PRESS-NEWS.org - Press Release Distribution
PRESS RELEASES DISTRIBUTION

Detecting vibrational sum-frequency generation signals from molecules confined within a nanoscale gap using a tightly confined optical near-field

Innovative nanoscale technique for determining absolute molecular orientations

2025-05-12
(Press-News.org) Vibrational sum-frequency generation (VSFG) is a nonlinear spectroscopic method widely used to investigate the molecular structure and dynamics of surface systems. However, in far-field observations, the spatial resolution of this method is constrained by the diffraction limit, which restricts its ability to resolve molecular details in inhomogeneous structures smaller than the wavelength of light. To address this limitation, we developed a tip-enhanced VSFG (TE-SFG) spectroscopy system based on scanning tunneling microscopy (STM). Using this system, we detected VSFG signals from molecules adsorbed on a gold substrate under ambient conditions. Phase analysis of the interferometric VSFG spectra provided insights into the molecular orientation. Furthermore, the observed VSFG signals were confirmed to originate from a highly localized region within the gap between the STM tip apex and sample substrate. Thus, this method offers an innovative platform for nonlinear optical nanospectroscopy, enabling the investigation of surface molecular systems beyond the diffraction limit.

Vibrational sum-frequency generation (VSFG) spectroscopy is a powerful technique for investigating molecular structures and dynamics of surface systems. In this method, a sample is simultaneously irradiated with infrared (IR) light that is resonant with molecular vibrations and visible or near-IR light at a different frequency. The resulting light, corresponding to the sum of the two input frequencies, reveals vibrational signatures unique to specific molecular species. A unique advantage of VSFG spectroscopy is its surface sensitivity, which enables the selective detection of molecules at interfaces. This capability has established VSFG spectroscopy as a powerful tool in surface science.

This technique can also reveal the absolute orientation of molecules--whether they are oriented upward or downward relative to a given surface. This information is critical because molecular orientation often influences chemical reactivity and functionality. Moreover, VSFG spectroscopy uses femtosecond laser pulses, which allow it to capture ultrafast nuclear motion, thereby facilitating detailed studies of dynamic molecular processes.

However, conventional far-field VSFG spectroscopy is constrained by the diffraction limit of light, which restricts spatial resolution to the sub-micrometer scale. Consequently, the measured signals typically represent averaged responses from ensembles of more than a million molecules. To address this limitation, spectroscopic techniques have been combined with scanning probe microscopy (SPM). Notably, when light is confined within the nanogap formed between the SPM tip and sample surface, it generates a highly localized optical near-field. Scanning near-field optical microscopy exploits this phenomenon to achieve nanoscale resolution.

In this study, researchers (Atsunori Sakurai, Shota Takahashi, Tatsuto Mochizuki, and Toshiki Sugimoto, Institute for Molecular Science(IMS), NINS) successfully integrated femtosecond-pulse VSFG spectroscopy with scanning tunneling microscopy (STM). Specifically, by focusing mid-IR and near-IR pulses into the nanogap between the STM tip and substrate, VSFG signals emitted by molecules adsorbed on the surface were detected. When the tip and substrate were separated by 50 nm, almost no signal was observed. However, as the tip and substrate were brought closer in the tunneling regime, a significant VSFG signal emerged, highlighting the critical role of near-field enhancement.

By tuning the mid-IR wavelength and acquiring eight different spectra, the researchers identified three characteristic vibrational features corresponding to the terminal methyl group in the adsorbed molecules: symmetric stretching; a Fermi resonance between the bending overtone and the symmetric stretching mode; and asymmetric stretching. Furthermore, the signal disappeared when the tip-substrate distance exceeded 1 nm, indicating that the VSFG signal originated from a region confined within 1 nm of the surface.

This extreme spatial confinement was realized through two synergistic effects: the antenna effect, which focuses IR light on the tip apex, and plasmonic enhancement in the nanogap, which increases the emission efficiency of visible VSFG signals. These synergistic field enhancements played a crucial role in enabling the detection of signals from a very limited number of molecules within the nanogap.

Additional analysis revealed a negative imaginary component of the second-order susceptibility, indicating that the terminal methyl groups were oriented such that their hydrogen atoms pointed away from the substrate. This finding confirmed that the technique could determine molecular orientation in highly localized regions.

