Mo Thin Films Research Articles

Role of growth temperature on microstructural and electronic properties of rapid thermally grown MoTe2 thin film for infrared detection

In the field of electronic and optoelectronic applications, two-dimensional materials are found to be promising candidates for futuristic devices. For the detection of infrared (IR) light, MoTe2possesses an appropriate bandgap for which p-MoTe2/n-Si heterojunctions are well suited for photodetectors. In this study, a rapid thermal technique is used to grow MoTe2thin films on silicon (Si) substrates. Molybdenum (Mo) thin films are deposited using a sputtering system on the Si substrate and tellurium (Te) film is deposited on the Mo film by a thermal evaporation technique. The substrates with Mo/Te thin films are kept in a face-to-face manner inside the rapid thermal-processing furnace. The growth is carried out at a base pressure of 2 torr with a flow of 160 sccm of argon gas at different temperatures ranging from 400 °C to 700 °C. The x-ray diffraction peaks appear around 2θ= 12.8°, 25.5°, 39.2°, and 53.2° corresponding to (002), (004), (006), and (008) orientation of a hexagonal 2H-MoTe2structure. The characteristic Raman peaks of MoTe2, observed at ∼119 cm-1and ∼172 cm-1, correspond to the in-plane E1gand out-of-plane A1gmodes of MoTe2, whereas the prominent peaks of the in-plane E12gmode at ∼234 cm-1and the out-of-plane B12gmode at ∼289 cm-1are also observed. Root mean square (RMS) roughness is found to increase with increasing growth temperature. The bandgap of MoTe2is calculated using a Tauc plot and is found to be 0.90 eV. Electrical characterizations are carried out using current-voltage and current-time measurement, where the maximum responsivity and detectivity are found to be 127.37 mA W-1and 85.21 × 107Jones for a growth temperature of 600 °C and an IR wavelength illumination of 1060 nm.

The n-MoO3/p-Si heterojunction photodiode: Influence of the MoO3 film thickness on the ultraviolet and infrared photodetector performance

Here, we studied the effect of the MoO3 thin film thickness on the ultraviolet (UV) and infrared (IR) photodiode properties of the n-MoO3/p-Si heterojunction structure. Initially, the metal molybdenum (Mo) thin films with different thicknesses (50,150, and 250 nm) were created via DC magnetron sputtering on a p-type Si substrate. Then, the MoO3 thin films were synthesized using a thermal oxidation method with an optimal oxygen flow rate of 60sccm. XRD and Raman analysis showed that the structure of prepared thin films has converted from an amorphous to an orthorhombic (α-MoO3) crystalline phase with increasing thickness. The optical transmittance of the layers was tuned by controlling the thickness, and the maximum transmittance for the 50 nm-thick film was achieved in the broad wavelength range of 300–1100 nm. The current density–voltage (J–V) characteristics indicate the prepared samples' rectifying behavior under dark conditions. The heterojunction photodiode with a 50 nm-thick MoO3 layer shows the best performance. This sample had a maximum amount of transmittance in the UV–visible and IR regions, compared to other samples, which leads to efficient electron-hole separation and transportation. This sample demonstrates a significant photoresponse ratio (ILight/IDark) of about 55 and 52.5 in the ultraviolet (UV) and infrared (IR) regions, respectively.

Enhancing flexible electronics: Unveiling the role of strain rate in the performance of molybdenum-coated PET films

