 1 ¯ 1 ¯ ⟩ ∥ sapphire (0001) [ 2 1 ¯ 1 ¯ 0 ]. The Al/sapphire interface was atomically ordered without any interfacial layers, as confirmed by in situ reflection high-energy electron diffraction (RHEED) and cross-sectional scanning transmission electron microscopy (STEM). All sample surfaces exhibited smoothness with a roughness in the range of 0.1–0.2 nm. The Al films are superconducting with critical temperatures ranging from 1.23 to around 2 K, depending on the film thickness. [ABSTRACT FROM AUTHOR]

We present diamond-like carbon (DLC) conversion surfaces to detect particles with energy below 2 keV. Conversion surfaces have been widely applied in measurements of low-energy particles by instruments onboard planetary and heliophysics missions. Their effectiveness is characterized by the efficiency in changing the charge state of the incident particles while maintaining a narrow angular distribution for the reflected particles. DLC as a conversion surface coating material has high conversion efficiency. We developed a conversion surface production process that provides ultra-smooth and ultra-thin DLC conversion surfaces. The process includes substrate preparation through precision cleaning, plasma immersion ion deposition of the DLC film, and diagnostics of the film parameters. The latter includes the measurement of the coating thickness, surface roughness, and the conversion efficiency for ion beams with energy below 2 keV. The process we developed provides the DLC conversion surface coating of repeatable parameters with a mean surface roughness of 3.4 ± 0.2 Å and a mean film thickness of 46.7 ± 0.8 nm uniform across the sample area. Ion beam measurements showed a negative ion yield of 1%–2% for hydrogen atoms and 8%–15% for oxygen atoms with an angular scatter distribution of 10°–20° at full width of half maximum. These results agree with those of other conversion surface coatings in the literature. The DLC conversion surfaces presented here are implemented in the conversion surface subsystem of the Interstellar Mapping and Acceleration Probe (IMAP)-Lo instrument of the IMAP mission scheduled for launch in 2025. [ABSTRACT FROM AUTHOR]

Copper (Cu) interconnections have been widely used in advanced electronic packaging due to their outstanding thermal and electric properties. Preparing a smooth and uniform Cu seed thin layer is one of the critical processes to obtain high-reliability Cu interconnections. The barrier layer between Cu and silicon (Si) devices is necessary to prevent the inter-diffusion between Cu and Si. However, little work has been done on the surface roughness analysis of the Cu seed layer deposited on the diffusion barrier layer. In this paper, the influences of deposition thickness, incident energy, barrier layer temperature, and surface morphology on the surface roughness of the Cu seed layer deposited on α-titanium (α-Ti) barrier layer were studied in detail by the molecular dynamics (MD). The simulation results indicated that appropriate parameters have a beneficial effect on reducing the surface roughness, and the surface morphology of the Cu seed layer strongly connects with that of the barrier layer. These results provided a foundation for optimizing the quality of the Cu seed layer. [ABSTRACT FROM AUTHOR]

We have measured the absolute doubly differential angular sputtering yield for 20 keV Kr+ impacting a polycrystalline Cu slab at an incidence angle of θi = 45° relative to the surface normal. Sputtered Cu atoms were captured using collectors mounted on a half dome above the sample, and the sputtering distribution was measured as a function of the sputtering polar, θs, and azimuthal, ϕs, angles. Absolute results of the sputtering yield were determined from the mass gain of each collector, the ion dose, and the solid angle subtended, after irradiation to a total fluence of ∼1 × 1018 ions/cm2. Our approach overcomes shortcomings of commonly used methods that only provide relative yields as a function of θs in the incidence plane (defined by the ion velocity and the surface normal). Our experimental results display an azimuthal variation that increases with increasing θs and is clearly discrepant with simulations using binary collision theory. We attribute the observed azimuthal anisotropy to ion-induced formation of micro- and nano-scale surface features that suppress the sputtering yield through shadowing and redeposition effects, neither of which are accounted for in the simulations. Our experimental results demonstrate the importance of doubly differential angular sputtering studies to probe ion sputtering processes at a fundamental level and to explore the effect of ion-beam-generated surface roughness. [ABSTRACT FROM AUTHOR]

Epitaxial Mn-doped indium tin oxide (ITO) films were deposited on single-crystal yttria stabilized zirconia (YSZ) substrates with (111), (110), and (100) crystal plane orientations using RF magnetron sputtering. The epitaxial relationship between the Mn-doped ITO films and the YSZ substrates was studied using x-ray diffraction (XRD) patterns in the ω–2θ scan mode and XRD pole figures. The Mn-doped ITO films on the YSZ(111) and YSZ(110) substrates exhibited a higher degree of crystallinity than the film on the YSZ(100) substrate as per the x-ray rocking curves. Fluctuations in the crystalline alignment were found to significantly influence the electrical properties of Mn-doped ITO films. Ferromagnetic hysteresis loops were observed at room temperature for all the epitaxial Mn-doped ITO films, irrespective of their crystallographic orientation. The magnetic properties of the epitaxial Mn-doped ITO films suggest that a combination of delocalized charge carrier-mediated interaction and bound magnetic polaron-driven interaction is required to explain the origin of ferromagnetism in these films. The Mn-doped ITO film on the YSZ(111) substrate exhibited the most desirable characteristics in terms of crystallinity, surface smoothness, electrical conductivity, and magnetic properties. [ABSTRACT FROM AUTHOR]

This study examines the impact of dimensionless roughness on flow separation structures and flow characteristics through a combination of experimental and numerical simulation methods. The findings indicate that a specific dimensionless roughness k + exists for the fixed airfoil that minimizes cascade loss. Furthermore, increasing surface dimensionless roughness can alter the flow separation structure and effectively prevent flow separation. The numerical simulation results indicate that as dimensionless roughness increases, the impact of open separation and separation bubbles on the flow state over the blade surface is reduced or eliminated. In cases where separation occurs in the cascade, increasing dimensionless roughness results in a reduction in the boundary layer thickness and the width of the wake jet, thereby leading to a smoother outlet angle and improved efficiency. Conversely, when there is no separation, increasing dimensionless roughness leads to the accumulation of low-energy fluid at the trailing edge of the cascade. This results in an increase in the boundary layer thickness and the width of the wake loss, a larger outlet angle of the blade, and a decrease in the efficiency of the cascade. By analyzing the influence of dimensionless roughness on flow separation in cascades, engineers can quickly identify the geometric roughness height to suppress flow separation. [ABSTRACT FROM AUTHOR]

