Low-pressure Thermal Chemical Vapor Research Articles

Triethylamine borane thermal decomposition for BN low pressure chemical vapour deposition

Triethylamine borane (TEAB) complex was studied as a potential precursor for the thermal low pressure chemical vapour deposition (LPCVD) of pure crystalline sp2-hybridised BN. In particular, its thermal decomposition with or without ammonia was characterised from thermodynamic and experimental points of view in the temperature ranges 400–2000 °C and 300–1300 °C, respectively. NH3 plays a role in the gas phase equilibrium by providing a nitriding source that promotes HCN formation at high temperatures. NH3 is also a source of hydrogen for light hydrocarbons formation as it decomposes. It is thus possible to promote gaseous carbon species formation at high temperatures and limit carbon introduction into coatings by adding ammonia. A turbostratic BN coating could be obtained by CVD from a TEAB/NH3/N2 mixture and conditions chosen thanks to the gas phase decomposition study.

Synthesis of organic functional thin films and their application tests of graphene based FET

This study investigated on the effects of gate dielectrics for field effect transistors (FETs). The gate dielectrics with organic and inorganic layers were deposited on Si (100) substrates using cyclohexane and tetraethyl orthosilicate (TEOS) by plasma enhanced chemical vapor deposition (PECVD) method. After the Si (100) substrates were dry-cleaned by in situ Ar plasma bombardment with 60 W for 15 min., the gate dielectric plasma polymer thin films deposited under plasma power between 20 W and 60 W with different precursor flow ratio. Also, the active graphene layer was grown on a Ni substrate using CH4 by low-pressure thermal chemical vapor deposition (CVD) method, and the Ni substrate was then etched away. In order to fabricate a back-gate graphene-based FET, the graphene layer was adsorbed onto the plasma-polymer gate dielectric film, then 80 nm thick Au electrodes were finally evaporated onto the graphene using a mask with a gap of 370 nm, and a probe-station system was utilized to characterize the devices. As the plasma power and flow rate of TEOS increases, the gate voltage moves at a positive voltage, indicting p-doping by high fragmented Si and O elements under high plasma power and TEOS flow rate.

Growth and characterization of porous sp2-BN films with hollow spheres under hydrogen etching effect via borazane thermal CVD

Porous sp2-boron nitride (sp2-BN) films were directly grown on c-plane Al2O3 substrates by low pressure thermal chemical vapor deposition (CVD) using borazane (NH3-BH3) as a single precursor and without any catalyst. It was found that the BN films grown under 20 mbar are porous and consist of nano-scaled hollow BN spheres of various sizes, with outer radius (ro) ranging from 7.20 nm to 13.32 nm. The B-N bonding was confirmed to be sp2-bonded by the Raman scattering whereas, the crystal structure was determined by TEM and XRD to be turbostratic BN (t-BN) having a lattice constant ‘c’ larger than the hexagonal BN (h-BN) bulk crystal. Homogenous nucleation played a vital role in the porous sp2-BN formation that is contrary to normal CVD growth under such low pressure i.e. 2 mbar for denser BN films. Additionally, because of the H2 chemical etching effect, the H2/N2 ratio shows a strong influence on the film growth. All of the as-grown films have shown good ultraviolet (UV) absorption edge near 210 nm, hence providing a feasible route towards the synthesis of porous sp2-BN with higher surface-volume ratio for high performance photo sensors and smart energy storage devices.

Growth temperature impact on film quality of hBN grown on Al2O3 using non-catalyzed borazane CVD

Hexagonal boron nitride (hBN) films were directly grown on c-plane Al2O3 substrates by low pressure thermal chemical vapor deposition (CVD) with single precursor i.e. borazane (NH3-BH3) without employing any extra catalysis. The growth temperature influence on the growth and properties of BN films were investigated. It was found that with a suitable source supply rate, the growth temperature could obviously influence the growth rate, chemical state, crystal structure and optical properties of BN films. High growth temperature depicts low thickness film grown, even there was no BN film deposited when the temperature was higher than or equal to 1400 °C. The B–N bonding type in all the deposited BN films were conformed as sp2 bonding, and films were evidenced to be amorphous BN (aBN) at lower growth temperature (i.e. less than 1350 °C) and hBN in turbostratic phase (tBN) between 1350 and 1400 °C. All the grown BN films on sapphire substrate showed good ultraviolet (UV) absorption edge near 210 nm, according to transmittance spectra. This work presents a feasible route towards combination of large-scale CVD-grown hBN film with traditional III-N compounds for applications in deep UV optoelectronic devices.

