Download or read book Chemical vapour deposition of boron carbon thin films from organoboron precursors written by Maiwulidan (Mewlude) Yimamu (Imam) and published by Linköping University Electronic Press. This book was released on 2016-01-13 with total page 29 pages. Available in PDF, EPUB and Kindle. Book excerpt: Boron-carbon (BxC) thin films enriched in 10B are potential neutron converting layers for 10Bbased solid-state neutron detectors given the good neutron absorption cross-section of 10B atoms in the thin film. Chemical Vapour Deposition (CVD) of such films faces the challenge that the maximum temperature tolerated by the aluminium substrate is 660 °C and low temperature CVD routes for BxC films are thus needed. This thesis presents the use of two different organoboron precursors, triethylboron –B(C2H5)3 (TEB) and trimethylboron – B(CH3)3 (TMB) as single-source precursors for CVD of BxC thin films. The CVD behaviour of TEB in thermal CVD has been studied by both BxC thin film deposition and quantum chemical calculations of the gas phase chemistry at the corresponding CVD conditions. The calculations predict that the gas phase reactions are dominated by ?-hydride eliminations of C2H4 to yield BH3. In addition, a complementary bimolecular reaction path based on H2-assisted C2H6 elimination to BH3 is also present at lower temperatures in the presence of hydrogen molecules. A temperature window of 600 – 1000 °C for deposition of X-ray amorphous BxC films with 2.5 ? x ? 4.5 is identified showing good film density (2.40 – 2.65 g/cm3) which is close to the bulk density of crystalline B4C, 2.52 g/cm3 and high hardness (29 – 39 GPa). The impurity level of H is lowered to < 1 at. % within the temperature window. Plasma chemical vapour deposition has been studied using TMB as single-source precursor in Ar plasma for investigating BxC thin film deposition at lower temperature than allowed by thermal CVD and further understanding of thin film deposition process. The effect of plasma power, total pressure, TMB and Ar gas flow on film composition and morphology are investigated. The highest B/C ratio of 1.9 is obtained at highest plasma power of 2400 W and TMB flow of 7 sccm. The H content in the films seems constant at 15±5 at. %. The B-C bond is dominant in the films with small amount of C-C and B-O bonds, which are likely due to the formation of amorphous carbon and surface oxidation, respectively. The film density is determined as 2.16±0.01 g/cm3 and the internal compressive stresses are measured to be <400 MPa.

Download or read book Chemical Vapour Deposition of sp2 Hybridised Boron Nitride written by Mikhail Chubarov and published by Linköping University Electronic Press. This book was released on 2014-12-04 with total page 54 pages. Available in PDF, EPUB and Kindle. Book excerpt: The aim of this work was to develop a chemical vapour deposition process and understand the growth of sp2 hybridised Boron Nitride (sp2-BN). Thus, the growth on different substrates together with the variation of growth parameters was investigated in details and is presented in the papers included in this thesis. Deposited films of sp2-BN were characterised with the purpose to determine optimal deposition process parameters for the growth of high crystal quality thin films with further investigations of chemical composition, morphology and other properties important for the implementation of this material towards electronic, optoelectronic devices and devices based on graphene/BN heterostructures. For the growth of sp2-BN triethyl boron and ammonia were employed as B and N precursors, respectively. Pure H2 as carrier gas is found to be necessary for the growth of crystalline sp2-BN. Addition of small amount of silane to the gas mixture improves the crystalline quality of the growing sp2-BN film. It was observed that for the growth of crystalline sp2-BN on c-axis oriented ?-Al2O3 a thin and strained AlN buffer layer is needed to support epitaxial growth of sp2-BN, while it was possible to deposit rhombohedral BN (r-BN) on various polytypes of SiC without the need for a buffer layer. The growth temperature suitable for the growth of crystalline sp2-BN is 1500 °C. Nevertheless, the growth of crystalline sp2-BN was also observed on ?-Al2O3 with an AlN buffer layer at a lower temperature of 1200 °C. Growth at this low temperature was found to be hardly controllable due to the low amount of Si that is necessary at this temperature and its accumulation in the reaction cell. When SiC was used as a substrate at the growth temperature of 1200 °C, no crystalline sp2-BN was formed, according to X-ray diffraction. Crystalline structure investigations of the deposited films showed formation of twinned r-BN on both substrates used. Additionally, it was found that the growth on ?-Al2O3 with an AlN buffer layer starts with the formation of hexagonal BN (h-BN) for a thickness of around 4 nm. The formation of h-BN was observed at growth temperatures of 1200 °C and 1500 °C on ?-Al2O3 with AlN buffer layer while there were no traces of h-BN found in the films deposited on SiC substrates in the temperature range between 1200 °C and 1700 °C. As an explanation for such growth behaviour, reproduction of the substrate crystal stacking is suggested. Nucleation and growth mechanism are investigated and presented in the papers included in this thesis.