We use computer simulations to investigate the effects of the tip diameter of an electrostatic force microscope (EFM) operating at a constant force on the extraction of the growth exponent β during film growing in a one-dimensional substrate. Laplace's equation is solved in the EFM simulation using the finite element method to determine the electrostatic force between the tip and the film interface. Importantly, for EFM tips with sufficiently large apex diameters, the topographies calculated with EFM and those computed with the transformed mean height profile (TMHP) method, where the interface is divided into bins of the same tip diameter size and the average height within each bin is used to transform the original interface, are almost identical. This was shown in the context of lattice models of the Kardar–Parisi–Zhang (KPZ) and Villain–Lai–Das–Sarma (VLDS) classes. The global roughness of the film surface, W , scales with the diameter of the EFM tip, ε , as W / a = (ε / a) α g [ Ψ ] , where a is the lattice parameter, α is the KPZ/VLDS roughness exponent, and g is a universal scaling function of the argument Ψ ≡ t / (ε / a) z , where t and z are the reduced time of deposition and the KPZ/VLDS dynamic exponent, respectively. These results provide a limit for ε from which a KPZ/VLDS growth exponent can be reliably determined with EFM at a constant force. When the EFM tip diameter is larger than the surface correlation length, a misleading effective growth exponent consistent with uncorrelated growth is found. [ABSTRACT FROM AUTHOR]

An accurate measurement of the bonding energy of an interface is important in many areas of applied research. We present a novel method for measuring the bonding energy, which is based on the principle of non-planar direct bonding, i.e., direct bonding of originally planar wafers onto non-planar substrates. We discuss in detail the advantages and disadvantages compared to the commonly used double cantilever beam method. To demonstrate the practical relevance, by using the example of glass wafers, the evolution of the bonding energy during different de-bonding steps is investigated, focusing on how the surface shape variations and the surface roughness affects water stress corrosion. We find that the bonding energy in the corroded state is not affected by the original surface shape variations and mid-spatial frequency range roughness, anymore. A molecular mechanism to explain this phenomenon is proposed. [ABSTRACT FROM AUTHOR]

The ever-present demand for high-performance HgCdTe infrared detectors with larger array size and lower cost than currently available technologies based on lattice-matched CdZnTe (211)B substrates has fuelled research into heteroepitaxial growth of HgCdTe and CdTe buffer layers on lattice-mismatched alternative substrates with a (211)B orientation. Driven by the large lattice mismatch, the heteroepitaxial growth of (Hg)CdTe can result in (133)B-orientated material, which, however, has been less explored in comparison to (211)B-oriented growth. Herein, we report on the structural properties of heteroepitaxially grown single-crystal II–VI CdTe (133)B-oriented buffer layers on III–V GaAs (211)B substrates. Azimuthal-dependent x-ray double-crystal rocking curve measurements for the CdTe buffer layers show that the full-width at half-maximum value obtained along the GaAs [ 1 ¯ 11 ] direction is narrower than that obtained along the GaAs [ 01 1 ¯ ] direction, which is presumably related to the in-plane anisotropic structural characteristics of the grown CdTe layers. By incorporating strained CdZnTe/CdTe superlattice-based dislocation filtering layers (DFLs), a significant improvement in material quality has been achieved in (133)B-orientated CdTe buffer layers, including a reduced etch pit density in the low-105 cm−2 range and improved surface roughness. These results indicate that the CdTe (133)B DFL buffer layer process is a feasible approach for growing high-quality CdTe and HgCdTe materials on large-area, low-cost alternative substrates. [ABSTRACT FROM AUTHOR]

We investigate the femtosecond laser ablation of 304 stainless steel (AISI 304), aiming to achieve a high ablation rate, while maintaining low surface roughness. We observe that the surface ablation with 1030 nm-wavelength laser pulses shows a higher ablation rate than that with the 515 nm-wavelength pulses, whereas the surface roughness obtained with the 1030 nm pulses is significantly higher as compared to that obtained with the ablation of 515 nm pulses. We also show that by the use of the two-color double-pulses at 1030 and 515 nm wavelengths, a much higher ablation rate has been achieved with a surface roughness comparable to that obtained with the ablation of 515 nm pulses. [ABSTRACT FROM AUTHOR]

Functional thin film superlattices with stability in extreme environments can lead to transformative performance in optical and thermal applications such as thermophotovoltaics. In this work, key issues associated with defects that prevent layer-by-layer growth in epitaxial, low-miscibility oxide superlattices are investigated. Layer protrusions, approximately 8 nm wide and 3 nm thick, arise from a strain relaxation mechanism in 8 nm bilayer superlattices of Ba(Zr0.5Hf0.5)O3/MgO and propagate through the subsequent superlattice layers forming an inverted pyramid structure that is spatially phase offset from the matrix. The density and size of these defects scales with the number of interfaces in the sample, indicating that surface roughness during growth is a significant factor in the formation of these defects. In situ high temperature transmission electron microscopy (1000 °C, in vacuo) measurement reveals that phase decomposition of Ba(Zr0.5Hf0.5)O3 and decoherence of the superlattice is nucleated by these defects. This work highlights that achieving optimum growth conditions is imperative to the synthesis of single-crystalline superlattices with sharp interfaces for optimized performance in extreme environments. [ABSTRACT FROM AUTHOR]

The present investigation reports the swift heavy ion induced effects on cerium oxide (CeO2) thin films. These thin films were deposited on Si (111) substrates by the electron-beam evaporation method and irradiated by a 100 MeV O7+ ion beam with different ion fluences. X-ray diffraction analysis of these films confirms the stable fluorite phase of CeO2 even after the higher fluence of irradiations. Raman measurement also supports the presence of the F2g phase of CeO2 and the presence of defect states. The Gaussian deconvolution of photoluminescence (PL) spectra reveals various defect-associated peaks. The broad peaks in the PL spectra are associated with oxygen vacancies and are red-shifted (494–520 nm) with ion fluences. The surface morphological images show the modification in the surface roughness with ion irradiation and the re-growth of smaller circular-formed nanoparticles on the surface is observed at the fluence of 5 × 1011 ions/cm2. Magnetic measurements show an enhancement in magnetic ordering with ion irradiation. All the samples demonstrate room temperature ferromagnetism with magnetic saturation (Ms) up to 14.57 emu/cm3. The saturation magnetization in irradiated thin films is directly correlated to the area under the peak of defect-associated PL emission. The mechanism such as the oxygen vacancy-based F-center exchange model is considered to understand the enhancement of ferromagnetism in ion irradiated CeO2 thin films. Some popular theoretical models are also employed to determine various magnetic parameters. [ABSTRACT FROM AUTHOR]

