Low-temperature Physical Vapor Deposition Research Articles

Low-Temperature Evaporation Combined with Pulsed Laser Annealing for the Preparation of High-Quality p-Type Single-Crystal Tellurium-Layered Material Thin Films

Two-dimensional (2D) materials are currently recognized as key materials for device miniaturization due to their advantages such as perfect surface, high carrier mobility, and the ability to reduce short-channel effect. Despite significant progress in n-type two-dimensional semiconductor materials, van der Waals semiconductors with high hole mobility as the main carriers still face challenges. Tellurium layered material thin films have attracted widespread attention due to their low processing temperature and high hole mobility characteristics. Compared to other p-type 2D materials, tellurium layered material thin films offer superior uniformity and environmental durability. In this work, high-quality single-crystal p-type two-dimensional semiconductor tellurium layered material thin films were grown using low-temperature physical vapor deposition and pulsed laser annealing. This technique offers precise control over material thickness, minimal surface roughness, high uniformity, reduced defects, and improved hole carrier mobility. Electron backscatter diffraction (EBSD) analysis revealed that untreated tellurium layered material thin films had grain sizes of up to 3 micrometers. Following pulsed laser treatment, grain sizes increased to over 4 micrometers, with the main grain direction changing from (01-10) to (10-10). X-ray diffraction (XRD) results post-pulsed laser annealing showed higher peak intensities and smaller full width at half maximum (FWHM) compared to untreated and conventionally thermal annealed conditions, confirming significant enhancements in crystallinity and grain size. Additionally, minimal color change was observed in the tellurium layered material thin films after pulsed laser annealing from KAM spectra. Furthermore, significant crystallinity enhancement was also observed from high-resolution transmission electron microscopy (HRTEM) and Raman spectra. Figure 1

The tribological performance of super-hard Ta:C DLC coatings obtained by low-temperature PVD

Diamond-like carbon (DLC) coatings are widely used in industry for decorative/protective purposes or to improve tribological performance in mechanical components. In this study, three types of commercial DLC coatings have been tested and analysed to verify their potential as functional coatings to improve the wear resistance of mechanical components. DLC coatings commercially known as Dianoir, Dropless5000, and Dropless7000 were deposited on AISI 52100 steel through a proprietary cathodic arc physical vapour deposition (PVD) technique, and their properties were compared considering the differences in morphology, thickness, scratch resistance and pin-on-disc test results. The tested coatings showed excellent performance in terms of wear resistance and friction reduction, thereby showing that these coatings may be successfully applied to mechanical components in several applications.

Highly Oriented Organic Ferroelectric Films with Single-Crystal-Level Properties from Restrained Crystallization

Crystallization is a key for ferroelectricity which is a collective behavior of microscopic electric dipoles. On the other hand, uncontrolled crystallization leads to uneven morphology and random crystal orientations, which undermines the application potential of ferroelectric thin films. In this work, we introduce a film fabrication method of low-temperature physical vapor deposition followed by restrained crystallization, with electrical properties monitored in real-time by in situ measurements. This method was adopted to fabricate films of 2-methylbenzimidazole (MBI), whose molecule crystals are proton-transfer type biaxial ferroelectrics and tend to grow into a hedgehog-shaped spherulites morphology. The in situ measurements confirm that the crystallization, corresponding to a clear transition of physical properties, occurs dominantly during post-deposition warming. This enables the fabrication of micron-thick films in disk-shaped morphology with one polarization axis aligned along the out-of-plane direction, while the measured spontaneous polarization and coercive field are comparable to the single-crystal values. These results mark an important advancement of film growth that is expected to benefit widely the fabrication of molecular materials films whose functional properties hinge on crystallization to achieve desirable morphology and crystallinity.

