Atomic Layer Deposition on Dispersed Materials in Liquid Phase by Stoichiometrically Limited Injections

Atomic layer deposition (ALD) is a well‐established vapor‐phase technique for depositing thin films with high conformality and atomically precise control over thickness. Its industrial development has been largely confined to wafers and low‐surface‐area materials because deposition on high‐surface‐area materials and powders remains extremely challenging. Challenges with such materials include long deposition times, extensive purging cycles, and requirements for large excesses of precursors and expensive low‐pressure equipment. Here, a simple solution‐phase deposition process based on subsequent injections of stoichiometric quantities of precursor is performed using common laboratory synthesis equipment. Precisely measured precursor stoichiometries avoid any unwanted reactions in solution and ensure layer‐by‐layer growth with the same precision as gas‐phase ALD, without any excess precursor or purging required. Identical coating qualities are achieved when comparing this technique to Al₂O₃ deposition by fluidized‐bed reactor ALD (FBR‐ALD). The process is easily scaled up to coat >150 g of material using the same inexpensive laboratory glassware without any loss in coating quality. This technique is extended to sulfides and phosphates and can achieve coatings that are not possible using classic gas‐phase ALD, including the deposition of phosphates with inexpensive but nonvolatile phosphoric acid.     

Ultra‐precision Surface Finishing by Ion Beam Techniques

Ion beam etching based ultra precision surface finishing is a versatile technology with a high degree of predictability due to the high stability of state of the art ion sources and the acquired knowledge of the physics of beam surface interaction. The independent control of the ion energy and the ion current density over wide ranges and the possible additional use of chemical reactive species in combination with physical sputter removal allow solving tasks in a wide variety of applications. The paper summarizes the present status of more than 20 years of development of ion beam finishing technology in IOM. It gives an overview on the equipment and the components developed for production purposes and on the ion beam technologies developed to achieve nanometer and sub‐nanometer depth accuracies over the entire spectrum of spatial surface wavelength from the full aperture size down to the microroughness level of only micrometer lateral feature size. Results of the finishing of high‐end optical surfaces shown demonstrate the outstanding performances of the techniques with topography and roughness control on the atomic scale.     

Highly Flexible Hybrid CMOS Inverter Based on Si Nanomembrane and Molybdenum Disulfide

2D semiconductor materials are being considered for next generation electronic device application such as thin‐film transistors and complementary metal–oxide–semiconductor (CMOS) circuit due to their unique structural and superior electronics properties. Various approaches have already been taken to fabricate 2D complementary logics circuits. However, those CMOS devices mostly demonstrated based on exfoliated 2D materials show the performance of a single device. In this work, the design and fabrication of a complementary inverter is experimentally reported, based on a chemical vapor deposition MoS₂ n‐type transistor and a Si nanomembrane p‐type transistor on the same substrate. The advantages offered by such CMOS configuration allow to fabricate large area wafer scale integration of high performance Si technology with transition‐metal dichalcogenide materials. The fabricated hetero‐CMOS inverters which are composed of two isolated transistors exhibit a novel high performance air‐stable voltage transfer characteristic with different supply voltages, with a maximum voltage gain of ≈16, and sub‐nano watt power consumption. Moreover, the logic gates have been integrated on a plastic substrate and displayed reliable electrical properties paving a realistic path for the fabrication of flexible/transparent CMOS circuits in 2D electronics.     

Initiated Chemical Vapor Deposition: A Versatile Tool for Various Device Applications

Advances in device technology have been accompanied by the development of new types of materials and device fabrication methods. Considering device design, initiated chemical vapor deposition (iCVD) inspires innovation as a platform technology that extends the application range of a material or device. iCVD serves as a versatile tool for surface modification using functional thin film. The building of polymeric thin films from vapor phase monomers is highly desirable for the surface modification of thermally sensitive substrates. The precise control of thin film thicknesses can be achieved using iCVD, creating a conformal coating on nano‐, and micro‐structured substrates such as membranes and microfluidics. iCVD allows for the deposition of polymer thin films of high chemical functionality, and thus, substrate surfaces can be functionalized directly from the iCVD polymer film or can selectively gain functionality through chemical reactions between functional groups on the substrate and other reactive molecules. These beneficial aspects of iCVD can spur breakthroughs in device fabrication based on the deposition of robust and functional polymer thin films. This review describes significant implications of and recent progress made in iCVD‐based technologies in three fields: electronic devices, surface engineering, and biomedical applications.