This work analyzes the mechanical and electrical properties of molybdenum (Mo) thin films at 100 and 200 nm thicknesses under different strain and strain rate circumstances. The study examines Mo film deposition by RF magnetron sputtering on PET substrates and their mechanical stress behavior. The investigation reveals distinct patterns of crack initiation and propagation, where primary cracks predominantly appear perpendicular to the direction of applied strain, and secondary cracks develop due to stress redistribution, displaying a complex interplay between film thickness, strain rate, and crack morphology. A key finding of this study is the observation of more advanced and irregular crack patterns in thicker films (200 nm) subjected to higher strain rates (1000 mm/min), suggesting a heightened sensitivity to mechanical stress and a more chaotic fracture process compared to thinner films or those under lower strain rates. Additionally, instances of film edge delamination, particularly under high strain conditions, highlight the challenges in maintaining film-substrate adhesion and integrity under extreme mechanical deformation. The research provides critical insights into the mechanical robustness and electrical performance of Mo thin films, emphasizing the influence of microstructural properties, deposition parameters, and external stressors on their applicability in high-tech industries. The findings underscore the importance of optimizing deposition techniques and understanding material behavior under stress to enhance the durability and reliability of Mo thin films in practical applications, ranging from semiconductor devices to photovoltaic systems.

The effect of annealing on micro-hardness of molybdenum single crystals

Molybdenum (Mo) crystals exhibit excellent mechanical properties such as high yield strength, high elastic modulus, very high melting point, and excellent corrosion resistance, making them a suitable choice for various industrial applications. The mechanical behaviour of these crystals has been investigated through tension, compression, and indentation experiments. The indentation experiments on annealed Mo single-crystal thin film show an increase in hardness with increase in annealing temperature from 400 °C–650 °C. However, it is not clear whether this behaviour is specific to the Mo thin films or these are applicable to the bulk samples of single crystals also. In order to address these issues, the Vickers indentation experiments are performed on as-received and annealed samples of (100) -, (110) -, and (111) -oriented Mo single crystals. The results show that the low-temperature annealing leads to an increase in micro-hardness by 9% for (100) oriented crystals. The x-ray diffraction (XRD), electron backscatter diffraction (EBSD) and energy dispersive x-ray spectroscopy (EDS) studies have shown that there is a drop in the number of dislocation sources or dislocation density ( ρ ) with no high-angle grain boundary formation or any microstructural changes or any oxide formation. This necessitates to enhance the applied stress required for significant yielding (or yield strength) which results in an increase in the hardness. Based on experimental observations, a hardening mechanism governed by dislocation annihilation during annealing has been proposed in the present study.

Native surface oxidation phenomena of DC-Sputtered molybdenum thin film in tropical environment

Molybdenum (Mo) is a versatile refractory metal that has been widely used as back contact in thin film photovoltaic cells. However, Mo tends to react with oxygen in ambient environment which influences its original properties. In this study, Mo thin films were stored in different environments (in vacuum desiccator and open air) for 8760 h. Subsequently, these films were characterized and analyzed by Grazing Incidence X-Ray Diffractometer (GIXRD), Raman spectroscopy, Field Emission Scanning Electron Microscopy coupled with Energy Dispersive X-Ray Spectroscopy (FESEM-EDX), Conductive Atomic Force Microscopy (C-AFM), and Hall Effect measurement system. It was found that Mo thin film kept in open air at room temperature undergoes surface oxidation which results in random growth of nanostructured MoOx. Formation of these observed oxide compounds on the surface is correlated with decrement in the electrical conductivity mainly through lower carrier mobility. Preliminary results highlighted from this study can serve as general guideline for handling, storage and transportation requirements forMo thin film in tropical environment.

Processing and Functionalization of Vertical Graphene Nanowalls by Laser Irradiation.

The processing of vertical graphene nanowalls (VGNWs) via laser irradiation is proposed as a means to modulate their physicochemical properties. The effects of the number of applied pulses and fluence of each pulse are examined. Raman spectroscopy studies the effect of irradiation on the chemical structure of the VGNWs. Results show a decrease in density of defects and number of layers, which points toward a mechanism including evaporation of amorphous or loosely bonded C from defective points and recrystallization of graphene. Moreover, the effect of laser irradiation parameters on the morphology of Mo thin films deposited on VGNWs is investigated. The received thermal dosage results in the formation of particles. In this case, the number of pulses and pulse fluence are found to affect the size and distribution of these particles. The study provides a novel approach for the functionalization of VGNWs via laser irradiation, which can be extended to other graphene-based nanostructures.

