VUV Irradiation Research Articles

VUV irradiation of carbon dioxide (CO 2) and ammonia (NH 3) complexes in argon matrix

In this study, we characterized by FTIR spectroscopy the 1:1 and 2:1 molecular complexes between NH 3 and CO 2 in argon matrix at low temperature. In addition we tentatively identified the 1:2 molecular complex. The structures of the complexes were established from B3LYP calculations. Moreover, we showed that the VUV irradiation of the 1:1 complex forms the NH 2OH:CO complex.

Regulation of Pattern Dimension as a Function of Vacuum Pressure: Alkyl Monolayer Lithography

Photopatterning of a hexadecyl (HD) monolayer has been demonstrated using vacuum ultraviolet (VUV; lambda = 172 nm) light under controlled vacuum pressure with the objective of minimizing the pattern dimension. X-ray photoelectron spectroscopy (XPS) and lateral force microscopy (LFM) studies reveal that photodegradation of the HD monolayer not only is limited to the regions exposed to VUV but also spreads under the masked regions. The strong oxidants generated by VUV irradiation to atmospheric oxygen and water vapor diffuse toward the masked regions through the nanoscopic channels and photodissociate the monolayer under the masked area, near the photomask apertures, resulting in broadening of the photopattern. Such broadening decreases with decreased vacuum pressure inside the VUV chamber, associated with a decrease of oxidant concentration and reduction of their diffusion. Gold nanoparticles (AuNPs) were immobilized on the VUV patterned features to probe the dimension of the chemically active pattern. Field emission electron microscopy reveals the construction of 565 nm wide pattern features at a vacuum pressure of 10 Pa. This pattern widens to 1,030 nm at 10 (4) Pa using the same size apertures (500 nm) as printed on the photomask. This study provides insight for fabricating submicron patterns with high reproducibility and its exploitation for different applications, which includes the patterning of nanoparticles, biopolymers, and other nano-objects at submicron dimensions.

Modification of Polyethylene by VUV Irradiation in the Presence of Trimethylsilane and Oxygen

AbstractThe photoassisted modification of LDPE by VUV irradiation in a reactive trimethylsilane/oxygen atmosphere was investigated. The modified LDPE surface was investigated by FT‐IR, XPS, contact‐angle measurements and electron microscopy. Attachment of alkylsilyl and Si–O units to LDPE was observed. Best results were obtained using an equimolar trimethylsilane/oxygen mixture. Low‐energy surfaces were obtained after a few minutes of irradiation at an intensity of 1.7 mW · cm−2. After prolonged irradiation, the thickness of the modified polyethylene layer is approximately 700 nm. Surface modifications of this type may be of interest to obtain protective and barrier layers on polyolefins.magnified image

Vacuum ultraviolet irradiation on siliceous coatings on polycarbonate substrates

We studied the effect of vacuum ultraviolet (vuv) irradiation on siliceous coatings of polycarbonate (PC) substrates derived by the sol–gel method, with the aim of improving the abrasion resistance of the substrate surface. Methyltriethoxysilane with colloidal silica was used to prepare the sol solution. The sol solution was spin-coated on PC and this was followed by vuv irradiation with a Xe excimer lamp at 172 nm under N2 atmosphere. The PC substrate with vuv irradiated coating retained its high transmittance in the visible region for about 3 or more times of scraping turns by a steel wool tester on the surface, compared with the non-irradiated or mercury lamp-irradiated coatings, which demonstrated the remarkable improvement of the abrasion resistance by the vuv irradiation. The chemical changes under the vuv irradiation were also investigated by FTIR–ATR spectroscopy, composition analysis conducted with X-ray photoelectron spectroscopy and hardness measurements. It was concluded that the vuv light irradiation resulted in degrading the Si–CH3 bond in sol–gel derived siliceous coatings to yield hardening of the coatings. The transmittance of the coating in vuv region also increased with the Xe lamp irradiation.

