TECH FRONT


New Way of Tuning Thermal Conductivity Cuts Heat in Devices


R


esearchers have found an unexpected way to control the thermal conductivity of 2D materials, which will allow electronics designers to dissipate heat in electronic devices that use these materials. To better understand the thermal conduction properties of 2D materials, a team of researchers from North Carolina State University (Raleigh, NC), the Uni- versity of Illinois at Urbana-Champaign (UI) and the Toyota Research Institute of North America (TRINA) began ex- perimenting with molybdenum disulfi de (MoS2


), which is a 2D material, or TMD. 2D materials have a layered struc-


ture, with each layer having strong bonds horizontally, or “in plane,” and weak bonds between the layers, or “out of plane.” The materials have unique electronic and chemical properties, and hold promise for use in creating fl exible, thin, lightweight electronic devices. In most electronics applications, it’s important to be able to dissipate heat effi ciently, which can be tricky, as in 2D materials heat is conducted differently in plane than it is out of plane. For example, in one class of TMD, heat is conducted at 100 W per meter per Kelvin (W/mK) in plane, but at only 2 W/mK out of plane. That gives it a “ther- mal anisotropy ratio” of about 50. The researchers found that, by introducing disorder to the MoS2


, they could signifi -


cantly alter the thermal anisotropy ratio. The researchers created this disorder


by introducing lithium ions between the layers of MoS2


. The presence of the


lithium ions does two things simultane- ously: it puts the layers of the 2D mate- rial out of alignment with each other, and it forces the MoS2


to rearrange the structure of its component atoms. January 2017 | AdvancedManufacturing.org 35 When the ratio of lithium ions to MoS2 reached 0.34,


the in-plane thermal conductivity was 45 W/mK, and the out-of-plane thermal conductivity dropped to 0.4 W/mK— increasing the material’s thermal anisotropy ratio from 50


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