Growth of nanocomposite films: From dynamic roughening to dynamic smoothening

This paper reports several new findings on the breakdown of dynamic roughening in thin film growth. With increasing energy flux of concurrent ion impingement during pulsed DC sputtering, a transition from dynamic roughening to dynamic smoothening is observed in the growth behavior of TiC/a-C nanocomposite films. The nanocomposite films show a negative growth exponent and ultra-smoothness (RMS roughness ～0.2 nm at a film thickness of 1.5 μm). Based on high-resolution cross-sectional transmission electron microscopy observations we conclude that during growth an amorphous front layer of 2 nm covers the nanocomposite film and suppresses the influence of nanocrystallites on the roughness evolution of the nanocomposite films. We were able to predict the evolution of surface roughness based on a linear equation of surface growth which contains two diffusivity parameters that control the atomic mobility along the growing outer surface. The model is in good agreement with atomic force microscopy measurements of roughness evolution.     

The effect of thickness on the properties of Ti-doped ZnO films by simultaneous r.f. and d.c. magnetron sputtering

For Ti-doped ZnO (ZnO:Ti) films, the crystallinity and degree of orientation of the ZnO:Ti films were closely related to the film thickness. The crystal size increased with the increase of film thickness. With decreasing film thickness, there were more defects existing in the ZnO:Ti films and surface roughness decreased. The resistivity increased with the decrease of film thickness. The main scattering mechanism in the thin ZnO:Ti films was defect scattering. The transmission in UV region decreased strongly with the increase of film thickness. Such behavior was due to the films with different thickness showing different structural and electrical properties. As the results, film thickness affected the properties of ZnO:Ti films significantly.     

Reactive magnetron sputtering of indium tin oxide films on acrylics—Electrical resistivity and optical properties

The effects of processing parameters on the deposition rate lattice parameters, stoichiometric compositions, surface morphology, and bonding state of indium tin oxide (ITO) films on acrylics had been previously reported. This study was a continuation of the previous investigation and focused on the electrical resistivity and optical properties of ITO films. The electrical resistivity decreased and then increased with oxygen flow rate. This was due to the effects of oxygen vacancies and impurity scattering. The resistivity of ITO films decreased with the applied bias voltage and film thickness. The transmittance of visible light increased with the oxygen flow rate and decreased with film thickness. Films deposited at oxygen flow rates having low electrical resistivity also had higher infrared radiation (IR) reflectance.     

Characteristics of the polyaniline films vacuum deposited at a high background pressure

Polyaniline films with different thickness were deposited on unheated glass substrates by vacuum evaporating HCl-doped polyaniline pellets at a high background pressure. Micromorphological, compositional, structural and electrical properties of the films were studied by using field emission scanning electron microscopy, energy dispersive of X-ray spectroscopy, Fourier transform infrared spectroscope and sub-femtoamp source meter. The polyaniline films consist of a large number of flakes. Some flakes are perpendicular to the substrate and they are more in the thick film compared with the thin film. No chlorine is detected in the films. The aromatic structure of polyaniline is retained in all the polyaniline films. However, the polar structure of polyaniline is destroyed in the films. The polyaniline film is in a higher oxidation state compared with the HCl-doped polyaniline pellet. The conductivity of the polyaniline films ranges from 10⁻⁸ to 10⁻⁹ S/cm and is lower than that of the HCl-doped polyaniline pellet as the starting material. Besides, the conductivity decreases with increasing film thickness.     

Nanocrystalline–amorphous transitions in Al–Mo thin films: Bulk and surface evolution

We investigate the bulk and surface features of the crystalline–amorphous transitions in binary Al–Mo alloy thin films as a function of Mo composition using transmission electron microscopy, X-ray diffraction and atomic force microscopy analysis, as well as thermodynamic modeling. Of the alloys tested, the minimum in the root mean square (rms) surface roughness and correlation length occurs at the Al–32 at.% Mo composition, which corresponds to the maximum volume fraction of the amorphous phase and the minimum volume fraction of the body centered cubic nanocrystallites. The rms surface roughness of the 32 at.% Mo films is on the order of a single nanometer, compared with nearly 80 nm for the 50 at.% Mo film. A structure–zone map is constructed to relate the surface morphology of the films to their bulk microstructure. A thermodynamic model developed by Miedema and coworkers was used to predict the general trends observed in the microstructural evolution as a function of film composition.     

