Surface evolution during crystalline silicon film growth by low-temperature hot-wire chemical vapor deposition on silicon substrates

We investigate the low-temperature growth of crystalline thin silicon films: epitaxial, twinned, and polycrystalline, by hot-wire chemical vapor deposition (HWCVD). Using Raman spectroscopy, spectroscopic ellipsometry, and atomic force microscopy, we find the relationship between surface roughness evolution and (i) the substrate temperature (230–350 °C) and (ii) the hydrogen dilution ratio (H2/SiH4=0–480). The absolute silicon film thickness for fully crystalline films is found to be the most important parameter in determining surface roughness, hydrogen being the second most important. Higher hydrogen dilution increases the surface roughness as expected. However, surface roughness increases with increasing substrate-temperature, in contrast to previous studies of crystalline Si growth. We suggest that the temperature-dependent roughness evolution is due to the role of hydrogen during the HWCVD process, which in this high hydrogen dilution regime allows for epitaxial growth on the rms roughest films through a kinetic growth regime of shadow-dominated etch and desorption and redeposition of growth species

Surface evolution during low temperature epitaxial silicon growth by hot-wire chemical vapor deposition: Structural and electronic properties

We report the surface and structural evolution of hotwire chemical vapor deposited (HWCVD) crystalline Si thin films with temperature, thickness, and hydrogen dilution and the resulting growth regimes and electronic properties. We focus on a low silane partial pressure regime that leads to epitaxial growth with a polycrystalline, rather than an amorphous transition. Using scanning electron microscopy and atomic force microscopy, we find the relationship between the deposition conditions and the evolution of the surface roughness. Increasing the hydrogen dilution changes the kinetic growth regime from growth predominantly from the wire to shadow-dominated etch and finally to a regime dominated by desorption and re-deposition of growth species. Transitions between these kinetic regimes are the dominant factors governing the epitaxial–polycrystalline transition in low temperature HWCVD growth along with their electronic properties

A Phase Diagram of Low Temperature Epitaxial Silicon Grown by Hot-wire Chemical Vapor Deposition for Photovoltaic Devices

We have investigated the low-temperature epitaxial growth of thin silicon films by hot-wire chemical vapor deposition (HWCVD). Using reflection high energy electron diffraction (RHEED) and transmission electron microscopy (TEM), we have found conditions for epitaxial growth at low temperatures achieving twinned epitaxial growth up to 6.8 µm on Si(100) substrates at a substrate temperature of 230°C. This opens the possibility of growing high quality films on low cost substrates. The H_2:SiH_4 dilution ratio was set to 50:1 for all growths. Consistent with previous results, the epitaxial thickness is found to decrease with an increase in the substrate temperature

Risk-Responsive Orbitofrontal Neurons Track Acquired Salience

SummaryDecision making is impacted by uncertainty and risk (i.e., variance). Activity in the orbitofrontal cortex, an area implicated in decision making, covaries with these quantities. However, this activity could reflect the heightened salience of situations in which multiple outcomes—reward and reward omission—are expected. To resolve these accounts, rats were trained to respond to cues predicting 100%, 67%, 33%, or 0% reward. Consistent with prior reports, some orbitofrontal neurons fired differently in anticipation of uncertain (33% and 67%) versus certain (100% and 0%) reward. However, over 90% of these neurons also fired differently prior to 100% versus 0% reward (or baseline) or prior to 33% versus 67% reward. These responses are inconsistent with risk but fit well with the representation of acquired salience linked to the sum of cue-outcome and cue-no-outcome associative strengths. These results expand our understanding of how the orbitofrontal cortex might regulate learning and behavior.Video Abstrac

Different methods of fear reduction are supported by distinct cortical substrates

Understanding how learned fear can be reduced is at the heart of treatments for anxiety disorders. Tremendous progress has been made in this regard through extinction training in which the aversive outcome is omitted. However, current progress almost entirely rests on this single paradigm, resulting in a very specialized knowledgebase at the behavioural and neural level of analysis. Here, we used a dual-paradigm approach to show that different methods that lead to reduction in learned fear in rats are dissociated in the cortex. We report that the infralimbic cortex has a very specific role in fear reduction that depends on the omission of aversive events but not on overexpectation. The orbitofrontal cortex, a structure generally overlooked in fear, is critical for downregulating fear when novel predictions about upcoming aversive events are generated, such as when fear is inflated or overexpected, but less so when an expected aversive event is omitted

HIV pre-exposure prophylaxis was associated with no impact on sexually transmitted infection prevalence in a high-prevalence population of predominantly men who have sex with men, Germany, 2018 to 2019

