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VNU Journal of Science, Mathematics - Physics 25 (2009) 47-55 47 Survey of WO 3 thin film structure built on ito/glass substrates by the Raman and xrd spectroscopies Le Van Ngoc 1, *, Tran Cao Vinh 1 , Le Quang Toai 1 , Nguyen Duc Thinh 1 Huynh Thanh Dat 2 , Tran Tuan 1 , Duong Ai Phuong 1 1 University of Science, Vietnam National University - Ho Chi Minh city, 227 Nguyen Van Cu, Vietnam 2 Vietnam National University - Ho Chi Minh city, Linh Trung, Thu Duc, Vietnam Received 17 January 2009; received in revised form 12 March 2009 Abstract. Tungsten oxide film was deposited on ITO-coated glass by using RF magnetron sputtering method from WO 3 ceramic target. Thin film preparation – process took place in Ar + O 2 plasma. The dependence of tungsten oxide film structure on experiment conditions was investigated by X-ray diffraction (XRD) Raman spectroscopy. In this paper, we considered that the thickness of ITO layers about 150nm to 350nm clearly effects on the Raman and XRD spectrograms of WO 3 films. Keywords: WO3 structure, WO3 /ITO/glass, Raman spectroscopy. 1. Introduction WO 3 thin films have been studied for along time due to their unique properties and their potential applications into. And the most promising application of WO 3 thin films is electrochromic devices based on electrochromism, in which optical properties WO 3 alter reversibly under electrical bias applied [1-3]. Moreover, recently WO 3 thin films have been studied to fabricate toxic gas sensors, such as NO x , H 2 S, NH 3 , CO and some popular others like H 2 , O 2 , O 3 , Cl 2 , SO 2 , CH 4 [4-7]. Both electrochromism and gaseous sensitization are based on the reversible diffusion of particles along the vacant tunnels of WO 3 perovskite structure. Thus, having large and oriented vacant tunnels will be a great advantage. Furthermore, many methods are used to prepare WO 3 thin films, such as sputtering [8-11], sol – gel [12], spray pyrolysis [13-14], anodizing technique [15], thermal evaporation [15-21]. And different preparation methods have respective advantages in film quality and application. Besides optical and electrical properties, WO 3 crystalline structure has been studied by utilizing XRD and Raman Spectroscopy. XRD surveys focus on 20 o – 25 o range of diffraction angles and Raman spectroscopy surveys focus on 200 cm -1 – 1000 cm -1 range of wave number. In this paper, WO 3 layers were deposited on ITO/glass substrates. The thickness of ITO layers is measured approximately 150, 200, 250, 300, 350 nm, respectively. From XRD spectrograms, we ______ * Corresponding author. Tel.: 0908283530 E-mail: lvngoc@phys.hcmuns.edu.vn L.V. Ngoc et al. / VNU Journal of Science, Mathematics - Physics 25 (2009) 47-55 48 considered that the thickness of ITO coaters clearly effect on WO 3 crystalline structure. In order to understand what occurred inside and whether nano particle phases exist, we used their Raman spectroscopy. And 600 cm -1 – 1000 cm -1 range was analyzed into different basic vibration. With samples with ITO layer about 300nm thickness and more, in Raman spectrum there is an odd peak at 680 cm -1 , which could be related to nano phases. However, the absence of 950 cm -1 refuses that assumption. The origin of this peak will be focused on in this paper. 2. Experimental In this research, Thin Film Interference Thin Film Interference Bởi: OpenStaxCollege The bright colors seen in an oil slick floating on water or in a sunlit soap bubble are caused by interference The brightest colors are those that interfere constructively This interference is between light reflected from different surfaces of a thin film; thus, the effect is known as thin film interference As noticed before, interference effects are most prominent when light interacts with something having a size similar to its wavelength A thin film is one having a thickness t smaller than a few times the wavelength of light, λ Since color is associated indirectly with λ and since all interference depends in some way on the ratio of λ to the size of the object involved, we should expect to see different colors for different thicknesses of a film, as in [link] These soap bubbles exhibit brilliant colors when exposed to sunlight (credit: Scott Robinson, Flickr) What causes thin film interference? [link] shows how light reflected from the top and bottom surfaces of a film can interfere Incident light is only partially reflected from the top surface of the film (ray 1) The remainder enters the film and is itself partially reflected from the bottom surface Part of the light reflected from the bottom surface can emerge from the top of the