Tetsuo Yano

Valence band electronic structure of carbon nitride from x-ray photoelectron spectroscopy

This article reviews the valence band (VB) electronic structure of carbon nitride and reports on results obtained from carbon nitride films prepared by pulsed laser deposition (PLD). In the present work, two series of carbon nitride films have been synthesized by nitrogen-ion-beam-assisted PLD and reactive PLD in nitrogen atmosphere, respectively. X-ray photoelectron spectroscopy (XPS) is applied to determine the VB electronic structures. XPS VB spectra reveal that the electronic structures of the prepared carbon nitride films depend on nitrogen supply manner. In the case of nitrogen-ion-beam-assisted deposition, four bands in the regions ∼0–6.2, ∼6.2–13.7, ∼13.7–20.8, and ∼20.8–30 eV are clearly observed in the VB electronic structure, which stem from C 2p electrons associated with π bonds and sp2N in a planar graphite structure, C 2p and N 2p electrons associated with σ bonds, a mixture of 2s and 2p electrons, and C 2s and N 2s electrons, respectively. For the films deposited by reactive PLD in a nitrog...

Impact of pulsed Nd:YAG laser irradiation on the growth and mortality of the biofilm forming marine bacterium Pseudoalteromonas carrageenovora

The impact of pulsed laser irradiation on the marine biofilm forming bacterium Pseudoalteromonas carrageenovora was investigated in the laboratory by monitoring mortality and the post-irradiation growth pattern. The impact of laser irradiation on bacterial mortality increased with the duration of irradiation. Laser irradiation at 532 nm (0.1 J cm m 2 ) for 15 min resulted in a 53% cell mortality immediately after irradiation. However, the impact after a period of 5 h (delayed impact) was more severe. The growth pattern of irradiated samples showed a prolonged lag phase compared to the reference, due to a reduction in total viable counts (TVC) in the irradiated samples. Nucleic acid staining is suggested to be a promising technique for monitoring laser inflicted bacterial mortality. Thus, the results suggest that laser irradiation could be considered as an alternative technique to reduce the number of biofilm forming bacteria and thereby biofilm formation on hard surfaces.

Pulsed laser irradiation impact on two marine diatoms Skeletonema costatum and Chaetoceros gracilis

The ability of pulsed laser irradiations to cause damage on the biofouling organisms is recently being investigated. If this technique is employed in industries such as power generation wherein a large quantity of water is being used for the cooling purpose, many organisms other than the targeted would get affected. In this study, we have investigated the damage caused by the pulsed laser irradiations from an Nd:YAG laser (fluence 0.1J/cm(2)) for varying durations such as 2, 5, 10, 30, 60 and 300 s on two marine diatom species namely Skeletonema costatum and Chaetoceros gracilis. Upon exposure to low power laser irradiations, these diatom species showed mortalities between 52.6+/-9.3% to 97.7+/-3.1% in the case of S. costatum and 57.8+/-2.5% to 98.9+/-0.6% in the case of C. gracilis for 2 and 300 s of irradiations, respectively. The mortality increased with the increase in the duration of laser irradiation. The estimation of the chlorophyll a concentration in the irradiated samples showed a considerable reduction varying between 9.8% and 57% in C. gracilis and 3% and 70.3% in S. costatum for 2 and 300 s of irradiations, respectively. The laser-survived cells grew as the non-irradiated (control) samples. C. gracilis frustules were broken by the laser whilst, the cell materials were drained out of the frustules in the case of S. costatum. The study therefore showed that the low power pulsed laser irradiations could cause significant damage on the two species of planktonic diatoms.

