Varying Substrate Temperature Research Articles

Investigation of CNT Growth by Substrate Temperature Control Using Thermal CVD Method

Influence of metal catalyst (Fe) surface condition was investigated for the growth of carbon nanotubes (CNTs). Surface condition of 5 nm thick Fe coated on Si substrate was changed by varying substrate temperature during the CNTs synthesis in a thermal CVD method. Acetylene and argon were used as precursor and carrier gas, respectively, for the synthesis of CNTs. After the growth, the CNTs were removed from the substrate and the post-growth condition of the substrate surface was studied by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Unlike the case of untreated Fe-coated Si substrate, XPS analysis shows Si peaks from the thermal treated substrate/samples, which indicates the formation of Fe nanoparticles. AFM results indicate that 750 degrees C is optimum temperature for the nanoparticle formation. Moreover, SEM results show that 700 degrees C is optimum temperature for the CNTs synthesis. The results of this study clarify that the optimum temperature for nanoparticle formation and CNT synthesis are different.

A multi-scale method for identifying groundwater exchanges sustaining critical thermal regimes in streams

A holistic understanding of heterogeneous groundwater-induced thermal regimes was developed for a Southern Ontario creek using a multi-scale field approach. To better understand the habitat characteristics sustained by the groundwater and surface water exchanges, the relationship between groundwater inputs and stream temperatures were investigated at stream, segment, geomorphic-unit and micro-habitat levels. Continuous point temperature measurements at various locations along the main channel were used to determine seasonal and spatial stream temperature trends and to identify areas of possible groundwater contributions. Methods effective for quantifying and locating groundwater inputs were evaluated, including the velocity-area method, stream temperature surveys and sediment temperature measurements. Sediment temperature mapping of riffle-pool and plane-bed geomorphic units illustrated highly varied substrate temperatures in the plan-view of the creek. The potential application of thermal imaging was also explored and thermal images successfully illustrated a groundwater-sustained micro-habitat. The results demonstrated that these multi-scale field techniques allow for different groundwater–surface water exchange processes to be observed and more effectively capture the complexity of these exchanges than single-level field approaches.

Flexible protective diamond-like carbon film on rubber

In this paper we report an experimental approach to deposit flexible diamond-like carbon (DLC) films on rubber via self-segmentation. By making use of the substantial thermal mismatch between the DLC film and rubber substrate a dense network of cracks forms in the DLC film, contributing to its flexibility. The size of the micro-segments can be controlled by tuning the substrate temperature variation during deposition by varying the bias voltage.

Synthesis of novel galactose containing chemicals by β-galactosidase from Enterobacter cloacae B5

The β-galactosidase from Enterobacter cloacae B5 was employed to synthesize novel galactose containing chemicals (GCCs) using mannitol, sorbose, and salicin as acceptors in the presence of o-nitrophenyl-β-d-galactopyranoside (oNPGal) as donor. The influences of the process parameters on GCC synthesis using mannitol as an acceptor, including effects of variations in initial substrate concentration, reaction time, and temperature, were studied in detail. The mannitol derivative reached a yield of 14.6% when the enzyme was used in the presence of 30mM oNPGal and 60mM mannitol at 50°C for 10min. The sorbose and salicin derivatives reached yields of 19.4% and 25.2%, respectively, under the same conditions except for acceptor concentrations. Through analysis of ESI-MS and NMR spectroscopy, the three derivatives were identified to be β-d-galactopyranosyl-(1→1′)-d-mannitol, β-d-galactopyranosyl-(1→1′)-l-sorbose, and 2-(hydroxymethyl) phenyl β-d-galactopyranosyl-(1→6′)-β-d-glucopyranoside.

