Effect Of Catalyst Thickness Research Articles

Development of silicon nanowires with optimized characteristics and fabrication of radial junction solar cells with < 100 nm amorphous silicon absorber layer

We report the growth and characterization of Silicon nanowires (SiNWs) via the VLS mechanism with two different tin (Sn) catalyst thicknesses of 2 and 4 nm at 400 and 500 °C by PECVD. The effect of catalyst thickness, plasma power density and growth temperature on the morphology of nanowires is investigated. The structural morphology of the grown NWs is analyzed using FESEM and HRTEM. It has been inferred the density, diameter and length of NWs can be effectively controlled by PECVD process parameters. HRTEM analysis demonstrates a highly crystalline silicon core with (111) plane as preferred orientation. Grazing incidence X-ray diffraction spectra of the samples prepared at two different temperatures confirmed the (111), (220) and (311) plane orientation of the grown NWs. Raman spectra of the SiNWs grown on glass substrate shown broadened spectrum centering at 508 cm-1 confirming the crystalline nature of NWs core surrounded with dense layer of a-Si. Optimized parameters are used to fabricate radial junction solar cells and the effect of catalyst thickness on the performance is explored. Short circuit current density of 13.53 mA/cm2 and open circuit voltage of 0.82 V for 0.25 cm2 solar cell having power conversion efficiency of 6.66% is obtained.

The Effect of Catalyst Thickness and the Hydrogen Annealing Time on Spin Capability of Carbon Nanotube Forest with a Fast Temperature Ramping Rate CVD System

In this paper, we report the effects of iron (Fe) thickness and the hydrogen (H2) annealing time on the spin-capability of vertically aligned carbon nanotube (CNT) forest. Using a chemical vapor deposition chamber with a magnetic arm and mobile furnace, quick heating and cooling were done on the sample. For the growth process of carbon nanotube forest, the sample was moved from room temperature to 780 °C in 3 seconds in helium (He) environment, and H2 and acetylene (C2H2) were used as annealing gas and carbon source, respectively. To study the effect of Fe thickness on spin-capability, 1.5, 2.5, and 3.5 nm of Fe thin film was deposited using e-beam deposition tool on top of a thin aluminum oxide (Al2O3) layer. Also, the duration of hydrogen annealing time for the Fe film to form Fe nanoparticles were varied from 10 ~ 60 seconds. Fe film thickness of 2.5 nm and 30 seconds of H2 annealing time resulted in well-spinning vertically aligned carbon nanotube forest.

Effects of catalyst thickness on the fabrication and performance of carbon nanotube-templated thin layer chromatography plates

The effects of iron catalyst thickness on the fabrication and performance of microfabricated, binder-free, carbon nanotube (CNT)-templated, thin layer chromatography (TLC) plates are demonstrated. The iron catalyst was deposited at thicknesses ranging from 4 to 18 nm in increments of 2 nm. Its thickness plays a key role in governing the integrity and separation capabilities of microfabricated TLC plates, as determined using a test dye mixture. Atomic force microscopy and scanning electron microscopy show that smaller and more numerous catalyst nanoparticles are formed from thinner Fe layers, which in turn govern the diameters and densities of the CNTs. The average diameter of the Fe nanoparticles, Dp, is approximately six times the initial Fe film thickness, tFe: Dp ≈ 6tFe. After deposition of relatively thick silicon layers on CNTs made with different Fe thicknesses, followed by oxidation, all of the resulting CNT-templated SiO2 wires had nearly the same diameter. Consequently, their surface areas were very similar, although their areal densities on the TLC plates were not because thinner catalyst layers produce denser CNT forests. For tFe = 6 nm, nanotube growth appears to be base growth, not tip growth. Best TLC separations of a test dye mixture were obtained with plates prepared with 6 or 4 nm of catalyst. Calculations suggest a loss of surface area for TLC plates made with thicker Fe layers as a result of fewer, thicker CNTs, where the density of silica nanotubes (device surface area) goes approximately as 1/tFe2. While the focus of this paper is toward a greater understanding of the processing conditions that lead to the best TLC plates, a baseline separation of three analgesics (caffeine, phenacetine, and propyphenazone) is shown on a normal phase TLC plate grown with 6 nm of iron.

