Nasogastric enteral feeding tubes modulate preterm colonization in early life.

BACKGROUND: Preterm infants are generally fed through nasogastric enteral feeding tubes (NEFTs). The aim of this work was to evaluate the role of NEFTs in the initial colonization of the preterm gut and its evolution within the first 2 weeks after birth. METHODS: For this purpose, fecal and NEFT-derived samples from 30 preterm infants hospitalized in a neonatal intensive care unit (NICU) were collected from birth to the second week of life. Samples were cultivated in ten culture media, including three for the isolation of antibiotic-resistant microorganisms. RESULTS: Isolates (561) were identified by 16S ribosomal RNA gene sequencing. Although the first NEFTs inserted into the neonates after birth were rarely colonized, analysis of NEFTs and fecal samples over time revealed a significant increase in bacterial abundance, diversity, and detection frequency. Results showed a parallel colonization between time-matched NEFTs and fecal samples, suggesting an ongoing bidirectional transfer of bacteria from the neonatal gut to the NEFTs and vice versa. CONCLUSIONS: In short-term hospitalization, length is by far the determinant factor for the early colonization of preterm infants. As NEFT populations reflect the bacterial populations that are colonizing the preterm in a precise moment, their knowledge could be useful to prevent the dissemination of antibiotic-resistant strains. IMPACT: The hospital environment modulates preterm colonization immediately after birth. The colonization of preterm feces and NEFTs occurs in parallel. There is an ongoing bidirectional transfer of microorganisms from the neonatal gut to the NEFTs and vice versa. Bacterial communities inside NEFTs could act as reservoirs of antibiotic resistance genes. NEFT populations reflect the bacteria that are colonizing the preterm at a precise moment.

Extension of Prophylactic Surgery in Medullary Thyroid Carcinoma. Differences Between Sporadic and Hereditary Tumours According to Calcitonin Levels and Lymph Node Involvement.

INTRODUCTION: Currently, there is no consensus on the indication of prophylactic surgery of the nodal compartments in the treatment of medullary thyroid carcinoma (MTC). The aim of our study was to perform a correlation study between preoperative calcitonin (basalCT) values and lymph node involvement to establish a criterion on which to base prophylactic surgery in these patients. MATERIAL AND METHODS: We conducted an observational, retrospective and multicentre study with 29 hospitals. Patients over 18 years of age with a diagnosis of MTC with a pre-surgical calcitonin registry were included. The minimum surgery in all patients had to have been total thyroidectomy (TT) with central compartment lymph node dissection (CCLND). Receiver operating characteristic (ROC) curve analysis was used to establish basalCT cut-off values as predictors of postoperative lymph node involvement. RESULTS: A total of 244 patients were included. Baseline calcitonin (basalCT) was a good predictor of nodal involvement (AUC 0.718 and 95%CI 0.66-0.978). Heritability was identified as a preoperative factor correlated with baseline tumour CT values (p = 0.000). With a probability of lymph node involvement below 10%, new cut-off points were established. A prophylactic bilateral lateral lymph node dissection in sporadic tumours should be performed at a basalCT > 600 pg/mL; in the case of RET-mutated tumours this value would be 200 pg/mL. CONCLUSION: The baseline CT value is a good predictor of postoperative lymph node involvement in MTC, however, cut-off points should depent on the hereditary nature of the tumour.

Eosinophilia Induced by Blocking the IL-4/IL-13 Pathway: Potential Mechanisms and Clinical Outcomes.

