AFM Surface Roughness Research Articles

High-Quality AlGaN/GaN HEMTs Growth on Silicon Using Al0.07Ga0.93N as Interlayer for High RF Applications

In this study, AlGaN/GaN high electron mobility transistor (HEMT) with different interlayer thicknesses of Al0.07Ga0.93N were grown by metal-organic chemical vapour deposition (MOCVD) is investigated. The AlGaN/GaN HEMTs have the same device’s structure, with the Al0.07Ga0.93N interlayer thickness varied from 0 to 800 nm. All of the samples demonstrate high crystal quality in the GaN channel, with low dislocation density of (1.34–3.81) × 109 cm−2 and low AFM surface roughness of 0.27–0.39 nm. The heterostructure with an interlayer exhibits better mobility (1750 cm2 V∙s−1) compared to the structure without an interlayer (1610 cm2 V∙s−1). Furthermore, the interlayer improves breakdown voltage, and reduces insertion loss. The DC characteristics show that the 300 nm-thick Al0.07Ga0.93N is beneficial in improving leakage current and iso-breakdown voltage up to 450 V at a spacing of 10 μm. The insertion loss reduces to –0.75 dB mm−1 compared to the structure without an interlayer. The device with a 300 nm-thick Al0.07Ga0.93N interlayer exhibits the potential of RF, including a measured transconductance of 440 mS∙mm−1 and cutoff frequencies of = 48/96 GHz at a given bias point.

Surface modification of Ti6Al7Nb employing pure waterjet and abrasive waterjet polishing for implant application: comparison study

Natural bones in vertebrates are replaced with implants when it fails under fatigue/impact loading conditions. The implants surface roughness is a vital parameter that enhances the osseointegration rate owing to mechanical stability by firm anchoring between the implant and the bone tissue. In this research article, surface modification of Ti6Al4Nb by the action of impingement erosion was executed under two conditions (i) Waterjet polishing (WP) without abrasives; (ii) Abrasive waterjet polishing (AWP) with biocompatible abrasives and studied in correlation to MRR and average surface roughness. The bio abrasives were made in a laboratory that endorses the bone healing characteristics availing 85% hydroxyapatite (HAp) and 15% yttrium stabilized zirconia. SEM, EDS, XRD, AFM and Non-contact surface roughness measurements were used to study the surface morphology of the bio-abrasives and the AWP surface. Experimentally the WP resulted in 73% more material removal rate and with higher average surface roughness Ra by 50% when compared to the AWP. The biocompatibility of Ti6Al4Nb post AWP was found to be favourable with more live cells after performing the MG63 Cell assay for the optimal exp run #11 obtained via the desirability function algorithm.

Wear and Friction properties of H-Al-17Si alloy with dry, lubrication and coated (DLC-Star) conditions under HFRR

Dry, lubrication (SAE15W40), and coated (DLC-Star) reciprocating tribological tests on rapid solidified AlSi17Cu3.5-4Mg0.6-0.8 alloy was conducted using a high frequency linear reciprocating rig (HFRR) at ambient temperature. The alloy fabricated with the rheo-stir squeeze casting procedure under T-6 condition. However, at different loading (0-30 N) conditions, wear and friction properties of rapid solidified H-Al-17Si alloy are investigated. It is observed that the lower friction coefficient value obtained for DLC-Star coated H-Al-17Si alloy compared to dry and lubrication conditions. Though, for dry and lubricated sliding, the obtained wear coefficient values are 2.9X10-3 mm3/N.m and 4.0X10-4 mm3/N.m. A lower coefficient of wear value of 5.4X10-5 mm3/N.m was recorded with DLC-star coating under dry conditions. The alloy wear coefficient values first increases with applied load (up to 20 N) and then decreases (20 N to 30 N). EDS, AFM surface roughness profilometer, SEM, and advanced metallurgical microscope (AMM) analysis techniques used for the characterization of surface morphologies. The developments in friction and wear coefficients were fundamentally ascribed to the dispersion and size of primary Si elements and the development of tribo-oxide films on the rapid solidified AlSi17 alloy coated (DLC-Star) surfaces.

