Structural and optical properties of plasma-deposited boron nitride films

The plasma-enhanced chemical vapor deposition of boron nitride films in a low pressure, parallel plate reactor incorporating an electromagnet was investigated. Films were deposited from gas mixtures of diborane, hydrogen and ammonia. The ratio of boron to nitrogen was approximately 1.7 when an ammonia-to-diborane ratio of 4 was used. The films had the following optical properties: a band gap in the range 5.6–5.8 eV, an absorption coefficient (at 6.0 eV) of about 1×10⁵ cm⁻¹ and an index of refraction of 1.7. In general the optical properties were identical, with or without the application of a low intensity magnetic field.     

Plasma-assisted deposition of BN thin films from B(N3)3

Thin boron nitride films have been deposited via plasma-assisted dissociation of the single-source precursor boron triazide. Infrared absorption and X-ray photoelectron spectroscopic studies have shown that the films are composed of sp²-bonded boron nitride, with a B/N ratio very near 1:1. The films are significantly more resistant to degradation in air and contain fewer impurities than those previously grown from dissociation of boron triazide. The film growth mechanism is discussed, along with information on the role ion bombardment plays in the resultant properties of the films.     

Entwicklung multifunktionaler,kubischer Bornitridschichten

Multifunctional cubic boron nitride coatings Low stress, thick cubic boron nitride films can be produced nowadays by means of almost all PVD and PECVD processes based on tailored coating concepts. This can be achieved by incorporating into the films a suitable third element at a correct concentration, for example 5 at.‐% oxygen in addition to boron and nitrogen. During processing, a defined, intense ion bombardment on the growing surface is necessary to achieve a phase transformation from hexagonal to cubic boron nitride. The relevant process parameters are documented and published in so‐called parameter maps. The films were thermally treated after deposition at 900°C vacuum for 2 hours.     

用PBⅡ方法在硼膜中注入氮形成BN的结构

用电子束蒸发纯硼,在硅片上沉积不同厚度的硼膜,然后用等离子体基离子注入（ＰＢⅡ）技术在硼膜上主入氮以形成氮化硼（ＢＮ）,用ＸＰＳ分析膜的成分深度分布及化学价态;用傅里叶变换红外（ＦＴＩＲ）透射谱分析膜的结构。氮在膜中呈类似高斯分布,随着注入电压增大,膜的Ｎ／Ｂ比增大且影响氮在膜中的分布,在较高的注入电压时,膜基间产生界面混合,对ＸＰＳＢｌｓ谱进行Ｇａｕｓｓ－ｏｒｅｎｔｚ拟合表明,硼在膜中以ＢＮ及游     

Characterization of ion-beam-deposited diamond-like carbon films

Diamond-like carbon (DLC) films are excellent prospects for a wide range of high-technology applications but their precise structure and properties are not well understood. The purpose of the present work was to use several complementary techniques to characterize the nature, structure and microstructure of DLC films. Thin DLC films were deposited on various substrates in the presence of a Si interlayer (500 Å thick) using CH₄ ion-beam deposition at an acceleration energy of 750 eV and a current density of about 2.5 mA cm⁻². The Si interlayer was deposited by either e-beam evaporation or Si evaporation enhanced by Ar⁺ beam bombardment (1 keV). The produced DLC films were featureless, very smooth and of high hardness (2900–3300 kg mm⁻²). Auger electron spectroscopy and electron diffraction showed that the films were mainly amorphous. Their microstracture was characterized by a three-dimensional network structure with a medium-range order of about 25 nm. Fourier transform infrared and Raman spectroscopies showed that the films were mainly composed of sp³ and sp² carbon-bonded hydrogen. The sp³/sp² ratio varied from 3.2 to 4.1 and was found to depend on the nature of the Si bond layer. The results showed that the nucleation of the diamondlike structure was promoted on the Si interlayer that was deposited under Ar⁺ beam bombardment. This effect can be explained by the higher surface roughness produced in this interlayer as suggested by the reflectivity measurements. Spectroscopic ellipsometry revealed that the films had an optical band gap between 1.56–1.64 eV. The present results are consistent with previous proposals suggesting that the DLC structure is composed of small graphitelike clusters (involving fused six-fold rings) that are interconnected by sp³-bonded carbon.     

