Field emission of vertically-aligned carbon nanotube arrays grown on porous silicon substrate

Vertically aligned arrays of multi-walled carbon nanotubes were grown by pyrolysis of acetylene on iron catalytic particles within a porous silicon template via chemical vapor deposition (CVD) at 700 °C. Using this method ordered nanotubes with diameters from 75 to 100 nm could be produced. The diode configuration field emission of the CNT arrays were performed and the onset electric field is 4 V/μm and the emission current can approach 1 mA/cm² at a electric field of 9.5 V/μm. The enhancement factor of the CNT arrays (4012) is derived from the F–N plot of the experiment data. To demonstrate the uniformity of the field emission, an ITO glass substrate with phosphor coated is used as anode in the field emission experiment. The average fluctuation of the emission current density was less than 5%. The result shows that the field emission of the CNT arrays on the silicon substrate is very uniform. These carbon nanotube arrays are useful for applications in field emission displays and sensors. The fabrication method shows the feasibility of integration between carbon nanotube arrays and silicon microelectronics.     

Synthesis of carbon nanotubes by catalytic chemical vapour deposition: A review on carbon sources,catalysts and substrates

Carbon nanotubes (CNTs) have been extensively studied during the past two decades and Catalytic Chemical Vapour Deposition (CCVD) technique has been untiredly employed by researchers to produce CNTs of various crystallographic configurations. In this paper the material aspects carbon sources, catalysts and substrates with regard to CCVD synthesis of carbon nanotubes are reviewed in light of latest developments and understandings in the field. The role of these materials in synthesis of CNTs is explained keeping the upto date literature in view. Latest research reports and their findings are presented with regard to effects of growth control aspects such as temperature, vapour pressure and catalyst concentration on CNT formation. Besides recent understandings with regard to preferential growth of CNTs are also discussed. From this literature review it is found that carbon diffusibility and carbon solubility of any catalyst are two important factors in determining CNT nucleation and growth. Moreover, addition of catalyst species to any transition metal catalyst can improve the catalyst performance and addition of water, air, alcohol etc. during CCVD process can increase the activity and lifetime of the catalyst besides enhances the production of CNTs.     

A rapid growth of aligned carbon nanotube films and high-aspect-ratio arrays

The remarkable properties of carbon nanotubes (CNTs) make them attractive for microelectronic applications, especially for interconnects and nanoscale devices. In this paper, we report an efficient process to grow well-aligned CNT films and high-aspect-ratio CNT arrays with very high area distribution density (>1600 μm⁻²). Chemical vapor deposition (CVD) was invoked to deposit highly aligned CNTs on Al₂O₃/Fe coated silicon substrates of several square centimeter area using ethylene as the carbon source, and argon and hydrogen as carrier gases. The nanotubes grew at a high rate of ∼100 μm/min. for nanotube films at 800°C, while the nanotube arrays grew at ∼140 μm/min. even at 750°C, due to the base growth mode. The CNTs were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and x-ray photoelectron spectroscopy (XPS). The results demonstrated that the CNTs are of high purity and form densely aligned arrays with controllable size and height. The as-grown CNT structures have considerable potential for thermal management and electrical interconnects for microelectronic devices.     

Chemical vapor deposition of AlxOyNz films

A chemical vapor deposition process for depositing dielectric films of aluminum oxynitride is described. AlCl₃, CO₂ and NH₃ were employed as the reactive gases in a nitrogen carrier. Films were grown from the mixed gases at 770 and 900°C in a resistively heated fused silica enclosure. The composition of the films could be varied over the entire range of the pseudobinary AlN-Al₂O₃ system by controlling the NH₃/CO₂ gas ratio with an appropriate flow of gaseous AlCl₃. Growth rate and index of refraction for the films were obtained using ellipsometric techniques. The film compositions reported were determined by electron microprobe analysis. Film structure, evaluated using transmission electron microscopy, and the electrical properties of the dielectric films have been correlated and are discussed separately in a companion paper entitled, “Some Properties of CVD Films of Al_xO_yN_z on Silicon”.     

Impact of the Cu-based substrates and catalyst deposition techniques on carbon nanotube growth at low temperature by PECVD

This article reports on carbon nanotubes (CNT) grown on TiN/Cu stacks by plasma enhanced chemical vapor deposition (PECVD) at 450 °C. Ni catalyst was deposited by two techniques - physical vapor deposition (PVD) and electrochemical deposition (ECD). First, the influence of the catalyst thickness and the catalyst deposition technique on grown CNTs is investigated. Second, the enhancement of the CNTs growth by use of electrodeposited catalysts is emphasized.     