Relationship between structure and electrical resistivity in nano-structured copper-containing carbon films

The microstructure evolution of carbon/copper (C/Cu) films and its relation to the variation of film electrical resistivity has been studied. The films doped with copper in the range of 1.4-22.6 at.% Cu, were deposited by dc magnetron sputtering of composite graphite-copper target. The microstructure of films was studied by Raman spectroscopy and electron diffraction. The electrical resistivity was measured parallel and perpendicular to the substrate surface. The introducing of copper atoms into carbon matrix which consists of disordered graphite-like nano-clusters results in additional distortion of film microstructure at low copper content and some ordering of it at high copper content. At low copper concentrations the additional distortion of graphite-like clusters prevails over the input to electrical conductivity from copper atoms thus increasing the electrical resistivity of C/Cu films. At high copper concentrations the input to electrical conductivity is predominant and the film resistivity decreases.     

氩离子溅射刻蚀对Ti-Si-C纳米复合薄膜XPS分析的影响

通过中频非平衡磁控溅射Ti80Si20复合靶在氩气和甲烷混合气氛中沉积Ti-Si-C复合薄膜。采用X射线衍射仪、Raman光谱和X射线光电子能谱分析薄膜微结构。结果显示:制备的薄膜为非晶碳(a-C:Si:H)包裹约10 nm TiC晶粒的复合结构,氩离子溅射刻蚀对XPS分析结果有显著影响。随氩离子刻蚀溅射刻蚀时间增加,薄膜表面C、O原子含量明显降低,而Ti、Si原子含量增加。氩离子溅射刻蚀导致薄膜非晶碳相发生石墨化转变,即sp3C-C(H)/sp2C-C比率减小,同时,C-Ti*/C-Ti和C-(Ti+Ti*)/C-C强度比明显增加。     

Texture Development and Phase Transformation Behavior of Sputtered Ni-Ti Films

It is essential to identify and control the preferential orientation of Ni-Ti shape memory alloy (SMA) films since it is a crucial factor in determining the shape memory behavior. In the present work, in situ studies by synchrotron radiation scattering enabled to identify the different steps of the structural evolution of Ni-Ti films during co-sputtering deposition. For micro-electromechanical systems (MEMS) integration, there is a need for an electrically and thermally insulating or sacrificial layer. Widening the scope of previous experiments concerning the influence of the deposition parameters on the structure of the Ni-Ti films, the incorporation of a TiN buffer layer has been tested. Here, it is established a relationship between the TiN substrates and Ni-Ti texture development (B2 phase). Ni-Ti films mainly containing grains with (110) or (211) planes of the B2 phase parallel to the film surface could be produced using TiN buffer layers with distinct thickness values. The electrical resistivity measurements performed during temperature cycling have shown that the crystallographic orientations of the Ni-Ti films influence their phase transformation characteristics. The resistivity increase during R-phase transformation, especially visible on cooling, is higher for Ni-Ti films with a higher fraction of grains of the B2 phase with (211) parallel to the film surface.     

The effect of substrate bias voltage on PbTe films deposited by magnetron sputtering

The PbTe films were deposited onto ITO glass substrate by radio frequency magnetron sputtering. Effect of external direct current electrical field applied between substrate and target on the quality of films was investigated. Stylus surface profile, X-ray diffraction (XRD), atomic force microscope (AFM) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the films. The film thickness was measured by a conventional stylus surface profile. The crystal structure and lattice parameters of films were determined by using XRD. The surface morphology of the films was measured by AFM. The absorption coefficients and optical band gaps of films were found from FTIR. The sheet resistance of the samples was measured with a four-point probe and the resistivity of the film was calculated. All the obtained films were highly textured with a strong (2 0 0) orientation. With increasing bias voltage to −30 V, the property of crystal structure, surface morphology and absorption coefficients and resistivity were improved. However, further increase of substrate bias leads to transformation of the property.     

单晶锗薄膜热导率的分子动力学模拟

采用非平衡分子动力学(NEMD)方法研究平均温度为400 K,厚度d=2.8288～11.315 nm的单晶锗薄膜法向的热导率.模拟结果表明,单晶锗薄膜热导率随薄膜厚度的增加以接近线性的规律增加,其数值明显低于同等温度下体态锗的试验值.当薄膜厚度一定时,单晶锗薄膜的热导率随温度增加变化幅度很小,与同体态锗热导率随温度的变化规律相比表现出明显的尺寸效应.     

