Matrix Sputtering Research Articles

Cosputtered SnO2–ZnO composite nanofilms with improved dual function

AbstractSnO2–ZnO composite thin films were grown by radio‐frequency and direct‐current cosputtering of ceramic ZnO and metallic Sn targets, respectively. During the cosputtering film growth, the SnO2 matrix sputtering power was fixed at 20 W, while the additive ZnO sputtering power was varied in the range of 40–80 W. Structural and compositional analysis results showed that the ZnO sputtering power increased the relative ZnO phase content in the composite film and its surface grain size. Compared to the single‐constituent compounds, the as‐synthesized SnO2–ZnO composite films exhibited enhanced photoelectrocatalytic performances for the degradation of methyl orange dyes under irradiation. The SnO2–ZnO composite film obtained at a ZnO sputtering power of 60 W (SZ60; Zn/Sn = 11.2%) exhibited the highest photoelectrocatalytic activity among the various samples. In addition, SZ60 exhibited superior ethanol gas‐sensing performances among the various thin‐film sensors. Owing to the formation of a suitable number of SnO2/ZnO heterojunctions, SZ60 exhibited a highly efficient photo‐induced charge separation and appropriate potential barrier height to improve the gas‐sensing ability. The experimental results demonstrate a promising approach to design oxide composite films with desirable photoelectrocatalytic and gas‐sensing functions by controlling the relative content of ZnO and SnO2 in the composite film through a cosputtering process.

Study of the optical properties of a NiO/AuNP/NiO nanocomposite film transferred onto a transparent flexible substrate

In this work a technique for optically active nanocomposite structures consisting of an oxide matrix with plasmonic NPs were demonstrated. A nanocomposite film was formed on a silicon substrate by NiO oxide matrix sputtering and gold nanoparticles dewetting. Studies of the morphology, elemental composition, and structure of the nanocomposite using SEM, EDS, XRD methods are presented. The transfer of the film onto a polymer substrate made it possible to study the optical characteristics of the obtained structures. It is shown that formed nanocomposite coatings on a polymer substrate are highly flexible and exhibit excellent mechanical properties.

Non-thermal desorption of complex organic molecules

Aims. Methanol ice is embedded in interstellar ice mantles present in dense molecular clouds. We aim to measure the sputtering efficiencies starting from different ice mantles of varying compositions experimentally, in order to evaluate their potential impact on astrochemical models. The sputtering yields of complex organic molecules is of particular interest, since few mechanisms are efficient enough to induce a significant feedback to the gas phase. Methods. We irradiated ice film mixtures made of methanol and carbon dioxide of varying ratios with swift heavy ions in the electronic sputtering regime. We monitored the evolution of the infrared spectra as well as the species released to the gas phase with a mass spectrometer. Methanol (12C) and isotopically labelled 13C-methanol were used to remove any ambiguity on the measured irradiation products. Results. The sputtering of methanol embedded in carbon dioxide ice is an efficient process leading to the ejection of intact methanol in the gas phase. We establish that when methanol is embedded in a carbon-dioxide-rich mantle exposed to cosmic rays, a significant fraction (0.2–0.3 in this work) is sputtered as intact molecules. The sputtered fraction follows the time-dependent bulk composition of the ice mantle, the latter evolving with time due to the radiolysis-induced evolution of the bulk. If methanol is embedded in a carbon dioxide ice matrix, as the analyses of the spectral shape of the CO2 bending mode observations in some lines of sight suggest, the overall methanol sputtering yield is higher than if embedded in a water ice mantle. The sputtering is increased by a factor close to the dominant ice matrix sputtering yield, which is about six times higher for pure carbon dioxide ice when compared to water ice. These experiments are further constraining the cosmic-ray-induced ice mantle sputtering mechanisms important role in the gas-phase release of complex organic molecules from the interstellar solid phase.

Sub-2 nm Single-Crystal Pt Nanoparticles via Sputtering onto a Liquid Polymer.

