Nanohole 3D-size tailoring through polystyrene bead combustion during thin film deposition

A novel approach is presented for nanohole 3D-size tailoring. The process starts with a monolayer of polystyrene (PS) beads spun coat on silicon wafer as a template. The holes can be directly prepared through combustion of PS beads by oxygen plasma during metal or oxide thin film deposition. The incoming particles are prevented from adhering on PS beads by H₂O and CO₂ generated from the combustion of the PS beads. The hole depth generally depends on the film thickness. The hole diameter can be tailored by the PS bead size, film deposition rate, and also the combustion speed of the PS beads. In this work, a series of holes with depth of 4-24 nm and diameter of 10-36 nm has been successfully prepared. The hole wall materials can be selected from metals such as Au or Pt and oxides such as SiO₂ or Al₂O₃. These templates could be suitable for the preparation and characterization of novel nanodevices based on single quantum dots or single molecules, and could be extended to the studies of a wide range of coating materials and substrates with controlled hole depth and diameters.     

Nanocrystalline formation and optical properties of germanium thin films prepared by physical vapor deposition

Amorphous and nanocrystalline germanium thin films were prepared on glass substrates by physical vapor deposition (PVD). The influence of thermal annealing on the characteristics of the Ge thin films has been investigated. X-ray diffraction (XRD) and SEM show amorphous structure of films deposited at room temperature. After thermal annealing, the crystallinity was improved when the annealing temperature increases. The Ge thin films annealed at different temperatures in air were nanocrystalline, having the face-centered cubic structure with preferred orientation along the 〈1 1 1〉 direction. The nanostructural parameters have been evaluated by using a single-order Voigt profile analysis. Moreover, the analysis of the optical transmission and reflection behavior was carried out. The values of direct and indirect band gap energies for amorphous and nanocrystalline phases are 0.86±0.02, 0.65±0.02 and 0.79±0.02, 0.61±0.02 eV, respectively. In addition, the complex optical functions for the wavelength range 600-2200 nm are reported. The refractive index of the nanocrystalline phase drops from 4.80±0.03 to 2.04±0.02, and amorphous phase changes from 5.18±0.03 to 2.42±0.02 for the whole wavelength range. The dielectric functions ε₁ and ε₂ of the deposited films were recorded as a function of wavelength within the range from 600 to 2200 nm.     

分步法高速沉积微晶硅薄膜

为提高微晶硅薄膜的纵向结晶性能, 在甚高频等离子体增强化学气相沉积技术的基础上, 采用过渡参数缓变和两步法相结合的方法在普通玻璃衬底上高速沉积薄膜. 当功率密度为2.1 W/cm², 硅烷浓度在6%和9.6%之间变化时, 从薄膜方向和玻璃方向测算的Raman晶化率的差异维持在2%以内. 硅烷浓度为9.6%时, 薄膜沉积速率可达3.43 nm/s, 从薄膜方向和玻璃方向测算的Raman晶化率分别为50%和48%, 差异的相对值仅为4.0%. 合理控制过渡阶段的参数变化, 可使两个方向的Raman晶化率差值下降到一个百分点. 表明采用新方法制备薄膜, 不仅可以抑制非晶孵化层的形成, 改善微晶硅薄膜的纵向结构, 还为制备优质薄膜提供了较宽的参数变化空间. 关键词： 微晶硅薄膜 非晶孵化层 高速沉积 甚高频等离子体增强化学气相沉积     

Atomistic study of deposition process of Al thin film on Cu substrate

In this paper we report molecular dynamics based atomistic simulations of deposition process of Al atoms onto Cu substrate and following nanoindentation process on that nanostructured material. Effects of incident energy on the morphology of deposited thin film and mechanical property of this nanostructured material are emphasized. The results reveal that the morphology of growing film is layer-by-layer-like at incident energy of 0.1-10 eV. The epitaxy mode of film growth is observed at incident energy below 1 eV, but film-mixing mode commences when incident energy increase to 10 eV accompanying with increased disorder of film structure, which improves quality of deposited thin film. Following indentation studies indicate deposited thin films pose lower stiffness than single crystal Al due to considerable amount of defects existed in them, but Cu substrate is strengthened by the interface generated from lattice mismatch between deposited Al thin film and Cu substrate.     

