Thermal deposition approaches for graphene growth over various substrates

In the course of the PhD thesis large area homogeneous strictly monolayer graphene films were successfully synthesized with chemical vapor deposition over both Cu and Si (with surface oxide) substrates. These synthetic graphene films were characterized with thorough microscopic and spectrometric tools and also in terms of electrical device performance. Graphene growth with a simple chemo thermal route was also explored for understanding the growth mechanisms. The formation of homogeneous graphene film over Cu requires a clean substrate. For this reason, a study has been conducted to determine the extent to which various pre-treatments may be used to clean the substrate. Four type of pre-treatments on Cu substrates are investigated, including wiping with organic solvents, etching with ferric chloride solution, annealing in air for oxidation, and air annealing with post hydrogen reduction. Of all the pretreatments, air oxidation with post hydrogen annealing is found to be most efficient at cleaning surface contaminants and thus allowing for the formation of large area homogeneous strictly monolayer graphene film over Cu substrate. Chemical vapor deposition is the most generally used method for graphene mass production and integration. There is also interest in growing graphene directly from organic molecular adsorbents on a substrate. Few studies exist. These procedures require multiple step reactions, and the graphene quality is limited due to small grain sizes. Therefore, a significantly simple route has been demonstrated. This involves organic solvent molecules adsorbed on a Cu surface, which is then annealed in a hydrogen atmosphere in order to ensure direct formation of graphene on a clean Cu substrate. The influence of temperature, pressure and gas flow rate on the one-step chemo thermal synthesis route has been investigated systematically. The temperature-dependent study provides an insight into the growth kinetics, and supplies thermodynamic information such as the activation energy, Ea, for graphene synthesis from acetone, isopropanol and ethanol. Also, these studies highlight the role of hydrogen radicals for graphene formation. In addition, an improved understanding of the role of hydrogen is also provided in terms of graphene formation from adsorbed organic solvents (e.g., in comparison to conventional thermal chemical vapor deposition). Graphene synthesis with chemical vapor deposition directly over Si wafer with surface oxide (Si/SiOx ) has proven challenging in terms of large area and uniform layer number. The direct growth of graphene over Si/SiO x substrate becomes attractive because it is free of an undesirable transfer procedure, necessity for synthesis over metal substrate, which causes breakage, contamination and time consumption. To obtain homogeneous graphene growth, a local equilibrium chemical environment has been established with a facile confinement CVD approach, inwhich two Si wafers with their oxide faces in contact to form uniform monolayer graphene. A thorough examination of the material reveals it comprises facetted grains despite initially nucleating as round islands. Upon clustering these grains facet to minimize their energy, which leads to faceting in polygonal forms because the system tends to ideally form hexagons (the lowest energy form). This is much like the hexagonal cells in a beehive honeycomb which require the minimum wax. This process also results in a near minimal total grain boundary length per unit area. This fact, along with the high quality of the