P‐239: Synthesis and Photoluminescence Properties of Tb3+‐Doped Lanthanide Orthophosphates (La1−xGdx)0.94Tb0.06PO4 (0.5≤x≤1.0)

AbstractThe photoluminescence properties of the (La1−xGdx)0.94Tb0.06PO4 (0.5≤x≤1.0) phosphors synthesized by ultrasonic spray pyrolysis were investigated under VUV irradiation. In order to understand the effect of Gd addition on the photoluminescence properties, we obtained the excitation and emission spectra of the (La1−xGdx)0.94Tb0.06PO4 phosphors with various Gd contents. Annealed (La1−xGdx)0.94Tb0.06PO4 phosphors showed a smooth, regular, and spherical morphology. The XRD spectra of the (La1−xGdx)0.94Tb0.06PO4 showed the solid solutions of the constituent lanthanide phosphates, which crystallized in a monoclinic monazite. The XRD peaks shifted slightly toward higher angles with increasing Gd content, indicating that the lattice parameter slightly decreased with an increase in Gd content. The phosphors emitted the green light due to the transition from 5D4 to 7Fj (j=3−6) at 489, 543, 585, and 621nm, respectively. (La0.25Gd0.75)0.94Tb0.06PO4 showed the strongest emission intensity.

Removal of VUV pre-treated natural organic matter by biologically activated carbon columns

A potential alternative water treatment process using VUV (185 nm+254 nm) irradiation followed by a biological treatment is described. The system uses sufficient VUV radiation (16 J cm −2) to significantly enhance the production of biologically degradable moieties prior to treatment with biologically activated carbon (BAC). Two similar activated carbons were used, one virgin and one taken from a water treatment plant with an established biofilm. The VUV–BAC process decreased the overall dissolved organic carbon (DOC) concentration of a natural water sample by 54% and 44% for the virgin carbon and previously used BAC, respectively. Furthermore, VUV–BAC treatment decreased the trihalomethane (THM) formation potential (THMFP) by 60–70% and the haloacetic acid (HAA) formation potential (HAAFP) by 74%. The BAC systems effectively removed the hydrogen peroxide residual produced by VUV irradiation. Although nitrite formation can result from VUV treatment of natural organic matter (NOM), none was detected before or after BAC treatment.

VUV irradiation studies of plasmid DNA in aqueous solution

Interactions of VUV light and DNA samples in aqueous solutions are reported. The damage induced by such radiation is quantified by monitoring both loss of supercoiled DNA and formation of single and double strand breaks using agarose gel electrophoresis. Irradiations were performed using synchrotron VUV photons of 130, 150, 170 and 190 nm. VUV irradiation experiments revealed enhanced damage upon irradiation with 170 nm photons as compared with irradiations with photons of 150 nm and 130 nm. Irradiations carried at 190 nm caused the least damage.

Characterization of AlN metal-semiconductor-metal diodes in the spectral range of 44–360nm: Photoemission assessments

The absolute responsivity of a metal-semiconductor-metal (MSM) photodiode based on high quality AlN material has been tested from the vacuum ultraviolet (vuv) to the near UV wavelength range (44–360nm). The metal finger Schottky contacts have been processed to 2μm in width with spacing between the contacts of 4μm. In the vuv wavelength region, the measurement methodology is described in order to distinguish the contribution of the photoemission current from the internal diode signal. In the wavelength range of interest, AlN MSM is sensitive and stable under brief vuv irradiation. The MSM shows a 200∕360nm rejection ratio of more than four orders of magnitude and demonstrates the advantages of wide band gap material based detectors in terms of high rejection ratio and high output signal for vuv solar observation missions.

A comparative study on the effect of VUV radiation in plasma SiO x-coated polyimide and polypropylene films

Wettability of polyimide (PI) and polypropylene (PP) films have been improved using SiO x -like thin layers deposited from a mixture of hexamethyldisiloxane (HMDSO) and oxygen in a microwave distributed electron cyclotron resonance plasma reactor. The films wettability evolution behaviors were evaluated through the results of contact angle measurements, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The plasma depositions of SiO x thin layers in presence of VUV radiation induce a contact angle decrease to about 7° and 35° for PI and PP films, respectively. XPS data showed that such difference in wettability is attributed to the increase of hydrophilic group's proportion at the surface of coated PI films due to VUV irradiation. AFM images showed that the PI surface topography remains relatively smooth when coated in presence of VUV radiation. However, in the case of PP films, AFM images revealed the growth of irregular structure due to a substrate etching effect supported by VUV radiation. For polymers coated without VUV irradiation, the deconvolution of the C1s peaks showed a significant decrease of C O bonds for both PI and PP substrates.