CuPc nanowires PVD preparation and its extra high gas sensitivity to chlorine

Efficient copper phthalocyanine gas sensors capable of sensitive and selective analysis of toxic gases at room temperature have shown their great potential for gas sensing in recent years. In this work, a gas sensor based on phthalocyanine copper (II) (CuPc) was prepared by a one-step low-temperature physical vapor deposition (PVD) method. The uniform cotton-wool nanowires film has high yield, and can also be easily peeled off. PVD preparation temperature had a significant influence on both the recovery and cyclic properties of the gas sensor to chlorine. High-performance CuPc nanowires prepared at 230 °C had the lowest detection limit of 1.5 ppm with a recovery time of 2.74 s (this time is over 100 times faster than previous results 260–600 s). In addition, it showed excellent light-induced gas-sensitive characteristics to Cl2 and at room temperature. This sensor can be potentially useful in photo-gas sensors, photocatalytic devices, or photoelectric devices.

Self-lubricating triboactive (Cr,Al)N+Mo:S coatings for fluid-free applications

Within this study, self-lubricating and triboactive (Cr,Al)N+Mo:S coatings were developed and investigated for the deposition on components in a low-temperature physical vapor deposition (PVD) hybrid process. Therefore, direct current magnetron sputtering (dcMS) and high power pulse magnetron sputtering (HPPMS) PVD were combined by using an industrial coating machine. Hereby, it was possible to deposit dense and smooth triboactive, self-lubricating nitride coatings with different chemical compositions and architectures on 16MnCr5E samples. Two coating architectures, a matrix monolayer and a graded coating structure, were developed to evaluate the effect on the tribological behavior. The morphology and coating thickness were analyzed by means of scanning electron microscopy (SEM). Furthermore, the indentation hardness and modulus of indentation as well as the compound adhesion between substrate materials and coating were analyzed. Tribological analyses of (Cr,Al)N+Mo:S-coated and uncoated samples were conducted under fluid-free friction regime at room temperature T = (20 ± 3) °C, a velocity v = 0.1 m/s and a distance s = 1000 m by varying the Hertzian contact pressure from 400 MPa ≤ pH ≤ 1300 MPa against steel counterparts, 100Cr6, in a pin-on-disk (PoD) tribometer. The graded coating architecture of (Cr,Al)N+Mo:S enabled a significant wear and friction reduction. Furthermore, Raman analyses prove the formation of solid lubrication tribofilm containing MoS2, MoO3 MoO2 and MoxOy at the toplayer of a graded (Cr,Al)N+Mo:S coating, which are responsible for the improved tribological behavior.

Grazing-incidence X-ray fluorescence analysis of thin chalcogenide materials deposited on Bragg mirrors

Advanced chalcogenide materials are key for state-of-the art memories, energy harvesting materials and photonics. The properties of thin chalcogenide layers are highly driven by their chemical composition, chemical depth-profiles and surface/interface effects. The combination of Grazing-Incidence X-ray Fluorescence (GIXRF) and X-ray Reflectometry (XRR) techniques allows for non-destructive access to such information, in the lab or at dedicated beamlines. However, the accuracy of the GIXRF-deduced composition slightly degrades with depth, as the enhancement of the XRF signal by the X-ray Standing Wave (XSW) field is usually limited to the first nanometers at the surface of the probed sample. In this paper, we suggest the use of (Mo/Si)*N Bragg mirrors, rather than bare silicon substrates for thin chalcogenide deposition, to improve the sensitivity of GIXRF/XRR analysis to small process-driven modifications. The aim of such multilayered substrates is to maintain high values of X-ray reflected intensity even at angles significantly higher than the critical angle, therefore generating an XSW-induced enhancement of the XRF signal not only at the surface but also in the depth of the layer of interest. The simulation of GIXRF-XRR data, collected at SOLEIL Metrology beamline and in the lab on Rigaku SmartLab diffractometer, on arsenic-free Ovonic Threshold Switch materials (Ge, Se, Sb) for advanced Phase Change memory (PCRAM) applications illustrates the interest of this approach, which is fully-compatible with numbers of PCRAM materials elaborated with low-temperature physical vapor deposition process.

