Absolute frequency of the molecular iodine transition R(56)32-0near 532 nm

The absolute frequency of the hyperfine component a₁₀ in the transition R(56)32-0 of iodine has been measured using the D₂ line in Rb at 780 mm and an iodine-stabilized 633-nm He-Ne laser as references. This measurement provides a secondary frequency standard within the tuning range of a doubled Nd:YAG laser. The measured frequency of the a₁₀ component is 563 260 223.480 MHz ±70 kHz     

High spectral purity CO2 laser stabilized using amolecular frequency reference

A CO₂ laser has been frequency stabilized to a molecular absorption line with a bandwidth of 10 kHz, yielding a laser noise spectral density reduction below 1 Hz/√ Hz and a relative accuracy of 10^-10. In the time domain, this corresponds to an Allan standard deviation of σ(2, τ)=3·10^-14 τ^-1/2, for τ>100 μs. This source allows experiments of very high resolution spectroscopy as well as the realization of accurate frequency standards in the 10-μm region     

Iodine-stabilized extended cavity diode laser at λ=633 nm

An extended cavity diode laser at 633 nm has been frequency stabilized to I₂-Doppler-free absorption signals of the P(33)6-3 transition using a third-harmonic detection technique. The frequency was measured by the beat-frequency technique with an iodine-stabilized He-Ne laser as reference. A minimum value for the two-probe relative standard uncertainty of 1× 10^-11 (5 kHz) is reached after 100 s. We also report measurements of the hyperfine splittings of the P(33)6-3 transition and laser frequency dependence on modulation amplitude and iodine pressure     

Relaxation peaks associated with the oxygen-ion diffusion in La2−xBixMo2O9 oxide-ion conductors

The effects of bismuth doping on the oxygen-ion diffusion in oxide-ion conductors La_2−xBi_xMo₂O₉ (x=0.05, 0.1, and 0.15) have been studied by both internal friction and dielectric relaxation techniques. Two internal friction peaks of relaxation type (P₁ and P₂ peak) were observed at a measurement frequency of 4 Hz around 380 and 430 K, respectively. As for the dielectric measurement, a prominent dielectric relaxation peak (P_d) was found in all the Bi-doped samples around 700 K at a measurement frequency of 50 kHz, which actually consists of two sub-peaks (denoted as P_d1 and P_d2 peak). With increasing Bi-doping content, two peaks shift to higher temperature and decrease in height, while the activation energy of both peaks increases. The main reason was interpreted as the introduction of the lone-pair electrons of bismuth, which tends to block the diffusion of oxygen ion.     

Precision frequency measurement of the 2S1/2 2D5/2 transition of Sr+ with a 674-nmdiode laser locked to an ultrastable cavity

We have measured the frequency of the 5s ²S_1/2 -4d ²D_5/2 clock transition of a single Sr ion confined in a Paul trap. A diode laser locked to an ultrastable Fabry-Perot (F-P) cavity was used to probe the transition with a resolution of 3.5 kHz. The absolute frequency was determined from heterodyne measurements referenced to an iodine stabilized HeNe laser and a CO₂ laser yielding a value for the S-D transition of (444 779 043 963±30) kHz. This work could lead to the development of a new optical frequency standard at 674 nm     

Secondary standard for PM and AM noise at 5, 10, and 100 MHz

A practical implementation of a portable secondary standard for phase modulation (PM) and amplitude modulation (AM) noise at 5, 10, and 100 MHz is described. The accuracy of the standard for both PM and AM noise is +0.14 dB, and the temperature coefficient is less than 0.02 dB/K. The noise floor S_φ (10 kHz) of the standard for PM noise measurements is less than -190 dBC relative to 1 rad²/Hz at 5, 10, and 100 MHz. The noise floor for AM measurements depends on the configuration. A calibrated level of PM and AM noise of approximately -130±0.2 dB relative to 1 rad² /Hz (for Fourier frequencies from approximately 1 Hz to 10% of the carrier frequency) is used to evaluate the accuracy versus Fourier frequency. Similar PM/AM noise standards are under test at 10 GHz. This new standard can also be used as an alternative to the normal method of calibrating the conversion sensitivity of the PM/AM detector for PM/AM measurements. Some types of time-domain measurement equipment can also be calibrated     

An ultralow noise microwave oscillator based on a high-Q liquidnitrogen cooled sapphire resonator

