Wetting of silicon carbide by copper alloys

This work reports on a study of the wetting of SiC by some Copper alloys. The work is intended to gain a deeper understanding on the weeting behaviour of selected CuTi alloys in contact with a polycristalline silicon carbide substrate. Although the main body of this work deals with the CuTi/SiC system a few observations are also reported on the interaction between a CuZr alloy and a silicon infiltrated SiC grade. The contact angles established between the liquid alloys and silicon carbide at 1200°C were measured by the sessile drop method using a vacuum between 10^–4 and 10^–5 Pa. Since the interface generated between the metallic and ceramic phases in a composite material is a region that plays a critical role in determining its mechanical properties the obtained specimens were subsequently characterised using a SEM fitted with EDS facilities. X-ray diffraction was used to determine the phases formed while DSC analyses were employed to determine the temperatures for the formation of reaction products.     

Stability of amorphous Fe-W alloys in multilayer metallizations on silicon

Co-sputtered amorphous Fe_0.37 W_0.63 alloys were investigated for applications as diffusion barriers in multilayer metallizations on silicon. Interface reactions and recrystallization during thermal annealing at 400–800°C were studied by back-scattering spectrometry and X-ray diffraction. On SiO₂ substrates the recrystallization of these films occurs at approximately 700°C. On silicon the recrystallization is accompanied by the formation of a silicide layer containing FeSi₂ and WSi₂ phases. No detectable reaction is observed when the alloy film is amorphous. In contact with an overlay metal such as aluminum, copper, nickel or platinum the amorphous Fe_0.37 W_0.63 layer prevents direct interaction between the silicon substrate and an overlay metal film 1000 Å thick during thermal annealing for 30 min at 650°C. The lifetime of the barrier is limited by dissolution and compound formation at the interface and at grain boundaries of the overlay metal.     

Physicochemical interaction at the MnSi1.71–1.75/Mo interface

Diffusion processes at the interface between higher manganese silicide (HMS) MnSi_1.71–1.75 and Mo at elevated temperatures have been studied by microstructural analysis and X-ray microanalysis. The results demonstrate the formation of a reaction diffusion zone at the HMS/metal interface. The compositions of the phases identified in intermediate layers are consistent with phase equilibria in the ternary system Mn-Mo-Si, and their electrical and thermal conductivity is high enough not to create an energy barrier in the contact zone with the semiconductor. The thermal expansion mismatch between the phases in contact may degrade the bonding between the layers.     

Reactive wetting in metal/metal systems: Dissolutive versus compound-forming systems

Reactive wetting in metal–metal systems involves complex interactions between the molten phase and the solid substrate. The simplest interaction involves only the dissolution of the substrate into the molten phase. The more complex interaction involves both dissolution of the substrate and compound formation at the solid–liquid boundary. The fundamental differences between these two types of reactive wetting are identified by studying the purely dissolutive system Bi–Sn and the compound-forming system Au–Sn. Experiments employ the traditional sessile drop technique as well as a novel two-dimensional drop transfer technique that enables real-time visualization of the solid–liquid interface evolution. Recent results from wetting of pure Sn on Au-coated Cu substrates are also presented and reveal a much richer wetting behavior than either Sn on Au or Sn on Cu binary systems.     

金属/半导体肖特基接触模型研究进展

在分析理想金属/半导体肖特基接触的基础上,概述了一般情形下肖特基接触的形成机理和影响因素。金属/半导体间的界面层使得肖特基势垒高度(SBH)对功函数的依赖减弱,也导致SBH与外加偏压有关。研究证实,多种因素,如界面晶向、原子结构、化学键和结构不完整性等,都会造成SBH的空间不均匀分布。该特性在肖特基接触中普遍存在,并对基于肖特基结的器件工作有显著影响。     

Wetting behaviour of lead-free Sn-based alloys on Cu and Ni substrates

The present work was carried out in the framework of the study of new lead-free solder alloys for technical applications in electronic devices. In the focus of this characterisation the wetting behaviour of several Sn-rich alloys belonging to the In–Sn, Au–Sn and Cu–Sn systems has been studied by measuring the contact angle variations on Cu and Ni substrates as a function of time and temperature. The interface between the alloy and the substrate has been analysed by the use of optical microscopy and scanning electron microscopy combined with energy-dispersive X-ray spectrometry in order to study the reaction between the alloy and the solid substrate and the possible formation of different compounds at the interface. A remarkable effect of the two different substrates on the behaviour of the contact angle as a function of temperature and on the morphology of the interface between the liquid solder and the solid substrate was observed for the In–Sn and Cu–Sn, while the Au–Sn system shows a very similar wetting behaviour on Cu and Ni.     