A high-performance infrared photoacoustic sensor with improved low-frequency response microphone

Infrared photoacoustic gas sensors with the advantages of good selectivity, low interference, fast response speed, good stability, high accuracy, good explosion-proof performance, high signal-to-noise ratio, and long service life, have developed rapidly in recent years. In order to solve the problem of poor low-frequency response performance of the MEMS piezoelectric thin film microphone sensor prepared with AlN and Mo thin films in infrared photoacoustic gas sensors, this article analyzes its principle and tests an improved solution. The internal stress distribution was changed through hot tempering experiments, significantly improving its structure. The article qualitatively and quantitatively analyzes the inherent mechanism of this phenomenon. The experimental results confirm that the improved scheme improves its response performance under low-frequency signals, with good stability and repeatability.

Tailoring the surface properties of molybdenum oxytelluride thin films by its compositional ratio

In this work, RF magnetron co‐sputtering was used to fabricate molybdenum oxytelluride thin films with different atomic ratios. Scanning electron micrographs and atomic force micrographs revealed that pure Mo thin films were segregated. Thin films with 40% Te content portrayed needle‐like structures and thus had the largest Rq value of 2.48 nm. Contact angle measurements further supported the findings as the thin films with 40% Te content were the most hydrophobic. X‐ray photoelectron spectroscopy results revealed that the major oxidation states of Mo from Te‐poor to Te‐rich TFs were changed from high (+6) to low (+4 and/or +2). X‐ray diffraction data showed that peaks pertaining to molybdenum oxide species appeared, notably at 33.048° and 33.115°. Ultraviolet photoelectron spectroscopy and Kelvin probe measurements evinced that the work function increases with increasing Te content. Four‐point probe measurements revealed that molybdenum oxytelluride thin films tend to have higher electrical conductivity than pure Mo and Te thin films.

Numerical evaluation of grain boundary electron scattering in molybdenum thin films: A critical analysis for advanced interconnects

We present a methodology for numerically evaluating grain boundary scattering in polycrystalline molybdenum (Mo) thin films. Two types of Mo films (an epitaxially grown (110)-single-crystal film and a <110>-fiber-textured polycrystalline thin film) were sputter-deposited under identical conditions on a lattice-matched (112‾0)-Al2O3 substrate and an amorphous glass substrate, respectively. This indicates equal background scattering (phonon and impurity scattering) for the two types. Further, the selected film thickness (236 nm) significantly exceeds Mo's inherent electron mean free path (11.2 nm), rendering surface scattering contributions negligible. The resistivity difference is therefore attributed to the grain boundary scattering. Using the Mayadas–Shatzkes model and an average grain size of 80.9 ± 2.8 nm (measured from a statistically significant number of grains (747)), the grain-boundary reflection coefficient for Mo films was determined to be 0.48 nm. The presented methodology, not limited to Mo, is expected to serve as a reliable analytical approach for advanced interconnects.

Role of Mo thickness in growth of nanostructured MoO3 and their optical sensing properties

The main objective of the present work is to investigate the role Mo thickness in growth of nanostructured MoO3 and their application for optical sensors like photodetectors. The devices were fabricated using standard scalable microfabrication techniques. MoO3 was synthesized by Mo thin film deposition using sputtering followed by dry oxidation at 550 °C. Further, these samples were tested as photodetectors for visible regions. The test results confirm that the devices are more sensitive towards 450 nm. The photodetector made on 80 nm Mo thickness exhibited a higher responsivity of 730 mA W–1, higher detectivity of 2.47 × 1011 Jones, and higher photo to dark current ratio (PDCR) of 1.33 × 102 compared to other tested samples. Moreover, the optimized photodetector showed higher repeatability and a faster speed of 13/11 ms. These developed photodetectors could be vital for the visible light optical sensing era.