Effects of deposition parameters on microstructure and thermal conductivity of diamond films deposited by DC arc plasma jet chemical vapor deposition

The uniform diamond films with 60 mm in diameter were deposited by improved DC arc plasma jet chemical vapor deposition technique. The structure of the film was characterized by scanning electronic microcopy(SEM) and laser Raman spectrometry. The thermal conductivity was measured by a photo thermal deflection technique. The effects of main deposition parameters on microstructure and thermal conductivity of the films were investigated. The results show that high thermal conductivity, 10.0 W/(K-cm), can be obtained at a CH4 concentration of 1.5% (volume fraction) and the substrate temperatures of 880-920 ℃ due to the high density and high purity of the film. A low pressure difference between nozzle and vacuum chamber is also beneficial to the high thermal conductivity.     

Numerical analysis on thickness effect of magnetic thin films on conduction noise absorption in microstrip line

Noise absorbing properties of two kinds of magnetic thin films (one is electrically conductive Co-Zr-O granular thin film and the other is Ni-Zn ferrite thin film with high electrical resistivity) are analyzed by the finite element method (FEM) with various film thicknesses. For the Ni-Zn ferrite film with high electrical resistivity (～2 × 10 ² Ωm), a low reflection parameter (S₁₁) value is predicted, and the value does not significantly change with increased film thickness up to 10 μm. However, the transmission parameter (S₂₁) is reduced with increased film thickness due to increased power absorption by magnetic loss. For the Co-Zr-O thin films with low electrical resistivity (～1.6 × 10^?5 Ωm), however, reflection signal is increased with increased film thickness due to diminished sheet resistance of the thin film. Transmission loss is not very sensitive to the thickness of the conductive film. Large power absorption is, therefore, predicted for conductive film of smaller thickness. It is concluded that film thickness is an important control parameter for the achievement of a highly absorptive thin film with increased electrical conductivity.     

Preparation and properties of CdS thin films grown by ILGAR method

CdS thin films were deposited by the ion layer gas reaction (ILGAR) method. Structural, chemical, topographical development as well as optical and electrical properties of as-deposited and annealed thin films were investigated by XRD,SEM, XPS, AFM and UV-VIS. The results showed that the thin films are uniform, compact and good in adhesion to the substrates, and the growth of the films is 2.8 nm/cycle. The evolution of structure undergoes from the cubic structure to the hexagonal one with a preferred orientation along the (002) plane after annealing at 673 K. An amount of C, O and C1 impudries can be reduced by increasing the drying temperature or by annealing in N2 atmosphere. It was found that the band gap of the CdS films shifts to higher wavelength after annealing or increasing film thickness. The electrical resistivity decreases with increasing annealing temperature and film thickness.     

Role of mechanical strain on thermal conductivity of nanoscale aluminum films

Thin film components of conventional and flexible solid-state devices experience mechanical strain during fabrication and operation. At the bulk scale, small values of strain do not affect thermal conductivity, but this may not true for grain sizes comparable with the electron and phonon mean free paths and for higher volume fraction of grain boundaries. To investigate this hypothesis, thermal and electrical conductivity of nominally 125-nm-thick aluminum films (average grain size 50 nm) were measured as functions of tensile thermo-mechanical strain, using a modified version of the 3-ω technique. Experimental results show pronounced strain–thermal conductivity coupling, with ～50% reduction in thermal conductivity at ～0.25% strain. The analysis shows that mechanical strain decreases the mean free path of the thermal conduction electrons, primarily through enhanced scattering at the moving grain boundaries. This conclusion is supported by similar effects of mechanical loading observed on the electrical conduction in the nanoscale aluminum specimens.     

RF magnetron sputtered ITO:Zr thin films for the high efficiency a-Si:H/c-Si heterojunction solar cells

ITO and ITO:Zr films with various thicknesses were prepared on glass substrates by RF magnetron sputtering. We observed a decrease in sheet resistance with increasing film thickness that in good agreement with Fuchs-Sondheimer theory. The ITO films doped with ZrO₂ (～0.2 wt%) showed improvement in some of the electrical and optical properties of ITO films. The surface roughness of ITO:Zr films increased with increasing film thickness. ITO:Zr films with thickness of 120 nm showed highest work function of 5.13 eV, as estimated from XPS data. The ITO:Zr films were employed as front electrodes in HIT solar cells; the best device performance was found to be: V_oc = 710 mV, J_sc = 34.44 mA/cm², FF = 74.8%, η = 18.30% at a thickness of 120 nm. A maximum quantum efficiency (QE) of 89% was recorded for HIT solar cells at a wavelength of 700 nm for 120 nm thick ITO:Zr films.     