Evolution of texture of CeO2 thin film buffer layers prepared by ion-assisted deposition

Evolution of texture in CeO₂ thin films was studied using biased magnetron sputtering and ion beam assisted magnetron sputtering. Films deposited onto polycrystalline Hastelloy metal substrates by biased magnetron sputtering develop preferential (002) growth as the energy of the ions is increased from zero to above 100 eV. For ion beam assisted magnetron sputtering (magnetron IBAD), with the ion beam directed at 55° to the substrate normal, the evolution of biaxial alignment is controlled by the ion beam energy and the ion/atom arrival rate ratio. Ion beam energies >200 eV and ion/atom ratios >0.3 lead to perfect biaxial alignment with one pole aligned along the ion beam direction. Epitaxial growth of CeO₂ films was observed for MgO(001) substrates at 750°C without any ion assistance, and on yttria-stabilised zirconia (001) buffer layers at room temperature and a bias of −80 V.     

合成硼碳氮体系薄膜的XPS研究

采用Ｘ射线光电子谱（ＸＰＳ）分析３００～５００℃等离子体源离子渗氮硼和碳化硼薄膜合成的氮化硼和硼碳氮薄膜。利用合成薄膜成分可控的特点,研究Ｂ、Ｃ、Ｎ对薄膜的ＸＰＳ影响。结果表明,ＸＰＳ分析合成氮化硼薄膜能够确定其化学组成,但不能确定ｓｐ＾２和ｓｐ＾３型键合结构特性;ＸＰＳ分析硼碳氮薄膜能够确定其成分和结构特性。在较高的工艺温度下,等离子体源离子渗氮合成的硼硕氮薄膜具有ｓｐ＾２和ｓｐ＾３型复合的键合     

Preparation and characterization of chemically deposited PbSnS3 thin films

High-quality and well-reproducible PbSnS₃ thin films have been prepared by a simple and inexpensive chemical-bath deposition method from an aqueous medium, using thioacetamide as a sulphide ion source. X-ray diffraction analysis of the deposited films revealed that the as-deposited films were amorphous, however, an amorphous-to-crystalline phase transition was observed as the result of thermal annealing at 425 K for 1 h. The X-ray structure analysis of the collected powder from the bath annealed at 425 K for 1.5 h revealed an orthorhombic phase.

Analysis of the optical absorption data of crystalline PbSnS₃ films revealed that both direct and indirect optical transitions exist in the photon energy range 1.24–2.48 eV with optical band gaps of 1.68 and 1.42 eV, respectively. However, a forbidden direct optical transition with a band gap value of 1.038 eV dominates at low energy (<1.24 eV). The refractive index changes from 3.38 to 2.16 in the range 500–1300 nm. The high frequency dielectric constant and the carrier concentration to the effective mass ratio calculated from the refractive index analysis were found to be 4.79 and 2.3×10²⁰ cm⁻³, respectively. The temperature dependence of the electrical resistivity of the deposited films follows the semiconductor behaviour with extrinsic and intrinsic conduction. The determined activation energies range are 0.35–0.42 and 0.76–85 eV, respectively.     

Computer modelling of point defects in ABO3 perovskites and MgO

We present results for basic intrinsic defects: F-type electron centers (O vacancy which trapped one or two electrons) and hole polarons bound to Mg or K vacancy in ionic MgO and partly covalent KNbO₃ perovskite, respectively. We demonstrate that a considerable covalency of the perovskite chemical bonding makes the F-type centers therein much more similar to defects in partly-covalent quartz-type oxides rather than the conventional F centers in alkali halides and ionic MgO. Both one-site (atomic) and two-site (molecular) polarons are expected to coexist in KNbO₃ characterized by close absorption energies. Our calculations confirm existence of the self-trapped electron polarons in KNbO₃, KTaO₃, BaTiO₃, and PbTiO₃ crystals. The self-trapped electron is mostly localized on B-type ion due to a combination of breathing and Jahn–Teller modes of nearest six oxygen ion displacements. The relevant lattice relaxation energies are typically 0.2–0.3 eV, whereas the optical absorption energies 0.7–0.8 eV, respectively. According to our calculations, the absorption energy of a bound electron polaron in KNbO₃ by 0.1 eV exceeds that for the self-trapped electron polaron and equals 0.88 eV.     