Iron–Nitrogen‐Doped Vertically Aligned Carbon Nanotube Electrocatalyst for the Oxygen Reduction Reaction

A highly active iron–nitrogen‐doped carbon nanotube catalyst for the oxygen reduction reaction (ORR) is produced by employing vertically aligned carbon nanotubes (VA‐CNT) with a high specific surface area and iron(II) phthalocyanine (FePc) molecules. Pyrolyzing the composite easily transforms the adsorbed FePc molecules into a large number of iron coordinated nitrogen functionalized nanographene (Fe–N–C) structures, which serve as ORR active sites on the individual VA‐CNT surfaces. The catalyst exhibits a high ORR activity, with onset and half‐wave potentials of 0.97 and 0.79 V, respectively, versus reversible hydrogen electrode, a high selectivity of above 3.92 electron transfer number, and a high electrochemical durability, with a 17 mV negative shift of E _1/2 after 10 000 cycles in an oxygen‐saturated 0.5 m H₂SO₄ solution. The catalyst demonstrates one of the highest ORR performances in previously reported any‐nanotube‐based catalysts in acid media. The excellent ORR performance can be attributed to the formation of a greater number of catalytically active Fe–N–C centers and their dense immobilization on individual tubes, in addition to more efficient mass transport due to the mesoporous nature of the VA‐CNTs.     

碳纳米管薄膜制备及其光电探测应用进展

光电探测器在遥感、夜视、侦察、医学成像、环境保护和化学检测等方面的应用十分广泛,而光电探测材料的结构与性能直接影响着光电探测器的性能.近年来碳纳米管由其所具有的独特光学和电学性能迅速成长为光电探测中不可或缺的材料.虽然前期研究主要集中在基于单根碳纳米管的光电响应机理研究,但由于未来应用场景中必然是以碳纳米管薄膜为基础的...     

钯膜上CVD法制备碳纳米管薄膜的研究

采用化学气相沉积法,以乙炔为碳源,在各种钯膜上制备了碳纳米管薄膜。通过电子显微镜观察了碳管薄膜和钯膜的表面形貌。结果表明,在真空气氛下磁控溅射的钯膜上无法生长碳纳米管。对溅射的钯膜进行大气气氛下的退火处理,则可生长出稀疏的碳纳米管团聚颗粒。采用在氧气气氛下磁控溅射的钯膜作为催化剂,则可显著提高碳管的生长密度和纯度,从而获得致密均匀的碳纳米管薄膜。     

Epitaxial garnet films by organometallic chemical vapor deposition

Epitaxial films of Y₃Fe₅O₁₂, Eu₃Fe₅O₁₂, (Eu, Y)₃Fe₅O₁₂, and Er₃Fe₅O₁₂ l-2μm thick have been chemically vapor deposited on <111> GGG and <100> SmGG garnet substrates from 1000°C to 1200°C in an oxygen atmosphere from metal organic source compounds. These source compounds which are used here for the first time in chemical vapor deposition are tris 2, 2, 6, 6, tetramethyl 3, 5 heptanedionate complexes, (thd or M(thd)₃) of the metals used. In the reactor, the individual compounds are volatilized in a helium carrier in separate source containers. The vapors are then combined, and premixed without reaction at about 300°C with a large excess of 0₂ and passed with high velocity, ∿500 cm/sec, onto an r.f. heated substrate. The growth rate under these conditions is 0.4 - 0.8μm/hr. X-ray double diffraction, glancing angle X-ray and microprobe analyses were employed to characterize the crystallinity and stoichiometry, respectively, of the resulting garnet films. They were single crystal and exhibited a lattice constant dependent upon the rare earth to Fe ratio. The Eu containing films were not pseudomorphic probably due to the large lattice mismatch between substrate and film in most cases. The erbium iron garnet films were apparently close to pseudomorphic as determined by measured film and substrate lattice constants.     

