Surface engineering of synthetic nanopores by atomic layer deposition and their applications

In the past decade, nanopores have been developed extensively for various potential applications, and their performance greatly depends on the surface properties of the nanopores. Atomic layer deposition （ALD） is a new technology for depositing thin films, which has been rapidly developed from a niche technology to an established method. ALD films can cover the surface in confined regions even in nanoscale conformally, thus it is proved to be a powerful tool to modify the surface of the synthetic nanopores and also to fabricate complex nanopores. This review gives a brief introduction on nanopore synthesis and ALD fundamental knowledge, and then focuses on the various aspects of synthetic nanopores processing by ALD and their applications, including single-molecule sensing, nanofiuidic devices, nanostructure fabrication and other applications.     

Atomic Layer Deposition of Nanostructured Materials for Energy and Environmental Applications

Atomic layer deposition (ALD) is a thin film technology that in the past two decades rapidly developed from a niche technology to an established method. It proved to be a key technology for the surface modification and the fabrication of complex nanostructured materials. In this Progress Report, after a short introduction to ALD and its chemistry, the versatility of the technique for the fabrication of novel functional materials will be discussed. Selected examples, focused on its use for the engineering of nanostructures targeting applications in energy conversion and storage, and on environmental issues, will be discussed. Finally, the challenges that ALD is now facing in terms of materials fabrication and processing will be also tackled.     

Spontaneous formation of vertical magnetic-metal-nanorod arrays during plasma-enhanced atomic layer deposition

A novel fabrication method of Co and Ni metal nanorods (NRs) without catalyst or template, based on the spontaneous formation of NRs during plasma-enhanced atomic layer deposition (PE-ALD) is developed. Pure Co and Ni NRs 9-10 nm in diameter are synthesized on SiO(2) and Si substrates by using metal-organic precursors and an NH(3) plasma mixed with a suitable amount of SiH(4) as a reactant. The lengths of the NRs are controlled on the nanometer scale by changing the number of PE-ALD growth cycles. Superconducting quantum interference device magnetometer measurements confirm the magnetic anisotropy of Co NRs caused by shape anisotropy.     

A Low-Temperature Batch Process for the Deposition of High-Quality Conformal Alumina Thin Films for Electronic Applications

High-quality, alumina thin films are extensively used as dielectrics, passivation layers, and barrier layers in electronics and many other applications. However, to achieve optimum stoichiometry and thus performance, the layers are often grown at elevated temperatures (>200 °C) using techniques such as atomic layer deposition (ALD). This is problematic for substrates or structures with low thermal budgets. Herein, alumina thin films are grown on 200 mm silicon substrates employing a versatile deposition method known as MVD at low deposition temperatures (35–150 °C). The chemical composition of the resulting films is investigated postdeposition using X-ray photoelectron spectroscopy (XPS) and variable angle spectroscopic ellipsometry, with fully stoichiometric Al₂O₃ achieved at deposition temperatures as low as 100 °C. Dielectric measurements confirm outstanding dielectric properties compared to typical thermal ALD layers deposited at much higher temperatures. This low-temperature deposition performance by considering the MVD reactor design and the “pump-type” regime of precursor delivery versus the “flow-type” regime of ALD is rationalized and understood. The results clearly demonstrate that alumina thin films grown with MVD are highly versatile for electronic applications and are of particular relevance and interest for the high-volume processing of dielectric, passivation, and barrier layers at low temperatures.     

柔性高阻隔薄膜材料的研究现状

目的为柔性高阻隔薄膜的应用提供理论指导。方法综述柔性高阻隔膜的应用现状及存在问题,总结热蒸发、化学气相沉积、原子层沉积等制备柔性高阻隔薄膜的方法、原理、特点及应用,展望高阻隔膜包装材料的发展前景。结果高阻隔薄膜制备工艺趋向于单次制备,采用等离子体辅助原子层沉积技术是制备超高阻隔薄膜的首选,原子层沉积(ALD)和分子层沉积(MLD)结合也是获得超高阻隔薄膜的未来发展方向。结论快速、高效地制备柔性高阻隔薄膜是包装工业的发展趋势。     

Applications of atomic layer deposition to nanofabrication and emerging nanodevices

Recently, with scaling down of semiconductor devices, need for nanotechnology has increased enormously. For nanoscale devices especially, each of the layers should be as thin and as perfect as possible. Thus, the application of atomic layer deposition (ALD) to nanofabrication strategies and emerging nanodevices has sparked a good deal of interest due to its inherent benefits compared to other thin film deposition techniques. Since the ALD process is intrinsically atomic in nature and results in the controlled deposition of films at the atomic scale, ALD produces layers with nanometer scale thickness control and excellent conformality. In this report, we review current research trends in ALD processes, focusing on the application of ALD to emerging nanodevices utilizing fabrication through nanotechnology.     

