Improved Surface Smoothness Research Articles

III-nitride growth and characteristics on ferroelectric materials using plasma-assisted molecular beam epitaxy

The characteristics and growth of III-nitride materials on ferroelectric lithium niobate with varying Li mole composition have been investigated to achieve a better device performance of AlGaN∕GaN heterojunction structures. III-nitride growth on lithium niobate has been performed after high temperature (1000°C) furnace thermal treatments in dry air environment resulting in atomically flat surfaces on lithium niobate (LN). However, while this furnace thermal treatment results in improved surface smoothness and III-nitride adhesion, it also causes repolarization, ferroelectric domain reversal from a +z spontaneous polarization to a −z spontaneous polarization in the surface of congruent LN (48.39mole% of Li2O). On the other hand, near-stoichiometric LN (49.9mole% of Li2O) did not develop repolarization during the identical thermal treatment. Furthermore, as determined in situ by spectroscopic ellipsometry, congruent LN (CLN) shows a bigger variation of the pseudorefractive index and pseudoextinction coefficient during annealing at various temperatures in the range of 100–800°C, indicating surface modification at those temperatures. On the other hand, near-stoichiometric LN (SLN) shows little change in these indexes implying that SLN provides better surface stability at elevated temperatures in the vacuum environment. This improved vacuum tolerance of SLN has allowed Al0.20Ga0.80N∕GaN heterostructures to be grown on CLN and SLN substrates, with two times higher channel mobility resulting on SLN substrates. Thus, SLN appears to be a viable substrate for molecular beam epitaxial growth of III-nitrides in various applications.

Improvement of Surface Smoothness of Vapor-Deposited Polyimide Coatings Using a Plastic Mesh Container as Bounce Pan

The surface of vapor-deposited polyimide (PI) coating onto a mechanically agitated mandrel has always been rougher than the NIF standard. The roughness has been attributed to various sources, including defects and contamination on substrate mandrels, abraded damage from mechanical agitation, or off-stoichiometric compositions.At near-stoichiometric deposition conditions, the surface roughness is primarily due to damages from collisions. Using a plastic mesh container with a suitable opening size and synchronized gentle tapping, we have greatly improved the surface quality of 1 mm diameter 4–5 μm thick polyimide shells. The plastic mesh improves the surface quality by limiting shell movements and reducing the impact force and number of collisions between the shells during coating. The surface smoothness of the as-deposited polyamic acid coating meets the NIF surface smoothness standard. Appropriate pressure and heat profiles are used to remove the mandrel and convert the thin polyamic acid coating into polyimide and preserve the surface smoothness. The AFM spheremaps, patch scans and WYKO optical interferometer measurement showed a root-mean-square smoothness ranging 3–5 nm.

A method for reducing surface roughness during the thermal desorption of silicon

An in situ method for inhibiting surface roughening during the thermal removal of the silicon native oxide layer is explored and developed. The method entails depositing a thin sacrificial silicon film at low temperature directly exterior to the native oxide, following which the sample is heated such that the native oxide preferentially reacts with the sacrificial film reducing wafer etching. The results indicate a significant improvement in surface smoothness, from an RMS roughness of 2.70 to 0.84 nm, while leaving an exposed surface which has been demonstrated to be suitable for epitaxial growth.

Transparent conducting sol–gel ATO coatings for display applications by an improved dip coating technique

Transparent conducting coatings of sol–gel ATO (antimony-doped tin oxide) were used to improve surface smoothness of commercial sputter-deposited ITO (indium tin oxide) coatings for application as display electrodes. In order to overcome the deteriorating evaporation-cooling during dip coating, the coating solution was heated moderately to 25 °C thus providing the substrate with the required heat. This way, the surface roughness of the ITO could be reduced with an only 45 nm thick ATO coating to R pv = 3.8 nm ( R a = 0.4 nm) compared to 31 nm (3.8 nm) for the ITO substrate. Another benefit of such additional coating is the possibility to tailor surface properties of the electrodes in wide ranges. This was used to increase the work function of the ITO substrate from initially 4.3–4.6 eV to about 4.8–5.2 eV by the ATO coating.