We report an ohmic contact metallization scheme for n-GaN based on a Re–Al–Ni–Au multilayer stack that offers low-resistivity and provides better edge sharpness and lower surface roughness at reduced annealing temperature compared to standard Ti–Al-based metallization. We studied three sets of samples with Re thicknesses of 10, 30, and 60 nm and measured specific contact resistances using the circular transmission line method. We obtained reliable ohmic contacts with specific contact resistance of the order of 10−6 Ω cm2 at 550 °C temperature with the contact stack having a large annealing temperature window of >300 °C for resistivity below 5 × 10−6 Ω cm2. The lowest contact resistivity, below 10−7 Ω cm2, is achieved at annealing temperature around 650–700 °C. A reduction in surface roughness by a factor of 4, with excellent edge definition for Re >30 nm thickness is observed as compared to Ti–Al contacts. Grazing incidence x-ray diffraction and electron dispersive x-ray spectroscopy (EDS) show intermetallic phases of RexNy, Re–Al–Ni, Al–Re, and Al–Au being formed. Atomic force microscope and EDS measurements show the formation of crystalline Re–Al–Ni agglomerates, surrounded by phases of AlAu2 and Al2Au5. The presence of Re seems to suppress the formation of viscous AlAu4 phase, thus minimizing the lateral flow of the metals and providing better edge acuity. The temperature dependence of contact resistivity suggests a field-emission mechanism for current transport across the contact. Our results show that Re-based ohmic contacts, with their lower annealing temperature and excellent edge definition, may offer a promising alternative to Ti–Al contacts. [ABSTRACT FROM AUTHOR]

In ultra-precision equipment, nanoscale rough surface contact widely exists, and the adhesion between interfaces has become a critical component in researching the friction phenomenon. However, adhesion is not considered in traditional friction models. In this study, the adhesion model between fractal contact surfaces is established by proposing the critical truncated area of adhesion, a c u t ′ , and a new friction model considering adhesion is established by combining with the traditional model. The present model shows that adhesion increases as the fractal dimension (D) increases or the surface roughness coefficient (G) decreases when contact occurs between nanoscale rough surfaces. The friction coefficient calculated based on the new model is larger than that of the traditional model, especially when G is small. In addition, a static friction force measurement system was built by using the reticle and vacuum chuck in the lithography system. The experimental system measured the maximum static friction between the chuck and the reticle under different normal loads, and the experimental results show that the new model proposed in this paper is more accurate in characterizing the static friction of nanoscale rough surfaces. [ABSTRACT FROM AUTHOR]

Controllability of the topological Hall resistivity (ρxyTHE) via the doping effect of light elements was investigated for the sputter-deposited (111)-oriented Mn4N single layer. The component of ρxyTHE relative to the anomalous Hall resistivity (ρxyAHE) for host Mn4N was found to increase with decreasing temperature. Boron (B), one of the 2p light elements acting as an interstitial impurity, was doped to the (111)-oriented Mn4N single layer. The microstrain, grain diameter, and surface roughness were found to decrease, resulting in the reduction of ρxyTHE for all temperatures without a change in the antiperovskite bone structure of Mn4N. These results show a dilution effect in the spin frustration state with topological spin texture by B-doping. The effect of B on ρxyTHE for a different orientation of (110) was similar to that of (111), while the enhancement of ρxyTHE was observed by a higher amount of B. B-doping could, thus, be a promising approach to realize tailor-made spintronic devices based on the topological spin state owing to its material versatility. [ABSTRACT FROM AUTHOR]

Any degree of surface roughness could play a significant role in determining the optical properties of ultra-thin films required for epsilon-near-zero (ENZ) applications. In this report, we have provided a systematic analysis of the evolution of an ENZ mode with increasing surface roughness values and established both experimentally and theoretically that roughness acts as a supporting mechanism for achieving a strong ENZ plasmon resonance response in randomly rough indium tin oxide thin films. For pulsed laser deposited indium tin oxide thin films, ENZ plasmon-mediated absorption is enhanced monotonically with the increasing surface roughness. A value of 99.75%, depicting near-perfect absorption, at a wavelength of 1335 nm for the incidence angle of 50 ° is demonstrated experimentally via Kretschmann–Raether configuration for the film with the highest surface roughness. A modified transfer matrix method based on the anisotropic Bruggemann effective medium approximation is being used to effectively simulate the experimental spectra, and based on this analysis, an even higher absorption is predicted at lower angles outside the experimentally viable domain. Such a high value of absorption just above the ENZ wavelength is due to the strong electric field enhancement inside the film layer, while in terms of absorption loss, surface roughness leads the way and contributes immensely toward the occurrence of perfect absorption in the collective media. Modification of the ENZ mode dispersion in the presence of a surface roughness layer is also discussed, and observed perfect absorption is recognized as the outcome of the crossover between the internal damping and radiation damping terms. [ABSTRACT FROM AUTHOR]

Electrothermal instability is responsible for degrading numerous applications of pulsed-power technology, yet the initial conditions from which it grows are not well understood. For the first time, metal surfaces have been tracked from characterization to self-emission. This reveals no clear correlation between non-uniform thermal emissions and surface metallurgical defects or crystallographic grains, while correlations are observed with surface topography for 5N metal but not 6061 metal. For 5N metal, surfaces with average roughness as small as 5 nm still admit thermal perturbations with δ T / T > 0.1. [ABSTRACT FROM AUTHOR]

Contactless photo-electrochemical (CL-PEC) etching was used to fabricate recessed-gate AlGaN/GaN high-electron-mobility transistors (HEMTs). Self-termination of etching was observed during CL-PEC etching on an AlGaN barrier layer whose residual thickness had a uniform value of 6 nm overall on the same chip. After tetramethylammonium hydroxide post-treatment, the root-mean-square roughness of the etched surface was around 0.4 nm, which had smoothness comparable to that of the unetched surface. Recessed-Schottky HEMTs showed a positive shift in Vth, the suppression of drain leakage currents, and an improvement in the subthreshold-slope value as compared with planar-gate HEMTs. By applying a metal–insulator–semiconductor (MIS)-gate structure, the gate and drain leakage currents were significantly reduced, leading to an increased input dynamic range. Furthermore, the standard deviations (σ) of the Vth of CL-PEC-etched recessed-Schottky HEMTs and recessed-MIS HEMTs were very small, 5.5 and 16.7 mV, respectively. These results showed that the CL-PEC etching process is promising for the fabrication of recessed-gate AlGaN/GaN HEMTs having excellent uniformity for normally-off device operations. [ABSTRACT FROM AUTHOR]

