TiO薄膜的制备及电输运性质

Preparation and electrical transport properties of TiO thin films

利用磁控溅射技术,通过改变氧分压在MgO (001)单晶基片上外延生长了一系列TiO薄膜,并对薄膜的结构、价态和电输运性质进行了系统研究. X射线衍射结果表明,所制备的薄膜具有岩盐结构,沿[001]晶向外延生长. X射线光电子能谱结果表明,薄膜中Ti元素主要以二价形式存在.所有样品均具有负的电阻温度系数,高氧分压下制备的薄膜表现出绝缘体的导电性质,低温下电阻与温度的关系遵从变程跳跃导电规律.低氧分压下制备的薄膜具有金属导电性质,并具有超导电性,超导转变温度最高可达3.05 K.所有样品均具有较高的载流子浓度,随着氧分压的降低,薄膜的载流子类型由电子主导转变为空穴主导.氧含量的降低可能加强了TiO中Ti—Ti键的作用,从而使低氧分压下制备的样品显现出与金属Ti相似的电输运性质,薄膜超导转变温度的提升可能与晶体结构或电子结构突变相关联.

Titanium monoxide has attracted great attention due to its unique superconducting characteristics and potential applications in microelectronics.In this work,a series of TiO thin films are prepared at room temperature by using the radio frequency magnetron sputtering method through changing the oxygen partial pressures.The crystal structures,valences of the elements,and electrical transport properties of the films are investigated systematically.X-ray diffraction results indicate that the films are epitaxially grown on MgO single crystal substrates along the[001]direction.After the surface of the TiO film is treated by ion etching,it is found that the Ti element mainly exists in a divalent form.For all films,the temperature coefficients of resistance are negative above superconducting transition temperature Tc.The films prepared under high oxygen partial pressures reveal insulator characteristics,and the temperature dependence of resistivity obeys the Motttype variable-range-hopping law in low temperature regime.The films prepared under low oxygen partial pressures exhibit metallic properties,and enter into a superconducting state at low temperature.The superconducting transition temperature Tc in our film can be as high as 3.05 K.The carrier concentrations of the films are in the vicinity of~2.0×10^(22) cm^(-3),which is comparable to those for the typical metals.Interestingly,it is found that the main species of the charge carriers in the films transforms from electrons to holes with the oxygen partial pressure decreasing.The crossover of the species of the charge carriers could related to the changing of energy-band structure with the oxygen content in TiO film.