Impact of Boundary-Layer Cutting and Flow Conditioning on Free-Surface Behavior in Turbulent Liquid Sheets

The HYLIFE-II conceptual design uses arrays of high-speed oscillating and stationary slab jets, or turbulent liquid sheets, to protect the reactor chamber first walls. A major issue in thick liquid protection is the hydrodynamic source term due to the primary turbulent breakup of the protective slab jets. During turbulent breakup, drops are continuously ejected from the surface of turbulent liquid sheets and convected into the interior of the cavity, where they can interfere with driver propagation and target injection. Experimental data for vertical turbulent sheets of water issuing downwards from nozzles of thickness (small dimension) δ = 1 cm into ambient air are compared with empirical correlations at a nearly prototypical Reynolds number Re = 1.2 × 105. A simple collection technique was used to estimate the amount of mass ejected from the jet surface. The effectiveness of boundary-layer cutting at various “depths” into the flow to reduce the source term and improve surface smoothness was evaluated. In all cases boundary-layer cutting was implemented immediately downstream of the nozzle exit. Planar laser-induced fluorescence (PLIF) was used to visualize the free-surface geometry of the liquid sheet in the near-field region up to 25δ downstream of the nozzle exit. Large-scale structures at the edges of the sheet, typically observed for Re < 5.0 × 104, reappeared at Re = 1.2 × 105 for sheets with boundary-layer cutting. The results indicate that boundary-layer cutting can be used to suppress drop formation, i.e. the hydrodynamic source term, for a well-conditioned jet but is not a substitute for well-designed flow conditioning.

Improvement of surface smoothness of Nd:KGd(WO4)2 films by nozzle-gas-assisted pulsed-laser deposition

We have demonstrated efficient film oxidation of Nd:KGW [or Nd:KGd(WO4)2] films using a newly developed nozzle-gas-assisted pulsed-laser deposition (NGA-PLD) method. This technique is systematically studied and experimentally compared to the conventional PLD (C-PLD) method. A dramatic improvement in the film surface morphology is achieved with NGA-PLD. The NGA-PLD enables the efficient film oxidation under lower ambient pressures than the C-PLD technique, which realizes well-crystallized films with smoother surfaces. This simple technique will be very useful for fabrication of a variety of multi-component oxide films.

Assessment and Control of Primary Turbulent Breakup of Thick Liquid Sheets in IFE Reactor Cavities: The “Hydrodynamic Source Term”

The “hydrodynamic source term” has been identified as a possible issue for thick liquid protection schemes in inertial fusion energy reactor cavities. The hydrodynamic source term refers to the ejected droplets due to the primary turbulent breakup of the jets themselves. Droplets are continuously ejected from the surface of the jets and spread about the chamber, possibly interfering with driver propagation and target injection. Published correlations are examined in order to estimate upper limits for the hydrodynamic source term in the case of the robust point design (RPD-2002), an update to the High-Yield Lithium Injection Fusion Energy II (HYLIFE-II) design. Experimental data for vertical turbulent sheets of water issuing into ambient air downward from nozzles of thickness (small dimension) δ = 1 cm and aspect ratio of 10 are compared with the empirical correlations at near-prototypical Reynolds numbers of 1.3 × 105. A simple mass collection technique was developed to estimate the amount of ejected droplets from the jet surface. Boundary layer cutting is examined as a means of reducing the source term and improving surface smoothness. Alternate flow conditioning schemes are also explored to establish the relative importance of “traditional” flow straightening elements. Planar laser-induced fluorescence was used to visualize the free-surface geometry of the liquid sheet in the near-field region up to 25δ downstream of the nozzle exit. These results indicate that boundary layer cutting can suppress the hydrodynamic source term for a well-conditioned jet but is not a substitute for proper flow conditioning.

Optimizing the abrasive sanding process of rubberwood (Hevea brasiliensis)

The abrasive sanding process is the most labor-intensive operation in the Rubberwood furniture manufacturing industry. Although the machining properties of Rubberwood (Hevea brasiliensis) are well established, information on its abrasive sanding characteristics is sparse. This study was carried out to establish the optimal abrasive sanding regime for Rubberwood. The results suggest that the abrasive sanding process can be optimized when well machine-planed Rubberwood stocks are used. Further, it was found that when the machine surface quality was good, abrasive sanding with a two-level sequence of grit sizes was sufficient to produce an acceptable surface smoothness. The improved surface smoothness also minimized the coating film spread on the wood surface. This finding will serve as a useful benchmark for machine-planing and abrasive sanding processes in the high-volume Rubberwood furniture manufacturing industry.