With the rapid development of the x-ray polycapillary optics, there is an increasing demand for an effective simulation tool, considering the real physical process and geometry model, to optimize their performance. In this paper, a Geant4-based Monte Carlo code for X-ray Polycapillary Simulation (GXPS) is developed. Based on the classical electromagnetic theory, an x-ray boundary process is developed using the dielectric model, including total external reflection, Fresnel reflection, and Fresnel refraction. The surface roughness of x-ray polycapillary is taken into account using a classical Gaussian slope distribution model. A new geometry solid for x-ray polycapillary modeling is constructed using a cubic function whose coefficients can be derived based on the parameters of a practical lens. To validate the effectiveness of this code, a point-to-parallel x-ray polycapillary lens is simulated with an x-ray energy of 8.04 keV (Cu K α) and the simulation result is compared with the experiment. Well agreement between the simulation and the experimental result is verified considering the transmission efficiency, the output beam profile, and the divergence angle of the lens. The focusing characteristics of the lens are also demonstrated using this code. The simulation result of the focal spot size agrees well with the predicted value calculated using the empirical relation. [ABSTRACT FROM AUTHOR]

Silicon pore optics are a new type of high-performance x-ray optics designed to enable future space-borne x-ray observatories such as European Space Agency's Athena. These optics will make it possible to build telescopes with effective areas of the order of a few square meters and angular resolutions better than 5 s of arc. During manufacturing of the optics, thin film metallic coatings are sputtered onto mirror plates to help achieve this large effective area. Then, these plates are stacked on top of each other using direct silicon bonding to achieve the shape of an approximate Wolter type-I telescope design. It is, therefore, necessary to verify the compatibility of the coating and bonding processes. We observe the unintentional removal of coatings on silicon pore optics plates after their wet chemical activation, a step required to make direct bonding possible. In this paper, we investigate plasma etching prior to thin film deposition as a solution to this problem. First, we ensure that plasma etching does not impact the low surface roughness required to achieve high imaging performance. Then, we demonstrate that plasma etching before thin film deposition prevents unintentional removal of the metallic coatings during the activation step, making coating deposition compatible with direct bonding of silicon pore optics plates. [ABSTRACT FROM AUTHOR]

The GaN substrate miscut angle has a significant effect on the optical properties of Mg-doped GaN grown by metal-organic chemical vapor deposition. We have studied the optical properties of epilayers grown on c-plane GaN wafers with nominal miscut angles of 0.3° and 4° toward the [ 1 1 ¯ 00 ] direction. Periodic surface steps are observed in thin films grown on 0.3° miscut substrates. The step separation and height, as well as the surface roughness, increase with layer thickness, leading to a decrease in Mg doping efficiency. For films grown on 4° miscut substrates, step bunching causes the formation of visually observable wavy features on the film surface with strong spatial variations in cathodoluminescence characteristics, indicating a significant effect of surface morphology on the nature of Mg incorporation and p-type characteristics. [ABSTRACT FROM AUTHOR]

Magnetoelectric (ME) composite thin films are promising candidates for novel applications in future nanoelectronics, spintronics, memory, and other multifunctional devices as they exhibit much higher ME coupling and transition temperatures (Tc) than well-known single phase multiferroics discovered to date. Among the three types of multiferroic composite nanostructures, (2–2) layered and (1–3) vertically aligned composite nanostructures exhibit comparatively smaller ME coupling due to different shortcomings that restrict their use in many applications. Here, we study the morphological, piezoresponse force microscopic (PFM), ferroelectric, magnetic, and magnetodielectric properties of 0–3 [magnetic nanoparticles (0) homogeneously distributed in ferroelectric matrices (3)] multiferroic composite thin films. The Pb(Fe0.5Nb0.5)O3 (PFN)–Ni0.65Zn0.35Fe2O4 (NZFO) particulate composite films were synthesized by pulsed laser deposition. These particulate composite thin films are completely c-axis oriented with very low surface roughness. We observed magnetic and ferroelectric Tc above room temperature (RT) for all composite thin films. The PFN–NZFO 0–3 composites exhibit large polarization, high saturated magnetization with low coercive field, and low dielectric loss along with magnetodielectric coupling at RT. These nanocomposites might be utilized in next generation nano/microelectronics and spintronic devices. [ABSTRACT FROM AUTHOR]

A third of the energy from fuel combustion in passenger car gasoline engines is lost due to friction. Carefully designed engine lubricants can recover some of these losses by reducing friction and wear by forming a nanometer-scale chemico-physico tribofilm between surfaces. Accordingly, attention has focused on developing oil formulations that form low-friction tribofilms. However, analyses of resultant tribofilms are typically conducted after tribo-tests with conventional characterization tools and do not offer insights into tribofilm formation and evolution, precluding information critical to tuning tribofilm properties. In this work, we developed a unique multimodal methodology based on Atomic Force Microscopy (AFM) with local probe heating for in situ tribological studies that activates friction modifiers and simultaneously captures the evolution of friction and surface roughness, with nanometer resolution. As a platform to demonstrate the ability of this methodology to visualize dynamics of tribofilm formation in situ, we apply it to molybdenum-based friction modifiers to distinguish key factors in their functionality and correlate nanoscale AFM and Friction Force Microscopy data to bench tribo-tests used in the industry. To decode the formation mechanisms observed in situ and underlying chemistry of tribofilms, we performed ab initio Molecular Dynamics (AIMD) simulations at comparable conditions. AIMD simulations confirmed both nanoscale and bench tribo-test results and showed deviations in molecular organization in tribofilms that are formed from different molybdenum-based friction modifiers that corroborates with surface functionality. With this innovative methodology, we demonstrate proof-of-principle in situ formation of molybdenum-based tribofilms directly on steel surfaces that could be applied generally to studying tribofilm formation. [ABSTRACT FROM AUTHOR]

Mixed transition metal oxide films are emerging as efficient and inexpensive potential alternatives to multilayer cermet spectrally selective coatings. However, to replace the current standards involving a complex metal–dielectric structure, oxides must be optimized in terms of their electronic structure and mainly their film morphology. In the present work, a simple ultrasonic nebulized spray pyrolysis technique is used to deposit CuCo2O4 films for solar absorber coatings. Their photothermal efficiencies are studied for solar thermal energy harvesting for different film thicknesses obtained by varying the deposition time. The film surface attributes are studied using atomic force microscopy and scanning electron microscopy. The films deposited for 5 and 10 min show relatively high visible absorptance (∼0.79) and relatively low thermal emittance (∼0.1) and thus are promising candidates for spectrally selective coatings. Meanwhile, increasing the deposition time (>10 min) increases the thickness, thereby increasing the solar absorptance. However, this results in an uncontrolled increase in the surface roughness, which affects the spectral selectivity adversely, leading to the films having higher thermal emittance of between 0.1 and ∼0.25. Analysis of the specular reflection contribution shows that this deterioration is governed predominantly by interference effects due to surface attributes. This study is important for the technological applications of spectrally selective coatings and makes a significant quantitative contribution to emphasize the importance of surface morphology in optics. [ABSTRACT FROM AUTHOR]