resultant graphene is reflected in its electrical performance which is highly comparable with graphene formed over other substrates, including Cu. In addition the graphene growth is self-terminating, which enables the wide parameter window for easy control. This chemical vapor deposition approach is easily scalable and will make graphene formation directly on Si wafers competitive against that from metal substrates which suffer from transfer. Moreover, this growth path shall be applicable for direct synthesis of other two dimensional materials and their Van der Waals hetero-structures.:Contents Quotation v Kurzfassung vii Abstract xi Contents xiii Acronyms xvii 1 Aims and objectives 1 2 Introduction 5 2.1 Carbon allotropes 6 2.1.1 Hybridized sp 2 carbon nanomaterials 6 2.1.2 Graphene 7 2.2 Properties of graphene 8 2.2.1 Crystalline structure 8 2.2.2 Electrical transport 10 2.2.3 Optical transparency 11 2.2.4 Other properties 12 2.3 Graphene deposition methods 13 2.3.1 Synthesis approaches 13 2.3.2 Chemical vapor deposition 14 2.3.3 Substrate selection 15 2.3.4 Substrate pretreatments 16 2.3.5 Carbon feedstock 17 2.3.6 Thermal chemical vapor deposition 17 2.3.7 Plasma chemical vapor deposition 18 2.3.8 Transfer protocol 19 2.4 Chemical vapor deposition for graphene growth 21 2.4.1 Thermodynamics 22 2.4.2 Arrhenius plots 22 2.4.3 Activation energy 24 2.4.4 Growth kinetics 25 2.4.5 Reaction mechanisms over Cu 27 2.4.6 Reaction mechanisms over Ni 29 2.4.7 Reaction mechanisms over non-metals 31 2.4.8 Reaction mechanisms of free-standing graphene 35 2.5 Summary 35 2.6 Scope of the thesis 36 3 Experimental setup and characterization techniques 37 3.1 Experimental setup of chemical vapor deposition 37 3.2 Optical microscopy 39 3.3 Scanning electron microscopy 40 3.4 Atomic force microscopy 41 3.5 Transmission electron microscopy 42 3.5.1 Selected area electron diffraction 44 3.5.2 Dark field transmission electron microscopy 46 3.6 Raman spectroscopy 47 3.7 Ultraviolet-Visible spectrophotometry 49 3.8 Electrical transport measurements 49 4 CVD growth of graphene on oxidized Cu substrates 51 4.1 Motivation 52 4.2 Experimental protocol 53 4.3 Influence of Cu pretreatments on graphene formation 54 4.4 Influence of Cu oxidation on graphene growth 60 4.5 Effect of oxidation pretreatment on Cu surface cleaning 64 4.6 Summary 66 5 Chemo-thermal synthesis of graphene from organic adsorbents 67 5.1 Motivation 67 5.2 Experimental protocol 69 5.3 Influence of reaction temperature on graphene growth 75 5.4 Influence of reaction pressure on graphene growth 78 5.5 Influence of reaction flow rate on graphene growth 80 5.6 Summary 81 6 Monolayer graphene synthesis directly over Si/SiO x 83 6.1 Motivation 83 6.2 Experimental protocol 86 6.3 Influence of substrate confinement configuration 87 6.4 Time dependent evolution for graphene formation 91 6.5 Grain boundaries in graphene film 95 6.6 Bubble clustering of faceted graphene grains 98 6.7 Electrical and optical performance of graphene 100 6.8 Summary 102 7 Conclusions 103 8 Outlook 107 A Graphene synthesis over Cu and transfer to Si/SiO x substrate 111 B Chemo-thermal synthesis of graphene over Cu 115 C CVD graphene growth directly over Si/SiO x substrate 127 Bibliography 147 List of Figures 193 List of Tables 197 Acknowledgements 199 List of publications 203 Erklaerung 205Im Zuge dieser Doktorarbeit wurden großflächige und homogene Graphen-Monolagen mittels chemischer Gasphasenabscheidung auf Kupfer- (Cu) und Silizium-(Si) Substraten erfolgreich synthetisiert. Solche monolagigen Graphenschichten wurden mithilfe mikroskopischer und spektrometrischer