Ion-beam Assisted Sputtering Research Articles

Ion-beam assisted sputtering of titanium nitride thin films

Titanium nitride is a material of interest for many superconducting devices such as nanowire microwave resonators and photon detectors. Thus, controlling the growth of TiN thin films with desirable properties is of high importance. This work aims to explore effects in ion beam-assisted sputtering (IBAS), were an observed increase in nominal critical temperature and upper critical fields are in tandem with previous work on Niobium nitride (NbN). We grow thin films of titanium nitride by both, the conventional method of DC reactive magnetron sputtering and the IBAS method, to compare their superconducting critical temperatures T_{c} as functions of thickness, sheet resistance, and nitrogen flow rate. We perform electrical and structural characterizations by electric transport and x-ray diffraction measurements. Compared to the conventional method of reactive sputtering, the IBAS technique has demonstrated a 10% increase in nominal critical temperature without noticeable variation in the lattice structure. Additionally, we explore the behavior of superconducting T_c in ultra-thin films. Trends in films grown at high nitrogen concentrations follow predictions of mean-field theory in disordered films and show suppression of superconducting T_c due to geometric effects, while nitride films grown at low nitrogen concentrations strongly deviate from the theoretical models.

Comparison of microstructural and optoelectronic properties of NiO:Cu thin films deposited by ion-beam assisted rf sputtering in different gas atmospheres

NiO thin films have been widely studied recently due to their intrinsic p-type conductivity and potential applications in various domains as transparent conductive oxides. However, the intrinsic p-type resistivity (ρ) of NiO is as high as 1013 Ω·cm, which needs to be optimized. In the current work, we devised an experiment to improve the electrical properties of NiO films through three methods: 1) encouraging monovalent Cu+ ions to substitute for Ni2+ ions in NiO:Cu films deposited from NiO-Cu composite targets; 2) introducing nickel vacancies and interstitial oxygen in the films deposited by oxygen ion assisted rf sputtering in Ar + O2 mixture; 3) adding group-V element N to replace O by employing Ar + N2 mixture as the sputtering gas. The results show that the first two methods can effectively enhance the film's p-type conductivity, while the carrier concentration in the films improves greatly. However, the last method reveals that when N atoms are introduced into NiO:Cu films they will reduce the film's p-type electrical properties. This indicates that N doping hinders the hole generation under our experimental conditions.

Structural and dielectric properties of ion beam deposited titanium oxynitride thin films

Titanium oxynitride ( $${\hbox {TiO}}_{x}{\hbox {N}}_{y}$$ ) thin films were fabricated by ion beam-assisted sputtering deposition. Effects of oxygen contribution, assisting ion energy ( $$E_{\mathrm{a}}$$ ), assisting ion beam current ( $$I_{\mathrm{a}}$$ ) on the microstructure and dielectric behavior of the films were analyzed. The results show that increasing O content made the films to turn from fcc-TiN (111)-oriented to fcc $${\hbox {TiO}}_{x}{{\hbox {N}}}_{y}$$ (220)-oriented. Proper $$E_{\mathrm{a}}$$ and low $$I_{\mathrm{a}}$$ can enhance the (220) orientation in $${\hbox {TiO}}_{x}{{\hbox {N}}}_{y}$$ thin films. The increase in oxygen content leads to the red-shift of plasmonic resonant frequency and makes the films more dielectric. Higher $$E_{\mathrm{a}}$$ and $$I_{\mathrm{a}}$$ make the $${\hbox {TiO}}_{x}{{\hbox {N}}}_{y}$$ films more metallic. Atomic composition is an important factor underlying the results. The study provides a method to control the plasmonic properties of oxynitride films in a wide range by atomic composition and assisting ions.

Room temperature deposition of superconducting niobium nitride films by ion beam assisted sputtering

We use room temperature ion beam assisted sputtering (IBAS) to deposit niobium nitride thin films. Electrical and structural characterizations were performed by electric transport and magnetization measurements at variable temperatures, X-ray diffraction and atomic force microscopy. Compared to reactive sputtering of NbN, films sputtered in presence of an ion beam show remarkable increase in the superconducting critical temperature T$_{\rm{c}}$, while exhibiting lower sensitivity to nitrogen concentration during deposition. Thickness dependence of the superconducting critical temperature is comparable to films prepared by conventional methods at high substrate temperatures and is consistent with behavior driven by quantum size effects or weak localization.