Five biological drugs are currently marketed for treatment of uncontrolled severe asthma. They all block type 2 inflammatory pathways by targeting IgE (omalizumab), the IL-5 pathway (mepolizumab, reslizumab, benralizumab), or the IL-4/IL-13 pathway (dupilumab). Hypereosinophilia has been observed in 4%-25% of patients treated with dupilumab and is transient in most cases, although there have been reports of persistent cases of symptomatic hypereosinophilia consistent with eosinophilic granulomatosis with polyangiitis (EGPA), eosinophilic pneumonia, eosinophilic vasculitis, and sudden worsening of asthma symptoms. Cases of EGPA have been reported with all biologics, including anti-IL-5 agents, and with leukotriene receptor antagonists in publications or in the EudraVigilance database. In many cases, EGPA appears during tapering of systemic corticosteroids or after switching from an anti-IL-5 biologic to dupilumab, suggesting that systemic corticosteroids or the anti-IL-5 agent were masking vasculitis. This review investigates plausible mechanisms of dupilumab-induced hypereosinophilia and review cases of symptomatic hypereosinophilia associated with dupilumab. Blockade of the IL-4/IL-13 pathway reduces eosinophil migration and accumulation of blood by inhibiting eotaxin-3, VCAM-1, and TARC without simultaneously inhibiting eosinophilopoiesis in bone marrow. When choosing the optimal biologic, it seems necessary to consider the presence of hypereosinophilia (>1500/µL), in which case an anti-IL-5/IL-5R agent is preferable. Furthermore, when switching from an anti-IL-5/5R to an anti-IL-4/13R agent, blood eosinophils and clinical progress should be closely monitored. Nevertheless, dual therapy with anti-IL-5/5R and anti-IL4/IL-13R agents may be needed for optimal control, since both the IL-5 and the IL-4/IL-13 pathways can simultaneously contribute to airway inflammation. This approach can prevent the development of EGPA and other types of symptomatic hypereosinophilia while maintaining control of nasal polyposis. In the near future, it will be possible to use a new generation of biological therapies for the treatment of severe asthma. These act at a higher level of the inflammatory cascade, as is the case of the antialarmins tezepelumab and itepekimab.

Biological behavior of familial papillary thyroid microcarcinoma: Spanish multicenter study.

PURPOSE: Familial papillary thyroid microcarcinoma (FPTMC) can present a more aggressive behavior than the sporadic microcarcinoma. However, few studies have analyzed this situation. The objective is to analyze the recurrence rate of FPTMC and the prognostic factors which determine that recurrence in Spain. METHODS: Spanish multicenter longitudinal analytical observational study was conducted. Patients with FPTMC received treatment with curative intent and presented cure criteria 6 months after treatment. Recurrence rate and disease-free survival (DFS) were analyzed. Two groups were analyzed: group A (no tumor recurrence) vs. group B (tumor recurrence). RESULTS: Ninety-four patients were analyzed. During a mean follow-up of 73.3 ± 59.3 months, 13 recurrences of FPTMC (13.83%) were detected and mean DFS was 207.9 ± 11.5 months. There were multifocality in 56%, bilateral thyroid involvement in 30%, and vascular invasion in 7.5%; that is to say, they are tumors with histological factors of poor prognosis in a high percentage of cases. The main risk factors for recurrence obtained in the multivariate analysis were the tumor size (OR: 2.574, 95% CI 1.210-5.473; p = 0.014) and the assessment of the risk of recurrence of the American Thyroid Association (ATA), both intermediate risk versus low risk (OR: 125, 95% CI 10.638-1000; p < 0.001) and high risk versus low risk (OR: 45.454, 95% CI 5.405-333.333; p < 0.001). CONCLUSION: FPTMC has a recurrence rate higher than sporadic cases. Poor prognosis is mainly associated with the tumor size and the risk of recurrence of the ATA.

Uncommon tumors in multiple endocrine neoplasia (MEN) type 1: Do they have a relationship with the prognosis of these patients?

INTRODUCTION: The prognosis of MEN 1 patients is not only determined by pancreatic disease; it is also related to other uncommon tumors. The objective of this study is to analyze the tumors associated with MEN 1 outside the classic triad and to investigate their relationship with mortality. MATERIALS AND METHODS: One hundred and five MEN 1 patients were studied in a tertiary referral hospital (1980-2019). RESULTS: With a follow-up of 11 ± 4 years, seven patients died (8%), four as a consequence MEN syndrome. Thirty-three percent had adrenal gland tumors. One patient died of adrenal cancer. Eight percent presented with a neuroendocrine thoracic neoplasm, and one patient died. Another patient died due to cutaneous T-cell lymphoma. A further patient died because of a gastrinoma with liver metastasis. CONCLUSIONS: To conclude, 75% of MEN-related deaths were the result of an uncommon pathology, and we, therefore, recommend that these tumors should be taken into account in the screening and follow-up of these patients.