Download or read book Chemical Vapor Deposition of Heteroepitaxial Boron Phosphide Thin Films written by John Daniel Brasfield and published by . This book was released on 2013 with total page 229 pages. Available in PDF, EPUB and Kindle. Book excerpt: Boron monophosphide (BP) is a group III-V compound semiconductor with a wide band gap of 2.3 eV. Its unique electrical properties make it a promising material for use as a room temperature thermal neutron detector and thermoelectric device in high temperature and radiation fields. A thin film of BP enriched in the boron-10 isotope can yield 2.8MeV of energy, which in solid-state BP can yield ∼0.5 million electron-hole pairs that would be detectable with minimal amplification in a device. The high carrier concentration, wide band gap, inertness and refractory nature make it an attractive material for use in the extreme environments of nuclear reactors. The main drawback to BP is the difficulty in synthesizing high quality thin films. The majority of the previous work on BP was performed on Si substrates. The high lattice mismatch between Si and BP incorporates strain in the BP film which causes varying defects and charge traps to be introduced, adversely affecting electrical performance. It is the purpose of this work to identify the parameters necessary to deposit highly ordered zincblende boron phosphide (BP) thin films on 4° off-axis C-face 4H-SiC(0001) substrates by chemical vapor deposition. SiC only has a 4% lattice mismatch from BP, which could greatly reduce the inherent strain from heteroepitaxial growth. Ultra high purity diborane and phosphineare used as reactive precursors, with hydrogen as the carrier gas. Conditions necessary for high quality BP thin films will be explored. SEM, XRD, TEM and Raman spectroscopy are used to characterize the BP films and identify the temperature, phosphine to diborane flow rate ratios, SiC wafer termination and wafer surface preparation to elucidate optimum BP thin films for eventual device fabrication.

Download or read book On the Synthesis and Chemical Vapour Deposition of Group 13 Precursors Towards Metal Oxide Thin Films written by L. G. Bloor and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Various routes towards novel chlorogallium bis(alkoxides) and heteroleptic gallium alkoxides have been investigated. Compounds of the type, [GaCl(OR2)2] and [Ga(OR2)2(OR')] (R = CH2CH2NMe2, CH2CH2NEt2, CH2CH2CH2NMe2; R' = Me, Et, iPr, tBu), were synthesised using air sensitive methods and analysed by a variety of techniques. The chlorogallium bis(alkoxides) showed diastereotopic NMR splitting and in depth 1H NMR studies and DFT calculations were carried out on [GaCl(OCH2CH2CH2NMe2)2] to investigate the in situ ring conversion mechanism. Thermogravimetric analysis was employed to study the decomposition characteristics of the compounds, which were then used as single-source precursors towards gallium oxide thin films using aerosol-assisted chemical vapour deposition (AACVD). Amorphous, transparent films of Ga2O3 were deposited at 450 °C onto glass and quartz substrates. Subsequent annealing at 1000 °C gave crystalline films. Nitrogen-doped indium oxide films were deposited by AACVD via the in situ reaction of [In{NtBu(SiMe3)}3] and three equivalents of HOCH2CH2NMe2. The resultant films had a range of morphologies depending on solvent and temperature employed during the deposition. The cubic phase In2O3 films deposited had band gaps of ~2.9 eV suggesting nitrogen incorporation. These films were tested on steel and titanium substrates for their visible light water-splitting properties. Films were tested for their hydrogen production but limited activity as a photocatalyst was observed in the visible region. However, In2O3 nanoparticles produced using a solvothermal method and Ti- and Ta-doped In2O3 thin films grown via AACVD were tested for their gas sensing properties. Sensors were tested against reducing oxidising gases. The In2O3 nanoparticles showed the highest response to all gases, in particular ethanol. In2O3:Ta also showed a significant response to ethanol and smaller responses to other gases. Overall, novel precursors have been used as single-source precursors to main group oxide thin films, which were deposited via AACVD. Photocatalytic and gas sensing applications of these films have been explored.