Comparison of real‐time methods for maximizing power output in microbial fuel cells

AbstractMicrobial fuel cells (MFCs) constitute a novel power generation technology that converts organic waste to electrical energy using microbially catalyzed electrochemical reactions. Since the power output of MFCs changes considerably with varying operating conditions, the online optimization of electrical load (i.e., external resistance) is extremely important for maintaining a stable MFC performance. The application of several real‐time optimization methods is presented, such as the perturbation and observation method, the gradient method, and the recently proposed multiunit method, for maximizing power output of MFCs by varying the external resistance. Experiments were carried out in two similar MFCs fed with acetate. Variations in substrate concentration and temperature were introduced to study the performance of each optimization method in the face of disturbances unknown to the algorithms. Experimental results were used to discuss advantages and limitations of each optimization method. © 2010 American Institute of Chemical Engineers AIChE J, 2010

Amorphous to nanocrystalline transition in HWCVD Si:H films by substrate temperature variation

AbstractThin films of hydrogenated silicon with band gap ranging from 2.0‐2.34 eV are prepared at deposition rate 8‐14 Å/sec in an indigenously fabricated HWCVD system keeping all parameters except substrate temperature fixed. The films grown at Ts ≤ 150 °C are found to be pure amorphous, whereas the formation of nanocrystalline phase starts at Ts ≥ 200 °C. With increase in Ts, crystalline fraction increases along with the increase in the band gap whereas the hydrogen content in the films and the deposition rate decreases. The variation of microstructure by varying substrate temperature without a significant decrease in deposition rate is useful for various device applications. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth of structurally homogeneous CVD ZnSe plates

A model for the formation of the CVD ZnSe structure is proposed which takes into account the heat exchange between the surface of the growing crystal and the flow of gaseous reactants and the secondary recrystallization process at a varied substrate temperature. The calculation results are compared to experimental data. The time variation of the substrate temperature is optimized to achieve CVD of ZnSe with a homogeneous structure across the plate.

Role of substrate temperature on the structural, optoelectronic and morphological properties of (400) oriented indium tin oxide thin films deposited using RF sputtering technique

RF sputtering process has been used to deposit highly transparent and conducting films of tin-doped indium oxide onto quartz substrates keeping the RF power constant at 250 W. The electrical, optical and structural properties have been investigated as a function of substrate temperature. XRD has shown that deposited films are polycrystalline and have (400) preferred orientation. Indium tin oxide layers with low resistivity values and high transmittance in the visible region have been deposited. Detailed Analyses based on X-ray diffraction, optical and electrical results are attempted to gain more insight into the factors that are governed by the influence of varying substrate temperature in this investigation. AFM pictures showed uniform surface morphology with very low surface roughness values. It has been observed that ITO films deposited in this study, keeping the substrate temperature at 150 °C, can provide the required optimum electrical and optical properties rendering them useful for developing many optoelectronic devices at a moderate temperature.

Temperature dependence of Zn 1− xMg xO films grown on c-plane sapphire by metal organic vapor phase epitaxy

Metal organic vapor phase epitaxy (MOVPE) has been used to grow ternary Zn 1− x Mg x O layers on c-plane sapphire substrates. The precursors nitrous oxide, bismethylcyclopentadienyl magnesium, and dimethylzinc-triethylamine were used as the oxygen, magnesium, and zinc sources, respectively. Nitrogen was the carrier gas. The concentration of magnesium in the gas phase was varied, relative to the zinc concentration, by adjusting the partial pressures ratio R II=P Mg/(P Mg+P Zn). Both R II and substrate temperature variations induce a strong dependence of the growth rate, structural and optical qualities, and magnesium content in the grown layer. When the R II ratio is increased from 0 to 0.8 at different substrate temperatures, the following are clearly observed: (i) a decrease of the growth rate, (ii) a shift of the Zn 1− x Mg x O (0 0 2) X-ray diffraction peak to higher diffraction angles from 34.44° (wurtzite ZnO) up to 34.63°, and (iii) a shift of the PL-near band edge emission from 3.36 eV (ZnO bandgap) up to 3.75 eV. This latter value corresponds to a magnesium concentration in the Zn 1− x Mg x O solid solution of approximately 20%.