Tunable laser thin film interrogation

Film thickness is not only a crucial parameter in producing processes, such as semiconductor and optics production, but also a monitored variable in chemistry and biology, for example for tissue microscopy. Many working principles have been demonstrated and are in use in different fields due to their different limitations (observation film thickness, accuracy, measurement speed, etc.). One of these working principles is thin film reflectometry (TFR). One method is based on a laser source and monitors the reflected intensity over growing film time. Another one employs a spectrally broad light source and measures the reflected intensity using a spectrometer. We introduce and demonstrate a measurement system based on a tunable laser stage. There are several different setups for laser wavelength tuning. One of the most promising solutions is based on monolithic laser diodes. Rapid tuning of the lasers wavelength is crucial for achieving high measurement rates. Monolithic laser diodes offer highest tuning rates and hence high performance. On the other hand, mechanically tunable lasers show broadband spectra that result in higher thickness accuracy in this particular application. Hence, we show a comparison of thin film measurements with a monolithic and a mechanically tunable laser source. This comparison shows that the measurement accuracy of the monolithic laser diode can compete with mechanical tuning. Furthermore, it is a promising approach when measurement tuning speed is an issue.     

Determination of diffusion profiles in thin film couples by means of x-ray-diffraction

An x-ray method for the determination of concentration profiles in thin film diffusion couples is presented. This method is based on the theory of Fourier analysis of x-ray diffraction profiles which is generalized to polycrystalline samples showing nonuniform lattice parameter. A Fourier synthesis of the concentration spectrum is possible when the influences of the particle size and the strain in the sample as well as the instrumental function are eliminated from the measured diffraction profile. This can be done by means of reference profiles obtained from layers of the diffusion components. Absorption of the radiation in the sample is negligible when diffusion couples of symmetrical sandwich structure are used. The method is tested experimentally in the system Au-Cu.     

Improvement of electrical characteristics of InGaZnO thin film transistors by using HMDSO/O2 plasma deposited SiOCH buffer layer

In this work, we present the performance improved InGaZnO thin film transistors by inserting low temperature processed 10 nm thick SiOCH buffer layers between SiN_x insulator and InGaZnO channel layer. The influences of oxygen flow rate during the deposition of SiOCH buffer layer have been intensively investigated. Basing on the analysis of hall effect measurement and Fourier transform infrared spectrum, the SiOCH buffer layer can effectively increase the carrier concentration of the channel layer by the hydrogen doping due to re-sputtering and diffusion effect. The InGaZnO thin film transistor with buffer layer exhibits an enhanced performance with mobility of 13.09 cm²/vs, threshold voltage of −0.55 V and I_on/I_off over 10⁶.     

The kinetic process of non-smooth substrate thin film growth via parallel Monte Carlo method

A Monte Carlo simulation model of thin film growth based on parallel algorithm is presented. Non-smooth substrate with special defect mode is introduced in such a model. The method of regionalizing is used to divide the substrate into sub-regions. This method is supposed to be modulated according to the defect mode. The effects of surface defect mode and substrate temperature, such as the nucleation ratio and the average island size, are studied through parallel Monte Carlo method. The kinetic process of thin film growth in the defect mode is also discussed. Results show that surface defect mode contributes to crystal nucleation. Analyzing parallel simulation results we find that density defect points, substrate temperature and the number of processors contribute decisively to the parallel efficiency and speedup. According to defect mode we can obtain large grain size more feasibly and the parallel algorithm of this model can guide the non-smooth substrate simulation work.     

Excimer laser deposition of thin amorphous carbon films

A new carbon film deposition technique, based upon excimer laser vaporization of graphite in a flowing gas system has been developed. The low temperature vapor (LTV) technique alleviates high temperatures occurring in most other deposition methods. In this technique the UV laser ablation occurs in an inert flowing gas atmosphere. Atoms and molecules evaporated from graphite are cooled by gas entrainment before condensing on a substrate. The resulting films of amorphous carbon or hydrogenated amorphous carbon are free from strain. Measurement of the optical band gap of these films shows that E_g can be controlled by the hydrogen content of the carrier gas.     