Systemic Corticosteroids in Patients with Bronchial Asthma: A Real-Life Study.

OBJECTIVES: The objective of the present study was to determine the use of systemic corti-costeroids (SCs) in patients with bronchial asthma using big data analysis. METHODS: We performed an observational, retrospective, noninterventional study based on secondary data captured from free text in the electronic health records. This study was per-formed based on data from the regional health service of Castille-La Mancha (SESCAM), Spain. We performed the analysis using big data and artificial intelligence via Savana® Manager version 3.0. RESULTS: During the study period, 103 667 patients were diagnosed with and treated for asthma at different care levels. The search was restricted to patients aged 10 to 90 years (mean age, 43.5 [95%CI, 43.4-43.7] years). Of these, 59.8% were women. SCs were taken for treatment of asthma by 58 745 patients at some point during the study period. These patients were older, with a higher prevalence of hypertension, dyslipidemia, diabetes, ob-esity, depression, and hiatus hernia. SCs are used frequently in the general population with asthma (31.4% in 2015 and 39.6% in 2019). SCs were prescribed mainly in primary care (59%), allergy (13%) and pulmonology (20%). The frequency of prescription of SCs had a direct impact on the main associated adverse effects. CONCLUSION: In clinical practice, SCs are frequently prescribed to patients with asthma, especially in primary care. Use of SCs is associated with a greater number of adverse events. It is necessary to implement measures to reduce prescription of SCs to patients with asthma, especially in primary care.

Medical treatment of type 2 diabetes mellitus: Recommendations of the Diabetes, Obesity and Nutrition Group of the Spanish Society of Internal Medicine. / Tratamiento médico de la diabetes mellitus tipo 2: recomendaciones del Grupo de Diabetes, Obesidad y Nutrición de la Sociedad Española de Medicina Interna.

Type 2 diabetes mellitus is a major health problem with high prevalence, morbidity and mortality, and its medical treatment is growing in complexity due to patients' diverse clinical conditions. This article presents a consensus document by the Diabetes, Obesity and Nutrition Group of the Spanish Society of Internal Medicine, with recommendations for the medical treatment of type 2 diabetes mellitus. The main objective of this article is to facilitate the therapeutic decision-making process to improve the care of patients with diabetes. The document prioritises treatments with cardiovascular benefits, especially those that benefit patients with heart and renal failure.

Consensus on basic conduct during the hospital admission of patients with acute heart failure. / Consenso de actuación básica durante el ingreso hospitalario por insuficiencia cardiaca aguda.

Acute heart failure (AHF) is a highly prevalent clinical entity in individuals older than 45years in Spain. AHF is associated with significant morbidity and mortality and is the leading cause of hospitalisation for individuals older than 65years in Spain, a quarter of whom die within 1year of the hospitalisation. In recent years, there has been an upwards trend in hospitalisations for AHF, which increased 76.7% from 2003 to 2013. Readmissions at 30days for AHF have also increased (from 17.6% to 22.1%), at a relative mean rate of 1.36% per year, with the consequent increase in the use of resources and the economic burden for the healthcare system. The aim of this document (developed by the Heart Failure and Atrial Fibrillation Group of the Spanish Society of Internal Medicine) is to guide specialists on the most important aspects of treatment and follow-up for patients with AHF during hospitalisation and the subsequent follow-up. The main recommendations listed in this document are as follows: (1)At admission, perform a comprehensive assessment, considering the patient's standard treatment and comorbidities, given that these determine the disease prognosis to a considerable measure. (2)During the first few hours of hospital care, decongestive treatment is a priority, and a staged diuretic therapeutic approach based on the patient's response is recommended. (3)To manage patients in the stable phase, consider starting and/or adjusting evidence-based drug treatment (e.g., sacubitril/valsartan or angiotensin-converting enzyme inhibitors/angiotensinII receptor blockers, beta blockers and aldosterone antagonists). (4)At hospital discharge, use a checklist to optimise the patient's management and identify the most efficient options for maintaining continuity of care after discharge.