Mechanism of nucleation and growth of cubic boron nitride thin films

The mechanism and the crystallography of the nucleation and growth of cubic boron nitride (c-BN) films deposited on 〈100〉-oriented silicon substrate by RF bias sputtering have been studied by means of cross-sectional high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. Both methods provide experimental information showing no sp²-bonded BN layer formation in the subsurface region of c-BN phase. This is clear evidence for layer-by-layer homoepitaxial growth of cubic boron nitride without graphitic monolayers in the near-surface region of the film. The turbostratic boron nitride (t-BN) consists of thin sub-layers, 0.5–2 nm thick, growing in such a way that a sub-layer normal is almost parallel to the growth direction. t-BN also comprises a large volume fraction of the grain boundaries with high interface energies. The present result and the finding by Shtansky et al. [Acta Mater. 48, 3745 (2000)], who showed that an individual sub-layer consists of parallel lamellae in both the hexagonal +h-BN) and rhombohedral (r-BN) configurations, demonstrate that high intrinsic stress in the films is due to the complex structure of sp²-bonded BN. The crystallography of c-BN films indicates heteroepitaxial nucleation of cubic phase on the graphitic BN structural precursor. The present results are consistent with stress-induced c-BN formation.     

Ion-activated interface adsorption of oxygen during silver deposition on silicon

The process of ion-activated oxygen adsorption on silicon has been investigated using an experimental concept with simultaneous deposition of silver films. Auger electron spectroscopy in combination with sputter depth profiling is subsequently performed to determine the amount of oxygen adsorbed at the Ag---Si interface. Noble gas ions (⁴He⁺, ²⁰Ne⁺ and ⁴⁰Ar⁺)with energies between 50 and 175 keV were used, and it was found that for substrate temperatures of 300–700 K the oxygen adsorption depends strongly on ion mass, ion energy and ion flux density. For flux densities of 5 × 10¹¹ cm⁻² s⁻¹ or less, adsorption dominates and, in particular, for light-ion bombardment the majority of adsorbed oxygen atoms form chemical bonds with the silicon surface atoms (Si---O). However, for heavy ions, physical sputtering starts to compete and limits the effective rate of adsorption. At sufficiently high ion fluxes the adsorption starts to decrease, and for all ions and energies used in this work it is found that, if the electronic energy deposition density exceeds a critical value of about 1.2 × 10²¹ eV cm⁻² s⁻¹, dissociation of the Si---O bonds prevails with a corresponding loss in the adsorbed oxygen quantity.     

The Deposition of Cubic Boron Nitride Fillms by Ion Beam Assisted Sputter Deposition

The relationship between film properties and assisting ion beam parameters such as the ion-to-atom arrival ratio, the mean energy transfer or the mean momentum transfer to a depositing atom has been established with a new method. We have made use of a focused assisting ion beam which generates zones of locally varying current densities on the film surface. By mapping these and the deposition rate, and measuring film properties as function of surface coordinates, we can determine their relationship from few samples. The: advantage is that the number of deposition runs can considerably be reduced, and errors can be avoided which may originate from slightly different deposition conditions (pressure, temperature, gas flow etc.) in different deposition runs.

This method has been applied to establish the relationship between the cubic phase formation of a boron nitride film and various assisting beam parameters. The BN films were characterized by transmission FTIR spectroscopy. The spectra were evaluated by fitting the absorption lines to Gaussian functions. The experiments show that the momentum transferred to a depositing atom is the relevant control parameter for the formation of the cubic phase and that a threshold exists at 250 (eV.amu)^1/2 above which the cubic phase is synthesized in accordance with results obtained by Kester and Messier. Below this threshold a small fraction of c-BN was also observed.     