Overall, this study demonstrates the successful detection of VSFG signals from a very limited number of molecules confined within nanoscale gaps, originating from regions less than 1 nm in size. This breakthrough paves the way for next-generation techniques, including single-molecule ultrafast spectroscopy and ultrahigh-spatial-resolution molecular imaging. These capabilities are expected to provide new insights into surface chemical processes, particularly in heterogeneous catalysis, and facilitate the rational design of highly active catalytic materials.

 

END


ELSE PRESS RELEASES FROM THIS DATE:

Opioid prescribing standards changed practices in BC, but with caveats

2025-05-12
VIEW EMBARGOED ARTICLE In an effort to curb misuse of opioids and prevent overdose deaths, the College of Physicians and Surgeons of British Columbia released a legally enforceable practice standard, Safe Prescribing of Drugs with Potential for Misuse/Diversion, in 2016. This document limited prescribing of opioids for chronic noncancer pain (CNCP) with specific prescribing practices that clinicians were obligated to follow. In research that tested the effects of the 2016 practice standard on prescribing to patients with CNCP, researchers found ...

AI could be the future for preserving marginalized cultures, say experts

2025-05-12
Promising new AI tools are being developed to protect and preserve the cultural traditions and heritage of marginalized or indigenous communities, including language, folklore, oral traditions, and community wisdom. These advances have prompted industry experts to highlight the potential for culturally aware AI systems, which can ensure unique traditions are not only remembered but also shared and reimagined across generations. But to continue this positive trend, tech companies must ensure the AI-based systems they develop are representative and build bridges across cultures, experts ...

Researchers from The University of Warwick warn marginalized young adults in low- and middle-income countries face “growing online abuse”

2025-05-12
A major new international study has found that young adults in low- and middle-income countries who are sex workers, gay men, transgender or living with HIV are facing a surge in online abuse - from harassment and blackmail to the non-consensual sharing of intimate images.   Researchers from The University of Warwick’s Centre for Interdisciplinary Methodologies warn this abuse is becoming increasingly normalised and is moving between online and in-person threats, with most victims having little access to support or justice.  The study — the largest of its kind — focuses ...

Credit ratings are a key check on CEO overconfidence in corporate acquisitions

2025-05-12
Overconfident chief executives and their risky behaviours can be partly restrained through credit ratings, new research finds. Researchers led by Bangor University in Wales in the United Kingdom and other institutions including Heriot-Watt University in Edinburgh, Scotland, Vlerick Business School in Brussels, Belgium and The University of Aberdeen in Scotland found that the creditworthiness of a company can hugely influence how its chief executive behaves – especially during corporate mergers and acquisitions (M&A). The research, which is published in the journal, European Financial Management, is based on data from 916 firms in the United States who were rated by American ...

Can the U.S. develop a strong national science diplomacy strategy?

2025-05-12
In a new editorial in the AAAS publication Science & Diplomacy, Kimberly Montgomery, Director of International Affairs and Science Diplomacy at AAAS, reflects on whether the United States should develop a national science diplomacy strategy amid significant change to U.S. federal policy. Montgomery believes that the Trump administration should develop such a strategy – to help define a vision and direction for the U.S. It should outline how related policies “can advance U.S. diplomatic objectives, including fostering economic growth,” she writes. “And that strategy should detail how it will work with the private ...

Failure to focus on covid suppression led to avoidable UK deaths, says expert

2025-05-11
Early in the covid-19 pandemic, the failure of UK government advisers to follow World Health Organization (WHO) advice and emerging evidence from East Asia that suppression could bring the virus under control quickly led to avoidable UK deaths, argues an expert in The BMJ today. Suppression aims to avoid national lockdowns and maintain economic activity for most of the population by introducing surveillance systems to bring new outbreaks under control quickly, thus reducing the reproductive rate of infection (R0) to below 1 and ...

GLP-1 receptor agonists show anti-cancer benefits beyond weight loss

2025-05-11
New research being presented at this year’s European Congress on Obesity (ECO) in Malaga, Spain (11-14 May) and published in the journal eClinicalMedicine finds that first generation weight-loss medications like liraglutide and exenatide appear to show anti-cancer benefits beyond weight loss. “Our study found a similar incidence of obesity-related cancer among patients treated with first-generation glucagon-like peptide-1 receptor agonists (GLP-1s) and with bariatric surgery over an average of ...