A review of crystallographic textures in chemical vapor-deposited diamond films

Diamond is one of the most important functional materials for film applications due to its extreme physical and mechanical properties, many of which depend on the crystallographic texture. The influence of various deposition parameters matters to the texture formation and evolution during chemical vapor deposition (CVD) of diamond films. In this overview, the texture evolutions are presented in terms of both simulations and experimental observations. The crystallographic textures in diamond are simulated based on the van der Drift growth selection mechanism. The film morphology and textures associated with the growth parameters α (proportional to the ratio of the growth rate along the 〈100〉 direction to that along the 〈111〉 direction) are presented and determined by applying the fastest growth directions. Thick films with variations in substrate temperature, methane concentration, film thickness, and nitrogen addition were analyzed using high-resolution electron back-scattering diffraction (HR-EBSD) as well as X-ray diffraction (XRD), and the fraction variations of fiber textures with these deposition parameters were explained. In conjunction with the focused ion beam (FIB) technique for specimen preparation, the grain orientations in the beginning nucleation zones were studied using HR-EBSD (50 nm step size) in another two sets of thin films deposited with variations in methane concentration and substrate material. The microstructures, textures, and grain boundary character were characterized. Based on the combination of an FIB unit for serial sectioning and HR-EBSD, diamond growth dynamics was observed using a 3D EBSD technique, with which individual diamond grains were investigated in 3D. Microscopic defects were observed in the vicinity of the high-angle grain boundaries by using the transmission electron microscopy (TEM) technique, and the advances of TEM orientation microscopy make it possible to identify the grain orientations in nano-crystalline diamond.

CMOS wireless temperature sensor with integrated radiating element

A novel fully integrated wireless temperature sensor realised in 0.35 μm CMOS technology, operating at 2.4 GHz, is presented. The realised chip emits an electromagnetic field at regular time instants, set by an on-board digital control circuit. The high frequency oscillator is a simple three-stag ring oscillator. The signal is transmitted by a small on-chip loop antenna structure. This ring oscillator with the on-chip antenna represent a building block of a wireless temperature sensor, which transforms the silicon substrate temperature variation into a frequency modulation. To easily recover the frequency- vs.-temperature information, the electronic design of the ring oscillator has been carefully tuned to get a linear dependence between them. However, the frequency oscillation of a ring oscillator presents an undesired dependence on the bias voltage. To solve this problem a technique was implemented based on the monitoring of two different signals, allowing the extraction of reliable information on temperature, regardless of the bias voltage variation. This concept is implemented using two three-stag ring oscillators with slightly different frequency- vs.-temperature characteristics, both close however to 2.4 GHz, switched alternatively on for a few milliseconds each. The experimental measurements show that the oscillators provide an electromagnetic field with a power level of −45 dBm at a distance of 1 m. The peak and average power consumptions are 3.3 mW and 500 μW, respectively.

Microtexture and Grain Boundaries in Freestanding CVD Diamond Films: Growth and Twinning Mechanisms

AbstractThree groups of free‐standing chemical vapor deposition (CVD) diamond films formed with variations in substrate temperature, methane concentration, and film thickness are analyzed using high‐resolution electron back‐scattering diffraction. Primarily {001}, {110}, and {111} fiber textures are observed. In addition, corresponding primary and higher order twinning components are found. As interfaces, high angle, low angle, primary twin, and secondary twin boundaries are observed. A growth and a twinning model are proposed based on the sp3 hybridization of the bond in the CH4 molecule that is used as the deposition medium.

Synthesis of a New Modification of Lithium Chloride Confirming Theoretical Predictions

AbstractIn accordance with prior calculations, the new polymorph β‐LiCl (wurtzite structure type) has been synthesised, by the low‐temperature atomic‐beam‐deposition (LT–ABD) technique, in a mixture with α‐LiCl (rock salt structure type) by depositing LiCl vapour (2 to 5.3 × 10–4 mbar) onto a cooled substrate (–30 to –60 °C). The maximum β‐LiCl fraction of 53 % was obtained using a sapphire (0001) substrate at –50 °C and 3.7 × 10–4 mbar LiCl vapour pressure. The proportion of the new polymorph contained in the bulk sample decreases as temperature or vapour pressure deviate from these values, until finally the rock salt type LiCl is found exclusively. When the samples are warmed up to room temperature, β‐LiCl irreversibly transforms to α‐LiCl. The X‐ray diffraction pattern of the two phase LiCl sample measured at –50 °C has been indexed and refined based on a hexagonal unit cell for β‐LiCl with the lattice constants a = 3.852(1) Å and c = 6.118(1) Å and a cubic unit cell for α‐LiCl with the lattice constant a = 5.0630(8) Å. By Rietveld refinement the wurtzite type ofstructure (P63mc, No. 186) was suggested for the new hexagonal modification of LiCl with the Li–Cl distances (2.32 and 2.34 Å) being 8 % smaller than those of α‐LiCl. Moreover, the cell volume decreases as much as 16 % during the transition from β‐LiCl to α‐LiCl. Both the shifts in bond lengths and volume correspond well with the situation encountered for LiBr and LiI. Besides the variation of LiCl vapour pressure and substrate temperature, also different substrate materials were employed for testing their influence on formation of the β‐LiCl polymorph.

