Teodorescu Valentin Serban, Ghica Cornel, Maraloiu Adrian Valentin, Vlaicu Mihai, Kuncser Andrei, Ciurea Magdalena Lidia, Stavarache Ionel, Lepadatu Ana M, Scarisoreanu Nicu Doinel, Andrei Andreea, Ion Valentin, Dinescu Maria
National Institute of Materials Physics, 105 bis Atomistilor Street, 077125 Bucharest-Magurele, Romania.
National Institute of Materials Physics, 105 bis Atomistilor Street, 077125 Bucharest-Magurele, Romania ; Academy of Romanian Scientists, Bucuresti 050094, Romania.
Beilstein J Nanotechnol. 2015 Apr 7;6:893-900. doi: 10.3762/bjnano.6.92. eCollection 2015.
Laser pulse processing of surfaces and thin films is a useful tool for amorphous thin films crystallization, surface nanostructuring, phase transformation and modification of physical properties of thin films. Here we show the effects of nanostructuring produced at the surface and under the surface of amorphous GeTiO films through laser pulses using fluences of 10-30 mJ/cm(2). The GeTiO films were obtained by RF magnetron sputtering with 50:50 initial atomic ratio of Ge:TiO2. Laser irradiation was performed by using the fourth harmonic (266 nm) of a Nd:YAG laser. The laser-induced nanostructuring results in two effects, the first one is the appearance of a wave-like topography at the film surface, with a periodicity of 200 nm and the second one is the structure modification of a layer under the film surface, at a depth that is related to the absorption length of the laser radiation. The periodicity of the wave-like relief is smaller than the laser wavelength. In the modified layer, the Ge atoms are segregated in spherical amorphous nanoparticles as a result of the fast diffusion of Ge atoms in the amorphous GeTiO matrix. The temperature estimation of the film surface during the laser pulses shows a maximum of about 500 °C, which is much lower than the melting temperature of the GeTiO matrix. GeO gas is formed at laser fluences higher than 20 mJ/cm(2) and produces nanovoids in the laser-modified layer at the film surface. A glass transition at low temperatures could happen in the amorphous GeTiO film, which explains the formation of the wave-like topography. The very high Ge diffusivity during the laser pulse action, which is characteristic for liquids, cannot be reached in a viscous matrix. Our experiments show that the diffusivity of atomic and molecular species such as Ge and GeO is very much enhanced in the presence of the laser pulse field. Consequently, the fast diffusion drives the formation of amorphous Ge nanoparticles through the segregation of Ge atoms in the GeTiO matrix. The nanostructuring effects induced by the laser irradiation can be used in functionalizing the surface of the films.
表面和薄膜的激光脉冲处理是用于非晶薄膜结晶、表面纳米结构化、相变以及薄膜物理性能改性的一种有用工具。在此，我们展示了通过使用10 - 30 mJ/cm²的能量密度的激光脉冲在非晶GeTiO薄膜表面和表面以下产生的纳米结构化效应。GeTiO薄膜通过射频磁控溅射获得，初始Ge:TiO₂原子比为50:50。激光辐照使用Nd:YAG激光的四倍频（266 nm）进行。激光诱导的纳米结构化产生两种效应，第一种是薄膜表面出现周期性为200 nm的波状形貌，第二种是薄膜表面以下一层的结构改性，其深度与激光辐射的吸收长度有关。波状起伏的周期小于激光波长。在改性层中，由于Ge原子在非晶GeTiO基体中的快速扩散，Ge原子偏析形成球形非晶纳米颗粒。激光脉冲期间薄膜表面的温度估计显示最高约500℃，这远低于GeTiO基体的熔化温度。当激光能量密度高于20 mJ/cm²时会形成GeO气体，并在薄膜表面的激光改性层中产生纳米空洞。非晶GeTiO薄膜在低温下可能发生玻璃化转变，这解释了波状形貌的形成。在粘性基体中无法达到激光脉冲作用期间液体所特有的非常高的Ge扩散率。我们的实验表明，在激光脉冲场存在的情况下，诸如Ge和GeO等原子和分子物种的扩散率大大提高。因此，快速扩散通过Ge原子在GeTiO基体中的偏析驱动非晶Ge纳米颗粒的形成。激光辐照诱导的纳米结构化效应可用于薄膜表面功能化。
