Helm Scientific Laboratory offers affordable 532 nm laser Raman and fluorescence spectrometers and spectroscopy systems for scientists, engineers, educators and spectroscopic enthusiasts in industrial, academic and educational labs and classrooms. We provide quality fluorescence and Raman spectrum analytical test services.

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All spectral products sold by Helm Scientific are covered automatically by limited warrantee on condition that a purchased product is under correct operation, handling and maintenance and without any tampering or modification. The limited warrantee includes (1) two-year warrantee of CCD spectrometer by OEM, (2) one-year warrantee of the optical and mechanical parts of sample optical chamber and stage, and (3) one-year warrantee of unopened laser unit. Lifetime technical support via email is provided.

Helm Scientific’s low-cost Raman spectrograph is specifically designed to measure Raman and photoluminescence spectra of silicon wafers, thin films and coatings, dilute aqueous and organic solutions of inorganic and organic compounds, liquids/fluids or solid samples under 532 nm laser excitation. In addition, it can test samples on glass slides for chemical, biological and surface-enhanced Raman scattering (SERS) analyses. The following Raman spectra scanned demonstrate our new Raman spectrograph's capabilities of ultra high sensitivity and superb signal-to-noise ratio (SNR).

Silicon single crystal wafer, i.e. Si(100)
Concentrated isopropyl alcohol (91% CH₃CH(OH)CH₃)
Dilute acetic acid (5% CH₃COOH)
Diluted isopropyl alcohol (1.7% CH₃CH(OH)CH₃)
Dilute aqueous solution of sodium hypochlorite (7.55% NaOCl)
In situ real-time monitoring of NaOCl + CH₃CH(OH)CH₃ Redox Reaction

Spectra 1~5 herein are raw or original without any data smoothing or baseline correction.

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The Raman spectrum of a small piece of single crystal Si(100) wafer is illustrated below. The narrow Raman peak of transverse optical (TO) phonon at ~520 cm^-1 has been widely used in semiconductor industry to evaluate silicon stress and morphology for IC engineering and manufacturing. For example, depending on growth conditions, SiO₂ and SiN_x:H thin films may cause tensile or compressive stress to Si substrate, shifting this Raman peak position. Polycrystalline Si shows a Raman peak at ~515 cm^-1 while nanocrystalline Si at ~502 cm^-1. Amorphous Si exhibits a broad Raman peak around ~480 cm^-1. Raman spectroscopy is also routinely used to study III-V (e.g. GaN), transition metal chalcogenide 2D thin film materials and devices.

The Raman spectrum of water diluted acetic acid (5%) is dominated by asymmetric (3398 cm^-1) and symmetric (3259 cm^-1) H-O-H stretching bands broadened by inter-molecular hydrogen bonding, and H-O-H bending peak at 1624 cm^-1. The C-H stretching, C=O stretching and C-C stretching bands of acetic acid appear at 2942, 1698 and 891 cm-1, respectively. The Raman peak at 1698 cm^-1 originates from C=O stretching vibration of hydroxylic -COOH group and has been extensively studied to reveal hydrogen bonding between acetic acid monomers to yield a cyclic dimers, between water molecules and acetic acid molecules. Dilution of liquid acetic acid with water results in a shift of the C=O stretching vibration band from 1665 to 1715 cm^-1 (J. Phys. Chem. A 1999, 103, 50, 10851–10858).

Chemical and biochemical reactions in aqueous solutions are the foundation of all lives on the earth and can be monitored and studied via Raman spectroscopy. A major challenge to detect the low-concentration solutes in water solvent using Raman spectrometers is analytic sensitivity or signal-to-noise ratio. By using a cooled image sensor, an improvement in detection sensitivity by a factor of >100 has been achieved. Below is the Raman spectrum of 1.7% isopropyl alcohol (CH₃-CH(OH)-CH₃). In addition to the symmetric O-H stretching, asymmetric O-H stretching and H-O-H bending vibrational Raman peaks of water molecules, the C-C stretching, C-O stretching, CH₃ bending, CH₃ and C-H stretching peaks of isopropyl alcohol molecules are clearly identifiable in the spectrum. The lower detection limit (LDL) of aqueous IPA solution is estimated to be ~0.5% when using the Raman peak at ~818 cm^-1. One application of the system is to study the kinetics and mechanisms of chemical and biochemical reactions in water solution and other liquids/fluids.

