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Research Papers: Micro/Nanoscale Heat Transfer

# Ultra-Low Thermal Conductivity in Nanoscale Layered Oxides

[+] Author and Article Information
J. Alvarez-Quintana, Ll. Peralba-Garcia

Department of Physics, Nanomaterials and Microsystems Group, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain

J. L. Lábár

Research Institute for Technical Physics and Materials Science, P.O. Box 49, Budapest 114 H-1525, Hungary

J. Rodríguez-Viejo1

Department of Physics, Nanomaterials and Microsystems Group, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain; MATGAS Research Center, Campus Universitat Autònoma de Barcelona, 08193 Bellaterra, Spainjavirod@gnam.uab.es

1

Corresponding author.

J. Heat Transfer 132(3), 032402 (Dec 28, 2009) (6 pages) doi:10.1115/1.4000052 History: Received February 21, 2009; Revised July 27, 2009; Published December 28, 2009; Online December 28, 2009

## Abstract

The cross-plane thermal conductivity of several nanoscale layered oxides $SiO2/Y2O3$, $SiO2/Cr2O3$, and $SiO2/Al2O3$, synthesized by e-beam evaporation was measured in the range from 30 K to 300 K by the $3ω$ method. Thermal conductivity attains values around $0.5 W/m K$ at room temperature in multilayer samples, formed by 20 bilayers of 10 nm $SiO2/10 nm Y2O3$, and as low as $0.16 W/m K$ for a single bilayer. The reduction in thermal conductivity is related to the high interface density, which produces a strong barrier to heat transfer rather than to the changes of the intrinsic thermal conductivity due to the nanometer thickness of the layers. We show that the influence of the first few interfaces on the overall thermal resistance is higher than the subsequent ones. Annealing the multilayered samples to $1100°C$ slightly increases the thermal conductivity due to changes in the microstructure. These results suggest a route to obtain suitable thermal barrier coatings for high temperature applications.

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## Figures

Figure 1

Amplitude of the temperature oscillations of the heater versus heater frequency. Closed squares and circles represent the measured thermal oscillations for the reference sample (Si substrate plus SiO2 insulating layer) and the SiO2/Y2O3 sample (Si substrate plus SiO2 insulating layer plus nanolaminate film), respectively. The dot lines represent the calculated thermal oscillations.

Figure 2

Thermal conductivity as a function of temperature for SiO2/Al2O3, SiO2/Cr2O3, and SiO2/Y2O3 nanolayered samples with a modulation length of 5 nm/5 nm. The solid symbols represent the data from the heat treated samples, whereas the open symbols are for the as-deposited samples. Representative error bars are only shown for the 1-SY20–5 sample.

Figure 3

Thermal conductivity as a function of temperature for oxide layers of 10 nm (down triangle) and 200 nm (up triangle) of Y2O3 and 200 nm SiOx (square). Also, it is shown for comparison data from Cahill 16 on 1 μm thick disordered Yttria (solid circle). The continuous line represents the value of the intrinsic thermal conductivity of the layers κlayers, i.e., without considering the contribution of the thermal boundary resistance.

Figure 4

Cross-sectional TEM images of the as-deposited 20 bilayer 10/20 SiO2/Y2O3 sample at several magnifications. Dark layers correspond to Yttria.

Figure 5

(a) One-dimensional temperature profile across a thin film in response to an applied heat flux. The temperature drop across an interior region of film is denoted by To. Ti indicates the temperature discontinuity resulting from the interfacial resistance. (b) Effective thermal conductivity for sample of group 2: 2-SY20–6 (squares), 2-SY20–10 (down triangle), and 2-SY20–20 (circles).

Figure 6

Effective thermal conductivity of SiO2/Y2O3 multilayers of group 3, with identical period thickness of 20 nm but with varying number of interfaces (total thickness): 3-SY1–10 (down triangle), 3-SY5–10 (square), 3-SY20–10 (up triangle), and 3-SY30–10 (circle)

Figure 7

(a) Overall thermal boundary resistance (open symbols, left axis) and interface resistivity (closed symbols, right axis) of the SiO2/Y2O3 multilayer system (group 3) versus the number of interfaces. The lines are only guides to the eye. Data of the overall TBR from 1-SY20–5 (square) and 2-SY20–6 (up triangle), and 2-SY20–10 (down triangle) and 2-SY20–20 (star), is included for comparison.

Figure 8

Averaged thermal boundary resistance associated to each interface for sample 2-SY20–6 as a function of temperature. The continuous line represents the interfacial resistance predicted by the DMM.

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