Mechanism of nucleation and growth of cubic boron nitride thin films

The mechanism and the crystallography of the nucleation and growth of cubic boron nitride (c-BN) films deposited on 100-oriented silicon substrate by RF bias sputtering have been studied by means of cross-sectional high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. Both methods provide experimental information showing no sp²-bonded BN layer formation in the subsurface region of c-BN phase. This is clear evidence for layer-by-layer homoepitaxial growth of cubic boron nitride without graphitic monolayers in the near-surface region of the film. The turbostratic boron nitride (t-BN) consists of thin sub-layers, 0.5–2 nm thick, growing in such a way that a sub-layer normal is almost parallel to the growth direction. t-BN also comprises a large volume fraction of the grain boundaries with high interface energies. The present result and the finding by Shtansky et al. [Acta Mater. 48, 3745 (2000)], who showed that an individual sub-layer consists of parallel lamellae in both the hexagonal (h-BN) and rhombohedral (r-BN) configurations, demonstrate that high intrinsic stress in the films is due to the complex structure of sp²-bonded BN. The crystallography of c-BN films indicates heteroepitaxial nucleation of cubic phase on the graphitic BN structural precursor. The present results are consistent with stress-induced c-BN formation.     

Molecular dynamics study of deposition mechanism of cubic boron nitride

We have performed molecular dynamics simulations of bombardment of graphitic boron nitride (gBN) by energetic boron and nitrogen particles in order to examine the roles of ion bombardment in ion/plasma-assisted deposition of cubic boron nitride (cBN) thin films. We have found that the interaction of the energetic particles with gBN creates four-fold coordinated local structures (sp³-formation) inside gBN. We have also found that clusters of sp³-formations are created as a result of successive bombardment, some of which have cBN-like structures. On the basis of these results, we propose an atomic-scale model of cBN nucleation in which successive sp³-formation converts gBN into cBN.     

Molecular dynamics study of deposition mechanism of cubic boron nitride

We have performed molecular dynamics simulations of bombardment of graphitic boron nitride (gBN) by energetic boron and nitrogen particles in order to examine the roles of ion bombardment in ion/plasma-assisted deposition of cubic boron nitride (cBN) thin films. We have found that the interaction of the energetic particles with gBN creates four-fold coordinated local structures (sp³-formation) inside gBN. We have also found that clusters of sp³-formations are created as a result of successive bombardment, some of which have cBN-like structures. On the basis of these results, we propose an atomic-scale model of cBN nucleation in which successive sp³-formation converts gBN into cBN.     

Focused ion beam induced deflections of freestanding thin films

Prominent deflections are shown to occur in freestanding silicon nitride thin membranes when exposed to a 50 keV gallium focused ion beam for ion doses between 10(14) and 10(17) ions/cm(2). Atomic force microscope topographs were used to quantify elevations on the irradiated side and corresponding depressions of comparable magnitude on the back side, thus indicating that what at first appeared to be protrusions are actually the result of membrane deflections. The shape in high-stress silicon nitride is remarkably flattopped and differs from that in low-stress silicon nitride. Ion beam induced biaxial compressive stress generation, which is a known deformation mechanism for other amorphous materials at higher ion energies, is hypothesized to be the origin of the deflection. A continuum mechanical model based on this assumption convincingly reproduces the profiles for both low-stress and high-stress membranes and provides a family of unusual shapes that can be created by deflection of freestanding thin films under beam irradiation.     

