Ethanol Cluster Ion Research Articles

Mass spectrometric study of the negative and positive secondary ions emitted from ethanol microdroplets by MeV-energy heavy ion impact

Abstract We have investigated the negative and positive secondary ions emitted from ethanol droplets by 4.0-MeV C3+ impact to reveal the characteristic features of the reaction processes induced by fast heavy ions at the liquid ethanol surface. Analysis of the secondary ions was performed by time-of-flight mass spectrometry for microdroplet targets in a high vacuum environment. Fragment ions, deprotonated cluster ions, and trace amounts of the reaction product ions are observed in the negative secondary ions. The main fragment anions are C2HmO− (m = 1, 3, and 5) and C2H− generated by loss of hydrogen and oxygen atoms. The reaction product anions include deprotonated glycols, larger alcohols, and their dehydrated and dehydrogenated forms generated by secondary reactions between fragments and radicals. Furthermore, C3Hm− (m = 0–2) and C4Hm− (m = 0 and 1) are observed, which could be produced through a plasma state generated in the heavy ion track. Deprotonated ethanol cluster ions, [(EtOH)n − H]−, are observed up to about n = 25. [(EtOH)n − H]− have smaller kinetic energies than the protonated cluster ions (EtOH)nH+. This probably represents the effect of the positive Coulomb potential transiently formed in the ion track. We also discuss the size distributions and structures of the water- and CH2OH-radical-attached ethanol cluster ions.

Interaction between water cluster ions and mica surface

Water cluster ion beams were irradiated on mica surfaces to investigate the interaction between molecular cluster ions and a mica surface. The contact angle of the mica surface increased with increasing dose of the water cluster ion beam, but the increase in the contact angle was smaller than that induced by an ethanol cluster ion beam. The surface roughness also increased with increasing dose of the water cluster ion beam, whereas the intensity of K 2p x-ray photoelectron spectroscopy peaks decreased with increasing dose of the water cluster ion beam. The decrease in the number of potassium atoms together with the increase in the surface roughness may be the causes of the increase in the contact angle.

Acetone cluster ion beam irradiation on solid surfaces

Acetone cluster ions were produced by the adiabatic expansion method without using a support gas. The acceleration voltage of the acetone cluster ion beam was from 3 to 9kV. The sputter depths of silicon irradiated with acetone cluster ion beams increased with acceleration voltage and fluence of the acetone cluster ion beams. The sputter depth was close to that induced by the ethanol cluster ion beam accelerated at the same acceleration voltage. The sputtering yield of silicon by the acetone cluster ion beam at an acceleration voltage of 9kV was approximately 100times larger than that for an argon monomer ion beam at 9keV. The sputter depths of silicon dioxide irradiated with the acetone cluster ion beams were smaller than those of silicon, but larger than those induced by ethanol cluster ion beams. The XPS analysis of silicon surface indicated that the silicon surface was more strongly oxidized by the irradiation of acetone cluster ion beam than ethanol cluster ion beam.

Cluster Composition Distributions of Pure Ethanol: Influence of Water and Ion–Molecule Reactions Revealed by Liquid-Ionization Tandem Mass Spectrometry

Studies of clusters in condensed phase at atmospheric pressure are very important for understanding the properties and structures of liquids. Liquid-ionization (LPI) mass spectrometry is useful to study hydrogen-bonded clusters at the liquid surface and in a gas phase. An improved ion source connected to a tandem mass spectrometer provides detailed information about clusters. Mass spectra of pure ethanol (99.5%) observed by the first mass analyzer (Q1) showed neat ethanol cluster ions (C2H5OH) m H(+) with m up to 10 and hydrate ions (C2H5OH) m (H2O) n H(+) with m larger than 7 and n=1, such as those with m-n=8-1 and 9-1. When the flow rate of ethanol (liquid) was increased, large ethanol cluster ions with m larger than 25 were observed by the second mass analyzer (Q3). It is interesting to note that neat ethanol cluster ions are more abundant than corresponding (with the same m) hydrate ions (n=1), and major hydrate ions contain only one molecule of water. Results indicate that ion-molecule reactions occur between Q1 and Q3, because such mass spectra have never been observed by Q1. Various results indicate that neat ethanol clusters exist at the liquid surface and are ionized to give cluster ions.