We use density functional theory and reactive-force-field methods to investigate the electrical and thermal transport properties of long disordered lithiated silicon nanowires. The latter could build the core of future lithium ion batteries with enhanced storage capacity. Due to the amorphous nature of these nanowires, disorder and surface roughness effects inevitably arise, affecting the lithiation process. It is found that the electrical conductivity of the nanowires steadily increases as a function of the lithium concentration, despite the presence of disorder, while the thermal conductivity follows the opposite trend and decreases significantly with reduced heat evacuation capabilities as a consequence. This behavior can be attributed to the influence of Li ions, which on one hand tend to metallize Si nanowires and thus enhance their electron mobility. On the other hand, the random distribution of Li atoms perturbs the phonon propagation through the nanowire, explaining the decrease in thermal conductivity. [ABSTRACT FROM AUTHOR]

We present the results of an experimental investigation of polystyrene's suitability as a dielectric material for designing narrowband, infrared metasurface-based absorbers. Our study included characterization of processing parameters of polystyrene films, such as surface roughness and film thickness, which are critical for device fabrication, and the dielectric properties, which we measured, using spectroscopic ellipsometry. Our results confirm that thin film polystyrene is a relatively low-loss dielectric material at long-wave infrared (LWIR) frequencies. Subsequently, this material was used as the dielectric substrate of a thin, narrowband, metasurface-based absorber at LWIR frequencies. The fabricated narrowband absorber demonstrates excellent performance in the LWIR band with absorptivity as high as 96% and a full-width-at-half-maximum bandwidth of 0.502 μ m or 4.87%. [ABSTRACT FROM AUTHOR]

Film thickness is very important in the preparation of film thermoelectric (TE) devices. To define the effect of the film thickness on the power factor and output power, the ZnO:Al films with thicknesses in the range of 100 nm–900 nm were prepared by thermal evaporation method assisted by radio frequency atomic source. The results show that the film thickness has no effect on the phase composition and the (002) preferred orientation of the wurtzite phase in the films. However, the grain size, surface particle size, and surface roughness increase with increasing film thickness. Transmittance significantly reduced for the 900 nm film. Meanwhile, the film thickness affects the carrier concentration and mobility through the defects and growth modes, so that the TE parameters of the films change with the film thickness. The 700 nm film has the highest power factor, and the maximum power factor is 627 μW m−1 K−2 at 560 K. The output power of the films increases as the increase of the temperature on the hot side and higher power factor results in higher output power. The maximum output power of the 700 nm film is 116.01 pW at temperature difference of 1 K. This indicates that film thickness, temperature difference, and power factor are the key factors affecting the film output power. [ABSTRACT FROM AUTHOR]

The density variations in reactively sputtered amorphous TaOx thin films deposited on planar and patterned substrates have been quantified by high-angle annular dark-field scanning transmission electron microscopy. The experiments have been performed both in plan-view and cross-sectional geometries. The planar films exhibit a cellular structure consisting of high-density cells with low-density boundaries. Laterally, cell sizes varied from 5 to 20 nm as the deposition temperature was changed from 298 K to 573 K. The corresponding density ratio of the cell boundary over the cell interior varied between 0.98 and 0.93 corresponding to 2%–7% free volume in the functional layer. The film microstructure is consistent with the self-shadowing effect of surface roughness. Similar low-density areas were found at the locations of steps of the patterned substrates with a local density decrease of up to 9%. The influence of the low-density region in the resistive random-access memory device is discussed. [ABSTRACT FROM AUTHOR]

Gas transport in nanopores plays an important role in modern industry, such as shale gas exploitation, sea water desalination, fuel battery, etc. Owing to the small pore size, gas transport in nanopores is dominated by Knudsen diffusion, where the gas molecular motion is fully determined by the gas-surface interaction at the boundary. Classic theories of Knudsen diffusion, such as the "Smoluchowski model" and "extended Smoluchowski model", were developed based on empirical gas-surface interaction models. These empirical boundary models may not be accurate to capture the key mechanism of Knudsen diffusion, particularly when the surface roughness is small, such as the case of carbon nanotubes. In this work, the influence of the empirical boundary models on Knudsen diffusion is studied in detail. Theoretical analysis indicates that the Knudsen diffusivity in one-dimensional pores critically depends on the correlation between gas molecular scattering angles on the pore surface. Benchmarked by molecular dynamics simulations, empirical boundary models show notable errors in the prediction of the scattering angle correlation, despite the fact that the accurate tangential momentum accommodation coefficient is used. In contrast, the physical-based boundary model, developed recently by our group, can accurately and efficiently reproduce the molecular dynamics simulation results. Its performance is further demonstrated in the modeling of the Knudsen diffusivity in a one-dimensional cylindrical pore, which predicts more accurate results than the Smoluchowski model and extended Smoluchowski model. [ABSTRACT FROM AUTHOR]

This paper presents a novel thermochromic induced transmittance filter (ITF) based on VO2 films. The ITF structure enables high transmittance in the short wavelength range with wide rejection at longer wavelengths, which meets the requirements of thermochromic VO2 for the metal-insulator transition. Thus, the VO2-based ITFs are designed and fabricated based on the induced transmittance effect, and a graded-index material TiO2 is initially adopted for the simplified structure of VO2-based ITF comparing standard ITFs. The VO2-based ITF's properties are characterized systematically and compared with those of VO2 films. Favorable results of crystallinity, surface roughness, hydrophobicity, the thermal hysteresis width, and pleasant appearance color are achieved in these VO2-based ITFs. Moreover, luminous transmittance Tlum (380–780 nm) of 48.8% and a solar modulation ability ΔTsol of 6.2% are achieved with an ideal spectrum shape in the VO2-based ITF, which provides a highly efficient solution to improve thermochromic VO2 films and related field. [ABSTRACT FROM AUTHOR]

Cu is a promising material to replace Al and Au in integrated circuits and microscale devices because of its low electrical resistivity, high electromigration resistance, and low cost. However, surface roughness affects the contact resistance of these devices, especially when the device is on a microscale or nanoscale. This paper focuses on surface roughness analysis of Cu films deposited on Si substrates by molecular dynamic simulation based on the mechanism of physical vapor deposition. The effects of film thickness, deposition temperature, deposition interval, and reflow temperature on the surface roughness of Cu films are studied in detail. The simulation results show that the surface roughness can be improved by appropriate adjustments of these parameters. They also provide a foundation for further work on the deposition of Cu films on Si substrates. [ABSTRACT FROM AUTHOR]