原子层沉积技术在新型太阳能电池中的应用

原子层沉积技术(ALD)是一项正处于发展之中、在许多领域具有巨大应用前景的新型材料制备技术,该技术在纳米结构和纳米复合结构的制备方面显示出独特的优势,在新型薄膜太阳能电池领域呈现出巨大的发展潜力和前景。首先概述了ALD技术的工作原理,简要介绍了近几年ALD技术在硅基太阳能电池和铜铟镓硒薄膜电池(CIGS)中的应用,然后重点综述了原子层沉积纳米功能薄膜在染料敏化太阳能电池(DSSCs)和有机-无机杂化钙钛矿太阳能电池(PSCs)为代表的新型薄膜太阳能电池中的应用。最后,总结了原子层沉积功能薄膜的特点和优势,展望了ALD在新能源材料与器件领域的应用前景和发展趋势。     

Atomic‐Layer‐Deposition‐Assisted Formation of Carbon Nanoflakes on Metal Oxides and Energy Storage Application

Nanostructured carbon is widely used in energy storage devices (e.g., Li‐ion and Li‐air batteries and supercapacitors). A new method is developed for the generation of carbon nanoflakes on various metal oxide nanostructures by combining atomic layer deposition (ALD) and glucose carbonization. Various metal oxide@nanoflake carbon (MO@f‐C) core‐branch nanostructures are obtained. For the mechanism, it is proposed that the ALD Al₂O₃ and glucose form a composite layer. Upon thermal annealing, the composite layer becomes fragmented and moves outward, accompanied by carbon deposition on the alumina skeleton. When tested as electrochemical supercapacitor electrode, the hierarchical MO@f‐C nanostructures exhibit better properties compared with the pristine metal oxides or the carbon coating without ALD. The enhancement can be ascribed to increased specific surface areas and electric conductivity due to the carbon flake coating. This peculiar carbon coating method with the unique hierarchical nanostructure may provide a new insight into the preparation of ‘oxides + carbon’ hybrid electrode materials for energy storage applications.     

Synthesis and Surface Engineering of Complex Nanostructures by Atomic Layer Deposition

Atomic layer deposition (ALD) has recently become the method of choice for the semiconductor industry to conformally process extremely thin insulating layers (high‐k oxides) onto large‐area silicon substrates. ALD is also a key technology for the surface modification of complex nanostructured materials. After briefly introducing ALD, this Review will focus on the various aspects of nanomaterials and their processing by ALD, including nanopores, nanowires and ‐tubes, nanopatterning and nanolaminates as well as low‐temperature ALD for organic nanostructures and biomaterials. Finally, selected examples will be given of device applications, illustrating recent innovative approaches of how ALD can be used in nanotechnology.     

Atomic layer deposition of thin films of ZnSe—structural and optical characterization

Thin films of sphalerite-type ZnSe were grown by atomic layer deposition (ALD) from elemental Zn and Se precursors. These films, grown on various substrates, show bright blue ‘edge’ emission accompanied by donor-acceptor pair emissions in the blue, green and red spectral regions. Red, green and blue emissions mixed together give a white color, with a color temperature between 2400 and 4500 K depending on a layer thickness and temperature. ZnSe grown by ALD is in consequence a promising material for the fabrication of semiconductor-based white light emitting thin film electroluminescence displays.     

Growth characteristics and electrical properties of La2O3 gate oxides grown by thermal and plasma-enhanced atomic layer deposition

We comparatively investigated thermal and plasma-enhanced atomic layer deposition (T-ALD and PE-ALD, respectively) of lanthanium oxide (La₂O₃) films using tris(isopropyl-cyclopentadienyl)lanthanum [La(iPrCp)₃] as a La precursor. H₂O and O₂ plasma were used as reactants for T-ALD and PE-ALD La₂O₃, respectively. Both of the processes exhibited ALD mode growth with good self-saturation behavior and produced pure La₂O₃ films. However, PE-ALD La₂O₃ showed higher growth rate and dielectric constant value than those of T-ALD La₂O₃. In addition, lower leakage current density and interface state density were observed for PE-ALD La₂O₃, compared to those of the T-ALD La₂O₃. These experimental results indicate that the PE-ALD La₂O₃ process using La(iPrCp)₃ precursor can be one of the viable options applicable into future microelectronic industry.     