Low Temperature Adsorption of Helium on Quench-Condensed Solid Neon Probed by Electron Emission from the Solid

Cyclotron resonance of free electrons (ECR) emitted from the solid Ne under VUV irradiation is observed. A flow of He gas supplied to the substrate avoiding a gas discharge zone is found to decrease the ECR amplitude. The decrease has been attributed to different mechanisms at the sample temperatures of 4.2 K and 1.6 K. He monolayer formation on the Ne surface is suggested in the low temperature region.

Probing defects at interfaces and interlayers of low-dimensional Si/insulator (HfO 2; LaAlO 3) structures by electron spin resonance

Electron spin resonance (ESR) spectroscopy enables to assess on atomic scale the nature and structural aspects of interfaces and interlayers in semiconductor/insulator hetero structures. This has been applied to (1 0 0)/insulator entities with nm-thin amorphous layers of HfO 2 and LaAlO 3 of high dielectric constant (>12) grown on clean (1 0 0)Si by atomic layer chemical vapor deposition and molecular beam deposition, respectively. Through analysis and monitoring of the occurring embedded paramagnetic point defects, including P b-type defects, E′, and EX, as a function of VUV irradiation and post-deposition heat treatment, basic information as to the nature, quality, and thermal stability of the interface and interfacial regions has been attained. On the basis of the analysis of P b-type defects (P b0, P b1), archetypal for the Si/SiO 2 interface, the (1 0 0)Si/LaAlO 3 stack is found to be truly abrupt, i.e., no evidence for an Si/SiO 2( x )-type transition in contrast with the Si/HfO 2 entity, where the interface is found to be Si/SiO 2( x ) type in the as-grown state. Analysis as a function of post-deposition heating indicates the Si/LaAlO 3 interface to remain stable and abrupt up to T an∼800 °C, above which an Si/SiO 2-type interface develops, while that in Si/HfO 2 evolves to one of closely standard Si/SiO 2 quality, with an SiO 2 interlayer of good quality. The differences in behavior of the studied Si/insulator stacks are discussed in a comparative analysis.

Photochemical Oxidation of Poly(dimethylsiloxane) Surface and Subsequent Coating with Biomimetic Phosphorylcholine Polymer

As a material for fabricating biomicrosystem devices called lab-on-a-chip or micro total analysis system (μTAS), poly(dimethylsiloxane) (PDMS) has been widely used. Generally, the devices used in biological applications require some surface modification in order to control the hydrophilicity and nonspecific adsorption of biomolecules on their surfaces. However, it is difficult to achieve surface modification that remains sufficiently stable over long enough duration for use in PDMS microfluidic devices. In this paper, we report a simple but reliable method of applying a surface coating of biomimetic polymer to PDMS surfaces by the combinative use of photochemical surface oxidation by VUV irradiation and subsequent coating of phospholipid copolymer containing 2-methacryloyloxyethyl phosphorylcholine (MPC) and 3-methacryloxytriethoxysilane (METESi). The effectiveness of this coating process has been demonstrated by a significant reduction in the nonspecific adsorption of serum albumin and the formation of a micropatterned surface coating using a photomask.

Direct VUV photolysis of chlorinated methanes and their mixtures in an oxygen stream using an ozone producing low-pressure mercury vapour lamp