Silicon–Carbon Core–Shell Hollow Nanotubular Configuration High-Performance Lithium-Ion Anodes

Silicon anode systems, due to their intrinsic high theoretical specific capacity, show tremendous potential in lithium ion batteries (LIBs). Unfortunately, commercial application still remains elusive due to the cycling-related colossal volume expansion issues following Li alloying and dealloying. Herein, core–shell C@Si@C hollow nanotubes with optimal Si thickness (∼60 nm) showing no microstructural damage during lithiation and delithiation processes, have been developed as a stable anode for LIBs with low first-cycle irreversible loss (FIR) of ∼13% and high areal capacity (∼3 mAhcm–2) for the first time. The hollow Si nanotubes (h-SiNTs) have been generated via our previously reported high-throughput and recyclable, sacrificial MgO wire template fabrication approach. Generation of Si films of varying thickness by low-pressure thermal chemical vapor deposition (LPCVD) with subsequent etching yields h-SiNTs. Modification/optimization of the h-SiNT physical characteristics exhibit improved performance in L...

Growth of Vertically Aligned Carbon Nanotube Arrays on Al Substrates through Controlled Diffusion of Catalyst

Atomic diffusion-induced catalyst evolution affects the iron catalyst lifetime and the collective termination of VACNT growth on a metal substrate. We demonstrated that controlled catalyst diffusion in the pretreatment stage is capable of extending the iron catalyst lifetime on an aluminum thin-film substrate to allow enhanced vertically aligned carbon nanotube (VACNT) growth by a conventional low-pressure thermal chemical vapor deposition. In adopting a fast-heating pretreatment to control the catalyst loss from diffusion, catalyst lifetime was extended, leading to the VACNT growth with heights up to 65% taller than those without the diffusion control strategy. Atomic diffusion of iron catalyst along the grain boundaries of aluminum thin films was found to play a critical role in the catalyst loss mechanism. This work provides the basic understanding of catalyst diffusion control to facilitate the growth of VACNT arrays on metallic substrates for various applications such as through silicon via interconn...

Dielectric/Si Interface Quality Characterization Using Room Temperature Photoluminescence

Advanced metal-oxide-semiconductor (MOS) and metal-insulator-semiconductor (MIS) devices employ ultra thin dielectric gate layers. The physical dimensions are in the range of single digit to double digit nanometers. The effective oxide thickness (EOT) is significantly less than 10 nm. Pure SiO2 or combinations of SiO2and SiN layers are typically used as gate dielectrics. High dielectric constant materials (high-k dielectrics) and metal gates are also frequently used, depending on chip design.Physical dimensions of dielectric layer(s) are typically measured using ellipsometry and high resolution cross-section transmission microscopy (HRXTEM). Electrical characteristics are typically characterized using either contact or non-contact C-V and I-V measurements tools. Non-contact characterization techniques are generally preferred for in-line monitoring applications. However, spatial resolution of non-contact C-V and I-V measurement techniques is in the range of a few millimeters, which are 3 orders of magnitude larger than typical dimensions of actual devices. High spatial resolution, non-contact dielectric/Si interface quality characterization techniques must be developed.In this paper, ultra thin (~7 nm) SiO2/Si and ultra thin SiN/SiO2/Si wafers were prepared by low pressure thermal chemical vapor deposition (CVD) and thermal oxidation. Dielectric/Si interface quality was characterized by room temperature spectroscopic photoluminescence (PL) measurements. The PL intensity and spectra from Si were measured under different excitation wavelengths which have different probing depths. PL is an optical characterization technique which does not require any sample preparation and physical contact. Typical spatial resolution is in the range of a few microns. Small variations in dielectric/Si interface quality modulates electronic carrier behaviors significantly which results in large variations in PL intensity and spectra. Significant variations in PL intensity and spectra were measured from ultra thin (~7 nm) SiO2/Si wafers prepared by and low pressure thermal CVD and thermal oxidation. Si wafers with thermal oxide films generally showed significantly stronger PL intensity than Si wafers with thermal CVD grown oxide films (Fig. 1). Trends in PL intensity and spectra indicate the SiO2/Si interface quality of the thermally oxidized SiO2/Si is superior to that of the thermal CVD grown SiO2/Si (Fig. 2). PL characterization is found to be very sensitive to the integrity of dielectric/Si interface and thus, is promising as an in-line, non-contact interface quality monitoring technique.The excitation wavelength dependence of PL intensity and spectra of SiO2/Si and SiN/SiO2/Si will be discussed along with conventional physical and electrical characterization results.