Adsorption and removal studies of heavy metal Pb(II) on their Water Solution on adsorbent surface of Vinyl Alcohol/Chitosan-Graphene Oxide

Chitosan/polyvinyl alcohol/graphene oxide (CH-g-PVA/GO) hydrogel was prepared by using iron chloride as a cross-linking agent. This hydrogel was used to remove lead ions as it was found to have a suitable surface area for adsorption time was 120 mint. The adsorption is proven using FESEM and FTIR analysis, TEM analysis, and knowledge of AFM surface roughness.. Also, TGA shows that the hydrogel is stable at high temperatures. The study of the hydrogel’s kinetic parameter was performed by using the lead ion applied to the adsorption of the pseudo-second-order because (R2) approximates the correct model.

Polylactide/graphene nanoplatelets composite films: Impact of high‐pressure on topography, barrier, thermal, and mechanical properties

AbstractIn this study, the compatibility of graphene nanoplatelets (GNPs) in the development of a polylactide (PLA)‐based sustainable composite films and its suitability under high‐pressure (HP) processing (300–600 MPa/15 min) were examined. The GNP concentrations relative to PLA were restricted to 2 wt% while 10 wt% polyethylene glycol (PEG) was blended as a plasticizer. The film properties were examined by monitoring the thermal, barrier, mechanical, and microstructure before and after the pressure treatments. Reinforcement of GNP and pressurization both significantly improved the glass transition and crystallization temperatures of the film. Both water vapor and oxygen permeabilities were increased with increasing HP intensity. Both the loading concentration and the applied pressure significantly influenced tensile, microstructure, and AFM surface roughness. This work demonstrates the limitations of thermal and mechanical properties of biodegradable single‐layer nanocomposite films in the HP environment and the future directions to improve those properties for industrial uses.

Direct plasma-enhanced atomic layer deposition of aluminum nitride for water permeation barriers

Oxygen-free, transparent, and insulating thin films at fabrication temperatures below 100 °C are important for sensitive materials and interfaces, like organic electronics. In this work, a capacitive coupled plasma-enhanced atomic layer deposition process of aluminum nitride with trimethylaluminum as a precursor and a mixture of hydrogen/nitrogen as the reactive gas was studied at 80 and 200 °C. The film properties were characterized by spectroscopic ellipsometry, x-ray photoelectron spectroscopy, scanning electron microscopy, and electrical measurements. The growth per cycle stayed constant at around 1 Å, and the refractive index decreased slightly from 1.97 at 200 °C to 1.93 at 80 °C. While the AFM surface roughness was below 0.5 nm at 80 °C deposition temperature, scanning electron microscopy images reveal blister generation at 200 °C on silicon. The x-ray photoemission spectroscopy measurements show a layer composition of Al:N of 1.0:0.9 with a few percent of oxygen and carbon, indicating good air stability and reasonable stoichiometry. The metal-insulator-metal capacitance measurements showed a dielectric constant of 11 at both temperatures. The water vapor transmission rate for a 20 nm thick film on polyethylene naphthalate films was lower than 0.5 mg/(m2⋅day) at 38 °C/90%.

Advancements in High Indium Content Alinn Grown Via Metal Modulated Epitaxy and Application Towards Polar/Non-Polar Optical Devices