The gas-phase photooxidations of CCl(4), CHCl(3), CH(2)Cl(2) and their binary mixtures in an O(2) stream were studied in a flow reactor under various experimental conditions using a low-pressure mercury lamp as light source covered with a high-purity silica sleeve being used. The 184.9 nm VUV irradiation emitted is responsible for the Cl-C bond rupture in the chlorinated methanes and for the formation of O(3) from O(2). The rate of degradation of H-containing chlorinated methanes increased sharply on increase of their initial concentrations, most probably of a (*)Cl chain reaction, as indicated by the increase in the molar ratio of the amount of HCl formed to the amount of H-containing target substance decomposed. The experimental results suggested that the further transformations of the radicals and products formed play an important role as (*)Cl sources, causing a considerably higher rate of decomposition of the H-containing target substances. In a humidified O(2) stream, the (*)OH formed opens up another route for oxidation of the target substances. Thus, the rates of degradation of CH(2)Cl(2) and CHCl(3) increased on increase of the relative humidity, whereas the water vapour had no effect at all on the decomposition of CCl(4). At the same time, competition occurs between (*)Cl or (*)OH for reactions with the target substance. The photooxidation of binary mixtures was investigated too. The addition of CCl(4) or CHCl(3) to CH(2)Cl(2) strongly increased its degradation rate. The addition of CH(2)Cl(2) did not have a considerable effect on the rate of degradation of CHCl(3).

VUV Induced Doping of Cu-Phthalocyanine Thin Films: A Possibility of n-Type Doping

The new type doping method, VUV-induced doping, has been applied to copper phthalocyanine (CuPc) thin film. The highest occupied molecular orbital (HOMO) peak in the ultraviolet photoelectron spectrum of CuPc film was gradually shifted toward high binding energy side upon the irradiation of He Iα radiation. Furthermore, the radiation induced gap states were observed up to the Fermi level. The shift of the HOMO peak in the low-dose region depends in a semi-logarithmic fashion on the irradiation time, indicating that the intentional n-type doping of CuPc film can be realized by VUV irradiation.

Modification of Hexatriacontane by O2–N2 Microwave Post-Discharges

Etch rates of hexatriacontane (HTC) as high as ~10 mg s−1 m−2 in late O2 post-discharge are obtained at 333 K where no significant UV nor VUV irradiation occurs. Introducing N2 in the gas mixture helps control the ratio of O/O2 densities, which is shown to play a key role in the functionalization or etching of the HTC. The oxygen atoms are required for any further modification of the HTC because they initiate the formation of the radical chains by abstraction of one hydrogen. O(3P) atoms do not contribute directly to break the alkane chain close to room temperature but they can functionalise it. O2 is the important reactive species for the etching because of the role played by the peroxide groups on the scission of the hydrocarbon chains.

Nitridation and reoxidation of high‐k metal oxide thin films using argon excimer sources

AbstractWe report for the first time the nitridation and reoxidation of metal oxide films with the active nitrogen and oxygen species produced by argon excimer sources. Preliminary results on 9 nm Ta2O5 films using this method exhibited excellent electrical properties with the leakage current density being up to 3 orders of magnitude lower than the as‐deposited films. Breakdown fields were found to be greater than 13 MV/cm. Accumulation capacitance with the nitrided film increased by 25% compared with the as‐deposited film. Optical transmittance was as high as 99% in the visible region and more than 74% in the UV region. The refractive index at 632.8 nm was high up to 2.2. The Ar excimer source emitted energetic VUV photons which could break nitrogen triple bonds to produce active nitrogen species and photodissociate O2 to form strong oxidant O3 and highly reactive O (1S) atoms, leading to the nitridation and reoxidation of Ta2O5 without the need for the use of H2O, NH3 and high temperature substrate heating. The nitridation process for a specific film thickness can be optimised by adjusting the VUV irradiation time to achieve increased accumulation capacitance and improved leakage property simultaneously. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Probing Semiconductor/Insulator Heterostructures Through Electron Spin Resonance of Point Defects: Interfaces, Interlayers, and Stress

AbstractElectron spin resonance (ESR) spectroscopy has become indispensable when it comes to the characterization on atomic-scale of structural, and correlated, electrical properties of actual semiconductor/insulator heterostructures. Through probing of paramagnetic point defects such as the Pb-type defects, E', and EX as a function of VUV irradiation and post deposition heat treatment, basic information as to the nature, quality, and thermal stability of the interface and interfacial regions can be established. This is illustrated by some specific examples of ESR analysis on contemporary Si/insulator structures promising for future developments in integrated circuits. First the impact of strain on the Si/SiO2 entity will be discussed. Through ESR analysis of thermally oxidized (111)Si substrates mechanically stressed in situ during oxidation, and tensile strained (100)sSi/SiO2 structures, it will be pointed out that in-plane tensile stress in Si can significantly improve the interface quality. Next, ESR results for stacks of (100)Si/SiOx/HfO2 and (100)Si/LaAlO3 are presented, revealing the potential to attain a high quality Si/SiO2 interface for the former and an abrupt, thermally stable interface for the latter.