Influence of selenization temperature on structure and optical band gap of MoSe&lt;sub&gt;2&lt;/sub&gt; thin film

In recent years, MoSe&lt;sub&gt;2&lt;/sub&gt;, as a kind of transition metal dichalcogenide, has aroused widespread research interest due to its special crystal structure with different electrical and optical properties. The band gap of molybdenum diselenide can be manipulated by different layers, strain engineering, doping, or the formation of heterostructures, which makes it potential advantages in optoelectronic devices and photovoltaic applications. In this work, we investigate the influence of selenization temperature on the structures and optical properties of the MoSe&lt;sub&gt;2&lt;/sub&gt; films. Molybdenum (Mo) thin films are prepared by RF magnetron sputtering, and then MoSe&lt;sub&gt;2&lt;/sub&gt; thin films are generated by selenization annealing. The surface morphology, crystal structure, and optical bandgap for each of the MoSe&lt;sub&gt;2&lt;/sub&gt; thin films are characterized and analyzed by using scanning electron microscopy, X-ray diffraction, and ultraviolet visible spectroscopy, respectively. The results show that the crystal structures of the MoSe&lt;sub&gt;2&lt;/sub&gt; thin films are closely related to the selenization temperature (&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;s&lt;/sub&gt;): with the increase of selenization temperature, the average grain size in the thin film decreases slightly and then increases rapidly from 24.82 nm to 55.76 nm. Meanwhile, the (002) crystal plane of MoSe&lt;sub&gt;2&lt;/sub&gt; also exhibits preferential growth with temperature increasing. Each MoSe&lt;sub&gt;2&lt;/sub&gt; thin film has a low absorption rate for short-wavelength light (around 600 nm). With the increase of selenization temperature, the bandgap waves of the MoSe&lt;sub&gt;2&lt;/sub&gt; thin films are blue-shifted, and the optical bandgaps decrease, which is attributed to the fact that different selenization temperatures cause the lattice size of MoSe&lt;sub&gt;2&lt;/sub&gt; to change, thereby affecting the spatial expansion of its electronic wave function. In addition, the structure and optical bandgap of MoSe&lt;sub&gt;2&lt;/sub&gt; can be effectively controlled by changing the selenization temperature, which provides more possibilities for the applications of the MoSe&lt;sub&gt;2&lt;/sub&gt; thin films in optical devices.

High-energy sputtering for the deposition of a conductive and adherent single molybdenum layer for solar cell applications

Molybdenum (Mo) thin films are thought to be an excellent back contact for CuIn1-xGaxSe2 (CIGS) solar cells. Mo films require high conductivity and good adhesion to glass substrates; however, these characteristics cannot be combined in sputtered Mo under the same deposition conditions. Direct current Magnetron Sputtering (DcMS) and High-Power Impulse Magnetron Sputtering (HiPIMS) were used to deposit Mo films on glass substrates, and the effects of working pressure and substrate bias on their characteristics were investigated. To begin, single layers of Mo were produced at pressures ranging from 0.2 to 1.4 Pa. The Mo films deposited at the lowest working pressure of 0.2 Pa were then subjected to a negative substrate bias varying from -50 to -200 V. All of the HiPIMS films adhered well to the glass substrate, whereas the DcMS films deposited at various pressures showed poor adhesion. Furthermore, our findings demonstrated that applying a negative substrate bias reduced the resistivity of Mo films to the lowest values of 2.56 × 10−5 Ω.cm and 2.771 × 10−5 Ω.cm, respectively, for the HiPIMS and DcMS-deposited films, while improving the adhesion of the DcMS-samples due to the development of films with homogenous stress distribution.