Download or read book Investigation of Reactively Sputtered Boron Carbon Nitride Thin Films written by Vinit O. Todi and published by . This book was released on 2011 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt: Research efforts have been focused in the development of hard and wear resistant coatings over the last few decades. These protective coatings find applications in the industry such as cutting tools, automobile and machine part etc. Various ceramic thin films like TiN, TiAlN, TiC, SiC and diamond-like carbon (DLC) are examples of the films used in above applications. However, increasing technological and industrial demands request thin films with more complicated and advanced properties. For this purpose, B-C-N ternary system which is based on carbon, boron and nitrogen which exhibit exceptional properties and attract much attention from mechanical, optical and electronic perspectives. Also, boron carbonitride (BCN) thin films contains interesting phases such as diamond, cubic BN (c-BN), hexagonal boron nitride (h-BN), B4C, [greek lower case letter beta]-C3N4. Attempts have been made to form a material with semiconducting properties between the semi metallic graphite and the insulating h-BN, or to combine the cubic phases of diamond and c-BN (BC2N heterodiamond) in order to merge the higher hardness of the diamond with the advantages of c-BN, in particular with its better chemical resistance to iron and oxygen at elevated temperatures. New microprocessor CMOS technologies require interlayer dielectric materials with lower dielectric constant than those used in current technologies to meet RC delay goals and to minimize cross-talk. Silicon oxide or fluorinated silicon oxide (SiOF) materials having dielectric constant in the range of 3.6 to 4 have been used for many technology nodes. In order to meet the aggressive RC delay goals, new technologies require dielectric materials with K[less than]3. BCN shows promise as a low dielectric constant material with good mechanical strength suitable to be used in newer CMOS technologies. For optical applications, the deposition of BCN coatings on polymers is a promising method for protecting the polymer surface against wear and scratching. BCN films have high optical transparency and thus can be used as mask substrates for X-ray lithography. Most of the efforts from different researchers were focused to deposit cubic boron nitride and boron carbide films. Several methods of preparing boron carbon nitride films have been reported, such as chemical vapor deposition (CVD), plasma assisted CVD, pulsed laser ablation and ion beam deposition. Very limited studies could be found focusing on the effect of nitrogen incorporation into boron carbide structure by sputtering. In this work, the deposition and characterization of amorphous thin films of boron carbon nitride (BCN) is reported. The BCN thin films were deposited by radio frequency (rf) magnetron sputtering system. The BCN films were deposited by sputtering from a high purity B4C target with the incorporation of nitrogen gas in the sputtering ambient. Films of different compositions were deposited by varying the ratios of argon and nitrogen gas in the sputtering ambient. Investigation of the oxidation kinetics of these materials was performed to study high temperature compatibility of the material. Surface characterization of the deposited films was performed using X-ray photoelectron spectroscopy and optical profilometry. Studies reveal that the chemical state of the films is highly sensitive to nitrogen flow ratios during sputtering. Surface analysis shows that smooth and uniform BCN films can be produced using this technique. Carbon and nitrogen content in the films seem to be sensitive to annealing temperatures. However depth profile studies reveal certain stoichiometric compositions to be stable after high temperature anneal up to 700°C. Electrical and optical characteristics are also investigated with interesting results. The optical band gap of the films ranged from 2.0 eV - 3.1 eV and increased with N2/Ar gas flow ratio except at the highest ratio. The optical band gap showed an increasing trend when annealed at higher temperatures. The effect of deposition temperature on the optical and chemical compositions of the BCN films was also studied. The band gap increased with the deposition temperature and the films deposited at 500°C had the highest band gap. Dielectric constant was calculated from the Capacitance-Voltage curves obtained for the MOS structures with BCN as the insulating material. Aluminum was used as the top electrode and the substrate was p-type Si. Effect of N2/Ar gas flow ratio and annealing on the values of dielectric constant was studied and the dielectric constant of 2.5 was obtained for the annealed BCN films. This by far is the lowest value of dielectric constant reported for BCN film deposited by sputtering. Lastly, the future research work on the BCN films that will be carried out as a part of the dissertation is proposed.