Electrical, structural and etching characteristics of ZnO:Al films prepared by rf magnetron

Al doped ZnO (AZO) films were prepared by radio frequency (rf) magnetron sputtering with varying substrate temperature, working Ar gas pressure and rf power imposed on 2-inch ZnO–Al 2O 3 (2 wt%) target, and their electrical and structural properties together with the corresponding etching behavior in 0.5% HCl solution were examined. The effect of rf power on the electrical and structural properties of AZO films was marginal, but in the case of working Ar gas pressure and substrate temperature, substantial variations in the electrical and structural properties were observed. The optimum electrical properties were obtained for AZO film deposited at 150 °C in lowest working pressure of 1.2 mTorr. The behavior of crater formation upon etching varied significantly depending on the structure of the film, and it was shown that the etching rate could be expressed in inversely proportional function of the crystallinity represented as (002) peak intensity. Also, for films with similar crystallinity, i.e. (002) peak intensity, dense structured film deposited at high temperature had much lower etching rate than open structured films deposited under high working Ar gas pressure.

VUV-Stimulated MO CVD Processes of Copper Layer Deposition

VUV-stimulated processes of copper layer deposition were investigated. A conventional compound, copper bis-hexafluoroacetylacetonate, was used as a precursor. Excimer lamps emitting light within the wavelength range 116-172 nm were used as the sources of VUV radiation. The results of quantum-chemical calculations were compared with the electronic spectra of copper bis-hexafluoroacetylacetonate in the gas phase. Calculations were carried out using the quantum chemical method of the density functional theory with Slater type of atomic wave functions (DFT/TZP). On the basis of thus determined electronic structure, allowed dipole-dipole electron transitions within the wavelength region 100-1200 nm were calculated; they were compared with the experimental spectra. Investigation of copper deposition processes was carried out under variation of substrate temperature and precursor, process time, presence of reactant gas, spectral characteristics of the excimer lamps. The resulting layers were characterized by means of SEM, ESCA, ellipsometry.

The effects of substrate temperature on the structure, morphology and photoluminescence properties of pulsed laser deposited SrAl2O4:Eu2+,Dy3+ thin films

Abstract In this study, SrAl 2 O 4 :Eu 2+ ,Dy 3+ thin film phosphors were deposited on Si (1 0 0) substrates using the pulsed laser deposition (PLD) technique. The films were deposited at different substrate temperatures in the range of 40–700 °C. The structure, morphology and topography of the films were determined by using X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). Photoluminescence (PL) data was collected in air at room temperature using a 325 nm He–Cd laser as an excitation source. The PL spectra of all the films were characterized by green phosphorescent photoluminescence at ∼530 nm. This emission was attributed to 4f 6 5d 1 →4f 7 transition of Eu 2+ . The highest PL intensity was observed from the films deposited at a substrate temperature of 400 °C. The effects of varying substrate temperature on the PL intensity were discussed.