Effect of in situ annealing on pulsed laser ablated mixed metal oxide (BixMyOz; M=Mn, Mo) thin film electrodes for flexible hybrid supercapacitor devices

Recently, solid-state thin film hybrid supercapacitor devices (TFHSCs) have had greater attention due to their miniaturized device assembly, portability, and superior cycling stability. Herein, for the first time, we assembled BiMnxOy ǁ PVA-KOH ǁ Bi2MoO6 thin-film solid-state supercapacitor devices by pulsed laser deposition (PLD) technique. In the present work, Bi2MoO6 and BiMnxOy thin film electrodes are fabricated at in-situ annealed conditions and their structural, morphological, and electrochemical performances are examined distinctly. We assembled a thin-film based BiMnxOy ǁ PVA-KOH ǁ BiMnxOy symmetric supercapacitor device (SSD) and that device delivers a functioning voltage of 1.4 V. Also, the device exhibits an extremely specific areal capacitance of 41 mF cm−2 at 1 mA cm−2. Similarly, a thin film-based Bi2MoO6 ǁ PVA-KOH ǁ Bi2MoO6 SSD attained a maximum specific areal capacitance of 13.33 mF cm−2. Further, the assembled BiMnxOy ǁ PVA-KOH ǁ Bi2MoO6 TFHSC device delivers a voltage of 1.6 V and the TFHSC device exhibited a maximum specific areal capacitance of 52 mF cm−2 at a fixed current density of about 2 mA cm−2. The BiMnxOy ǁ PVA-KOH ǁ Bi2MoO6 TFHSC device shows outstanding stability performances such as 99 % of capacitance retention as well as 93 % of coulombic efficiency after 25,000 charge/discharge cycles. Additionally, the TFHSC device delivers a maximum areal energy density and power density of 18.5 μWh.cm−2, and 978.7 μW cm−2, respectively.

Enhanced Diffuse Reflectance of Photons in Molybdenum Back Electrode Films Achieved via Surface Texturing for Thin Film Solar Cells

Molybdenum (Mo) thin film is widely used as the bottom electrode in substrate‐configured thin film solar cells due to its high conductivity and reflectivity. Mo grown onto microtextured substrates increases the diffuse reflection of incident photons via scattering/multiple reflections on the corner/edges, in addition to the contribution from increased surface area. Herein, bilayer Mo is grown using direct current magnetron sputtering onto plain and textured substrates. To texture the glass substrate surface, a periodic array of cross‐linked photoresist structures (SU‐8 2000.5 &amp; SU‐8 2005) is introduced via UV‐lithography process. Characterizations are done using X‐ray diffractometer, optical microscope, scanning electron microscope, and optical profilometer. Angle‐dependent specular reflectance, diffuse reflectance, and electrical measurements done on Mo grown on plain and textured substrates lead to a comprehensive understanding of the advantages of growing Mo films on textured substrates. The electrical resistivity of Mo grown on plain and textured substrates is of the same order, measuring 3.09 × 10−5 Ω cm, 3.25 × 10−5 Ω cm, and 3.87 × 10−5 Ω cm, respectively. A high‐diffuse reflectance of 62.7% is obtained for SU‐8 2005 textured Mo films. Investigations using COMSOL simulations support the optical reflectance analysis.

Understanding the Role of Underlying Substrates on Hydrogen Evolution Reaction (HER) Catalytic Activity of Atomically Dispersed Pt Atoms

Electrochemical water splitting is an environmentally friendly way of producing hydrogen, but this process requires highly efficient catalysts. Platinum (Pt) is known the best catalyst for hydrogen evolution reaction (HER) in acidic media, but the scarcity and high cost of Pt limits its applicability in widespread technologies. In this work, we have uncovered the role of underlying substrate on the HER activity of atomically dispersed Pt atoms. A DC magnetron sputtering technique has been utilized to deposit transition metal (Cu, Mo, W, Ti and Ta) thin films as underlying substrates for atomically dispersed and extremely low loading of Pt (< 1.5 at%). As synthesized samples were characterized as electrocatalysts for the HER in both alkali and acidic media. In combination of standard electrochemical experiments (e.g., CV), the differential electrochemical mass spectrometry (DEMS) results show that despite low loading of Pt, the prepared catalysts produce hydrogen at a rate comparable with that of a pristine Pt. Based on the XPS study, the excellent performance is attributed to the modified electronic properties of the Pt atoms due to interaction with underlying substrates. Additionally, the performance of the Pt atoms is significantly governed by the physical properties of underlying substances. Our catalysts also displayed good stability for HER activity and found to be stable after 1000 cycles of continuous operation.