分散定向碳纳米管阵列的制备及场发射性能

利用脉冲电化学沉积技术,以NiSO4·6H2O为电镀液在镀Cr硅基片上沉积低密度、直径在150nm左右的Ni催化剂颗粒,在此基础上,采用乙炔、氨气作为气源,采用等离子体增强化学气相沉积(PECVD)技术制备分散定向的碳纳米管阵列。研究了等离子体预处理技术对纳米管制备的影响以及该阵列的场发射性能,证明低密度的碳纳米管阵列阴极能有效地降低场屏蔽效应,进而提高场发射性能,其场发射的开启电场强度约为2.39V/μm。     

Effect of electrode material on transport and chemical sensing characteristics of metal/carbon nanotube contacts

In this paper, we report on the electrical transport characteristics and sensitivity to chemical exposure of single wall carbon nanotube devices fabricated on Pd, plasma-oxidized Pd, and Au electrodes. When the devices are exposed to vapors from ammonia, ethanol, and water, the response of current to each chemical is unique. However, there is essentially no difference in response between devices with different electrode materials. This finding suggests that for the chemical species tested in this study, the main interaction is on the nanotube or nanotube junction, and not on the effect stemming from electrode adsorption and the change in electrode work function.     

Characterization of developing source/drain current of carbon nanotube field-effect transistors with n-doping by polyethylene imine

An unsteady source/drain current induced by the source/drain bias of the n-type carbon nanotube field-effect transistors (n-CNTFETs), based on networked SWNTs, is reported. This current might affect the usual source/drain current regulated by the specified gate voltage and even overweighs the devices’ n-type characteristics. Through doping with polyethylene imine (PEI), the n-type devices here are made from the p-CNTFETs that were fabricated by printing interconnected CNTs between electrodes using the newly proposed laser transfer printing technique. To properly preserve the n-characteristics, devices with the PEI thickness less than 40 nm and with operating source/drain voltage below 0.5 V are recommended.     

Copper chemical vapor deposition from Cu(hexafluoroacetylacetonate)trimethylvinylsilane

Copper chemical vapor deposition using Cu-hexafluoroacetylacetonate (hfac) trimethylvinylsilane (TMVS) as precursor was performed in a cold-wall low pressure chemical vapor deposition (CVD) reactor. The design and operation of the reactor are described. Copper deposition on thermal SiO₂, W, and CoSi₂ substrate surfaces was investigated over the temperature range of 160–300°C and pressure range of 10–1000 mTorr. The activation energies of Cu CVD were determined to be 13.33 and 11.54 kcal/mole for the W and CoSi₂ substrates, respectively. The dependence of film resistivity, grain size, and growth rate on deposition pressure and temperature were also investigated. The film uniformity was found to be better than ten percent over a 4-inch diameter substrate. Experimental results also show that selective deposition can be achieved at a pressure of 10 mTorr within the temperature range of 160–200°C. In addition, hydrofluoric acid dipping was found to modify the SiO₂ surface and influence the copper deposition on it.     

Growth of high-quality 1.93-eV AIGaAs using metalorganic chemical vapor deposition

High-quality Al_xGa_1-xAs with a bandgap of 1.93 eV has been grown using metalorganic chemical vapor deposition (MOCVD). Levels exceeding 10₁₈ cm_-3 can be obtained for Se, Si and Zn dopants. In particular, incorporation of the re-type dopants at this bandgap is not appreciably less efficient than in lower-bandgap Al_xGa_1-xAs. The best material, as measured by photoluminescence intensity, is obtained using high V/III ratios (40 forp-type material and as high as 60 forn- type and low growth rates (300 Å/min). Purification of the arsine in situ with an Al/Ga/In eutectic bubbler to remove trace water and oxygen impurities is found to be essential for the growth of high-quality material, as indicated by photoluminescence intensity measurements. Solar cells fabricated from such material exhibit efficiencies as high as 12.1% under one-sun, airmass zero (AMO) conditions, with an open-circuit voltage of 1.38 V, short-circuit current density of 14.1 mA/cm², and fill factor of 0.84.     

Photoluminescence studies on InGaAlP layers grown by low-pressure metalorganic chemical vapor deposition

The optical properties for In_0.5(Ga_1-x Al _x )_0.5P (0 <x < 0.4) layers, grown by low-pressure Metalorganic Chemical Vapor Deposition, have been studied with photolominescence (PL) measurement. The PL intensity decreases with the increase of the Al composition (0 <x < 0.4). This dependence could not be accounted for only by the electron overflow from theΓ band to the X band. And the PL intensity is directly proportional to the excitation power at low temperature, below 50 K. On the other hand, the PL intensity is proportional to the second power of the excitation power at a high temperature range (>200 K). These results indicate that non-radiative recombination centers bound to theΓ band in In_0.5(Ga_1-x Al _x )_0.5P play a very important role in the radiation mechanism. PL dependence also shows these non-radiative recombination centers are thought to have strong relation to the aluminum substitution for In_0.5(Ga_1-x Al _x )_0.5P.     

