Spectroscopic study of plasmons in ion-irradiated single-walled carbon nanotubes

The electronic structure of single-walled carbon nanotubes was experimentally investigated using x-ray photoelectron spectroscopy, reflection electron energy-loss spectroscopy, and Auger electron spectroscopy. A shake-up satellite structure observed near the C 1s core-level lines in the x-ray photoelectron spectra at high binding energies in the range 284–330 eV due to excitation of π and π + σ plasmons was studied. The effect of irradiation by 1-keV argon ions on the shape of the spectra was analyzed. The shape of the C 1s satellite spectra was found to be sensitive to Ar⁺ irradiation in the electron energy loss range 10–40 eV corresponding to excitation of π + σ plasmons. Auger spectroscopy revealed the presence of argon on the surface of ion-irradiated samples. The argon content increased to ～4 at. % with increasing irradiation dose. An analysis of the results obtained and their comparison with the data available in the literature led to a qualitative conclusion that the bond angles of the carbon atoms making up the walls of single-walled carbon nanotubes are distorted at sites exposed to Ar⁺ irradiation.     

AES, EELS and TRIM investigation of InSb and InP compounds subjected to Ar ions bombardment

The interaction of ions with matter plays an important role in the treatment of material surfaces. In this paper we study the effect of argon ion bombardment on the InSb surface in comparison with the InP one. The Ar⁺ ions, accelerated at low energy (300 eV) lead to compositional and structural changes in InP and InSb compounds. The InP surface is more sensitive to Ar⁺ ions than that of InSb. These results are directly inferred from the qualitative Auger electron spectra (AES) and electron energy loss spectroscopy (EELS) analysis. However, these techniques alone do not allow us to determine with accuracy the disturbed depth in Ar⁺ ions of InP and InSb compounds. For this reason, we combine AES and EELS with the simulation method TRIM (transport and range of ions in matter) to show the mechanism of interaction between the ions and the InP or InSb and hence determine the disturbed depth as a function of Ar⁺ energy.     

Characterization of Ohmic contacts on GaN/AlGaN heterostructures

The surface morphology and electrical resistance of the contacts on semiconductor devices are strongly influenced by metallization scheme and annealing conditions. In this work is presented an investigation of Ohmic contacts formed by metal-semiconductor alloying on epitaxial GaN/AlGaN heterostructures. After the deposition of metallic multi-layers (Ti, Al, Au and Pt), the process of rapid thermal annealing was carried out in nitrogen, argon and forming gas atmosphere.A series of the samples with different sequences of metallic layers and diverse thicknesses was prepared by employing electron beam evaporation and lift-off deposition techniques. The chemical composition of the samples before and after annealing was studied by means of X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) techniques combined with low energy Ar⁺ ion sputtering. The sputtering has been carried out in two different modes: by using constant (square) or gradually narrowed sputtered area. The changes in the chemical state of constituent elements and compositional profiles of the contacts after thermal annealing were revealed from the obtained results. Among the technological problems, influencing on the quality of the contact, were found to be the oxidation and nitridation of the contact surface during thermal annealing, as well as the intermediate sub-layers of Al and Ti oxides, formed during the deposition of metallic multi-layered structure.     

Surface properties of platinum thin films as a function of plasma treatment conditions

We examined the surface properties of platinum (Pt) thin films exposed to oxygen and argon plasma treatments and compared them to as-deposited Pt films. The surface wetting properties, refractive index and extinction coefficient of the Pt films were monitored as a function of time after different plasma treatments. Surfaces treated with an oxygen plasma were dramatically different from as-deposited Pt, whereas argon plasma treated surfaces were similar to as-deposited films. X-ray photoelectron spectroscopy confirmed the formation of platinum oxide on films treated with an oxygen plasma, while such oxide diminished after argon plasma treatment. Surface morphology studied with atomic force microscopy indicated a strong dependence of the surface roughness of the Pt films on the power and duration of the argon plasma used for the treatment. Based on these studies, an oxygen plasma treatment followed by a brief low-power argon plasma etch was developed for the purpose of regenerating clean and metallic Pt surfaces, and at the same time providing the smoothest possible surface morphology.     

Ar+, He+，S+离子轰击n-InP单晶表面的机理研究

通过X射线光电子能谱和低能电子衍射实验研究了10～180 eV的Ar⁺、 He⁺、S⁺离子轰击n-InP(100)表面, 发现S⁺离子轰击可以产生In-S组分,减轻离子轰击对表面的物理损伤.对于Ar⁺离子轰击后的表面,经过S⁺离子处理和加热过程以后,表面损伤得到了修复,最终得到了2×2的InP表面,进一步验证了S⁺离子对InP表面的修复作用.     

