【作者】 吴慕鸿；

【导师】 隋郁；

【作者基本信息】 哈尔滨工业大学 ， 凝聚态物理， 2008， 硕士

【摘要】 近年来,科学家发现当物质的大小处于纳米尺度(1-100 nm)时,物质具有明显不同于宏观材料和原子、分子的物理和化学特性,其凝聚态结构特征对由其组成的宏观材料的光、电、磁、热、力学性能等有着巨大的影响。而化学气相沉积(CVD ,chemical-vapor deposition)方法是目前人们制备纳米材料最有效的技术手段之一。铬氧化物(Cr 2 O3和CrO2)在紫外发光和自旋电子学等领域有着重要的应用价值。因此,采用化学气相沉积(CVD)方法制备Cr 2 O3和CrO2纳米材料并研究其光学性质和磁性对于开发纳米紫外发光器件和纳米自旋电子学器件有着很重要的现实意义。本论文利用化学气相沉积(CVD)方法,用自建的低压化学气相沉积(LPCVD)系统,采用三氧化铬(CrO3 )作为原料,来制备Cr 2 O3和CrO2纳米材料;在普通玻璃衬底、Si(111)衬底上成功地制备出Cr 2 O3多晶薄膜和微(纳)米柱,在自制的阳极氧化铝(AAO)模板中成功地制备出Cr 2 O3单晶纳米管;利用同样的方法,在普通玻璃衬底上成功地制备出CrO2多晶薄膜,在自制的阳极氧化铝(AAO)模板中成功地制备出CrO2非晶纳米管。对于Cr 2 O3多晶薄膜,我们研究了其结构,形貌和物性。在研究Cr 2 O3多晶薄膜的光学性质的过程中发现由Cr3+离子的3d3电子跳跃而导致Cr 2 O3多晶薄膜PL发射峰与一般的Cr 2 O3体材料的禁带对应的发射波长相比有了18 nm左右的蓝移。在Cr 2 O3微(纳)米柱的制备中,采用了金属薄膜作为催化剂。尝试了10 nm Ag膜、Ag纳米颗粒膜以及15 nm Au膜三种催化剂,发现10 nm Ag膜不适合作为催化剂来制备Cr 2 O3微(纳)米柱;Ag纳米颗粒膜作为催化剂成功地制备出直径在150 nm左右,长度大于1.5μm,轴径比大于10:1的具有良好形貌的Cr 2 O3纳米柱;采用15nm Au膜作为催化剂采用不同衬底和温度分别制备出具有不同直径、长度和轴径比的Cr 2 O3微米柱。采用自制的阳极氧化铝(AAO)模板作为模板,合成出管壁厚度在几纳米至十几纳米量级、直径60 nm左右、长度在10μm左右、轴径比大于100:1的沿[110]晶向生长的单晶Cr2O3纳米管。并且单晶Cr2 O3纳米管的直径和长度可以通过调节阳极氧化铝(AAO)模板的孔径与厚度来控制。初步研究了单晶Cr 2 O3纳米管的光学性质。在研究其光学性质时发现由于受纳米尺寸效应的影响,单晶Cr2O3纳米管比Cr2O3多晶薄膜的4A2g→4T1g的电子跃迁吸收峰蓝移了28 nm,达到了365 nm。对于CrO2多晶薄膜,我们研究了其结构,形貌和物性。寻找出了在低压化学气相沉积(LPCVD)系统中制备CrO2纳米材料的最佳生长条件。并初步研究了其磁性。采用自制的阳极氧化铝(AAO)模板作为模板,合成出管壁厚度在5 nm左右、直径60 nm左右、长度在10μm左右、轴径比大于100:1的非晶CrO2纳米管。并且非晶CrO2纳米管的直径、长度和管壁厚度可以通过调节阳极氧化铝(AAO)模板的孔径与厚度以及生长时的沉积时间来控制。并研究了非晶CrO2纳米管阵列的磁性。在研究其结构时发现非晶CrO2纳米管拥有一端开口一端封闭的桶状结构,其形状完全复制了模板孔洞的形状,实现了纳米尺度的微观铸造。在研究其磁性时发现非晶CrO2纳米管具有宏观的铁磁性。由于受纳米尺寸效应的影响,我们制备的非晶CrO2纳米管阵列虽然在形貌表征上看来完全是非晶的,但是与传统的各向同性的非晶材料不同,我们在非晶CrO2纳米管阵列的磁性时还发现其交换偏置效应具有各向异性的行为:对于我们的样品,在温度为10K的条件下,外磁场与纳米管平行时交换偏置场H E∥的大小为1.0584×10 4 A/m(≈133 Oe);磁场与纳米管垂直时交换偏置场H E⊥的大小为4.3768×10 3 A/m(≈55 Oe)。我们可以通过一个简单的理论模型对此做出进一步的解释。更多还原