Download or read book Silicon Carbide written by Moumita Mukherjee and published by BoD – Books on Demand. This book was released on 2011-10-10 with total page 562 pages. Available in PDF, EPUB and Kindle. Book excerpt: Silicon Carbide (SiC) and its polytypes, used primarily for grinding and high temperature ceramics, have been a part of human civilization for a long time. The inherent ability of SiC devices to operate with higher efficiency and lower environmental footprint than silicon-based devices at high temperatures and under high voltages pushes SiC on the verge of becoming the material of choice for high power electronics and optoelectronics. What is more important, SiC is emerging to become a template for graphene fabrication, and a material for the next generation of sub-32nm semiconductor devices. It is thus increasingly clear that SiC electronic systems will dominate the new energy and transport technologies of the 21st century. In 21 chapters of the book, special emphasis has been placed on the materials aspects and developments thereof. To that end, about 70% of the book addresses the theory, crystal growth, defects, surface and interface properties, characterization, and processing issues pertaining to SiC. The remaining 30% of the book covers the electronic device aspects of this material. Overall, this book will be valuable as a reference for SiC researchers for a few years to come. This book prestigiously covers our current understanding of SiC as a semiconductor material in electronics. The primary target for the book includes students, researchers, material and chemical engineers, semiconductor manufacturers and professionals who are interested in silicon carbide and its continuing progression.

Download or read book Informe dado por la polic a ind gena sobre el primer proyecto de protectorado civil 1919 written by and published by . This book was released on 1919 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Low Pressure Chemical Vapor Deposition of Boron Nitride Thin Films from Triethylamine Borane Complex and Ammonia written by Narahari Ramanuja and published by . This book was released on 1998 with total page 178 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Ultrahigh Vacuum Metalorganic Chemical Vapor Deposition and in Situ Characterization of Nanoscale Titanium Dioxide Films written by Polly Wanda Chu and published by . This book was released on 1994 with total page 434 pages. Available in PDF, EPUB and Kindle. Book excerpt: Thin titanium dioxide films were produced by metalorganic chemical vapor deposition on sapphire(0001) in an ultrahigh vacuum (UHV) chamber. A method was developed for producing controlled submonolayer depositions from titanium isopropoxide precursor. Film thickness ranged from 0.1 to 2.7 nm. In situ X-ray photoelectron spectroscopy (XPS) was used to determine film stoichiometry with increasing thickness. The effect of isothermal annealing on desorption was evaluated. Photoelectron peak shapes and positions from the initial monolayers were analyzed for evidence of interface reaction. Deposition from titanium isopropoxide is divided into two regimes: depositions below and above the pyrolysis temperature. This temperature was determined to be 300 deg C. Controlled submonolayers of titanium oxide were produced by cycles of dosing with titanium isopropoxide vapor below and annealing above 300 deg C. Precursor adsorption below the pyrolysis temperature was observed to saturate after 15 minutes of dosing. The quantity absorbed was shown to have an upper limit of one monolayer. The stoichiometry of thin films grown by the cycling method were determined to be TiO2. Titanium dioxide film stoichiometry was unaffected by isothermal annealing at 700 deg C. Annealing produced a decrease in film thickness. This was explained as due to desorption. Desorption ceased at approximately 2.5 to 3 monolayers, suggesting bonding of the initial monolayers of film to sapphire is stronger than to itself. Evidence of sapphire reduction at the interface by the depositions was not observed. The XPS O is peak shifted with increased film thickness. The shifts were consistent with oxygen in sapphire and titanium dioxide having different O is photoelectron peak positions. Simulations showed the total shifts for thin films ranging in thickness of 0.1 to 2.7 nm to be -0.99 to -1.23 eV. Thick films were produced for comparison.