Surface irradiation and materials processing using polyatomic cluster ion beams

Abstract

Surface Interaction and Processing Using Polyatomic Cluster Ions

We developed two types of polyatomic cluster ion sources, one of which was a liquid cluster ion source using organic materials with a high-vapor pressure. Vapors of liquid material such as ethanol and water were ejected through a nozzle into a vacuum region, and liquid clusters were produced by an adiabatic expansion phenomenon. Another type was a cluster ion source using ionic liquids with a relatively low-vapor pressure. Positive and negative cluster ions were produced by a high-electric field emission. In addition, the interaction of polyatomic cluster ions with solid surfaces such as Si(100), SiO2, glass, and PMMA surfaces was investigated, and chemical sputtering was predominant for the Si(100) surfaces irradiated by ethanol cluster ion beams. Also, the irradiation damage of the Si(100) surfaces by ethanol and water cluster ion beams was smaller than that by Ar monomer ion irradiation at the same acceleration voltage. With regard to surface modification, PMMA surfaces were chemically modified by water cluster irradiation. Also, glass surfaces changed to electrically conductive surfaces by ionic liquid cluster ion irradiation. Furthermore, to demonstrate engineering applications of high-rate sputtering and low-damage irradiation by ethanol cluster ion beams, micro-patterning was performed on the Si surfaces.

Micro-patterning of Si(100) surfaces by ethanol cluster ion beams

The irradiation of Si(100) surfaces by ethanol cluster ion beams exhibited high-rate sputtering and low-damage formation. The sputtered depth increased with increase of the acceleration voltage for ethanol cluster ions, and the sputtering yield was a few hundreds times larger than that by Ar monomer ion beams. Also, the RBS channeling measurement showed that the irradiation damage was much less than that by Ar monomer ion irradiation. Furthermore, the AFM image showed that the surface roughness of the irradiated Si(100) surface was less than 1 nm. As well as the Si(100) surface, the sputtered depth of the photo-resist surface increased with increase of the acceleration voltage for ethanol cluster ions. Based on these results, micro-patterning with various sizes in a range of 3 μm to 100 μm was performed on the Si(100) surfaces by the ethanol cluster ion irradiation. Various kinds of photo-resist mask patterns such as circle, square and line patterns were made on a Si(100) surface by photo-resist technique. The SEM observation showed that micro-patterns were prepared on the Si (100) surface by the ethanol cluster ion irradiation.

Chemical erosion and sputtering of solid surfaces with liquid cluster ions

The sputtering phenomena of solid surfaces such as Si(111) and SiO 2 surfaces were investigated using ethanol and water cluster ion beams. To be compared with Ar monomer ion irradiation, the sputtering yield of Si surfaces was approximately 100 times higher for ethanol cluster ion irradiation and approximately 10 times higher for water cluster ion irradiation. Furthermore, for the ethanol cluster ion irradiation, chemical erosion such as silicon hydride and hydro-carbide reaction occurred on the Si surface, which resulted in the high-rate sputtering of the surface. On the other hand, for the water cluster ion irradiation, oxidation occurred on the Si surface, and physical sputtering was performed on the surface. Based on these results, chemical reaction at a nano-scale area on the Si(111) surfaces was discussed from the thermodynamic approach, and the impact of cluster ions on the surface exhibited high temperature such as a few tens of thousands degrees, which resulted in the enhancement of the chemical reaction. Thus, liquid cluster ion irradiation exhibited unique erosion and sputtering even at room temperature, which were not obtained by a conventional wet process.

Surface Processing by Polyatomic Cluster Ion Beams

We produced polyatomic clusters such as ethanol and water clusters by an adiabatic expansion phenomenon of vaporized material. The cluster ions were irradiated by changing the incident energy on various kinds of substrates such as mica, Si(100), SiO2 and photo-resist substrates. AFM observation showed that irradiation trace with the diameter of approximately 20 nm was formed on mica substrates by ethanol cluster ion irradiation. Also, it showed that surface roughness of Si(100) substrates irradiated was less than 1 nm, even though the surface was sputtered by ethanol and water cluster ion irradiation. Furthermore, RBS channeling measurement showed that the irradiation damage of Si(100) surfaces sputtered by ethanol and water cluster ions was smaller than that by the Ar monomer ion irradiation. With regards to sputtering and patterning, the sputtered depth of Si(100), SiO2 and photo-resist surfaces by ethanol cluster ion irradiation increased with increase of the acceleration voltage. The sputtering yield of the Si(100) surface was a few hundreds times higher than that by Ar monomer ion irradiation at the same acceleration voltage. In addition, micro-patterning was performed on the Si(100) surface, and sharp-edged patterns with a line-width of 0.5 μm to 3 μm were achieved by ethanol cluster ion irradiation. [DOI: 10.1380/ejssnt.2011.168]

Characteristics of liquid cluster ion beam for surface treatment

A liquid cluster ion source, which is an ion source for the cluster beams produced with liquid materials, has been developed for the surface treatment of solid materials. The electrodes were designed for increasing the cluster beam intensity by a computer simulation of beam trajectories. The peaks of the cluster size distributions of the water and ethanol cluster ion beams of 3 atm vapor pressure were approximately at 2.4x10(3) and 1.6x10(3) molecules, respectively. The cluster size distributions of ethanol clusters were not sensitive to the variations of the acceleration voltages (V(e)) and currents (I(e)) of the electrons for ionization when the V(e) and I(e) were larger than approximately 200 V and 200 mA, respectively.

