Costantini Jean-Marc, Miro Sandrine, Beuneu François, Toulemonde Marcel
CEA, DEN, SRMA, 91191 Gif-sur Yvette Cedex, France.
J Phys Condens Matter. 2015 Dec 16;27(49):496001. doi: 10.1088/0953-8984/27/49/496001. Epub 2015 Nov 18.
Pure and (Ca and Si)-substituted yttrium iron garnet (Y3Fe5O12 or YIG) epitaxial layers and amorphous films on gadolinium gallium garnet (Gd3Ga5O12, or GGG) single crystal substrates were irradiated by 50 MeV (32)Si and 50 MeV (or 60 MeV) (63)Cu ions for electronic stopping powers larger than the threshold value (~4 MeV μm(-1)) for amorphous track formation in YIG crystals. Conductivity data of crystalline samples in a broad ion fluence range (10(11)-10(16) cm(-2)) are modeled with a set of rate equations corresponding to the amorphization and recrystallization induced in ion tracks by electronic excitations. The data for amorphous layers confirm that a recrystallization process takes place above ~10(14) cm(-2). Cross sections for both processes deduced from this analysis are discussed in comparison to previous determinations with reference to the inelastic thermal-spike model of track formation. Micro-Raman spectroscopy was also used to follow the related structural modifications. Raman spectra show the progressive vanishing and randomization of crystal phonon modes in relation to the ion-induced damage. For crystalline samples irradiated at high fluences (⩾10(14) cm(-2)), only two prominent broad bands remain like for amorphous films, thereby reflecting the phonon density of states of the disordered solid, regardless of samples and irradiation conditions. The main band peaked at ~660 cm(-1) is assigned to vibration modes of randomized bonds in tetrahedral (FeO4) units.
在钆镓石榴石（Gd3Ga5O12，或GGG）单晶衬底上的纯的以及（钙和硅）取代的钇铁石榴石（Y3Fe5O12或YIG）外延层和非晶薄膜，被50 MeV的（32）Si离子以及50 MeV（或60 MeV）的（63）Cu离子辐照。这些离子的电子阻止本领大于YIG晶体中非晶径迹形成的阈值（约4 MeV μm-1）。在宽离子注量范围（1011 - 1016 cm-2）内，晶体样品的电导率数据用一组与电子激发在离子径迹中引起的非晶化和再结晶相对应的速率方程进行建模。非晶层的数据证实，在约1014 cm-2以上发生了再结晶过程。参照径迹形成的非弹性热尖峰模型，将从该分析中推导得到的这两个过程的截面与先前的测定结果进行了比较讨论。还使用了显微拉曼光谱来跟踪相关的结构变化。拉曼光谱显示，与离子诱导的损伤相关，晶体声子模式逐渐消失并随机化。对于高注量（⩾1014 cm-2）辐照的晶体样品，与非晶薄膜一样，仅剩下两个突出的宽带，从而反映了无序固体的声子态密度，而与样品和辐照条件无关。在约660 cm-1处出现峰值的主带被归因于四面体（FeO4）单元中随机键的振动模式。
