Source of a problem with Fourier transform spectroscopy

Tanner, D. B.; McCall, R. P.

doi:10.1364/ao.23.002363

Cited by 26 publications

(5 citation statements)

References 26 publications

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“…For heated samples FTIR data should to be corrected for the effects of sample emission when the sample and the detector are at different T [47][48][49] . We correct for sample emission by recording a spectrum with the IR source switched off and allowed 10 min to cool.…”

Section: Fourier Transform Infrared (Ftir) Reflectivity Measurementsmentioning

confidence: 99%

Origins of bad-metal conductivity and the insulator–metal transition in the rare-earth nickelates

et al. 2014

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For most metals, increasing temperature (T) or disorder hastens electron scattering. The electronic conductivity (σ ) decreases as T rises because electrons are more rapidly scattered by lattice vibrations. The value of σ decreases as disorder increases because electrons are more rapidly scattered by imperfections in the material. This is the scattering rate hypothesis, which has guided our understanding of metal conductivity for over a century. However, for so-called bad metals with very low σ this hypothesis predicts scattering rates so high as to conflict with Heisenberg's uncertainty principle 1,2 . Bad-metal conductivity has remained a puzzle since its initial discovery in the 1980s in high-temperature superconductors. Here we introduce the rare-earth nickelates (RNiO 3 , R = rare-earth) as a class of bad metals. We study SmNiO 3 thin films using infrared spectroscopy while varying T and disorder. We show that the interaction between lattice distortions and Ni-O covalence explains bad-metal conductivity and the insulator-metal transition. This interaction shifts spectral weight over the large energy scale established by the Ni-O orbital interaction, thus enabling very low σ without violating the uncertainty principle.The Drude model describes the dependence of σ on the lifetime (τ ) between scattering events, the free carrier concentration (n), the carrier effective mass (m * ), and the elementary charge (q): σ = nq 2 τ /m * . For metals the electron-phonon scattering rate increases with T , producing a linear dependence σ∝ T at sufficiently high T . Elementary quantum theory dictates that this relationship cannot continue indefinitely. According to Heisenberg's uncertainty principle the uncertainty E of a particle's energy is inversely proportional to its lifetime: E = h/τ . Therefore there exists a minimum τ below which the concept of a welldefined quasiparticle energy becomes unphysical. This lower bound on τ implies a minimum metallic conductivity (σ MIR ), which is called the Mott-Ioffe-Regel (MIR) limit 1,2 . Most metals reach their melting temperature well before the MIR limit. There are some so-called 'saturating' metals for which σ (T ) approaches σ MIR and saturates, thus validating the MIR limit. However, in bad metals the relationship σ −1 ∝ T continues unabated through the MIR limit. According to the Drude model these metals have lifetimes so short that the quasiparticles should be unstable (that is, decohere), producing an insulating state, and yet the transport properties remain metallic. Bad-metal conductivity is often found in strongly correlated materials such as the high-T superconductors and the Mott insulator-metal transition (IMT) system VO 2 . The phenomenon of bad-metal conductivity is a central problem in condensed matter physics 1-3 .Here we study bad-metal conductivity and the insulator-metal transition in the nickelates. The nickelate phase diagram features an antiferromagnetic insulator at low T and a paramagnetic metal (PM) at high T . For R = Sm and heavier there is also an in...

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Section: Fourier Transform Infrared (Ftir) Reflectivity Measurementsmentioning

confidence: 99%

Origins of bad-metal conductivity and the insulator–metal transition in the rare-earth nickelates

et al. 2014

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“…It has been shown that the introduction of a hot sample into the optical path will cause severe error in deriving spectral properties from the measurements of transmittance [16]: not only emission from all components in the source compartment is modulated and contributes to the interferogram, but the emission originating from the optics and hot test sample will be imaged into the Michelson's interferometric setup, modulated, and subsequently imaged back onto the detector. Fringes generated by the radiation, which is re ected back into the interferometric setup, are radians out of phase with those generated by the radiation from the internal source.…”

Section: Methodsmentioning

confidence: 99%

“…A number of measures have been proposed to correct this problem [16,17]. These include (1) modi cation of the interferometer such that the emission from the sample is not imaged onto the detector; (2) chopping of the source radiation and demodulation of the signal using a lock-in ampli er; (3) use of two sources, each operating at a different temperature.…”