Spreading of liquid lead droplets on metallic iron covered by silicon oxide particles or films

As well known, the spreading of a liquid metal droplet on a solid metal is very sensitive to the presence of chemical heterogeneities on the solid metal. In this study, wetting experiments with liquid lead on heterogeneous surfaces composed of iron and silicon oxide particles or films were performed using the dispensed drop technique. High purity iron and binary iron–silicon substrates with different silicon contents were studied. Before the wetting experiments, the substrates are annealed at 850 °C in a N₂–H₂ atmosphere in order to reduce iron oxides and to form silicon oxide particles or films on the surface. The liquid lead droplet is then released onto the metallic substrate partly or wholly covered by the oxides. The spreading of the liquid metal droplet strongly depends on the surface area fraction covered by the oxides.     

Wettability and phase formation in TiC/Al-alloys assemblies

The effect of alloying elements on the wetting behavior of TiC substrates by commercial aluminum alloys (1010, 2024, 6061, 7075) and its relation to phase formation at the metal–ceramic interface was investigated at 900 °C using a sessile drop technique. It was found that wetting behavior in Al-alloys/TiC is typical of reactive systems, furthermore, wettability of TiC by pure Al-1010 was better than the alloys. Interface examination revealed the formation of Al₄C₃ in all the cases; the thickness of the reaction layer varied within the samples and was discontinuous in nature, particularly for the 7075/TiC and 6061/TiC systems, which exhibited poor wetting. The formation of alloyed phases in the ceramic surface decreased the amount of the undesirable Al₄C₃ at the metal/ceramic interface.     

Wetting behaviors and interfacial characteristics of molten AlxCoCrCuFeNi high-entropy alloys on a WC substrate

The wettability of molten AlxCoCrCuFeNi(x is from 0 to 1.5,mol.％)high-entropy alloys(HEA)on a WC substrate was measured using a modified sessile drop method at 1823 K in an argon atmosphere.The wetting behaviors and interfacial characteristics between HEAs and WC were studied.Good wettability with final equilibrium contact angles of 0.5°-4.6° is obtained,and addition of Al deteriorates the wettabil-ity of the HEAs.The wetting of AlxCoCrCuFeNi/WC system can be roughly divided into an initially sharp spreading stage and a subsequent steady-state phase.In the first stage,the adsorption of Cr atoms at the solid-liquid interface primarily contributes to the wetting,and the contact angle drastically reduces.However,both the wetting behavior and interfacial microstructure are determined by the Al content of the HEA in the next stage.For x≤0.5,the wetting is mainly driven by the dissolution of WC,although a few reaction products of(W,Cr)2C are observed.Moreover,an obvious dissolution pit appears at the surface of the substrate.When the Al content of x≥1,the interfacial reaction is dominant in competition with the dissolution of WC,and massive reaction products precipitate at the HEA/WC interface,which leads to the formation of a continuous reaction layer.     

The effect of carbon nanolayers on wetting of alumina by NiSi alloys

Ionocovalent oxides such as alumina, silica or magnesia are not wetted by Si and Si-rich alloys, the contact angles being close to 90°. The aim of this work is to study the effect of submicron carbon layers on wetting in this type of system. In principle, silicon reacts with carbon to form silicon carbide, a compound wettable by Si alloys. However, the formation of silicon carbide at the interface can be affected by the dissolution of this compound into the molten alloy occurring in order to saturate the melt in carbon. These phenomena are studied using a model system consisting of Ni–63 at.%Si alloy and monocrystalline alumina substrate coated with carbon layers. Wetting experiments are performed by the dispensed drop technique in high vacuum varying the parameters: thickness of coating (from 0 to 100 nm), temperature and degree of carbon saturation of the alloy. The surfaces and reactive interfaces are characterised by SEM, X-ray microanalysis and XPS.     

