CaF2 Window Research Articles

Crystalline Orientation of CaF2 window determined by Neutron Transmission Imaging using a Delay Line Current-Biased Kinetic-Inductance Detector

The combination of a high speed two-dimensional neutron detector and an intensive pulsed neutron source provides not only neutron transmission imaging but also information on crystal structures, orientations and constituent elements by analyzing neutron transmission spectra. The delay-line current-biased kinetic-inductance detector (CB-KID) is a two-dimensional superconducting neutron detector with high spatial and temporal resolutions, and multi-hit tolerance. We demonstrated that the delay-line CB-KID with a 10B neutron conversion layer can be applied for neutron transmission measurements up to 100 keV. We observed two-different dip structures in the transmission spectra in a CaF2 single crystal, i.e., one is from the Bragg diffraction and the other is from nuclear resonance absorption. We consider that some duplicated structures in resonance absorption dips are originating from a double-bunch structure of proton pulses for producing pulsed neutrons in the accelerator.

Short-term damage and its mechanism of a CaF2 window for a DUV lithography machine

The CaF2 window is the laser exit of the DUV lithography machine as well as its sealing component. Bearing the irradiation, high pressure, and discharging pollutants, the window is easy to damage and directly deteriorate the performance and reliability of the laser. In this paper, considering the effects of the above factors, two typical short-term damages to the CaF2 window - high energy induced damage and pollutant-induced damage are studied quantitatively. Using an experimental design, theoretical calculation, characterization analysis, and numerical simulation, we found that the damage induced by high-energy irradiation is dominated by defect propagation at the initial stage. At the later stage, it is dominated by heat and thermal stress with thermal melting and evenly distributed microcracks of 1∼10 µm in size. Low-energy irradiation only causes expansion and deformation of the window, but the highly absorbent electrode discharging particles with a diameter of 0.1∼1 µm strongly absorb the laser. Strong local heat is caused during the melting and gasification of the particles, which easily leads to ablation and cracks. The damaged area is proportional to the particle size, and the damaged rate is proportional to the average power density at a high repetition frequency. High energy density and the defects with high absorptivity, the electrode discharging particles, and the heat accumulation effect, are the main factors for the two short-term damage, respectively.

Rate Constants for Reactions of HCCO and HCCCO Radicals with O2 over the Temperature Range 243-423 K.

A pulsed laser photolysis-photoionization mass spectrometer system has been employed to measure the rate constants of HCCO + O2 and HCCCO + O2 over the temperature range 243-423 K in 1.2-8.4 Torr of He or N2. Radicals of HCCO and HCCCO were produced by 193 nm ArF laser photolysis of ethyl ethynyl ether and methyl propiolate, respectively. HCCO was photoionized by a Kr resonance lamp with a CaF2 window (10.03 eV), and HCCCO was ionized by a Xe lamp with a sapphire window (8.44 eV). Both ions were detected as parent ions in a quadrupole mass spectrometer. From analysis of the time profiles of the ion signals for various O2 concentrations, the overall rate constants at 298 K are represented by the values k2 = (6.3 ± 1.0) × 10-13 for HCCO + O2 and k5 = (5.7 ± 0.6) × 10-12 for HCCCO + O2 in the units cm3 molecule-1 s-1. The rate coefficients for the two reactions can be described by k2(T) = (1.5-0.7+1.5) × 10-12 exp[-(225 ± 220)/T] and k5(T) = (1.8-0.9+1.9) × 10-12 exp[(343 ± 228)/T] in the units cm3 molecule-1 s-1 over the temperature range 243-423 K.

ATR-FTIR Characterization of Janus Nanoparticles—Part II: Follow-Up Skin Application

Attenuated total reflection by Fourier transform infrared (ATR-FTIR) was used to implement reliable infrared descriptors over time of Janus nanoparticles (JNP), to follow their behavior before and after cutaneous application. In the last study, ATR-FTIR spectroscopic analysis allowed us to identify the evolution of intensity ratio of ν(C=O) at 1739 cm−1 and δ(H-O-H) at 1639 cm−1 as a spectroscopic descriptor, for JNP before cutaneous application (on the CaF2 window). This descriptor can be used to follow the physical stability (presence) of nanoparticles over time. The purpose of this study was to understand the behavior of JNP on the surface of the human skin. Therefore, a comparative study with the untreated skin and the skin after cutaneous application of lipophilic phase (Labrafil) of JNP was conducted using Franz cells. The suitability of the ATR-FTIR descriptor of JNP was evaluated, and a research of other descriptors was performed to understand the interaction that may exist between nanoparticles and the skin.