Room-temperature sputtered electrocatalyst WSe2 nanomaterials for hydrogen evolution reaction

The low-temperature physical vapor deposition process of atomically thin two-dimensional transition metal dichalcogenide (2D TMD) has been gaining attention owing to the cost-effective production of diverse electrochemical catalysts for hydrogen evolution reaction (HER) applications. We, herein, propose a simple route toward the cost-effective physical vapor deposition process of 2D WSe2 layered nanofilms as HER electrochemical catalysts using RF magnetron sputtering at room temperature (<27 °C). By controlling the variable sputtering parameters, such as RF power and deposition time, the loading amount and electrochemical surface area (ECSA) of WSe2 films deposited on carbon paper can be carefully determined. The surface of the sputtered WSe2 films are partially oxidized, which may cause spherical-shaped particles. Regardless of the loading amount of WSe2, Tafel slopes of WSe2 electrodes in the HER test are narrowly distributed to be ~120–138 mV dec−1, which indicates the excellent reproducibility of intrinsic catalytic activity. By considering the trade-off between the loading amount and ECSA, the best HER performance is clearly observed in the 200W-15min sample with an overpotential of 220 mV at a current density of 10 mA cm−2. Such a simple sputtering method at low temperature can be easily expanded to other 2D TMD electrochemical catalysts, promising potentially practical electrocatalysts.

Comparative Experimental Study of Tribo-Mechanical Performance of Low-Temperature PVD Based TiN Coated PRCL Systems for Diesel Engine

Piston ring and cylinder liner (PRCL) interface is a major contributor to the overall frictional and wear losses in an IC engine. Physical vapor deposition (PVD) based ceramic coatings on liners and rings are being investigated to address these issues. High temperature requirements for applications of conventional coating systems compromise the mechanical properties of the substrate materials. In the current study, experimental investigation of tribo-mechanical properties is conducted for various titanium nitride (TiN) coated PRCL interfaces in comparison with a commercial PRCL system. Low-temperature PVD based TiN coating is successfully achieved on the grey cast iron cylinder liner samples. Surface roughness of the grey cast iron cylinder liner substrates and the thickness of TiN coating are varied. A comprehensive comparative analysis of various PRCL interfaces is presented and all the trade-offs between various mechanical and tribological performance parameters are summarized. Coating thickness between 5 and 6 micrometres reports best tribo-mechanical behaviour. Adhesion and hardness are found to be superior for the TiN coatings deposited on cylinder liner samples with higher roughness, i.e., ~ 5-micron Ra. Maximum 62 % savings on the COF is reported for a particular PRCL system. Maximum 97% saving in cylinder liner wear rate is reported for another PRCL system.

Experimental study of tribological and mechanical properties of TiN coating on AISI 52100 bearing steel

The surface coating is one of the novel approaches to enhance the performance and durability of the mechanical components by decreasing the wear and friction among two interacting bodies. In this study, tribological and mechanical properties of titanium nitride (TiN) coatings were investigated on the AISI 52100 bearing steel deposited by low-temperature physical vapor deposition system. Surface morphology and elemental composition of the TiN coating were analyzed by scanning electron microscope and energy-dispersive X-ray spectrum, respectively. Substrate surface roughness and coating thickness of TiN were varied for correlative analysis among adhesion, mechanical, and tribological properties. Scratch and tribo tests were performed for evaluating the adhesion and tribological properties, respectively. Samples having the substrate surface roughness (0.2 ± 0.05 µm) and the coating thickness of more than 2.83 µm presented relatively better adhesion, wear resistance, and lower coefficient of friction of the TiN coating.

Effect of interfacial layer on device performance of metal oxide thin-film transistor with a multilayer high-k gate stack

The amorphous indium gallium zinc oxide thin-film transistors (TFTs) with a multilayer high-k gate stack are investigated in this research. In order to achieve a high quality gate insulator for plastic flexible display application, the multilayer high-k gate stacks (SiO2/TiO2/HfO2) are deposited by a low-temperature physical vapor deposition (PVD) process. On the other hands, an interfacial layer between the high-k stack and metal oxide channel is important for the device performance. The effects of interfacial layer material (SiO2 or Ga2O3) are also discussed in this report. The devices with SiO2 interfacial layer show a high on/off current ratio of ~7 × 107 for its low gate leakage current, a small sub-threshold swing of 0.093 V/decade and a high field-effect mobility of ∼37.8 cm2/Vs for its good interface condition and low interface defeats. This research shows that the interface engineering of multilayer PVD gate stacks is necessary for oxide TFT fabrication.

