Three-dimensional inter-layer optical signal transmission realized by a monolithically integrated semiconductor-based carrier transport structure.

In this study, we proposed and demonstrated a brand new type of monolithic photonic devices which realizes the three-dimensional (3D) all-optical switching for inter-layer signal transmission. This device is composed of a vertical Si microrod which serves as optical absorption material within a SiN waveguide in one layer and as an index modulation structure within a SiN microdisk resonator lying in the other layer. The ambipolar photo-carrier transport property in the Si microrod was studied by measuring the resonant wavelength shifts under continuous-wave laser pumping. The ambipolar diffusion length can be extracted to be 0.88 µm. Based on the ambipolar photo-carrier transport in a Si microrod through different layers, we presented a fully-integrated all-optical switching operation using this Si microrod and a SiN microdisk with a pump-probe technique through the on-chip SiN waveguides. The switching time windows for the on-resonance operation mode and the off-resonance operation mode can be extracted to be 439 ps and 87 ps, respectively. This device shows potential applications for the future all-optical computing and communication with more practical and flexible configurations in monolithic 3D photonic integrated circuits (3D-PICs).

Minority carrier decay length extraction from scanning photocurrent profiles in two-dimensional carrier transport structures.

Carrier transport was studied both numerically and experimentally using scanning photocurrent microscopy (SPCM) in two-dimensional (2D) transport structures, where the structure size in the third dimension is much smaller than the diffusion length and electrodes cover the whole terminal on both sides. Originally, one would expect that with increasing width in 2D transport structures, scanning photocurrent profiles will gradually deviate from those of the ideal one-dimensional (1D) transport structure. However, the scanning photocurrent simulation results surprisingly showed almost identical profiles from structures with different widths. In order to clarify this phenomenon, we observed the spatial distribution of carriers. The simulation results indicate that the integrated carrier distribution in the 2D transport structures with finite width can be well described by a simple-exponential-decay function with the carrier decay length as the fitting parameter, just like in the 1D transport structures. For ohmic-contact 2D transport structures, the feasibility of the fitting formula from our previous 1D analytical model was confirmed. On the other hand, the application of a simple-exponential-decay function in scanning photocurrent profiles for the diffusion length extraction in Schottky-contact 2D transport structures was also justified. Furthermore, our simulation results demonstrate that the scanning photocurrent profiles in the ohmic- or Schottky-contact three-dimensional (3D) transport structures with electrodes covering the whole terminal on both sides will reduce to those described by the corresponding 1D fitting formulae. Finally, experimental SPCM on a p-type InGaAs air-bridge two-terminal thin-film device was carried out. The measured photocurrent profiles can be well fitted by the specific fitting formula derived from our previous 1D analytical model and the extracted electron mobility-lifetime product of this thin-film device is 6.6 × 10-7 cm2·V-1. This study allows us to extract the minority carrier decay length and to obtain the mobility-lifetime product which can be used to evaluate the performance of 2D carrier transport devices.

Static headspace gas chromatographic method for the determination of low and high boiling residual solvents in Betamethasone valerate.

Currently, there are no analytical methods available in the literature that can simultaneously separate and quantitate residual levels of acetone, methylene chloride, n-butyl ether and dimethylsulfoxide in Betamethasone valerate active pharmaceutical ingredient (API). This paper describes the development and validation of a simple, efficient, accurate and robust static headspace gas chromatography method for the determination of high and low boiling residual solvents, namely acetone, methylene chloride, n-butyl ether and dimethylsulfoxide, in Betamethasone valerate API. This method has been demonstrated to be accurate, linear, precise, reproducible, specific and robust for its intended purpose. Quantitation limits (QL) for acetone, methylene chloride and n-butyl ether are 20 ppm (20 µg/g of API) and 50 ppm (50 µg/g of API) for dimethylsulfoxide. Several other APIs (Loratadine and a few other corticosteroid compounds) were analyzed using the conditions of this method to evaluate and assess the versatility of this method for the purpose of residual solvents analysis for a wide range of APIs. The results of this evaluation strongly indicates that this method can be readily used (as-is or with minor modifications) to determine both low and high boiling residual solvents present in a wide range of APIs.

Development and validation of a stability-indicating RP-HPLC method for simultaneous assay of betamethasone dipropionate, chlorocresol, and for the estimation of betamethasone dipropionate related compounds in a pharmaceutical cream and ointment.

A new stability-indicating reversed-phase HPLC (RP-HPLC) method has been developed and validated for simultaneous assay of betamethasone dipropionate (BD) and chlorocresol and also for the estimation of BD related compounds in a pharmaceutical cream matrix. In addition, this newly developed RP-HPLC method was also demonstrated as suitable for a pharmaceutical ointment product that does not contain chlorocresol. The RP-HPLC method uses a Waters SymmetryShield RP18 analytical column (150 × 4.6 mm). Water (mobile phase A) and acetonitrile (mobile phase B) were used in the gradient elution with a flow rate of 1.5 mL/min and detection wavelength at 240 nm. A Waters XBridge Shield RP18 analytical column (150 × 4.6 mm) was identified as an alternate column. The limit of detection (LOD) and the limit of quantitation (LOQ) are 0.02 µg/mL and 0.05 µg/mL, respectively. The precision of the method for BD is less than 0.3% RSD, and the accuracy of BD ranged from 99.5% to 102.6%. The stability-indicating capability of this method has been demonstrated by analyzing aged samples of the product. This RP-HPLC method was successfully validated per ICH guidelines and proved to be suitable for routine quality control use.

Development and validation of a novel stability-indicating reversed-phase high-performance liquid chromatography method for assay of loratadine and determination of its related compounds.

Loratadine is an important active pharmaceutical ingredient used in a wide variety of prescription and over-the-counter products for the treatment and relief of allergy symptoms. A novel stability-indicating gradient ion-pair RP-HPLC method for assay of loratadine and determination of both of its degradation compounds and process impurities has been developed. This method can separate loratadine from its eight structurally related compounds; it can also separate all of the related compounds from each other in less than 20 min. The stability-indicating capability of this method has been demonstrated by analyzing aged stability samples of loratadine. A 15 cm x 4.6 mm id YMC-Pack Pro C18 HPLC column was the primary column and a 15 cm x 4.6 mm id SunFire C18 column has been identified as an alternate (truly equivalent) column for this method. This gradient method uses mobile phases consisting of acetonitrile and an aqueous solution of 10 mM sodium acetate and 5 mM sodium dodecyl sulfate at pH 5.5. The new HPLC method was validated according to International Conference on Harmonization guidelines and proved to be suitable for routine QC use.

Development and validation of a stability-indicating HPLC method for simultaneous determination of salicylic acid, betamethasone dipropionate and their related compounds in Diprosalic Lotion.

Diprosalic Lotion is an anti-inflammatory drug product that contains salicylic acid and betamethasone dipropionate as active pharmaceutical ingredients (APIs). A reversed-phase high performance liquid chromatography (RP-HPLC) method was developed for simultaneous determination of salicylic acid, betamethasone dipropionate, and their related compounds in Diprosalic Lotion. A 150 mm x 4.6 mm I.D. YMC J'sphere ODS-H80 column at 35 degrees C and UV detection at 240 nm was used. A gradient elution was employed using 0.05% (v/v) methanesulfonic acid solution and acetonitrile as mobile phases. A total of thirty three compounds from Diprosalic Lotion samples were separated in 38 min. The stability-indicating capability of this method has been demonstrated by the adequate separation of all the impurities and degradation products in expired stability samples of Diprosalic Lotion. The method was validated as per the current ICH guidelines.