Preparation of immobilized nano-columnar TiO2 grains by chemical vapor deposition

Nano-columnar TiO2 grains are prepared and immobilized by chemical vapor deposition using TiCl4, H2 and O2 at low temperature. The structure of TiO2 is analyzed by X-ray diffraction (XRD), the morphology is observed by scanning electron microscopy (SEM) and the adhesion is estimated by measuring the critical load in scratch test. Results show that the structure of TiO2 films depend on the deposition temperature changing from amorphous, anatase, rutile, and both anatase and rutile phases as prepared at temperatures of 200, 300, 400 and 500 degrees C, respectively. The nano-columnar TiO2 grains are formed in both rutile and anatase phases, while it could be only rutile phase by increasing TiCl4 flow rate. The morphologies of TiO2 changes from smooth to nano-columnar grains as the deposition temperature increased from 200 to 400 degrees C. Excellent adhesion strength of crystalline TiO2 was obtained and it could be improved by increasing the TiCl4 flow rate in range of 0.3-0.6 sccm, where the critical load of TiO2 increases from 17 to 21 N.     

Preparation of TiO2 thick film by laser chemical vapor deposition method

A TiO₂ film was prepared on Pt/Ti/SiO₂/Si substrate by a laser chemical vapor deposition method. The rutile TiO₂ film with pyramidal grains and columnar cross-section was obtained at a high deposition rate (R _dep = 11.4 μm h^?1). At 300 K and 1 MHz, the dielectric constant (ε _r) and loss (tanδ) of the TiO₂ film were about 73.0 and 0.0069, respectively. The electrical properties of TiO₂ film were investigated by ac impedance spectroscopy over ranges of temperature (300–873 K) and frequency (10²–10⁷ Hz). The Cole–Cole plots between real and imaginary parts of the impedance (Z′ and Z′′) in the above frequency and temperature range suggested the presence of two relaxation regimes that were attributed to grain and grain boundary responses. The ionic conduction in the rutile TiO₂ film was dominated by the oxygen vacancies.     

Superlattice formation of (Ba,Sr)TiO3 prepared by metal-organic chemical vapor deposition

Dielectric superlattices of (Ba_0.5Sr_0.5)TiO₃ (BST) grown by a metal-organic chemical vapor deposition (MOCVD) have been studied by transmission electron microscopy (TEM). A selected area of electron diffraction patterns clearly show satellite spots that indicate the formation of superlattice of BST film. A superlattice distance is 6.75Å, that is, 2.4 times of (110) BST plane distance. A high-resolution TEM study revealed that the superlattices were induced by the periodic composition modulation of Ba and Sr atoms. A possible atomic arrangement model of the superlattice was proposed by a simulation with a national center for electron microscopy simulation system (NCEMSS).     

TiO2纳米微晶的RF-PCVD法制备及表征

以TiCl4为原料,采用高频等离子化学气相沉积(RF-PCVD)法制备了TiO2纳米微晶,考察了控制粒径大小及晶相转化的关键操作条件.借助XPS、TEM、XRD、BET等技术对颗粒的化学组成、形貌、晶相结构等进行了表征.研究表明:所得TiO2纳米微晶大部分为球形体颗粒,粒径30～50 nm,单分散性良好;颗粒中锐钛相和金红石相两相共存,结晶完整;金红石相含量在26.7%～53.6%之间可调.     

Growth of TiO2 anti-reflection layer on textured Si (100) wafer substrate by metal-organic chemical vapor deposition method

Recently anti-reflective films (AR) have been intensely studied. Particularly for textured silicon solar cells, the AR films can further reduce the reflection of the incident light through trapping the incident light into the cells. In this work, TiO2 anti-reflection films have been grown on the textured Si (100) substrate which is processed in two steps, and the films are deposited using metal-organic chemical vapor deposition (MOCVD) with a precursor of titanium tetra-isopropoxide (TTIP). The effect of the substrate texture and the growth conditions of TiO2 films on the reflectance has been investigated. Pyramid size of textured silicon had approximately 2-9 microm. A well-textured silicon surface can lower the reflectance to 10%. For more reduced reflection, TiO2 anti-reflection films on the textured silicon were deposited at 600 degrees C using titanium tetra-isopropoxide (TTIP) as a precursor by metal-organic chemical vapor deposition (MOCVD), and the deposited TiO2 layers were then treated by annealing for 2 h in air at 600 and 1000 degrees C, respectively. In this process, the treated samples by annealing showed anatase and rutile phases, respectively. The thickness of TiO2 films was about 75 +/- 5 nm. The reflectance at specific wavelength can be reduced to 3% in optimum layer.     