Hyperfine structure measurements of neutral atomic iodine (127I) in the infrared region (1800-6000 cm−1)

Experimental measurements of high resolution emission spectra of neutral atomic iodine (I I) have been extended to cover the mid-infrared spectral regions (1800–6000 cm−1) using Fourier transform spectroscopy. A total of 354 spectral lines are reported here in the above spectral range. While the region between 3000 and 6000 cm−1 were recorded using a conventional quartz Electrodeless Discharge lamps (EDL), spectra in the region 1800–3000 cm−1 were detected using specially prepared EDLs with a CaF2 window. Hyperfine structure analysis has been carried out on 224 spectral lines, of which 176 are reported for the first time. The magnetic dipole constant (A) and electric quadrupole constant (B) have been derived for 97 energy levels.

High-pressure, high-temperature optical cell for mid-infrared spectroscopy

The design, characterization, and operation of a new high-temperature, high-pressure optical cell for infrared spectroscopy is presented. The optical cell uses 16 cm CaF2 window rods to penetrate the temperature gradient between the heated optical path length and the ambient conditions surrounding the system. Along the 21.3 cm optical path length, good temperature uniformity was measured with deviations being less than 2.4% of the mean absolute temperature. Further characterization of the optical cell revealed usable transmission up to ∼ 8 µm and pressure stability from vacuum to over 30 atm. Moreover, stable operation of the optical cell during simultaneous heating and pressurization to 800 K and over 30 atm was demonstrated. To illustrate the utility of the new facility, high-resolution measurements of the R-branch in the fundamental absorption band of nitric oxide near 5.2 µm were collected at several pressures (1-34 atm) and temperatures (294–802 K) using an external cavity quantum cascade laser. The measured spectra were compared with Voigt line shape simulations using the HITRAN/HITEMP databases. At high gas densities, deviations from the Voigt line shape model are observed, emphasizing the need to further study infrared molecular spectra at high temperatures and pressures.

Surface enhanced plasmon effects by gold nanospheres and nanorods in Langmuir-Blodgett films

Hydrophobic gold nanospheres and nanorods were synthesized by a reduction method and a seed-mediated growth method, respectively, and by the surface-modification with 1-dodecanethiol. Langmuir-Blodgett (LB) films of gold nanoparticles were prepared at different surface pressures and two-dimensional ordering of nanoparticles was evaluated. A plasmon band of nanospheres slightly red-shifted from 525nm in water to 543nm in chloroform but it was 634nm at LB film. Plasmon bands at 750 and 515nm of nanorods in water drastically changed to a band at 550nm in chloroform but it appeared at 621 and 1000nm. Moreover, Langmuir monolayer of eiocosanoic acid was transferred on LB films of nanospheres on CaF2 window and transmission surface enhanced infrared absorption spectra (SEIRAS) were measured. A CO stretching vibration band at 1702cm−1 was strongly enhanced compared to other vibration bands due to the selection rule of SEIRAS. That is, the dipole moment of CO stretching mode should be on the same direction as the surface enhanced electric field, which is perpendicular to the gold surface. From the comparison of SEIRAS for poly(amido amine) dendrimer on LB films of nanospheres and nanorods, it is apparent that the enhancement effect of nanorod LB film is higher than that of nanosphere LB film, although the surface coverage and the number density of nanorods in LB film are lower than those of nanosphere LB film, suggesting the effect of hot spots.

Real Time-NIR/MIR-Photorheology: A Versatile Tool for the in Situ Characterization of Photopolymerization Reactions.