AlInN has been a topic of recent study due to its unique property among III-nitrides of lattice matching to GaN at a composition of 18% indium, making it a strong candidate for power electronic and optoelectronic applications. A widely unexplored area is the application of AlInN towards visible/Near-IR optical devices. AlInN has a tunable bandgap, spanning the infrared to ultraviolet range, of 0.7 to 6.1eV. At a composition of about 70% indium AlInN has a perfect bandgap, 1.7eV, for tandem solar cells with silicon and for various optical communications applications. Challenges exist with the growth of AlInN as a result of the large lattice parameter mismatch and differences in growth regimes between the two binary components. At the low temperatures required for the growth of AlInN the aluminum adatoms have a low mobility, often leading to lateral phase separation in the film. Metal Modulated Epitaxy (MME) offers a good solution to the growth issues of AlInN. This flux modulated technique allows for growth under metal rich conditions, increasing surface diffusion lengths of the Aluminum while limiting droplet formation and terminating in a dry surface suitable for devices. For comparison ~100 nm thick high indium content AlInN samples were grown using nitrogen rich (0.8 III/V ratio) MBE and MME using a III/V ratio of 1.3 with a dose designed to prevent surface segregation (details supplied at the conference). Both films were grown cold at 375 degrees C to limit phase separation The MME sample showed improvement over the MBE sample in crystal quality and surface roughness, with the XRD (0002) reflection FWHM improving from 783 arcsec to 184 arcsec, the XRD (10-15) reflection FWHM improving from 2456 arcsec to 1421 arcsec, and the AFM surface roughness improving from 1.52nm rms to 0.882nm rms between the MBE and MME samples respectively. The carrier concentrations of both samples were found to be about 1E19 cm-3 via hall measurement implying that like InN, In-rich AlInN may suffer from excessive residual electron concentrations and/or surface fermi-level pinning. Optical measurements will be presented at the conference. The same MME growth conditions were used to grow 100nm of indium rich AlInN directly on a (111) p-silicon substrate. Simple indium contacts were used to contact the Si and AlInN. Vertical conduction and rectification between the silicon and AlInN layers were observed in this large area (~0.25x0.25 cm2) device. Understanding of the limitations of and physics governing this promising vertical polar/non-polar heterojunction will be given at the conference. Additionally, results from various growth conditions will be detailed. Figure 1

Ionic liquid functionalised reduced graphene oxide fluoroelastomer nanocomposites with enhanced mechanical, dielectric and viscoelastic properties

Utilization of Ionic Liquids (IL) as suitable candidate for nanofiller modification is of considerable interest in the current scenario owing to its peculiar properties. In the present study reduced graphene oxide (rGO) is modified with varying amount of IL to improve the dispersability and interaction with fluoroelastomer (FKM) matrix. The surface modification of rGO using IL, its dispersion and incorporation into the FKM matrix was confirmed by FTIR, Raman, XRD, and AFM surface roughness analysis. The prepared nanocomposites achieved better static and dynamic mechanical properties by the addition of 2 phr of IL to rGO. Moreover the nanocomposites showed an increase in glass transition temperature from DSC (−18.82 for FIL 0 to −14 for FIL 2) analysis that supports the enhanced interaction between FKM and modified filler. Dynamic mechanical analysis of the nanocomposites proved the reinforcing ability and the effectiveness of ILrGO to enhance the properties as a whole. The dielectric study of the nanocomposites showed improved AC conductivity, dielectric constant value (60 with 2 phr of IL content) and a decrease in dielectric heating coefficient value with increase in ILrGO content. These property combinations make the nanocomposites a multifunctional material.

Electric Double Layer Doping of WSe2 Field-Effect Transistors Using a Monolayer Electrolyte