film (ray 2) and interfere with light reflected from the top (ray 1) Since the ray that enters the film travels a greater distance, it may be in or out of phase with the ray reflected from the top However, consider for a moment, again, the bubbles in [link] The bubbles are darkest where they are thinnest Furthermore, if you observe a soap bubble carefully, you will note it gets dark at the point where it breaks For very thin films, the difference in path lengths of ray and ray in [link] 1/11 Thin Film Interference is negligible; so why should they interfere destructively and not constructively? The answer is that a phase change can occur upon reflection The rule is as follows: When light reflects from a medium having an index of refraction greater than that of the medium in which it is traveling, a 180º phase change (or a λ / shift) occurs Light striking a thin film is partially reflected (ray 1) and partially refracted at the top surface The refracted ray is partially reflected at the bottom surface and emerges as ray These rays will interfere in a way that depends on the thickness of the film and the indices of refraction of the various media If the film in [link] is a soap bubble (essentially water with air on both sides), then there is a λ / shift for ray and none for ray Thus, when the film is very thin, the path length difference between the two rays is negligible, they are exactly out of phase, and destructive interference will occur at all wavelengths and so the soap bubble will be dark here The thickness of the film relative to the wavelength of light is the other crucial factor in thin film interference Ray in [link] travels a greater distance than ray For light incident perpendicular to the surface, ray travels a distance approximately 2t farther than ray When this distance is an integral or half-integral multiple of the wavelength in the medium (λn = λ / n, where λ is the wavelength in vacuum and n is the index of refraction), constructive or destructive interference occurs, depending also on whether there is a phase change in either ray Calculating Non-reflective Lens Coating Using Thin Film Interference 2/11 Thin Film Interference Sophisticated cameras use a series of several lenses Light can reflect from the surfaces of these various lenses and degrade image clarity To limit these reflections, lenses are coated with a thin layer of magnesium fluoride that causes destructive thin film interference What is the thinnest this film can be, if its index of refraction is 1.38 and it is designed to limit the reflection of 550-nm light, normally the most intense visible wavelength? The index of refraction of glass is 1.52 Strategy Refer to [link] and use n1 = 100 for air, n2 = 1.38, and n3 = 1.52 Both ray and ray will have a λ / shift upon reflection Thus, to obtain destructive interference, ray will need to travel a half wavelength farther than ray For rays incident perpendicularly, the path length difference is 2t Solution To obtain destructive interference here, 2t = λn 2 , where λn2 is the wavelength in the film and is given by λn2 = λ n2 Thus, 2t = λ / n2 Solving for t and entering known values yields t = λ / n2 = 99.6 nm = (550 nm) / 1.38 Discussion Films such as the one in this example are most effective in producing destructive interference when the thinnest layer is used, since light over a broader range of incident angles will be reduced in intensity These films are called non-reflective coatings; this is only an approximately correct description, though, since other wavelengths will only be partially cancelled Non-reflective coatings are used in car windows and sunglasses Thin film ...Precision Thin Film Leaded Resistors MBA/SMA 0204, MBB/SMA 0207, MBE/SMA 0414 - Precision Vishay Beyschlag www.vishay.com For technical questions, contact: filmresistorsleaded@vishay.com Document Number: 28767 72 Revision: 12-Dec-12 THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT\rARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000 DESCRIPTION MBA/SMA 0204, MBB/SMA 0207 and MBE/SMA 0414 precision leaded thin film resistors combine the proven reliability of the professional products with an advanced level of precision and stability. Therefore they are perfectly suited for applications in the fields of test and measuring equipment along with industrial and medical electronics. FEATURES IECQ-CECC approved according to EN 140101-806 Advanced thin film technology Low TCR: ± 15 ppm/K to ± 25 ppm/K Precision tolerance of value: ± 0.1 % and ± 0.25 % Superior overall stability: Class 0.05 Wide precision range: 10 to 1.5 M Lead (Pb)-free termination wire Pure tin plating provides compatibility with lead (Pb)-free and lead containing soldering processes Material categorization: For definitions of compliance please see www.vishay.com/doc?99912 APPLICATIONS Test and measuring equipment Industrial electronics Medical electronics Notes • MB_ series has been merged with the related SMA series to form one series “MB_/SMA__” • These resistors do not feature a limited lifetime when operated within the permissible limits. However, resistance value drift increasing over operating time may result in exceeding a limit acceptable to the specific application, thereby establishing a functional lifetime. METRIC SIZE DIN 0204 0207 0414 CECC ABD TECHNICAL SPECIFICATIONS DESCRIPTION MBA/SMA 0204 MBB/SMA 0207 MBE/SMA 0414 CECC Size A B D Resistance Range 22 to 332 k 10 to 1 M 22 to 1.5 M Resistance Tolerance ± 0.25 %; ± 0.1 % Temperature Coefficient ± 25 ppm/K; ± 15 ppm/K Operation Mode Precision Standard Precision Standard Precision Standard Climatic Category (LCT/UCT/Days) 10/85/56 55/125/56 10/85/56 55/125/56 10/85/56 55/125/56 Rated Dissipation, P 70 0.07 W 0.25 W 0.11 W 0.40 W 0.17 W 0.65 W Operating Voltage, U max. AC/DC 200 V 350 V 500 V Film Temperature 85 C 125 C85C 125 C85C125C Max. Resistance Change at P 70 for Resistance Range, R/R max., After: 100 to 100 k 100 to 270 k 100 to 470 k 1000 h 0.05 % 0.25 % 0.03 % 0.15 % 0.05 % 0.25 % 8000 h 0.1 % 0.5 % 0.1 % 0.5 % 0.1 % 0.5 % 225 000 h 0.3 % 1.5 % 0.3 % 1.5 % 0.3 % 1.5 % Permissible Voltage Against Ambient (Insulation): 1 Minute; U ins 300 V 500 V 800 V Continuous 75 V 75 V 75 V Failure Rate: FIT observed 0.1 x 10 -9 /h Document Number: 28767 For technical questions, contact: filmresistorsleaded@vishay.com www.vishay.com Revision: 12-Dec-12 73 MBA/SMA 0204, MBB/SMA 0207, MBE/SMA 0414 - Precision Precision Thin Film Leaded Resistors Vishay Beyschlag THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT\rARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000 Notes (1) Approval is according to EN 140101-806, version A (2) Resistance values to be selected from E96 and E192 series, for other values please contact the factory • Resistance ranges printed in bold are preferred TCR/tolerance combinations with optimized availability • The PART NUMBER shown above is to facilitate the unified part numbering system for ordering products • Radial version (RB, UB) can not be qualified according to CECC so these can only be ordered with variant N or S PART NUMBER AND PRODUCT DESCRIPTION - CECC APPROVED PRODUCTS Enhancement-Mode Metal Organic Chemical Vapor Deposition-Grown ZnO Thin-Film Transistors on Glass Substrates Using N 2 O Plasma Treatment Kariyadan Remashan, Yong-Seok Choi 1 , Se-Koo Kang 2 , Jeong-Woon Bae 2 , Geun-Young Yeom 2 , Seong-Ju Park 1 , and Jae-Hyung Jang à Department of Information and Communications and Department of Nanobio Materials and Electronics, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea 1 Department of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju 500-712, Korea 2 Department of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon, Gyeonggi-do 440-746, Korea Received October 5, 2009; revised November 3, 2009; accepted November 9, 2009; published online April 20, 2010 Thin-film transistors (TFTs) were fabricated on a glass substrate with a metal organic chemical vapor deposition (MOCVD)-grown undoped zinc oxide (ZnO) film as a channel layer and plasma-enhanced chemical vapor deposition (PECVD)-grown silicon nitride as a gate dielectric. The as- fabricated ZnO TFTs exhibited depletion-type device characteristics with a drain current of about 24 mA at zero gate voltage, a turn-on voltage (V on )ofÀ24 V, and a threshold voltage (V T )ofÀ4 V. The field-effect mobility, subthreshold slope, off-current, and on/off current ratio of the as-fabricated TFTs were 5 cm 2 V À1 s À1 , 4.70 V/decade, 0.6 nA, and 10 6 , respectively. The postfabrication N 2 O plasma treatment on the as- fabricated ZnO TFTs changed their device operation to enhancement-mode, and these N 2 O-treated ZnO TFTs exhibited a drain current of only 15 pA at zero gate voltage, a V on of À1:5 V, and a V T of 11 V. Compared with the as-fabricated ZnO TFTs, the off-current was about 3 orders of magnitude lower, the subthreshold slope was nearly 7 times lower, and the on/off current ratio was 2 orders of magnitude higher for the N 2 O- plasma-treated ZnO TFTs. X-ray phtotoelectron spectroscopy analysis showed that the N 2 O-plasma-treated ZnO films had fewer oxygen vacancies than the as-grown films. The enhancement-mode device behavior as well as the improved performance of the N 2 O-treated ZnO TFTs can be attributed to the reduced number of oxygen vacancies in the channel region. # 2010 The Japan Society of Applied Physics DOI: 10.1143/JJAP.49.04DF20 1. Introduction Thin-film transistors (TFTs) are the building blocks of flat- panel displays based on liquid crystals and organic light- emitting diodes. At present, TFTs used in displays employ either amorphous silicon (a-Si) or polycrystalline silicon (poly-Si) as their active channel layer. In comparison with these materials, zinc oxide (ZnO) possesses attractive characteristics 1) such as a wide band gap ($3:3 eV at 300 K), high optical transparency (above 80%), low proc- essing temperature, and higher carrier mobility, and thus there has been active research on TFTs employing a ZnO film as the channel layer. 