Direct Observation of Terahertz Surface Modes in Nanometer-Sized Liquid Water Pools

Boyd, Joel E.; Briskman, Ari; Colvin, Vicki L.; Mittleman, Daniel M.

doi:10.1103/physrevlett.87.147401

Cited by 60 publications

(52 citation statements)

References 33 publications

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“…Terahertz spectroscopy in reverse micelles has revealed the low vibrational modes characteristic for confined water. 21 These modes are size-dependent and support the idea of a behavior specific to water in nanoconfinement. NMR has also proven to be a valuable tool for measuring the effect of confinement on the rotational dynamics by means of a molecular probe.…”

Section: Introductionsupporting

confidence: 56%

Structure and dynamics of water in nonionic reverse micelles: A combined time-resolved infrared and small angle x-ray scattering study

Loop

Panman

Lotze

et al. 2012

The Journal of Chemical Physics

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We study the structure and reorientation dynamics of nanometer-sized water droplets inside nonionic reverse micelles (water/Igepal-CO-520/cyclohexane) with time-resolved mid-infrared pumpprobe spectroscopy and small angle x-ray scattering. In the time-resolved experiments, we probe the vibrational and orientational dynamics of the O-D bonds of dilute HDO:H 2 O mixtures in Igepal reverse micelles as a function of temperature and micelle size. We find that even small micelles contain a large fraction of water that reorients at the same rate as water in the bulk, which indicates that the polyethylene oxide chains of the surfactant do not penetrate into the water volume. We also observe that the confinement affects the reorientation dynamics of only the first hydration layer. From the temperature dependent surfacewater dynamics, we estimate an activation enthalpy for reorientation of 45 ± 9 kJ mol −1 (11 ± 2 kcal mol −1 ), which is close to the activation energy of the reorientation of water molecules in ice.

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Section: Introductionsupporting

confidence: 56%

Structure and dynamics of water in nonionic reverse micelles: A combined time-resolved infrared and small angle x-ray scattering study

Loop

Panman

Lotze

et al. 2012

The Journal of Chemical Physics

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“…The dielectric properties in the terahertz spectral range (3-33 cm -1 ) have also been reported. 35 A resonance was observed that is not present in bulk water samples and is dependent on the size of the reverse micelle. The authors attributed it to surface modes.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of Nanoscopic Water: Vibrational Echo and Infrared Pump−Probe Studies of Reverse Micelles

2005

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The dynamics of water in nanoscopic pools 1.7-4.0 nm in diameter in AOT reverse micelles were studied with ultrafast infrared spectrally resolved stimulated vibrational echo and pump-probe spectroscopies. The experiments were conducted on the OD hydroxyl stretch of low-concentration HOD in the H 2 O, providing a direct examination of the hydrogen-bond network dynamics. Pump-probe experiments show that the vibrational lifetime of the OD stretch mode increases as the size of the reverse micelle decreases. These experiments are also sensitive to hydrogen-bond dissociation and reformation dynamics, which are observed to change with reverse micelle size. Spectrally resolved vibrational echo data were obtained at several frequencies. The vibrational echo data are compared to data taken on bulk water and on a 6 M NaCl solution, which is used to examine the role of ionic strength on the water dynamics in reverse micelles. Two types of vibrational echo measurements are presented: the vibrational echo decays and the vibrational echo peak shifts. As the water nanopool size decreases, the vibrational echo decays become slower. Even the largest nanopool (4 nm, ∼1000 water molecules) has dynamics that are substantially slower than bulk water. It is demonstrated that the slow dynamics in the reverse micelle water nanopools are a result of confinement rather than ionic strength. The data are fit using time-dependent diagrammatic perturbation theory to obtain the frequency-frequency correlation function (FFCF) for each reverse micelle. The results are compared to the FFCF of water and show that the largest differences are in the slowest time scale dynamics. In bulk water, the slowest time scale dynamics are caused by hydrogen-bond network equilibration, i.e., the making and breaking of hydrogen bonds. For the smallest nanopools, the longest time scale component of the water dynamics is ∼10 times longer than the dynamics in bulk water. The vibrational echo data for the smallest reverse micelle displays a dependence on the detection wavelength, which may indicate that multiple ensembles of water molecules are being observed.