An investigation into the effects of oxygen plasma discharge on tin-doped indium oxide thin films

The surfaces of tin-doped indium oxide (ITO) thin films for polymer light-emitting electrochemical cells (LECs) were modified by oxygen plasma discharge. The properties of the ITO surfaces were evaluated by means of the measurements of X-ray photoelectron spectroscopy (XPS), contact angle, surface free energy and polarity. The influence of surface properties of the ITO thin films on the performance of polymer LECs was investigated in terms of the turn-on voltage, injection current and luminance. When oxygen plasma discharge was employed to modify the ITO surfaces, the surface properties of ITO are optimized due to the improvement of surface stoichiometry and the enhancement of wettability. And the improved surface properties benefited from the oxygen plasma discharge is observed to decay with the time after the plasma discharge. The difference in chemical composition, surface free energy and polarity between the non-treated and treated ITO surfaces appears to become smaller with the increase of the time after plasma discharge. In addition, the electrical and optical performance of the devices is found to become worse with the increasing time after plasma discharge on ITO substrates. The results demonstrate that the device performance strongly depends on the ITO surface properties and the ITO/organic interface characteristics.     

Study of S ion-assisted sulfurization of n-GaAs (1 0 0) surface

The chemical structure and site location of sulfur atoms on n-GaAs (1 0 0) surface treated by bombardment of S⁺ ions over their energy range from 10 to 100 eV have been studied by X-ray photoelectron spectroscopy and low energy electron diffraction. The formation of Ga-S and As-S species on the S⁺ ion bombarded n-GaAs surface is observed. An apparent donor doping effect is observed for the n-GaAs by the 100 eV S⁺ ion bombardment. It is found that the S⁺ ions with higher energy are more effective in the formation of Ga-S species, which assists the n-GaAs (1 0 0) surface in reconstruction into an ordered (1 × 1) structure upon subsequent annealing. The treatment is further extended to repair Ar⁺ ion damaged n-GaAs (1 0 0) surface. It is found that after a n-GaAs (1 0 0) sample is damaged by 150 eV Ar⁺ ion bombardment, and followed by 50 eV S⁺ ion treatment and subsequent annealing process, finally an (1 × 1) ordering GaAs (1 0 0) surface with low surface states is obtained.     

Low energy (⩽ 100 eV) sputtering of thin molybdenum nitride films

Molybdenum nitride films formed by 100 eV N⁺₂ bombardment to saturation of polycrystalline Mo have been sputtered to high fluence by normally incident 100 eV Ar⁺ and He⁺ and 15 eV Ne⁺ while the surface nitrogen concentration was monitored by Auger electron spectroscopy (AES). The penetration distance of nitrogen atoms during film formation and subsequent sputtering is assumed to be small enough that AES will detect, to some degree, all of the nitrogen in the film. The nitrogen AES signal decays exponentially to unsputterable levels for the 15 eV Ne⁺ and 100 eV He⁺ cases and decays bi-exponentially to near the bulk contamination level for the 100 eV Ar⁺ case. The results are interpreted according to existing concepts, but the kinetics of nitrogen loss is modeled using a two-layer adaptation of the standard model for adsorbate monolayer sputtering kinetics. Fitting our proposed model to the data yields apparent cross-sections which are interpreted as composites of cross-sections for experimentally indistinguishable elementary processes; these elementary cross-sections for each process are geometrical averages on the polycrystalline surface. Processes considered, in addition to nitrogen sputtering, include bombardment-induced transport of nitrogen within the film and sputtering of the Mo lattice itself.     

ITO: Zr bi-layers deposited by reactive O2 and Ar plasma with high work function for silicon heterojunction solar cells

We report the influence of reactive oxygen (O₂) and argon (Ar) plasma based ITO:Zr bi-layers for silicon heterojunction (SHJ) solar cells. The purpose of reactive O₂ sputtered ITO:Zr was to improve the Hall mobility and work function while the Ar based ITO:Zr films play an important role to maintain good electrical characteristics. The thickness of reactive O₂ based ITO:Zr films was fixed at 15 nm while Ar based films was varied from 65 to 125 nm, respectively. ITO:Zr bi-layers with the thickness of 15/105 nm deposited by O₂ and Ar plasma, respectively, showed lowest resistivity of 2.358 × 10⁻⁴ Ω cm and high Hall mobility of 39.3 cm²/V · s. All ITO:Zr bi-layers showed an average transmittance of above 80% in the visible wavelength (380–800 nm) region. Work function of ITO:Zr bi-layers was calculated from the X-ray photoelectron spectroscopic (XPS) data. The ITO:Zr work function was enhanced from 5.3 eV to 5.16 eV with the variation of ITO:Zr bi-layers from 15/65 to 15/125 nm, respectively. Front barrier height in SHJ solar cells can be modified by using TCO films with high work function. The SHJ solar cells were fabricated by employing the ITO:Zr bi-layer as front anti-reflection coating. The SHJ solar cells fabricated on ITO:Zr bi-layer with the thickness of 15/105 nm showed the best photo-voltage parameters as; V_oc = 739 mV, J_sc = 39.12 mA/cm², FF = 75.97%, η = 21.96%.     