Childhood obesity can have long-term consequences on employment and study prospects, Swedish study finds

2025-05-11
Individuals who lived with obesity as children are less likely to be in work or studying in their mid-20s than their peers, new research being presented at year’s European Congress on Obesity (ECO 2025) has found. They are also more likely to be on long-term sick leave, the Swedish study of the long-term labour market outcomes of childhood obesity found. “Rates of childhood obesity are higher in individuals from lower socio-economic backgrounds than in those from higher socio-economic positions,” explains Dr Emilia Hagman, of the Karolinska Institutet, Stockholm, Sweden. “The reasons for this are complex but one contributing factor may be ...

Bigger bellies in childhood linked to development of metabolic and heart health risk by 10 years old

2025-05-11
New research being presented at this year’s European Congress on Obesity (ECO) in Malaga, Spain (11-14 May) reveals that adverse waist-to-height ratio trajectories (a marker for central obesity) during childhood may increase cardiometabolic and cardiovascular risk at 10 years old. Notably, children with gradually increasing central obesity from birth were more likely to show early signs of metabolic and cardiovascular risk by age 10. This included elevated blood pressure and higher levels of biomarkers linked to systemic inflammation and metabolic dysfunction, ...

Manuel Heitor to share perspectives on the future of research in Europe at launch of EndoCompass

2025-05-11
Endocrine diseases affect millions of people in Europe, yet research into hormone health remains underfunded and fragmented. EndoCompass aims to change this. By identifying key research priorities and knowledge gaps, the roadmap will guide future studies, funding programmes and policy decisions at European and national levels. Although the full publication is still to come, two dedicated sessions at the Joint Congress will offer an exclusive preview: • On Sunday 11 May, a Scientific Symposium will introduce key findings from ...

LAST 30 PRESS RELEASES:

Fat may play an important role in brain metabolism

New study finds no lasting impact of pandemic pet ownership on human well-being

New insights on genetic damage of some chemotherapies could guide future treatments with less harmful side effects

Gut microbes could protect us from toxic ‘forever chemicals’

Novel modelling links sea ice loss to Antarctic ice shelf calving events

Scientists can tell how fast you're aging from a single brain scan

U.S. uterine cancer incidence and mortality rates expected to significantly increase by 2050

Public take the lead in discovery of new exploding star

What are they vaping? Study reveals alarming surge in adolescent vaping of THC, CBD, and synthetic cannabinoids

ECMWF - delivering forecasts over 10 times faster and cutting energy usage by 1000

Brazilian neuroscientist reveals how viral infections transform the brain through microscopic detective work

Turning social fragmentation into action through discovering relatedness

Cheese may really be giving you nightmares, scientists find

Study reveals most common medical emergencies in schools

Breathable yet protective: Next-gen medical textiles with micro/nano networks

Frequency-engineered MXene supercapacitors enable efficient pulse charging in TENG–SC hybrid systems

Developed an AI-based classification system for facial pigmented lesions

Achieving 20% efficiency in halogen-free organic solar cells via isomeric additive-mediated sequential processing

New book Terraglossia reclaims language, Country and culture

The most effective diabetes drugs don't reach enough patients yet

Breast cancer risk in younger women may be influenced by hormone therapy

Strategies for staying smoke-free after rehab

Commentary questions the potential benefit of levothyroxine treatment of mild hypothyroidism during pregnancy

Study projects over 14 million preventable deaths by 2030 if USAID defunding continues

New study reveals 33% gap in transplant access for UK’s poorest children

Dysregulated epigenetic memory in early embryos offers new clues to the inheritance of polycystic ovary syndrome (PCOS)

IVF and IUI pregnancy rates remain stable across Europe, despite an increasing uptake of single embryo transfer

It takes a village: Chimpanzee babies do better when their moms have social connections

From lab to market: how renewable polymers could transform medicine

Striking increase in obesity observed among youth between 2011 and 2023

[Press-News.org] Detecting vibrational sum-frequency generation signals from molecules confined within a nanoscale gap using a tightly confined optical near-field
Innovative nanoscale technique for determining absolute molecular orientations