Laser-induced optical emission of carbon plume by excimer and Nd:YAG laser irradiation

Abstract We investigated the effect of additional laser irradiation on the energy state of a laser-ablated plume from a graphite target. Optical emissions from the plume were observed by a spectrometer equipped with an intensified charged couple device (ICCD) immediately after additional laser irradiation at various time delays relative to the ablation. The emission intensity from atomic carbon, ionic carbon, C2 and C3 increased when an ArF excimer laser irradiated the carbon plume. The atomic carbon absorbed the ArF excimer laser resonantly and was ionized. Using the fourth harmonic output of an Nd:YAG laser or a KrF excimer laser, the emission intensity from C2 and C3 only increased. However, no emission spectra change was observed with additional irradiation fundamental output of an Nd:YAG laser. The emission intensity from the atomic and ionic carbon and carbon clusters (C2 and C3) following ArF excimer laser irradiation of the plume was stronger than that using any other lasers.

Molecular level damages of low power pulsed laser radiation in a marine bacterium Pseudoalteromonas carrageenovora

Aim:  To study the molecular level damages in a marine bacterium, Pseudoalteromonas carrageenovora, exposed to low power pulsed laser radiation from an Nd:YAG laser.

Carbon nitride films with low friction coefficient synthesized by nitrogen-ion-beam-assisted pulsed laser deposition

Carbon nitride films were deposited on TiN coated stainless steel by pulsed laser ablation of graphite with assistance of low energy nitrogen-ion-beam bombardment. The film composition and bonding state were characterized by X-ray photoelectron spectroscopy. The friction properties of the carbon nitride films were studied under both dry lubrication in ambient atmosphere and wet lubrication in oil at a load up to 160 N by using a ball-on-disk apparatus. The synthesized carbon nitride films exhibited a lower friction coefficient compared with hard TiN film and commercial stainless steel. It was found that the friction coefficient of the carbon nitride films was independent of nitrogen content.

Impact of Pulsed Laser Irradiations from Nd:YAG Laser on the Larvae of the Fouling Barnacle Balanus amphitrite

The environmental hazards originating from the persistent use of antifouling agents containing toxic chemicals are alarming. Therefore, methods that do not rely on toxic elements are wanted. The effectiveness of pulsed laser irradiations from an Nd:YAG laser to induce damage to the larvae of a fouling barnacle, Balanus amphitrite, was evaluated in the laboratory. The average fluence tested was 0.1 J cmm 2. Three larval stages, viz. nauplii stage II and stage IV and cyprid larvae were exposed to laser irradiations for 2 s, 10 s, 30 s, 1 min, 5 min and 15 min in the case of nauplii stage II, and 2, 10 and 30 s in case of nauplii stage IV and cyprid larvae. Mortality occurred immediately after, as well as 1 and 3 d after the irradiation, and the settlement rate of cyprid larvae was investigated in the laboratory. Mortality in stage II, stage IV and cyprid larvae immediately after 2 s irradiation was 30.1 ± 0.5%, 9.3 ± 0.2 and 16.7 ± 4.8, respectively. Mortality after 3 d however showed higher values, viz. 84.4 ± 6.7%, 50 ± 4%, and 75 ± 9.4 in stage II, stage IV and cyprid larvae, respectively. Mortality increased with the period of laser irradiation. The stage II nauplii showed 100% mortality after 10 s irradiation. The mortality observed in stage IV and cyprid larvae was less than that found for the stage II nauplii. The IV stage larvae which survived could successfully moult to the next stage, whilst the irradiated cyprid larvae could not settle. The results thus showed that pulsed low power laser irradiations could cause significant damage to the larvae of this common fouling barnacle.

Lethal and sub‐lethal impacts of pulsed laser irradiations on the larvae of the fouling barnacle Balanus amphitrite