DC Saçtırma Metoduyla Üretilmiş Çift Katmanlı Mo İnce Filmlerin Yarı Kantitatif Doku Analizinin Yapılması ve Kutup Figürlerinin Araştırılması

Molibden (Mo) malzemesi benzersiz özellikleri sayesinde birçok farklı alanda kullanılmaktadır. İnce filmlerin doku analizleri sayesinde katmanlar arası arayüz durumlarının uyumluluğu araştırılmaktadır. Üretim parametrelerine ve sonrasında yapılan işlemlere göre filmlerin dokuları değişebilmektedir. Bu sebeple kullanım alanına bağlı olarak en uygun dokuya sahip Mo ince filmlerin üretilmesi için ideal üretim parametrelerinin belirlenmesi gerekmektedir. Bu çalışmada, CIGS güneş gözesi uygulamalarında sıklıkla istenen BCC yapısında ve (110) düzlemindeki Mo ince filmler üretilebilmiştir. Üretim, Mo filmin alttaş yüzeyine tutunumunu ve elektriksel iletkenliğini iyileştirmek için çift katmanlı üretim stratejisi kullanılarak gerçekleştirilmiştir. Üretilen filmlerin SEM, AFM ve XRD sistemleri ile yüzey, topoğrafya ve yapı analizleri gerçekleştirilmiş ayrıca yarı kantitatif doku analizleri yapılarak kutup figürleri elde edilmiştir. Topoğrafik ve detaylı yapısal analiz sonuçları birbirleri ile ve literatürde var olan diğer çalışmalar ile kıyaslandığında bu çalışmada ortaya koyulan üretim parametrelerinin kullanılabilirliği gösterilmiştir.

Parameters influencing the fracture of Mo films and their wider significance

Fragmentation testing has been used for decades to assess thin film fracture and delamination. Hooke’s law is generally used to determine a film fracture stress from the crack onset strain observed in micrographs or measured as an electrical resistance increase. While this method is in theory suitable in the elastic regime, it neglects important film characteristics, such as residual stress, microstructure, or film architecture. Thus, there is a need to improve fracture analysis using fragmentation to avoid significant errors in measuring fracture stress or apparent fracture toughness of thin films. In-situ X-ray diffraction fragmentation experiments can measure the film fracture stress even for individual layers being part of a multilayer. Which characteristics influence the apparent fracture behavior will be demonstrated on Mo thin films on polyimide.Graphical abstract

Study on the Deposition Characteristics of Molybdenum Thin Films Deposited by the Thermal Atomic Layer Deposition Method Using MoO2Cl2 as a Precursor

In this study, we conducted research on manufacturing molybdenum (Mo) thin films by a thermal atomic layer deposition method using solid MoO2Cl2 as a precursor. Mo thin films are widely used as gate electrodes and electrodes in metal-oxide semiconductor field-effect transistors. Tungsten (W) has primarily been used as a conventional gate electrode, but it suffers from reduced resistivity due to the residual fluorine component generated from the deposition process. Thus, herein, we developed a Mo thin film with low resistivity that can substitute W. The MoO2Cl2 precursor used to deposit the Mo thin film exists in a solid state. For solid precursors, the vapor pressure does not remain constant compared to that of liquid precursors, thereby making it difficult to set process conditions. Furthermore, the use of solid precursors at temperatures 600 °C and above has many limitations. Herein, H2 was used as the reactive gas for the deposition of Mo thin films, and the deposition temperature was increased to 650 °C, which was the maximum processing temperature of the aluminum nitride heater. Additionally, deposition rate, resistivity change, and surface morphology characteristics were compared. While resistivity decreased to 12.9 μΩ∙cm with the increase of deposition temperature from 600 °C to 650 °C, surface roughness (Rq) was increased to 0.560 nm with step coverage of 97%. X-ray diffraction analysis confirmed the crystallization change in the Mo thin film with increasing process temperature, and a certain thickness of the seed layer was required for nucleation on the initial wafer of the Mo thin film. Thus, the molybdenum nitride thin film was deposited after the 4 nm deposition of Mo thin film. This study confirmed that crystallinity of Mo thin films must be increased to reduce their resistivity and that a seed layer for initial nucleation is required.