An advanced fabrication method of highly ordered ZnO nanowire arrays on silicon substrates by atomic layer deposition

In this work, the controlled fabrication of highly ordered ZnO nanowire (NW) arrays on silicon substrates is reported. Si NWs fabricated by a combination of phase shift lithography and etching are used as a template and are subsequently substituted by ZnO NWs with a dry-etching technique and atomic layer deposition. This fabrication technique allows the vertical ZnO NWs to be fabricated on 4 in Si wafers. Room temperature photoluminescence and micro-photoluminescence are used to observe the optical properties of the atomic layer deposition (ALD) based ZnO NWs. The sharp UV luminescence observed from the ALD ZnO NWs is unexpected for the polycrystalline nanostructure. Surprisingly, the defect related luminescence is much decreased compared to an ALD ZnO film deposited at the same time ona plane substrate. Electrical characterization was carried out by using nanomanipulators. With the p-type Si substrate and the n-type ZnO NWs the nanodevices represent p–n NW diodes.The nanowire diodes show a very high breakthrough potential which implies that the ALD ZnO NWs can be used for future electronic applications.     

原子层沉积技术及其在半导体中的应用

首先简述原子层沉积（ALD）技术的发展背景，通过分析ALD的互补性和自限制性等工艺基础，介绍了它在膜层的均匀性、保形性以及膜厚控制能力等方面的优势，着重列举ALD在半导体互连技术、高k电介质等方面的应用。同时指出了目前ALD工艺中存在的主要问题。     

原子层沉积技术及其创新运用

本文分析并总结了涉及原子层沉积(atomic layer deposition,ALD)技术基本原理的若干问题.介绍了等离子增强原子层沉积(plasma enhanced atomic layer deposition,PEALD)技术的优势及常见运用.相对于传统ALD系统,PEALD最大的特点在于其能够通过等离子体放电来活化前驱体源,提高对前驱体源,尤其是气态源的利用.利用PEALD这一特点可以增加传统ALD技术中可用氮源的种类.同时PEALD原位掺杂作为一种掺杂方法能够用于对光催化材料的掺杂改性,提高其光催化性能.此外,PEALD技术还适用于温度敏感材料和柔性材料上的薄膜沉积,可以获得更低的电阻率和更高的薄膜密度等.本文重点介绍了本课题组提出的PEALD原位掺杂技术及其对TiO2光催化剂的掺杂改性运用.最后对原位掺杂技术的研究方向和发展进行了展望.     

纳米结构的倾斜角度沉积及性能优化

纳米材料发展的关键是纳米结构的制备、形貌调控和性能优化.倾斜角度沉积是以较大的角度(大于75°)倾斜入射沉积薄膜,通过控制沉积参数,得到具有特殊形貌纳米结构的方法,具有适用范围广,操作便捷,制备的薄膜面积大、纯度高、结构规整等特点,是一种理想的制备纳米材料的方法.本文介绍了采用倾斜角度沉积技术制备氧化铪抗反射薄膜和银基表面增强拉曼基底,详细分析了该方法的参数调控对纳米结构的形貌和性能的影响,并指出将倾斜角度沉积与其他先进技术相结合(以原子层沉积为例),可进一步优化纳米结构的性能,提高倾斜角度沉积的使用范围.     

Atomic layer deposition on phase-shift lithography generated photoresist patterns for 1D nanochannel fabrication

A versatile, low-cost, and flexible approach is presented for the fabrication of millimeter-long, sub-100 nm wide 1D nanochannels with tunable wall properties (wall thickness and material) over wafer-scale areas on glass, alumina, and silicon surfaces. This approach includes three fabrication steps. First, sub-100 nm photoresist line patterns were generated by near-field contact phase-shift lithography (NFC-PSL) using an inexpensive homemade borosilicate mask (NFC-PSM). Second, various metal oxides were directly coated on the resist patterns with low-temperature atomic layer deposition (ALD). Finally, the remaining photoresist was removed via an acetone dip, and then planar nanochannel arrays were formed on the substrate. In contrast to all the previous fabrication routes, the sub-100 nm photoresist line patterns produced by NFC-PSL are directly employed as a sacrificial layer for the creation of nanochannels. Because both the NFC-PSL and the ALD deposition are highly reproducible processes, the strategy proposed here can be regarded as a general route for nanochannel fabrication in a simplified and reliable manner. In addition, the fabricated nanochannels were used as templates to synthesize various organic and inorganic 1D nanostructures on the substrate surface.     

