本文選題：熱輸運(yùn) + 熱電�。� 參考：《南京大學(xué)》2017年碩士論文

【摘要】：納米結(jié)構(gòu)的引入對(duì)于熱學(xué)輸運(yùn)及熱電調(diào)控方面具有重要的應(yīng)用價(jià)值。由于德拜模型,非金屬態(tài)材料的熱導(dǎo)率主要受到熱容和各種傳輸機(jī)制的影響,如點(diǎn)缺陷,雜質(zhì),界面,倒逆散射等。另一方面,這些因素的引入往往也會(huì)對(duì)材料的熱電性能產(chǎn)生影響,是調(diào)控?zé)犭娤禂?shù)的一個(gè)方法;此外,為了測(cè)試低維納米結(jié)構(gòu)的熱學(xué)和電學(xué)輸運(yùn)性能,我們介紹了一種熱橋方法。這種熱橋方法可以同時(shí)測(cè)量納米線的幾個(gè)熱電參數(shù)。盡管如此,納米結(jié)構(gòu)引入的步驟通常較為復(fù)雜,且需要較極端的高溫合成條件;在低維納米材料中對(duì)熱電系數(shù)的調(diào)控尤其困難,且由于熱電各系數(shù)的相關(guān)性,我們很難同時(shí)定向調(diào)控并優(yōu)化材料的各個(gè)熱學(xué)和電學(xué)參數(shù)。另一方面,相變材料作為一種已經(jīng)較為深入研究的材料,可通過(guò)電學(xué)或激光脈沖改變材料的局部結(jié)構(gòu),完全改變材料的電學(xué)輸運(yùn)性質(zhì);但關(guān)于相變材料熱學(xué)性能的研究還比較少,且對(duì)脈沖前后熱學(xué)輸運(yùn)性質(zhì)隨溫度的變化了解不多。在這篇論文里,我們通過(guò)化學(xué)氣相沉積方法,合成了兩種相變材料納米線。并通過(guò)掃描電鏡,透射電鏡,X射線衍射譜等方法確定了對(duì)合成的納米線進(jìn)行了表征。我們分別在二氧化硅基底和熱橋芯片上進(jìn)行了電脈沖測(cè)試,并第一次實(shí)現(xiàn)了碲化鍺納米線在懸浮基底上的電脈沖相變。在將碲化鍺樣品轉(zhuǎn)移到熱橋芯片上后,我們對(duì)樣品的熱電參數(shù)進(jìn)行了隨溫度變化的測(cè)試。首先,通過(guò)電脈沖控制納米線不同相的形成,我們探究了相變碲化鍺納米線隨溫度變化的電導(dǎo)率的不同趨勢(shì),進(jìn)一步確定了納米線不同的相及不同的輸運(yùn)機(jī)制。其次,我們測(cè)試了碲化鍺非晶相納米線和晶相納米線的賽貝克系數(shù),發(fā)現(xiàn)盡管兩相之間電導(dǎo)率有幾個(gè)數(shù)量級(jí)的差距,塞貝克系數(shù)的變化和大小卻比較類似。我們推測(cè)是因?yàn)榉蔷鄡H占納米線的一小部分所致。最后,我們還測(cè)試了碲化鍺納米線通過(guò)電脈沖變?yōu)榕K金屬態(tài)納米線前后的熱導(dǎo)率,因?yàn)榧{米線尺寸上遠(yuǎn)大于其聲子平均自由程,其熱導(dǎo)率數(shù)值與體塊晶態(tài)納米線大小類似;我們第一次發(fā)現(xiàn)熱導(dǎo)率在脈沖前后的變化趨勢(shì)與電導(dǎo)率在脈沖前后的變化趨勢(shì)變化相反,這一點(diǎn)為對(duì)各相碲化鍺納米線的熱學(xué)輸運(yùn)機(jī)制的知識(shí)得到了提升,并為在各相納米線之中的電脈沖調(diào)控提供了很大的參考價(jià)值。通過(guò)綜合幾個(gè)測(cè)試數(shù)據(jù),我們得到了第一次碲化鍺非晶態(tài)納米線的熱電優(yōu)值。且發(fā)現(xiàn)在不同納米線相之間的調(diào)控或許可對(duì)熱電參數(shù)進(jìn)行同時(shí)的優(yōu)化。并實(shí)現(xiàn)了在測(cè)試熱橋芯片上對(duì)納米線性質(zhì)的原位調(diào)控。同時(shí),在之后的工作中,我們希望能實(shí)現(xiàn)同一個(gè)樣品各相在芯片上的脈沖總體調(diào)控,并對(duì)樣品進(jìn)行透射電鏡,表面電子散失譜等進(jìn)行進(jìn)一步的表征。并對(duì)熱學(xué)和電學(xué)的參數(shù)變化進(jìn)行理論上的模擬和解釋。
[Abstract]:The introduction of nanostructures plays an important role in thermal transport and thermoelectric regulation. Due to Debye model, the thermal conductivity of nonmetallic materials is mainly affected by heat capacity and various transport mechanisms, such as point defects, impurities, interface, inverse scattering and so on. On the other hand, the introduction of these factors often affects the thermoelectric properties of the materials and is a method of regulating thermoelectric coefficients. In addition, in order to test the thermal and electrical transport properties of low-dimensional nanostructures, We introduce a hot bridge method. This method can simultaneously measure several thermoelectric parameters of nanowires. Nevertheless, the steps introduced into nanostructures are usually more complex and require more extreme high temperature synthesis conditions; in low-dimensional nanomaterials, it is particularly difficult to regulate thermoelectric coefficients, and because of the correlation of thermoelectric coefficients, It is difficult to control and optimize the thermal and electrical parameters of materials simultaneously. On the other hand, as a kind of material which has been studied deeply, the phase change material can change the local structure