اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدNanoscale thermal conductivity of Kapton-derived carbonaceous materials
135
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
This study explores the potentialities of Scanning Thermal Microscopy (SThM) technique as a tool for measuring thermal transporting properties of carbon-derived materials issued from thermal conversion of organic polymers, such as the most commonly known polyimide (PI), Kapton. For quantitative measurements, the Null Point SThM (NP-SThM) technique is used in order to avoid unwanted effects as the parasitic heat flows through the air and the probe cantilever. Kapton HN films were pyrolysed in an inert atmosphere at temperatures up to 1200{deg}C to produce carbon-based residues with varying degree of conversion to free sp2 disordered carbon. The thermal conductivity of carbon materials ranges from 0.2 to 2 Wm-1K-1 depending on the temperature of the carbonization process (varied between 500{deg}C and 1200{deg}C). In order to validate the applicability of NP-SThM approach to these materials, the results were compared to those obtained with the three more traditional techniques, namely photo-thermal radiometry, flash laser analysis and micro-Raman thermometry. It was found that NP SThM data are in excellent agreement with previous work using more traditional techniques. We used the NP-SThM technique to differentiate structural heterogeneities or imperfections at the surface of the pyrolysed Kapton on the basis of measured local thermal conductivity.
قيم البحث
اقرأ أيضاً
The hot disk transient plane source (TPS) method is a widely used standard technique (ISO 22007-2) for the characterization of thermal properties of materials, especially the thermal conductivity, k. Despite its well-established reliability for a wid
e variety of common materials, the hot disk TPS method is also known to suffer from a substantial systematic errors when applied to low-k thermal insulation materials. Here, we present a combined numerical and experimental study on the influence of the geometry of hot disk sensor on measured value of low-k materials. We demonstrate that the error is strongly affected by the finite thickness and thermal mass of the sensors insulation layer was well as the corresponding increase of the effective heater size beyond the radius of the embedded metal heater itself. We also numerically investigate the dependence of the error on the sample thermal properties, confirming that the errors are worse in low-k samples. A simple correction function is also provided, which converts the apparent (erroneous) result from a standard hot disk TPS measurement to a more accurate value. A standard polyimide sensor was also optimized using both wet and dry etching to provide more accurate measurement directly. Experimentally corrected value of k for Airloy x56 aerogel and a commercial silica aerogel using the numerical correction factor derived based on the standard TPS sensor is in excellent agreement with the directly measured value from the TPS sensor using the optimized polyimide sensor. Both of these methods can reduce the errors to less than 4% as compared to around 40% error of overestimation from raw values measured with the pristine sensor. Such results show that both the numerical correction to a pristine senor or an optimized sensor are capable of providing highly accurate value of thermal conductivity for such materials.
Upon insertion and extraction of lithium, materials important for electrochemical energy storage can undergo changes in thermal conductivity (${Lambda}$) and elastic modulus ($it M$). These changes are attributed to evolution of the intrinsic thermal
carrier lifetime and interatomic bonding strength associated with structural transitions of electrode materials with varying degrees of reversibility. Using in situ time-domain thermoreflectance (TDTR) and picosecond acoustics, we systemically study $Lambda$ and $it M$ of conversion, intercalation and alloying electrode materials during cycling. The intercalation V$_{2}$O$_{5}$ and TiO$_{2}$ exhibit non-monotonic reversible ${Lambda}$ and $it M$ switching up to a factor of 1.8 (${Lambda}$) and 1.5 ($it M$) as a function of lithium content. The conversion Fe$_{2}$O$_{3}$ and NiO undergo irreversible decays in ${Lambda}$ and $it M$ upon the first lithiation. The alloying Sb shows the largest and partially reversible order of the magnitude switching in ${Lambda}$ between the delithiated (18 W m$^{-1}$ K$^{-1}$) and lithiated states (<1 W m$^{-1}$ K$^{-1}$). The irreversible ${Lambda}$ is attributed to structural degradation and pulverization resulting from substantial volume changes during cycling. These findings provide new understandings of the thermal and mechanical property evolution of electrode materials during cycling of importance for battery design, and also point to pathways for forming materials with thermally switchable properties.
We report on experimental investigation of thermal contact resistance of the noncuring graphene thermal interface materials with the surfaces characterized by different degree of roughness. It is found that the thermal contact resistance depends on t
he graphene loading non-monotonically, achieving its minimum at the loading fraction of ~15 wt.%. Increasing the surface roughness by ~1 micrometer results in approximately the factor of x2 increase in the thermal contact resistance for this graphene loading. The obtained dependences of the thermal conductivity, thermal contact resistance, and the total thermal resistance of the thermal interface material layer on the graphene loading and surface roughness indicate the need for optimization of the loading fraction for specific materials and roughness of the connecting surfaces. Our results are important for developing graphene technologies for thermal management of high-power-density electronics.
Low dimensional systems, nanowires, in particular, have exhibited excellent optical and electronic properties. Understanding the thermal properties in semiconductor nanowires is very important for their applications in their electronic devices. In th
e present study, the thermal conductivity of a freestanding silicon nanowire (NW) is estimated employing the Raman spectroscopy. The advantage of this technique is that the light source (laser) can be used both as heating and excitation source. The variations of the first-order Raman peak position of the freestanding silicon NW with respect to temperature and laser power are carried out. A critical analysis of effective laser power absorbed by exposed silicon NW, the detailed Raman study along with the concept of longitudinal heat distribution in silicon NW, the thermal conductivity of the freestanding silicon NW of 112 nm diameter is estimated to be ~53 W/m.K.
Beta-Ga2O3 has emerged as a promising candidate for electronic device applications because of its ultra-wide bandgap, high breakdown electric field, and large-area affordable substrates grown from the melt. However, its thermal conductivity is at lea
st one order of magnitude lower than that of other wide bandgap semiconductors such as SiC and GaN. Thermal dissipation in electronics made from beta-Ga2O3 will be the bottleneck for real-world applications, especially for high power and high frequency devices. Similar to GaN/AlGaN interfaces, beta-(AlxGa1-x)2O3/Ga2O3 heterogeneous structures have been used to form a high mobility two-dimensional electron gas (2DEG) where joule heating is localized. The thermal properties of beta-(AlxGa1-x)2O3/Ga2O3 are the key for heat dissipation in these devices while they have not been studied before. This work reports the first measurement on thermal conductivity of beta-(Al0.1Ga0.9)2O3/Ga2O3 superlattices from 80 K to 480 K. Its thermal conductivity is significantly reduced (5.7 times reduction) at room temperature comparing with that of bulk Ga2O3. Additionally, the thermal conductivity of bulk Ga2O3 with (010) orientation is measured and found to be consistent with literature values regardless of Sn doping. We discuss the phonon scattering mechanism in these structures by calculating their inverse thermal diffusivity. By comparing the estimated thermal boundary conductance (TBC) of beta-(Al0.1Ga0.9)2O3/Ga2O3 interfaces and Ga2O3 maximum TBC, we reveal that some phonons in the superlattices transmit through several interfaces before scattering with other phonons or structural imperfections. This study is not only important for Ga2O3 electronics applications especially for high power and high frequency applications, but also for the fundamental thermal science of phonon transport across interfaces and in superlattices.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