Interaction between ethanol cluster ion beam and silicon surface

The interaction between an ethanol cluster ion beam and a silicon surface was investigated. The sputtering depth of a silicon surface irradiated with an ethanol cluster ion beam increased with acceleration voltage. The number of disordered atoms on the silicon surface irradiated with an ethanol cluster ion beam initially showed a small dependence on retarding voltage and then a steep decrease with a further increase in retarding voltage.

High-Rate Sputtering of Si and SiO<sub>2</sub> with Atomically Flat Surfaces by Using Ethanol Cluster Ion Beams

High-Rate Sputtering of Si and SiO<sub>2</sub> with Atomically Flat Surfaces by Using Ethanol Cluster Ion Beams

Size distribution measurement and separation of ethanol cluster ion beams

The distributions of the number of molecules per cluster (cluster size) of ethanol cluster ion beams were measured by the time-of-flight method. The cluster sizes at the peak and minimum tail (minimum size) of the distribution increased with increase of the retarding voltage. A difference appeared between the measured minimum size and the calculated values using a formula based on the early measurements on the velocity distributions of gas clusters.

Quantification of methylamine in the headspace of ethanol of agricultural origin by selected ion flow tube mass spectrometry

Selected ion flow tube mass spectrometry, SIFT-MS, has been used to investigate if absolute levels of trace compounds in the headspace of ethanol/water vapour mixture can be quantified. This case study was directed towards the analysis of methylamine in distilled ethanol of agricultural origin because of its relevance to quality control legislation in the distillery industry. This has required a detailed study of the ion chemistry occurring – initiated by H 3O + precursor ions – when ethanol/water vapour mixtures are introduced into the H 3O +/helium carrier gas swarm and has resulted in the construction of a full scheme of the complex ionic reactions that occur. It has been found that under the SIFT-MS flow reactor conditions (He pressure 130 Pa and temperature 299 K) the terminating ions of the several parallel and sequential reactions that occur are the proton bound ethanol clusters ions, C 2H 5OH 2 +(C 2H 5OH) n , with n = 1,2,3, proton bound trimer ( n = 2) being the dominant species. These ethanol cluster ions can be used as precursor (reagent) ions for the chemical ionisation of the methylamine present in the ethanol/water vapour, which produces two characteristic product ions CH 3NH 2H +(C 2H 5OH) 1,2 that are used for the methylamine analysis. The ratio of the product ion count rate to the precursor ion count rate is used in an analogous way to the routinely used for SIFT-MS analyses to quantify the methylamine concentration. The results of calibration experiments show that using SIFT-MS it is possible to quantify methylamine in liquid ethanol/water mixtures at levels of 0.1 mg/L or greater.

In vivo analysis of palm wine ( Elaeis guineensis) volatile organic compounds (VOCs) by proton transfer reaction-mass spectrometry

The in vivo volatile organic compounds (VOCs) release patterns in palm wine was carried out using the PTR-MS. In order to analyze the complex mixtures of VOCs in palm wine, the fragmentation patterns of 14 known aroma compounds of palm wine were also investigated. Results revealed masses m/ z (43, 47, 61, 65, 75, 89 and 93) as the predominant ones measured in-breathe exhaled from the nose, during consumption of palm wine. Further studies of aroma's fragmentation patterns, showed that the m/ z 43 is characteristic of fragment of various compounds, while m/ z 47 is ethanol, m/ z 61(acetic acid), m/ z 65 (protonated ethanol cluster ions), m/ z 75 (methyl acetate), m/ z 89 (acetoin) and m/ z 93 (2-phenylethanol) respectively. The dynamic release parameters ( I max and t max) of the 7 masses revealed significant ( P = 0.05) differences, between maximum intensity ( I max) and no significant ( P = 0.05) differences between t max among VOCs respectively.

Angular dependence of sputtering effects by ethanol cluster ion irradiation on solid surfaces

In order to clarify the interactions of ethanol cluster ions with solid surfaces such as Si(100), SiO 2 and Au surfaces, sputtering effects were investigated by changing the acceleration voltage and incident angle ( θ) of the cluster ions. The sputtered depth at a normal incidence of θ = 0° increased with an increase of the acceleration voltage. The sputtering ratio of Si to SiO 2 was approximately 10, which suggested that chemical reactions between Si and ethanol produced silicon hydride as a dominant etching material. Furthermore, the sputtered depth of Si surfaces by ethanol cluster ion irradiation had a maximum value at an incident angle between 10° and 60°, and the angle corresponding to the maximum peak increased with an increase of the acceleration voltage. On the other hand, for the physical sputtering of Au surfaces by ethanol cluster ion irradiation, the sputtered depth decreased with the increase of the incident angle, and the change was in accordance with cos θ. With regards to the angular distribution of sputtered particles, Si surface atoms were ejected by ethanol cluster ion irradiation according to a cosine law distribution. This indicated that the Si surfaces were chemically sputtered by ethanol cluster ion irradiation. On the other hand, for the case of Au surfaces, the ejection of the sputtered particles changed to the under-cosine law. This was ascribed to the lateral sputtering effect of ethanol cluster ion irradiation.