Continuous ultra-thin MoS2 films grown by low-temperature physical vapor deposition

Uniform growth of pristine two dimensional (2D) materials over large areas at lower temperatures without sacrifice of their unique physical properties is a critical pre-requisite for seamless integration of next-generation van der Waals heterostructures into functional devices. This Letter describes a vapor phase growth technique for precisely controlled synthesis of continuous, uniform molecular layers of MoS2 on silicon dioxide and highly oriented pyrolitic graphite substrates of over several square centimeters at 350 °C. Synthesis of few-layer MoS2 in this ultra-high vacuum physical vapor deposition process yields materials with key optical and electronic properties identical to exfoliated layers. The films are composed of nano-scale domains with strong chemical binding between domain boundaries, allowing lift-off from the substrate and electronic transport measurements from contacts with separation on the order of centimeters.

GaN high electron mobility transistors on silicon substrates with MBE/PVD AlN seed layers

AbstractIn the present paper, we describe the development of new AlN seed layers obtained by combining molecular beam epitaxy and low temperature physical vapour deposition (magnetron sputtering). It is shown that it is possible to grow thick AlN seed layers with a good in‐plane crystal ordering. GaN based structures on silicon can then be regrown with device quality active layers, as attested by the realization of high electron mobility transistors. Furthermore, the low substrate bowing achieved with these structures is of high interest for the fabrication of large GaN‐on‐silicon wafers. (© 2014 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

CdTe grown under Cd/Te excess at very low temperatures for solar cells

A low-temperature physical vapour deposition method for CdTe absorber layers was developed in this study and the influence of the substrate temperature during absorber growth is discussed in terms of the phase diagram of CdTe. The composition of CdTe layers grown at substrate temperatures between 45 and 300 °C with 3 different evaporation source arrangements producing either a stoichiometric, a Te-rich or a Cd-rich material supply was investigated by energy-dispersive X-ray spectroscopy. Absorber layers which were produced below a substrate temperature of 190 °C with the standard evaporation method using stoichiometric CdTe as source material show a significant Te excess which leads to non working solar cells. The application of Cd-rich material supply yields a stoichiometric growth of the absorber layers and good solar cell characteristics for substrate temperatures as low as 100 °C.

Multicolor emission from large-area porous thin films constructed of nanowires of smallorganic molecules

We describe a facile low-temperature physical vapor deposition approach to fabricate porousnetwork thin films constructed of nanowires of small organic molecules on a large area.Supermolecular assemblies of pyrene nanowires based on a combination of van der Waals forces andπ–π stacking tend to hierarchically self-assemble to form uniform porous films using ourtechniques. The morphology of the films is studied and we also study several reasonsinfluencing the process of assembly such as evaporation temperature, depositiontemperature, and different kinds of substrate. The deposition temperature is determined tobe the main reason for hierarchical aggregation. Typically prepared films exhibit uniqueoptical properties, that is, multicolor red–green–blue emissions. This novel method can beapplied to other organic molecular systems and may be potentially used to placenanoscaled building blocks directly on solid surfaces for fabricating large-areananostructure-based flat screens.

Large-Scale Synthesis of a Novel Tri(8-Hydroxyquioline) Aluminum Nanostructure

A novel tri(8-hydroxyquioline) aluminum (AlQ3) nanostructure was prepared on large scale at low cost by low-temperature physical vapor deposition (PVD). The morphologies, the chemical bondings, and photoluminescence of the AlQ3 nanostructure were investigated by environmental scanning electronic microscopy (ESEM), Fourier transform infrared spectrum (FT-IR), and photoluminescence (PL) spectra, respectively. The AlQ3 nanostructure was composed of micro-sphere with nanowire-cluster growing on the surface. The diameter of micro-sphere and nanowire were about 5 microm and 80 nm, respectively. FT-IR results indicated that the AlQ3 molecule had a strong thermal stability under research conditions. The growth mechanism of the novel nanostructure was discussed. The novel organic nanostructure would be believed to attractive building field-emission devices and other optical devices.