Download or read book Synthesis of One dimensional Boron Related Nanostructures by Chemical Vapor Deposition written by Li Guo and published by . This book was released on 2008 with total page 147 pages. Available in PDF, EPUB and Kindle. Book excerpt: Motivated by the extensive research on carbon nanotubes (CNTs), boron and its related nano-structures have attracted increasing interest for potential applications in nanodevices and nanotechnologies, due to their extraordinary properties. In this work, different types of B-related nanostructures were successfully grown on oxidized Si substrates with or without transition metal catalysts in CVD processes. The gas chemistry was monitored by in-situ mass-spectroscopy and optical emission spectroscopy. These helped to identify the gas reactive species during the deposition, creating thereby a controllable, optimum synthesis process and helping in identifying the growth mechanism. The boron nitride nanotubes (BNNTs) were successfully synthesized at the low substrate temperatures of 600-800oC by a microwave plasma CVD process, using diborane and ammonia as the gas precursors. The optimum growth conditions of BNNTs were investigated by varying the experimental parameters, such as catalyst film thickness, substrate temperature, diborane flow rate, and growth time. The dense and crystalline BNNT deposits were obtained on 1nm nickel (Ni) or cobalt (Co) thin film coated oxidized Si (111) at a temperature of 800oC, a pressure of 15 torr, microwave power of 800 W, diborane flow rate (5 vol.% in hydrogen) of 5 sccm, ammonia flow rate of 27.5 sccm, hydrogen flow rate of 10sccm, and a deposition time of 1 hour. These nanotubes were either self-assembled in bundles or as a single tube with a diameter less than 10 nm. Raman spectra together with electron diffraction pattern indicated a hexagonal crystalline structure for these BN nanostructures. A growth mechanism of BNNTs involving dissolution-supersaturation- precipitation of BN in the metal catalysts was proposed. It was shown that the growth of BN nanostructures strongly depended on the catalyst and its film thickness, which resulted in the selective growth of BNNTs on the patterned catalyst islands. Ni dots with the diameters in the submicron range were used to synthesize aligned BNNTs. Fine BN nanostructures with a diameter around 10-20 nm and length up to 10 microns were grown and dispersed in the Ni dots. Nanosized Ni dots were suggested for the growth of the vertically aligned BNNTs. Boron nanowires (BNWs) were also grown by the decomposition of diborane using a thermal CVD process at a temperature of 900oC, a pressure of 20 torr, diborane flow rate (5 vol.% in hydrogen) of 5 sccm, and nitrogen flow rate of 55 sccm. These BNWs had diameters in a range of 20-200 nanometers and lengths up to several tens of micrometers. Repeatable Raman spectra indicated icosahedra B12 to be the basic building units forming the B nanowires. Amorphous BNWs with rough surface were obtained without any catalysts on different substrates, such as Si wafer or ZrB2 powders. A vapor-solid (VS) growth was proposed for the amorphous BNWs, in which the solid phase precipitated directly from the vapor phase reactions. The amorphous BNWs were modified for size and composition using a plasma CVD process containing argon, ammonia and hydrogen. The diameters of these BNWs were reduced from 200 nm to several tens of nanometers, and a small amount of N was incorporated into BNWs after the plasma treatment. On the other hand, the metal catalyst proved to be effective for the growth of crystalline BNWs. Tetragonal BNWs with smooth surface were grown on thin Ni film (1 nm) coated Si substrates. Ni attachment was observed at the tip of the BNW for the first time, which indicated that the vapor-liquid-solid (VLS) growth mechanism can be used for synthesis of the BNW. The diameters of these BNWs were strongly dependent on the size of the metal particles encapsulated in the BNWs. In summary, two boron-related nanostructures were synthesized by chemical vapor deposition (CVD) in this work. A new method was successfully developed