Low defect smooth substrates are essential to achieve high quality diamond epitaxial growth and high performance devices. The optimization of the Ar/O 2 /CF 4 reactive ion etching (RIE) plasma treatment for diamond substrate smoothing and its effectiveness to remove subsurface polishing damage are characterized. An O 2 /CF 4 RIE process and the effect of different process parameters (inductively coupled plasma, platen power, and pressure) were initially examined. This process, however, still produced a detrimental effect to surface roughness, with etch pits across the surface of the sample. The addition of argon to the process achieved near-zero surface pit density and reduced roughness by 20%–44% after 6 and 10 μ m etching. Iterative high-resolution X-ray diffraction measurements provided a nondestructive tool to examine the effectiveness of polishing damage removal and in this case reduced after removal of 6 μ m of material from the surface of the diamond substrate with the smoothing treatment. [ABSTRACT FROM AUTHOR]

Here, we investigated the static and the dynamic wetting behaviors of copper (Cu) thin films deposited by DC magnetron sputtering. The deposited films have random rough surfaces for which the rms roughness amplitude σ , the lateral correlation length ξ , and the roughness exponent α were obtained from the analysis of height topography images acquired by atomic force microscopy. The time-dependent height-height correlation functions indicated anomalous kinetic roughening with roughness exponents α ≈ 0.9 and evolving roughness parameters σ and ξ with deposition time. The latter yields a nonstationary local surface slope σ / ξ that has a crucial impact on the surface wettability. Indeed, static and dynamic contact angles' (CAs) measurements revealed two wetting regimes associated with different growth stages leading to a transition from a metastable Cassie-Baxter to a Wenzel-like state for the roughest films. Moreover, the increasing roughness with well distributed peaks and valleys leads to increasing CAs due to trapped air in surface cavities, while after some point the larger surface features lead to a decrement of the CAs that vary only slightly with further roughening. Although the apparent wetting transition with increasing surface roughness is not favored by the local Laplace pressure estimation, the energy of the system decreases with surface roughening, or equivalently increasing local surface slope, favoring energetically a Wenzel state. Under these conditions, the water droplet can spontaneously fill the surface cavities once the impregnation is initiated by the hydrophilic nature of the surface, in agreement with our experiments for significantly large local surface slopes ρ (>0.1) and large roughness exponents α ∼ 1. [ABSTRACT FROM AUTHOR]

Bactericidal efficiency of Au and Ag nanoparticles (NPs) is reported with and without photoactivation by white light. Au and Ag NPs were synthesized with an average size of 14 ± 1.2 nm and of 4.6 ± 0.5 nm , respectively. The size distribution of the Ag colloid was relatively wide. Less than 4 % of these NPs were largely decahedral, which, based on numerical calculations, determined the position of the optical band. In contrast, the Au colloid had a narrow optical band; a concentration of 1.3 μ g / ml was determined by theoretical and experimental spectra. Ag and Au NPs showed a superficial charge of − 35 mV and + 57 mV due to the presence of the citrate ions and cetyltrimethylammonium bromide on their surface, respectively. The effect of the NPs concentration on the viability of Escherichia coli and Staphylococcus aureus strains was investigated. It was found that Ag NPs were more effective against E. coli than Au NPs, whereas Au NPs were more effective against S. aureus than Ag NPs. The induced damage to the bacteria by the NPs was evaluated by AFM. The images show that the bacterial cell wall was changed in shape and in surface roughness, being more noticeable in S. aureus than in E. coli. The bactericidal activity of the photoactivated Ag NPs was almost doubled for both bacteria, whereas for the Au NPs, no bactericidal enhancement was observed for either strain. This can be explained by the high efficiency of Ag NPs to absorb white light and the consequent creation of hot spots that contribute to kill the bacteria. [ABSTRACT FROM AUTHOR]

Gas breakdown is typically driven by Townsend avalanche and predicted mathematically by Paschen's law (PL). Gas breakdown deviates from PL at microscale due to field emission, which depends critically on electrode condition; however, understanding of the impact of initial electrode surface roughness and multiple breakdown events on breakdown voltage is incomplete. This paper assesses the variation of breakdown voltage for a pin-to-plate electrode setup in air at atmospheric pressure for gap distances of 1 ± 0.5 μm, 5 ± 0.5 μm, and 10 ± 0.5 μm with different surface roughnesses. Breakdown voltage generally increases with increasing gap distance and decreasing surface roughness for a single breakdown event; however, the breakdown voltage after ten breakdown events does not depend on initial gap distance. Atomic force microscopy and optical microscopy show that multiple discharges create circular craters on the flat cathode up to 40 μm deep, with more pronounced craters created at smaller gap sizes and greater cathode surface roughness. The resulting effective gap distances (deff, the sum of cathode placement distance and crater depth) for subsequent breakdown events are similar to those of the initially larger gap distances. Moreover, deff becomes sufficiently large to exceed the Meek criterion for streamer formation, indicating a potential for breakdown mechanisms to change from field emission to Townsend avalanche to streamer formation for a single electrode separation distance. The resulting impact of this change in the breakdown mechanism could have significant implications for ensuring consistent microdevice operation. [ABSTRACT FROM AUTHOR]

Mechanical micro- and nano-patterning processes rely on engineering the interactions between a stamp and a substrate to accommodate surface roughness and particle defects while retaining the geometric integrity of printed features. We introduce a set of algorithms for rapidly simulating the stamp–substrate contact, and we use them to show that advantageous behavior can occur when the stamp consists of a finite-thickness layer bonded to a layer with different elastic properties. The simulations use two-dimensional load-response functions describing in discrete space the response of a stamp surface's shape to a localized unit load. These load-response functions incorporate the contributions both of local, indentation-like displacements and of plate-like bending of finite-thickness stamp layers. The algorithms solve iteratively for contact pressure distributions that, when spatially convolved with the load response, yield deformations consistent with the properties of the stamp and the substrate. We investigate three determinants of stamp performance: conformation to sinusoidal substrate topographies, distortion of material around stamp protrusions, and conformation to isolated spherical dust particles trapped between the stamp and the substrate. All simulation results are encapsulated in dimensionless models that can be applied to the efficient selection of stamp geometries, materials, and loading conditions. A particularly striking finding is that a stamp with a finite-thickness compliant coating bonded to a more rigid support can conform more closely to a trapped particle under a given load than a homogeneous stamp with the properties of the coating. This finding could be used to minimize the impact of particle defects on patterning processes. [ABSTRACT FROM AUTHOR]

