Frequency- and wavelength-modulation spectroscopies: Comparison of experimental methods using an AlGaAs diode laser

Low-wavelength modulation (1 kHz), high-wavelength modulation (100 MHz) and two-tone frequency modulation (390±5 MHz) spectroscopies are systematically compared by measuring the minimum detectable absorption achieved using an AlGaAs diode laser tuned on a third-overtone methane transition at 886 nm. From the S/N behavior has been extrapolated a minimum relative absorption (1 Hz of bandwidth) of 4.5(1)×10^–7 for the LMW, 9.7(3)×10^–8 for the HWM and 6.4(2)×10^–8 for the TTFM. In the LWM case the detection-limit value is represented by the laser amplitude 1/f excess noise, while for the high-frequency detection techniques this contribution is negligible with respect to other noise sources. These detection limits well agree with the calculated quantum limited values based on measured laser power, modulation index, noise figure of the electronic components, and other parameters of the apparatus.     

Surface modification of poly(propylene carbonate) by oxygen ion implantation

Poly(propylene carbonate) (PPC) was implanted by oxygen ion with energy of 40 keV. The influence of experimental parameters was investigated by varying ion fluence from 1 × 10¹² to 1 × 10¹⁵ ions/cm². XPS, SEM, surface roughness, wettability, hardness, and modulus were employed to investigate structure and properties of the as-implanted PPC samples. Eight chemical groups, i.e., carbon, CH, COC, CO, OCO, CO, , and groups were observed on surfaces of the as-implanted samples. The species and relative intensities of the chemical groups changed with increasing ion fluence. SEM images displayed that irradiation damage was related strongly with ion fluence. Both surface-recovering and shrunken behavior were observed on surface of the PPC sample implanted with fluence of 1 × 10¹⁵ ions/cm². As increasing ion fluence, the surface roughness of the as-implanted PPC samples increased firstly, reached the maximum value of 159 nm, and finally decreased down the minimum value. The water droplet contact angle of the as-implanted PPC samples changed gradually with fluence, and reached the minimum value of 70° with fluence of 1 × 10¹⁵ ions/cm². The hardness and modulus of the as-implanted PPC samples increased with increasing ion fluence, and reached their corresponding maximum values with fluence of 1 × 10¹⁵ ions/cm². The experimental results revealed that oxygen ion fluence closely affected surface chemical group, morphology, surface roughness, wettability, and mechanical properties of the as-implanted PPC samples.     

A test of special relativity with stored lithium ions

Laser spectroscopy at the heavy ion storage ring TSR in Heidelberg allows for precision experiments testing the limits of the special theory of relativity. With an optical-type three-level system of⁷Li⁺ the Doppler shift has been measured by saturation spectroscopy as a test of the time dilatation factor = (1 – ²)^–1/2 at an ion velocity of = 6.4% c. A precision of/ < 9 × 10^–9 has been obtained, which sets a second-order limit of 1.1 × 10^–6 for any deviation from the time dilatation factor. The fourth-order limit of this deviation is set below 2.7 × 10^–4 by the present experiment. These limits are given at a 1 confidence level.     

Hierarchy of symmetry breakings and neutral currents in anSU(6) grand unification model

In anSU(6) grand unification model with eight quarks and eight leptons belonging to 15-plet and singlet representations, the symmetry is spontaneously broken by the sequenceSU(6)SU(3) ^c ×SU(2)×U(1)×U(1)SU(3) ^c ×U(1). Fror two cases of symmetry breakings the effective weak neutral current coupling constants are compared with experiment. For theSU(3) ^c ×SU(2)×U(1)×U(1)×SU(3) ^c ×U(1) symmetry breaking, the coupling constants reproduce the Weinberg-Salam model with a small correction term. Agreement with the experimental mean values is improved with the correction term. Parity violation in atomic physics is also discussed.     

Plastic deformation at high strain rates

In the present paper a new method, an original testing device and techniques for the study of plastic deformation in materials at high strain rates up to 2×10⁴ s^–1 achieved with the use of very short stress pulses (length within 10–20 s) are described. The suggested method of yieldpoint determination respects the effects of delayed plastic deformation in the yield point at loading by very short intensive stress pulses. The investigations were carried out in polycrystalline ARMCO-iron and low-alloyed steel, and besides on the specimens irradiated by neutrons with integral dose 1·35×10¹⁹ ncm^–2. The experimental results obtained are interpreted from the point of view of the present knowledge of the process of plastic deformation in bcc metals.     