In photopolymerization reactions, mostly multifunctional monomers are employed, as they ensure fast reaction times and good final mechanical properties of the cured materials. Drawing conclusions about the influence of the components and curing conditions on the mechanical properties of the subsequently formed insoluble networks is challenging. Therefore, an in situ observation of chemical and mechanical characteristics during the photopolymerization reaction is desired. By coupling of an infrared spectrometer with a photorheometer, a broad spectrum of different photopolymerizable formulations can be analyzed during the curing reaction. The rheological information (i.e., time to gelation, final modulus, shrinkage force) can be derived from a parallel plate rheometer equipped with a UV- and IR-translucent window (glass for NIR and CaF2 window for MIR). Chemical information (i.e., conversion at the gel point and final conversion) is gained by monitoring the decrease of the corresponding IR-peak for the reactive monomer unit (e.g., C═C double bond peak for (meth)acrylates, H-S thiol and C═C double bond peak in thiol-ene systems, C-O epoxy peak for epoxy resins). Depending on the relative concentration of reactive functional groups in the sample volume and the intensity of the IR signal, the conversion can be monitored in the near-infrared region (e.g., acrylate double bonds, epoxy groups) or the MIR region (e.g., thiol signal). Moreover, an integrated Peltier element and external heating hood enable the characterization of photopolymerization reactions at elevated temperatures, which also widens the window of application to resins that are waxy or solid at ambient conditions. By switching from water to heavy water, the chemical conversion during photopolymerization of hydrogel precursor formulations can also be examined. Moreover, this device could also represent an analytical tool for a variety of thermally and redox initiated systems.

A cryogenic Herriott cell vacuum-coupled to a Bruker IFS-125HR

A new cryogenic Herriott cell and associated transfer optics have been designed and fabricated at Connecticut College under contract with NASA Langley Research Center to operate for the first time with the broad-band Bruker IFS-125HR Fourier transform spectrometer at the Jet Propulsion Laboratory (JPL). This 0.375m base-length optical cavity produces an absorption path length, at 293K, of 20.941 (±0.006)m. The Herriott cell, constructed from oxygen-free high conductivity copper, is placed inside its own vacuum enclosure, which is isolated from the transfer optics chamber by one CaF2 window and separately evacuated. The transfer optics chamber is in turn coupled to the sample compartment of the Bruker IFS-125HR holding another set of transfer optics. The entire spectrometer, including the transfer optics chamber can be evacuated to ∼10mTorr; the cell vacuum enclosure is cryogenically evacuated to pressures below 10−6Torr. A closed-cycle helium refrigerator cools the Herriott cell. Initially tested at Connecticut College for temperatures between 250 and 50K, the system has successfully been in operation for over two years at JPL. The cell has been used for recording spectra between 75 and 250K, achieving excellent temperature uniformity (± 0.15K) and long term stability (< 0.05K/day). Configured with a single indium-sealed CaF2 window, it has provided Doppler-limited infrared absorption spectra of a number of molecular species above 2000cm−1 to investigate detailed spectroscopic properties (e.g. molecular line parameters at temperatures and pressures relevant to planetary atmospheres). The design, performance and detailed characterization of the Herriott cell system are discussed.

Adding diffuse reflectance infrared Fourier transform spectroscopy capability to extended x-ray-absorption fine structure in a new cell to study solid catalysts in combination with a modulation approach

We describe a novel cell used to combine in situ transmission X-ray absorption spectroscopy (XAS) with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) in a single experiment. The novelty of the cell design compared to current examples is that both radiations are passed through an X-ray and IR transparent window in direct contact with the sample. This innovative geometry also offers a wide surface for IR collection. In order to avoid interference from the crystalline IR transparent materials (e.g., CaF2, MgF2, diamond) a 500 μm carbon filled hole is laser drilled in the center of a CaF2 window. The cell is designed to represent a plug flow reactor, has reduced dead volume in order to allow for fast exchange of gases and is therefore suitable for experiments under fast transients, e.g., according to the concentration modulation approach. High quality time-resolved XAS and DRIFTS data of a 2 wt.% Pt/Al2O3 catalyst are obtained in concentration modulation experiments where CO (or H2) pulses are alternated to O2 pulses at 150 °C. We show that additional information can be obtained on the Pt redox dynamic under working conditions thanks to the improved sensitivity given by the modulation approach followed by Phase Sensitive Detection (PSD) analysis. It is anticipated that the design of the novel cell is likely suitable for a number of other in situ spectroscopic and diffraction methods.

ChemInform Abstract: Deposition of Mass Selected Silver Clusters in Rare Gas Matrices.