Two liquid nitrogen-cooled sapphire loaded cavities (SLC's) operating at about 80 K have been successfully constructed, Both cavities were designed to operate on the whispering gallery (WG) E_{12, 1, δ} mode at a resonant frequency of 8.95 GHz. The first SLC was used as the frequency-determining element in a loop oscillator, while the second was used as a frequency discriminator to measure oscillator phase noise. The single sideband phase noise of a free running loop oscillator incorporating the first SLC was measured as -133 dBc/Hz at an offset frequency of 1 kHz, and was limited by the SLC Q-factor and the amplifier flicker phase noise. By using specially designed feedback electronics the oscillator phase noise was reduced to -156 dBc/Hz and -162 dBc/Hz at 1 and 10 kHz offset, respectively. This measurement was shown to be limited by the electronic flicker noise imposed by the phase detector in the feedback electronics, To our knowledge the phase noise and resonator Q-factor of 6×10⁷ represent the best results ever measured at liquid nitrogen temperatures or above     

Deposition and dielectric properties of CaCu3Ti4O12 thin films on Pt/Ti/SiO2/Si substrates using pulsed-laser deposition

CaCu₃Ti₄O₁₂ (CCTO) thin films were successfully deposited on Pt/Ti/SiO₂/Si(1 0 0) substrates using pulsed-laser deposition technique. The crystalline structure and the surface morphology of the CCTO thin films were greatly affected by the substrate temperature and oxygen pressure. Thin films with a (2 2 0) preferential orientation were obtained at the substrate temperature above 700 °C and oxygen pressure above 13.3 Pa. The 480-nm thin films deposited under 720 °C and 26.6 Pa have a fairly high dielectric constant of near 2000 at 10 kHz and room temperature. The values of the dielectric constant and loss and their temperature-dependence under different frequency are comparable with those obtained in the epitaxial CCTO films grown on oxide substrates.     

1/f frequency noise of 2-GHZ high-Q thin-film sapphire resonators

We present experimental results on intrinsic 1/f frequency modulation (FM) noise in high-overtone thin-film sapphire resonators that operate at 2 GHz. The resonators exhibit several high-Q resonant modes approximately 100 kHz apart, which repeat every 13 MHz. A loaded Q of approximately 20000 was estimated from the phase response. The results show that the FM noise of the resonators varied between S_y (10 Hz)=-202 dB relative (rel) to 1/Hz and -210 dB rel to 1/Hz. The equivalent phase modulation (PM) noise of an oscillator using these resonators (assuming a noiseless amplifier) would range from L(10 Hz)=-39 to -47 dBc/Hz     

Broad tuning ultra low phase noise dielectric resonator oscillators using SiGe amplifier and ceramic-based resonators

This paper describes the design of very low noise, tunable, X-band dielectric resonator oscillators (DROs) demonstrating phase-noise performance of -135 dBc/Hz at 10 kHz offset. SiGe transistors are used for the oscillator sustaining amplifiers that offer a circulating power of 12 dBm and a gain of 5.4 dB per stage as well as a low flicker noise corner of 40 kHz. A variety of resonator configurations utilising BaTiO₃ resonators are presented demonstrating unloaded Qs from 10 000 to 22 000. These resonators are optimised and coupled to the amplifiers for minimum phase noise where Q_L/Q₀ = 1/2, and hence S₂₁ = -6 dB. To incorporate tuning with low additional phase noise, a phase shifter is also investigated. The theory for the low noise oscillator design is included; experimental results demonstrate close correlation with the theory.     

Traps identification in silicon nanocrystals memories by low noise technique

This work reports the extraction of oxide traps properties of n-metal–oxide–semiconductor field-effect transistors with W × L = 0.5 × 0.1 μm² using random telegraph signals (RTS) techniques. RTS study of nc-Si has been performed on thin tunnel oxides from 0.8 to 2.0 nm. RTS signals were two or more levels switching events observed on the drain current of transistors with and without nc-Si. The simple two levels RTS₁ noise was observed on samples without nc-Si. On transistors with nc-Si we distinguish two different RTSs (RTS₂ and RTS₃). RTS signal variations with temperature have shown that there's three slow interfacial traps located at E_c — 0.26 eV (trap1), E_c — 0.23 eV (trap2) and E_c — 0.2 eV (trap3). The spatial localization of traps 1, 2 and 3 from the Si–SiO₂ interface are determined using numerical simulations (x_Trap1 ≈ 0.6 nm, x_Trap2 ≈ 0.8 nm and x_Trap3 ≈ 0.4 nm). RTS noise observed on these devices is attributed to traps localized precisely at the interface thermal oxide/deposited control oxide. (RTS₁) noise is attributed to trap1 and (RTS₂, RTS₃) to traps 2 and 3. From RTS analysis in frequency domain, we extract the power spectrum density of the drain current noise (PSD). From these PSDs we have measured the cut-off frequencies of a single trap even at very low frequencies (for RTS₁ noise f_c = 5 Hz (trap1) and for RTS₂ noise f_c1 = 2 Hz (trap2), f_c2 = 130 Hz (trap3)). These results are in good agreement with those obtained by analysis in time domain and confirm the localization of each trap from the Si–SiO₂ interface.     

