臺灣博碩士論文加值系統

測量用直徑為250nm和210nm 二氧化矽小球包圍住金屬鎵在轉變為超導態時的磁性變化。在樣品中我們發現鎵金屬只填滿一半的空隙，由於磁滯曲線顯現良好的可逆性，以及磁冷和零磁冷磁強隨溫度的變化幾乎重合，在空隙中的金屬鎵可被視為分離的鎵粒子。直接測量此奈米尺度下鎵粒子的超導相變，可以發現奈米粒子鎵中具有 �� 相（��-Ga）和少量的 �� 相（��-Ga）或者是 �� 相（��-Ga）。測量這些奈米粒子鎵的相變臨界溫度(Tc)分別是6.1、7.0和7.8K，與塊狀的鎵中所看到的 �牷A�� 和 �� 相的相變臨界溫度完全相同。這些被限制在球與球空隙之間鎵粒子超導臨界磁場隨溫度的變化，可以用Hc2 = H0 [1- (T/Tc)�娭來模合，其模合後的參數 �� 趨近於 2.9（�� ~ 2.9）。且其H0值分別為3.4 和3.6 kOe，這些磁場約為塊狀鎵金屬中 �� 相（��-Ga）高臨界磁場的六倍。在低磁場中，當溫度在2K附近時，用零磁場降溫冷卻升溫測量（zero-field-cooled ；ZFC）法所量得的磁化強度和交流磁化率的實部（�荂�(T)），隨溫度的減少，磁化強度急劇下降，顯現明確的反磁現像，這種行為可能是由一個臨界溫度約為 2 K的新超導相所導致的。

The superconductivity of gallium in a compact package of equal-size silica spheres with diameters 210 and 250 nm has been investigated by magnetic measurements. Since only half of the cavities between the touching spheres are filled with gallium, the gallium grains in cavities are well separated and apt to be considered as isolated particles. A direct measurement of superconducting transitions indicated that these gallium nanoparticles are composed of ��-Ga with small amount of ��-Ga or ��-Ga. The Tc of ��-Ga, ��-Ga, and ��-Ga in these nanoparticles are still 6.1, 7.0, and 7.8 K respectively, which is exactly the same as those in a bulk gallium. The upper critical fields of these gallium grains in opals can be described as Hc2 = H0 [1- (T/Tc)�娭 with �� ~ 2.9. The H0 are 3.4 and 3.6 kOe for gallium in 210 and 250 nm samples respectively, which is nearly six times as large as the critical field (560 Oe) of bulk ��-Ga. The zero-field-cooled magnetization MZFC(T) and the real components of ac susceptibilities �荂�(T) drop significantly at ~2 K, which might relate to a new superconducting phase with critical temperature at ~ 2 K.

目錄
摘要I
目錄IV
第一章 大綱.....................................1
第二章 實驗方法.................................3
2-1 樣本製作....................................3
2-2 兩個計算孔隙填充率的方式....................5
2-3 兩個樣品體積計算方式........................9
2-4 磁化量的測量方式............................11
2-5 磁場及磁化率之單位..........................12
第三章 理論介紹與實驗儀器介紹...................13
3-1交流磁化率實驗的原理與裝置...................13
3-2交流磁化率理論...............................19
3-3超導熱力學理論...............................21
第四章 實驗結果與討論...........................26
第五章 結論.....................................48
參考文獻........................................49
自述............................................51

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