Considerable improvement of optical property of GaInNAs/GaAs quantum well

We have found that antimony (Sb) plays an important role for the improvement of optical properties of the GaInNAs/GaAs quantum well in the 1.3 μm region grown by metalorganic vapor-phase epitaxy. Non-annealed samples grown with pre-flow of trimethylantimony (TMSb) showed good optical properties equivalent to that of annealed samples grown without TMSb. These samples showed higher tolerance to thermal annealing and maintained good photoluminescence (PL) intensity up to 720 °C. The atomic force microscope image showed the improvement of surface smoothness. These results suggest supplying TMSb only before the growth of the quantum well is effective for the improvement of interface between GaInNAs and GaAs.

Epitaxial growth on gas cluster ion-beam processed GaSb substrates using molecular-beam epitaxy

Chemical mechanical polished (CMP) (100) GaSb substrates were processed using gas cluster ion beams (GCIB) to improve surface smoothness, reduce subsurface damage, and produce a thermally desorbable oxide layer for molecular-beam epitaxy (MBE) overgrowth. In this article, we report the growth of GaSb/AlGaSb epilayers on GCIB processed GaSb substrates. The substrates were processed using either O2 or CF4/O2 as the gas cluster in a dual-energy recipe that included a moderate energy (10 keV) etch step followed by a low-energy (3 keV) smoothing step, with a relatively low total dose of 4×1015 ions/cm2. Half of each wafer was masked such that the epitaxial layers were grown on both CMP and GCIB polished surfaces. Atomic force microscopy showed the elimination of CMP surface scratches on the GCIB processed surfaces. X-ray photoelectron spectroscopy results indicate that the surface oxide composition and thickness can be engineered through the GCIB process recipes. AlGaSb marker layers were used to chart the evolution of the overgrown layers. Cross-sectional transmission electron microscope images of the substrate/epi-interface show that the CMP finished regions contained defects that propagated into the epilayers as compared to the GCIB finished region that showed no penetrating defects, indicating an improved substrate/epi-interface. This work demonstrated that GCIB processing of semiconductor materials has the potential to produce “epiready” surfaces.

Recycling of ethylene propylene diene monomer (EPDM) waste. III. Processability of EPDM rubber compound containing ground EPDM vulcanizates

AbstractThe rheological behavior of ethylene propylene diene monomer (EPDM) compounds containing ground EPDM waste (W‐EPDM) of known composition was studied by using a Monsanto processability tester in a temperature range of 90–110°C and a shear rate range of 306.7–1533.24 s−1. It is found that the shear viscosity decreases slightly with increasing W‐EPDM loading because of wall slip that results from the migration of lubricants from the W‐EPDM. The addition of W‐EPDM to raw EPDM results in a decreased die swell at all temperatures and shear rates. SEM photomicrographs of the EPDM extrudate surface show improved surface smoothness and reduced extrudate distortion when EPDM is blended with W‐EPDM. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2204–2215, 2003

GaN/AlGaN Two-Dimensional Electron Gas Grown by Ammonia-MBE on MOCVD GaN Template

The growth of high quality GaN/AlGaN two-dimensional electron gas on MOCVD GaN template substrates by ammonia-MBE is reported. The homoepitaxial growth required a significantly lower growth temperature than that needed for growth on SiC or sapphire substrates, and yielded significantly improved surface smoothness, and consequently improved electrical characteristics of the two-dimensional electron gas. A low temperature Hall mobility of 14300 cm 2 /V s and quantum mobility of 2000 cm 2 /V s were obtained, representing the highest values observed in the GaN/AlGaN structures grown by the ammonia-MBE technique. A correlation between the surface roughness and increased Hall mobility to quantum mobility ratio was observed, suggesting that the surface roughness could be a source of small-angle scattering in these structures.