Size effect of resistivity due to surface roughness scattering in alternative interconnect metals: Cu, Co, Ru, and Mo

The resistivity size effect of thin films due to atomically rough surfaces is investigated using first-principles quantum transport simulations with the disorder scattering treated by the nonequilibrium mean-field approach. Within the exact muffin-tin orbital--based first-principles method, the Madelung potential of film in device structure is constructed by implementing the boundary-condition correction. Cu(001), Co(0001), Ru(0001), and Mo(001) thin films are modeled with the thickness $d=1--10$ nm. The random surface roughness is represented by an alloy model, consisting of one monolayer of ${\text{M}}_{x}{\text{Va}}_{1\ensuremath{-}x}$ and ${\text{M}}_{1\ensuremath{-}x}{\text{Va}}_{x}$ on the respective top and bottom surfaces. The results of all metal films indicate that the first-principles resistivity ${\ensuremath{\rho}}_{s}$ induced by surface roughness scattering is proportional to $1/d$. Our simulated resistivity results are consistent with the experimental measurements of epitaxial metal layers. We find that, for the same thickness, Mo films present the highest ${\ensuremath{\rho}}_{s}$, significantly larger than the other metals. The thin-film resisitivity ${\ensuremath{\rho}}_{s}$ of Co is about 1.6 times that of Cu, while Ru results is slightly higher than Cu results. For all metal films, we obtain the parameter ${\ensuremath{\gamma}}_{s}$ characterizing the intensity of surface roughness scattering as a function of $x$. Furthermore, we find the proportionality constant ${\ensuremath{\alpha}}_{s}$ versus $x$ for the mean-free path ${\ensuremath{\lambda}}_{s}={\ensuremath{\alpha}}_{s}\ifmmode\times\else\texttimes\fi{}d$ for surface roughness scattering. Our results show that at the high $x&gt;0.2, {\ensuremath{\alpha}}_{s}$ is rather close to a constant, with values of 4.5, 2.8, 2.1, and 1.0 for the respective Cu, Ru, Co, and Mo. We conclude that, compared to Co, Ru is competitive in resistivity size effect of surface roughness for an alternative to Cu interconnect for future technology nodes.

Structural Analysis of Mo Thin Films on Sapphire Substrates for Epitaxial Growth of AlN.

Aluminum nitride (AlN) thin film/molybdenum (Mo) electrode structures are typically required in microelectromechanical system applications. However, the growth of highly crystalline and c-axis-oriented AlN thin films on Mo electrodes remains challenging. In this study, we demonstrate the epitaxial growth of AlN thin films on Mo electrode/sapphire (0001) substrates and examine the structural characteristics of Mo thin films to determine the reason contributing to the epitaxial growth of AlN thin films on Mo thin films formed on sapphire. Two differently oriented crystals are obtained from Mo thin films grown on sapphire substrates: (110)- and (111)-oriented crystals. The dominant (111)-oriented crystals are single-domain, and the recessive (110)-oriented crystals comprise three in-plane domains rotated by 120° with respect to each other. The highly ordered Mo thin films formed on sapphire substrates serve as templates for the epitaxial growth by transferring the crystallographic information of the sapphire substrates to the AlN thin films. Consequently, the out-of-plane and in-plane orientation relationships among the AlN thin films, Mo thin films, and sapphire substrates are successfully defined.