of the material by electricity or laser pulse, and completely change the electrical transport property of the material. However, there are few studies on the thermal properties of phase change materials, and little is known about the change of thermal transport properties with temperature before and after pulse. In this paper, we synthesized two phase change nanowires by chemical vapor deposition. The synthesized nanowires were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). We have carried out the electric pulse test on silicon dioxide substrate and thermal bridge chip respectively, and have realized the electric pulse phase transition of germanium telluride nanowires on the suspension substrate for the first time. After the germanium telluride sample was transferred to the thermal bridge chip, the thermoelectric parameters of the sample were measured with the change of temperature. Firstly, by controlling the formation of different phases of nanowires by electric pulse, we investigate the different trends of conductivity of phase change germanium telluride nanowires with temperature, and further determine the different phases and transport mechanisms of nanowires. Secondly, we have measured the Seebeck coefficient of amorphous and crystalline germanium telluride nanowires. It is found that the variation and magnitude of Seebeck coefficient are similar even though there are several orders of magnitude difference in conductivity between the two phases. We speculate that the amorphous phase accounts for only a small part of the nanowires. Finally, we also measured the thermal conductivity of germanium telluride nanowires before and after they were transformed into dirty metal nanowires by electric pulse, because the size of nanowires was much larger than the average free path of phonon, and the thermal conductivity of nanowires was similar to that of bulk nanowires. For the first time, we found that the change trend of thermal conductivity before and after pulse is opposite to that of electrical conductivity before and after pulse, which is an improvement in the knowledge of thermal transport mechanism of germanium telluride nanowires. It also provides a great reference value for the control of electric pulse in various phase nanowires. The thermoelectric excellent values of the first amorphous germanium telluride nanowires have been obtained by synthesizing several test data. It is found that the thermoelectric parameters can be optimized simultaneously by the regulation of different nanowires. The in-situ control of the properties of nanowires is realized on the test hot bridge chip. At the same time, in the later work, we hope to realize the pulse control of each phase of the same sample on the chip, and to further characterize the sample by transmission electron microscope, surface electron dissipation spectrum and so on. The variation of thermal and electrical parameters is simulated and explained theoretically.
【學(xué)位授予單位】：南京大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：O614.431;TB383.1
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本文編號(hào)：1991293