Matrix sputtering with the use of a low vapor pressure liquid as its matrix becomes a green technique to prepare nanoparticles dispersed in liquid. In the present study, we proposed using this method with polyethylene glycol (PEG, molecular weight = 600) as the liquid matrix to produce highly uniform Pt nanoparticles with a small size (below 2.0 nm) and a narrow size distribution. The results indicated that particle sizes were tailorable from 0.9 ± 0.3 to 1.4 ± 0.3 nm by varying the sputtering current (5-50 mA) with negligible particle aggregation that occurred in PEG during sputtering. The slight growth of the particle size observed after sputtering was attributed to the addition of free Pt atoms to the existing Pt nanoparticles. All samples formed stable dispersion in PEG for 5 month storage. This result suggested an advantage of using a liquid matrix to produce and stabilize nanoparticles.

Matrix Sputtering Method: A Novel Physical Approach for Photoluminescent Noble Metal Nanoclusters.

Noble metal nanoclusters are believed to be the transition between single metal atoms, which show distinct optical properties, and metal nanoparticles, which show characteristic plasmon absorbance. The interesting properties of these materials emerge when the particle size is well below 2 nm, such as photoluminescence, which has potential application particularly in biomedical fields. These photoluminescent ultrasmall nanoclusters are typically produced by chemical reduction, which limits their practical application because of the inherent toxicity of the reagents used in this method. Thus, alternative strategies are sought, particularly in terms of physical approaches, which are known as "greener alternatives," to produce high-purity materials at high yields. Thus, a new approach using the sputtering technique was developed. This method was initially used to produce thin films using solid substrates; now it can be applied even with liquid substrates such as ionic liquids or polyethylene glycol as long as these liquids have a low vapor pressure. This revolutionary development has opened up new areas of research, particularly for the synthesis of colloidal nanoparticles with dimensions below 10 nm. We are among the first to apply the sputtering technique to the physical synthesis of photoluminescent noble metal nanoclusters. Although typical sputtering systems have relied on the effect of surface composition and viscosity of the liquid matrix on controlling particle diameters, which only resulted in diameters ca. 3-10 nm, that were all plasmonic, our new approach introduced thiol molecules as stabilizers inspired from chemical methods. In the chemical syntheses of metal nanoparticles, controlling the concentration ratio between metal ions and stabilizing reagents is a possible means of systematic size control. However, it was not clear whether this would be applicable in a sputtering system. Our latest results showed that we were able to generically produce a variety of photoluminescent monometallic nanoclusters of Au, Ag, and Cu, all of which showed stable emission in both solution and solid form via our matrix sputtering method with the induction of cationic-, neutral-, and anionic-charged thiol ligands. We also succeeded in synthesizing photoluminescent bimetallic Au-Ag nanoclusters that showed tunable emission within the UV-NIR region by controlling the composition of the atomic ratio by a double-target sputtering technique. Most importantly, we have revealed the formation mechanism of these unique photoluminescent nanoclusters by sputtering, which had relatively larger diameters (ca. 1-3 nm) as determined using TEM and stronger emission quantum yield (max. 16.1%) as compared to typical photoluminescent nanoclusters prepared by chemical means. We believe the high tunability of sputtering systems presented here has significant advantages for creating novel photoluminescent nanoclusters as a complementary strategy to common chemical methods. This Account highlights our journey toward understanding the photophysical properties and formation mechanism of photoluminescent noble metal nanoclusters via the sputtering method, a novel strategy that will contribute widely to the body of scientific knowledge of metal nanoparticles and nanoclusters.

Au/Cu Bimetallic Nanoparticles via Double-Target Sputtering onto a Liquid Polymer.

Alloy nanoparticles (NPs) of a bimetal system, Au/Cu, that form intermetallic compounds in a bulk state have been successfully produced using a double-target sputtering technique onto a low-cost and biocompatible liquid polymer (polyethylene glycol, PEG). The formation of an Au/Cu solid solution alloy in individual NPs was revealed by scanning transmission electron microscopy-energy-dispersive X-ray elemental mapping analysis. Altering the sputter currents for Au and Cu targets resulted in a tailored NP composition, but the particle sizes did not significantly vary. We found similar structures, sizes, and optical properties of Au/Cu NPs obtained by double-head sputtering on carbon-coated transmission electron microscopy grids or PEG and by Au/Cu alloy target sputtering. Random alloy formation occurred in matrix sputtering using double-target heads. This method is advantageous for manipulating the alloy composition through highly independent control of sputter parameters for each metal target.