     

Ultrasensitive 2D Bi2O2Se Phototransistors on Silicon Substrates

2D materials are considered as intriguing building blocks for next‐generation optoelectronic devices. However, their photoresponse performance still needs to be improved for practical applications. Here, ultrasensitive 2D phototransistors are reported employing chemical vapor deposition (CVD)‐grown 2D Bi₂O₂Se transferred onto silicon substrates with a noncorrosive transfer method. The as‐transferred Bi₂O₂Se preserves high quality in contrast to the serious quality degradation in hydrofluoric‐acid‐assisted transfer. The phototransistors show a responsivity of 3.5 × 10⁴ A W^?1, a photoconductive gain of more than 10⁴, and a time response in the order of sub‐millisecond. With back gating of the silicon substrate, the dark current can be reduced to several pA. This yields an ultrahigh sensitivity with a specific detectivity of 9.0 × 10¹³ Jones, which is one of the highest values among 2D material photodetectors and two orders of magnitude higher than that of other CVD‐grown 2D materials. The high performance of the phototransistor shown here together with the developed unique transfer technique are promising for the development of novel 2D‐material‐based optoelectronic applications as well as integrating with state‐of‐the‐art silicon photonic and electronic technologies.     

Nitrogen‐Plasma‐Activated Hierarchical Nickel Nitride Nanocorals for Energy Applications

Developing transition metal nitrides with unique nanomorphology is important for many energy storage and conversion processes. Here, a facile and novel one‐step approach of growing 3D hierarchical nickel nitride (hNi₃N) on Ni foam via nitrogen plasma is reported. Different from most conventional chemical synthesis, the hNi₃N is obtained in much shorter growth duration (≤15 min) without any hazardous or reactive sources and oxide precursors at a moderate reaction zone temperature of ≤450 °C. Among possible multifunctionalities of the obtained nanocoral hNi₃N, herein the performance in reversible lithium ion storage and electrocatalytic oxygen evolution reaction (OER) is demonstrated. The as‐obtained hNi₃N delivers a considerable cycling performance and rate stability as a lithium ion battery anode, and its property can be further enhanced by coating the hNi₃N surface with graphene quantum dots. The hNi₃N also serves as an active OER catalyst with high activity and stability. Additionally, on the basis of controlled growth under different nitrogen plasma treatment time, the formation mechanism of the nanocoralline hNi₃N is outlined for further extension to other materials. The results on time‐ and energy‐efficient nitrogen‐plasma‐based preparation of hNi₃N pave the way for the development of high‐performance metal nitride electrodes for energy storage and conversion.     

Efficient surface functionalization of vertically-aligned carbon nanotube arrays using an atmospheric pressure plasma jet system

We demonstrate the facile and efficient surface functionalization of vertically-aligned carbon nanotube (VCNT) arrays using an atmospheric pressure plasma jet (APPJ) system. The VCNT arrays were synthesized on Fe-deposited SiO₂ wafers using an acetylene carbon source by thermal chemical vapor deposition method. To functionalize the surface of the VCNT arrays, the APPJ system was ignited using nitrogen gas at high voltage of 15 kV and frequency of 25 kHz. We varied the treatment time of the APPJ and the inter-distance between plasma jet and top surface of the VCNT in order to systematically investigate the optimal conditions of the APPJ system. The hydrophobic nature of the as-grown VCNT arrays was drastically changed to hydrophilic character via the facile APPJ treatment. X-ray photoelectron spectroscopy confirmed the formation of hydrophilic functional groups such as hydroxyl and carboxyl groups, and nitrogen-doping-related functionalities such as amines, in addition to pyrrolic- and pyridinic-bonding. The results prove that the APPJ treatment is a facile and efficient method for the surface modification of nanomaterials.     

Plasmachemische Gasphasenabscheidung – eine Technologie zur Deposition organischer und anorganischer Schichten. Plasma Enhanced Chemical Vapor Deposition – a Thin Film Technique for Organic and Inorganic Layers

Plasma enhanced chemical vapor deposition (PECVD) has a wide range of interest for thin films up to some μm thickness. It has widespread applications for high quality dielectric and semiconducting silicon alloys at deposition temperatures below 450 °C and pressures at 1 mbar on plane substrates and attracts growing attention for the surface modification of polymers. The PECVD takes advantages of the possibility to alter the film properties in a wide range easily, and the coatings can achieve a variety of useful properties unobtainable by other coating techniques. An environmentally friendly plasma chemical reactor etch cleaning of SiO_x, SiN_x and other film materials can be applied by changing the process gas and without breaking the vacuum. PECVD can be used in a fixed substrate and continuous substrate flow mode. An capacitively coupled parallel‐plate electrode assembly using radio‐frequency (RF) excitation of the discharge is most widely used for substrate areas up to a few square meters. Among the capacitively excitation an inductively and electromagnetically excitation at frequencies in the RF and UHF range has also succeeded in achieving a high rate PECVD. Two applications are presented to show the characteristics and the potential of this technique, the PECVD of semiconducting hydrogenated amorphous silicon, intrinsic or doped, with low power densities using monosilane as a source gas for solar cells, thin films transistors and digital image sensors and the plasma polymerisation of organosilicon protection layers employing the HMDSO monomer and high power densities for mirrors and lenses.     