Low-temperature growth and Raman scattering study of vertically aligned ZnO nanowires on Si substrate

High-density ZnO nanowires (ZnONWs) were aligned onto Au-catalyzed Si substrate through a simple low-temperature physical vapor deposition method. Scanning electron microscope (SEM) observations, x-ray diffraction (XRD) analysis, and photoluminescence spectra showed that the ZnONWs were single-crystalline, with a hexagonal wurzite structure. All of the results inferred from the SEM observations, the XRD rocking curves, and the Raman spectra for the investigated samples confirm that the ZnONWs are well aligned and c-axis oriented. The Raman spectra also indicated that the ZnONWs on Si substrates are under the biaxial compressive stress. Since it takes the advantage of low-cost, easily controlled deposition spot (due to the selective deposition trait of the Au layer), potential for scale-up production, and ability to integrate with Si substrate, this technique has a potential in future for fabricating the ZnONW array-based optoelectronic devices.

Tungsten and tungsten-carbon PVD multilayered structures as erosion-resistant coatings

Abstract The aerospace industry is faced with a major erosive wear problem of engine components operating in dust environments. Various physical vapor deposition (PVD) or chemical vapor deposition (CVD) protective coatings have been used previously with limited success. The present paper deals with the elaboration and characterization of W/W-C multilayer coatings produced by magnetron sputtering from a W target in Ar and in an Ar+methane mixture respectively. This low temperature PVD process, compared with CVD processes, enables the deposition of protective coatings on Ti6A14V substrates at temperatures below 400°C. The microhardness of W-C films was found to be strongly dependent on the carbon concentration; two maximum hardness values of 26 000 MPa were obtained with W-C layers containing either 14–15 at.% or 40–45 at.%°C. This change in microhardness with the carbon content was correlated with the evolution of the crystallographic structure. Multilayer coatings of total thickness 60 μm composed of various W/W-C stacking arrangements have been elaborated with hard W-C films containing 14–15 at.% or 40–45 at.%C. These samples were subjected to erosive wear tests using a sand blast unit. As a comparison, Mo/Mo-C and Cr/Cr-C structures containing more than 10 at.%C were also tested. W/W-C coatings with an appropriate stacking arrangement and a C concentration of 14–15 at.% in W-C layers exhibited an erosion resistance improved by more than two orders of magnitude compared with that of uncoated Ti6A14V substrates. Complementary tests of the fatigue performance of Ti6A14V specimens coated with these very promising erosion-resistant coatings were also performed.

Interface Stabilization of W-N Coatings by Chromium Alloying

ABSTRACTNew metastable materials can be deposited using low temperature physical vapour deposition (PVD) techniques. During reactive sputtering, the atoms condensing in an intermixed state attempt to achieve a stable configuration. Due to low mobility of the adatoms, equilibrium phases cannot form and metastable structures are observed. Reactive sputtering can be used to deposit films with different stoichiometries and structures in the W-N system. The metastable phases α-W. β-W. W2N and WN1−x are obtained. All coatings are, however, thermally unstable. At temperatures above 570 °C. all phases are transformed into the a-W modification. By alloying chromium to the coatings in the W-N system, it is possible to stabilize all tungsten and tungsten nitride modifications as well as the interface layer between the substrate and the thin films.

On the Stability of Hetastable and Amorphous Pvd-Compound Films

ABSTRACTIn using low temperature physical vapour deposition (PVD) techniques new metastable and amorphous materials can be deposited. Structural order in a coating is produced largely by the mobility of the adatoms. Low mobility does not allow the formation of equilibrium phases and metastable and/or amorphous structures are observed. These coatings have sufficient thermal stability for tools, and for both wear- and corrosion-protection. Examples are given within the systems Al-O-N, Ti-Al-N and Cr-Al-N and the properties, crystalline and thermodynamic state of the coatings are characterized. An example of decomposition phenomena is given in metastable thin coatings by the Ti-Zr-N system.