Effect of substrate bias in amorphous carbon films having embedded nanocrystallites

The effect of substrate bias on the structural, morphological, electrical and mechanical properties of amorphous carbon (a―C) films having embedded nanocrystallites deposited by filtered cathodic jet carbon arc technique has been investigated. X-ray diffraction exhibits predominantly an amorphous nature of the film. High resolution transmission electron microscope investigations reveal largely an amorphous structure. However, an ultra-fine nanograined microstructure with the average grain size between 20 and 50 nm was observed throughout the entire film and the majority of the individual grains were single crystallites with the preferred interplanar spacing of about 0.2 nm. All the parameters evaluated were seen to depend strongly on the negative substrate bias and exhibit maxima or minima in the properties of the films deposited at − 150 V substrate bias. These a-C films having embedded nanocrystallites act as hard coating materials.     

In-situ polymerized polyaniline films

Polyaniline hydrochloride was prepared by the oxidation of aniline hydrochloride with ammonium peroxodisulfate in dilute hydrochloric acid. The polyaniline films were produced during the polymerization on the glass surfaces immersed in the reaction mixture. The surface composition of the film was characterized by X-ray photoelectron spectroscopy. The thickness of the films d_f was determined by the optical interferometry and linked to their optical absorption at the wavelength 400 nm, A₄₀₀=(5.4±0.2)×10⁻³ d_f (in nm). The effect of the polymerization temperature and concentration of the reactants on the thickness and electrical properties of polyaniline films are reported. The electrical conductivity of the films and of bulk polyaniline produced simultaneously is about the same. A relation between the thickness of the films and the molecular weight of the produced polyaniline was found.     

Bi2-xSbxTe3热电薄膜的电化学沉积及表征

采用电化学沉积法,在ITO导电玻璃及钛片上沉积Bi2-xSbxTe3热电薄膜。采用循环伏安、SEM、XRD、EDX等技术分别对电化学沉积过程和薄膜的形貌、相结构、组成进行研究,并对其室温时的热电性能进行测试。结果表明,在含有Bi3＋、HTeO2+和SbO+的硝酸溶液中,采用控电位沉积模式,可以实现铋、锑、碲三元共沉积,得到Bi2-xSbxTe3薄膜。薄膜热处理前用冷等静压处理可以提高薄膜的密实度和平整度,并有利于热电性能的提高。     

ZnO:Si透明导电薄膜厚度对其光电性能的影响

目的研究ZnO∶Si薄膜厚度对其生长速率、结晶度、光透率和电阻率的影响。方法用直流磁控溅射系统在玻璃基片上沉积不同的时间,获得5个厚度不同的ZnO∶Si薄膜样品,对比研究了其薄膜生长取向和结构特性、微观形貌、电学参数及透过率曲线。结果 5个ZnO∶Si薄膜样品都为多晶膜,具有单一的(002)衍射峰,沿垂直于基片的c轴方向择优生长。当薄膜厚度从207.6 nm增加到436.1 nm时,薄膜的晶粒尺寸增大,晶化程度提高,电阻率变小;膜厚增至497.8 nm时,薄膜的晶化程度反而降低,电阻率增加。在可见光范围内,5个薄膜样品的平均透过率都高于91.7%。结论膜厚对ZnO∶Si薄膜的电学性能有较大影响,对光学性能的影响则较小。     

Nanocrystalline p-type-cuprous oxide thin films by room temperature chemical bath deposition method

Nanocrystalline cuprous oxide (Cu₂O) thin films were synthesized on amorphous glass substrate by using simple room temperature chemical route namely, chemical bath deposition (CBD) method. The deposition kinetics played important role to get good quality nanocrystalline films with uniform thickness. The structural, surface morphological, optical and electrical properties of the films were investigated. Crystallization and growth processes obtained micro-spherical shaped grains of Cu₂O due to agglomeration of smaller nanoparticles. An optical and electrical characterization was performed to study the optical band gap and type of electrical conductivity of the film.