Enhancing crystallization of silicon nanocrystal embedded in silicon-rich oxide by ion beam-assisted sputtering

This study examined the material and optical properties of Si nanocrystals (NCs) embedded in Si-rich oxide (SRO) films prepared through ion beam-assisted sputtering (IBAS). Transmission electron microscopy and grazing-incidence X-ray diffraction revealed that IBAS improved the formation of the Si NCs in the SRO films. The size and density of Si NCs were predominantly controlled by IBAS with varying anode voltage. The photoluminescence levels of the SRO films were enhanced, which was associated with the quantum confinement effect of the Si NCs. The benefits of an Ar ion beam used on the SRO films are discussed in this paper. The results indicate that IBAS is a promising approach for the development of highly efficient Si-based optoelectronic devices.

Effect of SiO2 layers on electroluminescence from Si nanocrystal/SiO2 superlattices prepared using argon ion beam assisted sputtering

This study investigated the electroluminescence (EL) properties of Si-rich oxide (SRO)/SiO2 superlattices light emitting devices (LEDs). Each SiO2 layer of the superlattices was prepared by using argon ion beam assisted sputtering (IBAS). Transmission electron microscopy revealed that the treatment of Ar ion beams on the SiO2 layers did not affect the size or distribution of the Si nanocrystals in the SRO layers, but enhanced the thin-film quality of the SiO2 and formed a clear SiO2/SRO interface. The refractive index of SiO2 was increased by IBAS because of an increase in the density of SiO2. The EL efficiency was doubled for the IBAS device compared with that of a reference device. According to the retention property, the enhanced EL intensity of the IBAS device was ascribed to lower the charge loss rate through enhancing injection barrier of SiO2. The mechanism of the EL enhancement of the IBAS LED was discussed.

Electrical and optical properties of Al:ZnO films prepared by ion-beam assisted sputtering

Al-doped ZnO (AZO) thin film is an important transparent and conducting electrode in optoelectronic devices. Further reduction of the resistivity and an increase in the transmittance of AZO are required. This paper proposes AZO films that are prepared using ion-beam assisted sputtering (IBAS). A low-energy Ar ion-beam with a kinetic energy between 0 and 50eV is used. The electrical and optical properties of IBAS AZO films are studied in terms of the substrate temperature (RT-300°C). The results show that the resistivity of AZO films decreases as the amount of chemisorbed oxygen and O–Zn bonds decrease, which increases the number of oxygen vacancies. The transmittance in the visible region is increased because of the high crystallinity of AZO films. The resistivity of IBAS AZO deposited at 300°C with an anode voltage of 30V is reduced to 5.6×10−3Ωcm because of the high carrier concentration and mobility. This shows that that ion-beam treatment changes the surface/adatom reaction during the growth of AZO films, which is similar to the effect of substrate heating. The electrical and optical properties of the AZO films that depend on the ion-beam energy and substrate temperature are discussed.

Low temperature growth of Co2MnSi films on diamond semiconductors by ion-beam assisted sputtering

High quality Schottky junctions using Co2MnSi/diamond heterostructures were fabricated. Low temperature growth at ∼300–400 °C by using ion-beam assisted sputtering (IBAS) was necessary to obtain abrupt Co2MnSi/diamond interfaces. Only the Co2MnSi films formed at ∼300–400 °C showed both saturation magnetization comparable to the bulk values and large negative anisotropic magnetoresistance, which suggests half-metallic nature of the Co2MnSi films, of ∼0.3% at 10 K. Schottky junctions formed using the Co2MnSi films showed clear rectification properties with rectification ratio of more than 107 with Schottky barrier heights of ∼0.8 eV and ideality factors (n) of ∼1.2. These results indicate that Co2MnSi films formed at ∼300–400 °C by IBAS are a promising spin source for spin injection into diamond semiconductors.

3J3-2 Growth of c-axis parallel oriented ScAlN films by ion-beam assisted sputtering and their application in pure shear mode resonators

3J3-2 Growth of c-axis parallel oriented ScAlN films by ion-beam assisted sputtering and their application in pure shear mode resonators

Fabrication of epitaxial Co2MnSi films on lattice-matched MgAl2O4 substrates by ion-beam assisted sputtering

We show that epitaxial Co2MnSi films can be fabricated on lattice-matched MgAl2O4 substrates using an ion-beam-assisted sputtering method. Low temperature growth below ~500°C with Ar ion-beam assistance enabled high-quality Co2MnSi films with ideal saturation magnetization and highly-ordered L21 structures. The Co2MnSi films also demonstrated a negative anisotropic magnetoresistance of ~0.1% at room temperature, which is a typical characteristic of half-metals. These results suggest that ion-beam assisted sputtering is an effective method of fabricating high-quality, half-metallic Co2MnSi films at low growth temperatures.