Electric double layer (EDL) doping using a polymer electrolyte or ionic liquid is a common technique to explore transport in two-dimensional (2D) materials. The doping relies on the formation of an EDL due to the accumulation of mobile ions at the interface between an electrolyte and a 2D semiconductor. The induced image charge yields large capacitance densities (1-10 μF/cm2) and sheet carrier densities (~1014 cm-2) in 2D crystal field-effect transistors (FETs).1 Our group has developed a monolayer electrolyte that is a single molecule thick and can electrostatically dope the surface of 2D semiconductors.2 The monolayer electrolyte has several advantages over liquid-phase electrolytes because it is solid state, bistability has been demonstrated,2 and DFT calculations predict a low switching voltages (sub-volt) at fast speeds (sub-ns).3 We have demonstrated EDL doping on graphene2 and MoS2 using the monolayer electrolyte. Bistability, state retention and a sheet carrier density of 3.2×1012 cm-2 have been demonstrated. In this study, WSe2 is selected as the 2D channel because it is ambipolar with a sizable bandgap (1.4 eV), large on/off ratio (> 106) and high carrier mobility (~140 cm2V-1s-1).4 The monolayer electrolyte consists of cobalt crown ether phthalocyanine (CoCrPc) and lithium perchlorate (LiClO4) (Fig.1 (a)). CoCrPc is an atomically thin and electrically insulating molecule (band gap ~1.34 eV) that can lie flat on a 2D surface.5 It includes four crown ethers, and each of them can solvate one Li+.6 An ordered array of CoCrPc can be deposited on a 2D material by drop-casting and annealing.5 Back-gated WSe2 FETs were fabricated by electron beam lithography (EBL), and the monolayer electrolyte was deposited on the surface of the WSe2 FETs by drop-casting and annealing. The WSe2 channel surface was cleaned by contact-mode AFM to remove e-beam resist residue before electrolyte deposition to avoid interference to the packing arrangement of the monolayer electrolyte. The quality of the cleaning is confirmed by AFM topography and surface roughness measurements; the roughness after the cleaning equals the value of freshly exfoliated flakes (Rq ~0.22 nm) (Fig.1 (c) and (d)). The cleaning does not deteriorate the back-gated device performance, as indicated by transfer characteristics after the AFM cleaning (Fig.1 (b), no monolayer electrolyte). The device transfer characteristics before and after doping with the monolayer electrolyte will be presented, along with our work on top-gating the devices using h-BN and graphene to create an all-2D EDL FET. References Kim, Se Hyun, et al. Advanced Materials 25.13 (2013): 1822-1846.Xu, Ke, et al. ACS nano (2017).Wang, Wei-Hua, et al. Solid State Ionics 301 (2017): 176-181.Fang, Hui, et al. Nano letters 12.7 (2012): 3788-3792.Lu, H., et al. The Journal of Physical Chemistry C 119.38 (2015): 21992-22000.De, S., et al. Journal of Molecular Structure: THEOCHEM 941.1 (2010): 90-101. ACKNOWLEDGEMENTS: This work was supported by NSF-ECCS/GOALI 1408425 and by the Center for Low Energy Systems Technology (LEAST), a STARnet Semiconductor Research Corporation program sponsored by MARCO and DARPA. Figure 1

Growth of Columnar Co3Pt Strucrure with Ru Buffer Layer at Room Temperature

Magnetic Co3Pt films were sputtered on a Ru(0002)/Pt(111) bilayer on glass substrate at room temperature. The effects of a Ru buffer layer thickness (t nm) on magnetic properties and microstructures were studied. AFM surface roughness results revealed that the root mean square roughness (Rrms) of the Ru/Pt bilayer surface is smaller than 1.5 nm. Granular Ru topography was observed as t is larger than 7 nm, which played an important role in influencing the magnetic properties and microstructures of Co3Pt thin film. In this study, Ru(0002) grew along the Pt(111) underlayer and then became a template for epitaxially growing Co3Pt(0002) film, in order to enhance the perpendicular magnetic anisotropy (PMA). Maximum Hc were obtained as t=15, due to the columnar structure formed in the whole Co3Pt/Ru/ Pt film. It demonstrates that a Ru buffer layer is helpful to enhance the PMA of Co3Pt magnetic thin film and increase out-of-plane squareness (S⊥) and Hc.

Controlling intercalations of PBDTTT-EFT side chain to initiate suitable network for charge extraction in PBDTTT-EFT:PC71BM blended bulk heterojunction solar cell

Electrical, optical and structural properties, based on blend of PBDTTT-EFT:PC71BM bulk heterojunction solar cell is investigated. We have shown the presence of PC71BM in the blend facilitates interfaces for charge transfer mechanisms leading to PCEs of ~ 9.38%. GIXRD line profile obtained reveals that quantitative presence of PC71BM initiates a change in preferred orientation. It is proposed that PC71BM facilitates polymer alkyl side chain intercalations causing reduced d100 spacing, leading to larger π-π stacking of the back bone. The data obtained from d200 plane associated with PC71BM, reveals correlation between increased vertical stacking and PC71BM loading, suggesting a bicontinuous network for electron transport. Raman spectroscopy results provides evidence of PC71BM impact on frequency shift associated with C = C stretching mode of side chain thiophene rings responsible for of π-π spacing. Correlations between AFM surface roughness and blend ratio reveals migration of PC71BM to the film surface.