Coating of TiO2 thin films on particles by a plasma chemical vapor deposition process

TiO₂ thin films were experimentally coated on glass beads by means of a rotating cylindrical plasma chemical vapor deposition (PCVD) reactor. The morphologies and growth rates of the TiO₂ thin films before and after heat treatment were measured for various process conditions. The precursors for the TiO₂ films were generated from TTIP by plasma reactions, and they were deposited on the glass beads to become TiO₂ thin films. The TiO₂ thin films coated on the glass beads became more uniform by heat treatment. The TiO₂ thin films grew more quickly on the glass beads with increasing mass flow rate of TTIP, reactor pressure, or rotation speed of the reactor. As the applied electric power decreases, the thickness of the thin films on the glass beads increases. This experimental study shows that the use of a rotating cylindrical PCVD reactor can be a good method to coat high-quality TiO₂ thin films uniformly on particles.     

Towards controlled synthesis of 2D crystals by chemical vapor deposition (CVD)

The emergence of two-dimensional (2D) materials has captured the imagination of researchers since graphene was first exfoliated from graphite in 2004. Their exotic properties give rise to many exciting potential applications in advanced electronic, optoelectronic, energy and biomedical technologies. Scalable growth of high quality 2D materials is crucial for their adoption in technological applications the same way the arrival of high quality silicon single crystals was to the semiconductor industry. A huge amount of effort has been devoted to grow large-area, highly crystalline 2D crystals such as graphene and transition metal dichalcogenides (TMDs) through various methods. While CVD growth of wafer-scale monolayer graphene and TMDs has been demonstrated, considerable challenges still remain. In this perspective, we advocate for the focus on the crystal growth morphology as an underpinning for understanding, diagnosing and controlling the CVD process and environment for 2D material growth. Like snowflakes in nature, 2D crystals exhibit a rich variety of morphologies under different growth conditions. The mapping of crystal shapes in the growth parameter space “encodes” a wealth of information, the deciphering of which will lead to better understanding of the fundamental growth mechanism and materials properties. To this end, we envision a collective effort by the 2D materials community to establish the correlation between crystal shapes and the intrinsic thermodynamic and kinetic parameters for CVD reactions through integrated crystal growth experiment, database development and machine learning assisted predictive modeling, which will pave a robust path towards controlled synthesis of 2D materials and heterostructures.     

Comparison of the characteristics of TiO2 films prepared by low-pressure and plasma-enhanced chemical vapor deposition

Thin films of titanium dioxide (TiO₂) were deposited on silicon wafers at 450 °C by low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD), in the same reactor, using Ti(O-i-C₃H₇)₄ and oxygen as the reactants. The crystal structure, surface morphology, composition, chemical binding state and refractive index of the TiO₂ films, deposited with various r.f. powers, were characterized. Without plasma, LPCVD TiO₂ films show polycrystalline anatase structure, with a rough, granular surface and a typical refractive index of 2.43. On the contrary, the PECVD TiO₂ films are amorphous, with a smooth surface. By varying the r.f. power from 50 to 150 W, the refractive index of PECVD TiO₂ film increases with increasing power and becomes higher than 2.8 at 125 and 150 W. Despite the very different crystal structure, surface morphology and optical properties, the composition and chemical binding states of LPCVD and PECVD TiO₂ films are similar. The effect of plasma on the characteristics of CVD TiO₂ films is discussed.     

Initiated chemical vapor deposition of poly(2-hydroxyethyl methacrylate) hydrogels

Initiated chemical vapor deposition (iCVD), a low temperature variant of hot-wire chemical vapor deposition (HWCVD) is a solvent-free polymerization technique. It was used to synthesize thick, free-standing films of the hydrogel poly(2-hydroxyethyl methacrylate) (PHEMA). In this work, we show that the iCVD technique can yield PHEMA which is free from residual entrained monomer, has low non-specific protein adsorption and is capable of supporting good cell adhesion and proliferation.     

新型纳米TiO2膜电极的制备及应用研究

采用常压金属有机物化学气相沉积技术在钛板上沉积了TiO2膜电极,研究了其制备的重要工艺参数,进行了光化学、电化学特性的测试和表征,并应用于典型有机污染物苯酚的光电催化降解研究.结果表明,沉积温度是影响TiO2膜电极制备的重要因素.XRD图谱表明,沉积温度为500℃时负载的TiO3晶型结构为锐钛矿,600℃时出现金红石相.光电流测试表明,500℃时制备的TiO2膜的光电流最佳.以苯酚为污染物进行了光电催化降解实验,结果表明,其光电催化效果高于光催化、电催化降解效果,显示了较好的废水处理应用前景.     