High-Q thermoelectric-stabilized sapphire microwave resonators forlow-noise applications

Two low-noise high-Q sapphire-loaded cavity (SLC) resonators, with unloaded Q values of 2×10⁵ and very low densities of spurious modes, have been constructed. They were designed to operate at 0°C with a center frequency of 10.000000 GHz. The cavity was cooled with a thermoelectric (TE) Peltier element, and in practice achieved the required center frequency near 1°C. The resonator has a measured frequency-temperature coefficient of -0.7 MHz/K, and a Q factor which is measured to be proportional to T^-2.5. An upper limit to the SLC residual phase noise of ℒ (100) Hz=-147 dBc/Hz, ℒ (1 kHz)=-155 dBc/Hz, and ℒ (10) kHz=-160 dBc/Hz has been measured. Also, we have created a free-running loop oscillator based on one of the SLC resonators, and measured a phase noise of ℒ(f)~-10-30log [f] dBc/Hz between f=10 /Hz and 25 kHz, using the other as a discriminator     

Frequency measurement of the 2S-12D transitions in hydrogen anddeuterium, new determination of the Rydberg constant

We have performed the first pure frequency measurement of the 2S-12D two-photon transitions in atomic hydrogen and deuterium. These frequencies are compared to two optical standards, the CO₂ laser stabilized on the OsO₄ molecule and the optical rubidium laser standard (LD/Rb) (namely, a laser diode at 778 nm stabilized on the 5S_1/2-5D_5/2 two-photon transition of rubidium). The main part of the experiment is located in the Laboratoire Kastler-Brossel (LKB), one part of the frequency chain is in the Laboratoire Primaire du Temps et des Frequences (LPTF), and two 3 km long optical fibers link the two parts of this experiment. The new value of the Rydberg constant is R_∞=109 737.315 686 06 (79) cm^-1     

Judd–Ofelt parametrization and radiative transitions analysis of Tm doped alkali chloroborophosphate glasses

Absorption spectra for Tm³⁺ doped alkali chloroborophosphate glasses are recorded in the UV–VIS and NIR regions. The assigned energy level data of Tm³⁺ (4f¹²) in these glasses are analysed in terms of a parametrized Hamiltonian model that includes 14 free-ion parameters. From the measured oscillator strengths of the absorption bands, the intensity parameters, Ω_λ, are calculated by using the Judd–Ofelt theory. Using these data, radiative transition probabilities, radiative lifetimes, branching ratios and integrated absorption cross-sections for ³P₀, ¹D₂ and ¹G₄ fluorescent levels are calculated. Certain laser transitions are predicted.     

Microwave dielectric properties of W-doped Ba0.6Sr0.4TiO3 thin films grown on (001) MgO by pulsed laser deposition with a variable oxygen deposition pressure

The microwave dielectric properties of Ba_0.6Sr_0.4TiO₃ 1 mol% W-doped thin films deposited using pulsed laser deposition, are improved by a novel oxygen deposition profile. The thin films were deposited onto (001) MgO substrates at a temperature of 720 °C. A comparison is made between three different oxygen ambient growth conditions. These include growth at a single oxygen pressure (6.7 Pa) and growth at two oxygen pressures, one low (6.7 Pa) and one high (46.7 Pa). Films were deposited in a sequence that includes both a low to high and a high to low transition in the oxygen deposition pressure. Following deposition, all films were post-annealed in 1 atm of oxygen at 1000 °C for 6 h. The dielectric Q (defined as 1 / tanδ) and the dielectric constant, ε_r, were measured at room temperature, at 2 GHz, using gap capacitors fabricated on top of the dielectric films. The percent dielectric tuning (defined as (ε_r(0 V) − ε_r(40 V)) / ε_r(0 V) × 100) and figure of merit (FOM) (defined as percent dielectric tuning × Q(0 V)) were calculated. The film deposited using the two-stage growth conditions, 6.7 / 46.7 Pa oxygen, showed a maximum Q(0 V) value with high percent dielectric tuning and gave rise to a microwave FOM twice as large as the single stage growth condition. The improved dielectric properties are due to initial formation of a film with reduced interfacial strain, due to the formation of defects at the film/ substrate interface resulting in a high Q(0 V) value, followed by the reduction of oxygen vacancies which increases the dielectric constant and tuning.     