Influence of deposition conditions on texture development and mechanical properties of TiN coatings

Abstract The influence of varying substrate temperature, N2 partial pressure, ion energy, and ion-to-Ti flux ratio on the texture development and mechanical properties of TiN is investigated in detail. We show that during low substrate temperature (T s = 300 °C) reactive sputtering of TiN in a mixed Ar + N2 discharge a change from 111- to 001-oriented growth occurs when increasing the ion-to-Ti ratio J i/J Ti above 2.5 while using a low ion energy E i of 30 eV. This texture change can be reversed to a 111-oriented growth by increasing the ion energy to 60 and 90 eV when using high ion-to-Ti ratios J i/J Ti of 2.5 and 9, without introducing strain. Thereby the hardness can be increased from ∼31 to 37 GPa with only minor changes in compressive stresses. Consequently, by defining the ion-to-Ti ratio and the ion energy during low substrate temperature reactive sputtering of TiN the texture development towards 111- or 001-oriented growth can be controlled. Based on previous studies and the texture development as a function of substrate temperature and N2-partial pressure, we propose that varying the ion-to-Ti ratio and the ion energy result in different N-terminated surfaces and hence different Ti-fluxes from 111- to 001-oriented grains and vice versa.

Structural and Dielectric Properties of Sputter-Deposited Ba0.48Sr0.52TiO3 / LaNiO3 Artificial Superlattice Films

Artificial superlattices consisting of dielectric (BST) and conductive (LNO) were fabricated on an Nb-doped (001) single-crystal substrate with radio-frequency magnetron sputtering at temperatures in the range of . A symmetric structure with a sublayer thickness of 3 nm was deposited at varied substrate temperatures; the superlattices contained 10 periods of BST/LNO bilayers. The microstructure of these films was characterized with measurements of X-ray reflectivity and diffraction at high resolution. The formation of a superlattice structure was confirmed through the appearance of both the Bragg peaks separated by Kiessig fringes in X-ray reflectivity curves and the satellite peaks of a (002) diffraction pattern and the secondary-ion mass spectrometry profile. The clearly discernible main feature and satellite features observed in the (002) crystal truncation rod indicate the high quality of the BST/LNO artificial superlattice structure formed on a substrate at all temperatures of deposition. The higher the temperature of deposition, the smaller the full width at half-maximum of the in-plane rocking curve and the better the crystalline quality. These BST/LNO artificial superlattices show a dielectric constant significantly enhanced relative to the BST single layers of the same effective thickness. Both the lattice strain and the interface quality affect the dielectric properties of the BST/LNO superlattices.

Fabrication of <emphasis emphasistype="italic">In-Situ</emphasis> <formula formulatype="inline"><tex Notation="TeX">${\rm MgB}_{2}$</tex></formula> Films Using Evaporation and Sputtering Simultaneous Deposition Technique

The evaporation and sputtering simultaneous deposition (ESSD) system was developed for <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in-situ</i> deposition of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin films. Mg was evaporated from the nozzle of cylinder crucible which is heated by high frequency induction heating, while B was sputtered by RF-magnetron sputtering. The nozzle-substrate distance was small enough to keep high vapor pressure of Mg on the substrate. The Mg-flux coming out of the nozzle was controlled by means of regulating the temperature of Mg source, was monitored and was calculated in detail with the variation of the distance from its nozzle. The optimal deposition condition with the variations of substrate temperature, the temperature of Mg source and the power of RF-magnetron sputtering, was investigated. MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films with onset T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> of 14 K was obtained. The T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> of the film is lower than the bulk value of 39 K. Further works are in progress to improve the quality of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films by further optimization of deposition parameters and improvement of the ESSD system.

Morphology and photoluminescence properties of zinc oxide films grown by pulsed laser deposition

Zinc oxide films with different morphologies have been grown by pulsed laser deposition, varying substrate temperature and oxygen pressure. At low oxygen pressure and low substrate temperature continuous films with different roughness have been obtained, while at high substrate temperature a film with sparse hexagonal pyramids has been observed. Increasing the oxygen pressure the film became rougher and at 100 Pa a rod-array has been deposited. The columns of this rod-array grew along the wurtzite c-axis perpendicularly to the substrate surface as proved by X-ray diffraction measurements. Near to the sample borders the columns were slightly tilted towards the center of the sample. The possible growth mechanisms giving rise to the different morphologies have been discussed. Low-temperature photoluminescence measurements allowed to get information about the film quality, showing the variations of the excitonic peak and two defect bands (green and violet-blue) with the different deposition parameters.