We report on the successful ‘‘soft landing’’ of size selected silver dimers and trimers in solid krypton matrices. Silver cluster cations, produced by sputtering, were mass selected in a quadrupole mass filter and then codeposited with krypton on a cooled sapphire or CaF2 window in the presence of low energy electrons. Neutralized cluster samples were interrogated in situ by excitation and fluorescence spectroscopy. Deposition of slow (≤20 eV) silver dimer cations gave rise to strong excitation bands (centered at λ=275 and 390 nm) from Ag2 plus the characteristic triplet signal of the atom. The spectra imply that fewer than 25% of the dimers were fragmented during the neutralization and deposition steps. In similar experiments with Ag3 we were able to assign trimer absorption bands at 331, 364, 402, 421, 458, and 514 nm and identify characteristic emission features at 381, 560, and 626 nm.

On the origin of selectivity and anisotropy loss during microstructure release etch

The origin of the loss of Si anisotropy and selectivity to barrier metals during the release etch process of a CMOS-MEMS fabrication flow is investigated experimentally using in situ infrared imaging. The release etch is performed in an inductively coupled plasma etch chamber fitted with a CaF2 window to maximize IR transmission. Suspended disk test structures of varying plan area, thickness, transverse suspension cross-section and suspension length are etched at various bias voltages using a SF6/O2/C4F8 time-multiplexed, Bosch-type, anisotropic DRIE process followed by an O2 polymer removal process and an isotropic SF6 process. Temperatures up to 150 °C are reported for suspended disk test structures during the isotropic SF6 process while the temperature rise during the anisotropic DRIE and polymer removal processes is less than 7 °C. A physical model based on the power balance of the suspended disk test structures is developed and used to extract the proportion of etch heat absorbed by the structures, which is determined to be 0.26. The model predicts that exothermic heat of reaction of Si with neutral F species is the dominant source of heat and is supported by the observed temperature trends.

Novel Lipofuscin Bisretinoids Prominent in Human Retina and in a Model of Recessive Stargardt Disease

Bisretinoid adducts accumulate as lipofuscin in retinal pigment epithelial (RPE) cells of the eye and are implicated in the pathology of inherited and age-related macular degeneration. Characterization of the bisretinoids A2E and the all-trans-retinal dimer series has shown that these pigments form from reactions in photoreceptor cell outer segments that involve all-trans-retinal, the product of photoisomerization of the visual chromophore 11-cis-retinal. Here we have identified two related but previously unknown RPE lipofuscin compounds. By high performance liquid chromatography-electrospray ionization-tandem mass spectrometry, we determined that the first of these compounds is a phosphatidyl-dihydropyridine bisretinoid; to indicate this structure and its formation from two vitamin A-aldehyde (A2), we will refer to it as A2-dihydropyridine-phosphatidylethanolamine (A2-DHP-PE). The second pigment, A2-dihydropyridine-ethanolamine, forms from phosphate hydrolysis of A2-DHP-PE. The structure of A2-DHP-PE was corroborated by Fourier transform infrared spectroscopy, and density functional theory confirmed the presence of a dihydropyridine ring. This lipofuscin pigment is a fluorescent compound with absorbance maxima at approximately 490 and 330 nm, and it was identified in human, mouse, and bovine eyes. We found that A2-DHP-PE forms in reaction mixtures of all-trans-retinal and phosphatidylethanolamine, and in mouse eyecups we observed an age-related accumulation. As compared with wild-type mice, A2-DHP-PE is more abundant in mice with a null mutation in Abca4 (ATP-binding cassette transporter 4), the gene causative for recessive Stargardt macular degeneration. Efforts to clarify the composition of RPE lipofuscin are important because these compounds are targets of gene-based and drug therapies that aim to alleviate ABCA4-related retinal disease.

Selective reflection spectroscopy at the interface between a calcium fluoride window and Cs vapour

A special vapour cell has been built, that allows the measurement of the atom–surface van der Waals interaction exerted by a CaF2 window at the interface with Cs vapour. Mechanical and thermal fragility of fluoride windows make common designs of vapour cells impractical, so that we have developed an all-sapphire sealed cell with an internal CaF2 window. Although some impurities have remained when filling up the prototype cell, leading to line broadening and a shift, the selective reflection spectrum of the Cs D1 line (894 nm) makes apparent the weak van der Waals surface interaction. The uncertainties introduced by the effects of these impurities in the van der Waals measurement are nearly eliminated when comparing the selective reflection signal at the CaF2 interface of interest and at a sapphire window of the same cell. The ratio of the interactions respectively exerted by a sapphire interface and a CaF2 interface is found to be 0.55±0.25, in good agreement with the theoretical evaluation of ∼0.67.