Methoden gründlich charakterisiert. Außerdem wurde der Wachstumsmechanismus von Graphen anhand eines chemo-thermischen Verfahrens untersucht. Die Bildung von homogenen Graphenschichten auf Cu erfordert eine sehr saubere Substratoberfläche, weshalb verschiedene Substratvorbehandlungen und dessen Einfluss auf die Substratoberfläche angestellt wurden. Vier Vorbehandlungsarten von Cu-Substraten wurden untersucht: Abwischen mit organischen Lösungsmitteln, Atzen mit Eisen-(III)-Chloridlösung, Wärmebehandlung an Luft zur Erzeugung von Cu-Oxiden und Wärmebehandlung an Luft mit anschließender Wasserstoffreduktion. Von diesen Vorbehandlungen ist die zuletzt genannte Methode für die anschließende Abscheidung einer großflächigen Graphen-Mono-lage am effektivsten. Die chemische Gasphasenabscheidung ist die am meisten verwendete Methode zur Massenproduktion von Graphen. Es besteht aber auch Interesse an alternativen Methoden, die Graphen direkt aus organischen, auf einem Substrat adsorbierten Molekülen, synthetisieren konnen. Jedoch gibt es derzeit nur wenige Studien zu derartigen alternativen Methoden. Solche Prozessrouten erfordern mehrstufige Reaktionen, welche wiederrum die Qualität der erzeugten Graphenschicht limitieren, da nur kleine Korngrößen erreicht werden konnen. Daher wurde in dieser Arbeit ein deutlich einfacherer Weg entwickelt. Es handelt sich dabei um ein Verfahren, bei dem auf einer Cu-Substratoberfläche adsorbierte, organische Lösungsmittelmoleküle in einer Wasserstoffatmosphäre geglüht werden, um eine direkte Bildung von Graphen auf einem sauberen Cu-Substrat zu gewahrleisten.Der Einfluss von Temperatur, Druck und Gasfluss auf diesen einstufigen chemothermischen Syntheseweg wurde systematisch untersucht. Die temperaturabhängigen Untersuchungen liefern einen Einblick in die Wachstumskinetik und thermodynamische Größen, wie zum Beispiel die Aktivierungsenergie Ea, für die Synthese von Graphen aus Aceton, Isopropanol oder Ethanol. Diese Studien untersuchen außerdem die Rolle von Wasserstoffradikalen auf die Graphensynthese. Weiterhin wurde ein verbessertes Verständnis der Rolle von Wasserstoff auf die Graphen-synthese aus adsorbierten, organischen Lösungsmitteln erlangt (beispielsweise im Vergleich zur konventionellen thermischen Gasphasenabscheidung). Die direkte Graphensynthese mittels chemischer Gasphasenabscheidung auf Si-Substraten mit einer Oxidschicht (Si/SiOx ) ist extrem anspruchsvoll in Bezug auf die großflächige und einheitliche Abscheidung (Lagenanzahl) von Graphen-Monolagen. Das direkte Wachstum von Graphen auf Si/SiOx -Substrat ist interessant, da es frei von unerwünschten Übertragungsverfahren ist und kein Metall-substrat erfordert, welche die erzeugten Graphenschichten brechen lassen können. Um ein homogenes Graphenwachstum zu erzielen wurde durch den Kontakt zweier Si-Wafer, mit ihren Oxidflachen zueinander zeigend, eine lokale Umgebung im chemischen Gleichgewicht erzeugt. Diese Konfiguration der Si-Wafer ist nötig, um eine einheitliche Graphen-Monolage bilden zu können. Eine gründliche Untersuchung des abgeschiedenen Materials zeigt, dass trotz der anfänglichen Keimbildung von runden Inseln facettierte Körner erzeugt werden. Aufgrund der Bestrebung der Graphenkörner ihre (Oberflächen-) Energie zu minimieren, wird eine Facettierung der Körner in polygonaler Form erzeugt, was darin begründet liegt, dass das System idealerweise eine Anordnung von hexagonal geformten Körnern erzeugen würde (niedrigster Energiezustand). Der Prozess ist vergleichbar mit der sechseckigen Zellstruktur einer Bienenstockwabe, welche ein Minimum an Wachs erfordert. Dieser Prozess