Ru Film Characterization Correlated to Advanced CMP Slurry Performance

Ruthenium has been considered as a barrier liner film for copper in advanced back-end-of-the-line (BEOL) metallization schemes in particular for the 10 nm and beyond technology nodes [1]. Ru shows a lower resistivity than traditionally used barrier films such as Ta or TaN [2] as well as negligible solubility with Cu [3] and Ru films can be deposited with a variety of techniques like CVD or PVD [4], which makes it an attractive candidate. However, new advanced BEOL barrier CMP slurries will have to be developed for this application and Ru is considered a very hard material and chemically inert. Hence it is a big challenge to develop advanced node Ru CMP slurries. Since Ru films can be deposited with various deposition techniques and onto different substrates the removal rate response of these different films to a given slurry can also be dramatically different. For example we found that the removal with a standard Cu-barrier slurry without any additional additives on Ru film type A was only 20 Å/min whereas it was 200 Å/min on the type B film even though both films had been deposited by PVD. Further investigation of the two films showed that the morphology and in particular the grain size was quite different as shown in the SEM images below. Interestingly, these two images correlate very well with images in [5] of two films which have been deposited at different plasma pressures and the difference in removal rate can be explained by different residual stresses in the two films as a result of the different plasma pressures. In this paper we will present the characterization of several different Ru films by XRF (film density), XRD (crystal structure), SEM (grain size and structure), AFM (surface roughness), XPS (atomic composition), contact angle (surface energy) and film hardness by micro/nano indentation. The analytical results will be correlated to CMP polishing performance and in particular on how the different films respond to rate boosting additives in the slurry. The goal is to be formulate a customized slurry by understanding the properties of individual Ru films.

4H-SiC Epitaxial Layer Grown on 150 mm Automatic Horizontal Hot Wall Reactor PE106

Preliminary results of 150mm SiC 4H 4°off have been obtained with the new 150mm automatic horizontal hot wall reactor PE1O6, using chlorinated chemistry (SiHCl3 + C2H4). A new injection system has been tested in two configurations and results will be shown in this paper. AFM surface roughness measurements and epi defect density have been reported.

Particle clustering in photocurable nanocomposites: Dependence of curing kinetics and viscoelastic properties

ABSTRACTThe aim of this article is to investigate the effect of nanoparticle clustering on the mobility of nanoparticles in nanocomposites, using spectroscopic methods (Brillouin and Raman). Special attention is paid to the effect of particle clustering on photocuring kinetics. The model system was poly(2‐hydroxyethyl acrylate) filled with fumed nanosilica in concentration range encompassing the percolation threshold. Results obtained from Brillouin spectroscopy show substantial changes in the sound velocity and the attenuation coefficient with increasing filler content. The damping of acoustic waves reaches the maximum at the percolation threshold (∼15 wt %), which is related to changes in the mechanism of acoustic wave propagation. The formation of the cocontinuous silica phase strongly affects the curing kinetics of the monomer/silica system: the polymerization rate is the highest at a silica content corresponding to the percolation threshold. These results correlate well with the results of AFM surface roughness analysis. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39895.

Characteristics of Al-doped TiO<SUB align="right">2 thin films grown by pulsed laser deposition

Al-doped TiO2 (TiO2:Al) thin films were deposited at 450oC onto glass substrates using pulsed laser deposition method. X-rays diffraction spectra showed that the obtained films are polycrystalline of anatase structure with preferential orientation of (101) direction. AFM images, nanoparticles size and surface roughness mean square values showed that the surfaces of TiO2:Al films are smoother than that of undoped TiO2 films. A blue shift in the absorption edge of TiO2 with increasing Al concentration in the film is noteworthy as it leads to increase in the width of the optical transmission. The optical waveguiding performances of the TiO2:Al films were demonstrated by using the m-lines spectroscopy technique and the results were correlated to the structural properties. Spectroscopic ellipsometry was used to extract the optical constants of the films. The determined band gap of undoped and Al doped films varies from 3.43 to 3.61 eV, which is in accordance to Burstein-Moss shift.