The effect of age and sex on the diagnostic yield of the echocardiogram in patients with syncope. / Efecto de la edad y el sexo en el rendimiento diagnóstico del ecocardiograma en pacientes con síncope.

INTRODUCTION: Syncope is the motivation for numerous diagnostic tests, among them transthoracic echocardiography (TTE); however, previous evidence suggests there is little utility in this test. Our objective was to assess its diagnostic yield in syncope, analysing the effect of age and sex. MATERIAL AND METHODS: We conducted an observational study that included patients with syncope and who underwent TTE between 1990-2015. We defined diagnostic findings related to syncope and performed a descriptive analysis, assessing the diagnostic yield (overall and according to age and sex). RESULTS: The study included 3,302 patients and measured a diagnostic yield of 8.8%; the most common finding was ventricular dysfunction (4.5%). The probability of a diagnostic TTE significantly increased with age (p<.001) but was low for patients younger than 50 years (2.3%). The male sex was significantly related with a diagnostic TTE (p<.001), mostly due to the higher rate of ventricular dysfunction. CONCLUSIONS: The diagnostic yield of TTE in patients with syncope is moderate, low in patients younger than 50 years and lower in women than in men. These factors should be considered when conducting a diagnostic study of patients with syncope.

Demonstration of Single-Barium-Ion Sensitivity for Neutrinoless Double-Beta Decay Using Single-Molecule Fluorescence Imaging.

A new method to tag the barium daughter in the double-beta decay of ^{136}Xe is reported. Using the technique of single molecule fluorescent imaging (SMFI), individual barium dication (Ba^{++}) resolution at a transparent scanning surface is demonstrated. A single-step photobleach confirms the single ion interpretation. Individual ions are localized with superresolution (∼2 nm), and detected with a statistical significance of 12.9σ over backgrounds. This lays the foundation for a new and potentially background-free neutrinoless double-beta decay technology, based on SMFI coupled to high pressure xenon gas time projection chambers.

Redox cycling induces spermptosis and necrosis in stallion spermatozoa while the hydroxyl radical (OH•) only induces spermptosis.

Oxidative stress is a major factor explaining sperm dysfunction of spermatozoa surviving freezing and thawing and is also considered a major inducer of a special form of apoptosis, visible after thawing, in cryopreserved spermatozoa. To obtain further insights into the link between oxidative stress and the induction of apoptotic changes, stallion spermatozoa were induced to oxidative stress through redox cycling after exposure to 2-methyl-1,4-naphthoquinone (menadione), or hydroxyl radical formation after FeSO4 exposure. Either exposure induced significant increases (p < 0.05) in two markers of lipid peroxidation: 8-iso-PGF2α and 4-hydroxynonenal (4-HNE). While both treatments induced changes indicative of spermptosis (caspase-3 activation and decreased mitochondrial membrane potential) (p < 0.01), menadione induced sperm necrosis and a dramatic reduction in motility and thiol content in stallion spermatozoa. Thus, we provided evidence that oxidative stress underlies spermptosis, and thiol content is a key factor for stallion sperm function.

Computational flow cytometry reveals that cryopreservation induces spermptosis but subpopulations of spermatozoa may experience capacitation-like changes.