2–24) The available experimental data on ZnO TFTs indicates their potential use in the field of displays as well as for realizing transparent and flexible electronics. Vario us growth methods have been employed to realize ZnO films for use as the active channel of ZnO TFTs, including molecular beam epitaxy, 2) sputtering, 3–10) pulsed laser deposition, 11–15) atomic layer deposition, 16–21) and metal organic chemical vapor deposition (MOCVD). 22–24) In principle, MOCVD offers the advantages of good reproducibility from run to run and high-quality film with better thickness uniformity. 25) In addition to these merits, it may also be possible to use MOCVD to realize TFTs employing ZnO-based heterostructures similar to Ž. Sensors and Actuators B 67 2000 270–274 www.elsevier.nlrlocatersensorb Gas sensing properties of metal-organics derived Pt dispersed-TiO thin 2 film fired in NH 3 I. Hayakawa a,) , Y. Iwamoto a,1 , K. Kikuta b , S. Hirano b a Fine Ceramics Research Association, Synergy Ceramics Laboratory, 2-4-1, Mutsuno, Atsuta-ku, Nagoya, 456-8587, Japan b Graduate School of Engineering, Nagoya UniÕersity, Nagoya, 464-8603, Japan Received 20 December 1999; received in revised form 23 April 2000; accepted 25 April 2000 Abstract Metal-organic precursor solution for coating was synthesized using Ti alkoxide derivative, amino acid, platinum salt and methanol as a solvent, in which TiO sol was also added to control the pore structure. This solution was spin coated on glass substrate and pretreated in 2 wet air, followed by firing in 3% H rAr. The thin film fired at 4508C showed the highest gas sensitivity and selectivity to H . However, 2 2 the film fired at 6008C showed no sensitivity to reducing gases. In contrast, high gas sensitivity and selectivity to H was observed on the 2 film fired in NH at 6008C, in which the solid solution of nitrogen into TiO was observed. The firing in NH is considered to suppress 3 23 the degradation of sensitivity resulting from SMSI. q 2000 Elsevier Science S.A. All rights reserved. Keywords: Sensor; Thin film; TiO ; Platinum; NH ; SMSI; Metal-organics; TiO sol 23 2 1. Introduction A great deal of efforts has been put into developing new sensing materials with improved sensor properties. Of these, n-type semiconducting materials such as SnO , ZnO 2 wx and TiO are promising materials for gas sensor 1 . 2 TiO has been mainly studied as a material of O 22 sensor at high temperature as high as 8008C in the form of wx bulk or thick film 2,3 . However, there is little trial to develop TiO -based thin film to detect a gas at low 2 temperature, because gas sensitivity of TiO is quite low 2 compared with that of SnO that has commonly been used. 2 A salt of noble metal is sometimes added to a sensor material for the purpose of improving gas sensitivity. A TiO -based sensor material added with a noble metal salt 2 is generally fired in a reducing atmosphere to form fine metal particles or to offer n-type semiconductivity, which contributes to supply electrons necessary for adsorption of oxygen. However, it is known in the field of catalyst that ) Corresponding author. Present address: Planning Department, Corpo- rate Research and Development, Group, NGK Insulators, Ltd., Nagoya, Japan. 1 Present address: Darmstadt University of Technology, Darmstadt, Germany. the degradation of catalytic activity happens in the system Ž TiO -noble metal: especially Pt, by SMSI Strong Metal 2 . Substrate Interaction effect when it was heated in H 2 wx atmosphere above 5008C 4–9 . In these papers, SMSI is explained by the effect of encapsulation or decoration of the metal by the reduced support or electronic interaction of the reduced support with the metal. SMSI decreases the adsorption of H or CO on the metal particle. This will 2 decrease the reactivity of O adsorbed on the metal with 2 H . Therefore, TiO –Pt with SMSI will not greatly change 22 the resistance when H was introduced. 