The effect of thermodynamic properties of Me–Ti (Me = In,Sn, Ga,Au, and Ge) melts on the wetting of the CaF<Subscript>2</Subscript> substrate

The effect of Ti additions on the wetting behavior of CaF₂ by non-reactive liquid metals (In, Sn, Ga, Au, Ge) was investigated. Pure metals do not wet CaF₂ while minor additions of Ti improve wetting. Small changes of the contact angle were observed in the CaF₂/Au–Ti and CaF₂/Ge–Ti systems, which are characterized by strong Me–Ti interaction in the melt, while considerable decrease of contact angle was obtained in the CaF₂/In–Ti, CaF₂/Sn–Ti and CaF₂/Ga–Ti systems, which display a relatively weak Me–Ti interaction. According to a thermodynamic analysis and experiential observations, Ti does not react with the substrate to form condensed phases at the metal/CaF₂ interface. Therefore, it was assumed that the mechanism of the wetting improvement is attributed to the Ti segregation at the interface. The results of the XPS analysis confirm a Ti enrichment of the region close to the interface, moreover, according to the high resolution XPS spectrum, obtained from this region, the position of the In4d peak has a chemical shift, which is typical for In–Ti intermetallic compounds. The XPS analysis does not provide sufficient evidence for the formation of the intermetallic interfacial layer at elevated temperature. Thus, further investigations have to be designed and conducted in order to clarify this issue.     

On the Wetting States of Low Melting Point Metal Galinstan® on Silicon Microstructured Surfaces

The primary goal of this article is to measure the wetting characteristics of a low melting point metal to determine the efficacy of this type of material for possible use in thermal energy storage applications. Galinstan®, a commercially available alloy consisting of Gallium, Indium, and Tin is subjected to contact angle measurements on various silicon surfaces at varying temperatures. Due to the oxidation characteristics of Galinstan, all experiments are conducted in an inert nitrogen environment (<0.5 ppm oxygen) to maintain fluid‐like properties. This work finds that although contact angle changes with substrate and surface structure, temperature has no observable effect on contact angle. Contact angles range from 141° on smooth silicon to greater than 160° on silicon micropillars. Although a temperature dependence is not observed over the range of temperatures studied, having wetting properties of Galinstan on various surfaces is a step toward better understanding the capabilities of this and similar materials in energy management.

     

金属与半导体肖特基接触势垒模型及其载流子传输机制的研究进展

肖特基结具有整流特性,在整流器和光电检测等电子元器件制造中有极其重要的应用,重点介绍了相关研究人员在金属与半导体肖特基接触势垒的形成机理、相关数学模型及其影响因素等方面的研究进展。有研究表明,肖特基势垒的形成主要是由于费米能级的钉扎,而费米能级钉扎则源于界面新相的形成或界面极化键的存在。同时,在肖特基势垒的相关模型中,热电子激发模型是目前应用最为广泛的、用于解释界面载流子传输机制的肖特基接触势垒模型。随着对接触界面载流子传输机制的深入研究,热发射-扩散、热场发射等载流子传输机制模型相继被研究者提出。另外,相关研究表明,快速退火处理可导致肖特基接触界面处的原子扩散、重排、新相生成等现象,对肖特基接触的稳定性产生重要影响。     

Reactive wetting of alumina by Ti-rich Ni–Ti–Zr alloys

Active brazing is a commonly used method for joining ceramic materials. In the present study, the wetting behavior of four Ti-rich ternary Ni–Ti–Zr alloys was investigated through sessile drop experiments on alumina disks of 96 and 99.9 % purity. The microstructure at the metal/alumina interface was analyzed using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Three of the analyzed alloys exhibited reactive wetting with final contact angles between 40° and 70°. The reaction phases at the metal/alumina interface had a thickness of about 1 µm and were of a similar composition for all alloys. Dilatometer measurements showed thermal expansion coefficients between 13.2 and 15.8 × 10^?6 °C^?1. The lowest wetting angle of 40° was achieved with the alloy 61Ti–20Zr–19Ni at temperatures above 980 °C.     

Thermoelectric voltage at a nanometer-scale heated tip point contact

We report thermoelectric voltage measurements between the platinum-coated tip of a heated atomic force microscope (AFM) cantilever and a gold-coated substrate. The cantilevers have an integrated heater-thermometer element made from doped single crystal silicon, and a platinum tip. The voltage can be measured at the tip, independent from the cantilever heating. We used the thermocouple junction between the platinum tip and the gold substrate to measure thermoelectric voltage during heating. Experiments used either sample-side or tip-side heating, over the temperature range 25-275?°C. The tip-substrate contact is ～4?nm in diameter and its average measured Seebeck coefficient is 3.4?μV?K(-1). The thermoelectric voltage is used to determine tip-substrate interface temperature when the substrate is either glass or quartz. When the non-dimensional cantilever heater temperature is 1, the tip-substrate interface temperature is 0.593 on glass and 0.125 on quartz. Thermal contact resistance between the tip and the substrate heavily influences the tip-substrate interface temperature. Measurements agree well with modeling when the tip-substrate interface contact resistance is 10(8)?K?W(-1).     