führt auch zu einer nahezu minimalen Gesamtkorn-grenzlänge pro Flächeneinheit. Diese Tatsache zusammen mit der hohen Qualität der resultierenden Graphenschicht spiegelt sich auch in dessen elektrischer Leistungsfähigkeit wider, die in hohem Maße mit der auf anderen Substraten gebildeten Graphenschichten (inklusive Cu-Substrate) vergleichbar ist. Darüber hinaus ist das Graphenwachstum selbstabschliessend, wodurch ein großes Parameterfenster für eine einfache und kontrollierte Synthese eröffnet wird. Dieser Ansatz zur chemischen Gasphasenabscheidung von Graphen auf Si- Substraten ist leicht skalierbar und gegenüber der Abscheidung auf Metallsubstraten konkurrenzfähig, da keine Substratübertragung notig ist. Darüber hinaus ist dieser Prozess auch für die direkte Synthese anderer zweidimensionalen Materialien und deren Van-der-Waals-Heterostrukturen anwendbar.:Contents Quotation v Kurzfassung vii Abstract xi Contents xiii Acronyms xvii 1 Aims and objectives 1 2 Introduction 5 2.1 Carbon allotropes 6 2.1.1 Hybridized sp 2 carbon nanomaterials 6 2.1.2 Graphene 7 2.2 Properties of graphene 8 2.2.1 Crystalline structure 8 2.2.2 Electrical transport 10 2.2.3 Optical transparency 11 2.2.4 Other properties 12 2.3 Graphene deposition methods 13 2.3.1 Synthesis approaches 13 2.3.2 Chemical vapor deposition 14 2.3.3 Substrate selection 15 2.3.4 Substrate pretreatments 16 2.3.5 Carbon feedstock 17 2.3.6 Thermal chemical vapor deposition 17 2.3.7 Plasma chemical vapor deposition 18 2.3.8 Transfer protocol 19 2.4 Chemical vapor deposition for graphene growth 21 2.4.1 Thermodynamics 22 2.4.2 Arrhenius plots 22 2.4.3 Activation energy 24 2.4.4 Growth kinetics 25 2.4.5 Reaction mechanisms over Cu 27 2.4.6 Reaction mechanisms over Ni 29 2.4.7 Reaction mechanisms over non-metals 31 2.4.8 Reaction mechanisms of free-standing graphene 35 2.5 Summary 35 2.6 Scope of the thesis 36 3 Experimental setup and characterization techniques 37 3.1 Experimental setup of chemical vapor deposition 37 3.2 Optical microscopy 39 3.3 Scanning electron microscopy 40 3.4 Atomic force microscopy 41 3.5 Transmission electron microscopy 42 3.5.1 Selected area electron diffraction 44 3.5.2 Dark field transmission electron microscopy 46 3.6 Raman spectroscopy 47 3.7 Ultraviolet-Visible spectrophotometry 49 3.8 Electrical transport measurements 49 4 CVD growth of graphene on oxidized Cu substrates 51 4.1 Motivation 52 4.2 Experimental protocol 53 4.3 Influence of Cu pretreatments on graphene formation 54 4.4 Influence of Cu oxidation on graphene growth 60 4.5 Effect of oxidation pretreatment on Cu surface cleaning 64 4.6 Summary 66 5 Chemo-thermal synthesis of graphene from organic adsorbents 67 5.1 Motivation 67 5.2 Experimental protocol 69 5.3 Influence of reaction temperature on graphene growth 75 5.4 Influence of reaction pressure on graphene growth 78 5.5 Influence of reaction flow rate on graphene growth 80 5.6 Summary 81 6 Monolayer graphene synthesis directly over Si/SiO x 83 6.1 Motivation 83 6.2 Experimental protocol 86 6.3 Influence of substrate confinement configuration 87 6.4 Time dependent evolution for graphene formation 91 6.5 Grain boundaries in graphene film 95 6.6 Bubble clustering of faceted graphene grains 98 6.7 Electrical and optical performance of graphene 100 6.8 Summary 102 7 Conclusions 103 8 Outlook 107 A Graphene synthesis over Cu and transfer to Si/SiO x substrate 111 B Chemo-thermal synthesis of graphene over Cu 115 C CVD graphene growth directly over Si/SiO x substrate 127 Bibliography 147 List of Figures 193 List of Tables 197 Acknowledgements 199 List of publications 203 Erklaerung 20

