Influence of Growth Temperature and Carrier Flux on the Structure and Transport Properties of Highly Oriented CrO2 on Al2O3 (0001)

Sousa, Paulo; Dias, S. A.; Conde, O.; Silvestre, A. J.; Branford, W. R.; Morris, B.; Yates, K. A.; Cohen, L. F.

doi:10.1002/cvde.200706592

Cited by 23 publications

(10 citation statements)

References 31 publications

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“…The CrO 2 growth kinetics depends on a number of factors such as the geometry of the reactor, substrate material and crystallographic orientation, substrate and precursor temperatures, carrier gas, and carrier gas flow rate [28,29]. This section will focus on the role of the carrier gas on the thickness and growth rate of CrO 2 films for both types of single crystal substrates.…”

Section: Film Thickness and Growth Ratementioning

confidence: 99%

“…Indeed, CrO 2 has been used in industry covering a wide range of applications e.g. audio, video, instrumentation and computer technology due to its exceptional properties as a magnetic storage material [13].Although some attempts have been pursued to grow thin films of the single CrO 2 compound by physical vapor deposition methods [23][24][25], only chemical vapor deposition (CVD) has shown to lead to high quality CrO 2 layers [26][27][28][29][30]. CrO 2 epitaxial layers are currently grown on TiO 2 rutile phase and sapphire substrates by CVD using CrO 3 as the chromium precursor, which is carried out into the reaction zone by an oxygen flux.…”

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confidence: 99%

“…">Experimental detailsThe CrO 2 films were prepared in a tubular single-zone CVD furnace with independent control of the substrate temperature. Details of this setup were described in previous papers [28,29]. The thin films were grown onto TiO 2 (110) and TiO 2 (100) single crystal rutile substrates 0.5 mm thick and with 105 mm 2 surface area.…”

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Argon assisted chemical vapor deposition of CrO2: An efficient process leading to high quality epitaxial films

Duarte

Franco

Viana

et al. 2016

Journal of Alloys and Compounds

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A comparative study of the structural, microstructural and magnetic properties of CrO 2 thin films grown onto (110) and (100) TiO 2 rutile single crystal substrates by chemical vapor deposition (CVD), using CrO 3 as chromium precursor and either oxygen or argon as carrier gas is presented. Our results show that growth under argon carrier gas leads to high quality CrO 2 epilayers with structural and magnetic properties similar to those obtained using the more standard oxygen carrier gas. Furthermore, we interpret the larger magnetic coercivity observed for the (110) oriented films in terms of their microstructure, in particular of the highest strain and edge roughness of the building structures of the CrO 2 epilayers, which are settled by the substrate crystallographic orientation. * [19][20][21][22]. But the studies on chromium dioxide have not been limited to fundamental or applied science. Indeed, CrO 2 has been used in industry covering a wide range of applications e.g. audio, video, instrumentation and computer technology due to its exceptional properties as a magnetic storage material [13].Although some attempts have been pursued to grow thin films of the single CrO 2 compound by physical vapor deposition methods [23][24][25], only chemical vapor deposition (CVD) has shown to lead to high quality CrO 2 layers [26][27][28][29][30]. CrO 2 epitaxial layers are currently grown on TiO 2 rutile phase and sapphire substrates by CVD using CrO 3 as the chromium precursor, which is carried out into the reaction zone by an oxygen flux. While chromium precursors other than CrO 3 , e.g. Cr 8 O 21 [31] and CrO 2 Cl 2 [8,10], have also been used in the CVD of CrO 2 yielding films with similar properties, the use of an oxygen flux has been pointed out as critical for the overall CrO 2 synthesis process. To our knowledge, only the work of Ivanov et al. [31] briefly refers that the use of argon as carrier gas makes the process very inefficient and leads to films with poorer crystallinity.Currently, the demand for fast and cost-efficient fabrication processes of high-quality materials and devices is on the agenda. Hence, an in-depth study of the feasibility of growing high quality epitaxial films of CrO 2 using argon as carrier gas becomes crucial, especially because of the well-known price difference between the two gases, with cost advantage to Page 3 of 27 argon. Besides, argon is a more user-friendly gas. Therefore, the fact that the use of argon could eventually limit the CrO 2 synthesis reaction may be seen as a drawback to the envisaged scaling-up of the CrO 2 CVD process at an industrial level.This work reports on the synthesis and properties of CrO 2 thin films grown onto single crystal TiO 2 rutile substrates by CVD, using CrO 3 as chromium precursor and either oxygen or argon as carrier gas. A comparative study of the structural, microstructural and magnetic properties of the different films are presented. Experimental detailsThe CrO 2 films were prepared in a tubular single-zone CVD furnace with independent control...