Physical and chemical sputterings of solid surfaces irradiated by ethanol cluster ion beams

In order to clarify the interactions of ethanol cluster ion beams with solid surfaces, sputtering processes for Si, SiO(2) and Au surfaces were investigated by changing the acceleration voltage, the retarding voltage, and the incident angle. For the case of the normal incidence, the sputtered depth increased with increase of the acceleration voltage, and the sputtering ratio of Si to SiO(2) was approximately 10 at an acceleration voltage of 9 kV. Furthermore, with regard to the incident angle dependence, the sputtered depth for the Si surfaces had a maximum value at an incident angle between 10 degrees and 60 degrees . On the other hand, for the case of the physical sputtering by ethanol cluster ion irradiation on Au surfaces, the sputtered depth decreased with increase of the incident angle. With regard to the retarding voltage dependence, the sputtered depth had a maximum value for the Si surfaces, and the retarding voltage corresponding to the peak value changed according to the acceleration voltage applied. In addition, for the case of Au surfaces, the sputtered depth decreased with increase of the retarding voltage, and the physical sputtering was influenced by the minimum size of the cluster.

Dependence of size distribution for liquid cluster ions on retarding voltage

We have succeeded in producing liquid clusters such as ethanol and water clusters by an adiabatic expansion phenomenon, and the cluster size distribution was analyzed by using the time-of-flight method. For ethanol cluster ions, the size was distributed between a few hundreds and a few thousands, and the peak size was approximately 1200 molecules per cluster. For water cluster ions, the size distribution shifted to higher values, and the peak size was approximately 2500 molecules per cluster. Furthermore, the cluster size distribution was measured by changing the retarding voltage, and it was found that the minimum size increased with increase of the retarding voltage. In addition, the minimum size was larger than the critical size estimated by the theoretical calculation.

Irradiation effects of liquid cluster ion beams on silicon surfaces

We have developed a liquid cluster ion source, and produced liquid clusters such as ethanol and water clusters by an adiabatic expansion phenomenon. The average size was about 500 to 1000 molecules for the ethanol and about 2500 molecules for the water, respectively. The intensity of the cluster ion beams increased with increase of the vapor pressures. The irradiation effects of the liquid cluster ion beams on Si(100) surfaces were investigated. The sputtered depth increased with increase of an acceleration voltage for the ethanol and water cluster ions. In particular, the ethanol cluster ion irradiation sputtered the Si surface with the sputtering yield of approximately 100 times larger than that for Ar monomer ion irradiation. In addition, the Si surfaces after sputtering had an average roughness of less than 1 nm. Furthermore, the RBS channeling measurement showed that the irradiation damage of the Si surfaces by the ethanol and water cluster ions was smaller than that by the Ar monomer ion irradiation. This indicates that the low energy ion irradiation effect is predominant for the liquid cluster ion beams. As an engineering application of the liquid cluster ion beam process, the etching and patterning process were performed on the Si surfaces using metal masks. The mask patterns were formed very swiftly and finely by irradiation of the ethanol cluster ion beams.

Interactions of liquid cluster ion beams with metal surfaces

In order to investigate the interactions of ethanol and water cluster ion beams with metal surfaces, titanium (Ti) substrates were irradiated at different acceleration voltages. The sputtered depth increased with increase of the acceleration voltage. The sputtering yield of Ti at an acceleration voltage of 9kV for the ethanol cluster ions was approximately 100 times larger than that by argon (Ar) ion beams. On the other hand, for the case of the water cluster ion irradiation, the sputtering yield was a few tens times larger than that for Ar monomer ion irradiation. In addition, the AFM observation showed that the sputtered surfaces by the ethanol and water cluster ion beams had an average roughness of less than 1nm. For other metal surfaces such as Al, Ni, Cu, Ag and Au surfaces, the sputtering yield by the liquid cluster ion beams was also much larger than that by Ar monomer ion beams at the same acceleration voltage. Furthermore, the wettability of the Ti surfaces was changed drastically by the species of the cluster ions as well as the acceleration voltage. For the Ti surfaces irradiated by the ethanol cluster ion beams, the contact angle decreased with increase of the acceleration voltage, and it became about 10° at higher acceleration voltages. However, for the case of the water cluster ion irradiation, the contact angle was almost the same at various acceleration voltages, and it was about 80° which was larger than that of unirradiated surface.