Image Cluster Berdasarkan Warna Untuk Identifikasi Kematangan Buah Tomat Dengan Metode Valley Tracing

Ciri yang digunakan dalam identifikasi kematangan buah adalah ciri warna (fitur R, G, dan B). Selanjutnya dilakukan clustering dengan metode Single Linkage Hierarchical Method (SLHM) terhadap ciri warna yang diperoleh. Dalam clustering, umumnya harus dilakukan inisialisasi jumlah cluster yang diinginkan terlebih dahulu, padahal pada beberapa kasus clustering, user bahkan tidak tahu berapa banyak cluster yang bisa dibangun. Untuk itu, dalam penelitian ini diaplikasikan metode Valley Tracing. Metode ini merupakan constraint yang akan melakukan identifikasi terhadap pergerakan variance dari tiap tahap pembentukan cluster, dan menganalisa polanya untuk membentuk suatu cluster secara otomatis (automatic clustering). Jumlah cluster yang diperoleh menunjukkan jumlah buah yang diidentifikasi, kemudian nama buah dan jenis kematangan masing-masing buah diperoleh dengan membandingkan nilai centroid tiap cluster dengan nilai centroid data training yang sebelumnya telah disimpan dalam database dan mempunyai label nama buah

Graphene-Like ZnO: A Mini Review

The isolation of a single layer of graphite, known today as graphene, not only demonstrated amazing new properties but also paved the way for a new class of materials often referred to as two-dimensional (2D) materials. Beyond graphene, other 2D materials include h-BN, transition metal dichalcogenides (TMDs), silicene, and germanene, to name a few. All tend to have exciting physical and chemical properties which appear due to dimensionality effects and modulation of their band structure. A more recent member of the 2D family is graphene-like zinc oxide (g-ZnO) which also holds great promise as a future functional material. This review examines current progress in the synthesis and characterization of g-ZnO. In addition, an overview of works dealing with the properties of g-ZnO both in its pristine form and modified forms (e.g., nano-ribbon, doped material, etc.) is presented. Finally, discussions/studies on the potential applications of g-ZnO are reviewed and discussed

A wafer-scale two-dimensional platinum monosulfide ultrathin film via metal sulfurization for high performance photoelectronics

2D nonlayered materials have attracted enormous research interests due to their novel physical and chemical properties with confined dimensions. Platinum monosulfide as one of the most common platinum-group minerals has been less studied due to either the low purity in the natural product or the extremely high-pressure conditions for synthesis. Recently, platinum monosulfide (PtS) 2D membranes have emerged as rising-star materials for fundamental Raman and X-ray photoelectron spectral analysis as well as device exploration. However, a large-area homogeneous synthesis route has not yet been proposed and released. In this communication, we report a facile metal sulfurization strategy for the synthesis of a 4-inch wafer-scale PtS film. Enhanced characterization tools have been employed for thorough analysis of the crystal structure, chemical environment, vibrational modes, and atomic configuration. Furthermore, through theoretical calculations the phase diagram of the Pt–S compound has been plotted for showing the successful formation of PtS in our synthesis conditions. Eventually, a high-quality PtS film has been reflected in device demonstration by a photodetector. Our approach may shed light on the mass production of PtS films with precise control of their thickness and homogeneity as well as van der Waals heterostructures and related electronic devices

Applications of MXenes in human-like sensors and actuators

Human beings perceive the world through the senses of sight, hearing, smell, taste, touch, space, and balance. The first five senses are prerequisites for people to live. The sensing organs upload information to the nervous systems, including the brain, for interpreting the surrounding environment. Then, the brain sends commands to muscles reflexively to react to stimuli, including light, gas, chemicals, sound, and pressure. MXene, as an emerging two-dimensional material, has been intensively adopted in the applications of various sensors and actuators. In this review, we update the sensors to mimic five primary senses and actuators for stimulating muscles, which employ MXene-based film, membrane, and composite with other functional materials. First, a brief introduction is delivered for the structure, properties, and synthesis methods of MXenes. Then, we feed the readers the recent reports on the MXene-derived image sensors as artificial retinas, gas sensors, chemical biosensors, acoustic devices, and tactile sensors for electronic skin. Besides, the actuators of MXene-based composite are introduced. Eventually, future opportunities are given to MXene research based on the requirements of artificial intelligence and humanoid robot, which may induce prospects in accompanying healthcare and biomedical engineering applications. [Figure not available: see fulltext.

Single “Swiss-roll” microelectrode elucidates the critical role of iron substitution in conversion-type oxides

Advancing the lithium-ion battery technology requires the understanding of electrochemical processes in electrode materials with high resolution, accuracy, and sensitivity. However, most techniques today are limited by their inability to separate the complex signals from slurry-coated composite electrodes. Here, we use a three-dimensional “Swiss-roll” microtubular electrode that is incorporated into a micrometer-sized lithium battery. This on-chip platform combines various in situ characterization techniques and precisely probes the intrinsic electrochemical properties of each active material due to the removal of unnecessary binders and additives. As an example, it helps elucidate the critical role of Fe substitution in a conversion-type NiO electrode by monitoring the evolution of Fe2O3 and solid electrolyte interphase layer. The markedly enhanced electrode performances are therefore explained. Our approach exposes a hitherto unexplored route to tracking the phase, morphology, and electrochemical evolution of electrodes in real time, allowing us to reveal information that is not accessible with bulk-level characterization techniques

Development and validation of a sensitive enzyme-linked immunosorbent assay for clonidine hydrochloride in pig urine and pork samples