High‐Quality,Ultraconformal Aluminum‐Doped Zinc Oxide Nanoplasmonic and Hyperbolic Metamaterials

Aluminum‐doped zinc oxide (AZO) is a tunable low‐loss plasmonic material capable of supporting dopant concentrations high enough to operate at telecommunication wavelengths. Due to its ultrahigh conformality and compatibility with semiconductor processing, atomic layer deposition (ALD) is a powerful tool for many plasmonic applications. However, despite many attempts, high‐quality AZO with a plasma frequency below 1550 nm has not yet been realized by ALD. Here a simple procedure is devised to tune the optical constants of AZO and enable plasmonic activity at 1550 nm with low loss. The highly conformal nature of ALD is also exploited to coat silicon nanopillars to create localized surface plasmon resonances that are tunable by adjusting the aluminum concentration, thermal conditions, and the use of a ZnO buffer layer. The high‐quality AZO is then used to make a layered AZO/ZnO structure that displays negative refraction in the telecommunication wavelength region due to hyperbolic dispersion. Finally, a novel synthetic scheme is demonstrated to create AZO embedded nanowires in ZnO, which also exhibits hyperbolic dispersion.     

Atomic Layer Deposition for Membranes,Metamaterials, and Mechanisms

Bending and folding techniques such as origami and kirigami enable the scale‐invariant design of 3D structures, metamaterials, and robots from 2D starting materials. These design principles are especially valuable for small systems because most micro‐ and nanofabrication involves lithographic patterning of planar materials. Ultrathin films of inorganic materials serve as an ideal substrate for the fabrication of flexible microsystems because they possess high intrinsic strength, are not susceptible to plasticity, and are easily integrated into microfabrication processes. Here, atomic layer deposition (ALD) is employed to synthesize films down to 2 nm thickness to create membranes, metamaterials, and machines with micrometer‐scale dimensions. Two materials are studied as model systems: ultrathin SiO₂ and Pt. In this thickness limit, ALD films of these materials behave elastically and can be fabricated with fJ‐scale bending stiffnesses. Further, ALD membranes are utilized to design micrometer‐scale mechanical metamaterials and magnetically actuated 3D devices. These results establish thin ALD films as a scalable basis for micrometer‐scale actuators and robotics.     

Scalable production of ultra small TiO2 nano crystal/activated carbon composites by atomic layer deposition for efficient removal of organic pollutants

A high surface area photo-catalytic composite material is synthesized by depositing thin films of titanium dioxide (TiO₂) on activated carbon (AC) particles using atomic layer deposition (ALD). A rotary ALD reactor is developed for scalable fabrication of powder and grams of the catalyst is prepared in each batch. The processes of TiO₂ ALD are monitored by mass spectrometry. Saturated ALD surface reactions are confirmed so that the entire surface of the AC support is covered by conformal coatings of TiO₂. For composites fabricated by 3 or more ALD cycles of TiO₂, the amorphous oxide layers can be converted to crystalline films by high temperature annealing. The as-prepared TiO₂/AC composites are highly reactive in photo-catalyzed degradation of methyl orange. The excellent catalytic performance is attributed to the abundant and uniformly dispersed active phase, formation of very active ultra small (<5 nm) TiO₂ crystals, and easy accessibility of the active sites.     

TEM-based metrology for HfO2 layers and nanotubes formed in anodic aluminum oxide nanopore structures

Nanotubes are fabricated by atomic layer deposition (ALD) into nanopore arrays created by anodic aluminum oxide (AAO). A transmission electron microscopy (TEM) methodology is developed and applied to quantify the ALD conformality in the nanopores (thickness as a function of depth), and the results are compared to existing models for ALD conformality. ALD HfO2 nanotubes formed in AAO templates are released by dissolution of the Al2O3, transferred to a grid, and imaged by TEM. An algorithm is devised to automate the quantification of nanotube wall thickness as a function of position along the central axis of the nanotube, by using a cylindrical model for the nanotube. Diffusion-limited depletion occurs in the lower portion of the nanotubes and is characterized by a linear slope of decreasing thickness. Experimentally recorded slopes match well with two simple models of ALD within nanopores presented in the literature. The TEM analysis technique provides a method for the rapid analysis of such nanostructures in general, and is also a means to efficiently quantify ALD profiles in nanostructures for a variety of nanodevice applications.