Optimal operating conditions and characteristics of acetone∕CaF2 detector for inverse photoemission spectroscopy

Performance and characteristics of a band-pass photon detector using acetone gas and CaF2 window (acetone∕CaF2) have been studied and compared with an ethanol∕MgF2 detector. The optimal operating conditions are found to be 4mbar acetone pressure and 745±20V anode voltage. The count rate obtained by us is about a factor of 3 higher than what has been reported earlier for the acetone detector. Unlike other gas filled detectors, this detector works in the proportional region with very small dead time (4μs). A detector bandpass of 0.48±0.01eV full width at half maximum is obtained.

Measurements of Two-Dimensional Distribution of Refrigerant Concentration in EHL Film Using Micro FT-IR and Effect of Variation of Concentration on Oil Film Thickness

The dissolution of refrigerant into a lubricant causes a decrease in viscosity of the oil and it gives a large effect on the lubrication of sliding parts in a refrigerant compressor. This paper describes an application of micro FT-IR to measure the two-dimensional concentration distribution of refrigerant held in solution in the EHL film surrounded by the refrigerant gas and discusses the refrigerant concentration variation in the vicinity of the Hertzian contact area. In order to measure the concentration distribution, an apparatus which can observe the EHL film in a point contact in the refrigerant atmosphere was developed. The refrigerant concentration was measured using micro FT-IR through a CaF2 window from outside of the apparatus with polyol ester as a base oil in an atmosphere pressurized with HFC-134a refrigerant gas. The results indicate that the concentration of HFC-134a refrigerant reduces in the inlet boost region of EHL contact and the Hertzian contact area but in the side region of Hertzian contact area it is greater than that in the bulk fluid. In addition, the effect of the variation on the oil film thickness is discussed.

Hollow-glass waveguide delivery of an infrared free-electron laser for microsurgical applications

The purpose of this research is to deliver free-electron-laser (FEL) pulses for intraocular microsurgery. The FEL at Vanderbilt University is tunable from 1.8 to 10.8 microm. To deliver the FEL beam we used a metallic-coated hollow-glass waveguide of 530-mum inner diameter. A 20-gauge cannula with a miniature CaF2 window shielded the waveguide from water. Open-sky retinotomy was performed on cadaver eyes. The system delivered as much as 6 x 10(5) W of FEL peak power to the intraocular tissues without damage to the waveguide or to the surgical probe.

A comparison of two high performance inverse photoemission bandpass detectors

By performing inverse photoemission experiments on the same sample at the same time with two different detectors, their performance has been directly compared. The first detector is based on one of the most promising solid-state detector designs. It is comprised of a focused mesh electron multiplier and a CaF2 window. The second detector is a Geiger–Müller tube which uses dimethyl ether and a MgF2 window. Although it has already been demonstrated that detectors based on this design work, the dimethyl ether Geiger–Müller tubes are not widely used, and we show that it is essential to compensate for detector dead time effects for the detector to be practicably useful. Once this is done, the dimethyl ether Geiger–Müller tube has a sensitivity that is approximately 20 times greater than that of the solid-state detector. Furthermore, it is easy to operate and it does not appear to suffer from the problems that are normally associated with iodine Geiger–Müller detectors.

Pattern recognition for the HADES RICH detector

The planned High Acceptance DiElectron Spectrometer HADES [1] uses a Ring Imaging CHerenkov (RICH) detector for electron identification. The RICH detector, consisting of a gas radiator, a spherical mirror and a UV detector with CaF2 window and solid photocathode, covers the polar angle range from 18° to 88°. In a full simulation, including all known background processes, the basic properties of this detector were determined. The ring recognition, both for the off-line analysis as well as for a fast (10μs) second level trigger, was studied.

High-sensitivity bandpass UV photon detector for inverse photoemission

The authors describe a new type of high-efficiency UV photon detector which is simple and reliable, obtained by combining the high- and low-pass filtering of a KBr coated photocathode and a CaF2 window. This device is suitable for isochromatic inverse photoemission spectroscopy.