Papers

ICMCTF2002 Session D3-1: Mechanical, Electrical, Optical and Thermal Properties and Applications of Boron Nitride, Carbon-based Films and Related Materials

Thursday, April 25, 2002 8:30 AM in Room Royal Palm Salon 1-3

Thursday Morning

Start	Invited?	Item
8:30 AM		D3-1-1 Carbon Nanotube Based Flat Panel Displays R.P.H. Chang (Northwestern University)
9:10 AM		D3-1-3 Field Emission from Well-aligned Carbon Nano-tips on Various Patterned Substrates C.-L. Tsai, C.-F. Chen (National Chiao-Tung University, Taiwan, ROC) Vertically well-aligned carbon nano-tips have been directly grown on patterned substrates using bias assisted microwave plasma chemical vapor deposition (BAMPCVD). The carbon nano-tips nucleate and grow from various catalysts on silicon substrate. By the means of scanning electron microscopy (SEM), it is found that the catalyst could dominate the morphology, growth rate, tip angle and the density of carbon nano-tips. In addition, the size and uniformity of the catalyst film also affect the growth of carbon nano-tips. By transmission electron microscopy (TEM) and optical emission spectroscopy (OES), the possible growth mechanism of carbon nano-tips are discussed. The measurement of field emission from the diode structure with the carbon nano-tips shows different results on various substrates. The difference maybe resulted from the shape, aspect ratio and the property of the carbon nano-tips. The further information will be presented at conference.
9:30 AM		D3-1-4 Increase of Ion-induced Electron Emission from CVD Undoped Submicron Diamond Films Sh. Michaelson, V. Richter, R. Kalish (Technion-Israel Institute of Technology, Israel); E. Cheifetz (WeizmannInstitute of Science, Israel); A. Hoffman (Technion-Israel Institute of Technology, Israel) The number of electrons emitted per impinging ion is known to be very high for hydrogenated B doped diamond surfaces. However, following ion bombardment the yield of emitted electrons rapidly decreases due to negative electron affinity loss and graphitization of diamond coating. We found that ion-induced electron emission from undoped and hydrogenated diamond polycritalline films deteriorates less upon similar ion bombardment and discuss processes involved.
9:50 AM		D3-1-5 Electron Injection Enhancement by Diamond-like Carbon Film in Organic Electroluminescence Devices D-W. Han, H.-K. Baik, S.-M. Jeoung (Yonsei University, Korea); S.-J. Lee (KyoungSung University, Korea) Electron injection enhancement by diamond-like carbon (DLC) layer as an electron injection layer between MEH-PPV and Al metal in organic electroluminescence device (OELD) is investigated. The heterojunction structures of these devices are consisted of indium tin oxide (ITO)/MEH-PPV/DLC/Al. [poly (2-methoxy-5- (2â€™ -ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) is used as emission layer. The DLC layer is deposited by Cs ion gun sputter deposition system (Cs+ IGSDS) and DLC layer property is controlled by deposition energy. The relationships between the properties of DLC deposited at various deposition energy and light emission property are investigated. Raman spectroscopy and X-ray photoelectron spectroscopy are used for characterization of DLC layer. The driving voltage is reduced by insertion of DLC layer and the reduced values are varied by DLC properties. These results mean that there is highly efficient electron injection from DLC layer into emitting polymer and that different DLC property makes different electron injection enhancement.
10:10 AM		D3-1-6 Effects of Ar Dilution on the Properties of Hydrogenated Amorphous Carbon Thin Film C.H.P Poa, R.G. Lacerda, D.C. Cox, S.R.P. Silva (University of Surrey, United Kingdom) In the past years, there have been several studies aim at obtaining the ideal plasma conditions for growth of a-C:H films with suitable mechanical and electronic properties. However, most of the work has been focused on changing standard parameters such as bias (ion bombardment) and gas pressure. Little is known about the structural changes that occur in the a-C:H due to Ar dilution. It has been suggested that the Ar dilution reduces the sp² concentration or the clusters size within the film structure. In this work, we present a systematic study on the influence of Ar dilution on the properties of a-C:H films. The films were deposited by rf-Plasma enhanced chemical vapour deposition technique by fixing the negative self-bias voltage at -200 V and varying the Ar partial pressure from 0 to about 90%. Electron energy loss spectroscopy was used to probe the changes on the sp² concentration of the films. With no Ar, the films have a sp² content of about 75%, having an abrupt decrease to about 65% as soon as the Ar is introduced. However, unexpected behaviour was observed with increasing Ar dilution, which resulted in the concentration of sp² bonds further increasing. The sp² content reaching 75% with 90% of Ar dilution. These results are in agreement with the optical band gap and infared measurements. Field emission results show an initial threshold field of about 25 V/µm, and with Ar dilution (60%) results in an increase to about 35 V/µm, which then decreases to 20 V/µm for 90% Ar dilution. The results presented shows that the Ar dilution affects growth in two regimes. Small amounts of Ar lead to a material with polymer-like properties, soft with high band gap, whereas further dilution cause a graphitisation of the films. The field emission from these films can be explained by the dependence of sp² concentration, which agrees with the proposed non-geometric field enhancement model.