Ferromagnetic Schottky junctions using half-metallic Co2MnSi/diamond heterostructures

We demonstrate half-metallic Heusler Co2MnSi films epitaxially grown on diamond semiconductors using the ion-beam assisted sputtering method. Lower temperature growth below ∼400 °C is key for obtaining abrupt Co2MnSi/diamond interfaces. The Co2MnSi films on diamond showed a negative anisotropic magnetoresistance of ∼0.2% at 10 K, suggesting the half-metallic nature of the Co2MnSi films. Schottky junctions formed using the Co2MnSi/diamond heterostructures at 400 °C showed clear rectification properties with a rectification ratio of ∼103. The Schottky barrier heights of the Co2MnSi/diamond interfaces were estimated to be ∼0.8 eV. These results indicate that Co2MnSi is a promising spin source for spin injection into diamond.

Improving efficiency of organic solar cells by preparing aluminum-doped zinc oxide films by ion beam-assisted sputtering

This paper reports on the improvement of the efficiency of organic solar cells (OSCs) by using ion beam-assisted sputtering (IBAS) to synthesize the alumina-doped zinc oxide (AZO) anodes that are used therein. The anode voltage of the ion source and the substrate temperature during IBAS were varied. When the substrate temperature was 460°C, increasing the anode voltage from 0 to 40V increased the efficiency of the OSCs by ∼50%. The optical, electrical, morphological, and interfacial properties of the AZO and organic layers were investigated. The improvement of OSCs was associated with an increase in the conductivity, FOM, surface work function of the AZO films, and a decrease in the contact resistance in AZO/CuPc interface.

Structure control of sputtered zinc oxide films by utilizing zinc oxide seed layers tailored by ion beam assisted sputtering

Reactively sputtered zinc oxide thin films typically exhibit a c-oriented (0 0 0 1) texture of low crystalline order when deposited on unheated substrates. The structural order can be significantly improved upon heating the substrates during deposition. Here it will be demonstrated that by utilizing c-textured seed layers, which are grown by an ion beam assisted sputtering (IBAS) process, films can be deposited at room temperature with significantly improved c-texture. These films are significantly less sensitive to detrimental oxygen ion bombardment. By tailoring the IBAS process, even seed layers with dominant a-texture can be produced. Subsequently thick ZnO films can be grown on appropriate seed layers which are pre-dominantly a-textured.

The Effect of Ion-Beam Treatment on TiO2Coatings Deposited on Polycarbonate Substrates

The effect of an Ar plasma treatment on polycarbonate substrates was investigated using <TEX>$TiO_2$</TEX> coatings produced by reactive ion-beam assisted sputtering. The typical pressure used during sputtering was about <TEX>$10^{-4}$</TEX> Torr. After the Ar plasma treatment, the contact angle of a water droplet was reduced from <TEX>$88^{\circ}$</TEX> to <TEX>$52^{\circ}$</TEX> and then further decreased to <TEX>$12^{\circ}$</TEX> with the addition of oxygen into the chamber. The surface of the polycarbonate substrate hanged from hydrophobic to hydrophilic with these treatments and revealed its changing nano-scale roughness. The <TEX>$TiO_2$</TEX> films on the treated surface showed various colors and periodic ordering dependant on the film thickness due to optical interference.

Structure refinement and hardness enhancement of titanium nitride films by addition of copper

Titanium nitride films with a low added copper content were synthesized by ion beam-assisted sputtering deposition. The role of copper was examined with regard to the structure, hardness and elastic/plastic deformation capacity of the composite films produced. It was found that copper had significant modifying effects on the structure and property of titanium nitride films. When a very low content of Cu (<2 at.%) was added, the film showed apparent hardness enhancement. Films with low content of Cu also displayed highly elastic characteristics (91% elastic recovery under nanoindentation). On the contrary, films with >2 at.% copper were comparatively soft, up to 53% of the deformation under indentation could be plastic in this case. In addition, copper additions could also be used to tune the grain size of TiN in the range of 25–5 nm, at the same time causing a transition from a strong (111) preferred orientation to random polycrystalline morphology.