Production of BiPbSrCaCuO Thin Films on MgO and Ag/MgO Substrates by Electron Beam Deposition Techniques

Superconducting BiPbSrCaCuO thin films were prepared on MgO(001) and Ag/MgO substrates using an electron beam (e-beam) evaporation technique. The effects of annealing temperature and Ag diffusion on the crystalline structure and some superconducting properties, respectively, were investigated by X-ray diffraction, atomic force microscopy, and by measurements of the critical temperature and the critical current density. It was shown that an annealing of both types of films at 845 or 860 °C resulted in the formation of mixed Bi-2223 and Bi-2212 phases with a high degree of preferential orientation with the c-axis perpendicular to the substrates. The slight increase of the critical temperature from 103 K to 105 K, the enhancement of the critical current density from 2 x 10 3 to 6 x 10 4 A/cm 2 , and the improved surface smoothness are due to a possible silver doping from the substrate.

Novel Time-modulated Chemical Vapor Deposition Process for Growing Diamond Films

Smooth polycrystalline diamond films were deposited onto silicon substrates using a newly developed time-modulated chemical vapor deposition (TMCVD) process. The distinctive feature of the TMCVD process involves pulsing the hydrocarbon gas, methane, at different flow rates for varying durations into the vacuum reactor during the chemical vapor deposition (CVD) process. Generally, CVD diamond films display nonuniformity in the crystal sizes and surface roughness along the film growth profile. The TMCVD method was specifically developed to (i) deposit smooth films, (ii) control film microstructure and morphology, and (iii) improve film reliability. We show that the TMCVD process produces diamond films with improved surface smoothness as compared to films of similar thickness produced by conventional CVD method under similar conditions. Surprisingly perhaps, the TMCVD method gave growth rates much higher than the conventional CVD method without reducing the film quality as revealed by the SEM micrographs and micro-Raman spectra.

Strong Photoluminescence Emission from Polycrystalline GaN Grown on Metal Substrate by NH3 Source MBE

Polycrystalline GaN layers were grown on Mo and electron-beam-deposited Mo/glass substrates with improved surface smoothness by NH 3 source molecular beam epitaxy. X-ray diffraction rocking curves showed preferential GaN(0002) orientation. Strong photoluminescence (PL) emission without yellow luminescence was observed from these polycrystalline GaN layers. For the previously-grown GaN on metal substrates two PL peaks were observed at around 3.48 and 3.27 eV at 77 K, while for the GaN grown in this study the 3.27 eV peak was eliminated. This improvement is considered to be mainly due to the improved surface morphology of the substrates and the origin of the 3.27 eV peak was attributed to the cubic GaN phase. The 3.48 eV peak is the excitonic peak from the hexagonal GaN phase.

Structural and optical properties of LiNbO3 thin films grown by pulsed laser deposition

We report the deposition of good quality, highly textured LiNbO 3 thin films on sapphire substrates using the pulsed laser deposition technique. Thin films composition and structure have been determined using Rutherford Backscattering Spectroscopy (RBS) and X-Ray Diffraction (XRD) experiments. The influence of deposition parameters such as substrate temperature and oxygen pressure on the structure of the films has been studied. To improve surface smoothness of the film, an off-axis geometry has been used. The substrate surface lies in the plane defined by the plasma plume. The optical waveguiding properties of the as-obtained films have been demonstrated by m-line measurements of transverse-magnetic and transverse-electric modes at 633 nm.

Anisotropic etching of {100} and {110} planes in (100) silicon

Anisotropic etching of (100) silicon using KOH with 45° alignment tothe primary ⟨110⟩ wafer flat was investigated. It was shownthat in KOH solution with isopropyl alcohol added, high KOH concentration andtemperature caused the selection of {100} instead of {110} walls, allowingreliable fabrication of {100} walls with improved surface smoothness due tothe isopropyl alcohol. TMAOH solutions with methanol and isopropyl alcoholwere also found to produce both types of wall, with excellent surfacesmoothness for the {110} walls. A new maskless etching technique wasdeveloped for corner compensation of structures bounded by {110} walls.