X-Ray Photoelectron Spectroscopy Study of SnO<SUB>2</SUB> and SnO<SUB>2+<I>x</I></SUB> Thin Films

SnO2 thin films were fabricated using low-pressure thermal chemical vapor deposition. The results of X-ray photoelectron spectroscopy revealed that the SiO2 layer with an O1S-binding energy of 531.2 eV was formed before the SnO2 layer with an O1S-binding energy of 530.5 eV was formed. In the beginning, the SnO2 thin film showed Sn3d5-binding energy peaks of 485 eV and 486.5 eV. Subsequently, it grew in the direction of 486.5 eV. The Sn3d5-binding strength of the SnO2+x thin film that was annealed in oxygen atmosphere was weaker than that of the SnO2 thin film. Additionally, the Sn3d5-binding strength decreased linearly as the depth of the thin film increased. The surface O1S-binding strength of the SnO2+x thin film annealed in oxygen atmosphere was stronger than that of the SnO2 thin film; however, this strength became weaker than that that of the SnO2 thin film when the depth of the thin film was 2500A or higher.

Electrosorption of different cations and anions with membrane capacitive deionization based on carbon nanotube/nanofiber electrodes and ion-exchange membranes

A membrane capacitive deionization (MCDI) device, which combines ion-exchange membranes and carbon nanotube and carbon nanofiber (CNT-CNF) film electrodes, has been developed to investigate the selective electrosorption of different cations and anions. The CNT-CNF films are synthesized by low pressure and low temperature thermal chemical vapor deposition. The experimental results show that multivalent cations and anions are better adsorbed from aqueous solution and for cations or anions with same charge, the one with smaller hydrated radius will be more effectively removed.

Electrosorption Behavior of Carbon Nanotube and Carbon Nanofiber Film Electrodes

In this review work, the synthesis of cost-effective, large area carbon nanotube and nanofiber (CNT-CNF) film by low pressure and low temperature thermal chemical vapor deposition and its electrosorption properties in salt solutions are studied. Successful purification of water with good reproducibility by electrosorption of CNT-CNF films is achieved because of optimal pore size distribution that results in lower electrical double-layer overlapping effect. It is found that electrosorption of CNT-CNF film electrodes is mainly due to Coulombic interaction on the electrical double-layer and the ion sorption followed a Langmuir isotherm, indicating monolayer adsorption. The kinetics and thermodynamics analyses indicate that the electrosorption of NaCl onto CNT-CNF electrodes follows first order kinetics model and is driven by a physisorption process. Several experiments are conducted to study the ion removal capacity and selectivity of CNT-CNF film electrodes, showing that multivalent cations are preferentially adsorbed from the aqueous solution. For cations with same charge, the one with smaller hydrated radius will be more effectively removed. Keywords: Electrosorption, Carbon nanotubes, Capacitive deionization, Langmuir isotherm, Hydrated radius, Carbon Nanofiber, CNT-CNF, electrical double-layer overlapping effect, monolayer adsorption, physisorption process, deionization technologies, evaporation, reverse osmosis, electrodialysis, water purification technology, distillation columns, thermal heaters, pore microstructure, pore size distribution, arbon aerogel material, carbon aerogels, mass-transfer resistance, activated carbon cloth, chemical vapor deposition (CVD), Conductive plates, surface morphology, JEOL JSM-6700F, scanning electron microscopy (SEM), JEOL JEM-1200EX transmission electron microscopy (TEM), Raman spectroscopy, pore size distribution and Brunauer-Emmet-Teller (BET), counter electrode, reference electrode, polymethyl methacrylate plate, rectangular nylon spacer, rubber spacer, Batch-mode Electrosorption, CNT-CNF electrode, low mass-transfer, adsorption process, adsorption, –, desorption curves, mesoporous material, oxidation/reduction peaks, interaction, electrochemical reaction, double-layer capacitance (DLC), electrode surface inhomogeneity, Electrosorption Capacity, Freundlich isotherms, Electrosorption Kinetics, first-order, second-order, parabolic diffusion, Electrosorption Thermodynamics, Free energy of adsorption (DG0), enthalpy (DH0), van’t Hoff plots