10:30 AM		D3-1-7 Structural, Electrical and Optical Properties of DLC Films Deposited by DC Magnetron Sputtering E. Broitman (College of William and Mary); A. Lindquist (Linköping University, Sweden); N. Hellgren (Frederick Seitz Materials Research Laboratory, University of Illinois); L. Hultman (Linköping University, Sweden); B.C. Holloway (College of William and Mary) The electrical and optical properties of diamond-like carbon (DLC) films deposited by direct current (d.c.) magnetron sputtering on Si substrates at room temperature have been measured as a function of the argon pressure, bias voltage and discharge current. Changes in the resistivity and optical absorption have been related to changes in the microstructure, morphology, growth rate, surface roughness, and sp²/sp³ ratio. Langmuir probe measurements as a function of Ar pressure and target current show changes in the ion-to-neutral flux ratio at the substrate location. Plan-view HRTEM reveals an amorphous microstructure, however cross-sectional SEM shows a columnar structure at the higher negative bias voltage. The film optical properties obtained from spectroscopic ellipsometry measurements between 1.24 and 5 eV indicate a bandgap that varies from semimetallic to semiconducting, depending on deposition parameters. A correlation of film properties to plasma conditions will be discussed.
10:50 AM		D3-1-8 DLC-Si Protective Coatings for Polycarbonates J.C. Damasceno, S.S. Camargo Jr. (Universidade Federal do Rio de Janeiro, Brazil); M. Cremona (Pontifícia Universidade Católica do Rio de Janeiro, Brazil) Polycarbonates are light in weight, can be mass produced and are very cheap materials. Because of their excellent breakage resistance, polycarbonates have replaced glass in many applications, such as automobile headlamps, safety shields of windows, ophthalmic lenses, sunglasses and the like. However, low hardness and low scratch resistance of polycarbonates limit their full utilization. To overcome this limitation, methods for producing hard transparent protective coatings on polycarbonate materials have been studied, including the deposition of diamond-like amorphous carbon (DLC) by several deposition techniques. In this work, a-C:H:Si (DLC-Si) films were produced onto crystalline silicon and polycarbonate substrates by the rf-PACVD technique from gaseous mixtures of CH₄ + SiH₄ and C₂H₂ + SiH₄. The inclusion of silicon in DLC films helps to reduce intrinsic film stress, increase adhesion and band gap, guaranteeing good transparency and mechanical resistance. The effects of self-bias and gas composition upon mechanical and optical properties of the films were investigated. Micro-hardness, residual stress, roughness and refractive index measurements were employed for characterization. By incorporating low concentrations of silicon and by exploring the more favorable conditions for the rf-PACVD deposition technique, highly adherent Si-DLC thin films were produced with reduced internal stresses (lower than 1 GPa), high hardness (around 20 GPa) and high deposition rates (up to 9 µm/h). It is also discussed results that show the technological viability of this material for its application as protective coatings for polycarbonates.
11:30 AM		D3-1-10 Thermal Expansion Coefficient of Amorphous Carbon Nitride Thin Films A. Champi (Universidade Estadual de Campinas, UNICAMP, Brazil); R.G. Lacerda (Universidade Estadual de Campinas, UNICAMP); F.C. Marques (Universidade Estadual de Campinas, UNICAMP, Brazil) Recently we developed hard a-C:H films at a significant growth rate (~0.7 nm/s), with high hardness (~19 GPa), and relatively low stress (~1.3 GPa) [1,2]. These films were obtained by the decomposition of methane in a plasma enhanced chemical vapor deposition system under unusual condition of high bias (- 800 V) and high pressure (~12 Pa). In the present work, we explored this condition to study the effect of the nitrogen incorporation into the carbon matrix. The films were deposited under the same condition described above, but introducing nitrogen (N₂) in the chamber (N₂/(N₂ + CH₄) varying from 0-10 % gas mixture), and keeping the total pressure constant at 12 Pa. The films were analyzed by FTIR, nanohardness, SEM, and stress. It was observed that the incorporation of nitrogen reduces the deposition rate, band-gap, hardness, and the elastic constant of the films. In spite of that, films with relatively good properties were deposited. In particular, we deposited stable and thick (~2 micron) films at relatively high deposition rate (0.3 nm/s), high hardness (13 GPa), and low stress (0.6 GPa). The thermal expansion coefficient of the a-CNx:H films was determined, for the first time, by the thermally induced bending technique. These measurements were performed in films deposited simultaneously on c-Si, c-Ge, sapphire, 7059 Corning glass, and 211 Precision glass substrates. The use of several substrates was adopted in order to achieve good accuracy. We observed that the thermal expansion coefficient increases as the nitrogen concentration increases, varying from about 2 to 7 x10-6 K-1 in the range of nitrogen concentration investigated. [1] R.G. Lacerda and F. C. Marques, Diamond and Related Materials (to be published) [2] F.C. Marques et al. Thin Solid Films 343-344 (1999) 222.