Improvement of the Polyimide Surface Wettability Using SiOx Films Deposited in a DECR Reactor from HMDSO/O2 Mixtures

AbstractSummary: Polyimide (PI) foils were coated with thin SiOx films for surface wettability improvement. The deposition was carried out in a microwave DECR (Distributed Electron Cyclotron Resonance) plasma reactor from a mixture of HMDSO/O2. During deposition, the PI substrate was located downstream, exposed to long‐lived reactive precursors and to VUV radiation (position I) or located again downstream but shielded from VUV radiation (position II). Deposition time was varied in order to observe different stages of the film growth. The surfaces of the deposited films were investigated by means of contact angle, atomic force microscopy (AFM) and X‐ray photoelectron spectroscopy (XPS) measurements. According to contact angle measurements, the coated PI surface became hydrophilic already at a thickness of about 2.8 nm and stayed nearly at the same level still for thicker coating. The plasma deposition of the ultra‐thin SiOx layer increased significantly the polar component of the surface energy from 9 to 53 mJ · m−2 and consequently enhanced the wettability of the material. The treated surfaces were only moderately affected after eight weeks storage time in air, indicating stable surface treatments. AFM images revealed that during deposition, the PI surface topography remains relatively smooth when coated in position I. However, for PI coated in position II, the surface roughness becomes more pronounced as thickness is increased. XPS analysis showed that VUV irradiation of the PI surface leads to the formation of a high proportion of polar species which enhance the wettability of the surface. Curve fitting of the Si2p peak showed that, as the film thickness increases, the deposited film becomes more oxidized.Surface roughness of 6.6 nm thick SiOx film (Rav = 1.8 nm, Rrms = 2.3 nm).magnified imageSurface roughness of 6.6 nm thick SiOx film (Rav = 1.8 nm, Rrms = 2.3 nm).

Direct Si oxidation with fluorine incorporation using an argon excimer VUV source

AbstractDirect Si oxidation using an Ar excimer VUV source without substrate heating has led to the rapid growth of oxide layers, with a film thickness of 8 nm being obtained for only 10 min VUV irradiation. With fluorine incorporation, the film thickness was further increased to 21 nm. The 1073 cm–1 absorption band in the infrared spectra for the Si–O stretching vibration was shifted to a higher wavenumber up to 1096 cm–1 while its full width at half maximum (FWHM) was reduced from 64 to 54 cm–1. The resulting SiOF films were OH‐free. The rapid Si oxidation could be caused by the highly reactive O (1S) generated by VUV photons, the availability of more Si dangling bonds produced from the replacement of Si in the Si–Si bond by F, and more VUV‐induced O3 formation at low substrate temperatures. Fluorine incorporated into the Si–O network was directly provided by the VUV dissociated PTFE materials in the reaction chamber. The F contents in the SiOF films could be controlled by varying the VUV source parameters such as the excimer gas pressure. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Excimer VUV formation of erbium‐doped silica layers

AbstractErbium‐doped silica sol–gel layers with post‐process excimer VUV irradiation at a low temperature of 400 °C have exhibited a strong room temperature Er luminescence at ∼1.53 µm. The VUV irradiation has led to the formation of Er oxides in the silica matrix while significantly reducing nonradiative decay channels associated with the OH groups in the sol–gel layers. High‐resolution transmission electron micros‐copy results revealed the formation of Er2O3 crystallites in the silica layers. The Er–O coordination and crystallisation altered the chemical environment of the Er ions in the silica while possibly reducing the quenching effect of the Er–Er cross‐relaxation, resulting in the strong Er luminescence emitted. Moreover, the low temperature VUV process would not produce the luminescence background offset which was found to be present in all the luminescence spectra of the silica layers processed thermally at 900 °C. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)