to decrease the substrate temperature more than 400oC to fabricate boron nitride nanotubes in a microwave plasma enhanced chemical vapor deposition process using gas reactions of diborane and ammonia. The catalytic growth of BNNTs done in this work provided a novel way to selectively grow BNNTs in thin film form on Ni or Co coated Si substrates. For boron nanowires, the co-existence of two growth mechanisms was discovered having completely different morphology and crystallinity using the thermal CVD process. The metal catalyst assisted the growth of the crystalline BNWs by vapor-liquid-solid mechanism, which amorphous BNWs were produced without the use of the catalyst. These results are expected to open up more pathways to scale up the fabrication of vertically aligned BNNTs and BNWs for studies of their properties and applications.

Download or read book Ion assisted Chemical Vapor Deposition of Thin Film Cubic Boron Nitride written by Darren Herman Berns and published by . This book was released on 1998 with total page 173 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Deposition of Cubic Boron Nitride Thin Films by Supersonic D C Plasma enhanced Chemical Vapor Deposition written by Eric Runde and published by . This book was released on 2004 with total page 122 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Bulk and Interfacial Electronic and Chemical Structure of Amorphous Hydrogenated Boron Carbide written by Marcus Sky Driver and published by . This book was released on 2013 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt: The chemical and electronic structure, as related to the surface, interface and bulk of amorphous hydrogenated boron carbide (a-BxC:Hy), is of interest in neutron detection and microelectronics. This dissertation investigates the chemical and electronic structure of semiconducting thin-film a-BxC:Hy grown by plasma enhanced chemical vapor deposition (PECVD) of ortho-carborane (1,2-C2B10H12). Experimental methods used include: x-ray and ultraviolet photoelectron spectroscopies (XPS/UPS) and x-ray absorption/emission spectroscopies (XAS/XES). These methods were used to investigate the chemical species, bonding and hybridizations, and band gaps of a-BxC:Hy prepared or treated under varying conditions. Additionally, a detailed examination of the formation of Schottky barriers was implemented. Throughout this dissertation the chemical structure was studied. One study was to understand various growth conditions. The effects of the PECVD growth parameters were evaluated by comparing changes in atomic percentages (at.%'s) between thin-films from various substrate temperatures. Additionally, detailed studies of the photoelectron core level under two different growth conditions were undertaken to evaluate the effects of pre-/post- argon ion etching (Ar+) for the following: the chemical structural change for both an as grown (AG) and in-situ thermal treatment (500°C), and post Ar+ etch of samples thermally treated ranging from as grown to 850°C. The as grown and in-situ treated samples were used in conjunction to determine the formation of the Schottky barrier. The electronic structure was determined by the changes within the valence band of the thermally treated samples and formation of Schottky barrier. Thermally treated samples (as grown to 850°C) were further evaluated with respect to their occupied and unoccupied electronic states. The atomic percentage gave a stoichiometry range for a-BxC:Hy (given as x=1.5 to 3.0 with y= decreases with thermal treatment and Oz: z= 0.2 to 0.5). Studies of films with respect to thermal treatment reveal two discrete state changes that occur at 400°C and 850°C. These changes are due to segregation of carbon and oxygen by the reorganization of the hydrocarbon chains between icosahedra. Additionally, the Schottky barrier study indicates that a clean surface was necessary before deposition of an ohmic contact and from the metals studied. Such studies are important to applications for high temperature thermoelectric converters, high-efficiency direct-conversion solid-state neutron detectors and microelectronics.