Controlling structural quality of ZnO thin film on c-plane sapphire during pulsed laser deposition

The pulsed laser deposition (PLD) of ZnO thin film on c-plane sapphire has been studied as a function of various growth parameters such as nucleation layer temperature, annealing duration, laser pulse frequency, number of steps of ZnO deposition, final growth temperature and pressure. Among various growth parameters, laser pulse frequency was found to have significant influence to form single crystal ZnO film on c-plane sapphire through elimination of misaligned crystal domains completely. Allowing relaxation to the seeding layer by slowing down laser pulse frequency to 1 Hz established the complete epitaxial relationship between ZnO and sapphire over large plan view area, which is confirmed by plan view single crystal diffraction pattern, whereas ZnO grown at 5 Hz laser pulse frequency showed significant rotation between crystallites as evident from ring diffraction pattern from plan view TEM image. Using higher pressure (10 −2 Torr) forms ZnO nanobullet during second stage of growth. AFM surface roughness improved to ∼2.4 nm for the sample grown with relaxed nucleation layer. Hall mobility also increased to ∼58 cm 2 V −1 s −1 for this sample.

The transparence comparison of Ga- and Al-doped ZnO thin films

The Ga-doped ZnO (GZO) and Al-doped ZnO (AZO) thin films were grown on quartz glass substrates by pulsed laser deposition under different oxygen partial pressures ( P O 2 ) . The transparent performances of films versus properties of structure and conductivity were discussed. With the increase of P O 2 , the transmittance of both GZO films and AZO films increased to maximum and then decreased which were in according with the change of crystallization quality. The transmittance of GZO films was higher than that of AZO films, which were not dominated by the impurity ions induced by doping. AFM images and surface roughness mean square coefficients showed that the surfaces of GZO films were smoother than that of AZO films, which were due to the dopant Ga acting as the surfactant and smoothed the GZO films surface.

Electron Paramagnetic Resonance Studies of Shallow Donors Behavior in Hydrogenated ZnO Films

Photoassisted metalorganic chemical vapor deposition (photo-MOCVD) technique was used for depositing of as-grown (ZnO) and hydrogenated (ZnO:H) zinc oxide polycrystalline thin films under different growth and hydrogen doping conditions. The structure and morphology of the films was controlled using SEM and AFM microscopy and surface roughness measurements. The studies of paramagnetic defects behavior and magnetic susceptibility in as-grown and hydrogenated samples were provided in the temperature range 77-300 K using X-band EPR spectrometer. It was found that all the samples exhibited a single symmetric strong Lorentzian line at g = 1.96 while the line intensity was shown to increase upon H-doping. The concentration of paramagnetic defects, associated with the concentration of the hydrogen donors, was extracted. The behavior of the magnetic susceptibility curves was described by Curie and Pauli contributions. We have shown that the excess concentration of paramagnetic defects, appeared after hydrogen doping, correlated with the increase of the Pauli term of magnetic susceptibility and followed the increase of free carrier concentration

Correlation of structural inhomogeneities with transport properties in amorphous silicon germanium alloy thin films

Amorphous silicon–germanium (a-Si 1− x Ge x :H) alloy thin films were studied over a wide range of Ge content ( x=0–1.00) grown by radio frequency plasma CVD (rf PECVD) technique with variation of different deposition parameters such as H 2 dilution, rf power and square wave pulse modulation (SWPM) of rf amplitude. Structural properties like microstructure factor ( R ⁎) and AFM surface roughness ( R RMS ) were correlated with the transport properties such as mobility-lifetime product ( μτ) and ambipolar diffusion length ( L d ) of these films. Near the middle composition range ( x=0.32–0.70), the R ⁎ in these films varies between 0.20 and 0.42 and L d ranges between 50 and 60 nm. Films deposited near the pure silicon and pure germanium ends have improved structural and transport properties. By SWPM method we have been able to significantly lower the R ⁎ value of the a-Si 1− x Ge x :H films to 0.15 with x=0.40–0.45 resulting in L d =100 nm and μτ=1.0×10 −6 cm 2 V −1.

Impact of near-surface defects and morphology on ZnO luminescence

We have used depth-resolved cathodoluminescence spectroscopy (DRCLS) to measure the distribution of deep level defects at and below the surface of ZnO crystals grown by vapor phase transport, hydrothermal, and melt-growth methods. DRCLS reveals large variations in defect distributions with depth on a nanometer scale that correlate with maps of potential and surface morphology measured by Kelvin probe force and atomic force (AFM) microscopies, respectively. A strong correlation between the optical emission efficiency of the nanoscale subsurface region and the AFM surface roughness reveals a figure of merit for substrate polishing and etching.