Diffusion profiles of arsenic and antimony in undoped and carbon doped germanium (Ge), respectively, were analysed by means of scanning spreading resistance microscopy (SSRM). Whereas earlier secondary ion mass spectrometry analyses have determined the distribution of the chemical concentration of dopants and carbon, the electrically active defect concentration is quantified by SSRM using appropriate calibration samples and a preparation technique that reduces the surface roughness and its density of electronic states. Pronounced differences between the chemical and electrical dopant profiles are observed and consistently described by the formation of inactive dopant defect complexes in the framework of the vacancy mediated diffusion of donor atoms in Ge. This reveals that donor deactivation occurs during dopant diffusion at elevated temperatures. [ABSTRACT FROM AUTHOR]

Analytic expressions for low field mobility have been obtained in the high strained p-type silicon structures with three- and two-dimensional hole gases. Much attention is paid to study how confinement in one spatial dimension changes the strain mobility enhancement in comparison with bulk material. The mobility enhancement factor has been calculated when applying both the uniaxial and biaxial strains. Acoustic and optic phonons, charged impurities, and surface roughness have been accepted as a scattering system. Our theoretical consideration is based on the quantum kinetic equation and a special form of the non-equilibrium distribution function (shifted Fermi distribution). Results of the calculation are compared with known experimental data. [ABSTRACT FROM AUTHOR]

In this paper, we calculate the effect of a graphene coating on the transmission coefficient of a Cu thin film with surface disorder. The nonequilibrium coherent potential approximation combined with the linear muffin-tin orbital formulation, which is based on first principles, is applied by assuming that there is surface disorder. The graphene coating mitigates the effect of Cu surface scattering on the transmission coefficient. The weak interaction between Cu and graphene and the upward shift of the Fermi level with respect to the Dirac point improve the transport characteristics by offering more conduction bands. Moreover, graphene-coated Cu with a perfect surface has a completely specular transmission coefficient. The surface disorder decreases the transmission coefficient due to the nonconserved transverse momentum (k) of the scattering wave through the central area of the two-probe system. However, for a graphene coating on a Cu thin film with surface disorder x < 3.90 % , length l < 5.09 nm , width 0.25 nm, and thickness 1.23 nm, the transmission coefficient is higher. The increased transmission coefficient due to graphene coating can overcome the diffusive scattering originating from the surface disorder. The coherent potential approximation band structure shows that graphene bands are less affected by Cu surface disorder than Cu bands, which enhances the total conduction by offering additional channels for electrons. Our results demonstrate that graphene is a potential liner material for a Cu thin film with low surface disorder. [ABSTRACT FROM AUTHOR]

We use molecular dynamics simulations to characterize the effect of various surface terminations on phonon thermal transport in nanoscale Cu slabs. Specifically, we studied Cu slabs approximately 4 nm in thickness with atomistically flat (111) surfaces, slabs with ∼ 30 % surface vacancies to mimic atomic-level roughness, and slabs with a surface oxide. Motivated by recent experimental observations, we study the effect of capping these surfaces with single layer graphene. From the thermal conductivity of the various samples as a function of length, we extracted conductivity and phonon mean free paths in the absence of boundary scattering other than that originating from the surfaces under study. As expected, both surface vacancies and an oxide layer reduce thermal conductivity and we characterize the effect in terms of the specularity parameter. While capping the slabs with graphene increases the conductivity, the poor thermal contact between Cu and graphene results in less than ideal performance of the hybrid material. Interestingly, the simulations reveal that the graphene capping layer reduces surface scattering on the Cu slabs, and this effect is significantly more pronounced in the case of a defective surface. The results provide insights into the use of graphene capping to improve transport in nanoscale interconnects for nanoelectronics. [ABSTRACT FROM AUTHOR]

One problem with current 3D printed microwave components is that they usually have more surface roughness than components manufactured with traditional machining processes. To estimate the multipactor threshold of 3D printed microwave components, it is important to evaluate the total secondary electron yield (TSEY) of the random rough surface. In this work, taking copper as an example, we conduct TSEY simulations for random rough surfaces. First, we generate both isotropic and anisotropic Gaussian type random rough surfaces; then, the dependence of the TSEY on both the roughness and correlation length is studied using Monte-Carlo simulations. Results show that when the root-mean-square roughness increases from 0 to 30 μm, the maximum TSEY increases slowly at first and then decreases rapidly. In other words, roughness can also enhance and not just suppress the TSEY. The results can be interpreted as follows: for a relatively smooth/rough surface, the TSEY enhancement/suppression induced by oblique incidence/a shadowing effect plays a dominant role. Simulation results also show that correlation length has a notable effect on the TSEY. Furthermore, for anisotropic surfaces, the azimuthal angle also influences the TSEY. Compared with currently published work, we provide an optional evaluation method for the TSEY of random rough surfaces. The predictions in this work not only confirm existing observations (the TSEY suppression effect) but also present new predictions (the TSEY enhancement effect and the azimuthal angle effect). [ABSTRACT FROM AUTHOR]

Local droplet etching (LDE) drills self-assembled nanoholes into AlGaAs surfaces and represents a powerful technique for the fabrication of versatile quantum structures like quantum dots, rings, and molecules. Usually, LDE is performed at temperatures T = 600 − 680 ° C if Al is used as the etching material. Now, atomic force microscopy establishes that Al-LDE drills nanoholes also at very low temperatures down to T = 360 ° C which is 300 ° C below the melting point of bulk Al. Several possible etching mechanisms like a melting-point depression, solid-state etching, and alloying are discussed. Selective wet-chemical etching experiments using HF indicate significant alloying with Ga from the substrate, and thus the formation of Al-Ga droplets for etching. The upper limit of x ≤ 50 % for the Al content inside the Al-Ga droplets is indicated by the selectivity of the HF acid. This value is in agreement with an estimation of x = 0.42, which is based on the measured droplet and hole volumes. A comparison with the Al-Ga phase diagram indicates that a completely liquid phase of the droplets is essential for etching. [ABSTRACT FROM AUTHOR]

Edge roughness is expected to play a major role in narrow ribbons obtained from two-dimensional materials, due to the large length/surface ratio of the disordered edges with respect to the whole system surface. In the case of semiconducting transition metal dichalcogenides, a physical and quantitative understanding of the impact of edge roughness on the transport properties of ribbons with nanometer widths is essential in view of their potential applications in ultrascaled nanoelectronics. By means of atomistic quantum transport simulations, we show that the conductance due to edge states within the bulk gap is strongly suppressed by roughness. The corresponding localization length is found to be in the order of few nanometers. At low carrier energies outside the gap, edge roughness drives the system into the diffusive transport regime. The study of the mean free path, under different conditions of roughness and for different ribbon widths, shows that the conductance is moderately affected for widths above 10 nm and lengths in the order of 100 nm, with a more significant degradation for ultra-narrow ribbons. [ABSTRACT FROM AUTHOR]