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“…[4][5][6][7] This is an exciting development, as it is becoming increasingly clear that many systems of interest, including biological molecules and a variety of artificial nanostructures, have absorption features in the THz frequency range, but are far smaller than the wavelength of the THz radiation. [8][9][10][11] These developments therefore offer great promise for THz microscopy. In the THz ANSOM experiments, two different detection techniques are currently employed: THz electric fields are either detected in the nearfield of the tip using electro-optic sampling, or in the far-field of the tip with a receiver.…”

mentioning

confidence: 99%

Antenna effects in terahertz apertureless near-field optical microscopy

Wang

Mittleman

Valk

et al. 2004

Applied Physics Letters

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126

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We have performed measurements on terahertz (THz) apertureless near-field microscopy that show that the temporal shape of the observed near-field signals is approximately proportional to the time-integral of the incident field. Associated with this signal change is a bandwidth reduction by approximately a factor of 3 which is observed using both a near-field detection technique and a far-field detection technique. Using a dipole antenna model, it is shown how the observed effects can be explained by the signal filtering properties of the metal tips used in the experiments. Apertureless near-field scanning optical microscopy (ANSOM) is an attractive technique for obtaining subwavelength resolution in optical imaging at visible and midinfared wavelengths. [1][2][3] In this technique, light is scattered off a subwavelength-sized metal tip which is held close to a surface. The scattered light is collected in the far-field, giving subwavelength resolution in the immediate neighborhood of the tip apex. Very recently, there have been reports showing how ANSOM can be adapted for the terahertz (THz) frequency domain, by combining it with THz time-domain spectroscopy. [4][5][6][7] This is an exciting development, as it is becoming increasingly clear that many systems of interest, including biological molecules and a variety of artificial nanostructures, have absorption features in the THz frequency range, but are far smaller than the wavelength of the THz radiation. [8][9][10][11] These developments therefore offer great promise for THz microscopy. In the THz ANSOM experiments, two different detection techniques are currently employed: THz electric fields are either detected in the nearfield of the tip using electro-optic sampling, or in the far-field of the tip with a receiver. In the latter case, near-field information from the tip apex is obtained by vibrating the metal tip at a high frequency, followed by phase-sensitive detection at this frequency. However, an important aspect of both experiments remains unexplained: The measured temporal profile of the near-field signals is very different from that of the incident THz pulses. Associated with this shape change is a bandwidth reduction of about a factor of 3, which could limit the utility of the technique in spectroscopic measurements. For practical applications, such as THz microscopy, it is essential that the origin of this bandwidth reduction is understood.Here, we present measurements and calculations which demonstrate that the observed bandwidth reduction is a consequence of the antenna properties of the metal tips used in the experiments. We demonstrate that, regardless of whether the near-field signal is observed directly under the tip or in the far-field, it is approximately proportional to the timeintegral of the incident THz signal. Near-field calculations based on a dipole antenna model qualitatively reproduce all the essential features observed in the measurements and provide insight into ANSOM experiments in general.The two THz ANSOM configurations, used ...

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Direct Observation of Terahertz Surface Modes in Nanometer-Sized Liquid Water Pools

Cited by 60 publications

References 33 publications

Structure and dynamics of water in nonionic reverse micelles: A combined time-resolved infrared and small angle x-ray scattering study

Structure and dynamics of water in nonionic reverse micelles: A combined time-resolved infrared and small angle x-ray scattering study

Dynamics of Nanoscopic Water: Vibrational Echo and Infrared Pump−Probe Studies of Reverse Micelles

Antenna effects in terahertz apertureless near-field optical microscopy

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