The reduced lifespan of cryopreserved spermatozoa in the mare reproductive tract has been attributed to both capacitative and apoptotic changes. However, there is a lack of studies investigating both phenomena simultaneously. In order to improve our knowledge in this particular point, we studied in raw and frozen-thawed samples apoptotic and capacitative markers using a wide battery of test based in flow cytometry. Apoptotic markers evaluated were caspase 3 activity, externalization of phosphatidylserine (PS), and mitochondrial membrane potential. Markers of changes resembling capacitation were membrane fluidity, tyrosine phosphorylation, and intracellular sodium. Conventional and computational flow cytometry using nonlinear dimensionally reduction techniques (t-distributed stochastic neighbor embedding (t-SNE)) and automatic classification of cellular expression by nonlinear stochastic embedding (ACCENSE) were used. Most of the changes induced by cryopreservation were apoptotic, with increase in caspase 3 activation (P < 0.01), PS translocation to the outer membrane (P < 0.001), loss of mitochondrial membrane potential (P < 0.05), and increase in intracellular Na+ (P < 0.01). Average values of markers of capacitative changes were not affected by cryopreservation; however, the analysis of the phenotype of individual spermatozoa using computational flow cytometry revealed the presence of subpopulations of spermatozoa experiencing capacitative changes. For the first time advanced computational techniques were applied to the analysis of spermatozoa, and these techniques were able to disclose relevant information of the ejaculate that remained hidden using conventional flow cytometry.

In vivo imaging of brain microglial activity in antipsychotic-free and medicated schizophrenia: a [11C](R)-PK11195 positron emission tomography study.

Positron emission tomography (PET) imaging of the 18 kDa translocator protein (TSPO) has been used to investigate whether microglial activation, an indication of neuroinflammation, is evident in the brain of adults with schizophrenia. Interpretation of these studies is confounded by potential modulatory effects of antipsychotic medication on microglial activity. In the first such study in antipsychotic-free schizophrenia, we have used [11C](R)-PK11195 PET to compare TSPO availability in a predominantly antipsychotic-naive group of moderate-to-severely symptomatic unmedicated patients (n=8), similarly symptomatic medicated patients with schizophrenia taking risperidone or paliperidone by regular intramuscular injection (n=8), and healthy comparison subjects (n=16). We found no evidence for increased TSPO availability in antipsychotic-free patients compared with healthy controls (mean difference 4%, P=0.981). However, TSPO availability was significantly elevated in medicated patients (mean increase 88%, P=0.032) across prefrontal (dorsolateral, ventrolateral, orbital), anterior cingulate and parietal cortical regions. In the patients, TSPO availability was also strongly correlated with negative symptoms measured using the Positive and Negative Syndrome Scale across all the brain regions investigated (r=0.651-0.741). We conclude that the pathophysiology of schizophrenia is not associated with microglial activation in the 2-6 year period following diagnosis. The elevation in the medicated patients may be a direct effect of the antipsychotic, although this study cannot exclude treatment resistance and/or longer illness duration as potential explanations. It also remains to be determined whether it is present only in a subset of patients, represents a pro- or anti-inflammatory state, its association with primary negative symptoms, and whether there are significant differences between antipsychotics.

Randomized controlled trial of the Valencia model of waking hypnosis plus CBT for pain, fatigue, and sleep management in patients with cancer and cancer survivors.

BACKGROUND: This study evaluated the efficacy of an intervention combining the Valencia model of waking hypnosis with cognitive-behavioral therapy (VMWH-CBT) in managing cancer-related pain, fatigue, and sleep problems in individuals with active cancer or who were post-treatment survivors. We hypothesized that four sessions of VMWH-CBT would result in greater improvement in participants' symptoms than four sessions of an education control intervention. Additionally, we examined the effects on several secondary outcome domains that are associated with increases in these symptoms (depression, pain interference, pain catastrophizing, and cancer treatment distress). METHODS: The study design was a randomized controlled crossover clinical trial comparing the VMWH-CBT intervention with education control. Participants (N = 44) received four sessions of both treatments, in a counterbalanced order (n = 22 per order condition). RESULTS: Participants were 89% female (N = 39) with mean age of 61 years (SD = 12.2). They reported significantly greater improvement after receiving the active treatment relative to the control condition in all the outcome measures. Treatment gains were maintained at 3-month follow-up. CONCLUSIONS: This study supports the beneficial effects of the VMWH-CBT intervention relative to a control condition and that treatment gains remain stable. VMWH-CBT-trained clinicians should be accessible for managing symptoms both during and after cancer treatment, though the findings need to be replicated in larger samples of cancer survivors.