Clonidine hydrochloride (CLO) is a new substitute for a traditionally used adrenergic agonist. The illegal use of CLO in the livestock industry possess potential harm to human health. Hence, it is an urgent need for the rapid detection of CLO residues. Here, we prepared a highly sensitive and specific monoclonal antibody (mAb) and it used to develop an indirect competitive ELISA (ic-ELISA) for the rapid screening of CLO residues. The limit of detection and limit of quantification values of ic-ELISA were as follows: 0.033 and 0.054 ng/mL for pig urine and 0.061 and 0.096 ng/mL for pork, respectively. Recovery experiment indicated that the ic-ELISA posed outstanding accuracy and precision. Furthermore, the results of ic-ELISA were strongly correlated to the results of HPLC. Thus, the ic-ELISA provided a sensitive and rapid on-site detection of CLO residues in pig urine and pork samples

Applications of nanogenerators for biomedical engineering and healthcare systems

The dream of human beings for long living has stimulated the rapid development of biomedical and healthcare equipment. However, conventional biomedical and healthcare devices have shortcomings such as short service life, large equipment size, and high potential safety hazards. Indeed, the power supply for conventional implantable device remains predominantly batteries. The emerging nanogenerators, which harvest micro/nanomechanical energy and thermal energy from human beings and convert into electrical energy, provide an ideal solution for self‐powering of biomedical devices. The combination of nanogenerators and biomedicine has been accelerating the development of self‐powered biomedical equipment. This article first introduces the operating principle of nanogenerators and then reviews the progress of nanogenerators in biomedical applications, including power supply, smart sensing, and effective treatment. Besides, the microbial disinfection and biodegradation performances of nanogenerators have been updated. Next, the protection devices have been discussed such as face mask with air filtering function together with real‐time monitoring of human health from the respiration and heat emission. Besides, the nanogenerator devices have been categorized by the types of mechanical energy from human beings, such as the body movement, tissue and organ activities, energy from chemical reactions, and gravitational potential energy. Eventually, the challenges and future opportunities in the applications of nanogenerators are delivered in the conclusive remarks. The combination of nanogenerator and biomedicine have been accelerating the development of self‐powered biomedical devices, which show a bright future in biomedicine and healthcare such as smart sensing, and therapy

A wafer-scale two-dimensional platinum monosulfide ultrathin film via metal sulfurization for high performance photoelectronics

2D nonlayered materials have attracted enormous research interests due to their novel physical and chemical properties with confined dimensions. Platinum monosulfide as one of the most common platinum-group minerals has been less studied due to either the low purity in the natural product or the extremely high-pressure conditions for synthesis. Recently, platinum monosulfide (PtS) 2D membranes have emerged as rising-star materials for fundamental Raman and X-ray photoelectron spectral analysis as well as device exploration. However, a large-area homogeneous synthesis route has not yet been proposed and released. In this communication, we report a facile metal sulfurization strategy for the synthesis of a 4-inch wafer-scale PtS film. Enhanced characterization tools have been employed for thorough analysis of the crystal structure, chemical environment, vibrational modes, and atomic configuration. Furthermore, through theoretical calculations the phase diagram of the Pt-S compound has been plotted for showing the successful formation of PtS in our synthesis conditions. Eventually, a high-quality PtS film has been reflected in device demonstration by a photodetector. Our approach may shed light on the mass production of PtS films with precise control of their thickness and homogeneity as well as van der Waals heterostructures and related electronic devices.Web of Science331505149

Applications of MXenes in human-like sensors and actuators

Human beings perceive the world through the senses of sight, hearing, smell, taste, touch, space, and balance. The first five senses are prerequisites for people to live. The sensing organs upload information to the nervous systems, including the brain, for interpreting the surrounding environment. Then, the brain sends commands to muscles reflexively to react to stimuli, including light, gas, chemicals, sound, and pressure. MXene, as an emerging two-dimensional material, has been intensively adopted in the applications of various sensors and actuators. In this review, we update the sensors to mimic five primary senses and actuators for stimulating muscles, which employ MXene-based film, membrane, and composite with other functional materials. First, a brief introduction is delivered for the structure, properties, and synthesis methods of MXenes. Then, we feed the readers the recent reports on the MXene-derived image sensors as artificial retinas, gas sensors, chemical biosensors, acoustic devices, and tactile sensors for electronic skin. Besides, the actuators of MXene-based composite are introduced. Eventually, future opportunities are given to MXene research based on the requirements of artificial intelligence and humanoid robot, which may induce prospects in accompanying healthcare and biomedical engineering applications.Web of Scienc