11:50 AM		D3-1-11 Phase and Thickness Dependence of Thermal Diffusivity in SiC_xN_y and BC_xN_y S. Chattopadhyay, L.C. Chen, S.C. Chien, S.T. Lin (National Taiwan University, Taiwan); C.T. Wu, K.H. Chen (Institute of Atomic and Molecular Sciences, Academia Sinica, Taiwan) Amorphous silicon carbon nitride (a-SiC_xN_y) and boron carbon nitride (a-BC_xN_y) are potential candidates for hard coatings. For protective coatings, the thermal conductivity is one of the most important properties that need to be investigated thoroughly. Thermal diffusivity (α) in a-SiC_xN_y and a-BC_xN_y thin films on silicon has been measured by the traveling wave technique. The technique involves local heating of the sample by a harmonically modulated source and measuring the phase difference of the traveling thermal wave as a function of distance from the heat source, along the length of the sample surface. The bonding structure of the film was probed by X-ray photoelectron spectroscopy in order to isolate the effects of a defective phase on the thermal diffusivity. Thermal diffusivity in a-SiC_xN_y and a-BC_xN_y on silicon, as a function of its carbon content, was studied. In both a-SiC_xN_y and a-BC_xN_y a maximum α value of ~0.4 cm²/s and 0.6 cm²/s, respectively, was observed at a carbon content of ~30 at. %. Thereafter the α value decreased steadily with increasing carbon content. The variation could be explained with the help of the bonding characteristics and density of the network. The thickness dependence of α was studied for metal thin films in addition to a-SiC_xN_y and a-BC_xN_y on silicon having about 30 at. % of carbon in them. In case of the metal thin films, a substrate dependence of α was also studied. For the layered structure of a film on a substrate, it was found that the α value decreased rapidly as the film thickness is reduced and even for a very thick film, α would stay below their respective bulk values because of the thermal resistance at the film-substrate interface. An empirical relation depicting the variation of α with thickness will be discussed.
12:10 PM		D3-1-12 Electronic Properties of Unhydrogenated Carbon Nitride Thin Films Studied by Electron Paramagnetic Resonance and DC Conductivity Measurements T. Chritidis, M. Tabbal, S. Isber, S. Rizk (American University of Beirut, Lebanon); P. Merel, M. Chaker (INRS- Energie et Materiaux, Canada) Carbon nitride (CN_x)thin films with nitrogen content ranging from 17 to 25 % atomic have been deposited, at room temperature on Si by plasma assisted pulsed laser ablation. X-Band Electron paramagnetic resonance and DC conductivity measurements were performed on the films, as a function of temperature, in an attempt to identify the dominant paramagnetic defects and to elucidate the conduction mechanisms in the layers. The density of the paramagnetic centers, evaluated to be of the order of 10²⁰ spins/cm³, decreases with nitrogen content in the films. For all the films, the g-value was measured to be close to 2.0028 and the EPR signal was found to be an exchange narrowed pure Lorentzian line, indicating that the paramagnetic centers in the films are most probably clustered sp² carbon related defects. The strong exchange interaction of the spins is confirmed by the short value of the spin lattice relaxation time T₁ deduced from the power saturation behavior of the EPR signal. The EPR linewidth also shows a decrease from 3.7 to 2.6 Gauss with increasing nitrogen content but it broadens with measurement temperature, thus suggesting some hopping motion of the spins between graphitic clusters that may contribute to the conduction process. The value of the resistivity at room temperature was found to decrease by nearly two orders of magnitude with increasing nitrogen incorporation, going from 3 to 0.06 Ω.cm. The thermal dependence of the conductivity will also be presented and analyzed in conjunction with the EPR measurements.