2 NH is a strong reducing gas because hydrogen pro- 3 duced by the decomposition exerts the high reduction wx effect on TiO 10 . Also, nitrogen produced at the same 2 time reacts with oxide to form a solid solution or a nitride wx 11 . Formation of Ti–N bonds is considered to affect the activity of Pt that is related to gas A vailable online at www.sciencedirect.com Sensors and Actuators B 129 (2008) 888–895 Highly sensitive thin film NH 3 gas sensor operating at room temperature based on SnO 2 /MWCNTs composite Nguyen Van Hieu a,b,∗ , Luong Thi Bich Thuy a , Nguyen Duc Chien a,b,c a International Training Institute for Materials Science (ITIMS), Hanoi University of Technology (HUT), Viet Nam b Hanoi Advanced School of Science and Technology (HAST), Hanoi University of Technology (HUT), Viet Nam c Institute of Engineering Physics (IEP), Hanoi University of Technology (HUT), Viet Nam Received 21 February 2007; received in revised form 26 September 2007; accepted 27 September 2007 Available online 13 October 2007 Abstract A SnO 2 /MWCNTs composite-based NH 3 sensor working at room temperature was fabricated by thin film microelectronic technique. The gas- sensitive composite thin film was prepared by using both commercially available multi-walled carbon nanotubes (MWCNTs) and nanosized SnO 2 dispersion. Microstructure and surface morphology of the composite were investigated and they revealed that the MWCNTs were still present and well embedded by SnO 2 particles in the composite powder as well as in the composite thin film at calcination temperatures up to 550 ◦ C. The effect of the preparation process of the sensitive composite thin film on gas-sensing properties was examined, and the preparation process parameters such as MWCNTs content, MWCNTs diameter, calcination temperature, and film thickness were optimized. At room temperature, the optimal composite sensor exhibited much higher response and faster response-recovery (less than 5 min) to NH 3 gas of concentrations ranging from 60 to 800 ppm, in comparison with the carbon nanotubes-based NH 3 sensor. Based on the experimental observations, a model of potential barrier to electronic conduction at the grain boundary for the CNTs/SnO 2 composite sensors was also discussed. © 2007 Elsevier B.V. All rights reserved. Keywords: Nanocomposites; Carbon nanotubes; Gas sensors 1. Introduction SnO 2 -based sensors have been extensively investigated since they can detect a wide variety of gases with high sensitivity and good stability at low production cost [1–3]. However, like other semiconductor type gas sensors, SnO 2 sensors should be operated above room temperature, which brings about much inconvenience for practical applications and sometimes it is even unsafe for detecting combustion gases [4–6]. Currently, SnO 2 and noble metal doped SnO 2 -based sensors are commercially available [7,8]. Still, much effort has been made to improve gas-sensitivity as well as to reduce operating temperature by introducing dopants or decreasing SnO 2 particle size to the nanoscale (<10 nm) [2,4,5,9]. ∗ Corresponding author at: International Training Institute for Materials Sci- ence (ITIMS), Hanoi University of Technology (HUT), No. 1 Dai Co Viet Road, Hanoi, Viet Nam. Tel.: +84 4 8680787; fax: +84 4 8692963. E-mail address: hieunv-itims@mail.hut.edu.vn (N. Van Hieu). Carbon nanotubes (CNTs) special geometry and their amaz- ing feature of being all surface reacting materials offer great potential applications as gas sensor devices working at room temperature. It has been reported that the CNTs are very sensi- tive to surrounding environment. The presence of O 2 ,NH 3 ,NO 2 gases and many other molecules can either donate or accept electrons, resulting in an alteration of the overall conductiv- ity [10,11]. Such properties make CNTs ideal for nanoscale gas-sensing materials, and CNTs field effect transistors and conductive-based devices have already been demonstrated as gas sensors [12–15]. However, the CNTs still have certain lim- itations for gas sensor application such as long recovery time, detection of limited gases, and strong ... the United States currency includes a thin film interference effect Making Connections: Take-Home Experiment Thin Film Interference One feature of thin film interference and diffraction gratings... For thin film interference, you will have constructive interference for a total shift that is an integral number of wavelengths You will have destructive interference for a 7/11 Thin Film Interference. .. destructive interference occurs, depending also on whether there is a phase change in either ray Calculating Non-reflective Lens Coating Using Thin Film Interference 2/11 Thin Film Interference