Electrosorptive desalination by carbon nanotubes and nanofibres electrodes and ion-exchange membranes

A novel membrane capacitive deionization (MCDI) device, integrating both the advantages of carbon nanotubes and carbon nanofibers (CNTs–CNFs) composite film and ion-exchange membrane, was proposed with high removal efficiency, low energy consumption and low cost. The CNTs–CNFs film was synthesized by low pressure and low temperature thermal chemical vapor deposition. Several experiments were conducted to compare desalination performance of MCDI with capacitive deionization (CDI), showing that salt removal of the MCDI system was 49.2% higher than that of the CDI system. The electrosorption isotherms of MCDI and CDI show both of them follow Langmuir adsorption, indicating no change in adsorption behavior when ion-exchange membranes are introduced into CDI system. The better desalination performance of MCDI than that of CDI is due to the minimized ion desorption during electrosorption.

Electrosorption behavior of cations with carbon nanotubes and carbon nanofibres composite film electrodes

The cost-effective, large area carbon nanotubes and carbon nanofibres (CNTs–CNFs) composite film was synthesized on graphite substrate by low pressure and low temperature thermal chemical vapor deposition. Cyclic voltammetry and ac impedance spectroscopy were employed to systematically study the electrochemical properties of CNTs–CNFs film. The electrosorption in salt solutions by CNTs–CNFs film electrodes was studied. It is found that electrosorption of CNTs–CNFs film electrodes is mainly due to Coulombic interaction on the electrical double-layer. Several experiments were conducted to study the ion removal capacity and selectivity of CNTs–CNFs film electrodes, showing that multivalent cations were preferentially adsorbed from the aqueous solution. For cations with same charge, the one with smaller hydrated radius would be more effectively removed.

ELECTRIC DOUBLE LAYER CAPACITORS WITH CARBON NANOTUBES ELECTRODES AND GEL POLYMER/POLYACID ELECTROLYTES

Electric double layer capacitors (EDLCs) with carbon nanotubes (CNTs) film electrodes and gel polymer/polyacid electrolytes have been demonstrated. The low-cost CNTs film is directly grown on Cu – Ni current collector by low pressure and low temperature thermal chemical vapor deposition. The electrolytes consist of gel polymer poly(vinyl alcohol), polyacid phosphomolybdic acid (PMA) with different concentrations from 10 to 40 wt.% and KCl . The electrochemical measurement of the EDLCs by cyclic voltammetry and chronopotentiometry shows that gel polymer/polyacid electrolytes can work stable at a wide potential range of -1.5 to 1.5 V and EDLCs with electrolytes containing 30 wt.% PMA exhibit optimum capacitive behavior with 8.09 F/g specific capacitance.

Effects of Laser Ablation on Growth of ZnO/ZnS/ZnO Multilayer Structured Nanorods by Chemical Vapor Deposition