Si衬底上无坑洞3C-SiC的外延生长研究

在冷壁式不锈钢超高真空系统上 ,利用低压化学气相淀积 (LPCVD)方法在直径为 5 0 mm的单晶 Si(1 0 0 )和 Si(1 1 1 )晶向衬底上生长出了高取向无坑洞的晶态立方相碳化硅 (3 C-Si C)外延材料 ,利用反射高能电子衍射 (RHEED)和扫描电镜 (SEM)技术详细研究了 Si衬底的碳化过程、碳化层的表面形貌及缺陷结构 ,获得了界面平整光滑、没有空洞形成的 3 C-Si C外延材料 ,并采用 X-射线衍射 (XRD)、双晶 X-射线衍射 (DXRD)和霍尔(Hall)测试等技术研究了外延材料的结构和电学特性     

Metalorganic chemical vapor deposition of HgCdTe for photodiode applications

Metalorganic chemical vapor depositon (MOCVD) in situ growth of p-on-n junctions for long wavelength infrared (LWIR) and medium wavelength infrared (MWIR) photodiodes is reported. The interdiffused multilayer process was used for the growth of the HgCdTe junctions on CdTe and CdZnTe substrates. The n-type region was grown undoped while the p-type layer was arsenic doped using tertiarybutylarsine. Following a low temperature anneal in Hg vapor, carrier densities of (0.2-2) x 10¹⁵ cm³ and mobilities of (0.7-1.2) x 10⁵ cm²/V-s were obtained for n-type LWIR (x ~ 0.22) layers at 80K. Carrier lifetimes of these layers at 80 K are ~l-2 μs. For the p-type region arsenic doping was controlled in the range of (1-20) x 10¹⁶ cm^-3. Arsenic doping levels in the junctions were determined by calibrated secondary ion mass spectroscopy depth profile measurements. Composition and doping of the p-on-n heterojunctions could be independently controlled so that the electrical junction could be located deeper than the change in the composition. The graded composition region between the narrow and wide (x = 0.28-0.30) bandgap regions are 1–2 μm depending on the growth temperature. Backside-illuminated variable-area circular mesa photodiode arrays were fabricated on the grown junctions as well as on ion implanted n-on-p MWIR junctions. The spectral responses are classical in shape. Quantum efficiencies at 80K are 42–77% for devices without anti-reflection coating and with cutoff wavelengths of 4.8–11.0 μm. Quantum efficiencies are independent of reverse bias voltage and do not decrease strongly at lower temperatures indicating that valence band barrier effects are not present. 80K R_oA of 15.9 Ω-cm² was obtained for an array with 11.0 μm cutoff. Detailed measurements of the characteristics of the MOCVD in situ grown and implanted photodiodes are reported.     

影响碳纳米管生长与结构的参数研究

采用负偏压增强热丝化学气相沉积(CVD)方法，在沉积有NiFe催化剂层及Ta或Ti过渡层的Si衬底上，通过改变沉积条件制备出不同结构的碳纳米管。扫描电子显微镜的研究结果表明，当过渡层为Ta时，碳纳米管的生长速度比Ti过渡层的大；在沉积过程中，有或无辉光放电时，生长出的碳纳米管分别是定向和弯曲的；同时还观察到随着反应气体中NH3浓度的加大，碳纳米管的生长速度会随之增大。     

激光CVD纳米氮化硅的制备工艺研究

研究了激光诱导化学气相沉积纳米氮化硅的制备工艺过程，探讨了制备工艺参数与粉末特征的关系，获得较佳的工艺参数：激光功率密度２０００Ｗ／ｃｍ２，反应气体配比ΦＮＨ３／ΦＳＨ４＝４，反应气体总流量２００ｃｍ３／ｓ，反应池压力３５ｋＰａ。     

Selective silicon epitaxy by photo-chemical vapor deposition at a very low temperature of 160°C

We have grown epitaxial Si films by the photo-chemical vapor deposition (photo-CVD) technique with SiH₄ and H₂ at a very low-temperature of 160°C. Epitaxial films were grown on silicon substrates, while amorphous-like films were deposited on glass substrates. Furthermore, it was found from the atomic hydrogen etching which was produced by photo-dissociation of hydrogen that the etching rate of amorphous silicon was much higher than that of crystal silicon. By using these selectively, we have demonstrated selective epitaxial growth of silicon by the photo-CVD technique followed by the atomic hydrogen photo-etching. Furthermore, heavily phosphorus-doped silicon films (>1 × 10²¹ cm¹⁻³) were also selectively grown by this novel technique.