Preparation of Aluminum Nitride Thin Films by CVD

AlN films were prepared by CVD using aluminum halide (AlCl₃) and aluminum alkyl ((CH₃)3Al) precursors. The appropriate deposition conditions to obtain polycrystalline AlN films using A1C1₃ precursor were found at T_dep = 1173 K, P_tot = 66.6 Pa and N₂/NH₃ = 0.75. It was found that AlN films of different crystallinity can be obtained from (CH₃)₃Al precursor at T_de = 973-1023 K, P_tot = 1.99 kPa, only under a H₂ atmosphere. AlN films can be grown highly oriented in the (210) direction on amorphous quartz substrates depending on their thicknesses. The 0.1 -0.2 μm thick AlN films were transparent and their refractive indexes were about 1.4-1.6.     

硅片上集成高介电调谐率的柱状纳米晶BaTiO3铁电薄膜

钛酸钡(BaTiO₃)具有优异的介电、铁电、压电和热释电等性能, 在微电子机械系统和集成电路领域具有广泛的应用。降低BaTiO₃薄膜的制备温度使其与现有的CMOS-Si工艺兼容, 已成为应用研究和技术开发中亟需解决的问题。本研究引入与BaTiO₃晶格常数相匹配的LaNiO₃作为缓冲层, 以调控其薄膜结晶取向, 在单晶Si(100)基底上450 ℃溅射制备了结构致密的柱状纳米晶BaTiO₃薄膜。研究表明：450 ℃溅射温度在保持连续柱状晶结构和(001)择优取向的前提下, 能获得相对较大的柱状晶粒(平均晶粒直径27 nm), 一定残余应变也有助于其获得了较好的铁电和介电性能。剩余极化强度和最大极化强度分别达到了7和43 μC·cm^-2。该薄膜具有良好的绝缘性, 在 0.8 MV·cm^-1电场下, 漏电流密度仅为10^-5 A·cm^-2。其相对介电常数ε_r展现了优异的频率稳定性：在1 kHz时ε_r为155, 当测试频率升至1 MHz, ε_r仅轻微降低至145。薄膜的介电损耗较小, 约为0.01~0.03 (1 kHz ~ 1 MHz)。通过电容-电压测试, 该薄膜材料展示出高达51%的介电调谐率, 品质因子亦达到17(@1 MHz)。本研究所获得的BaTiO₃薄膜在介电调谐器件中有着良好的应用前景。     

A Study of Fullerene Preparation Technique

A new homemade are fullerene generator used in this experiment is reported. The comparation of yields of fullerenes (C₆₀/C₇₀ mixture) was studied by different power supplies (AC and DC), different gaps of two graphite rods and different He pressure between 0.4×10⁴- 2.8×10⁴ Pa. In our experiment, the highest yield up to 13% was achieved, when DC discharge was used and the optimum He pressure was near 0.8×10⁴ - 1.6×10⁴ Pa.

The mixed fullerene was analyzed by electron impact masa spectnun (EIMS). The relative amount af C₆₀ to C₇₀ was 4.2 to 1. After column chromatography aeperation with hexane on alumina, 99.9% Cso was obtained. FTIR and ^1aC-NMR epectrum were ueed to characterize the pure C₆₀ samples.     

Transparent conducting F-doped SnO2 thin films grown by pulsed laser deposition

Transparent conducting fluorine-doped tin oxide (SnO₂:F) films have been deposited on glass substrates by pulsed laser deposition. The structural, electrical and optical properties of the SnO₂:F films have been investigated as a function of F-doping level and substrate deposition temperature. The optimum target composition for high conductivity was found to be 10 wt.% SnF₂ + 90 wt.% SnO₂. Under optimized deposition conditions (T_s = 300 °C, and 7.33 Pa of O₂), electrical resistivity of 5 × 10^− 4 Ω-cm, sheet resistance of 12.5 Ω/□, average optical transmittance of 87% in the visible range, and optical band-gap of 4.25 eV were obtained for 400 nm thick SnO₂:F films. Atomic force microscopy measurements for these SnO₂:F films indicated that their root-mean-square surface roughness ( 6 Å) was superior to that of commercially available chemical vapor deposited SnO₂:F films ( 85 Å).     

Frequency of a methane-stabilized helium-neon laser

A phase-locked laser frequency chain was used to measure the absolute frequency of a HeNe/CH₄ laser relative to the primary Cs standard, with measurement uncertainty less than ±1 part in 10¹². The frequency depends on laser parameters; a spread of 8.3×10^-11 was observed. This was attributed to the variation of Lamb dip asymmetry resulting from the gas-lens effect and the accompanying diffraction loss variation near resonance. Means of improving laser frequency reproducibility by reducing cavity diffraction loss variation were studied experimentally. The frequency obtained with a cavity exhibiting the smallest Lamb dip asymmetry was found to be 88 376 181 599.07±0.07 kHz