Cross Section Investigations of Compositions and Sub‐Structures of Tips Obtained by Focused Electron Beam Induced Deposition

The spatial evolution of compositions and sub‐structures inside focused‐electron‐beam‐deposited tips from dicobalt‐octacarbonyl Co₂(CO)₈ precursor at 25 keV and varying beam current (20 pA – 3 μA) is extensively studied for the first time by means of energy dispersive X‐ray spectroscopy, transmission electron microscopy, back‐scattered electron imaging, and ion‐induced secondary electron imaging. Transverse and longitudinal tip cross sections and lamellae were prepared by focused ion beam milling. Two sub‐structure types can be distinguished: a nano‐composite sub‐structure is grown during the initial deposition stage (small‐aspect‐ratio tips). It consists of cobalt nano‐crystals embedded in a carbonaceous matrix. A second distinct cobalt‐grain‐rich sub‐structure develops in high‐aspect ratio tips. Both sub‐structures vary in appearance and composition with increasing beam current: the initial nano‐composite sub‐structure increases in cobalt content and nano‐crystal size, and the cobalt‐grain sub‐structure develops polycrystal‐, texture‐, whisker‐, or platelet‐like habits. The directed precursor flux from a micro‐tube prevents a radial symmetry of the sub‐structures with respect to the impinging focused electron beam, at medium to high beam current. Homogeneous nano‐composite high‐resolution tips with small diameter and length were obtained at low beam current. Observations suggest an additional contribution to pure electron induced precursor molecule decomposition. The influence of electron beam heating and related chemical reactions is discussed.     

Kalte Normaldruck‐Jetplasmen zur lokalen Oberflächenbehandlung

Cold non‐thermal plasma jets for local surface treatment under normal pressure Plasmas at normal pressure are of considerable interest for surface technology because the industrial application requires no vacuum devices. Among other approaches, cold non‐thermal plasma jets represent an emerging technique to generate plasmas at normal pressure with attractive advantages. They allow ambient process temperatures and require only moderate operating voltages (1.5‐2.5 kV). They offer the advantage that the treated surfaces are not placed between the electrodes thus favoring local treatment of non flat, structured 3D surfaces. Moreover, the dimension of the sources is scalable and their integration into automated processes is simple. A capacitively coupled version (27.12 MHz) of a cold plasma jet suitable for surface treatment at atmospheric pressure is presented along with its plasma physical and technical properties and a series of successful applications, including plasma activation of surfaces for increasing printability, adhesion control, surface cleaning, microfluidics, decontamination, its use in plasmamedicine and for deposition of thin SiO₂ films as protective coatings. The device allows the operation with rare gases (e.g. Ar) and reactive gases as N₂, air or admixtures of silicon‐containing compounds.     

Self‐Formed Channel Devices Based on Vertically Grown 2D Materials with Large‐Surface‐Area and Their Potential for Chemical Sensor Applications

2D layered materials with sensitive surfaces are promising materials for use in chemical sensing devices, owing to their extremely large surface‐to‐volume ratios. However, most chemical sensors based on 2D materials are used in the form of laterally defined active channels, in which the active area is limited to the actual device dimensions. Therefore, a novel approach for fabricating self‐formed active‐channel devices is proposed based on 2D semiconductor materials with very large surface areas, and their potential gas sensing ability is examined. First, the vertical growth phenomenon of SnS₂ nanocrystals is investigated with large surface area via metal‐assisted growth using prepatterned metal electrodes, and then self‐formed active‐channel devices are suggested without additional pattering through the selective synthesis of SnS₂ nanosheets on prepatterned metal electrodes. The self‐formed active‐channel device exhibits extremely high response values (>2000% at 10 ppm) for NO₂ along with excellent NO₂ selectivity. Moreover, the NO₂ gas response of the gas sensing device with vertically self‐formed SnS₂ nanosheets is more than two orders of magnitude higher than that of a similar exfoliated SnS₂‐based device. These results indicate that the facile device fabrication method would be applicable to various systems in which surface area plays an important role.     