ABSTRACTZnO is an attractive II-VI compound semiconductor material for various optoelectronic devices. Recently, growth of various nanostructures of ZnO such as nanorod, nanobelt, nanowall, etc. has been reported, and ZnO has been considered as a promising material for nanodevices. We have studied on fabrication of aligned ZnO nanorods by a low-pressure thermal chemical vapor deposition (CVD) method cooperated with laser ablation of Mn pellet. In this paper, we report on fabrication of ZnO/ZnS/ZnO multilayer structured nanorods and particularly on effects of laser ablation on the morphology of the nanorods intending to develop a new electroluminescent device including ZnO nanorods. The fabrication method of ZnO/ZnS/ZnO multilayer structured nanorods is almost same method used in our previous study. Metal Zn vapor and O2 gas or H2S are used as precursors to synthesize ZnO or ZnS, and N2 is used as carrier gas. A Mn pellet is placed near a Si(111) substrate in a deposition chamber and ablated by a pulsed Nd:YAG laser beam (wavelength =1.064 mm, pulse width = 8 ns, repetition frequency = 10 shots/sec). The pressure is 13.3 Pa and the temperature is 550 C. When ZnO is grown, O2 of 0.88 SCCM mass flow rate is used as a precursor. When ZnS is grown, on the other hand, H2S of 2.0 SCCM mass flow rate is used as a precursor. The growth time is 15 min for each layer. Firstly, ZnO nanorods are grown. Laser ablation of Mn is executed for initial 3 min and only CVD is performed for remaining 12 min. The vertically aligned ZnO nanorods with 100 nm diameter and 1500 nm height are grown. Secondly, ZnS nanorod is grown on the top surface of the first ZnO nanorods. In this process, the morphology is not so dependent on execution of laser ablation of Mn for initial 3 min in this growth process. Finally, ZnO layer is again grown on ZnS/ZnO nanorods described above. When the laser ablation of Mn for initial 3 min is not executed, many fine ZnO whiskers with long length are grown with random directions on the top surface and on the side surfaces of ZnS/ZnO nanorods. When the laser ablation of Mn for initial 3 min is executed, on the other side, a thick whisker is grown on top surface of ZnS/ZnO nanorods. The shape is not nanorod. The diameter is abruptly decreased and the tip is very sharp. The growth of ZnO whisker on the side surface of ZnS/ZnO nanorods is not almost observed. It is found that the laser ablation of Mn for initial 3 min in the third ZnO growth strongly influences the morphology of the third ZnO layer. We estimate that the Mn species that are ablated from a Mn pellet and reaches the surface of ZnS/ZnO nanorods change any quality of the surface of ZnS/ZnO nanorods. We are now studying of finding the growth conditions of the third ZnO layer with morphology of nanorod on ZnS/ZnO nanorods that is considered to be suitable for electroluminescent devices.

Novel Inorganic DC Lateral Thin Film Electroluminescent Devices Composed of ZnO Nanorods and ZnS Phosphor

ABSTRACTA novel inorganic thin-film electroluminescence (TFEL) device exhibiting bright EL emission when driven by a low DC voltage is demonstrated. The DC-TFEL device is based on a composite layer in which aluminum-doped ZnO nanorods are vertically embedded in ZnS:Mn as an EL phosphor. The DC driving voltage is then applied laterally to the composite layer via two side electrodes set 3.5 mm apart. The aluminum-doped ZnO nanorods were synthesized on a glass substrate by low-pressure thermal chemical vapor deposition combined with laser ablation, and the composite layer was formed by electron-beam deposition of ZnS:Mn onto the ZnO nanorods. The thickness of the composite layer was about 160 nm. After electrical modification to breakdown a basal conduction ZnO path, the lateral DC-TFEL device exhibited bright EL emission without avalanche breakdown, achieving a luminance of 747 cd/m2 at 4200 V with a luminous efficiency of 9.2×10−3 lm/W.

ELECTROSORPTION OF FeCl3 SOLUTIONS WITH CARBON NANOTUBES AND NANOFIBERS FILM ELECTRODES GROWN ON GRAPHITE SUBSTRATES

The cost-effective, large area Carbon Nanotubes and Nanofibers (CNTs–CNFs) film was synthesized on graphite substrate by low pressure and low temperature thermal chemical vapor deposition (CVD). Successful removal of Fe 3+ from water by electrosorption of CNTs–CNFs films was achieved. The electrosorption capacities of CNTs–CNFs film electrodes were approximately 3.89–49.3 μmol/g at different voltages from 0.6 to 1.4 V, when the initial concentrations of ferric chloride ( FeCl 3) are kept around 89.1 μmol/L. The ion adsorption followed a Langmuir isotherm indicating monolayer adsorption.