Investigation of Low‐Pressure Bimetallic Cobalt‐Iron Catalyst‐Grown Multiwalled Carbon Nanotubes and Their Electrical Properties

A bimetallic cobalt‐iron catalyst was utilized to demonstrate the growth of multiwalled carbon nanotubes (CNTs) at low gas pressure through thermal chemical vapor deposition. The characteristics of multiwalled CNTs were investigated based on the effects of catalyst thickness and gas pressure variation. The results revealed that the average diameter of nanotubes increased with increasing catalyst thickness, which can be correlated to the increase in particle size. The growth rate of the nanotubes also increased significantly by ~2.5 times with further increment of gas pressure from 0.5 Torr to 1.0 Torr. Rapid growth rate of nanotubes was observed at a catalyst thickness of 6 nm, but it decreased with the increase in catalyst thickness. The higher composition of 50% cobalt in the cobalt‐iron catalyst showed improvement in the growth rate of nanotubes and the quality of nanotube structures compared with that of 20% cobalt. For the electrical properties, the measured sheet resistance decreased with the increase in the height of nanotubes because of higher growth rate. This behavior is likely due to the larger contact area of nanotubes, which improved electron hopping from one localized tube to another.

Controlled growth of carbon nanofibers using plasma enhanced chemical vapor deposition: Effect of catalyst thickness and gas ratio

The characteristics of carbon nanofibers (CNFs) grown, using direct current plasma enhanced chemical vapor deposition system reactor under various acetylene to ammonia gas ratios and different catalyst thicknesses were studied. Nickel/Chromium-glass (Ni/Cr-glass) thin film catalyst was employed for the growth of CNF. The grown CNFs were then characterized using Raman spectroscopy, field emission scanning electron microscopy and transmission electron microscopy (TEM). Raman spectroscopy showed that the Ni/Cr-glass with thickness of 15nm and gas ratio acetylene to ammonia of 1:3 produced CNFs with the lowest ID/IG value (the relative intensity of D-band to G-band). This indicated that this catalyst thickness and gas ratio value is the optimum combination for the synthesis of CNFs under the conditions studied. TEM observation pointed out that the CNFs produced have 104 concentric walls and the residual catalyst particles were located inside the tubes of CNFs. It was also observed that structural morphology of the grown CNFs was influenced by acetylene to ammonia gas ratio and catalyst thickness.

Effect of Catalyst Thickness and Plasma Pretreatment on the Growth of Carbon Nanotubes and Their Field Emission Properties

We demonstrated that the diameter and the density of carbon nanotubes (CNTs) which had a close relation to electric-field-screening effect could be easily changed by the control of catalytic Ni thickness combined with NH3 plasma pretreatment. Since the diameter and the density of CNTs had a tremendous impact on the field-emission characteristics, optimized thickness of catalyst and application of plasma pretreatment greatly improved the emission efficiency of CNTs. In the field emission test using diode-type configuration, well-dispersed thinner CNTs exhibited lower turn-on voltage and higher field enhancement factor than the densely-packed CNTs. A CNT film grown using a plasma-pretreated 25 angstroms-thick Ni catalyst showed excellent field emission characteristics with a very low turn-on field of 1.1 V/microm @ 10 microA/cm2 and a high emission current density of 1.9 mA/cm2 @ 4.0 V/microm, respectively.

Effect of Catalyst Thickness and Plasma Pretreatment on the Growth of Carbon Nanotubes and Their Field Emission Properties

We demonstrated that the diameter and the density of carbon nanotubes (CNTs) which had a close relation to electric-field-screening effect could be easily changed by the control of catalytic Ni thickness combined with NH3 plasma pretreatment. Since the diameter and the density of CNTs had a tremendous impact on the field-emission characteristics, optimized thickness of catalyst and application of plasma pretreatment greatly improved the emission efficiency of CNTs. In the field emission test using diode-type configuration, well-dispersed thinner CNTs exhibited lower turn-on voltage and higher field enhancement factor than the densely-packed CNTs. A CNT film grown using a plasma-pretreated 25 Å-thick Ni catalyst showed excellent field emission characteristics with a very low turn-on field of 1.1 V/μm @ 10 μA/cm2 and a high emission current density of 1.9 mA/cm2 @ 4.0 V/μm, respectively.

Effects Of Catalyst Layers On Carbon Nanotubes Growth

catalyst Carbon nanotubes growth on varied thicknesses of nickel catalyst by hot filament chemical vapor deposition (HFCVD) is reported. The nanotubes were grown using C2H2 acetylene as carbon feedstock in hydrogen and nitrogen atmosphere. The catalyst layers were deposited by magnetron sputtering technique with thicknesses varied from 25 nm to 200 nm. Deposited films were annealed at 600 °C for 10 min before exposing to C2H2 for the growth of nanotubes at same temperature for another 10 min. The effects of catalyst thickness have been investigated with reference to nanotubes formation. The morphology and microstructure of the films were measured and analyzed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Raman analysis was also conducted to determine the atomic bonding structure of nanotubes. The catalyst thickness has significant effects on the nanotubes alignment and the uniformity of nanotube diameters. However, the thickness shows no obvious effects on the atomic structure of the nanotubes grown.