PTCDA growth on Ge(111)-[Formula: see text] surfaces: a scanning tunneling microscopy study.

The initial stages of growth of PTCDA (3,4,9,10 perylene tetracarboxylic dianhydride) at room temperature (RT) on Ge(111)-[Formula: see text] surfaces have been studied by means of scanning tunneling microscopy (STM) under ultrahigh vacuum conditions. The results show that PTCDA molecules have a high mobility at RT on the well ordered areas of the semiconductor substrate, since nucleation is only observed in domain walls, steps and surface defects. However, no molecular ordering has been detected at submonolayer coverage. For higher coverages, the formation of three-dimensional (3D) molecular islands has been observed. These 3D islands present a crystalline nature as demostrated by molecularly resolved STM images. According to these STM measurements, PTCDA molecules are ordered in a herringbone structure, similar to the one observed in PTCDA bulk crystals. Moreover, the 3D crystallites are grown on top of a disordered molecular layer, which acts as a passivating layer.

Effects of increasing amount of dietary Prosopis laevigata pods on performance, meat quality and fatty acid profile in growing lambs.

A study with finishing lambs assessed the effect of dietary inclusion of Prosopis laevigata pods (PLPs) on performance, carcass characteristics, meat traits and fatty acid profile of subcutaneous fat. Twenty-one Rambouillet lambs (27.0 ± 3.0 kg BW) were assigned to one of three experimental diets with 0, 150 and 300 g PLP/kg DM. Evaluation of growth performance lasted 49 days. The experimental design was completely randomized and analysed with a mixed model. Lambs fed diets with 0, 150 and 300 g PLP had similar growth performance. Lambs fed diets with 300 g PLP/kg DM had better (p < 0.05) carcass yield and classification, less (p < 0.05) fat deposition and lower lightness (L*) value (p < 0.05) in meat than lambs fed diets with 0 and 150 g PLP/kg DM. Saturated fatty acids (palmitic and stearic) decreased (p < 0.05) and unsaturated fatty acids (oleic and linoleic) increased (p < 0.05) in subcutaneous fat of lambs fed diets with 150 and 300 g pods as compared with lambs not fed PLP. Prosopis laevigata pods are a safe feedstuff that can replace a third of conventional ingredients and reduce feed costs in growing lambs. Addition of PLP reduced (p < 0.05) total feed cost by 21%.

Family Screening in Familial Papillary Carcinoma: The Early Detection of Thyroid Disease.

INTRODUCTION: Blood relatives of patients with familial papillary thyroid carcinoma (FPTC) have a higher rate of thyroid disease. This study analyzed the utility of a screening protocol for thyroid disease on blood relatives of patients with FPTC. STUDY POPULATION: Members of families diagnosed with FPTC. INCLUSION CRITERIA: (1) first- and second-degree relatives; and (2) older than age 11 years. Screening: This includes the subject's clinical history, a physical examination, blood tests, and an ultrasound examination. CONTROL GROUP: A nonrelated healthy population paired by age and sex with the study group. RESULTS: Sixty-eight percent of blood relatives (128/189) accepted having the screening. The results showed 44.5 % (n = 57) of the relatives did not have disease, 44 % (n = 56) had benign thyroid disease, and 11.5 % (n = 15) had a disease suggestive of malignancy. After the screening, surgery was indicated in 26 patients, and the final results of the study were: (1) 44.5 % (n = 57) were healthy subjects; (2) 50 % (n = 64) had benign thyroid disease (26 cases with a functional disease, and/or 56 with an organic disease); and (3) 5.5 % (n = 7) had malignant thyroid disease. The first-degree relatives had a higher tendency to have the disease than second degree ones (64 vs. 46 %; p = 0.0482). In the control group, the incidence of thyroid cancer was 1.3 % compared with 5.5 % in the study group (p = 0.0182). CONCLUSIONS: Screening allows for the early detection of papillary carcinoma and benign thyroid disease and for this reason we recommend that it is performed periodically. However, more studies, with larger sample sizes, are needed to determine the benefit of screening.