Quantization of helicity on a compact spacetime

The Dirac operator arises naturally on from the connection on the Lie group U(1)×SU(2) and maps spacetime rays into rays in the Lie algebra. We construct both simple harmonic and pulse solutions to the neutrino equations on , classified by helicity and holonomy, using this map. Helicity is interpreted as the internal part of the Noether charge that arises from translation invariance; it is topologically quantized in integral multiples of a constant g that converts a Lie-algebra phase shift into an action. The fundamental unit of helicity is associated with a full twist in u(1)×su(2) phase per global lightlike cycle. If we pass to the projective space P¹xP³, we get half-integral helicity.     

The second hyperpolarizability of CdTe nanocrystals using polarization-resolved degenerate four-wave mixing

Polarization-resolved forward degenerate four-wave mixing (DFWM) in a nonresonant region revealed the effective third-order nonlinear susceptibility of colloidal CdTe nanocrystals (NCs) with the size near the Bohr radius and various concentrations. The second hyperpolarizabilities, and , of the CdTe NCs were ∼1.15 × 10⁻⁴¹ m⁵/V² and ∼3.01 × 10⁻⁴² m⁵/V² from the measurement of the concentration-dependent third-order nonlinear susceptibility of CdTe NCs, respectively. The ratio (/) of the hyperpolarizabilities was ∼0.26, which indicated a large contribution of an electronic polarization process to the third-order nonlinearity of CdTe NCs.     

Ultra-sensitive ambient ammonia detection using CO<Subscript>2</Subscript>-laser-based photoacoustic spectroscopy

An ambient trace-ammonia sensor that uses resonant photoacoustic spectroscopy and a line-tunable CO₂ laser has been developed. This system achieves a 1 replicate precision of 32 parts-per-trillion (ppt) with an averaging time of 5 s and a total measurement time of 40 s. This 32-ppt precision corresponds to a minimum detectable fractional absorbance of 8.8×10^-9, a minimum detectable absorption coefficient of 9.6×10^-10 cm^-1, and a minimum path-length-normalized detectivity of 1.1×10^-8 Wcm^-1/Hz^1/2. Background interference from CO₂, H₂O, and cell-window absorption were subtracted by switching to a neighboring off-resonance laser wavelength . PACS 42.62.Fi; 82.80.Gk; 82.80.Kq     

A spontaneously broken quintet Baryon model for strong interactions

A gauge type model of quantum field theory for strong interactions based on a quinted of observed fields, namely the proton, neutron, , _c and _b baryon fields is proposed. Gauging the resulting global symmetry groupK= SU(3)×¹ U(1)ײ U(1)׳ U(1) for matter fields, one obtains boson-fermion field theory with eleven gauge bosons. The analysis of admissible Higgs sector indicates that the Higgs multiple consists of one adjoint and two fundamental representationsSU(3) and three scalar representations of¹ U(1),² U(1) and³ U(1). The structure of the Higgs sector implies that the original symmetry group extends to the groupK×U(2). Breaking spontaneously the obtained field theory, one converts gauge bosons into the eleven massive vector bosons which can be identified with the observed , K^*, ¯K^*, , , J/ and Y vector mesons. The surviving global symmetry is isomorphic with the symmetry groupSU(2)× ⁰ U(1)× ×¹ U(1)ײ U(1)׳ U(1) corresponding to the isospin, strangeness, baryon number, charm and beauty conservation observed in strong interactions. The surviving Higgs scalars have the same quantum numbers as , K, ¯K, , S, , , and _b mesons. The model gives a newSU(3) classification scheme for baryons without charm and beauty in terms of triplets, sextets and 15-plets. These multiplets can be identified with the observed baryons; the scheme also includes the observed Z₀ and Z₁ baryons (the experimental evidence of which is, nevertheless, still weak). The model predicts the existence and the specific quantum numbers of new mesons and baryons with charm and beauty, and provides a very simple framework for the dibaryon analysis. Since all final physical fields are massive, this model is free from infrared divergences.Invited talk presented at the International Conference Selected Topics in Quantum Field Theory and Mathematical Physics, Bechyn, Czechoslovakia, June 23–27, 1986.     

Quantized IR properties reconfirmed in the CO and SiO surface oscillators present in the surface layer of A bamboo stem

From analysis of diffusion diagrams of CO stretching band (25002180 cm^–1), bending band (800200 cm^–1) and SiO stretching band (1100700 cm^–1) measured in a skin surface layer of a bamboo stem (silicate cellulose), azimuthal directions where oscillators oriented were shown as ('=-90) _N=a·N-b, with a=28.3, 2×28, 22.7, b=25, 47.5, 10. And N=1,2.....14, N=1, .....6. N=1,2.....16. The optical activity (reflection integral) was shown for the CO stret. band as M_i(N)=a·N+b, with a=21.8, b=42 and N =1,2.....9. And for the bending band as M_i(N)=a·N² +b·N–c, with a=1.87×10¹, b=3.73×10³, c=7.06×10² with N=1,2.....9. Six stepnized fine series in CO weak reflection bands were confirmed as, and with N=1,2.....22. Mean values of the vibrational quantized states of the A, B and C-series in the SiO stretching weak band with R1.0% were shown as, (meV) with .     