等离子增强原子层沉积低温生长AlN薄膜

采用等离子增强原子层沉积技术在单晶硅基体上成功制备了AlN晶态薄膜, 利用椭圆偏振仪、原子力显微镜、小角掠射X射线衍射仪、高分辨透射电子显微镜、 X射线光电子能谱仪对样品的生长速率、表面形貌、晶体结构、薄膜成分进行了表征和分析, 结果表明, 采用等离子增强原子层沉积制备AlN晶态薄膜的最低温度为200 ℃, 薄膜表面平整光滑, 具有六方纤锌矿结构与(100)择优取向, Al_2p与N_1S的特征峰分别为74.1 eV与397.0 eV, 薄膜中Al元素与N元素以Al-N键相结合, 且成分均匀性良好. 关键词： 氮化铝 等离子增强原子层沉积 低温生长 晶态薄膜     

SILAR deposited Bi2S3 thin film towards electrochemical supercapacitor

Bi₂S₃ thin film electrode has been synthesized by simple and low cost successive ionic layer adsorption and reaction (SILAR) method on stainless steel (SS) substrate at room temperature. The formation of interconnected nanoparticles with nanoporous surface morphology has been achieved and which is favourable to the supercapacitor applications. Electrochemical supercapacitive performance of Bi₂S₃ thin film electrode has been performed through cyclic voltammetry, charge-discharge and stability studies in aqueous Na₂SO₄ electrolyte. The Bi₂S₃ thin film electrode exhibits the specific capacitance of 289 Fg⁻¹ at 5 mVs⁻¹ scan rate in 1 M Na₂SO₄ electrolyte.     

Growth and characterization of thin ZnO films deposited on glass substrates by electrodeposition technique

Electrodeposition technique was used in order to produce nanometric zinc oxide films on glass insulating substrates. The effect of electrolyte concentration and applied current density on the formation and growth of electrodeposited Zn thin films in aqueous solutions of ZnSO₄ were studied. After a thermal oxidation, a characterization of the structural morphology of the films deposited was carried out by optical microscopy (OM), atomic force microscopy (AFM), scanning electron microscopy (SEM) and by grazing incidence X-rays diffraction (GIXD). These characterization techniques show that the grains size of the films after oxidation at temperature 450 °C is between 5 and 15 nm, as well as the structure is polycrystalline nature with several orientations. UV/vis spectrophotometry confirms that it is possible to obtain transparent good ZnO films with an average transmittance of approximately 80% within the visible wavelength region, as well as the optical gap of obtained ZnO films is 3.17 eV.     

Preparation of hard magnetic materials in thin film form

We report on the preparation, by means of pulsed laser ablation deposition, of trilayers of nominal composition Cr/SmCo₅/Cr//Si with thicknesses in the order of 250/240/125 nm, respectively. According to the results of the structural, chemical and magnetic characterizations performed in our as-deposited samples, the Sm–Co layer was structurally amorphous, exhibited abrupt compositional interfaces with the capping and buffering layers, and coercivities of a few hundreds of Oe. Magnetic hardness was developed upon submitting the samples to current anneals under vacuum at temperatures in the range of 540–670 °C. The hardening process was followed in detail by correlating the phase distribution, the nature of the interlayer atomic diffusion processes, the occurrence of textures and the temperature dependence of the coercive force. From our results we conclude about (i) the occurrence of a large degree of Co diffusion/segregation, which results in the detection, from the diffraction and magnetometric results, of the presence of CoCr alloys in the treated samples, and (ii) the close correlation, evidenced from the fits of the temperature dependence of the coercive force to the micromagnetic model, between the coercivity optimization and the crystallinity enhancement of the SmCo₅ grains.     

Metal thin film ablation with femtosecond pulsed laser

Micromachining thin metal films coated on glass are widely used to repair semiconductor masks and to fabricate optoelectrical and MEMS devices. The interaction of lasers and materials must be understood in order to achieve efficient micromachining. This work investigates the morphology of thin metal films after machining with femtosecond laser ablation using about 1 μm diameter laser beam. The effect of the film thickness on the results is analyzed by comparing experimental images with data obtained using a two-temperature heat transfer model. The experiment was conducted using a high numerical aperture objective lens and a temporal pulse width of 220 fs on 200- and 500-nm-thick chromium films. The resulting surface morphology after machining was due to the thermal incubation effect, low thermal diffusivity of the glass substrate, and thermodynamic flow of the metal induced by volumetric evaporation. A Fraunhofer diffraction pattern was found in the 500-nm-thick film, and a ripple parallel to the direction of the laser light was observed after a few multiple laser shots. These results are useful for applications requiring micro- or nano-sized machining.     