X-ray photoionization cross sections for quantitative analysis

The relative photoemission intensities from subshells of 51 elements and simple compounds have been measured using X-ray photoelectron spectroscopy. The chemical composition of each specimen surface was monitored by Auger electron spectroscopy and contamination was minimized by Ar⁺ ion bombardment. Experimental photoelectron cross sections derived for MgKα (1254 eV) radiation were compared with theoretical Hartree-Slater subshell photoionization cross sections calculated by Scofield. Good correlation (r = 0.96) between theory and experiment was observed over two orders of magnitude for most of the elements studied. Relative cross sections for subshells of a given element are also consistent with theoretical values, with several notable exceptions. The results indicate that quantitative analysis of ESCA spectra is possible using the Scofield cross sections.     

Characterization of Cr/6H-SiC(0 0 0 1) nano-contacts by current-sensing AFM

The electrical properties and interface chemistry of Cr/6H-SiC(0 0 0 1) contacts have been studied by current-sensing atomic force microscopy (CS-AFM) and X-ray photoelectron spectroscopy (XPS). Cr layers were vapor deposited under ultrahigh vacuum onto both ex situ etched in H₂ and in situ Ar⁺ ion-bombarded samples. The Cr/SiC contacts are electrically non-uniform. Both the measured I-V characteristics and the modeling calculations enabled to estimate changes of the Schottky barrier height caused by Ar⁺ bombardment. Formation of ohmic nano-contacts on Ar⁺-bombarded surfaces was observed.     

X-ray photoelectron spectroscopic studies of PbO surfaces bombarded with He+, Ne+, Ar+, Xe+ and Kr+

The surface composition of PbO has been studied with X-ray photoelectron spectroscopy after bombardment with several inert gas ions of 400 eV. The results show reduction of PbO to metallic Pb with the degree of damage following the order He⁺ > Ne⁺ >Ar⁺. Both Kr⁺ and Xe⁺ did not reduce the oxide. The depth of damage varied from ≈9 Å for He⁺ to ≈1 Å for Ar⁺ bombardment. The results were compared to a collisional and a thermal model of the sputtering process.     

Surface modifications of ITO electrodes for polymer light-emitting devices

Surface modifications were performed on the indium tin oxide (ITO) substrates for polymer light-emitting devices, using the different treatment methods including solvent cleaning, hydrochloric acid treatment and oxygen plasma. The influence of modifications on the surface properties of ITO electrodes were investigated by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact angle, and four-point probe. The surface energies of the ITO substrates were also calculated from the measured contact angles. Experimental results demonstrate that the surface properties of the ITO substrates strongly depend on the modification methods, and oxygen plasma more effectively improves the ITO surface properties compared with the other treatments. Furthermore, the polymer light-emitting electrochemical cells (LECs) with the differently treated ITO substrates as device electrodes were fabricated and characterized. It is observed that the surface modifications on ITO electrodes have a certain degree of influence upon the injection current, luminance and efficiency, but hardly upon the turn-on voltages of current injection and light emission which are close to the measured energy gap of electroluminescent polymer. Oxygen plasma treatment on the ITO electrode yields the better performance of the LECs, due to the improvement of interface formation and electrical contact of the ITO electrode with the polymer blend in the LECs.     

Optimum ion implantation and annealing conditions for stimulating secondary negative ion emission

The type, energy, ion dose, and heating temperature required to ensure a stable minimum work function of a surface in one experimental cycle (at least 2–3 min) are determined. Secondary ion mass spectrograms are recorded using Cs⁺, Ba⁺, and Ar⁺ ions. Cu, Al, and Mo samples are studied. The optimum ion implantation conditions and the activation temperature that provide a stable minimum work function of the sample surfaces are found. The samples implanted by Ba⁺ ions withstand higher temperature and current loads than the samples implanted by Cs⁺ ions. However, the work function in the case of Cs⁺ ions decreases stronger (to 1.9 eV). It is shown that neutral sputtered particles do not leave the surface at eφ ≤ 1.85–1.90 eV.     

Effects of (NH4)2Sx treatment on surface work function and roughness of indium-tin-oxide

In this study, the effects of an (NH₄)₂S_x treatment on the surface work function (SWF) and roughness of indium-tin-oxide (ITO) have been investigated. From the observed X-ray photoelectron spectroscopy results, optical transmittance measurements, atomic force microscopy measurements and four-point probe measurements, it is suggested that the surface chemical changes and an increase in the sheet resistance had strong effects on the SWF of ITO. We find that the S occupation of oxygen vacancies near the ITO surface after (NH₄)₂S_x treatment may result in a marked increase in the SWF and a slight increase in the surface roughness.     