Performance of a prototype microwave frequency standard based on laser-detected,trapped171Yb+ ions

A microwave frequency standard based on buffer gas-cooled¹⁷¹Yb⁺ ions confined in a linear Paul trap has been demonstrated in prototype form. The standard exhibits a fractional frequency instability characterised by an Allan deviation of (_y() = 2.9 × 10^–13–1/2 for < 2 × 10⁴ s. Factors affecting the stability of the standard have been systematically investigated.     

Two distinguishable fluorescent modes of 1-anilino-8-naphthalenesulfonate bound to human albumin

We study the interaction of 1-anilino-8-naphthalenesulfonate (ANS) with human (HSA) and bovine serum albumin (BSA) by phase and modulation fluorescence spectroscopy. We determined that both HSA and BSA show one or two distinguishable fluorescent sites, depending of the ANS/serum albumin ratio. At above a 11 ANS/HSA molar ratio, the steady-state emission spectra for ANS can be resolved in two components: component 1, emitting with a lifetime (₁) of 16 ns and a _1max of 478 nm, with a quantum yield (_f1) of 0.67, and component 2, with a lifetime (₂) of 2–4 ns and a _2max of 483 nm, with an average quantum yield (_f2) of about 0.11. Considering these findings, the binding analysis is fitted with a model of two independent sites. Site 1 has an association constantK _as1=0.87×10⁶M^–1 and a capacity of 1.04 mol of ANS/mol of HSA, and site 2 aK _as2=0.079×10⁶M^–1 and a capacity of 2.34 mol of ANS/mol of HSA. Analysis of fluorescence lifetime distributions shows that the rigidity of the fluorophore environment at site 1 changes when site 2 is occupied. These findings suggest an interconnection between the two sites and that ligands can stabilize the protein's globular structure. To assess the identity of the ANS binding sites we used diazepam as a marker of the site located at the IIIA HSA subdomain and aspirin as a marker of sites located at the IIIA and IIA HSA subdomains. Both ligands displace ANS only from site 1, suggesting that it corresponds to the binding site located at the IIIA sub-domain of the protein. We determined that theK _as values for diazepam and aspirin are 0.113× 10⁶ and 0.021×10⁶ M ^–1 respectively.     

Electrical properties and defect model of tin-doped indium oxide layers

Tin-doped In₂O₃ layers were prepared by the spray technique with doping concentrationsc _Sn between 1 and 20 at. % and annealed at 500 °C in gas atmospheres of varying oxygen partial pressures. The room-temperature electrical properties were measured. Maximum carrier concentrationsN=1.5×10²¹cm^–3 and minimum resistivities =1.3×10^–4 cm are obtained if the layers are doped withc _Sn9 at. % and annealed in an atmosphere of oxygen partial pressurep _O2 10^–20 bar. At fixed doping concentration, the carrier mobility increases with decreasing oxygen pressure. The maximum obtainable mobility can be described in terms of electron scattering by ionized impurities. From an analysis of the carrier concentration and additional precision measurements of the lattice constants and film thicknesses, a defect model for In₂O₃:Sn is developed. This comprises two kinds of interstitial oxygen, one of which is loosely bound to tin, the other forming a strongly bound Sn₂O₄ complex. At low doping concentrationc _Sn4 at. % the carrier concentration is governed by the loosely bound tin-oxygen defects which decompose if the oxygen partial pressure is low. The carrier concentration follows from a relationN=K ₁ ·p _O2 ^–1/8 ·(3 ×10¹⁰ × c_Sn –N)^1/4 with an equilibrium constantK ₁=1.4×10¹⁵ cm^–9/4bar^1/8, determined from our measurements.     

Nearest neighbor effect on capture cross sections measured in IR phototransients on Si:In

The extrinsic photoconductive decay at T=20–100 K is analyzed in FZ-grown Si: In material after pulsed irradiation by a PbSSe infrared laser (=4 m). Trapping time constants (=10 ns-100 s) are resolved for the prevalent In acceptor (N _In=10¹⁶–10¹⁷ cm^–3) and for additional shallow acceptors B, Al, and the X(In)-center present at low concentrations (N=10¹²–10¹⁴ cm^–3). Hole capture cross sections determined for the acceptor levels show a large scatter over up to 4 orders of magnitude. It is shown that the capture cross section is dependent on all the dopant concentrations present in the sample due to nearest neighbor interaction. Due to the formation of donor-acceptor dipoles, the capture cross section assumes low values. A model calculation of the interaction based on only fundamental parameters of Si is in accordance with the experimental data within the experimental error. The hole capture cross sections for isolated acceptors are _p=1×10^–12, 1×10^–14, 1×10^–13, 2.5×10^–13 cm² for indium, X-center, aluminum, and boron at the temperatures T=95 K, 100 K, 70 K, 45 K, respectively.     