Properties of Ag-Cu alloy substrate for Y-Ba-Cu-O superconducting tape

Textured structure, surface morphology and tensile strength of Ag-Cu alloy tapes and Ag-Cu/Ni alloy clad tapes are studied by using XRD, pole figure, SEM and AFM. An addition of Cu was effective for improving surface smoothness; [210] textured structure, on which YBCO film aligns in-plane, was obtained in Ag-Cu tape. Clad tapes which have 2-4 times higher proof stress 60.2 than pure Ag at 700/spl deg/C were obtained. These clad tapes are expected to be useful for obtaining low-cost and high-J/sub c/ YBCO superconducting tape.

The fibre characteristics of shives initiating web rupture

The thesis comprises three parts: Existing methods for characterisation of fibre crosssections have been improved, and new methods have been developed. These methods have then been applied to study the effects of wood characteristics and the pulping process on mechanical pulp fibres. Links have been established between fibre structure and paper properties such as surface smoothness and light scattering coefficient.New methods, based on SEM-images and image analysis, are described for providing cross-sectional fibre dimensions for large fibre populations, for wood tracheids (app. 60 000 tracheids in a wood trunk) and for processed pulp fibres (app. 1000 fibres per sample). The methods are suited e.g. for evaluation of changes in the fibre cross-sections from wood to the finished paper, or for mapping of fibre parameters within and between growth rings in a wood trunk. The treatment of data is discussed, showing how one may examine the changes in different groups of fibres (earlywood fibres, latewood fibres, split fibres) throughout a process.It is known from the literature that groundwood-based paper is superior to TMP-based paper with respect to printability. Fibres from SGW and PGW-pulp were found to be much more split in the longitudinal direction than TMP-fibres at comparable freeness. Intact groundwood fibres had thicker walls than intact TMP-fibres, but nevertheless super calendered hand sheets made from groundwood fibres were less roughened by moistening than were TMP-based sheets. Both for groundwood pulps and for TMPpulps, it was shown that reduced fibre wall thickness and increased fibre splitting was beneficial for improved surface smoothness and opacity.Latewood defibrate easier than earlywood during refining. In the case of grinding, there was no particular preference for earlywood or latewood to be defibrated. Reject refining of groundwood reject was, however, found to be very important for defibration of latewood-containing shives. Pulps made from a raw material with more compact fibres (high wall area to lumen area ratio) were found to defibrate easier, and contain less shives. It was found that refining tends to reduce wall thickness most on thickwalled parts of the fibre, thus causing a reduction of the wall thickness variation around the perimeter.Earlywood fibres were found to be preferentially split during refining. Most fibre splitting occurs during the primary stage, while the fibres are firmly attached to chips or fibre bundles. Latewood fibre wall thickness decreases considerably more than earlywood fibre wall thickness during refining. It seems that choosing an appropriate raw material is more effective than using excessive energy on reducing the wall thickness of thickwalled fibres. Earlywood fibres became more flattened during refining compared to latewood fibres, possibly due to repeated compressions and relaxations in the refiner.The energy consumption to a given freeness was found to be considerably larger for Scots Pine than for Norway Spruce. However, the fibre transverse dimensions did not differ much between Norway Spruce and Scots Pine. Pine pulps were far less developed than spruce pulps at similar energy level. A possible explanation for the large energy consumption may be that redistribution of extractives at the fibre surface could reduce friction in the refiner. This hypothesis should be further explored.The results in this study improve the knowledge of which fibre parameters that matter for surface smoothness and opacity of wood-containing publication paper. Further, this study elucidates how important fibre parameters such as wall thickness and fibre splitting are altered during a refining process. The results may be utilized to identify possible ways of modifying the TMP-process in order to produce paper with improved surface smoothness and opacity.

The Effect of Er Concentration on the Morphology and Photoluminescence of GaN:Er

The surface morphology and the room temperature 1.54 μm photoluminescence (PL) intensity have been investigated as a function of Er flux in GaN:Er grown by metallorganic molecular beam epitaxy. Unlike AlN, GaN:Er showed improved surface smoothness as evidenced by atomic force microscopy and scanning electron microscopy, with root mean square roughness values improving from 18.1 to 2.0 nm as the Er cell temperatures were increased from 1250 to 1450°C. Similarly the PL emission increased with increasing Er concentration and showed no evidence of saturation or concentration quenching. © 2000 The Electrochemical Society. All rights reserved.