Nanostructured cathode thin films with vertically-aligned nanopores for thin film SOFC and their characteristics

Nanostructured cathode thin films with vertically-aligned nanopores (VANP) were processed using a pulsed laser deposition technique (PLD). These VANP structures enhance the oxygen-gas phase diffusivity, thus improve the overall thin film SOFC performance. La_0.5Sr_0.5CoO₃ (LSCO) and La_0.4Sr_0.6Co_0.8Fe_0.2O₃ (LSCFO) were deposited on various substrates (YSZ, Si and pressed Ce_0.9Gd_0.1O_1.95 disks). Microstructures and properties of the nanostructured cathodes were characterized by TEM, HRTEM, SEM and electrochemical measurements. Additionally these well-aligned VANP structures relieve or partially relieve the internal thermal stress and lattice strain caused by the differences of thermal expansion coefficients and lattice mismatch between the electrode and the electrolyte.     

Stabilization of organic thin film transistors by ion implantation

We report on the effects of low energy ion implantation (N and Ne) in the reduction and control of the degradation of pentacene organic thin film transistors (OTFTs) due to the exposure to atmosphere (i.e. oxygen and water). We have observed that a controlled damage depth distribution preserves the functionality of the devices, even if ion implantation induces significant molecular structure modifications, in particular a combination of dehydrogenation and carbonification effects. No relevant changes in the pentacene thin film thickness have been observed. The two major transport parameters that characterize OTFT performance are the carrier mobility and the threshold voltage. We have monitored the effectiveness of this process in stabilizing the device by monitoring the carrier mobility and the threshold voltage over a long time (over 2000 h). Finally, we have assessed by depth resolved X-ray Photoemission Spectroscopy analyses that, by selectively implanting with ions that can react with the hydrocarbon matrix (e.g. N⁺), it is possible to locally modify the charge distribution within the organic layer.     

Room-temperature flexible thin film transistor with high mobility

We report a room-temperature and high-mobility InGaZnO thin-film transistor on flexible substrate. To gain both high gate capacitance and low leakage current, we adopt stacked dielectric of Y₂O₃/TiO₂/Y₂O₃. This flexible IGZO TFT shows a low threshold voltage of 0.45 V, a small sub-threshold swing of 0.16 V/decade and very high field-effect mobility of 40 cm²/V. Such good performance is mainly contributed by improved gate stack structure and thickness modulation of IGZO channel that reduce the interface trap density without apparent mobility degradation.     

Nano-structured Fe thin film deposition using plasma focus device

This paper reports the deposition of nano-structured Fe thin films using 3.3 kJ Mather-type plasma focus. The conventional hollow copper anode was replaced by anode fitted with solid Fe top and the deposition was done using different numbers of deposition shots at two different angular positions. Scanning Electron Microscopy shows that the size of nano-phase agglomerate is smaller when the sample is deposited using either lesser number of deposition shots or at higher angular position with respect to anode axis. X-ray Diffraction shows that crystal structure characteristics change with increase in number of deposition shots. Measurements of magnetic properties using Vibrating Sample Magnetometer identify intermediate magnetization and coercivity in Fe thin films deposited at smaller angular position with respect to anode axis. It is concluded that the morphological, structural and magnetic characteristics of Fe thin films deposited using plasma focus device depend not only on the number of focus deposition shots but also on the angular position of the sample.     

ZnS thin films grown by atomic layer deposition on GaAs and HgCdTe substrates at very low temperature

ZnS films grown on GaAs and HgCdTe substrates by atomic layer deposition (ALD) under very low temperature were investigated in this work. ZnS films were grown under several temperatures lower than 140 °C. The properties of the films were investigated with high-resolution X-ray diffraction (HRXRD), scanning electron microscope (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The results showed the ZnS films were polycrystalline. The growth rate monotonically decreased with temperature, as well as the root mean square (r.m.s) roughness measured by AFM. XPS measurement revealed the films were stoichiometric in Zn and S.     

DNA thin film coated optical fiber biosensor

We present a simple but highly sensitive biotinylated DNA double crossover thin film coated fiber optic reflectance biosensor (DTF FORS) for the detection of streptavidin aerosols as a building block towards sensing bio-aerosols. The DNA double crossover lattice with biotin was dropped on the polymer optical fiber end face to prepare DNA Thin Film. The streptavidin aerosols were prepared using conventional aerosol technology. The DTF FORS response to streptavidin aerosol was few seconds and the sensor repeatability for air and streptavidin aerosol was found to be excellent. The presented FORS sensing approach, where the film can be changed on the end face of the optical fiber, is expected to detect atmospheric bio-aerosols with great sensitivity and effective specificity.