Surface Modification of Iron Carbon Alloys by Plasma Detonation Treatment

Plasma detonation method (PDM) is based on the use of pulse plasma jets formed by transformation of a detonation wave into a plasma pulse. Energy density in such a jet amounts to 10⁷ W cm_-2, Consumable electrodes used here allow the vapors of various metals to be introduced into the jet. PDM is applied for heat treatment of surfaces, their alloying, as well as for coating deposition. The process of surface modification of carbon steels using various electrodes is investigated. The effect of the treatment conditions and the electrode materials on surface hardening is discussed.     

Study of plasma enhanced chemical vapor deposition of ZnO films by non-thermal plasma jet at atmospheric pressure

Plasma enhanced chemical vapor deposition using a non-thermal plasma jet was applied to deposition of ZnO films. Using vaporized bis(octane-2,4-dionato)zinc flow crossed by the plasma jet, the deposition rate was as high as several tens of nm/s. From the results of infrared spectra, the films deposited at the substrate temperature T_sub = 100 °C contained a significant amount of carbon residue, while the films prepared at T_sub = 250 °C showed less carbon fraction. The experimental results confirmed that the plasma jet decomposed bis(octane-2,4-dionato)zinc in the gaseous phase and on the substrate, and that there should be the critical T_sub to form high-quality ZnO films in the range from 100 to 250 °C.     

Deposition of zinc oxide thin films by an atmospheric pressure plasma jet

The ZnO thin film deposition process by using an atmospheric pressure (AP) plasma jet is studied. In this process, nebulized ZnCl₂ solution is sprayed into the downstream of the nitrogen plasma jet to perform thin film deposition. X-ray diffraction analysis confirms that this AP jet has the capability to convert ZnCl₂ solution to well-crystallized ZnO thin films with a hexagonal wurtzite structure in a short time. This film exhibits a smooth and mirror-like appearance visually. Scanning electron microscopy and atomic force microscopy show that the deposited film is dense and continuous with a root mean square surface roughness of 8.6 nm. A 1.29 nm/s deposition rate is obtained using this process. Given the fast deposition rate, we believe that both the temperature and the reactivity of the plasma play important roles. A ZnO film on a larger substrate is fabricated, which suggests the process capability in large area and continuous processing applications.     

Deposition Temperature Effect on the Structure and Optical Property of RF‐PACVD‐Derived Hydrogenated SiCNO Film

Amorphous hydrogenated silicon oxocarbonitride (SiCNO:H) films have been deposited by plasma‐assisted chemical vapour deposition (PACVD) using bis(trimethylsilyl)carbodiimide (BTSC) as a single source precursor in a argon (Ar) radio‐frequency plasma. In this work the SiCNO:H films deposited at different deposition temperatures were studied in terms of deposition rate, refractive index, surface roughness, microstructure, and chemical composition including bonding state. The results showed that a higher deposition temperature enhanced the formation of Si‐N bonds, and disfavoured the formation of N=C=N, Si‐NCN, C‐H and Si‐CH₃ bonds. A higher deposition temperature also decreased the deposition rate and increased the refractive index of the resulting SiCNO:H film. With increasing temperature a denser film was formed, indicating a change of the deposition mechanism, i.e., transformation from particle precipitation to heterogeneous surface reaction. Except for the coatings deposited at room temperature, the surface of the films was smooth with a roughness of around 4 nm at the centre in the range of 5 μm x 5 μm area. Moreover, the films contained 8 ～ 16 at.% oxygen bonded to Si, which originated from the remnant H₂O in the deposition chamber.     

ITO‐coatings by reactive low‐voltage ion plating: film properties and plasma analysis

Transparent conductive oxides (TCO) are widely used materials for multifarious applications. According to today's state of knowledge, indium‐tin‐oxide (ITO) still offers the best electrical properties among numerous TCOs. However, ITO films produced by ion plating have only rarely been reported to be investigated. For most coating processes, ITO films need to be deposited under high temperature conditions (some 100 °C substrate heating) or require post‐deposition heat treatment in order to obtain high film quality. In this study, reactive low‐voltage ion plating (RLVIP) was used, which allows ‐ due to plasma assistance during the coating process ‐ deposition of ITO films at temperatures below 100 °C. Essential film properties, i.e. resistivity and optical transmission, were optimised by variation of arc current, gas pressure and deposition rate. These quantities ‐ particularly arc current and gas pressure ‐ have huge influence on the characteristics of the supporting plasma. This was shown by analysing the plasma with a mass‐spectrometric plasma monitoring system and with a Langmuir probe. In comparison with formerly studied coating materials (Ta₂O₅,Nb₂O₅,HfO₂), different plasma compositions regarding the presence of metal oxide ions were determined, which could be attributed to elemental and molecular energy properties (ionisation and binding energies).     