Laboratory experiments were conducted to study the impact of laser irradiation on the larvae of the fouling barnacle Balanus amphitrite. Research pertaining to fouling invertebrate larvae‐laser interaction is sparse and, hence, data on this aspect were thought significant in order to consider pulsed low power laser irradiations as a possible future antifouling tool. Lethal and sub‐lethal impacts of four very low laser fluences, viz. 0.013, 0.025, 0.05 and 0.1 J cm‐2 for three different durations, viz. 2, 10 and 30 s were investigated. Three growth stages of barnacle larvae, viz. nauplii stage II, nauplii stage IV and cyprids were exposed to the mentioned laser fluences for different durations. While lethal impact was assessed immediately after and 1 d after irradiation, sub‐lethal impacts were studied by monitoring the success rate of the irradiated nauplii in reaching the cyprid stage. In addition, the swimming speed of VIth stage nauplii after irradiation was studied. In the case of cyprids, in addition to the mortality measurement immediately after and 1 d after irradiation, the settlement rate was investigated. In all the above experiments, non‐irradiated larvae served as controls. The results showed an increase in mortality with increasing laser fluence and duration of irradiation. Irradiation for 2 s resulted in significant mortality in nauplii, while it was less in the case of cyprids. In IInd stage nauplii, the mortality immediately after irradiation for 2 s varied from 14.8±2.12 to 97.1±4.1% for laser fluences of 0.013 and 0.1 J cm‐2, respectively. However, in cyprids, the mortality immediately after irradiation for 2 s varied from 12.2±3 to 13.4±1.2% for fluences of 0.013 and 0.1 J cm‐2, respectively. The mortality in IVth stage nauplii was less than that for IInd stage nauplii but more than that for cyprids. There was a significant increase in mortality with time after irradiation. The formation of cyprids from the irradiated larvae was significantly less than that observed for non‐irradiated larvae. Also, the irradiated larvae showed a significantly slower swimming speed compared to the control samples. The settlement rate in cyprids was reduced significantly by the laser irradiation. This was true even for the lowest fluence and shortest period of irradiation tested. Thus, the results of the experiment showed that even a low power pulsed laser irradiation of 0.013 J cm‐2 for 2 s can cause significant damage to fouling barnacle larvae.

Laser Impact on Bacterial ATP: Insights into the Mechanism of Laser-Bacteria Interactions

The mechanisms of laser action on bacteria are not adequately understood. Here, an attempt has been made to study the fluctuation in ATP (adenosine triphosphate) concentration following laser irradiation from a pulsed Nd:YAG laser on a marine biofilm-forming bacterium Pseudoalteromonas carrageenovora. A stationary phase bacterial suspension (density 107-8 mlm 1) was exposed to pulsed laser irradiations at a fluence of 0.1 J cmm 2 (pulse width 5 ns, repetition rate 10 Hz) for different durations, ranging from 2 s to 15 min. The total viable count (TVC) and ATP concentration of the irradiated samples were determined immediately after the laser irradiation. While the maximum reduction in the TVC observed with respect to the control was 59% immediately after 15 min irradiation, the ATP concentration showed a reduction of about 86% for the same duration. The ATP concentration showed an abrupt reduction from 3 min of laser irradiation and continued to reduce significantly with increasing duration of irradiation. Thus, 3 min irradiation at a fluence of 0.1 J cmm 2 is considered as an approximate threshold for ATP production in this bacterium. As the decreased level of ATP production continued, bacterial mortality resulted. The reduction in ATP production could be due to damage caused by the laser irradiations on bacterial metabolic processes such as cellular respiration.

Laser damage to marine plankton and its application to checking biofouling and invasion by aquatic species: a laboratory study

In this laboratory study, the ability of low-power pulsed laser irradiation to kill planktonic organisms in a flowing water system was examined, thus, to test the possibility of using this technique as a water treatment strategy to reduce biofouling growth in condenser tubes of power plants and to reduce bioinvasion via the ballast water of ships. Two flow rates (4.6 and 9.0 l h−1) were tested on three planktonic organisms: two marine centric diatoms viz. Skeletonema costatum and Chaetoceros gracilis and a dinoflagellate, Heterocapsa circularisquama. A low-power pulsed laser irradiation at 532 nm with a fluence of 0.1 J cm−2 from a frequency-doubled Nd:YAG laser was used as the irradiation source. The laser irradiation resulted in a heavy mortality of the test cells. The mortality observed was >90% for S. costatum and H. circularisqama and >70% for C. gracilis. The results suggest that laser irradiation has the potential to act as a water treatment strategy to reduce biofouling of condenser tubes in power plants as well as to reduce species invasion via the ballast water of ships.