Semi-insulating electrical properties of undoped inp after heat treatment in a phosphorus atmosphere

Nominally undoped InP wafers have been annealed in a phosphorus atmosphere under a pressure of about 5 bar at temperatures of 900 °C for about 80 h. It was found that the electrical properties of the samples changed considerably after this treatment. A room temperature resistivity of up to 2×10⁷cm (semi-insulating behaviour) was obtained in the bulk of the samples. The resistivity finally obtained depends on the starting carrier concentration of the untreated samples. The Hall coefficient and Hall mobility have been measured up to 600 °C. The results can be interpreted in terms of a deep electronic level (E _A=0.63 ... 0.65 eV below the conduction band). The Hall coefficient was always found to be negative resulting in a Hall mobility of 1.4 to 4.9×10³ cm²/Vs. The highest resistivity in nominally undoped bulk InP so far reported in the literature [1] was =3.6 × 10⁵cm. Therefore, this paper demonstrates for the first time that a really semi-insulating behaviour of >10⁷ cm can be achieved for bulk InP with the purity of nominally undoped material (10¹⁵ to 10¹⁶cm^–3).     

Contactless density measurement of high-temperature BiFeO<Subscript>3</Subscript> and BaTiO<Subscript>3</Subscript>

The density of liquid and undercooled BiFeO₃ and high-temperature solid, liquid, and undercooled BaTiO₃ was measured with an electrostatic levitation furnace. The density was obtained with an ultraviolet-based imaging technique that allowed excellent sample contrast throughout all phases of processing, including at elevated temperatures. Over the 1250- to 1490-K temperature range, the density of liquid BiFeO₃ can be expressed as _L(T)=6.70×10³–1.31(T-T_m)(kgm^-3) (±2 per cent) with T_m=1423 K, yielding a volume coefficient of thermal expansion _L(T)=1.9×10^-4 K^-1. For BaTiO₃, the density of the solid can be expressed as _S(T)=5.04×10³–0.21(T-T_m) (T_m=1893 K) over the 1220- to 1893-K range, yielding a volume coefficient of thermal expansion _S(T)=4.2×10^-5 K^-1, whereas that of the liquid can be expressed as _L(T)=4.04×10³-0.34(T-T_m) over the 1300- to 2025-K range with _L(T)=8.4×10^-5 K^-1. PACS 77.84.-s; 81.05.Je; 81.20.n     

Nickel bolometers

A modified method of the production of nickel bolometers and their properties are described. A typical example is a bolometer of dimensions 005×2 mm and resistance 14.9 , the NEP (noise equivalent power) of which is 6.23×10^–11 Wc^–1/2 in air and 1.9×10^–11 Wc^–1/2 in vacuo. The paper also describes the influence of cooling the surroundings with liquid nitrogen on the properties of the bolometer. The NEP of a bolometer that works in vacuo with cooled surroundings is 5 times lower. A method is given for correcting the characteristics of two similar bolometers for use in a d.c. bridge which makes the equilibrium of the bridge independent of bridge-current fluctuations in a large range of current.     

Reaction of cyanide ions with copper on Si surfaces and its use for Si cleaning

A Si cleaning method has been developed by use of potassium cyanide (KCN) dissolved in methanol. When silicon dioxide (SiO₂)/Si(1 0 0) specimens with 10¹⁴ atom/cm² order copper (Cu) contaminants are immersed in 0.1 M KCN solutions of methanol at 25 °C, the Cu concentration is reduced to below the detection limit of total X-ray fluorescence spectrometer of ∼3 × 10⁹ atoms/cm². X-ray photoelectron spectra show that the thickness of the SiO₂ layers is unchanged after cleaning with the KCN solutions. 10¹⁴ cm⁻² order Cu contaminants on the Si surface can also be removed below ∼3 × 10⁹ atoms/cm², without causing contamination by potassium ions. UV spectra show that Cu-cyano complex ions are formed in the KCN solutions after the cleaning. The main Cu species in the KCN solutions is ions with the concentration of []:[Cu⁺] = 1:1.6 × 10²³. Even when the KCN solutions are contaminated with 64 ppm Cu²⁺ ions in the solutions, which form ions, the cleaning ability does not decrease, showing that ions are not re-adsorbed. The KCN solutions can also passivate defect states such as Si/SiO₂ interface states, leading to the improvement of characteristics of Si devices.