化学气相沉积制备V2O5-WO3/TiO2催化剂及表征

以蜂窝堇青石为基体,采用化学气相沉积技术结合浸渍工艺制备出V2O5-WO3/TiO2脱硝催化剂,通过SEM、BET、XRD和EDS完成载体以及催化剂微观结构和成分表征,并利用活性评价装置测试了催化剂NO脱出率。试验结果表明,化学气相沉积技术制备的载体表面为锐钛矿型TiO2,其颗粒聚集成团块状,BET为62.73m2/g,平均孔径为9.8nm。制备的V2O5-WO3/TiO2催化剂孔结构规律与TiO2载体相似,V2O5在TiO2载体上无定形态单层分散,微量V2O5在微区长大成针状,宽度100nm;在350℃、4000h-1、n(NH3)/n(NO)=1时,催化剂NO脱出率ηNO达到96.7%。     

Growth and characterization of well-aligned densely-packed rutile TiO(2) nanocrystals on sapphire substrates via metal-organic chemical vapor deposition

Well-aligned densely-packed rutile TiO(2) nanocrystals (NCs) have been grown on sapphire (SA) (100) and (012) substrates via metal-organic chemical vapor deposition (MOCVD), using titanium-tetraisopropoxide (TTIP, Ti(OC(3)H(7))(4)) as a source reagent. The surface morphology as well as structural and spectroscopic properties of the as-deposited NCs were characterized using field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected-area electron diffractometry (SAED), x-ray diffraction (XRD) and micro-Raman spectroscopy. FESEM micrographs reveal that vertically aligned NCs were grown on SA(100), whereas the NCs on the SA(012) were grown with a tilt angle of ～33° from the normal to substrates. TEM and SAED measurements showed that the TiO(2) NCs on SA(100) with square cross section have their long axis directed along the [001] direction. The XRD results reveal TiO(2) NCs with either (002) orientation on SA(100) substrate or (101) orientation on SA(012) substrate. A strong substrate effect on the alignment of the growth of TiO(2) NCs has been demonstrated and the probable mechanism for the formation of these NCs has been discussed.     

定向碳纳米管的化学气相沉积制备法

报道了一种简便有效的合成定向碳纳米管 (CNTs)的化学气相沉积 (CVD)制备方法。以铁为催化剂 ,乙炔为碳源 ,采用单一反应炉 ,直接在石英基底上沉积催化剂颗粒薄膜 ,成功合成了定向性好、管径均匀的高质量大密度的碳纳米管     

Synthesis of centimeter-scale WS2 membrane by chemical vapor deposition

Journal of Materials Science: Materials in Electronics - Transition metal dichalcogenides (TMDCs) are among the most widely studied two-dimensional materials due to their unique physical...     

Processes in silicon deposition by hot-wire chemical vapor deposition

Hot-wire chemical vapor deposition is a rapidly developing CVD technique for the deposition of silicon thin films and silicon alloys and may become a competitor of the plasma-enhanced (PE) CVD method due to significant advantages such as high deposition rate, efficient source gas utilization, lack of ion bombardment, and low equipment cost. Little is known, however, about the mechanisms for catalytic decomposition of the source gases, gas phase reactions at commonly used pressures, and the growth reactions. In this article, the differences in the reactions at various filament materials are discussed and it is shown that the subsequent reactions in the gas phase and reactions contributing to film growth can be substantially different from those in PE-CVD, due to the lack of energetic electrons and ions. Further work is necessary to identify the role of each precursor for the deposition of amorphous and microcrystalline films.     

Selective ultrathin gold deposition by organometallic chemical vapor deposition onto organic self-assembled monolayers (SAMs)

We demonstrate a selective deposition of ultrathin gold layers via OMCVD (organometallic chemical vapor deposition) onto self-assembled dithiols. Dithiols have been self-assembled to produce a thiolated surface. The gold layer deposited from a gold precursor, present in the vapor around the sample, is bound to the exposed thiol groups. We demonstrate that it is possible to deposit gold only onto the areas where the binding thiol groups are located, and investigate the growth process with spontaneous desorption time-of-flight mass spectrometry, Rutherford backscattering spectroscopy, atomic absorption spectroscopy and atomic force microscopy.     

Plasmon-assisted chemical vapor deposition

We introduce a new chemical vapor deposition (CVD) process that can be used to selectively deposit materials of many different types. The technique makes use of the plasmon resonance in nanoscale metal structures to produce the local heating necessary to initiate deposition when illuminated by a focused low-power laser. We demonstrate the technique, which we refer to as plasmon-assisted CVD (PACVD), by patterning the spatial deposition of PbO and TiO(2) on glass substrates coated with a dispersion of 23 nm gold particles. The morphology of both oxide deposits is consistent with local laser-induced heating of the gold particles by more than 150 degrees C. We show that temperature changes of this magnitude are consistent with our analysis of the heat-loss mechanisms. The technique is general and can be used to spatially control the deposition of virtually any material for which a CVD process exists.