Formation and optical properties of fluorescent gold nanoparticles obtained by matrix sputtering method with volatile mercaptan molecules in the vacuum chamber and consideration of their structures.

This paper proposes a novel methodology to synthesize highly fluorescent gold nanoparticles (NPs) with a maximum quantum yield of 16%, in the near-infrared (IR) region. This work discusses the results of using our (previously developed) matrix sputtering method to introduce mercaptan molecules, α-thioglycerol, inside the vacuum sputtering chamber, during the synthesis of metal NPs. The evaporation of α-thioglycerol inside the chamber enables to coordinate to the "nucleation stage" very small gold nanoclusters in the gas phase, thus retaining their photophysical characteristics. As observed through transmission electron microscopy, the size of the Au NPs obtained with the addition of α-thioglycerol varied from approximately 2-3 nm to approximately 5 nm. Plasmon absorption varied with the size of the resultant nanoparticles. Thus, plasmon absorption was observed at 2.4 eV in the larger NPs. However, it was not observed, and instead a new peak was found at approximately 3.4 eV, in the smaller NPs that resulted from the introduction of α-thioglycerol. The Au NPs stabilized by the α-thioglycerol fluoresced at approximately 1.8 eV, and the maximum wavelength shifted toward the red, in accordance with the size of the NPs. A maximum fluorescent quantum yield of 16% was realized under the optimum conditions, and this value is extremely high compared to values previously reported on gold NPs and clusters (generally ∼1%). To our knowledge, however, Au NPs of size >2 nm usually do not show strong fluorescence. By comparison with results reported in previous literature, it was concluded that these highly fluorescent Au NPs consist of gold-mercaptan complexes. The novel method presented in this paper therefore opens a new door for the effective control of size, photophysical characteristics, and structure of metal NPs. It is hoped that this research contributes significantly to the science in this field.

Preparation of Copper Nanoparticles in Liquid by Matrix Sputtering Process

As a new method for nanoparticles preparation, magnetron sputtering of metal atoms and clusters into organic liquids has been intensively used recently. In this study, metallic copper nanoparticles dispersed in pentaerythritol ethoxylate were prepared by this process. Their size control was achieved by controlling the sputtering current. Specific absorption at ca. 580 nm was detected by UV-Vis measurement which is attributed to the specific plasmon absorption of metallic copper. TEM observation also revealed the formation of metallic nanoparticles.

Preparation of Optical Resins Containing Dispersed Gold Nanoparticles by the Matrix Sputtering Method

Preparation of Optical Resins Containing Dispersed Gold Nanoparticles by the Matrix Sputtering Method

Preparation of Optical Resins Containing Dispersed Gold Nanoparticles by the Matrix Sputtering Method

Ganz transparent: Die mit dem Titelverfahren erhaltenen transparenten hellgelben AuNP-Thiourethanharze mit <1 nm großen Goldnanopartikeln (AuNPs) fluoreszieren bei 690 nm (siehe Bild). Die analogen transparenten Urethanharze sind wegen der Oberflächenplasmonenabsorption durch die AuNPs rot gefärbt.

Molten matrix sputtering synthesis of water-soluble luminescent Au nanoparticles with a large Stokes shift

Water-soluble luminescent AuNPs of 1.3 ± 0.3 nm in diameter with a large Stokes shift were facilely synthesized by a new molten matrix sputtering (MMS) method.

Interface broadening in sputter depth profiling through alternating layers of isotopically purified silicon: I. Experimental results

Samples composed of alternating layers of 30Si and 28Si were sputter depth profiled at near normal incidence using a variety of primary ion beams (Ne +, Ar +, Xe +, N 2 +, O 2 + and Cs +) at energies between 2 and 10 keV. The profiles exhibit the well-known asymmetric interface broadening, i.e. a relatively sharp rise of the signal at the leading edge (described by a characteristic width δ) and a comparatively slow exponential fall-off at the trailing edge (defined by a decay length λ). Both δ and λ increase with increasing beam energy. For inert gas and cesium ion bombardment at a fixed energy, the width δ reveals the qualitatively expected decrease with increasing primary ion mass. By contrast, the decay length λ does not show any dependence on the projectile mass or on the matrix sputtering yield. These findings are discussed in terms of ion ranges, cascade mixing, and possible shapes of the stationary internal mixing profiles. The interface broadening observed under N 2 + and O 2 + bombardment is much (up to a factor of more than two) smaller than expected on the basis of the data for inert gas and cesium ion bombardment. This effect is attributed to beam induced nitride and oxide formation which results in a reduced depth of mixing in the Si subsystem. Comparison of the present data with previous results shows that the decay length for several impurities in Si is shorter than for Si in Si.