Introduction: Despite increased use of pre-exposure prophylaxis (PrEP) in Germany, HIV infection rates are not declining and little is known about how this prevention method affects the prevalence of sexually transmitted infections (STI) among men who have sex with men (MSM). Aim: We studied, in a large multicentre cohort, STI point prevalence, co-infection rates, anatomical location and influence of PrEP. Methods: The BRAHMS study was a prospective cohort study conducted at 10 sites in seven major German cities that enrolled MSM reporting increased sexual risk behaviour. At screening visits, MSM were tested for Mycoplasma genitalium (MG), Neisseria gonorrhoeae (NG), Chlamydia trachomatis (CT) and Treponema pallidum (TP), and given a behavioural questionnaire. With binomial regression, we estimated prevalence ratios (PR) and 95% confidence intervals (CI) for the association of PrEP and STI. Results: We screened 1,043 MSM in 2018 and 2019, with 53.0% currently using PrEP. At screening, 370 participants (35.5%) had an STI. The most common pathogen was MG in 198 (19.0%) participants, followed by CT (n = 133; 12.8%), NG (n = 105; 10.1%) and TP (n = 37; 3.5%). Among the 370 participants with at least one STI, 14.6% (n = 54) reported STI-related symptoms. Infection prevalence was highest at anorectal site (13.4% MG, 6.5% NG, 10.2% CT). PrEP use was not statistically significant in adjusted models for STI (PR: 1.10; 95% CI: 0.91–1.32), NG/CT, only NG or only CT. Conclusions: Prevalence of asymptomatic STI was high, and PrEP use did not influence STI prevalence in MSM eligible for PrEP according to national guidelines.Peer Reviewe

Persons living with HIV in sero-discordant partnerships experience improved HIV care engagement compared with persons living with HIV in sero-concordant partnerships: a cross-sectional analysis of four African countries

Background Persons living with HIV (PLWH) who are members of sero-discordant and sero-concordant relationships may experience psychological stressors or motivators that affect HIV care. We assessed the association between sero-discordance status, antiretroviral therapy (ART) uptake, and viral suppression in the African Cohort Study (AFRICOS). Methods AFRICOS enrolls PLWH and HIV-uninfected individuals at 12 sites in Uganda, Kenya, Tanzania, and Nigeria. At enrollment, we determined ART use through self-report. Viral suppression was defined as HIV RNA < 1000 copies/mL. We analyzed PLWH who were index participants within two types of sexual dyads: sero-discordant or sero-concordant. Binomial regression models were used to estimate prevalence ratios (PRs) and 95% confidence intervals (95% CIs) for factors associated with ART use and viral suppression at study enrollment. Results From January 2013 through March 2018, 223 index participants from sero-discordant dyads and 61 from sero-concordant dyads were enrolled. The majority of the indexes were aged 25–34 years (50.2%), female (53.4%), and married (96.5%). Sero-discordant indexes were more likely to disclose their status to partners compared with sero-concordant indexes (96.4% vs. 82.0%, p < 0.001). After adjustment, sero-discordant index participants were more likely to be on ART (aPR 2.8 [95% CI 1.1–6.8]), but no more likely to be virally suppressed. Results may be driven by unique psycho-social factors and global implementation of treatment as prevention. Conclusions PLWH in sero-discordant sexual partnerships demonstrated improved uptake of ART compared with those in sero-concordant partnerships. Interventions are needed to increase care engagement by individuals in sero-concordant relationships to improve HIV outcomes

Deficient histone H3 propionylation by BRPF1-KAT6 complexes in neurodevelopmental disorders and cancer

Lysine acetyltransferase 6A (KAT6A) and its paralog KAT6B form stoichiometric complexes with bromodomain- and PHD finger-containing protein 1 (BRPF1) for acetylation of histone H3 at lysine 23 (H3K23). We report that these complexes also catalyze H3K23 propionylation in vitro and in vivo. Immunofluorescence microscopy and ATAC-See revealed the association of this modification with active chromatin. Brpf1 deletion obliterates the acylation in mouse embryos and fibroblasts. Moreover, we identify BRPF1 variants in 12 previously unidentified cases of syndromic intellectual disability and demonstrate that these cases and known BRPF1 variants impair H3K23 propionylation. Cardiac anomalies are present in a subset of the cases. H3K23 acylation is also impaired by cancer-derived somatic BRPF1 mutations. Valproate, vorinostat, propionate and butyrate promote H3K23 acylation. These results reveal the dual functionality of BRPF1-KAT6 complexes, shed light on mechanisms underlying related developmental disorders and various cancers, and suggest mutation-based therapy for medical conditions with deficient histone acylation

Deficient histone H3 propionylation by BRPF1-KAT6 complexes in neurodevelopmental disorders and cancer

Lysine acetyltransferase 6A (KAT6A) and its paralog KAT6B form stoichiometric complexes with bromodomain- and PHD finger-containing protein 1 (BRPF1) for acetylation of histone H3 at lysine 23 (H3K23). We report that these complexes also catalyze H3K23 propionylati