Section: Methodsmentioning

confidence: 99%

Measurement of Infrared Absorption Coefficients of Molten Glasses

Zhang¹,

Modest²,

Bharadwaj³

2001

Experimental Heat Transfer

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In this article, a method based on the "submerged mirror" technique to measure the absorption coef cient of molten glass is presented. Infrared light, which is modulated by Michelson's interferometeric setup, passes through the molten glass and is collected by a mercury-cadmium-telluride (MCT) or a silicon detector. The signal is processed by a Fourier transform infrared (FTIR) spectrometer to yield the spectral intensity of the infrared light. The processes are repeated with different thicknesses of molten glass layer. The spectral absorption coef cient is calculated from the apparent transmittance. Tests of the apparatus have been made with distilled water, for which the results agree well with existing data. Measurements were carried out for a number of calcia-alumina-silicate glasses at temperatures ranging from 1,200 to 1,300 C.Radiative heat transfer is an important-if not the most dominant-mode of heat transfer during the drawing of E-glass through bushings. For optimal control of the ber drawing process, the radiative heat losses must be accurately determined and/or tailored, which requires detailed and accurate knowledge of the glass's absorption coef cient at high temperature.Methods to measure optical properties of liquids can be broadly classi ed into emission techniques [1, 2], acousto-optics [3], ellipsometry [4,5], Kramers-Kronig transforms [6,7], pole-t procedures [8], transmission techniques [9-13], and submerged-mirror techniques [14,15].An error analysis using representative errors in emissivity measurements shows that emission techniques are very sensitive to temperature measurement errors. The use of acousto-optics requires microphones that can withstand temperatures greater than 1,000°C, which have not been developed yet. The performance-to-cost ratio of setups in ellipsometric methods justify their use only for high-accuracy measurements of the complex index of refraction. Kramers-Kronig transforms need measurements over a wide spectral range to achieve reasonable accuracy. Mackenzie [10] and Greenberg [9] have performed transmission measurements by holding a thin lm of liquid with platinum

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“…20 Additionally, the use of corner-cube or cat's eye retroreflectors in the interferometer has been reported to decrease the effect of emission by spatially offsetting the optical paths taken by radiation emitted by the sample/cell versus that from the IR source. 21,22 In most interferometers that incorporate retroreflectors, however, their purpose is to reduce the effects of mirror tilt, and the beam from the IR source is centered within the corner of the mirror cubes. In such cases, there is no built-in offset between the emitted radiation from the cell and that from the IR source.…”

Section: Sample Emission Correctionmentioning

confidence: 99%

Quantitative Infrared Spectroscopy of Tetrakis(dimethylamido)Titanium for Process Measurements

Sperling

Kimes

Maslar

2014

ECS J. Solid State Sci. Technol.

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Infrared spectroscopy has been widely used for in situ analysis of the gas phase during chemical vapor deposition (CVD) and atomic layer deposition (ALD). For both process monitoring and research applications, accurate determination of absorptivity is often necessary for quantitative work. In this study, we measure reference spectra for vapor-phase tetrakis(dimethylamido)titanium (TDMAT), an organometallic precursor commonly used for both CVD and ALD. The gas cell is heated over the temperature range of (352 to 476) K. We take steps to correct for sample emission, which otherwise is found to cause errors. Systematic changes are observed as the temperature is varied, but integrated absorbance is insensitive to temperature. The implications for infrared-based process measurements are discussed. In the course of this work, we do not observe rapid thermal decomposition of TDMAT at 476 K, which had been reported elsewhere in the literature.

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Source of a problem with Fourier transform spectroscopy

Abstract: Thermal radiation from sample and detector can affect internally modulated Michelson interferometers (for example, rapid scanning, phase-modulated, or internally chopped) and cause serious systematic errors in the spectra measured by these instruments.

Cited by 26 publications

References 26 publications

Origins of bad-metal conductivity and the insulator–metal transition in the rare-earth nickelates

Origins of bad-metal conductivity and the insulator–metal transition in the rare-earth nickelates

Measurement of Infrared Absorption Coefficients of Molten Glasses

Quantitative Infrared Spectroscopy of Tetrakis(dimethylamido)Titanium for Process Measurements

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