Atomic-Scale Variations of the Mechanical Response of 2D Materials Detected by Noncontact Atomic Force Microscopy.

We show that noncontact atomic force microscopy (AFM) is sensitive to the local stiffness in the atomic-scale limit on weakly coupled 2D materials, as graphene on metals. Our large amplitude AFM topography and dissipation images under ultrahigh vacuum and low temperature resolve the atomic and moiré patterns in graphene on Pt(111), despite its extremely low geometric corrugation. The imaging mechanisms are identified with a multiscale model based on density-functional theory calculations, where the energy cost of global and local deformations of graphene competes with short-range chemical and long-range van der Waals interactions. Atomic contrast is related with short-range tip-sample interactions, while the dissipation can be understood in terms of global deformations in the weakly coupled graphene layer. Remarkably, the observed moiré modulation is linked with the subtle variations of the local interplanar graphene-substrate interaction, opening a new route to explore the local mechanical properties of 2D materials at the atomic scale.

Growth of ordered molecular layers of PTCDA on Pb/Si(111) surfaces: a scanning tunneling microscopy study.

The growth of well-ordered layers of PTCDA (3,4,9,10-perylene-tetracarboxylic-dianhydride) molecules on Pb/Si(111) surfaces has been investigated by scanning tunneling microscopy (STM) under ultra-high vacuum conditions. These Pb/Si(111) substrates, which present several distinct phases with different reconstructions, have allowed the exploration of new passivation schemes for the growth of ordered organic layers on Si(111) surfaces. According to our STM measurements, the higher Pb coverage phases (namely the so-called hexagonal incommensurate and [Formula: see text] reconstructions) present rather inert surfaces that allow easy diffusion of PTCDA molecules at room temperature and the formation of a well ordered first molecular layer which displays a herringbone reconstruction. For multilayer PTCDA coverage on these Pb/Si(111) phases, the formation of three-dimensional crystallites, with structure similar to that of the bulk PTCDA crystal, has been observed, indicating that a Stranski-Krastanov growth mode is dominant. On lower Pb coverage substrates (presenting the defective [Formula: see text] and mosaic [Formula: see text] reconstructions) no long range PTCDA order has been obtained. The systematic variation of the substrate reconstruction has allowed in the present work the relation of the surface reactivity of each reconstruction to the formation of ordered layers of PTCDA on Pb/Si(111) substrates.

Visualizing the interface state of PTCDA on Au(111) by scanning tunneling microscopy.

We have investigated by means of scanning tunneling microscopy (STM) and spectroscopy (STS) the electronic structure of PTCDA (3,4,9,10-perylene-tetracarboxylic-dianhydride) molecular monolayers grown on Au(111). Thanks to our STM/STS measurements, performed under ultra-high vacuum conditions and low temperature, an interface state directly derived from the Shockley-type surface state of pristine Au(111) has been detected. Low bias voltage STM images show the formation of standing wave patterns both on Au(111) and on Au(111) covered by a PTCDA monolayer. These patterns result from the scattering of quasi-free 2D electron surface states with surface defects. By Fourier transforming STM images, the corresponding wavevectors have been extracted. In particular, the simultaneous imaging of both pristine and PTCDA covered Au(111) areas has allowed to measure the Fermi contours and the Fermi wavevectors of both systems. These measurements show that one monolayer PTCDA on Au(111) presents an interface state with an isotropic circular Fermi contour and smaller Fermi wavector ([Formula: see text]) than the corresponding Fermi wavector of pristine Au(111) ([Formula: see text]). This picture is consistent with an upward shift of the Shockley-type surface state due to the presence of the molecular monolayer.