Sodium hypochlorite (NaOCl) solution is widely used as a household bleaching agent or disinfectant. For example, Clorox Performance Bleach contains 7.55% sodium hypochlorite and 92.45% "OTHER INGREDIENTS" per its label. Helm Scientific's Raman spectrograph can easily detect the low concentration of hypochlorite anions, i.e. OCl^- as shown in the spectrum below. Clearly, vibrational Raman peaks characteristic of water molecule (H₂O) dominate the spectrum, with the Raman shifts of asymmetric O-H stretching, symmetric O-H stretching and H-O-H bending modes being located at 3423, 3280 and 1636 cm^-1, respectively. The small Raman peak at 720 cm^-1 originates from the stretching vibration of hypochlorite (OCl^-) anions according to published papers. The O-Cl bond length is ~1.7 A while that of O-H is ~0.96 A with a H-O-H bond angle of ~104 degrees. The lower detection limit (LDL) of NaOCl is about ~0.2% based on experiment.

Our Raman spectrograph's high sensitivity makes it suitable for in situ real-time investigation of chemical reaction kinetics and mechanisms in both aqueous and organic solvents. After mixing ~1.5 mL 7.55% sodium hypochlorite (NaOCl) aqueous solution with ~0.5 mL 91% IPA in a 2 mL standard glass vial at room temperature, the reduction of OCl^- anions by CH₃CH(OH)CH₃ molecules was monitored in situ in real-time for 33 minutes by scanning 16 high-quality Raman spectrographs from which 16 Raman spectra were extracted and plotted below. The time origin (t=0 s) of the plot is the time when the first Raman spectrograph acquisition was initiated. The concentrations of NaOCl and IPA immediately after mixing were ~5.7% and ~22.3%, respectively. It is estimated that ~36% NaOCl had reacted with IPA when the first spectrograph acquisition started. Despite the presence of the dominant Raman scattering bands associated with relatively high IPA and H₂O concentrations, the Raman spectral band at 720 cm^-1 reveals the real-time hypochlorite anion concentration (i.e. [OCl^-], see peaks in a red rectangle and their zoom-in insert) as OCl^- anions oxidize IPA reductant. The Raman band at 720 cm^-1 originates from the stretching vibration of hypochlorite (OCl^-) anions according to published papers. By integrating their peak areas between 680 and 760 cm^-1for all 16 spectra, the concentration of [OCl^-] as a function of reaction time has been plotted as well. Obviously, kinetic rate equation containing redox reaction orders, activation energy and pre-exponential factor can be obtained by more quantitative experiments at various temperatures.

Helm Scientific

A Semiconductor Device and Chemical Analysis Laboratory

Applications of High Sensitivity Laser Raman Spectrograph

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1. Raman Spectroscopy of Si(100) Single Crystal Wafer

2. Raman Spectrograph and Spectrum of 91% Isopropyl Alcohol (CH3-CH(OH)-CH3)

3. Raman Spectrum of 5% Acetic Acid (CH3-COOH)

4. Raman Spectrum of 1.7% Isopropyl Alcohol (CH3-CH(OH)-CH3)

5. Raman Spectrum of 7.55% Aqueous Solution of Sodium Hypochlorite (NaOCl)

6. In Situ Real-Time Raman Spectral Monitoring of NaOCl + CH3CH(OH)CH3 Redox Reaction

Helm Scientific
Laboratory: 1680 Toronto Way, Costa Mesa, California 91626, U. S. A
Headquarter: Fountain Valley, CA 92708, U. S. A.
E-mail: Device.Lab@HelmScientific.com
Phone: (714) 9646958