Effect of matrix composition and impact angle on the fractional ion yield of Be+ sputtered from oxygen-bombarded silicon and compound semiconductors

Using two different secondary ion mass spectrometers we have determined fractional ion yields of Be+ sputtered from seven beryllium-implanted semiconductor matrices (Si, GaAs, AlxGa1−x, InGaAs, and InP) by O+2 bombardment. The measurements were performed at five different impact angles θ ranging from near-normal beam incidence, i.e., θ=2°, to θ=42°. The fractional yields δY+Be show a strong matrix dependent variation (up to a factor of more than 100) as well as a pronounced θ dependence. Even though the two instruments differ considerably with respect to the geometry and the strength of the secondary ion extraction field, the matrix-dependent variations in δY+Be were almost the same for the same θ. On the basis of these findings previously reported discrepancies in the magnitude of the Be matrix effect can be attributed almost completely to the θ dependence of the ionization probability. Moreover, it is shown that a universal relationship between the ion yield δY+ and the matrix sputtering yield Y cannot be established because of functional dependence δY+(Y,θ) is different for each impact angle. Further evidence in this respect is obtained from the Y dependence of the ionization probability of Be+, derived by roughly correcting the measured fractional ion yields for θ-dependent variations in transmission of the employed quadrupole based instrument. A first-order correction to the Be+ matrix effect can be obtained from the O+ intensity measured quasisimultaneously with the Be+ intensity.

Assessment of the extent of atomic mixing from sputtering experiments

Ion-bombardment-induced atomic mixing effects are investigated, taking into account the depth dependence of the quantities of relevance. It is shown that in the dilute limit the fluence dependence of tracer (overlayer) atom removal is characterized by an exponential tail. The slope σi of this tail is determined by the differential escape rate of the dopant atoms, as well as the shape of the ’’mixing profile.’’ The extent of mixing (and selective sputtering) in a given system can be characterized by the ratio Ym/σi, where Ym is the matrix sputtering yield. Intermixing of Au with Si is found to be much stronger than expected on the basis of mere collisional relocation of atoms. Some comments are made concerning the use of Rutherford backscattering spectrometry and Auger electron spectroscopy for the determination of escape rates and selective sputtering effects.

Implications in the use of reactive ion bombardment for secondary ion yield enhancement

Secondary ion yield enhancement effects introduced by bombardment with “reactive” ions (oxygen, cesium) are reviewed. It is shown that simple retention models cannot account for the observed effects. The stationary surface concentration of the yield-enhancing species is found to be matrix-dependent. In general, the erosion rate or the matrix sputtering yield are not as important as assumed previously. It is suggested that the problem of ion retention in the presence of sputtering can be solved only if the depth dependence of the escape rates is taken into account.

Mechanism of the SIMS matrix effect

Quantization of ion microprobe mass spectrometric analyses has been complicated by the variation in the ion yield of an element contained in different matrices. This work demonstrates that, for O− and Cs+ bombardment, these ion-yield variations are solely attributable to variations in the matrix sputtering yield. It is argued that the matrix sputtering yield determines the near-surface concentration of the ion-yield-enhancing species O and Cs.

A unified explanation for secondary ion yields

The pure element secondary ion yields under oxygen and cesium ion bombardment are shown to be solely dependent on a) the ionization potential (or electron affinity for negative ionization) of the sputtered atom and b) the reciprocal of the matrix sputtering yield which determines the equilibrium concentration of implanted oxygen or cesium. This unified approach accounts for the yields of C±, Si±, Ge± and Sn± from the pure elements as well as of Ga± and As± from gallium arsenide.