【Abstract】 Recently, the scientists found that the physical and chemical properties of the materials are different from atom, molecule and macroscopical materials, when the size of the materials is in nanoscale (1~100 nm). The optical, electrical, magnetic, thermal and mechanical properties of the macroscopical materials, which were made up of the nanomaterials, are influenced enormously by the characteristic of their condensed structure. And the chemical-vapor deposition (CVD) method is one of the most impactful methods for growing the nanomaterials. Chromium oxide (Cr2O3 and CrO2) has high value in ultraviolet(UV) luminescence and spin electronics areas etc. for application. So growing Cr2O3 and CrO2 nanomaterials by CVD method and researching their optical and magnetic properties was significant for exploiting UV-luminescence devices and spin electronics devices.In this thesis, we growed Cr 2 O3 and CrO2 nanomaterials using the self-regulating low press CVD (LPCVD) system with CrO3 as a precursor by CVD method. According to this method, we attained different kinds of materials as following: the polycrystalline Cr2 O3 thin film, Cr 2 O3 nanoposts and microposts on the glass substrates or Si (111) substrates, and the single crystalline Cr 2 O3 nanotubes in the self-regulating anodic aluminum oxide (AAO) templates. And the polycrystalline CrO2 thin film on the glass substrates, and the amorphous CrO2 nanotubes in AAO templates were growed similarly.The structure, externality and physical properties of the polycrystalline Cr 2 O3 thin film were researched. When researching optical properties of the polycrystalline Cr 2 O3 thin film, we found that its photoluminescence (PL) apex moved to the blue side about 18 nm, compared with the macroscopical materials of Cr 2 O3 .During the growing of Cr 2 O3 nanoposts and microposts, the metal thin film was used as an activator. Silver thin film with 10 nm thick, silver nanoparticle thin film and gold thin film with 15 nm thick were tried as the activator. And we found that the silver thin film didn’t adapt to the activator for growthing Cr2 O3 nanoposts and microposts. Cr 2 O3 nanoposts with nice shape, which diameter is about 150 nm, length is longer than 1.5μm, and the rate of the length and the diameter is larger than 10:1, were seccessfuly growed by using silver nanoparticle thin film as the activator. For gold thin film with 15 nm thick as the activator, Cr2 O3 microposts with different diameter, length and rate of the length and the diameter were growed on different substrates with different growth temperature.Using the self-regulating AAO templates as the templates, single crystalline Cr 2 O3 nanotubes with growing along the [110] direction, which wall thickness is from several nanometers to duodenary nanometers, outer diameter is about 60 nm, length is about 10μm, and the rate of the length and the outer diameter is larger than 100:1, were seccessfuly growed. The length and outer diameter of the single crystalline Cr2O3 nanotubes can be easily and independently controlled by tuning the thickness and diameter of the AAO templates. The optical properties of the single crystalline Cr 2 O3 nanotubes were studied primarily. When researching the optical properties of the single crystalline Cr2 O3 nanotubes, we found that its UV-visible absorption spectrum apex, which was derived from the absorption of 4A2g→4T1g electron transition, moved to the blue side about 28 nm and thus reached 365 nm, compared with the polycrystalline Cr2 O3 thin film.The structure, externality and physical properties of the polycrystalline CrO2 thin film were also studied. Through various experiments on CrO2 nanomaterials, we acquired the best growth parameters in the LPCVD system.Using the self-regulating AAO templates as the templates, the amorphous CrO2 nanotubes, which wall thickness is about 5 nm, outer diameter is about 60nm, length is about 10μm, and the rate of the length and the outer diameter is larger than 100:1, were seccessfuly growed. The length, the outer diameter and the wall thickness of the amorphous CrO2 nanotubes can be easily and independently controlled by tuning the thickness and diameter of the AAO templates and the deposition time/rate of the layer. The magnetism of the amorphous CrO2 nanotubes was researched primarily. When researching the structure of the amorphous CrO2 nanotubes, we found that the amorphous CrO2 nanotubes had a tubby structure with one end closed and another opend. And the shape of the amorphous CrO2 nanotubes was completely replicated the shape of the AAO templates’hole, achieved the foundry of nanoscale. When researching the magnetism of the amorphous CrO2 nanotubes, we found that the amorphous CrO2 nanotubes had macroscopical ferromagnetism. Although the structure of the amorphous CrO2 nanotubes was completely amorphous, different from the isotropy of the ordinary amorphous materilas, the exchange bias field of the amorphous CrO2 nanotubes was found anisotropic behavior due to the influence of nanoscale effect. For our samples, with the applied magnetic field parallel to the nanotubes, the parallel exchange bias field HE∥=133 Oe; and with the applied magnetic field perpendicular to the nanotubes, the perpendicular exchange bias field HE⊥=55 Oe. It can be explained more clearly by a simple theoretical mode.更多还原