Electroless deposition,post annealing and characterization of nickel films on silicon

Electroless deposition of nickel (EN) films on n-type silicon has been investigated under different process conditions. The interface between the film and substrate has been characterized for electrical properties by probing the contact resistances. X-ray diffraction and atomic force microscopy have been performed to obtain information about the structural and morphological details of the films. As a comparative study, nickel films have also been sputter deposited on silicon substrates. An as-deposited electroless film is observed to form non-ohmic contact while in a sputtered film prepared without the application of substrate heating, the formation of metal-insulating-semiconductor type junction is seen.     

The tribovoltaic effect

Contact electrification (or triboelectrification) (CE) is a universal phenomenon between any two materials or two phases of materials. But a contact between two different materials may results in different output. When a p-type semiconductor sliding on a n-type semiconductor surface, the current flowing between the two electrodes on the top of the p-type and the bottom of the n-type is a direct current. This phenomenon is called tribovoltaic effect discovered in the last few years. The mechanism of the tribovoltaic effect is resulted from the electron-hole pairs generated at the PN junction due to the energy released by the formation of the newly formed chemical bonds at the interface due to mechanical sliding, and the inner field built at the PN junction separates the electrons from the holes, resulting in a DC output. The energy released by forming a chemical bond is called “bindington”, which serves as the exciton for exciting the electron-hole pairs, in analogy to the photovoltaic effect. Here, we first review the recent works on the tribovoltaic effect observed at different interfaces. Then, the mechanism of the tribovoltaic effect is presented. The surface chemical methods for regulating the tribovoltaic effect are discussed. Finally, a technique of hybrid tribovoltaic nanogenerator based on the tribovoltaic effect and its potential applications are elaborated.     

On the Role of Contact Resistance and Electrode Modification in Organic Electrochemical Transistors

Contact resistance is renowned for its unfavorable impact on transistor performance. Despite its notoriety, the nature of contact resistance in organic electrochemical transistors (OECTs) remains unclear. Here, by investigating the role of contact resistance in n‐type OECTs, the first demonstration of source/drain‐electrode surface modification for achieving state‐of‐the‐art n‐type OECTs is reported. Specifically, thiol‐based self‐assembled monolayers (SAMs), 4‐methylbenzenethiol (MBT) and pentafluorobenzenethiol (PFBT), are used to investigate contact resistance in n‐type accumulation‐mode OECTs made from the hydrophilic copolymer P‐90, where the deliberate functionalization of the gold source/drain electrodes decreases and increases the energetic mismatch at the electrode/semiconductor interface, respectively. Although MBT treatment is found to increase the transconductance three‐fold, contact resistance is not found to be the dominant factor governing OECT performance. Additional morphology and surface energy investigations show that increased performance comes from SAM‐enhanced source/drain electrode surface energy, which improves wetting, semiconductor/metal interface quality, and semiconductor morphology at the electrode and channel. Overall, contact resistance in n‐type OECTs is investigated, whilst identifying source/drain electrode treatment as a useful device engineering strategy for achieving state of the art n‐type OECTs.     

高温下前驱膜形成机制的研究进展

本文综述了高温下前驱膜的形成机制，即表面扩散机制、蒸发-凝结机制、皮下渗透机制和快速吸附-薄层漫流机制。在实验表征的金属/金属润湿体系中，最有可能的机制为皮下渗透机制，其形成与表观接触角、接触半径、固体金属与氧化膜的间隙大小有关。在金属/陶瓷体系中，前驱膜的形成通常为快速吸附-薄层漫流机制。前驱膜为吸附机制时，需要满足液/固界面的相对惰性和高亲和力这一矛盾体。同时介绍了高温反应润湿体系中，前驱膜的另一种可能的机制，即薄膜传输机制；指出研究前驱膜的难点在于前驱膜的不可预测性和不稳定性，其发展方向应趋于系统化，并建立相应的理论模型。