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Section: Film Thickness and Growth Ratementioning

confidence: 99%

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confidence: 99%

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Argon assisted chemical vapor deposition of CrO2: An efficient process leading to high quality epitaxial films

Duarte

Franco

Viana

et al. 2016

Journal of Alloys and Compounds

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“…As reported previously [6] films were grown within a broad range of deposition temperatures from 320 to 410 ºC, and oxygen carrier gas flow rates of 50 -500 sccm. Herein we will show the results obtained for two films grown at 340 and 360 ºC with 100 sccm oxygen.…”

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“…Here we report on high resolution electron microscopy structural and analytical studies of CrO 2 films deposited onto Al 2 O 3 (0001) by atmospheric pressure CVD from CrO 3 precursor. As reported previously [6] films were grown within a broad range of deposition temperatures from 320 to 410 ºC, and oxygen carrier gas flow rates of 50 -500 sccm. Herein we will show the results obtained for two films grown at 340 and 360 ºC with 100 sccm oxygen.…”

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Structural and Microanalytical Studies of CrO₂ Thin Films on c-Sapphire by High Resolution Electron Microscopy Methods

et al. 2008

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Chromium dioxide (CrO 2 ) has been extensively used in the magnetic recording industry. However, it is its ferromagnetic half-metallic nature that has more recently attracted much attention, primarily for the development of spintronic devices. CrO 2 is the only stoichiometric binary oxide theoretically predicted to be fully spin polarized at the Fermi level. It presents a Curie temperature of ~ 396 K, i.e. well above room temperature, and a magnetic moment of 2 μ B per formula unit [1][2][3][4][5]. However an antiferromagnetic native insulating layer of Cr 2 O 3 is always present on the CrO 2 surface which enhances the CrO 2 magnetoresistance and might be used as a barrier in magnetic tunnel junctions.Here we report on high resolution electron microscopy structural and analytical studies of CrO 2 films deposited onto Al 2 O 3 (0001) by atmospheric pressure CVD from CrO 3 precursor. As reported previously [6] films were grown within a broad range of deposition temperatures from 320 to 410 ºC, and oxygen carrier gas flow rates of 50 -500 sccm. Herein we will show the results obtained for two films grown at 340 and 360 ºC with 100 sccm oxygen.Cross-sectional specimens for TEM were prepared by mechanical grinding, dimpling and argon ion-milling of the samples in a liquid-nitrogen-cooled holder with an acceleration voltage of 5 keV and an incidence angle of 8º. Analytical TEM and HREM studies were carried out using a Philips Tecnai 20F FEG microscope operating at 200 keV, equipped with an Energy Dispersive X-Ray (EDX) analysis system and a scanning transmission electron microscopy modulus (STEM) with a high angle annular detector (HAAD) for Z-contrast imaging and composition mapping. Electron diffraction pattern (EDP) and simulations using Fast Fourier transform (FFT) of the HREM images were used to analyze the crystal structure.Bright field images of the sapphire substrate and of the chromium oxide film deposited at 360 ºC are shown in figure 1. Two different growth areas were identified. At the first stages of deposition a three-dimensional (3D) growth forming pyramidal structures of Cr 2 O 3 is observed. Defects and distortions at the substrate-film interface can be seen. The corresponding high resolution image is also shown in figure 1, as well as the simulated patterns using FFT which indicate that both aluminium and chromium oxides show corundum structure with an orientation relationship between the substrate and the 3D layer of the type (0001) Al 2 O 3 || (0001) Cr 2 O 3 . The top part of the layer that appears with a clear contrast is a mixture of Cr 2 O 3 and tetragonal rutile CrO 2 . The observed contrast in the top layer suggests a columnar growth and the defects observed along the layer indicate epitaxial stress during growth.

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Epitaxial Growth and Properties of Doped Transition Metal and Complex Oxide Films

2009

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The detailed science and technology of crystalline oxide film growth using vacuum methods is reviewed and discussed with an eye toward gaining fundamental insights into the relationships between growth process and parameters, film and interface structure and composition, and electronic, magnetic and photochemical properties. The topic is approached first from a comparative point of view based on the most widely used growth methods, and then on the basis of specific material systems that have generated very high levels of interest. Emphasis is placed on the wide diversity of structural, electronic, optical and magnetic properties exhibited by oxides, and the fascinating results that this diversity of properties can produce when combined with the degrees of freedom afforded by heteroepitaxy.

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Influence of Growth Temperature and Carrier Flux on the Structure and Transport Properties of Highly Oriented CrO₂ on Al₂O₃ (0001)

Cited by 23 publications

References 31 publications

Argon assisted chemical vapor deposition of CrO2: An efficient process leading to high quality epitaxial films

Argon assisted chemical vapor deposition of CrO2: An efficient process leading to high quality epitaxial films

Structural and Microanalytical Studies of CrO₂ Thin Films on c-Sapphire by High Resolution Electron Microscopy Methods

Epitaxial Growth and Properties of Doped Transition Metal and Complex Oxide Films

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Influence of Growth Temperature and Carrier Flux on the Structure and Transport Properties of Highly Oriented CrO2 on Al2O3 (0001)

Cited by 23 publications

References 31 publications

Argon assisted chemical vapor deposition of CrO2: An efficient process leading to high quality epitaxial films

Argon assisted chemical vapor deposition of CrO2: An efficient process leading to high quality epitaxial films

Structural and Microanalytical Studies of CrO2 Thin Films on c-Sapphire by High Resolution Electron Microscopy Methods

Epitaxial Growth and Properties of Doped Transition Metal and Complex Oxide Films

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Influence of Growth Temperature and Carrier Flux on the Structure and Transport Properties of Highly Oriented CrO₂ on Al₂O₃ (0001)

Structural and Microanalytical Studies of CrO₂ Thin Films on c-Sapphire by High Resolution Electron Microscopy Methods