Download or read book Metallo organic Low pressure Chemical Vapor Deposition of Ta sub 2 sub O sub 5 sub Using TaC sub 12 sub H sub 30 sub O sub 5 sub N as Precursor for Batch Fabrication of Microsystems written by and published by . This book was released on with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Ta2O5 thin films were produced by metallo-organic low pressure chemical vapor deposition using Tantalum(V) Tetraethoxydimethylaminoethoxide (TaC12H30O5N) as precursor. This liquid precursor at room temperature makes it possible to deposit thin films of Ta2O5 on wafer batches of up to 35 wafers. In this communication, we report on the processing and equipment development to achieve batch fabrication, and on the optimization of the deposited thin films properties for their application in microsystems. An evaporator was linked to a horizontal hot wall furnace. The deposition of Ta2O5 was performed at 425 °C and the influence of a post-annealing at higher temperatures on the chemical, electrical and optical properties of the films was evaluated. Annealing treatments in oxygen were found to reduce the amount of residual carbon and hydrogen in the films. An annealing in oxygen followed by an annealing in forming gas was used to improve the charge levels and hysteresis. The optical properties of the amorphous Ta2O5 films varied slightly with the annealing treatment. Annealing the films at a temperature of 700 °C and higher caused their crystallization, leading to a decrease of their optical bandgap. The processed films have found applications in microsystems as chemical resistant coatings, optical coatings for wave guides, and chemical sensitive layers for Ion-Sensitive Field-Effect Transistors.

Download or read book Semiconducting Aromatic Boron Carbide Films for Neutron Detection and Photovoltaic Applications written by Adeola O. Oyelade and published by . This book was released on 2019 with total page 102 pages. Available in PDF, EPUB and Kindle. Book excerpt: Semiconducting aromatic-boron carbide composite/alloyed films formed by plasma enhanced chemical vapor deposition from carborane and aromatic precursors have been demonstrated to be excellent detectors for thermal neutrons because of the large 10B cross section. The electronic properties of these films derived from XPS show that the properties of boron carbide can be tuned by co-deposition of aromatic compounds and carborane. Aromatic doping results in narrower indirect band gaps (1.1 - 1.7 eV vs ̃3 eV for orthocarborane-derived boron carbide without aromatics) and average charge transport lifetimes (as long as 2.5 ms for benzene-orthocarborane and 1.5 - 2.5 ms for indole-orthocarborane) that are superior to those of boron carbide (35 μs). The films also show enhanced electron-hole separation that is also superior to those of boron carbide where the states at the top of the valence band is made of aromatic components while states at the bottom of the conduction band is a combination of aromatic and carborane moeities. These properties result in greatly enhanced (̃850%) charge collection, relative to films without aromatic content, in thermal neutron exposures at zero-bias, and are gamma-blind. Such films are therefore excellent candidates for zero-bias neutron detector applications. These properties also show little variation with increasing aromatic content beyond a critical concentration, indicating that at some point, excess aromatic results in the formation of regions of polymerized aromatic within the film, rather than in additional carborane/aromatic linkages. While previous studies on these aromatic-boron carbide materials indicate the potential for neutron detection due to the narrowed band gap, enhanced electron-hole separation and charge transport lifetimes compared to the boron carbide counterpart, the mechanisms of charge transport and photoconductivity (important for photovoltaic applications) of these materials have remained unexplored. Properties such as narrowed band gap, efficient electron-hole separation and long charge transport lifetimes, are also desirable in photovoltaic applications. This, plus ease of fabrication and environmental robustness makes aromatic-boron carbide films promising candidates for photovoltaic applications. Plasma enhanced chemical vapor deposition (PECVD) has been used to synthesize these aromatic-boron carbide composite films by co-deposition of pyridine, aniline or indole with orthocarborane/metacarborane. Film