Humidity-sensitive electrical properties and switching characteristics of BN films

This paper reports on the electrical properties of polycrystalline boron nitride (BN) films deposited on silicon substrates in a B₂H₆---NH₃---H₂ system. Virgin (unformed) samples exhibit humidity-sensitive electrical resistances. A current obeying Ohm's law at low humidities and low fields becomes space-charge-limited at high humidities and high fields. Some of the properties fundamental to their use as humidity sensors are also examined. After electroforming, BN films in the form of Ag/BN/Si/Al sandwiches begin to exhibit threshold switching only in atmospheres containing moisture. This switching behavior depends not only on the humidity but also on the sweep speed, the frequency of oscillation and the polarity of the applied sawtooth voltage pulse trains. A revised form Dearnaley's filamentary model is proposed.     

DC magnetron reactive sputtered InN thin film electrodes as photoanodes in aqueous solution. A study of as prepared and nitrogen annealed electrodes

Thin films of indium nitride, InN, were produced by reactive magnetron DC sputtering. By post treatment in dinitrogen, N₂, in the temperature range 350–500 °C a set of films gradually going from InN to indium oxide, In₂O₃ was obtained (due to dioxygen impurities in the annealing gas). Those films were characterized by X-ray diffraction, optical-, resistivity- and photoelectrochemical measurements for the aim of direct watersplitting in a photoelectrochemical cell.

Surprisingly, the caused change in the film composition by annealing gave no significant change in the room temperature resistivity, but the free electron density and the optical properties were affected. In 0.1 M NaOH annealing improved the photoresponse of the thin films. A pronounced optimum was observed for films annealed at 425 °C. Even for those films the quantum efficiency was low; at most 2% of the photons at 350 nm were transformed into readable photoelectrons. The onset wavelength for photocurrent was located around 600 nm (2.1 eV), which is far off from the onset of absorption 900 nm (1.4 eV).     

Structural and optical properties of amorphous oxygenated iron boron nitride thin films produced by reactive co-sputtering

Amorphous oxygenated iron boron nitride (a-FeBN:O) thin films were prepared by reactive radio-frequency (RF) sputtering, from hexagonal boron nitride chips placed on iron target, under a total pressure of a gas mixture of argon and oxygen maintained at 1 Pa. The films were deposited onto silicon and glass substrates, at room temperature. The power of the generator RF was varied from 150 to 350 W. The chemical and structural analyses were investigated using X-ray photoelectron spectroscopy (XPS), energy dispersive of X-ray and X-ray reflectometry (XRR). The optical properties of the films were obtained from the optical transmittance and reflectance measurements in the ultraviolet-visible-near infrared wavelengths range. XPS reveals the presence of boron, nitrogen, iron and oxygen atoms and also the formation of different chemical bonds such as Fe-O, B-N, B-O and the ternary BNO phase. This latter phase is predominant in the deposited films as observed in the B 1s and N 1s core level spectra. As the RF power increases, the contribution of N-B bonds in the as-deposited films decreases. The XRR results show that the mass density of a-FeBN:O thin films increases from 2.6 to 4.12 g/cm³ with increasing the RF power from 150 to 350 W. This behavior is more important for films deposited at RF power higher than 150 W, and has been associated with the enhancement of iron atoms in the film structure. The optical band gap decreases from 3.74 to 3.12 eV with increasing the RF power from 150 to 350 W.     

Growth of primary and secondary amine films from polyatomic ion deposition

Amine-containing organic films are deposited onto silicon substrates from mass-selected beams of 5-200 eV Si₂NC₈H₁₉⁺ (silazane) and 15-100 eV C₃H₆N⁺ (allylamine) ions produced by electron impact ionization of 1,3-divinyltetramethyldisilazane and allylamine. Silazane films are also deposited onto aluminum substrates. These ion-deposited films are analysed directly and/or after air exposure by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Chemical derivatization prior to XPS analysis is utilized to distinguish primary and secondary amine groups in the films from non-amine nitrogen. Primary amines are absent in silazane films. Secondary amine containing films form at low silazane ion energies whereas the higher ion energies lead to formation of more inorganic, silico-carbo-nitride-like films. The ion energy trend is similar for films from allylamine ions, except for the fact that both primary and secondary amines are detected. The primary amines from allylamine ions survive film ageing in air for periods of several days. Ion-induced film-substrate reactions are observed for silazane films.