Vapor−Solid−Solid Synthesis of Ge Nanowires from Vapor-Phase-Deposited Manganese Germanide Seeds

We report the sequential synthesis of solid-phase manganese germanide seed particles and crystalline Ge nanowires using low-pressure thermal chemical vapor deposition. Mn was deposited on inert substrates from a gas-phase precursor. Mn particles were converted to solid manganese germanide particles upon exposure to germane gas, and these seed particles directed the one-dimensional growth of Ge nanowires. Growth rates for this vapor−solid−solid process approached 200 nm per minute, and the diameter distribution was tightly clustered around 18 nm. This approach to Ge nanowire growth has at least three attractive features: (1) the seed particle is not Au, avoiding the potentially negative influence of Au impurities on electrical properties; (2) the vapor-phase deposition and self-assembly of the seed greatly simplifies the nanowire synthesis process; and (3) the self-assembled seed naturally produces a narrow distribution of nanowire diameters.

Control of diameter of ZnO nanorods grown by chemical vapor deposition with laser ablation of ZnO

Abstract We made a study of controlling diameters of well-aligned ZnO nanorods grown by low-pressure thermal chemical vapor deposition combined with laser ablation of a sintered ZnO target, which was developed by us. Until now, it has been impossible to control diameters of ZnO nanorods, while the growth orientation was maintained well-aligned. In this study we developed a multi-step growth method to fabricate well-aligned nanorods whose diameters could be controlled. Metal Zn vapor and O2 are used as precursors to grow ZnO nanorods. N2 is used as a carrier gas for the precursors. A substrate is an n -Si (111) wafer. A sintered ZnO target is placed near the substrate and ablated by a Nd–YAG pulsed laser during ZnO nanorod growth. The growth temperature is 530 ∘C and the pressure is 66.5 Pa. A vertical growth orientation of ZnO nanorods to the substrate is realized in the first-step growth although the diameter cannot be controlled in this step. When an O2 flow rate is 1.5 sccm, well-aligned nanorods with 100 nm diameter are grown. Next, the second-step nanorods are grown on only the flat tip of the first-step nanorods. The diameters of the second-step nanorods can be controlled by adjusting the O2 flow rate, and the growth direction is kept the same as that of the first-step nanorods. When the O2 flow rate in second-step growth is smaller than 0.6 sccm, the diameter of the second-step nanorods is 30–50 nm. When the O2 flow rate is between 0.75 and 3.0 sccm, the diameter is almost same as that of the first-step nanorods. When the O2 flow rate is larger than 4.5 sccm, the diameter is increased with increasing O2 flow rate. Further, the third-step ZnO nanorods with gradually increased diameters can be grown on the second-step nanorods with 1.5 sccm O2 flow rate and without laser ablation.

Investigating thin film stresses in stacked silicon dioxide/silicon nitride structures and quantifying their effects on frequency response

We have investigated the frequency shift caused by thin film stresses in silicon nitride (Si3N4) and silicon dioxide (SiO2) layers used during the fabrication of lead zirconium titanate (PZT) microelectromechanical (MEMS) devices. The films are deposited via thermal oxidation and low pressure chemical vapor deposition onto bare silicon wafers. Although previous research has reported stresses in these films, this paper introduces approaches to measure, model and predict the effects of these stresses on the frequency response of MEMS devices. Thin film stresses in each layer of a PZT stack are measured using a curvature measurement system, and these measurements are correlated to finite element analysis results and experimental vibration data. These comparisons illustrate the significance of the thin film stresses and their effect on the mechanical behavior of MEMS devices, in particular that as the membrane structures get thinner the frequency shift becomes much larger.

Field emission properties of carbon nanotubes film grown on NiCr alloy films

Carbon nanotubes (CNTs) are prepared on NiCr alloy films by low pressure thermal chemical vapor deposition at 600 °C. NiCr alloy films are deposited by magnetic co-sputtering method, and the various thickness and Ni/NiCr ratios are controlled by sputtering power. The diameter and length of CNTs, as well as the roughness of the CNTs films, mainly depend on the Ni/NiCr ratio. The field emission current density of the CNTs film increases with the increasing Ni/NiCr ratio from 65 wt% to 83 wt%, and decreases when the Ni/NiCr ratio is more than 87 wt% in the alloy film.