Beschichtung von metallischen Membranen mittels Pulsed Laser Deposition

Coating of metallic membranes by pulsed laser deposition There is increasing demand to functionalize meso‐ and nano‐porous materials by coating and make the porous substrate biocompatible or environment friendly. However, coating on a meso‐porous substrate poses great challenges, especially if the pore aspect ratio is high. In the current work the pulsed laser deposition (PLD) method is used for coating Ni₃Al‐based meso‐porous membranes with diamond‐like carbon (DLC) layers of high thickness homogeneity and adhesion.     

Plasma processing for surface optical modifications of PET films

The plasma interaction with the surface produces modifications of its chemical structure or morphology. Surface modifications through cold plasma occur, thanks to the high plasma reactivity and ability to affect the surface of materials.The present work shows the surface modification of polyethylene terephthalate (PET) films after the exposure both to low-pressure plasma (film deposition by plasma enhanced chemical vapour deposition) and to an atmospheric pressure dielectric barrier discharge (surface etching). After plasma treatment we have analysed the effect on the PET surface.For the atmospheric pressure plasma-treated samples, contact angle and atomic force microscope analysis enable us to determine roughness changes. For the low-pressure plasma samples, contact angles and Fourier transform infrared absorption spectroscopy analysis are used to estimate the chemical composition of the deposition and focused ion beam analysis to collect the image and calculate the thickness of plasma deposition.Both plasma treatments (film deposition and etching) cause changes in optical properties as indicated by reflectivity measurements.     

Plasma‐aktivierte Bedampfung von flexiblen Materialien. Plasma‐activated vapour deposition on flexible substrates

The vacuum coating of flexible materials such as plastic webs is being used worldwide to change the surface properties for specific applications. The physical properties of interest e.g. density, hardness, refractive index and permeation are influenced by the microstructure of the coated layer. This paper describes, that this microstructure can be improved significantly by plasma enhanced evaporation techniques. At Fraunhofer Institute for Electron Beam and Plasma Technology (FEP), a method for plasma‐activated high rate deposition has been developed. This method is based on a hollow cathode arc discharge. This plasma‐source can be used for high productive roll coaters with boat evaporators or electron beam evaporators.     

Gefilterte Bogenbeschichtung – alte Probleme und neue Lösungen

Currently, the vacuum arc deposition (VAD) technique is well established in industry, primarily to deposit wear protective hard coatings such as metal nitrides and carbides onto tools and components. From the beginning of the industrial development of the vacuum arc deposition, it was obvious that the emission of macroparticles or droplets is a fundamental drawback of this coating technology. The emission is caused by the highly dynamic process of plasma generation and limits the fields of application significantly. Different methods have been proposed to minimize the macroparticle flux to the substrate surface. But the only way to hinder droplets from reaching the substrate reliable is to separate the plasma from particles by using curved magnetic fields. This filtered arc technique has proven its superiority of depositing high quality films compared to conventional arc applications in numerous laboratory tests. Current demands have stimulated new developments at the Fraunhofer IWS of more compact and higher productive filtered arc sources. One important application of ultra thin protective films is the topcoat on hard disks. In order to increase the storage density, the head‐to‐media spacing as well as the thickness of the overcoat has been reduced continuously. Until now, the thickness of the sputtered films was reduced to about 4 nm. The limit for this technology seems to be achieved. Filtered arc deposition is one of the most promising candidates for the deposition of thinner films – down to 1.3 nm with an even improved mechanical and chemical resistance. Another application area is the manufacturing of metallic lines and interconnections with high aspect ratios in the deep sub‐micron region in microelectronics. The excellent properties of this new filtered source for the deposition of conducting lines in microelectronics were been demonstrated. Actually, the technology for the subsequent deposition of barrier films and conducting wires is under development. Besides the micro technologies, there are a lot of applications requiring higher quality but not (yet) such a perfect film surface. Therefore, using a quite simple filter design – the so‐called Venetian blind filter – a filter unit was developed which can be used at the common industrial vacuum arc deposition machines. The filter does not reduce the deposition area, so the standard deposition processes can be used furthermore. With this filter, the number of droplets can reduced dramatically. A plasma transmission through the filter of approximately 20 % could be measured. Such filter module was realized and is in use now.