Low thermal conductivity and high power factor are desirable for thermoelectric materials. These properties can be achieved by patterning devices into nano-structures such as nanowires (NWs). The thermal conductivity can be further reduced by altering the NW geometry through the introduction of surface roughness (SR) or stacking faults (SFs). In this paper, relaxation times for scattering of phonons at SFs and SR are developed to accurately compute the impact of both effects on the thermal conductivity of InAs NWs with different diameters. It is found that similar reductions of the thermal conductivity can be obtained with SFs instead of SR. For the shortest possible distance between SFs along a NW, the room temperature thermal conductivity can be reduced to 25 % compared to an ideal NW. For a NW with rough surface, a more than 80 % decrease of the thermal conductivity is possible for specific roughness profiles. All available experimental data on the lattice thermal conductivity of InAs NWs confirm the theoretical models and simulation results. [ABSTRACT FROM AUTHOR]

The surface morphology of metal influences its optical absorptivity. Recent experiments have demonstrated that the femtosecond laser induced surface structures on metals could be dynamically controlled by the fluence of laser and the number of pulses. In this paper, we formulate an analytical model to calculate the optical absorption of a rough metallic surface by modeling the roughness as a fractal slab. For a given experimental image of the surface roughness, we characterize the roughness with a fractal parameter by using the box-counting method. With this parameter as an input, we calculate the absorption of an 800 nm laser pulse impinging on gold, copper, and platinum, and the calculated results show excellent agreements. In terms of physics, our model can be viewed as a fractional version of the Fresnel coefficients, and it will be useful for designing suitable surface structures to tune the light absorption on metals from purely reflective to highly absorptive based on different applications. [ABSTRACT FROM AUTHOR]

Plasma-induced surface roughening and ripple formation has been studied based on Monte Carlo simulations of plasma-surface interactions and feature profile evolution during Si etching in Cl-based plasmas, with emphasis being placed on the role and effects of ion reflection from microstructural feature surfaces on incidence. The simulation model included the effects of Cl+ ion reflection (and/or its penetration into substrates) through calculating the momentum and energy conservation in successive two-body elastic collisions with substrate Si atoms every ion incidence. The "reflection coefficient ri" was then further introduced in the model (0 ≤ ri ≤ 1), representing the fraction of ions incident on surfaces with the reflection/penetration calculation scheme turned on. The coefficient ri is, in a sense, a measure of the reflection probability for impacts of an ion species onto Si surfaces relative to that for Cl+ impacts. Simulations for ion incidence angles of θi = 0°, 45°, and 75° onto substrate surfaces with incident energies in the range Ei = 20−500 eV showed that as ri is slightly decreased from unity, the roughness decreases substantially, and the ripple formation fades away: the roughness remains at the low level of stochastic roughening during etching for decreased ri ≤ ri* ≈ 0.95−0.75 (the critical ri* tends to be lower at higher Ei and θi) with no ripple structures at off-normal θi. This elucidates that the ion reflection is indispensable in surface roughening and rippling during plasma etching, and their degree relies significantly on the reflectivity of ions. Simulations further showed that at intermediate off-normal θi = 45°, the ripple wavelength increases significantly with decreasing ri, while the increase in amplitude is relatively less significant; thus, sawtooth-like ripple profiles pronounced for ri = 1 tend to be collapsed with decreasing ri. These effects of reduced ion reflection on plasma-induced surface roughening and ripple formation are discussed in terms of effectively enhanced smoothing due to neutral reactants, which competes with the roughening and rippling caused by ion bombardment. [ABSTRACT FROM AUTHOR]

The surface roughness of deposited conducting thin films is responsible for various materials reliability problems in nanoelectronics and nanofabrication technologies. Here, we report a modeling and simulation study that aims at optimizing the electrical surface treatment of deposited conducting thin films as a physical processing strategy for their surface roughness reduction. Our study is based on a continuum model of film surface morphological evolution that accounts for the residual stress in the deposited conducting thin film, the film's wetting of the substrate layer that it is deposited on, film texture and surface diffusional anisotropy, and surface electromigration. Through systematic linear stability analysis and dynamical simulation protocols, we examine in detail the effects of film surface crystallographic orientation and applied electric field direction toward minimizing the electric field strength required for film surface smoothening. We find that the critical electric field strength requirement for surface roughness reduction on {110}, {100}, and {111} surfaces of face-centered cubic crystalline conducting thin films exhibits a very strong dependence on the applied electric field direction, expressed as the electric field misalignment with respect to the principal residual stress directions in the film and the fast surface diffusion directions. Based on these findings, we optimize the electrical treatment strategy for surface roughness reduction of conducting thin films with respect to all relevant processing and material parameters. [ABSTRACT FROM AUTHOR]

Presently, models to describe surface roughness scattering combine intrinsic and extrinsic effects, where extrinsic effects include process-induced interactions and intrinsic effects are due to inherent atomic structure. In this work, we present a general method for extracting the intrinsic surface roughness scattering rate of a material interface from the atomic structure, using Density Functional Theory and Fermi's Golden Rule. We find for the case of the 4H-SiC/SiO2 interface, intrinsic surface roughness mobility is several orders of magnitude greater than the extrinsic mobility which depends on process induced nonidealities. This result suggests that a path forward for higher mobility SiC devices may be the reduction of extrinsic miscut roughness. [ABSTRACT FROM AUTHOR]

The effect of rough structures on the electron emission under electron impact between 10 eV and 2 keV is investigated with a new version of the low energy electromagnetic model of GEANT4 (MicroElec). The inelastic scattering is modeled, thanks to the dielectric function theory and the Mott's model of partial waves to describe the elastic scattering. Secondary electron emission is modeled for grooved and checkerboard patterns of different dimensions for aluminum and silver. The analyses are performed according to two shape parameters h/L and d/L, h being the height, L the width of the structures, and d the spacing between two neighboring structures. The secondary electron emission is demonstrated to decrease when h/L and d/L ratios increase. When the height reaches 10 times the lateral dimensions, the electron emission yield is divided by two compared to that of a flat sample. The optimization of the two aspect ratios leads to a reduction of the electron emission yield of 80% for grooved patterns and of 98% for checkerboard patterns. This purely geometric effect is similar for aluminum and silver materials. A simple analytical model, capable of reproducing the effect on the electron emission yield of checkerboard and grooved patterns, is proposed. This model is found to be in good agreement with the Monte Carlo simulations and some experimental measurements performed in our irradiation facility. [ABSTRACT FROM AUTHOR]