chemical composition and bonding were characterized by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), variable angle spectroscopic ellipsometry (VASE) and (in collaboration with Dowben Group at UNL) charge transport and photoconductivity measurements. Results show narrowed band gaps (indirect) where the top of the valence band is made up of the aromatic moiety and the conduction band minimum us made of aromatic and carborane moeities, improved charge carrier mobilities that is stoichiometry and frequency dependent (aniline-orthocarborane films). Photoconductivity measurement results obtained from ̃2.6:1 indole-orthocarborane film show fourth quadrant conductivity. I(V) curves indicate a photocurrent of 2.36 μA at zero bias, with an appreciable open-circuit voltage of 1V. The ability for these aromatic-boron carbide films to operate at zero bias for both neutron detection and photovoltaic applications is an excellent advantage that indicates low cost of operation of these materials.

Download or read book Chemical Vapor Deposition Growth and Characterization of Two Dimensional Hexagonal Boron Nitride written by Roland Yingjie Tay and published by Springer Theses. This book was released on 2019-07-19 with total page 162 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Chemical Vapor Deposited Boron Doped Polycrystalline Diamond Thin Film Growth on Silicon and Sapphire Growth Doping Metallization and Characterization written by Hassan Golestanian and published by . This book was released on 1997 with total page 272 pages. Available in PDF, EPUB and Kindle. Book excerpt: Diamond's unique properties are potentially superior among the existing substrate materials for electronic applications. Among these properties, diamond's physical hardness, molar density, thermal conductivity, and sound velocity are the highest while its thermal expansion coefficient, compressibility, and bulk modules are the lowest. Because of this unique combination of properties, diamond has diverse applications in electronics, optics, and material coatings. Scientists around the world have been studying possible applications of diamond and its synthesis by chemical vapor deposition (CVD) in the semiconductor industry for almost the latter half of this century. The use of bulk crystals severely limits semiconductor applications of diamond due to difficulty in doping, device integration, high cost, and small area of bulk diamond. Therefore, a great deal of effort has been undertaken by researchers around the world on diamond synthesis by chemical vapor deposition (CVD). With some of the same limitations, homoepitaxial growth of diamond is not considered to be a feasible solution. As a result, heteroepitaxial growth of diamond is being considered to be an attractive possibility. Heteroepitaxial diamond growth has been the main subject of research since the first successful growth of diamond thin films on foreign substrates was reported. Polycrystalline and highly oriented diamond thin films grown on various substrates, especially silicon, have been reported over the years. There also have been reports of device fabrication on diamond such as diamond based point contact transistors, Schottky diodes, and field effect transistors at a laboratory level. The technology has been very challenging and there remain many obstacles to overcome before diamond based devices are to become part of the semiconductor industry. For example, epitaxial growth of CVD diamond, selective doping, n-type doping, and metallization of the grown films are not totally understood due to the polycrystalline nature of CVD diamond films. The objective of this work is the study of hot-filament chemical vapor deposited boron doped polycrystalline diamond thin films grown on both silicon and sapphire. A new horizontal gas flow configuration rather than the typical vertical gas flow configuration is utilized to provide larger area and better quality films grown on these substrates. The study includes characterization of grown films using scanning electron microscopy, Raman spectroscopy, X-ray diffraction analysis, and electrical characterization. Two types of contacts to the films grown on silicon substrates are fabricated enabling various electrical measurements. However, on sapphire substrates, low volume resistivity diamond films are grown despite severe adhesion problems. The effects of various substrate pre-treatments, growth conditions, and doping concentrations are presented.