Surface oxidation of Fe-Si alloy

The phase compositions at the surface of Fe₉₄Si₆ alloy samples were investigated. The phase analyses of the surfaces of samples annealed in vacuum, oxygen, and argon atmospheres were performed by Mössbauer spectroscopy and photoelectron spectroscopy (XPS). The formation of pure α-Fe, fayalite, hematite, and magnetite was observed in dependence on surface preparation and chemical composition of surrounding atmospheres during heat treatments.     

Reduction of hexavalent chromium with colloidal and supported palladium nanocatalysts

Zinc oxide (ZnO) nanowires (NWs) are exposed to energetic proton (H⁺), nitrogen (N⁺), phosphorus (P⁺), and argon (Ar⁺) ions to understand the radiation hardness and structural changes induced by these irradiations. High-resolution transmission electron microscopy is utilized to see the irradiation effects in NWs. Multiple doses and energies of radiation at different temperatures are used for different set of samples. The study reveals that wurtzite (crystalline)-structured ZnO NWs experience amorphization, degradation, and morphological changes after the irradiation. At room temperature, deterioration of the crystalline structure is observed under high fluence of H⁺, N⁺, and P⁺ ions. While for ZnO NWs, bombarded by Ar⁺ and P⁺ ions, nano-holes are produced. The ZnO NWs surfaces also show corrugated morphology full of nano-humps when irradiated by Ar⁺ ions at 400 °C. The corrugated surface could serve as tight-holding interface when interconnecting it with other NWs/nanotubes. These nano-humps may have the function of increasing the surface for surface-oriented sensing applications in the future.     

Direct patterning of gold oxide thin films by focused ion-beam irradiation

For direct writing of electrically conducting connections and areas into insulating gold oxide thin films a scanning Ar⁺ laser beam and a 30 keV Ga⁺ focused ion beam (FIB) have been used. The gold oxide films are prepared by magnetron sputtering under argon/oxygen plasma. The patterning of larger areas (dimension 10–100 μm) has been carried out with the laser beam by local heating of the selected area above the decomposition temperature of AuO_x (130–150 °C). For smaller dimensions (100 nm to 10 μm) the FIB irradiation could be used. With both complementary methods a reduction of the sheet resistance by 6–7 orders of magnitude has been achieved in the irradiated regions (e.g. with FIB irradiation from 1.5×10⁷ Ω/□ to approximately 6 Ω/□). The energy-dispersive X-ray analysis (EDX) show a considerably reduced oxygen content in the irradiated areas, and scanning electron microscopy (SEM), as well as atomic force microscopy (AFM) investigations, indicate that the FIB patterning in the low-dose region (10¹⁴ Ga⁺/cm²) is combined with a volume reduction, which is caused by oxygen escape rather than by sputtering. Received: 30 May 2000 / Accepted: 31 May 2000 / Published online: 13 July 2000     

Work function measurements on indium tin oxide films

We determined the work function of indium tin oxide (ITO) films on glass substrates using photoemission spectroscopy (PES). The ITO coated glass substrates were chemically cleaned ex-situ, oxygen plasma treated ex-situ, or sputtered in-situ. Our results suggest that the performance of ultraviolet photoemission spectroscopy (UPS) measurements can induce a significant work function reduction on the order of 0.4–0.5 eV, on ex-situ chemically and oxygen-plasma treated ITO samples. This was demonstrated by the use of low intensity X-ray photoemission spectroscopy (XPS) work function measurements before and after the UPS measurements were carried out.     

Physical-morphological and chemical changes leading to an increase in adhesion between plasma treated polyester fibres and a rubber matrix

The effects of plasma treatment, used to increase adhesion strength between poly(ethylene terephtalate) (PET) fibres and a rubber matrix, were investigated and compared. Morphological changes as a result of atmospheric plasma treatment were observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Wettability analysis using a surface energy evaluation system (SEE system) suggested that the plasma treated fibre was more wetting towards a polar liquid. When treated, these fibres showed a new lamellar crystallization, as shown by a new melting peak using differential scanning calorimetry (DSC). X-ray photoelectron spectroscopy (XPS) has been used to study the chemical effect of inert (argon), active and reactive (nitrogen and oxygen) microwave-plasma treatments of a PET surface. Reactive oxygen plasma treatment by a de-convolution method shows new chemical species that drastically alter the chemical reactivity of the PET surface. These studies have also shown that the surface population of chemical species formed after microwave-plasma treatment is dependent on the plasma gas. All these changes cause better adhesion strength of the PET fibres to the rubber matrix.